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-"http://www.w3.org/TR/html4/loose.dtd">
-
-<html>
-
-<head>
- <title>Basic Graphics Programming With The XCB Library</title>
- <meta http-equiv="content-type" content="text/html; charset=iso-8859-1">
- <link href="xcb.css" rel="stylesheet" type="text/css">
-</head>
-
-<body>
- <div class="title">
- Basic Graphics Programming With The XCB Library
- </div>
- <div class="toc">
- <ol>
- <li><a class="section" href="#intro">Introduction</a>
- <li><a class="section" href="#Xmodel">The client and server model of the X window system</a>
- <li><a class="section" href="#asynch">GUI programming: the asynchronous model</a>
- <li><a class="section" href="#notions">Basic XCB notions</a>
- <ol>
- <li><a class="subsection" href="#conn">The X Connection</a>
- <li><a class="subsection" href="#requestsreplies">Requests and replies: the Xlib killers</a>
- <li><a class="subsection" href="#gc">The Graphics Context</a>
- <li>Object handles
- <li>Memory allocation for XCB structures
- <li><a class="subsection" href="#events">Events</a>
- </ol>
- <li><a class="section" href="#use">Using XCB-based programs</a>
- <ol>
- <li><a class="subsection" href="#inst">Installation of XCB</a>
- <li><a class="subsection" href="#comp">Compiling XCB-based programs</a>
- </ol>
- <li><a class="section" href="#openconn">Opening and closing the connection to an X server</a>
- <li><a class="section" href="#screen">Checking basic information about a connection</a>
- <li><a class="section" href="#helloworld">Creating a basic window - the "hello world" program</a>
- <li><a class="section" href="#drawing">Drawing in a window</a>
- <ol>
- <li><a class="subsection" href="#allocgc">Allocating a Graphics Context</a>
- <li><a class="subsection" href="#changegc">Changing the attributes of a Graphics Context</a>
- <li><a class="subsection" href="#drawingprim">Drawing primitives: point, line, box, circle,...</a>
- </ol>
- <li><a class="section" href="#xevents">X Events</a>
- <ol>
- <li><a class="subsection" href="#register">Registering for event types using event masks</a>
- <li><a class="subsection" href="#loop">Receiving events: writing the events loop</a>
- <li><a class="subsection" href="#expose">Expose events</a>
- <li><a class="subsection" href="#userinput">Getting user input</a>
- <ol>
- <li><a class="subsubsection" href="#mousepressrelease">Mouse button press and release events</a>
- <li><a class="subsubsection" href="#mousemvnt">Mouse movement events</a>
- <li><a class="subsubsection" href="#mouseenter">Mouse pointer enter and leave events</a>
- <li><a class="subsubsection" href="#focus">The keyboard focus</a>
- <li><a class="subsubsection" href="#keypress">Keyboard press and release events</a>
- </ol>
- <li><a class="subsection" href="#eventex">X events: a complete example</a>
- </ol>
- <li><a class="section" href="#font">Handling text and fonts</a>
- <ol>
- <li><a class="subsection" href="#fontstruct">The Font structure</a>
- <li><a class="subsection" href="#openingfont">Opening a Font</a>
- <li><a class="subsection" href="#assigningfont">Assigning a Font to a Graphic Context</a>
- <li><a class="subsection" href="#drawingtext">Drawing text in a drawable</a>
- <li><a class="subsection" href="#fontcompleteexample">Complete example</a>
- </ol>
- <li>Windows hierarchy
- <ol>
- <li>Root, parent and child windows
- <li>Events propagation
- </ol>
- <li><a class="section" href="#wm">Interacting with the window manager</a>
- <ol>
- <li><a class="subsection" href="#wmprop">Window properties</a>
- <li><a class="subsection" href="#wmname">Setting the window name and icon name</a>
- <li>Setting preferred window size(s)
- <li>Setting miscellaneous window manager hints
- <li>Setting an application's icon
- <li>Obeying the delete-window protocol
- </ol>
- <li><a class="section" href="#winop">Simple window operations</a>
- <ol>
- <li><a class="subsection" href="#winmap">Mapping and unmapping a window</a>
- <li><a class="subsection" href="#winconf">Configuring a window</a>
- <li><a class="subsection" href="#winmove">Moving a window around the screen</a>
- <li><a class="subsection" href="#winsize">Resizing a window</a>
- <li><a class="subsection" href="#winstack">Changing windows stacking order: raise and lower</a>
- <li>Iconifying and de-iconifying a window
- <li><a class="subsection" href="#wingetinfo">Getting informations about a window</a>
- </ol>
- <li><a class="section" href="#usecolor">Using colors to paint the rainbow</a>
- <ol>
- <li><a class="subsection" href="#colormap">Color maps</a>
- <li><a class="subsection" href="#colormapalloc">Allocating and freeing Color Maps</a>
- <li><a class="subsection" href="#alloccolor">Allocating and freeing a color entry</a>
- <li>Drawing with a color
- </ol>
- <li><a class="section" href="#pixmaps">X Bitmaps and Pixmaps</a>
- <ol>
- <li><a class="subsection" href="#pixmapswhat">What is a X Bitmap ? An X Pixmap ?</a>
- <li>Loading a bitmap from a file
- <li>Drawing a bitmap in a window
- <li><a class="subsection" href="#pixmapscreate">Creating a pixmap</a>
- <li><a class="subsection" href="#pixmapsdraw">Drawing a pixmap in a window</a>
- <li><a class="subsection" href="#pixmapsfree">Freeing a pixmap</a>
- </ol>
- <li><a class="subsection" href="#mousecursor">Messing with the mouse cursor</a>
- <ol>
- <li><a class="subsection" href="#mousecursorcreate">Creating and destroying a mouse cursor</a>
- <li><a class="subsection" href="#mousecursorset">Setting a window's mouse cursor</a>
- <li><a class="subsection" href="#mousecursorexample">Complete example</a>
- </ol>
- <li><a class="subsection" href="#translation">Translation of basic Xlib functions and macros</a>
- <ol>
- <li><a class="subsection" href="#displaystructure">Members of the Display structure</a>
- <ol>
- <li><a class="subsection" href="#ConnectionNumber">ConnectionNumber</a>
- <li><a class="subsection" href="#DefaultScreen">DefaultScreen</a>
- <li><a class="subsection" href="#QLength">QLength</a>
- <li><a class="subsection" href="#ScreenCount">ScreenCount</a>
- <li><a class="subsection" href="#ServerVendor">ServerVendor</a>
- <li><a class="subsection" href="#ProtocolVersion">ProtocolVersion</a>
- <li><a class="subsection" href="#ProtocolRevision">ProtocolRevision</a>
- <li><a class="subsection" href="#VendorRelease">VendorRelease</a>
- <li><a class="subsection" href="#DisplayString">DisplayString</a>
- <li><a class="subsection" href="#BitmapUnit">BitmapUnit</a>
- <li><a class="subsection" href="#BitmapBitOrder">BitmapBitOrder</a>
- <li><a class="subsection" href="#BitmapPad">BitmapPad</a>
- <li><a class="subsection" href="#ImageByteOrder">ImageByteOrder</a>
- </ol>
- <li><a class="subsection" href="#screenofdisplay">ScreenOfDisplay related functions</a>
- <ol>
- <li><a class="subsection" href="#ScreenOfDisplay">ScreenOfDisplay</a>
- <li><a class="subsection" href="#DefaultScreenOfDisplay">DefaultScreenOfDisplay</a>
- <li><a class="subsection" href="#RootWindow">RootWindow / RootWindowOfScreen</a>
- <li><a class="subsection" href="#DefaultRootWindow">DefaultRootWindow</a>
- <li><a class="subsection" href="#DefaultVisual">DefaultVisual / DefaultVisualOfScreen</a>
- <li><a class="subsection" href="#DefaultGC">DefaultGC / DefaultGCOfScreen</a>
- <li><a class="subsection" href="#BlackPixel">BlackPixel / BlackPixelOfScreen</a>
- <li><a class="subsection" href="#WhitePixel">WhitePixel / WhitePixelOfScreen</a>
- <li><a class="subsection" href="#DisplayWidth">DisplayWidth / WidthOfScreen</a>
- <li><a class="subsection" href="#DisplayHeight">DisplayHeight / HeightOfScreen</a>
- <li><a class="subsection" href="#DisplayWidthMM">DisplayWidthMM / WidthMMOfScreen</a>
- <li><a class="subsection" href="#DisplayHeightMM">DisplayHeightMM / HeightMMOfScreen</a>
- <li><a class="subsection" href="#DisplayPlanes">DisplayPlanes / DefaultDepth / DefaultDepthOfScreen / PlanesOfScreen</a>
- <li><a class="subsection" href="#DefaultColormap">DefaultColormap / DefaultColormapOfScreen</a>
- <li><a class="subsection" href="#MinCmapsOfScreen">MinCmapsOfScreen</a>
- <li><a class="subsection" href="#MaxCmapsOfScreen">MaxCmapsOfScreen</a>
- <li><a class="subsection" href="#DoesSaveUnders">DoesSaveUnders</a>
- <li><a class="subsection" href="#DoesBackingStore">DoesBackingStore</a>
- <li><a class="subsection" href="#EventMaskOfScreen">EventMaskOfScreen</a>
- </ol>
- <li><a class="subsection" href="#misc">Miscellaneaous macros</a>
- <ol>
- <li><a class="subsection" href="#DisplayOfScreen">DisplayOfScreen</a>
- <li><a class="subsection" href="#DisplayCells">DisplayCells / CellsOfScreen</a>
- </ol>
- </ol>
- </ol>
- </div>
- <div class="section">
- <ol>
- <li class="title"><a name="intro">Introduction</a>
- <p>
- This tutorial is based on the
- <a href="http://users.actcom.co.il/~choo/lupg/tutorials/xlib-programming/xlib-programming.html">Xlib Tutorial</a>
- written by <a href="mailto:choor at atcom dot co dot il">Guy Keren</a>. The
- author allowed me to take some parts of his text, mainly the text which
- deals with the X Windows generality.
- </p>
- <p>
- This tutorial is intended for people who want to start to program
- with the <a href="http://xcb.freedesktop.org">XCB</a>
- library. keep in mind that XCB, like the
- <a href="http://tronche.com/gui/x/xlib/introduction">Xlib</a>
- library, isn't what most programmers wanting to write X
- applications are looking for. They should use a much higher
- level GUI toolkit like Motif,
- <a href="http://www.lesstif.org">LessTiff</a>,
- <a href="http://www.gtk.org">GTK</a>,
- <a href="http://www.trolltech.com">QT</a>,
- <a href="http://www.enlightenment.org">EWL</a>,
- <a href="http://www.enlightenment.org">ETK</a>, or use
- <a href="http://cairographics.org">Cairo</a>.
- However,
- we need to start somewhere. More than this, knowing how things
- work down below is never a bad idea.
- </p>
- <p>
- After reading this tutorial, one should be able to write very
- simple graphical programs, but not programs with decent user
- interfaces. For such programs, one of the previously mentioned
- libraries should be used.
- </p>
- <p>
- But what is XCB? Xlib has been
- the standard C binding for the <a href="http://www.x.org">X
- Window System</a> protocol for many years now. It is an
- excellent piece of work, but there are applications for which it
- is not ideal, for example:
- </p>
- <ul>
- <li><b>Small platforms</b>: Xlib is a large piece of code, and
- it's difficult to make it smaller
- <li><b>Latency hiding</b>: Xlib requests requiring a reply are
- effectively synchronous: they block until the reply appears,
- whether the result is needed immediately or not.
- <li><b>Direct access to the protocol</b>: Xlib does quite a
- bit of caching, layering, and similar optimizations. While this
- is normally a feature, it makes it difficult to simply emit
- specified X protocol requests and process specific
- responses.
- <li><b>Threaded applications</b>: While Xlib does attempt to
- support multithreading, the API makes this difficult and
- error-prone.
- <li><b>New extensions</b>: The Xlib infrastructure provides
- limited support for the new creation of X extension client side
- code.
- </ul>
- <p>
- For these reasons, among others, XCB, an X C binding, has been
- designed to solve the above problems and thus provide a base for
- </p>
- <ul>
- <li>Toolkit implementation.
- <li>Direct protocol-level programming.
- <li>Lightweight emulation of commonly used portions of the
- Xlib API.
- </ul>
- <br>
- <li class="title"><a name="Xmodel">The client and server model of the X window system</a>
- <p>
- The X Window System was developed with one major goal:
- flexibility. The idea was that the way things look is one thing,
- but the way things work is another matter. Thus, the lower
- levels provide the tools required to draw windows, handle user
- input, allow drawing graphics using colors (or black and white
- screens), etc. To this point, a decision was made to separate
- the system into two parts. A client that decides what to do, and
- a server that actually draws on the screen and reads user input
- in order to send it to the client for processing.
- </p>
- <p>
- This model is the complete opposite of what is used to when
- dealing with clients and servers. In our case, the user sits
- near the machine controlled by the server, while the client
- might be running on a remote machine. The server controls the
- screens, mouse and keyboard. A client may connect to the server,
- request that it draws a window (or several windows), and ask the
- server to send it any input the user sends to these
- windows. Thus, several clients may connect to a single X server
- (one might be running mail software, one running a WWW
- browser, etc). When input is sent by the user to some window,
- the server sends a message to the client controlling this window
- for processing. The client decides what to do with this input,
- and sends the server requests for drawing in the window.
- </p>
- <p>
- The whole session is carried out using the X message
- protocol. This protocol was originally carried over the TCP/IP
- protocol suite, allowing the client to run on any machine
- connected to the same network that the server is. Later on, the
- X servers were extended to allow clients running on the local
- machine with more optimized access to the server (note that an X
- protocol message may be several hundreds of KB in size), such as
- using shared memory, or using Unix domain sockets (a method for
- creating a logical channel on a Unix system between two processes).
- </p>
- <li class="title"><a name="asynch">GUI programming: the asynchronous model</a>
- <p>
- Unlike conventional computer programs, that carry some serial
- nature, a GUI program usually uses an asynchronous programming
- model, also known as "event-driven programming". This means that
- that program mostly sits idle, waiting for events sent by the X
- server, and then acts upon these events. An event may say "The
- user pressed the 1st button mouse in spot (x,y)", or "The window
- you control needs to be redrawn". In order for the program to be
- responsive to the user input, as well as to refresh requests, it
- needs to handle each event in a rather short period of time
- (e.g. less that 200 milliseconds, as a rule of thumb).
- </p>
- <p>
- This also implies that the program may not perform operations
- that might take a long time while handling an event (such as
- opening a network connection to some remote server, or
- connecting to a database server, or even performing a long file
- copy operation). Instead, it needs to perform all these
- operations in an asynchronous manner. This may be done by using
- various asynchronous models to perform the longish operations,
- or by performing them in a different process or thread.
- </p>
- <p>
- So the way a GUI program looks is something like that:
- </p>
- <ol>
- <li>Perform initialization routines.
- <li>Connect to the X server.
- <li>Perform X-related initialization.
- <li>While not finished:
- <ol>
- <li>Receive the next event from the X server.
- <li>Handle the event, possibly sending various drawing
- requests to the X server.
- <li>If the event was a quit message, exit the loop.
- </ol>
- <li>Close down the connection to the X server.
- <li>Perform cleanup operations.
- </ol>
- <br>
- <li class="title"><a name="notions">Basic XCB notions</a>
- <p>
- XCB has been created to eliminate the need for
- programs to actually implement the X protocol layer. This
- library gives a program a very low-level access to any X
- server. Since the protocol is standardized, a client using any
- implementation of XCB may talk with any X server (the same
- occurs for Xlib, of course). We now give a brief description of
- the basic XCB notions. They will be detailed later.
- </p>
- <ol>
- <li class="subtitle"><a name="conn">The X Connection</a>
- <p>
- The major notion of using XCB is the X Connection. This is a
- structure representing the connection we have open with a
- given X server. It hides a queue of messages coming from the
- server, and a queue of pending requests that our client
- intends to send to the server. In XCB, this structure is named
- 'xcb_connection_t'. It is analogous to the Xlib Display.
- When we open a connection to an X server, the
- library returns a pointer to such a structure. Later, we
- supply this pointer to any XCB function that should send
- messages to the X server or receive messages from this server.
- </p>
- <li class="subtitle"><a name="requestsreplies">Requests and
- replies: the Xlib killers</a>
- <p>
- To ask for information from the X server, we have to make a request
- and ask for a reply. With Xlib, these two tasks are
- automatically done: Xlib locks the system, sends a request,
- waits for a reply from the X server and unlocks. This is
- annoying, especially if one makes a lot of requests to the X
- server. Indeed, Xlib has to wait for the end of a reply
- before asking for the next request (because of the locks that
- Xlib sends). For example, here is a time-line of N=4
- requests/replies with Xlib, with a round-trip latency
- <b>T_round_trip</b> that is 5 times long as the time required
- to write or read a request/reply (<b>T_write/T_read</b>):
- </p>
- <pre class="text">
- W-----RW-----RW-----RW-----R
-</pre>
- <ul>
- <li>W: Writing request
- <li>-: Stalled, waiting for data
- <li>R: Reading reply
- </ul>
- <p>
- The total time is N * (T_write + T_round_trip + T_read).
- </p>
- <p>
- With XCB, we can suppress most of the round-trips as the
- requests and the replies are not locked. We usually send a
- request, then XCB returns to us a <b>cookie</b>, which is an
- identifier. Then, later, we ask for a reply using this
- <b>cookie</b> and XCB returns a
- pointer to that reply. Hence, with XCB, we can send a lot of
- requests, and later in the program, ask for all the replies
- when we need them. Here is the time-line for 4
- requests/replies when we use this property of XCB:
- </p>
- <pre class="text">
- WWWW--RRRR
-</pre>
- <p>
- The total time is N * T_write + max (0, T_round_trip - (N-1) *
- T_write) + N * T_read. Which can be considerably faster than
- all those Xlib round-trips.
- </p>
- <p>
- Here is a program that computes the time to create 500 atoms
- with Xlib and XCB. It shows the Xlib way, the bad XCB way
- (which is similar to Xlib) and the good XCB way. On my
- computer, XCB is 25 times faster than Xlib.
- </p>
- <pre class="code">
-#include <stdlib.h>
-#include <stdio.h>
-#include <string.h>
-#include <sys/time.h>
-
-#include <xcb/xcb.h>
-
-#include <X11/Xlib.h>
-
-double
-get_time(void)
-{
- struct timeval timev;
-
- gettimeofday(&timev, NULL);
-
- return (double)timev.tv_sec + (((double)timev.tv_usec) / 1000000);
-}
-
-int
-main ()
-{
- xcb_connection_t *c;
- xcb_atom_t *atoms;
- xcb_intern_atom_cookie_t *cs;
- char **names;
- int count;
- int i;
- double start;
- double end;
- double diff;
-
- /* Xlib */
- Display *disp;
- Atom *atoms_x;
- double diff_x;
-
- c = xcb_connect (NULL, NULL);
-
- count = 500;
- atoms = (xcb_atom_t *)malloc (count * sizeof (atoms));
- names = (char **)malloc (count * sizeof (char *));
-
- /* init names */
- for (i = 0; i < count; ++i) {
- char buf[100];
-
- sprintf (buf, "NAME%d", i);
- names[i] = strdup (buf);
- }
-
- /* bad use */
- start = get_time ();
-
- for (i = 0; i < count; ++i)
- atoms[i] = xcb_intern_atom_reply (c,
- xcb_intern_atom (c,
- 0,
- strlen(names[i]),
- names[i]),
- NULL)->atom;
-
- end = get_time ();
- diff = end - start;
- printf ("bad use time : %f\n", diff);
-
- /* good use */
- start = get_time ();
-
- cs = (xcb_intern_atom_cookie_t *) malloc (count * sizeof(xcb_intern_atom_cookie_t));
- for(i = 0; i < count; ++i)
- cs[i] = xcb_intern_atom (c, 0, strlen(names[i]), names[i]);
-
- for(i = 0; i < count; ++i) {
- xcb_intern_atom_reply_t *r;
-
- r = xcb_intern_atom_reply(c, cs[i], 0);
- if(r)
- atoms[i] = r->atom;
- free(r);
- }
-
- end = get_time ();
- printf ("good use time : %f\n", end - start);
- printf ("ratio : %f\n", diff / (end - start));
- diff = end - start;
-
- /* free var */
- free (atoms);
- free (cs);
-
- xcb_disconnect (c);
-
- /* Xlib */
- disp = XOpenDisplay (getenv("DISPLAY"));
-
- atoms_x = (Atom *)malloc (count * sizeof (atoms_x));
-
- start = get_time ();
-
- for (i = 0; i < count; ++i)
- atoms_x[i] = XInternAtom(disp, names[i], 0);
-
- end = get_time ();
- diff_x = end - start;
- printf ("Xlib use time : %f\n", diff_x);
- printf ("ratio : %f\n", diff_x / diff);
-
- free (atoms_x);
- for (i = 0; i < count; ++i)
- free (names[i]);
- free (names);
-
- XCloseDisplay (disp);
-
- return 0;
-}
-</pre>
- <li class="subtitle"><a name="gc">The Graphic Context</a>
- <p>
- When we perform various drawing operations (graphics, text,
- etc), we may specify various options for controlling how the
- data will be drawn (what foreground and background colors to
- use, how line edges will be connected, what font to use when
- drawing some text, etc). In order to avoid the need to supply
- hundreds of parameters to each drawing function, a graphical
- context structure is used. We set the various drawing options
- in this structure, and then we pass a pointer to this
- structure to any drawing routines. This is rather handy, as we
- often need to perform several drawing requests with the same
- options. Thus, we would initialize a graphical context, set
- the desired options, and pass this structure to all drawing
- functions.
- </p>
- <p>
- Note that graphic contexts have no client-side structure in
- XCB, they're just XIDs. Xlib has a client-side structure
- because it caches the GC contents so it can avoid making
- redundant requests, but of course XCB doesn't do that.
- </p>
- <li class="subtitle"><a name="events">Events</a>
- <p>
- A structure is used to pass events received from the X
- server. XCB supports exactly the events specified in the
- protocol (33 events). This structure contains the type
- of event received (including a bit for whether it came
- from the server or another client), as well as the data associated with the
- event (e.g. position on the screen where the event was
- generated, mouse button associated with the event, region of
- the screen associated with a "redraw" event, etc). The way to
- read the event's data depends on the event type.
- </p>
- </ol>
- <br>
- <li class="title"><a name="use">Using XCB-based programs</a>
- <br>
- <ol>
- <li class="subtitle"><a name="inst">Installation of XCB</a>
- <p>
- <b>TODO:</b> These instructions are out of date.
- Just reference the <a href="http://xcb.freedesktop.org/">main XCB page</a>
- so we don't have to maintain these instructions in more than
- one place.
- </p>
- <p>
- To build XCB from source, you need to have installed at
- least:
- </p>
- <ul>
- <li>pkgconfig 0.15.0
- <li><a href="http://www.gnu.org/software/automake/">automake 1.7</a>
- <li><a href="http://www.gnu.org/software/autoconf/">autoconf 2.50</a>
- <li><a href="http://www.check.org">check</a>
- <li><a href="http://xmlsoft.org/XSLT/">xsltproc</a>
- <li><a href="http://www.gnu.org/software/gperf/">gperf 3.0.1</a>
- </ul>
- <p>
- You have to checkout in the git repository the following modules:
- </p>
- <ul>
- <li>Xau from xlibs
- <li>xcb-proto
- <li>xcb
- </ul>
- <p>
- Note that xcb-proto exists only to install header
- files, so typing 'make' or 'make all' will produce the message
- "Nothing to be done for 'all'". That's normal.
- </p>
- <li class="subtitle"><a name="comp">Compiling XCB-based programs</a>
- <p>
- Compiling XCB-based programs requires linking them with the XCB
- library. This is easily done thanks to pkgconfig:
- </p>
- <pre class="text">
-gcc -Wall prog.c -o prog `pkg-config --cflags --libs xcb`
-</pre>
- </ol>
- <li class="title"><a name="openconn">Opening and closing the connection to an X server</a>
- <p>
- An X program first needs to open the connection to the X
- server. There is a function that opens a connection. It requires
- the display name, or NULL. In the latter case, the display name
- will be the one in the environment variable DISPLAY.
- </p>
- <pre class="code">
-<span class="type">xcb_connection_t</span> *xcb_connect (<span class="keyword">const</span> <span class="type">char</span> *displayname,
- <span class="type">int</span> *screenp);
-</pre>
- <p>
- The second parameter returns the screen number used for the
- connection. The returned structure describes an XCB connection
- and is opaque. Here is how the connection can be opened:
- </p>
- <pre class="code">
-#<span class="include">include</span> <span class="string"><xcb/xcb.h></span>
-
-<span class="type">int</span>
-<span class="function">main</span> ()
-{
- <span class="type">xcb_connection_t</span> *c;
-
- /* Open the connection to the X server. Use the DISPLAY environment variable as the default display name */
- c = xcb_connect (NULL, NULL);
-
- <span class="keyword">return</span> 0;
-}
-</pre>
- <p>
- To close a connection, it suffices to use:
- </p>
- <pre class="code">
-<span class="type">void</span> xcb_disconnect (<span class="type">xcb_connection_t</span> *c);
-</pre>
- <div class="comp">
- <div class="title">
- Comparison Xlib/XCB
- </div>
- <div class="xlib">
- <ul>
- <li>XOpenDisplay ()
- </ul>
- </div>
- <div class="xcb">
- <ul>
- <li>xcb_connect ()
- </ul>
- </div>
- <div class="xlib">
- <ul>
- <li>XCloseDisplay ()
- </ul>
- </div>
- <div class="xcb">
- <ul>
- <li>xcb_disconnect ()
- </ul>
- </div>
- </div>
- <br>
- <li class="title"><a name="screen">Checking basic information about a connection</a>
- <p>
- Once we have opened a connection to an X server, we should check some
- basic information about it: what screens it has, what is the
- size (width and height) of the screen, how many colors it
- supports (black and white ? grey scale ?, 256 colors ? more ?),
- and so on. We get such information from the xcb_screen_t
- structure:
- </p>
- <pre class="code">
-typedef struct {
- xcb_window_t root;
- xcb_colormap_t default_colormap;
- uint32_t white_pixel;
- uint32_t black_pixel;
- uint32_t current_input_masks;
- uint16_t width_in_pixels;
- uint16_t height_in_pixels;
- uint16_t width_in_millimeters;
- uint16_t height_in_millimeters;
- uint16_t min_installed_maps;
- uint16_t max_installed_maps;
- xcb_visualid_t root_visual;
- uint8_t backing_stores;
- uint8_t save_unders;
- uint8_t root_depth;
- uint8_t allowed_depths_len;
-} xcb_screen_t;
-</pre>
- <p>
- We could retrieve the first screen of the connection by using the
- following function:
- </p>
- <pre class="code">
-xcb_screen_iterator_t xcb_setup_roots_iterator (xcb_setup_t *R);
-</pre>
- <p>
- Here is a small program that shows how to use this function:
- </p>
- <pre class="code">
-#include <stdio.h>
-
-#include <xcb/xcb.h>
-
-int
-main ()
-{
- xcb_connection_t *c;
- xcb_screen_t *screen;
- int screen_nbr;
- xcb_screen_iterator_t iter;
-
- /* Open the connection to the X server. Use the DISPLAY environment variable */
- c = xcb_connect (NULL, &screen_nbr);
-
- /* Get the screen #screen_nbr */
- iter = xcb_setup_roots_iterator (xcb_get_setup (c));
- for (; iter.rem; --screen_nbr, xcb_screen_next (&iter))
- if (screen_nbr == 0) {
- screen = iter.data;
- break;
- }
-
- printf ("\n");
- printf ("Informations of screen %ld:\n", screen->root);
- printf (" width.........: %d\n", screen->width_in_pixels);
- printf (" height........: %d\n", screen->height_in_pixels);
- printf (" white pixel...: %ld\n", screen->white_pixel);
- printf (" black pixel...: %ld\n", screen->black_pixel);
- printf ("\n");
-
- return 0;
-}
-</pre>
- <li class="title"><a name="helloworld">Creating a basic window - the "hello world" program</a>
- <p>
- After we got some basic information about our screen, we can
- create our first window. In the X Window System, a window is
- characterized by an Id. So, in XCB, a window is of type:
- </p>
- <pre class="code">
-typedef uint32_t xcb_window_t;
-</pre>
- <p>
- We first ask for a new Id for our window, with this function:
- </p>
- <pre class="code">
-xcb_window_t xcb_generate_id(xcb_connection_t *c);
-</pre>
- <p>
- Then, XCB supplies the following function to create new windows:
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_create_window (xcb_connection_t *c, /* Pointer to the xcb_connection_t structure */
- uint8_t depth, /* Depth of the screen */
- xcb_window_t wid, /* Id of the window */
- xcb_window_t parent, /* Id of an existing window that should be the parent of the new window */
- int16_t x, /* X position of the top-left corner of the window (in pixels) */
- int16_t y, /* Y position of the top-left corner of the window (in pixels) */
- uint16_t width, /* Width of the window (in pixels) */
- uint16_t height, /* Height of the window (in pixels) */
- uint16_t border_width, /* Width of the window's border (in pixels) */
- uint16_t _class,
- xcb_visualid_t visual,
- uint32_t value_mask,
- const uint32_t *value_list);
-</pre>
- <p>
- The fact that we created the window does not mean that it will
- be drawn on screen. By default, newly created windows are not
- mapped on the screen (they are invisible). In order to make our
- window visible, we use the function <span class="code">xcb_map_window()</span>, whose
- prototype is
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_map_window (xcb_connection_t *c,
- xcb_window_t window);
-</pre>
- <p>
- Finally, here is a small program to create a window of size
- 150x150 pixels, positioned at the top-left corner of the screen:
- </p>
- <pre class="code">
-#include <unistd.h> /* pause() */
-
-#include <xcb/xcb.h>
-
-int
-main ()
-{
- xcb_connection_t *c;
- xcb_screen_t *screen;
- xcb_window_t win;
-
- /* Open the connection to the X server */
- c = xcb_connect (NULL, NULL);
-
- /* Get the first screen */
- screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
-
- /* Ask for our window's Id */
- win = xcb_generate_id(c);
-
- /* Create the window */
- xcb_create_window (c, /* Connection */
- XCB_COPY_FROM_PARENT, /* depth (same as root)*/
- win, /* window Id */
- screen->root, /* parent window */
- 0, 0, /* x, y */
- 150, 150, /* width, height */
- 10, /* border_width */
- XCB_WINDOW_CLASS_INPUT_OUTPUT, /* class */
- screen->root_visual, /* visual */
- 0, NULL); /* masks, not used yet */
-
- /* Map the window on the screen */
- xcb_map_window (c, win);
-
- /* Make sure commands are sent before we pause, so window is shown */
- xcb_flush (c);
-
- pause (); /* hold client until Ctrl-C */
-
- return 0;
-}
-</pre>
- <p>
- In this code, you see one more function - <span class="code">xcb_flush()</span>, not explained
- yet. It is used to flush all the pending requests. More
- precisely, there are 2 functions that do such things. The first
- one is <span class="code">xcb_flush()</span>:
- </p>
- <pre class="code">
-int xcb_flush (xcb_connection_t *c);
-</pre>
- <p>
- This function flushes all pending requests to the X server (much
- like the <span class="code">fflush()</span> function is used to
- flush standard output). The second function is
- <span class="code">xcb_aux_sync()</span>:
- </p>
- <pre class="code">
-int xcb_aux_sync (xcb_connection_t *c);
-</pre>
- <p>
- This functions also flushes all pending requests to the X
- server, and then waits until the X server finishing processing
- these requests. In a normal program, this will not be necessary
- (we'll see why when we get to write a normal X program), but for
- now, we put it there.
- </p>
- <p>
- The window that is created by the above code has a non defined
- background. This one can be set to a specific color,
- thanks to the two last parameters of
- <span class="code">xcb_create_window()</span>, which are not
- described yet. See the subsections
- <a href="#winconf">Configuring a window</a> or
- <a href="#winconf">Registering for event types using event masks</a>
- for examples on how to use these parameters. In addition, as no
- events are handled, you have to make a Ctrl-C to interrupt the
- program.
- </p>
- <p>
- <b>TODO</b>: one should tell what these functions return and
- about the generic error
- </p>
- <div class="comp">
- <div class="title">
- Comparison Xlib/XCB
- </div>
- <div class="xlib">
- <ul>
- <li>XCreateWindow ()
- </ul>
- </div>
- <div class="xcb">
- <ul>
- <li>xcb_generate_id ()
- <li>xcb_create_window ()
- </ul>
- </div>
- </div>
- <br>
- <li class="title"><a name="drawing">Drawing in a window</a>
- <p>
- Drawing in a window can be done using various graphical
- functions (drawing pixels, lines, rectangles, etc). In order to
- draw in a window, we first need to define various general
- drawing parameters (what line width to use, which color to draw
- with, etc). This is done using a graphical context.
- </p>
- <ol>
- <li class="subtitle"><a name="allocgc">Allocating a Graphics Context</a>
- <p>
- As we said, a graphical context defines several attributes to
- be used with the various drawing functions. For this, we
- define a graphical context. We can use more than one graphical
- context with a single window, in order to draw in multiple
- styles (different colors, different line widths, etc). In XCB,
- a Graphics Context is, as a window, characterized by an Id:
- </p>
- <pre class="code">
-typedef uint32_t xcb_gcontext_t;
-</pre>
- <p>
- We first ask the X server to attribute an Id to our graphic
- context with this function:
- </p>
- <pre class="code">
-xcb_gcontext_t xcb_generate_id (xcb_connection_t *c);
-</pre>
- <p>
- Then, we set the attributes of the graphic context with this function:
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_create_gc (xcb_connection_t *c,
- xcb_gcontext_t cid,
- xcb_drawable_t drawable,
- uint32_t value_mask,
- const uint32_t *value_list);
-</pre>
- <p>
- We give now an example on how to allocate a graphic context
- that specifies that each drawing function that uses it will
- draw in foreground with a black color.
- </p>
- <pre class="code">
-#include <xcb/xcb.h>
-
-int
-main ()
-{
- xcb_connection_t *c;
- xcb_screen_t *screen;
- xcb_drawable_t win;
- xcb_gcontext_t black;
- uint32_t mask;
- uint32_t value[1];
-
- /* Open the connection to the X server and get the first screen */
- c = xcb_connect (NULL, NULL);
- screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
-
- /* Create a black graphic context for drawing in the foreground */
- win = screen->root;
- black = xcb_generate_id (c);
- mask = XCB_GC_FOREGROUND;
- value[0] = screen->black_pixel;
- xcb_create_gc (c, black, win, mask, value);
-
- return 0;
-}
-</pre>
- <p>
- Note should be taken regarding the role of "value_mask" and
- "value_list" in the prototype of <span class="code">xcb_create_gc()</span>. Since a
- graphic context has many attributes, and since we often just
- want to define a few of them, we need to be able to tell the
- <span class="code">xcb_create_gc()</span> which attributes we
- want to set. This is what the "value_mask" parameter is
- for. We then use the "value_list" parameter to specify actual
- values for the attribute we defined in "value_mask". Thus, for
- each constant used in "value_list", we will use the matching
- constant in "value_mask". In this case, we define a graphic
- context with one attribute: when drawing (a point, a line,
- etc), the foreground color will be black. The rest of the
- attributes of this graphic context will be set to their
- default values.
- </p>
- <p>
- See the next Subsection for more details.
- </p>
- <div class="comp">
- <div class="title">
- Comparison Xlib/XCB
- </div>
- <div class="xlib">
- <ul>
- <li>XCreateGC ()
- </ul>
- </div>
- <div class="xcb">
- <ul>
- <li>xcb_generate_id ()
- <li>xcb_create_gc ()
- </ul>
- </div>
- </div>
- <br>
- <li class="subtitle"><a name="changegc">Changing the attributes of a Graphics Context</a>
- <p>
- Once we have allocated a Graphic Context, we may need to
- change its attributes (for example, changing the foreground
- color we use to draw a line, or changing the attributes of the
- font we use to display strings. See Subsections Drawing with a
- color and
- <a href="#assigningfont">Assigning a Font to a Graphic Context</a>).
- This is done by using this function:
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_change_gc (xcb_connection_t *c, /* The XCB Connection */
- xcb_gcontext_t gc, /* The Graphic Context */
- uint32_t value_mask, /* Components of the Graphic Context that have to be set */
- const uint32_t *value_list); /* Value as specified by value_mask */
-</pre>
- <p>
- The <span class="code">value_mask</span> parameter could take
- any combination of these masks from the xcb_gc_t enumeration:
- </p>
- <ul>
- <li>XCB_GC_FUNCTION
- <li>XCB_GC_PLANE_MASK
- <li>XCB_GC_FOREGROUND
- <li>XCB_GC_BACKGROUND
- <li>XCB_GC_LINE_WIDTH
- <li>XCB_GC_LINE_STYLE
- <li>XCB_GC_CAP_STYLE
- <li>XCB_GC_JOIN_STYLE
- <li>XCB_GC_FILL_STYLE
- <li>XCB_GC_FILL_RULE
- <li>XCB_GC_TILE
- <li>XCB_GC_STIPPLE
- <li>XCB_GC_TILE_STIPPLE_ORIGIN_X
- <li>XCB_GC_TILE_STIPPLE_ORIGIN_Y
- <li>XCB_GC_FONT
- <li>XCB_GC_SUBWINDOW_MODE
- <li>XCB_GC_GRAPHICS_EXPOSURES
- <li>XCB_GC_CLIP_ORIGIN_X
- <li>XCB_GC_CLIP_ORIGIN_Y
- <li>XCB_GC_CLIP_MASK
- <li>XCB_GC_DASH_OFFSET
- <li>XCB_GC_DASH_LIST
- <li>XCB_GC_ARC_MODE
- </ul>
- <p>
- It is possible to set several attributes at the same
- time (for example setting the attributes of a font and the
- color which will be used to display a string), by OR'ing these
- values in <span class="code">value_mask</span>. Then
- <span class="code">value_list</span> has to be an array which
- lists the value for the respective attributes. <b>These values
- must be in the same order as masks listed above.</b> See Subsection
- Drawing with a color to have an example.
- </p>
- <p>
- <b>TODO</b>: set the links of the 3 subsections, once they will
- be written :)
- </p>
- <p>
- <b>TODO</b>: give an example which sets several attributes.
- </p>
- <li class="subtitle"><a name="drawingprim">Drawing primitives: point, line, box, circle,...</a>
- <p>
- After we have created a Graphic Context, we can draw on a
- window using this Graphic Context, with a set of XCB
- functions, collectively called "drawing primitives". Let see
- how they are used.
- </p>
- <p>
- To draw a point, or several points, we use
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_poly_point (xcb_connection_t *c, /* The connection to the X server */
- uint8_t coordinate_mode, /* Coordinate mode, usually set to XCB_COORD_MODE_ORIGIN */
- xcb_drawable_t drawable, /* The drawable on which we want to draw the point(s) */
- xcb_gcontext_t gc, /* The Graphic Context we use to draw the point(s) */
- uint32_t points_len, /* The number of points */
- const xcb_point_t *points); /* An array of points */
-</pre>
- <p>
- The <span class="code">coordinate_mode</span> parameter
- specifies the coordinate mode. Available values are
- </p>
- <ul>
- <li><span class="code">XCB_COORD_MODE_ORIGIN</span>
- <li><span class="code">XCB_COORD_MODE_PREVIOUS</span>
- </ul>
- <p>
- If XCB_COORD_MODE_PREVIOUS is used, then all points but the first one
- are relative to the immediately previous point.
- </p>
- <p>
- The <span class="code">xcb_point_t</span> type is just a
- structure with two fields (the coordinates of the point):
- </p>
- <pre class="code">
-typedef struct {
- int16_t x;
- int16_t y;
-} xcb_point_t;
-</pre>
- <p>
- You could see an example in xpoints.c. <b>TODO</b> Set the link.
- </p>
- <p>
- To draw a line, or a polygonal line, we use
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_poly_line (xcb_connection_t *c, /* The connection to the X server */
- uint8_t coordinate_mode, /* Coordinate mode, usually set to XCB_COORD_MODE_ORIGIN */
- xcb_drawable_t drawable, /* The drawable on which we want to draw the line(s) */
- xcb_gcontext_t gc, /* The Graphic Context we use to draw the line(s) */
- uint32_t points_len, /* The number of points in the polygonal line */
- const xcb_point_t *points); /* An array of points */
-</pre>
- <p>
- This function will draw the line between the first and the
- second points, then the line between the second and the third
- points, and so on.
- </p>
- <p>
- To draw a segment, or several segments, we use
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_poly_segment (xcb_connection_t *c, /* The connection to the X server */
- xcb_drawable_t drawable, /* The drawable on which we want to draw the segment(s) */
- xcb_gcontext_t gc, /* The Graphic Context we use to draw the segment(s) */
- uint32_t segments_len, /* The number of segments */
- const xcb_segment_t *segments); /* An array of segments */
-</pre>
- <p>
- The <span class="code">xcb_segment_t</span> type is just a
- structure with four fields (the coordinates of the two points
- that define the segment):
- </p>
- <pre class="code">
-typedef struct {
- int16_t x1;
- int16_t y1;
- int16_t x2;
- int16_t y2;
-} xcb_segment_t;
-</pre>
- <p>
- To draw a rectangle, or several rectangles, we use
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_poly_rectangle (xcb_connection_t *c, /* The connection to the X server */
- xcb_drawable_t drawable, /* The drawable on which we want to draw the rectangle(s) */
- xcb_gcontext_t gc, /* The Graphic Context we use to draw the rectangle(s) */
- uint32_t rectangles_len, /* The number of rectangles */
- const xcb_rectangle_t *rectangles); /* An array of rectangles */
-</pre>
- <p>
- The <span class="code">xcb_rectangle_t</span> type is just a
- structure with four fields (the coordinates of the top-left
- corner of the rectangle, and its width and height):
- </p>
- <pre class="code">
-typedef struct {
- int16_t x;
- int16_t y;
- uint16_t width;
- uint16_t height;
-} xcb_rectangle_t;
-</pre>
- <!-- There's no coordinate_mode. Is it normal? -->
- <!-- [iano] Yes, it's not in the protocol. -->
- <p>
- To draw an elliptical arc, or several elliptical arcs, we use
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_poly_arc (xcb_connection_t *c, /* The connection to the X server */
- xcb_drawable_t drawable, /* The drawable on which we want to draw the arc(s) */
- xcb_gcontext_t gc, /* The Graphic Context we use to draw the arc(s) */
- uint32_t arcs_len, /* The number of arcs */
- const xcb_arc_t *arcs); /* An array of arcs */
-</pre>
- <p>
- The <span class="code">xcb_arc_t</span> type is a structure with
- six fields:
- </p>
- <pre class="code">
-typedef struct {
- int16_t x; /* Top left x coordinate of the rectangle surrounding the ellipse */
- int16_t y; /* Top left y coordinate of the rectangle surrounding the ellipse */
- uint16_t width; /* Width of the rectangle surrounding the ellipse */
- uint16_t height; /* Height of the rectangle surrounding the ellipse */
- int16_t angle1; /* Angle at which the arc begins */
- int16_t angle2; /* Angle at which the arc ends */
-} xcb_arc_t;
-</pre>
- <div class="emph">
- <p>
- Note: the angles are expressed in units of 1/64 of a degree,
- so to have an angle of 90 degrees, starting at 0,
- <span class="code">angle1 = 0</span> and
- <span class="code">angle2 = 90 << 6</span>. Positive angles
- indicate counterclockwise motion, while negative angles
- indicate clockwise motion.
- </p>
- </div>
- <!-- I think that (x,y) should be the center of the
- ellipse, and (width, height) the radius. It's more logical. -->
- <!-- iano: Yes, and I bet some toolkits do that.
- But the protocol (and many other graphics APIs) define arcs
- by bounding rectangles. -->
- <p>
- The corresponding function which fill inside the geometrical
- object are listed below, without further explanation, as they
- are used as the above functions.
- </p>
- <p>
- To Fill a polygon defined by the points given as arguments ,
- we use
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_fill_poly (xcb_connection_t *c,
- xcb_drawable_t drawable,
- xcb_gcontext_t gc,
- uint8_t shape,
- uint8_t coordinate_mode,
- uint32_t points_len,
- const xcb_point_t *points);
-</pre>
- <p>
- The <span class="code">shape</span> parameter specifies a
- shape that helps the server to improve performance. Available
- values are
- </p>
- <ul>
- <li><span class="code">XCB_POLY_SHAPE_COMPLEX</span>
- <li><span class="code">XCB_POLY_SHAPE_NONCONVEX</span>
- <li><span class="code">XCB_POLY_SHAPE_CONVEX</span>
- </ul>
- <p>
- To fill one or several rectangles, we use
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_poly_fill_rectangle (xcb_connection_t *c,
- xcb_drawable_t drawable,
- xcb_gcontext_t gc,
- uint32_t rectangles_len,
- const xcb_rectangle_t *rectangles);
-</pre>
- <p>
- To fill one or several arcs, we use
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_poly_fill_arc (xcb_connection_t *c,
- xcb_drawable_t drawable,
- xcb_gcontext_t gc,
- uint32_t arcs_len,
- const xcb_arc_t *arcs);
-</pre>
- <br>
- <a name="points.c"></a>
- <p>
- To illustrate these functions, here is an example that draws
- four points, a polygonal line, two segments, two rectangles
- and two arcs. Remark that we use events for the first time, as
- an introduction to the next section.
- </p>
- <p>
- <b>TODO:</b> Use screen->root_depth for depth parameter.
- </p>
- <pre class="code">
-#include <stdlib.h>
-#include <stdio.h>
-
-#include <xcb/xcb.h>
-
-int
-main ()
-{
- xcb_connection_t *c;
- xcb_screen_t *screen;
- xcb_drawable_t win;
- xcb_gcontext_t foreground;
- xcb_generic_event_t *e;
- uint32_t mask = 0;
- uint32_t values[2];
-
- /* geometric objects */
- xcb_point_t points[] = {
- {10, 10},
- {10, 20},
- {20, 10},
- {20, 20}};
-
- xcb_point_t polyline[] = {
- {50, 10},
- { 5, 20}, /* rest of points are relative */
- {25,-20},
- {10, 10}};
-
- xcb_segment_t segments[] = {
- {100, 10, 140, 30},
- {110, 25, 130, 60}};
-
- xcb_rectangle_t rectangles[] = {
- { 10, 50, 40, 20},
- { 80, 50, 10, 40}};
-
- xcb_arc_t arcs[] = {
- {10, 100, 60, 40, 0, 90 << 6},
- {90, 100, 55, 40, 0, 270 << 6}};
-
- /* Open the connection to the X server */
- c = xcb_connect (NULL, NULL);
-
- /* Get the first screen */
- screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
-
- /* Create black (foreground) graphic context */
- win = screen->root;
-
- foreground = xcb_generate_id (c);
- mask = XCB_GC_FOREGROUND | XCB_GC_GRAPHICS_EXPOSURES;
- values[0] = screen->black_pixel;
- values[1] = 0;
- xcb_create_gc (c, foreground, win, mask, values);
-
- /* Ask for our window's Id */
- win = xcb_generate_id(c);
-
- /* Create the window */
- mask = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK;
- values[0] = screen->white_pixel;
- values[1] = XCB_EVENT_MASK_EXPOSURE;
- xcb_create_window (c, /* Connection */
- XCB_COPY_FROM_PARENT, /* depth */
- win, /* window Id */
- screen->root, /* parent window */
- 0, 0, /* x, y */
- 150, 150, /* width, height */
- 10, /* border_width */
- XCB_WINDOW_CLASS_INPUT_OUTPUT, /* class */
- screen->root_visual, /* visual */
- mask, values); /* masks */
-
- /* Map the window on the screen */
- xcb_map_window (c, win);
-
-
- /* We flush the request */
- xcb_flush (c);
-
- while ((e = xcb_wait_for_event (c))) {
- switch (e->response_type & ~0x80) {
- case XCB_EXPOSE: {
- /* We draw the points */
- xcb_poly_point (c, XCB_COORD_MODE_ORIGIN, win, foreground, 4, points);
-
- /* We draw the polygonal line */
- xcb_poly_line (c, XCB_COORD_MODE_PREVIOUS, win, foreground, 4, polyline);
-
- /* We draw the segements */
- xcb_poly_segment (c, win, foreground, 2, segments);
-
- /* We draw the rectangles */
- xcb_poly_rectangle (c, win, foreground, 2, rectangles);
-
- /* We draw the arcs */
- xcb_poly_arc (c, win, foreground, 2, arcs);
-
- /* We flush the request */
- xcb_flush (c);
-
- break;
- }
- default: {
- /* Unknown event type, ignore it */
- break;
- }
- }
- /* Free the Generic Event */
- free (e);
- }
-
- return 0;
-}
-</pre>
- </ol>
- <li class="title"><a name="xevents">X Events</a>
- <p>
- In an X program, everything is driven by events. Event painting
- on the screen is sometimes done as a response to an event (an
- <span class="code">Expose</span> event). If part of a program's
- window that was hidden, gets exposed (e.g. the window was raised
- above other widows), the X server will send an "expose" event to
- let the program know it should repaint that part of the
- window. User input (key presses, mouse movement, etc) is also
- received as a set of events.
- </p>
- <ol>
- <li class="subtitle"><a name="register">Registering for event types using event masks</a>
- <p>
- During the creation of a window, you should give it what kind
- of events it wishes to receive. Thus, you may register for
- various mouse (also called pointer) events, keyboard events,
- expose events, and so on. This is done for optimizing the
- server-to-client connection (i.e. why send a program (that
- might even be running at the other side of the globe) an event
- it is not interested in ?)
- </p>
- <p>
- In XCB, you use the "value_mask" and "value_list" data in the
- <span class="code">xcb_create_window()</span> function to
- register for events. Here is how we register for
- <span class="code">Expose</span> event when creating a window:
- </p>
- <pre class="code">
- mask = XCB_CW_EVENT_MASK;
- valwin[0] = XCB_EVENT_MASK_EXPOSURE;
- win = xcb_generate_id (c);
- xcb_create_window (c, depth, win, root->root,
- 0, 0, 150, 150, 10,
- XCB_WINDOW_CLASS_INPUT_OUTPUT, root->root_visual,
- mask, valwin);
-</pre>
- <p>
- <span class="code">XCB_EVENT_MASK_EXPOSURE</span> is a constant defined
- in the xcb_event_mask_t enumeration in the "xproto.h" header file. If we wanted to register for several
- event types, we can logically "or" them, as follows:
- </p>
- <pre class="code">
- mask = XCB_CW_EVENT_MASK;
- valwin[0] = XCB_EVENT_MASK_EXPOSURE | XCB_EVENT_MASK_BUTTON_PRESS;
- win = xcb_generate_id (c);
- xcb_create_window (c, depth, win, root->root,
- 0, 0, 150, 150, 10,
- XCB_WINDOW_CLASS_INPUT_OUTPUT, root->root_visual,
- mask, valwin);
-</pre>
- <p>
- This registers for <span class="code">Expose</span> events as
- well as for mouse button presses inside the created
- window. You should note that a mask may represent several
- event sub-types.
- </p>
- <p>
- The values that a mask could take are given
- by the <span class="code">xcb_cw_t</span> enumeration:
- </p>
- <pre class="code">
-typedef enum {
- XCB_CW_BACK_PIXMAP = 1L<<0,
- XCB_CW_BACK_PIXEL = 1L<<1,
- XCB_CW_BORDER_PIXMAP = 1L<<2,
- XCB_CW_BORDER_PIXEL = 1L<<3,
- XCB_CW_BIT_GRAVITY = 1L<<4,
- XCB_CW_WIN_GRAVITY = 1L<<5,
- XCB_CW_BACKING_STORE = 1L<<6,
- XCB_CW_BACKING_PLANES = 1L<<7,
- XCB_CW_BACKING_PIXEL = 1L<<8,
- XCB_CW_OVERRIDE_REDIRECT = 1L<<9,
- XCB_CW_SAVE_UNDER = 1L<<10,
- XCB_CW_EVENT_MASK = 1L<<11,
- XCB_CW_DONT_PROPAGATE = 1L<<12,
- XCB_CW_COLORMAP = 1L<<13,
- XCB_CW_CURSOR = 1L<<14
-} xcb_cw_t;
-</pre>
- <div class="emph">
- <p>Note: we must be careful when setting the values of the valwin
- parameter, as they have to follow the order the
- <span class="code">xcb_cw_t</span> enumeration. Here is an
- example:
- </p>
- </div>
- <pre class="code">
- mask = XCB_CW_EVENT_MASK | XCB_CW_BACK_PIXMAP;
- valwin[0] = XCB_NONE; /* for XCB_CW_BACK_PIXMAP (whose value is 1) */
- valwin[1] = XCB_EVENT_MASK_EXPOSURE | XCB_EVENT_MASK_BUTTON_PRESS; /* for XCB_CW_EVENT_MASK, whose value (2048) */
- /* is greater than the one of XCB_CW_BACK_PIXMAP */
-</pre>
- <p>
- If the window has already been created, we can use the
- <span class="code">xcb_change_window_attributes()</span> function to set
- the events that the window will receive. The subsection
- <a href="#winconf">Configuring a window</a> shows its
- prototype. As an example, here is a piece of code that
- configures the window to receive the
- <span class="code">Expose</span> and
- <span class="code">ButtonPress</span> events:
- </p>
- <pre class="code">
-const static uint32_t values[] = { XCB_EVENT_MASK_EXPOSURE | XCB_EVENT_MASK_BUTTON_PRESS };
-
-/* The connection c and the window win are supposed to be defined */
-
-xcb_change_window_attributes (c, win, XCB_CW_EVENT_MASK, values);
-</pre>
- <div class="emph">
- <p>
- Note: A common bug programmers do is adding code to handle new
- event types in their program, while forgetting to add the
- masks for these events in the creation of the window. Such a
- programmer then should sit down for hours debugging his
- program, wondering "Why doesn't my program notice that I
- released the button?", only to find that they registered for
- button press events but not for button release events.
- </p>
- </div>
- <li class="subtitle"><a name="loop">Receiving events: writing the events loop</a>
- <p>
- After we have registered for the event types we are interested
- in, we need to enter a loop of receiving events and handling
- them. There are two ways to receive events: a blocking way and
- a non-blocking way:
- </p>
- <ul>
- <li>
- <span class="code">xcb_wait_for_event (xcb_connection_t *c)</span>
- is the blocking way. It waits (so blocks...) until an event is
- queued in the X server. Then it retrieves it into a newly
- allocated structure (it dequeues it from the queue) and returns
- it. This structure has to be freed. The function returns
- <span class="code">NULL</span> if an error occurs.
-
- <br>
- <li>
- <span class="code">xcb_poll_for_event (xcb_connection_t *c, int
- *error)</span> is the non-blocking way. It looks at the event
- queue and returns (and dequeues too) an existing event into
- a newly allocated structure. This structure has to be
- freed. It returns <span class="code">NULL</span> if there is
- no event. If an error occurs, the parameter <span
- class="code">error</span> will be filled with the error
- status.
- </ul>
- <p>
- There are various ways to write such a loop. We present two
- ways to write such a loop, with the two functions above. The
- first one uses <span class="code">xcb_wait_for_event_t</span>, which
- is similar to an event Xlib loop using only <span
- class="code">XNextEvent</span>:
- </p>
- <pre class="code">
- xcb_generic_event_t *e;
-
- while ((e = xcb_wait_for_event (c))) {
- switch (e->response_type & ~0x80) {
- case XCB_EXPOSE: {
- /* Handle the Expose event type */
- xcb_expose_event_t *ev = (xcb_expose_event_t *)e;
-
- /* ... */
-
- break;
- }
- case XCB_BUTTON_PRESS: {
- /* Handle the ButtonPress event type */
- xcb_button_press_event_t *ev = (xcb_button_press_event_t *)e;
-
- /* ... */
-
- break;
- }
- default: {
- /* Unknown event type, ignore it */
- break;
- }
- }
- /* Free the Generic Event */
- free (e);
- }
-</pre>
- <p>
- You will certainly want to use <span
- class="code">xcb_poll_for_event(xcb_connection_t *c, int
- *error)</span> if, in Xlib, you use <span
- class="code">XPending</span> or
- <span class="code">XCheckMaskEvent</span>:
- </p>
- <pre class="code">
- while (XPending (display)) {
- XEvent ev;
-
- XNextEvent(d, &ev);
-
- /* Manage your event */
- }
-</pre>
- <p>
- Such a loop in XCB looks like:
- </p>
- <pre class="code">
- xcb_generic_event_t *ev;
-
- while ((ev = xcb_poll_for_event (conn, 0))) {
- /* Manage your event */
- }
-</pre>
- <p>
- The events are managed in the same way as with <span
- class="code">xcb_wait_for_event_t</span>.
- Obviously, we will need to give the user some way of
- terminating the program. This is usually done by handling a
- special "quit" event, as we will soon see.
- </p>
- <div class="comp">
- <div class="title">
- Comparison Xlib/XCB
- </div>
- <div class="xlib">
- <ul>
- <li>XNextEvent ()
- </ul>
- </div>
- <div class="xcb">
- <ul>
- <li>xcb_wait_for_event ()
- </ul>
- </div>
- <div class="xlib">
- <ul>
- <li>XPending ()
- <li>XCheckMaskEvent ()
- </ul>
- </div>
- <div class="xcb">
- <ul>
- <li>xcb_poll_for_event ()
- </ul>
- </div>
- </div>
- <br>
- <li class="subtitle"><a name="expose">Expose events</a>
- <p>
- The <span class="code">Expose</span> event is one of the most
- basic (and most used) events an application may receive. It
- will be sent to us in one of several cases:
- </p>
- <ul>
- <li>A window that covered part of our window has moved
- away, exposing part (or all) of our window.
- <li>Our window was raised above other windows.
- <li>Our window mapped for the first time.
- <li>Our window was de-iconified.
- </ul>
- <p>
- You should note the implicit assumption hidden here: the
- contents of our window is lost when it is being obscured
- (covered) by either windows. One may wonder why the X server
- does not save this contents. The answer is: to save
- memory. After all, the number of windows on a display at a
- given time may be very large, and storing the contents of all
- of them might require a lot of memory. Actually, there is a
- way to tell the X server to store the contents of a window in
- special cases, as we will see later.
- </p>
- <p>
- When we get an <span class="code">Expose</span> event, we
- should take the event's data from the members of the following
- structure:
- </p>
- <pre class="code">
-typedef struct {
- uint8_t response_type; /* The type of the event, here it is XCB_EXPOSE */
- uint8_t pad0;
- uint16_t sequence;
- xcb_window_t window; /* The Id of the window that receives the event (in case */
- /* our application registered for events on several windows */
- uint16_t x; /* The x coordinate of the top-left part of the window that needs to be redrawn */
- uint16_t y; /* The y coordinate of the top-left part of the window that needs to be redrawn */
- uint16_t width; /* The width of the part of the window that needs to be redrawn */
- uint16_t height; /* The height of the part of the window that needs to be redrawn */
- uint16_t count;
-} xcb_expose_event_t;
-</pre>
- <li class="subtitle"><a name="userinput">Getting user input</a>
- <p>
- User input traditionally comes from two sources: the mouse
- and the keyboard. Various event types exist to notify us of
- user input (a key being presses on the keyboard, a key being
- released on the keyboard, the mouse moving over our window,
- the mouse entering (or leaving) our window, and so on.
- </p>
- <ol>
- <li class="subsubtitle"><a name="mousepressrelease">Mouse button press and release events</a>
- <p>
- The first event type we will deal with is a mouse
- button-press (or button-release) event in our window. In
- order to register to such an event type, we should add one
- (or more) of the following masks when we create our window:
- </p>
- <ul>
- <li><span class="code">XCB_EVENT_MASK_BUTTON_PRESS</span>: notify us
- of any button that was pressed in one of our windows.
- <li><span class="code">XCB_EVENT_MASK_BUTTON_RELEASE</span>: notify us
- of any button that was released in one of our windows.
- </ul>
- <p>
- The structure to be checked for in our events loop is the
- same for these two events, and is the following:
- </p>
- <pre class="code">
-typedef struct {
- uint8_t response_type; /* The type of the event, here it is xcb_button_press_event_t or xcb_button_release_event_t */
- xcb_button_t detail;
- uint16_t sequence;
- xcb_timestamp_t time; /* Time, in milliseconds the event took place in */
- xcb_window_t root;
- xcb_window_t event;
- xcb_window_t child;
- int16_t root_x;
- int16_t root_y;
- int16_t event_x; /* The x coordinate where the mouse has been pressed in the window */
- int16_t event_y; /* The y coordinate where the mouse has been pressed in the window */
- uint16_t state; /* A mask of the buttons (or keys) during the event */
- uint8_t same_screen;
-} xcb_button_press_event_t;
-
-typedef xcb_button_press_event_t xcb_button_release_event_t;
-</pre>
- <p>
- The <span class="code">time</span> field may be used to calculate "double-click"
- situations by an application (e.g. if the mouse button was
- clicked two times in a duration shorter than a given amount
- of time, assume this was a double click).
- </p>
- <p>
- The <span class="code">state</span> field is a mask of the buttons held down during
- the event. It is a bitwise OR of any of the following (from the xcb_button_mask_t and
- xcb_mod_mask_t enumerations):
- </p>
- <ul>
- <li><span class="code">XCB_BUTTON_MASK_1</span>
- <li><span class="code">XCB_BUTTON_MASK_2</span>
- <li><span class="code">XCB_BUTTON_MASK_3</span>
- <li><span class="code">XCB_BUTTON_MASK_4</span>
- <li><span class="code">XCB_BUTTON_MASK_5</span>
- <li><span class="code">XCB_MOD_MASK_SHIFT</span>
- <li><span class="code">XCB_MOD_MASK_LOCK</span>
- <li><span class="code">XCB_MOD_MASK_CONTROL</span>
- <li><span class="code">XCB_MOD_MASK_1</span>
- <li><span class="code">XCB_MOD_MASK_2</span>
- <li><span class="code">XCB_MOD_MASK_3</span>
- <li><span class="code">XCB_MOD_MASK_4</span>
- <li><span class="code">XCB_MOD_MASK_5</span>
- </ul>
- <p>
- Their names are self explanatory, where the first 5 refer to
- the mouse buttons that are being pressed, while the rest
- refer to various "special keys" that are being pressed (Mod1
- is usually the 'Alt' key or the 'Meta' key).
- </p>
- <p>
- <b>TODO:</b> Problem: it seems that the state does not
- change when clicking with various buttons.
- </p>
- <li class="subsubtitle"><a name="mousemvnt">Mouse movement events</a>
- <p>
- Similar to mouse button press and release events, we also
- can be notified of various mouse movement events. These can
- be split into two families. One is of mouse pointer
- movement while no buttons are pressed, and the second is a
- mouse pointer motion while one (or more) of the buttons are
- pressed (this is sometimes called "a mouse drag operation",
- or just "dragging"). The following event masks may be added
- during the creation of our window:
- </p>
- <ul>
- <li><span class="code">XCB_EVENT_MASK_POINTER_MOTION</span>: events of
- the pointer moving in one of the windows controlled by our
- application, while no mouse button is held pressed.
- <li><span class="code">XCB_EVENT_MASK_BUTTON_MOTION</span>: Events of
- the pointer moving while one or more of the mouse buttons
- is held pressed.
- <li><span class="code">XCB_EVENT_MASK_BUTTON_1_MOTION</span>: same as
- <span class="code">XCB_EVENT_MASK_BUTTON_MOTION</span>, but only when
- the 1st mouse button is held pressed.
- <li><span class="code">XCB_EVENT_MASK_BUTTON_2_MOTION</span>,
- <span class="code">XCB_EVENT_MASK_BUTTON_3_MOTION</span>,
- <span class="code">XCB_EVENT_MASK_BUTTON_4_MOTION</span>,
- <span class="code">XCB_EVENT_MASK_BUTTON_5_MOTION</span>: same as
- <span class="code">XCB_EVENT_MASK_BUTTON_1_MOTION</span>, but
- respectively for 2nd, 3rd, 4th and 5th mouse button.
- </ul>
- <p>
- The structure to be checked for in our events loop is the
- same for these events, and is the following:
- </p>
- <pre class="code">
-typedef struct {
- uint8_t response_type; /* The type of the event */
- uint8_t detail;
- uint16_t sequence;
- xcb_timestamp_t time; /* Time, in milliseconds the event took place in */
- xcb_window_t root;
- xcb_window_t event;
- xcb_window_t child;
- int16_t root_x;
- int16_t root_y;
- int16_t event_x; /* The x coordinate of the mouse when the event was generated */
- int16_t event_y; /* The y coordinate of the mouse when the event was generated */
- uint16_t state; /* A mask of the buttons (or keys) during the event */
- uint8_t same_screen;
-} xcb_motion_notify_event_t;
-</pre>
- <li class="subsubtitle"><a name="mouseenter">Mouse pointer enter and leave events</a>
- <p>
- Another type of event that applications might be interested
- in, is a mouse pointer entering a window the program
- controls, or leaving such a window. Some programs use these
- events to show the user that the application is now in
- focus. In order to register for such an event type, we
- should add one (or more) of the following masks when we
- create our window:
- </p>
- <ul>
- <li><span class="code">xcb_event_enter_window_t</span>: notify us
- when the mouse pointer enters any of our controlled
- windows.
- <li><span class="code">xcb_event_leave_window_t</span>: notify us
- when the mouse pointer leaves any of our controlled
- windows.
- </ul>
- <p>
- The structure to be checked for in our events loop is the
- same for these two events, and is the following:
- </p>
- <pre class="code">
-typedef struct {
- uint8_t response_type; /* The type of the event */
- uint8_t detail;
- uint16_t sequence;
- xcb_timestamp_t time; /* Time, in milliseconds the event took place in */
- xcb_window_t root;
- xcb_window_t event;
- xcb_window_t child;
- int16_t root_x;
- int16_t root_y;
- int16_t event_x; /* The x coordinate of the mouse when the event was generated */
- int16_t event_y; /* The y coordinate of the mouse when the event was generated */
- uint16_t state; /* A mask of the buttons (or keys) during the event */
- uint8_t mode; /* The number of mouse button that was clicked */
- uint8_t same_screen_focus;
-} xcb_enter_notify_event_t;
-
-typedef xcb_enter_notify_event_t xcb_leave_notify_event_t;
-</pre>
- <li class="subsubtitle"><a name="focus">The keyboard focus</a>
- <p>
- There may be many windows on a screen, but only a single
- keyboard attached to them. How does the X server then know
- which window should be sent a given keyboard input ? This is
- done using the keyboard focus. Only a single window on the
- screen may have the keyboard focus at a given time. There
- is a XCB function that allows a program to set the keyboard
- focus to a given window. The user can usually set the
- keyboard focus using the window manager (often by clicking
- on the title bar of the desired window). Once our window
- has the keyboard focus, every key press or key release will
- cause an event to be sent to our program (if it regsitered
- for these event types...).
- </p>
- <li class="subsubtitle"><a name="keypress">Keyboard press and release events</a>
- <p>
- If a window controlled by our program currently holds the
- keyboard focus, it can receive key press and key release
- events. So, we should add one (or more) of the following
- masks when we create our window:
- </p>
- <ul>
- <li><span class="code">XCB_EVENT_MASK_KEY_PRESS</span>: notify us when
- a key was pressed while any of our controlled windows had
- the keyboard focus.
- <li><span class="code">XCB_EVENT_MASK_KEY_RELEASE</span>: notify us
- when a key was released while any of our controlled
- windows had the keyboard focus.
- </ul>
- <p>
- The structure to be checked for in our events loop is the
- same for these two events, and is the following:
- </p>
- <pre class="code">
-typedef struct {
- uint8_t response_type; /* The type of the event */
- xcb_keycode_t detail;
- uint16_t sequence;
- xcb_timestamp_t time; /* Time, in milliseconds the event took place in */
- xcb_window_t root;
- xcb_window_t event;
- xcb_window_t child;
- int16_t root_x;
- int16_t root_y;
- int16_t event_x;
- int16_t event_y;
- uint16_t state;
- uint8_t same_screen;
-} xcb_key_press_event_t;
-
-typedef xcb_key_press_event_t xcb_key_release_event_t;
-</pre>
- <p>
- The <span class="code">detail</span> field refers to the
- physical key on the keyboard.
- </p>
- <p>
- <b>TODO:</b> Talk about getting the ASCII code from the key code.
- </p>
- </ol>
- <li class="subtitle"><a name="eventex">X events: a complete example</a>
- <p>
- As an example for handling events, we show a program that
- creates a window, enters an events loop and checks for all the
- events described above, and writes on the terminal the relevant
- characteristics of the event. With this code, it should be
- easy to add drawing operations, like those which have been
- described above.
- </p>
- <pre class="code">
-#include <stdlib.h>
-#include <stdio.h>
-
-#include <xcb/xcb.h>
-
-void
-print_modifiers (uint32_t mask)
-{
- const char **mod, *mods[] = {
- "Shift", "Lock", "Ctrl", "Alt",
- "Mod2", "Mod3", "Mod4", "Mod5",
- "Button1", "Button2", "Button3", "Button4", "Button5"
- };
- printf ("Modifier mask: ");
- for (mod = mods ; mask; mask >>= 1, mod++)
- if (mask & 1)
- printf(*mod);
- putchar ('\n');
-}
-
-int
-main ()
-{
- xcb_connection_t *c;
- xcb_screen_t *screen;
- xcb_window_t win;
- xcb_generic_event_t *e;
- uint32_t mask = 0;
- uint32_t values[2];
-
- /* Open the connection to the X server */
- c = xcb_connect (NULL, NULL);
-
- /* Get the first screen */
- screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
-
- /* Ask for our window's Id */
- win = xcb_generate_id (c);
-
- /* Create the window */
- mask = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK;
- values[0] = screen->white_pixel;
- values[1] = XCB_EVENT_MASK_EXPOSURE | XCB_EVENT_MASK_BUTTON_PRESS |
- XCB_EVENT_MASK_BUTTON_RELEASE | XCB_EVENT_MASK_POINTER_MOTION |
- XCB_EVENT_MASK_ENTER_WINDOW | XCB_EVENT_MASK_LEAVE_WINDOW |
- XCB_EVENT_MASK_KEY_PRESS | XCB_EVENT_MASK_KEY_RELEASE;
- xcb_create_window (c, /* Connection */
- 0, /* depth */
- win, /* window Id */
- screen->root, /* parent window */
- 0, 0, /* x, y */
- 150, 150, /* width, height */
- 10, /* border_width */
- XCB_WINDOW_CLASS_INPUT_OUTPUT, /* class */
- screen->root_visual, /* visual */
- mask, values); /* masks */
-
- /* Map the window on the screen */
- xcb_map_window (c, win);
-
- xcb_flush (c);
-
- while ((e = xcb_wait_for_event (c))) {
- switch (e->response_type & ~0x80) {
- case XCB_EXPOSE: {
- xcb_expose_event_t *ev = (xcb_expose_event_t *)e;
-
- printf ("Window %ld exposed. Region to be redrawn at location (%d,%d), with dimension (%d,%d)\n",
- ev->window, ev->x, ev->y, ev->width, ev->height);
- break;
- }
- case XCB_BUTTON_PRESS: {
- xcb_button_press_event_t *ev = (xcb_button_press_event_t *)e;
- print_modifiers(ev->state);
-
- switch (ev->detail) {
- case 4:
- printf ("Wheel Button up in window %ld, at coordinates (%d,%d)\n",
- ev->event, ev->event_x, ev->event_y);
- break;
- case 5:
- printf ("Wheel Button down in window %ld, at coordinates (%d,%d)\n",
- ev->event, ev->event_x, ev->event_y);
- break;
- default:
- printf ("Button %d pressed in window %ld, at coordinates (%d,%d)\n",
- ev->detail, ev->event, ev->event_x, ev->event_y);
- }
- break;
- }
- case XCB_BUTTON_RELEASE: {
- xcb_button_release_event_t *ev = (xcb_button_release_event_t *)e;
- print_modifiers(ev->state);
-
- printf ("Button %d released in window %ld, at coordinates (%d,%d)\n",
- ev->detail, ev->event, ev->event_x, ev->event_y);
- break;
- }
- case XCB_MOTION_NOTIFY: {
- xcb_motion_notify_event_t *ev = (xcb_motion_notify_event_t *)e;
-
- printf ("Mouse moved in window %ld, at coordinates (%d,%d)\n",
- ev->event, ev->event_x, ev->event_y);
- break;
- }
- case XCB_ENTER_NOTIFY: {
- xcb_enter_notify_event_t *ev = (xcb_enter_notify_event_t *)e;
-
- printf ("Mouse entered window %ld, at coordinates (%d,%d)\n",
- ev->event, ev->event_x, ev->event_y);
- break;
- }
- case XCB_LEAVE_NOTIFY: {
- xcb_leave_notify_event_t *ev = (xcb_leave_notify_event_t *)e;
-
- printf ("Mouse left window %ld, at coordinates (%d,%d)\n",
- ev->event, ev->event_x, ev->event_y);
- break;
- }
- case XCB_KEY_PRESS: {
- xcb_key_press_event_t *ev = (xcb_key_press_event_t *)e;
- print_modifiers(ev->state);
-
- printf ("Key pressed in window %ld\n",
- ev->event);
- break;
- }
- case XCB_KEY_RELEASE: {
- xcb_key_release_event_t *ev = (xcb_key_release_event_t *)e;
- print_modifiers(ev->state);
-
- printf ("Key released in window %ld\n",
- ev->event);
- break;
- }
- default:
- /* Unknown event type, ignore it */
- printf("Unknown event: %d\n", e->response_type);
- break;
- }
- /* Free the Generic Event */
- free (e);
- }
-
- return 0;
-}
-</pre>
- </ol>
- <li class="title"><a name="font">Handling text and fonts</a>
- <p>
- Besides drawing graphics on a window, we often want to draw
- text. Text strings have two major properties: the characters to
- be drawn and the font with which they are drawn. In order to
- draw text, we need to first request the X server to load a
- font. We then assign a font to a Graphic Context, and finally, we
- draw the text in a window, using the Graphic Context.
- </p>
- <ol>
- <li class="subtitle"><a name="fontstruct">The Font structure</a>
- <p>
- In order to support flexible fonts, a font type is
- defined. You know what ? It's an Id:
- </p>
- <pre class="code">
-typedef uint32_t xcb_font_t;
-</pre>
- <p>
- It is used to contain information about a font, and is passed
- to several functions that handle fonts selection and text drawing.
- We ask the X server to attribute an Id to our font with the
- function:
- </p>
- <pre class="code">
-xcb_font_t xcb_generate_id (xcb_connection_t *c);
-</pre>
- <br>
- <li class="subtitle"><a name="openingfont">Opening a Font</a>
- <p>
- To open a font, we use the following function:
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_open_font (xcb_connection_t *c,
- xcb_font_t fid,
- uint16_t name_len,
- const char *name);
-</pre>
- <p>
- The <span class="code">fid</span> parameter is the font Id
- defined by <span class="code">xcb_generate_id()</span> (see
- above). The <span class="code">name</span> parameter is the
- name of the font you want to open. Use the command
- <span class="code">xlsfonts</span> in a terminal to know which
- are the fonts available on your computer. The parameter
- <span class="code">name_len</span> is the length of the name
- of the font (given by <span class="code">strlen()</span>).
- </p>
- <li class="subtitle"><a name="assigningfont">Assigning a Font to a Graphic Context</a>
- <p>
- Once a font is opened, you have to create a Graphic Context
- that will contain the informations about the color of the
- foreground and the background used when you draw a text in a
- Drawable. Here is an exemple of a Graphic Context that will
- allow us to draw an opened font with a black foreground and a
- white background:
- </p>
- <pre class="code">
- /*
- * c is the connection
- * screen is the screen where the window is displayed
- * window is the window in which we will draw the text
- * font is the opened font
- */
-
- uint32_t value_list[3];
- xcb_gcontext_t gc;
- uint32_t mask;
-
- gc = xcb_generate_id (c);
- mask = XCB_GC_FOREGROUND | XCB_GC_BACKGROUND | XCB_GC_FONT;
- value_list[0] = screen->black_pixel;
- value_list[1] = screen->white_pixel;
- value_list[2] = font;
- xcb_create_gc (c, gc, window, mask, value_list);
-
- /* The font is not needed anymore, so we close it */
- xcb_close_font (c, font);
-</pre>
- <li class="subtitle"><a name="drawingtext">Drawing text in a drawable</a>
- <p>
- To draw a text in a drawable, we use the following function:
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_image_text_8 (xcb_connection_t *c,
- uint8_t string_len,
- xcb_drawable_t drawable,
- xcb_gcontext_t gc,
- int16_t x,
- int16_t y,
- const char *string);
-</pre>
- <p>
- The <span class="code">string</span> parameter is the text to
- draw. The location of the drawing is given by the parameters
- <span class="code">x</span> and <span class="code">y</span>.
- The base line of the text is exactly the parameter
- <span class="code">y</span>.
- </p>
- <li class="subtitle"><a name="fontcompleteexample">Complete example</a>
- <p>
- This example draw a text at 10 pixels (for the base line) of
- the bottom of a window. Pressing the Esc key exits the program.
- </p>
- <pre class="code">
-#include <stdlib.h>
-#include <stdio.h>
-#include <string.h>
-
-#include <xcb/xcb.h>
-
-#define WIDTH 300
-#define HEIGHT 100
-
-
-
-static xcb_gc_t gc_font_get (xcb_connection_t *c,
- xcb_screen_t *screen,
- xcb_window_t window,
- const char *font_name);
-
-static void text_draw (xcb_connection_t *c,
- xcb_screen_t *screen,
- xcb_window_t window,
- int16_t x1,
- int16_t y1,
- const char *label);
-
-static void
-text_draw (xcb_connection_t *c,
- xcb_screen_t *screen,
- xcb_window_t window,
- int16_t x1,
- int16_t y1,
- const char *label)
-{
- xcb_void_cookie_t cookie_gc;
- xcb_void_cookie_t cookie_text;
- xcb_generic_error_t *error;
- xcb_gcontext_t gc;
- uint8_t length;
-
- length = strlen (label);
-
- gc = gc_font_get(c, screen, window, "7x13");
-
- cookie_text = xcb_image_text_8_checked (c, length, window, gc,
- x1,
- y1, label);
- error = xcb_request_check (c, cookie_text);
- if (error) {
- fprintf (stderr, "ERROR: can't paste text : %d\n", error->error_code);
- xcb_disconnect (c);
- exit (-1);
- }
-
- cookie_gc = xcb_free_gc (c, gc);
- error = xcb_request_check (c, cookie_gc);
- if (error) {
- fprintf (stderr, "ERROR: can't free gc : %d\n", error->error_code);
- xcb_disconnect (c);
- exit (-1);
- }
-}
-
-static xcb_gc_t
-gc_font_get (xcb_connection_t *c,
- xcb_screen_t *screen,
- xcb_window_t window,
- const char *font_name)
-{
- uint32_t value_list[3];
- xcb_void_cookie_t cookie_font;
- xcb_void_cookie_t cookie_gc;
- xcb_generic_error_t *error;
- xcb_font_t font;
- xcb_gcontext_t gc;
- uint32_t mask;
-
- font = xcb_generate_id (c);
- cookie_font = xcb_open_font_checked (c, font,
- strlen (font_name),
- font_name);
-
- error = xcb_request_check (c, cookie_font);
- if (error) {
- fprintf (stderr, "ERROR: can't open font : %d\n", error->error_code);
- xcb_disconnect (c);
- return -1;
- }
-
- gc = xcb_generate_id (c);
- mask = XCB_GC_FOREGROUND | XCB_GC_BACKGROUND | XCB_GC_FONT;
- value_list[0] = screen->black_pixel;
- value_list[1] = screen->white_pixel;
- value_list[2] = font;
- cookie_gc = xcb_create_gc_checked (c, gc, window, mask, value_list);
- error = xcb_request_check (c, cookie_gc);
- if (error) {
- fprintf (stderr, "ERROR: can't create gc : %d\n", error->error_code);
- xcb_disconnect (c);
- exit (-1);
- }
-
- cookie_font = xcb_close_font_checked (c, font);
- error = xcb_request_check (c, cookie_font);
- if (error) {
- fprintf (stderr, "ERROR: can't close font : %d\n", error->error_code);
- xcb_disconnect (c);
- exit (-1);
- }
-
- return gc;
-}
-
-int main ()
-{
- xcb_screen_iterator_t screen_iter;
- xcb_connection_t *c;
- const xcb_setup_t *setup;
- xcb_screen_t *screen;
- xcb_generic_event_t *e;
- xcb_generic_error_t *error;
- xcb_void_cookie_t cookie_window;
- xcb_void_cookie_t cookie_map;
- xcb_window_t window;
- uint32_t mask;
- uint32_t values[2];
- int screen_number;
-
- /* getting the connection */
- c = xcb_connect (NULL, &screen_number);
- if (!c) {
- fprintf (stderr, "ERROR: can't connect to an X server\n");
- return -1;
- }
-
- /* getting the current screen */
- setup = xcb_get_setup (c);
-
- screen = NULL;
- screen_iter = xcb_setup_roots_iterator (setup);
- for (; screen_iter.rem != 0; --screen_number, xcb_screen_next (&screen_iter))
- if (screen_number == 0)
- {
- screen = screen_iter.data;
- break;
- }
- if (!screen) {
- fprintf (stderr, "ERROR: can't get the current screen\n");
- xcb_disconnect (c);
- return -1;
- }
-
- /* creating the window */
- window = xcb_generate_id (c);
- mask = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK;
- values[0] = screen->white_pixel;
- values[1] =
- XCB_EVENT_MASK_KEY_RELEASE |
- XCB_EVENT_MASK_BUTTON_PRESS |
- XCB_EVENT_MASK_EXPOSURE |
- XCB_EVENT_MASK_POINTER_MOTION;
- cookie_window = xcb_create_window_checked (c,
- screen->root_depth,
- window, screen->root,
- 20, 200, WIDTH, HEIGHT,
- 0, XCB_WINDOW_CLASS_INPUT_OUTPUT,
- screen->root_visual,
- mask, values);
- cookie_map = xcb_map_window_checked (c, window);
-
- /* error managing */
- error = xcb_request_check (c, cookie_window);
- if (error) {
- fprintf (stderr, "ERROR: can't create window : %d\n", error->error_code);
- xcb_disconnect (c);
- return -1;
- }
- error = xcb_request_check (c, cookie_map);
- if (error) {
- fprintf (stderr, "ERROR: can't map window : %d\n", error->error_code);
- xcb_disconnect (c);
- return -1;
- }
-
- xcb_flush(c);
-
- while (1) {
- e = xcb_poll_for_event(c);
- if (e) {
- switch (e->response_type & ~0x80) {
- case XCB_EXPOSE: {
- char *text;
-
- text = "Press ESC key to exit...";
- text_draw (c, screen, window, 10, HEIGHT - 10, text);
- break;
- }
- case XCB_KEY_RELEASE: {
- xcb_key_release_event_t *ev;
-
- ev = (xcb_key_release_event_t *)e;
-
- switch (ev->detail) {
- /* ESC */
- case 9:
- free (e);
- xcb_disconnect (c);
- return 0;
- }
- }
- }
- free (e);
- }
- }
-
- return 0;
-}
-</pre>
- </ol>
- <li class="title"><a name="wm">Interacting with the window manager</a>
- <p>
- After we have seen how to create windows and draw on them, we
- take one step back, and look at how our windows are interacting
- with their environment (the full screen and the other
- windows). First of all, our application needs to interact with
- the window manager. The window manager is responsible to
- decorating drawn windows (i.e. adding a frame, an iconify
- button, a system menu, a title bar, etc), as well as handling
- icons shown when windows are being iconified. It also handles
- ordering of windows on the screen, and other administrative
- tasks. We need to give it various hints as to how we want it to
- treat our application's windows.
- </p>
- <ol>
- <li class="subtitle"><a name="wmprop">Window properties</a>
- <p>
- Many of the parameters communicated to the window manager are
- passed using data called "properties". These properties are
- attached by the X server to different windows, and are stored
- in a format that makes it possible to read them from different
- machines that may use different architectures (remember that
- an X client program may run on a remote machine).
- </p>
- <p>
- The property and its type (a string, an integer, etc) are
- Id. Their type are <span class="code">xcb_atom_t</span>:
- </p>
- <pre class="code">
-typedef uint32_t xcb_atom_t;
-</pre>
- <p>
- To change the property of a window, we use the following
- function:
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_change_property (xcb_connection_t *c, /* Connection to the X server */
- uint8_t mode, /* Property mode */
- xcb_window_t window, /* Window */
- xcb_atom_t property, /* Property to change */
- xcb_atom_t type, /* Type of the property */
- uint8_t format, /* Format of the property (8, 16, 32) */
- uint32_t data_len, /* Length of the data parameter */
- const void *data); /* Data */
-</pre>
- <p>
- The <span class="code">mode</span> parameter coud be one of
- the following values (defined in enumeration xcb_prop_mode_t in
- the xproto.h header file):
- </p>
- <ul>
- <li>XCB_PROP_MODE_REPLACE
- <li>XCB_PROP_MODE_PREPEND
- <li>XCB_PROP_MODE_APPEND
- </ul>
- <br>
- <li class="subtitle"><a name="wmname">Setting the window name and icon name</a>
- <p>
- The first thing we want to do would be to set the name for our
- window. This is done using the
- <span class="code">xcb_change_property()</span> function. This
- name may be used by the window manager as the title of the
- window (in the title bar), in a task list, etc. The property
- atom to use to set the name of a window is
- <span class="code">WM_NAME</span> (and
- <span class="code">WM_ICON_NAME</span> for the iconified
- window) and its type is <span class="code">STRING</span>. Here
- is an example of utilization:
- </p>
- <pre class="code">
-#include <string.h>
-
-#include <xcb/xcb.h>
-#include <xcb/xcb_atom.h>
-
-int
-main ()
-{
- xcb_connection_t *c;
- xcb_screen_t *screen;
- xcb_window_t win;
- char *title = "Hello World !";
- char *title_icon = "Hello World ! (iconified)";
-
-
-
- /* Open the connection to the X server */
- c = xcb_connect (NULL, NULL);
-
- /* Get the first screen */
- screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
-
- /* Ask for our window's Id */
- win = xcb_generate_id (c);
-
- /* Create the window */
- xcb_create_window (c, /* Connection */
- 0, /* depth */
- win, /* window Id */
- screen->root, /* parent window */
- 0, 0, /* x, y */
- 250, 150, /* width, height */
- 10, /* border_width */
- XCB_WINDOW_CLASS_INPUT_OUTPUT, /* class */
- screen->root_visual, /* visual */
- 0, NULL); /* masks, not used */
-
- /* Set the title of the window */
- xcb_change_property (c, XCB_PROP_MODE_REPLACE, win,
- WM_NAME, STRING, 8,
- strlen (title), title);
-
- /* Set the title of the window icon */
- xcb_change_property (c, XCB_PROP_MODE_REPLACE, win,
- WM_ICON_NAME, STRING, 8,
- strlen(title_icon), title_icon);
-
- /* Map the window on the screen */
- xcb_map_window (c, win);
-
- xcb_flush (c);
-
- while (1) {}
-
- return 0;
-}
-</pre>
- <div class="emph">
- <p>Note: the use of the atoms needs our program to be compiled
- and linked against xcb_atom, so that we have to use
- </p>
- </div>
- <pre class="text">
-gcc prog.c -o prog `pkg-config --cflags --libs xcb_atom`
-</pre>
- <div class="emph">
- <p>
- for the program to compile fine.
- </p>
- </div>
- </ol>
- <li class="title"><a name="winop">Simple window operations</a>
- <p>
- One more thing we can do to our window is manipulate them on the
- screen (resize them, move them, raise or lower them, iconify
- them, and so on). Some window operations functions are supplied
- by XCB for this purpose.
- </p>
- <ol>
- <li class="subtitle"><a name="winmap">Mapping and un-mapping a window</a>
- <p>
- The first pair of operations we can apply on a window is
- mapping it, or un-mapping it. Mapping a window causes the
- window to appear on the screen, as we have seen in our simple
- window program example. Un-mapping it causes it to be removed
- from the screen (although the window as a logical entity still
- exists). This gives the effect of making a window hidden
- (unmapped) and shown again (mapped). For example, if we have a
- dialog box window in our program, instead of creating it every
- time the user asks to open it, we can create the window once,
- in an un-mapped mode, and when the user asks to open it, we
- simply map the window on the screen. When the user clicked the
- 'OK' or 'Cancel' button, we simply un-map the window. This is
- much faster than creating and destroying the window, however,
- the cost is wasted resources, both on the client side, and on
- the X server side.
- </p>
- <p>
- To map a window, you use the following function:
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_map_window (xcb_connection_t *c,
- xcb_window_t window);
-</pre>
- <p>
- To have a simple example, see the <a href="#helloworld">example</a>
- above. The mapping operation will cause an
- <span class="code">Expose</span> event to be sent to our
- application, unless the window is completely covered by other
- windows.
- </p>
- <p>
- Un-mapping a window is also simple. You use the function
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_unmap_window (xcb_connection_t *c,
- xcb_window_t window);
-</pre>
- <p>
- The utilization of this function is the same as
- <span class="code">xcb_map_window()</span>.
- </p>
- <li class="subtitle"><a name="winconf">Configuring a window</a>
- <p>
- As we have seen when we have created our first window, in the
- X Events subsection, we can set some attributes for the window
- (that is, the position, the size, the events the window will
- receive, etc). If we want to modify them, but the window is
- already created, we can change them by using the following
- function:
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_configure_window (xcb_connection_t *c, /* The connection to the X server*/
- xcb_window_t window, /* The window to configure */
- uint16_t value_mask, /* The mask */
- const uint32_t *value_list); /* The values to set */
-</pre>
- <p>
- We set the <span class="code">value_mask</span> to one or
- several mask values that are in the xcb_config_window_t enumeration in the xproto.h header:
- </p>
- <ul>
- <li><span class="code">XCB_CONFIG_WINDOW_X</span>: new x coordinate of the window's top left corner
- <li><span class="code">XCB_CONFIG_WINDOW_Y</span>: new y coordinate of the window's top left corner
- <li><span class="code">XCB_CONFIG_WINDOW_WIDTH</span>: new width of the window
- <li><span class="code">XCB_CONFIG_WINDOW_HEIGHT</span>: new height of the window
- <li><span class="code">XCB_CONFIG_WINDOW_BORDER_WIDTH</span>: new width of the border of the window
- <li><span class="code">XCB_CONFIG_WINDOW_SIBLING</span>
- <li><span class="code">XCB_CONFIG_WINDOW_STACK_MODE</span>: the new stacking order
- </ul>
- <p>
- We then give to <span class="code">value_mask</span> the new
- value. We now describe how to use
- <span class="code">xcb_configure_window_t</span> in some useful
- situations.
- </p>
- <li class="subtitle"><a name="winmove">Moving a window around the screen</a>
- <p>
- An operation we might want to do with windows is to move them
- to a different location. This can be done like this:
- </p>
- <pre class="code">
-const static uint32_t values[] = { 10, 20 };
-
-/* The connection c and the window win are supposed to be defined */
-
-/* Move the window to coordinates x = 10 and y = 20 */
-xcb_configure_window (c, win, XCB_CONFIG_WINDOW_X | XCB_CONFIG_WINDOW_Y, values);
-</pre>
- <p>
- Note that when the window is moved, it might get partially
- exposed or partially hidden by other windows, and thus we
- might get <span class="code">Expose</span> events due to this
- operation.
- </p>
- <li class="subtitle"><a name="winsize">Resizing a window</a>
- <p>
- Yet another operation we can do is to change the size of a
- window. This is done using the following code:
- </p>
- <pre class="code">
-const static uint32_t values[] = { 200, 300 };
-
-/* The connection c and the window win are supposed to be defined */
-
-/* Resize the window to width = 10 and height = 20 */
-xcb_configure_window (c, win, XCB_CONFIG_WINDOW_WIDTH | XCB_CONFIG_WINDOW_HEIGHT, values);
-</pre>
- <p>
- We can also combine the move and resize operations using one
- single call to <span class="code">xcb_configure_window_t</span>:
- </p>
- <pre class="code">
-const static uint32_t values[] = { 10, 20, 200, 300 };
-
-/* The connection c and the window win are supposed to be defined */
-
-/* Move the window to coordinates x = 10 and y = 20 */
-/* and resize the window to width = 10 and height = 20 */
-xcb_configure_window (c, win, XCB_CONFIG_WINDOW_X | XCB_CONFIG_WINDOW_Y | XCB_CONFIG_WINDOW_WIDTH | XCB_CONFIG_WINDOW_HEIGHT, values);
-</pre>
- <li class="subtitle"><a name="winstack">Changing windows stacking order: raise and lower</a>
- <p>
- Until now, we changed properties of a single window. We'll see
- that there are properties that relate to the window and other
- windows. One of them is the stacking order. That is, the order
- in which the windows are layered on top of each other. The
- front-most window is said to be on the top of the stack, while
- the back-most window is at the bottom of the stack. Here is
- how to manipulate our windows stack order:
- </p>
- <pre class="code">
-const static uint32_t values[] = { XCB_STACK_MODE_ABOVE };
-
-/* The connection c and the window win are supposed to be defined */
-
-/* Move the window on the top of the stack */
-xcb_configure_window (c, win, XCB_CONFIG_WINDOW_STACK_MODE, values);
-</pre>
- <pre class="code">
-const static uint32_t values[] = { XCB_STACK_MODE_BELOW };
-
-/* The connection c and the window win are supposed to be defined */
-
-/* Move the window on the bottom of the stack */
-xcb_configure_window (c, win, XCB_CONFIG_WINDOW_STACK_MODE, values);
-</pre>
- <li class="subtitle"><a name="wingetinfo">Getting information about a window</a>
- <p>
- Just like we can set various attributes of our windows, we can
- also ask the X server supply the current values of these
- attributes. For example, we can check where a window is
- located on the screen, what is its current size, whether it is
- mapped or not, etc. The structure that contains some of this
- information is
- </p>
- <pre class="code">
-typedef struct {
- uint8_t response_type;
- uint8_t depth; /* depth of the window */
- uint16_t sequence;
- uint32_t length;
- xcb_window_t root; /* Id of the root window *>
- int16_t x; /* X coordinate of the window's location */
- int16_t y; /* Y coordinate of the window's location */
- uint16_t width; /* Width of the window */
- uint16_t height; /* Height of the window */
- uint16_t border_width; /* Width of the window's border */
-} xcb_get_geometry_reply_t;
-</pre>
- <p>
- XCB fill this structure with two functions:
- </p>
- <pre class="code">
-xcb_get_geometry_cookie_t xcb_get_geometry (xcb_connection_t *c,
- xcb_drawable_t drawable);
-xcb_get_geometry_reply_t *xcb_get_geometry_reply (xcb_connection_t *c,
- xcb_get_geometry_cookie_t cookie,
- xcb_generic_error_t **e);
-</pre>
- <p>
- You use them as follows:
- </p>
- <pre class="code">
- xcb_connection_t *c;
- xcb_drawable_t win;
- xcb_get_geometry_reply_t *geom;
-
- /* You initialize c and win */
-
- geom = xcb_get_geometry_reply (c, xcb_get_geometry (c, win), NULL);
-
- /* Do something with the fields of geom */
-
- free (geom);
-</pre>
- <p>
- Remark that you have to free the structure, as
- <span class="code">xcb_get_geometry_reply_t</span> allocates a
- newly one.
- </p>
- <p>
- One problem is that the returned location of the window is
- relative to its parent window. This makes these coordinates
- rather useless for any window manipulation functions, like
- moving it on the screen. In order to overcome this problem, we
- need to take a two-step operation. First, we find out the Id
- of the parent window of our window. We then translate the
- above relative coordinates to the screen coordinates.
- </p>
- <p>
- To get the Id of the parent window, we need this structure:
- </p>
- <pre class="code">
-typedef struct {
- uint8_t response_type;
- uint8_t pad0;
- uint16_t sequence;
- uint32_t length;
- xcb_window_t root;
- xcb_window_t parent; /* Id of the parent window */
- uint16_t children_len;
- uint8_t pad1[14];
-} xcb_query_tree_reply_t;
-</pre>
- <p>
- To fill this structure, we use these two functions:
- </p>
- <pre class="code">
-xcb_query_tree_cookie_t xcb_query_tree (xcb_connection_t *c,
- xcb_window_t window);
-xcb_query_tree_reply_t *xcb_query_tree_reply (xcb_connection_t *c,
- xcb_query_tree_cookie_t cookie,
- xcb_generic_error_t **e);
-</pre>
- <p>
- The translated coordinates will be found in this structure:
- </p>
- <pre class="code">
-typedef struct {
- uint8_t response_type;
- uint8_t same_screen;
- uint16_t sequence;
- uint32_t length;
- xcb_window_t child;
- uint16_t dst_x; /* Translated x coordinate */
- uint16_t dst_y; /* Translated y coordinate */
-} xcb_translate_coordinates_reply_t;
-</pre>
- <p>
- As usual, we need two functions to fill this structure:
- </p>
- <pre class="code">
-xcb_translate_coordinates_cookie_t xcb_translate_coordinates (xcb_connection_t *c,
- xcb_window_t src_window,
- xcb_window_t dst_window,
- int16_t src_x,
- int16_t src_y);
-xcb_translate_coordinates_reply_t *xcb_translate_coordinates_reply (xcb_connection_t *c,
- xcb_translate_coordinates_cookie_t cookie,
- xcb_generic_error_t **e);
-</pre>
- <p>
- We use them as follows:
- </p>
- <pre class="code">
- xcb_connection_t *c;
- xcb_drawable_t win;
- xcb_get_geometry_reply_t *geom;
- xcb_query_tree_reply_t *tree;
- xcb_translate_coordinates_reply_t *trans;
-
- /* You initialize c and win */
-
- geom = xcb_get_geometry_reply (c, xcb_get_geometry (c, win), NULL);
- if (!geom)
- return 0;
-
- tree = xcb_query_tree_reply (c, xcb_query_tree (c, win), NULL);
- if (!tree)
- return 0;
-
- trans = xcb_translate_coordinates_reply (c,
- xcb_translate_coordinates (c,
- win,
- tree->parent,
- geom->x, geom->y),
- NULL);
- if (!trans)
- return 0;
-
- /* the translated coordinates are in trans->dst_x and trans->dst_y */
-
- free (trans);
- free (tree);
- free (geom);
-</pre>
- <p>
- Of course, as for <span class="code">geom</span>,
- <span class="code">tree</span> and
- <span class="code">trans</span> have to be freed.
- </p>
- <p>
- The work is a bit hard, but XCB is a very low-level library.
- </p>
- <p>
- <b>TODO:</b> the utilization of these functions should be a
- prog, which displays the coordinates of the window.
- </p>
- <p>
- There is another structure that gives informations about our window:
- </p>
- <pre class="code">
-typedef struct {
- uint8_t response_type;
- uint8_t backing_store;
- uint16_t sequence;
- uint32_t length;
- xcb_visualid_t visual; /* Visual of the window */
- uint16_t _class;
- uint8_t bit_gravity;
- uint8_t win_gravity;
- uint32_t backing_planes;
- uint32_t backing_pixel;
- uint8_t save_under;
- uint8_t map_is_installed;
- uint8_t map_state; /* Map state of the window */
- uint8_t override_redirect;
- xcb_colormap_t colormap; /* Colormap of the window */
- uint32_t all_event_masks;
- uint32_t your_event_mask;
- uint16_t do_not_propagate_mask;
-} xcb_get_window_attributes_reply_t;
-</pre>
- <p>
- XCB supplies these two functions to fill it:
- </p>
- <pre class="code">
-xcb_get_window_attributes_cookie_t xcb_get_window_attributes (xcb_connection_t *c,
- xcb_window_t window);
-xcb_get_window_attributes_reply_t *xcb_get_window_attributes_reply (xcb_connection_t *c,
- xcb_get_window_attributes_cookie_t cookie,
- xcb_generic_error_t **e);
-</pre>
- <p>
- You use them as follows:
- </p>
- <pre class="code">
- xcb_connection_t *c;
- xcb_drawable_t win;
- xcb_get_window_attributes_reply_t *attr;
-
- /* You initialize c and win */
-
- attr = xcb_get_window_attributes_reply (c, xcb_get_window_attributes (c, win), NULL);
-
- if (!attr)
- return 0;
-
- /* Do something with the fields of attr */
-
- free (attr);
-</pre>
- <p>
- As for <span class="code">geom</span>,
- <span class="code">attr</span> has to be freed.
- </p>
- </ol>
- <li class="title"><a name="usecolor">Using colors to paint the rainbow</a>
- <p>
- Up until now, all our painting operation were done using black
- and white. We will (finally) see now how to draw using colors.
- </p>
- <ol>
- <li class="subtitle"><a name="colormap">Color maps</a>
- <p>
- In the beginning, there were not enough colors. Screen
- controllers could only support a limited number of colors
- simultaneously (initially 2, then 4, 16 and 256). Because of
- this, an application could not just ask to draw in a "light
- purple-red" color, and expect that color to be available. Each
- application allocated the colors it needed, and when all the
- color entries (4, 16, 256 colors) were in use, the next color
- allocation would fail.
- </p>
- <p>
- Thus, the notion of "a color map" was introduced. A color map
- is a table whose size is the same as the number of
- simultaneous colors a given screen controller. Each entry
- contained the RGB (Red, Green and Blue) values of a different
- color (all colors can be drawn using some combination of red,
- green and blue). When an application wants to draw on the
- screen, it does not specify which color to use. Rather, it
- specifies which color entry of some color map to be used
- during this drawing. Change the value in this color map entry
- and the drawing will use a different color.
- </p>
- <p>
- In order to be able to draw using colors that got something to
- do with what the programmer intended, color map allocation
- functions are supplied. You could ask to allocate entry for a
- color with a set of RGB values. If one already existed, you
- would get its index in the table. If none existed, and the
- table was not full, a new cell would be allocated to contain
- the given RGB values, and its index returned. If the table was
- full, the procedure would fail. You could then ask to get a
- color map entry with a color that is closest to the one you
- were asking for. This would mean that the actual drawing on
- the screen would be done using colors similar to what you
- wanted, but not the same.
- </p>
- <p>
- On today's more modern screens where one runs an X server with
- support for 16 million colors, this limitation looks a little
- silly, but remember that there are still older computers with
- older graphics cards out there. Using color map, support for
- these screen becomes transparent to you. On a display
- supporting 16 million colors, any color entry allocation
- request would succeed. On a display supporting a limited
- number of colors, some color allocation requests would return
- similar colors. It won't look as good, but your application
- would still work.
- </p>
- <li class="subtitle"><a name="colormapalloc">Allocating and freeing Color Maps</a>
- <p>
- When you draw using XCB, you can choose to use the standard
- color map of the screen your window is displayed on, or you
- can allocate a new color map and apply it to a window. In the
- latter case, each time the mouse moves onto your window, the
- screen color map will be replaced by your window's color map,
- and you'll see all the other windows on screen change their
- colors into something quite bizzare. In fact, this is the
- effect you get with X applications that use the "-install"
- command line option.
- </p>
- <p>
- In XCB, a color map is (as often in X) an Id:
- </p>
- <pre class="code">
-typedef uint32_t xcb_colormap_t;
-</pre>
- <p>
- In order to access the screen's default color map, you just
- have to retrieve the <span class="code">default_colormap</span>
- field of the <span class="code">xcb_screen_t</span> structure
- (see Section
- <a href="#screen">Checking basic information about a connection</a>):
- </p>
- <pre class="code">
-#include <stdio.h>
-
-#include <xcb/xcb.h>
-
-int
-main ()
-{
- xcb_connection_t *c;
- xcb_screen_t *screen;
- xcb_colormap_t colormap;
-
- /* Open the connection to the X server and get the first screen */
- c = xcb_connect (NULL, NULL);
- screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
-
- colormap = screen->default_colormap;
-
- return 0;
-}
-</pre>
- <p>
- This will return the color map used by default on the first
- screen (again, remember that an X server may support several
- different screens, each of which might have its own resources).
- </p>
- <p>
- The other option, that of allocating a new colormap, works as
- follows. We first ask the X server to give an Id to our color
- map, with this function:
- </p>
- <pre class="code">
-xcb_colormap_t xcb_generate_id (xcb_connection_t *c);
-</pre>
- <p>
- Then, we create the color map with
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_create_colormap (xcb_connection_t *c, /* Pointer to the xcb_connection_t structure */
- uint8_t alloc, /* Colormap entries to be allocated (AllocNone or AllocAll) */
- xcb_colormap_t mid, /* Id of the color map */
- xcb_window_t window, /* Window on whose screen the colormap will be created */
- xcb_visualid_t visual); /* Id of the visual supported by the screen */
-</pre>
- <p>
- Here is an example of creation of a new color map:
- </p>
- <pre class="code">
-#include <xcb/xcb.h>
-
-int
-main ()
-{
- xcb_connection_t *c;
- xcb_screen_t *screen;
- xcb_window_t win;
- xcb_colormap_t cmap
-
- /* Open the connection to the X server and get the first screen */
- c = xcb_connect (NULL, NULL);
- screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
-
- /* We create the window win here*/
-
- cmap = xcb_generate_id (c);
- xcb_create_colormap (c, XCB_COLORMAP_ALLOC_NONE, cmap, win, screen->root_visual);
-
- return 0;
-}
-</pre>
- <p>
- Note that the window parameter is only used to allow the X
- server to create the color map for the given screen. We can
- then use this color map for any window drawn on the same screen.
- </p>
- <p>
- To free a color map, it suffices to use this function:
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_free_colormap (xcb_connection_t *c, /* The connection */
- xcb_colormap_t cmap); /* The color map */
-</pre>
- <div class="comp">
- <div class="title">
- Comparison Xlib/XCB
- </div>
- <div class="xlib">
- <ul>
- <li>XCreateColormap ()
- </ul>
- </div>
- <div class="xcb">
- <ul>
- <li>xcb_generate_id ()
- <li>xcb_create_colormap ()
- </ul>
- </div>
- <div class="xlib">
- <ul>
- <li>XFreeColormap ()
- </ul>
- </div>
- <div class="xcb">
- <ul>
- <li>xcb_free_colormap ()
- </ul>
- </div>
- </div>
- <br>
- <li class="subtitle"><a name="alloccolor">Allocating and freeing a color entry</a>
- <p>
- Once we got access to some color map, we can start allocating
- colors. The informations related to a color are stored in the
- following structure:
- </p>
- <pre class="code">
-typedef struct {
- uint8_t response_type;
- uint8_t pad0;
- uint16_t sequence;
- uint32_t length;
- uint16_t red; /* The red component */
- uint16_t green; /* The green component */
- uint16_t blue; /* The blue component */
- uint8_t pad1[2];
- uint32_t pixel; /* The entry in the color map, supplied by the X server */
-} xcb_alloc_color_reply_t;
-</pre>
- <p>
- XCB supplies these two functions to fill it:
- </p>
- <pre class="code">
-xcb_alloc_color_cookie_t xcb_alloc_color (xcb_connection_t *c,
- xcb_colormap_t cmap,
- uint16_t red,
- uint16_t green,
- uint16_t blue);
-xcb_alloc_color_reply_t *xcb_alloc_color_reply (xcb_connection_t *c,
- xcb_alloc_color_cookie_t cookie,
- xcb_generic_error_t **e);
-</pre>
- <p>
- The fuction <span class="code">xcb_alloc_color()</span> takes the
- 3 RGB components as parameters (red, green and blue). Here is an
- example of using these functions:
- </p>
- <pre class="code">
-#include <malloc.h>
-
-#include <xcb/xcb.h>
-
-int
-main ()
-{
- xcb_connection_t *c;
- xcb_screen_t *screen;
- xcb_window_t win;
- xcb_colormap_t cmap;
- xcb_alloc_color_reply_t *rep;
-
- /* Open the connection to the X server and get the first screen */
- c = xcb_connect (NULL, NULL);
- screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
-
- /* We create the window win here*/
-
- cmap = xcb_generate_id (c);
- xcb_create_colormap (c, XCB_COLORMAP_ALLOC_NONE, cmap, win, screen->root_visual);
-
- rep = xcb_alloc_color_reply (c, xcb_alloc_color (c, cmap, 65535, 0, 0), NULL);
-
- if (!rep)
- return 0;
-
- /* Do something with r->pixel or the components */
-
- free (rep);
-
- return 0;
-}
-</pre>
- <p>
- As <span class="code">xcb_alloc_color_reply()</span> allocates
- memory, you have to free <span class="code">rep</span>.
- </p>
- <p>
- <b>TODO</b>: Talk about freeing colors.
- </p>
- </ol>
- <li class="title"><a name="pixmaps">X Bitmaps and Pixmaps</a>
- <p>
- One thing many so-called "Multi-Media" applications need to do,
- is display images. In the X world, this is done using bitmaps
- and pixmaps. We have already seen some usage of them when
- setting an icon for our application. Lets study them further,
- and see how to draw these images inside a window, along side the
- simple graphics and text we have seen so far.
- </p>
- <p>
- One thing to note before delving further, is that XCB (nor Xlib)
- supplies no means of manipulating popular image formats, such as
- gif, png, jpeg or tiff. It is up to the programmer (or to higher
- level graphics libraries) to translate these image formats into
- formats that the X server is familiar with (x bitmaps and x
- pixmaps).
- </p>
- <ol>
- <li class="subtitle"><a name="pixmapswhat">What is a X Bitmap? An X Pixmap?</a>
- <p>
- An X bitmap is a two-color image stored in a format specific
- to the X window system. When stored in a file, the bitmap data
- looks like a C source file. It contains variables defining the
- width and the height of the bitmap, an array containing the
- bit values of the bitmap (the size of the array is
- (width+7)/8*height and the bit and byte order are LSB), and
- an optional hot-spot location (that will
- be explained later, when discussing mouse cursors).
- </p>
- <p>
- An X pixmap is a format used to stored images in the memory of
- an X server. This format can store both black and white images
- (such as x bitmaps) as well as color images. It is the only
- image format supported by the X protocol, and any image to be
- drawn on screen, should be first translated into this format.
- </p>
- <p>
- In actuality, an X pixmap can be thought of as a window that
- does not appear on the screen. Many graphics operations that
- work on windows, will also work on pixmaps. Indeed, the type
- of X pixmap in XCB is an Id like a window:
- </p>
- <pre class="code">
-typedef uint32_t xcb_pixmap_t;
-</pre>
- <p>
- Like Xlib, there is no difference between a Drawable, a Window
- or a Pixmap:
- </p>
- <pre class="code">
-typedef uint32_t xcb_drawable_t;
-</pre>
- <p>
- in order to avoid confusion between a window and a pixmap. The
- operations that will work the same on a window or a pixmap
- will require a <span class="code">xcb_drawable_t</span>
- </p>
- <div class="emph">
- <p>
- Remark: In Xlib, there is no specific difference between a
- <span class="code">Drawable</span>, a
- <span class="code">Pixmap</span> or a
- <span class="code">Window</span>: all are 32 bit long
- integer. XCB wraps all these different IDs in structures to
- provide some measure of type-safety.
- </p>
- </div>
- <li class="subtitle"><a name="pixmapscreate">Creating a pixmap</a>
- <p>
- Sometimes we want to create an un-initialized pixmap, so we
- can later draw into it. This is useful for image drawing
- programs (creating a new empty canvas will cause the creation
- of a new pixmap on which the drawing can be stored). It is
- also useful when reading various image formats: we load the
- image data into memory, create a pixmap on the server, and
- then draw the decoded image data onto that pixmap.
- </p>
- <p>
- To create a new pixmap, we first ask the X server to give an
- Id to our pixmap, with this function:
- </p>
- <pre class="code">
-xcb_pixmap_t xcb_generate_id (xcb_connection_t *c);
-</pre>
- <p>
- Then, XCB supplies the following function to create new pixmaps:
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_create_pixmap (xcb_connection_t *c, /* Pointer to the xcb_connection_t structure */
- uint8_t depth, /* Depth of the screen */
- xcb_pixmap_t pid, /* Id of the pixmap */
- xcb_drawable_t drawable,
- uint16_t width, /* Width of the window (in pixels) */
- uint16_t height); /* Height of the window (in pixels) */
-</pre>
- <p>
- <b>TODO</b>: Explain the drawable parameter, and give an
- example (like <a href="xpoints.c">xpoints.c</a>)
- </p>
- <li class="subtitle"><a name="pixmapsdraw"></a>Drawing a pixmap in a window
- <p>
- Once we got a handle to a pixmap, we can draw it on some
- window, using the following function:
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_copy_area (xcb_connection_t *c, /* Pointer to the xcb_connection_t structure */
- xcb_drawable_t src_drawable, /* The Drawable we want to paste */
- xcb_drawable_t dst_drawable, /* The Drawable on which we copy the previous Drawable */
- xcb_gcontext_t gc, /* A Graphic Context */
- int16_t src_x, /* Top left x coordinate of the region we want to copy */
- int16_t src_y, /* Top left y coordinate of the region we want to copy */
- int16_t dst_x, /* Top left x coordinate of the region where we want to copy */
- int16_t dst_y, /* Top left y coordinate of the region where we want to copy */
- uint16_t width, /* Width of the region we want to copy */
- uint16_t height); /* Height of the region we want to copy */
-</pre>
- <p>
- As you can see, we could copy the whole pixmap, as well as
- only a given rectangle of the pixmap. This is useful to
- optimize the drawing speed: we could copy only what we have
- modified in the pixmap.
- </p>
- <p>
- <b>One important note should be made</b>: it is possible to
- create pixmaps with different depths on the same screen. When
- we perform copy operations (a pixmap onto a window, etc), we
- should make sure that both source and target have the same
- depth. If they have a different depth, the operation would
- fail. The exception to this is if we copy a specific bit plane
- of the source pixmap using the
- <span class="code">xcb_copy_plane_t</span> function. In such an
- event, we can copy a specific plane to the target window (in
- actuality, setting a specific bit in the color of each pixel
- copied). This can be used to generate strange graphic effects
- in a window, but that is beyond the scope of this tutorial.
- </p>
- <li class="subtitle"><a name="pixmapsfree"></a>Freeing a pixmap
- <p>
- Finally, when we are done using a given pixmap, we should free
- it, in order to free resources of the X server. This is done
- using this function:
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_free_pixmap (xcb_connection_t *c, /* Pointer to the xcb_connection_t structure */
- xcb_pixmap_t pixmap); /* A given pixmap */
-</pre>
- <p>
- Of course, after having freed it, we must not try accessing
- the pixmap again.
- </p>
- <p>
- <b>TODO</b>: Give an example, or a link to xpoints.c
- </p>
- </ol>
- <li class="title"><a name="mousecursor">Messing with the mouse cursor</a>
- <p>
- It it possible to modify the shape of the mouse pointer (also
- called the X pointer) when in certain states, as we otfen see in
- programs. For example, a busy application would often display
- the sand clock over its main window, to give the user a visual
- hint that he should wait. Let's see how we can change the mouse
- cursor of our windows.
- </p>
- <ol>
- <li class="subtitle"><a name="mousecursorcreate">Creating and destroying a mouse cursor</a>
- <p>
- There are two methods for creating cursors. One of them is by
- using a set of predefined cursors, that are supplied by the X
- server, the other is by using a user-supplied bitmap.
- </p>
- <p>
- In the first method, we use a special font named "cursor", and
- the function <span class="code">xcb_create_glyph_cursor</span>:
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_create_glyph_cursor (xcb_connection_t *c,
- xcb_cursor_t cid,
- xcb_font_t source_font, /* font for the source glyph */
- xcb_font_t mask_font, /* font for the mask glyph or XCB_NONE */
- uint16_t source_char, /* character glyph for the source */
- uint16_t mask_char, /* character glyph for the mask */
- uint16_t fore_red, /* red value for the foreground of the source */
- uint16_t fore_green, /* green value for the foreground of the source */
- uint16_t fore_blue, /* blue value for the foreground of the source */
- uint16_t back_red, /* red value for the background of the source */
- uint16_t back_green, /* green value for the background of the source */
- uint16_t back_blue) /* blue value for the background of the source */
-</pre>
- <p>
- <b>TODO</b>: Describe <span class="code">source_char</span>
- and <span class="code">mask_char</span>, for example by giving
- an example on how to get the values. There is a list there:
- <a href="http://tronche.com/gui/x/xlib/appendix/b/">X Font Cursors</a>
- </p>
- <p>
- So we first open that font (see <a href="#loadfont">Loading a Font</a>)
- and create the new cursor. As for every X ressource, we have to
- ask for an X id with <span class="code">xcb_generate_id</span>
- first:
- </p>
- <pre class="code">
-xcb_font_t font;
-xcb_cursor_t cursor;
-
-/* The connection is set */
-
-font = xcb_generate_id (conn);
-xcb_open_font (conn, font, strlen ("cursor"), "cursor");
-
-cursor = xcb_generate_id (conn);
-xcb_create_glyph_cursor (conn, cursor, font, font,
- 58, 58 + 1,
- 0, 0, 0,
- 0, 0, 0);
-</pre>
- <p>
- We have created the cursor "right hand" by specifying 58 to
- the <span class="code">source_fon</span>t argument and 58 + 1
- to the <span class="code">mask_font</span>.
- </p>
- <p>
- The cursor is destroyed by using the function
- </p>
- <pre class="code">
-xcb_void_cookie_t xcb_free_cursor (xcb_connection_t *c,
- xcb_cursor_t cursor);
-</pre>
- <p>
- In the second method, we create a new cursor by using a pair
- of pixmaps, with depth of one (that is, two colors
- pixmaps). One pixmap defines the shape of the cursor, while
- the other works as a mask, specifying which pixels of the
- cursor will be actually drawn. The rest of the pixels will be
- transparent.
- </p>
- <p>
- <b>TODO</b>: give an example.
- </p>
- <li class="subtitle"><a name="mousecursorset">Setting a window's mouse cursor</a>
- <p>
- Once the cursor is created, we can modify the cursor of our
- window by using <span class="code">xcb_change_window_attributes</span>
- and using the <span class="code">XCB_CWCURSOR</span> attribute:
- </p>
- <pre class="code">
-uint32_t mask;
-uint32_t value_list;
-
-/* The connection and window are set */
-/* The cursor is already created */
-
-mask = XCB_CWCURSOR;
-value_list = cursor;
-xcb_change_window_attributes (conn, window, mask, &value_list);
-</pre>
- <p>
- Of course, the cursor and the font must be freed.
- </p>
- <li class="subtitle"><a name="mousecursorexample">Complete example</a>
- <p>
- The following example displays a window with a
- button. When entering the window, the window cursor is changed
- to an arrow. When clicking once on the button, the cursor is
- changed to a hand. When clicking again on the button, the
- cursor window gets back to the arrow. The Esc key exits the
- application.
- </p>
- <pre class="code">
-#include <stdlib.h>
-#include <stdio.h>
-#include <string.h>
-
-#include <xcb/xcb.h>
-
-#define WIDTH 300
-#define HEIGHT 150
-
-
-
-static xcb_gc_t gc_font_get (xcb_connection_t *c,
- xcb_screen_t *screen,
- xcb_window_t window,
- const char *font_name);
-
-static void button_draw (xcb_connection_t *c,
- xcb_screen_t *screen,
- xcb_window_t window,
- int16_t x1,
- int16_t y1,
- const char *label);
-
-static void text_draw (xcb_connection_t *c,
- xcb_screen_t *screen,
- xcb_window_t window,
- int16_t x1,
- int16_t y1,
- const char *label);
-
-static void cursor_set (xcb_connection_t *c,
- xcb_screen_t *screen,
- xcb_window_t window,
- int cursor_id);
-
-
-static void
-button_draw (xcb_connection_t *c,
- xcb_screen_t *screen,
- xcb_window_t window,
- int16_t x1,
- int16_t y1,
- const char *label)
-{
- xcb_point_t points[5];
- xcb_void_cookie_t cookie_gc;
- xcb_void_cookie_t cookie_line;
- xcb_void_cookie_t cookie_text;
- xcb_generic_error_t *error;
- xcb_gcontext_t gc;
- int16_t width;
- int16_t height;
- uint8_t length;
- int16_t inset;
-
- length = strlen (label);
- inset = 2;
-
- gc = gc_font_get(c, screen, window, "7x13");
-
- width = 7 * length + 2 * (inset + 1);
- height = 13 + 2 * (inset + 1);
- points[0].x = x1;
- points[0].y = y1;
- points[1].x = x1 + width;
- points[1].y = y1;
- points[2].x = x1 + width;
- points[2].y = y1 - height;
- points[3].x = x1;
- points[3].y = y1 - height;
- points[4].x = x1;
- points[4].y = y1;
- cookie_line = xcb_poly_line_checked (c, XCB_COORD_MODE_ORIGIN,
- window, gc, 5, points);
-
- error = xcb_request_check (c, cookie_line);
- if (error) {
- fprintf (stderr, "ERROR: can't draw lines : %d\n", error->error_code);
- xcb_disconnect (c);
- exit (-1);
- }
-
- cookie_text = xcb_image_text_8_checked (c, length, window, gc,
- x1 + inset + 1,
- y1 - inset - 1, label);
- error = xcb_request_check (c, cookie_text);
- if (error) {
- fprintf (stderr, "ERROR: can't paste text : %d\n", error->error_code);
- xcb_disconnect (c);
- exit (-1);
- }
-
- cookie_gc = xcb_free_gc (c, gc);
- error = xcb_request_check (c, cookie_gc);
- if (error) {
- fprintf (stderr, "ERROR: can't free gc : %d\n", error->error_code);
- xcb_disconnect (c);
- exit (-1);
- }
-}
-
-static void
-text_draw (xcb_connection_t *c,
- xcb_screen_t *screen,
- xcb_window_t window,
- int16_t x1,
- int16_t y1,
- const char *label)
-{
- xcb_void_cookie_t cookie_gc;
- xcb_void_cookie_t cookie_text;
- xcb_generic_error_t *error;
- xcb_gcontext_t gc;
- uint8_t length;
-
- length = strlen (label);
-
- gc = gc_font_get(c, screen, window, "7x13");
-
- cookie_text = xcb_image_text_8_checked (c, length, window, gc,
- x1,
- y1, label);
- error = xcb_request_check (c, cookie_text);
- if (error) {
- fprintf (stderr, "ERROR: can't paste text : %d\n", error->error_code);
- xcb_disconnect (c);
- exit (-1);
- }
-
- cookie_gc = xcb_free_gc (c, gc);
- error = xcb_request_check (c, cookie_gc);
- if (error) {
- fprintf (stderr, "ERROR: can't free gc : %d\n", error->error_code);
- xcb_disconnect (c);
- exit (-1);
- }
-}
-
-static xcb_gc_t
-gc_font_get (xcb_connection_t *c,
- xcb_screen_t *screen,
- xcb_window_t window,
- const char *font_name)
-{
- uint32_t value_list[3];
- xcb_void_cookie_t cookie_font;
- xcb_void_cookie_t cookie_gc;
- xcb_generic_error_t *error;
- xcb_font_t font;
- xcb_gcontext_t gc;
- uint32_t mask;
-
- font = xcb_generate_id (c);
- cookie_font = xcb_open_font_checked (c, font,
- strlen (font_name),
- font_name);
-
- error = xcb_request_check (c, cookie_font);
- if (error) {
- fprintf (stderr, "ERROR: can't open font : %d\n", error->error_code);
- xcb_disconnect (c);
- return -1;
- }
-
- gc = xcb_generate_id (c);
- mask = XCB_GC_FOREGROUND | XCB_GC_BACKGROUND | XCB_GC_FONT;
- value_list[0] = screen->black_pixel;
- value_list[1] = screen->white_pixel;
- value_list[2] = font;
- cookie_gc = xcb_create_gc_checked (c, gc, window, mask, value_list);
- error = xcb_request_check (c, cookie_gc);
- if (error) {
- fprintf (stderr, "ERROR: can't create gc : %d\n", error->error_code);
- xcb_disconnect (c);
- exit (-1);
- }
-
- cookie_font = xcb_close_font_checked (c, font);
- error = xcb_request_check (c, cookie_font);
- if (error) {
- fprintf (stderr, "ERROR: can't close font : %d\n", error->error_code);
- xcb_disconnect (c);
- exit (-1);
- }
-
- return gc;
-}
-
-static void
-cursor_set (xcb_connection_t *c,
- xcb_screen_t *screen,
- xcb_window_t window,
- int cursor_id)
-{
- uint32_t values_list[3];
- xcb_void_cookie_t cookie_font;
- xcb_void_cookie_t cookie_gc;
- xcb_generic_error_t *error;
- xcb_font_t font;
- xcb_cursor_t cursor;
- xcb_gcontext_t gc;
- uint32_t mask;
- uint32_t value_list;
-
- font = xcb_generate_id (c);
- cookie_font = xcb_open_font_checked (c, font,
- strlen ("cursor"),
- "cursor");
- error = xcb_request_check (c, cookie_font);
- if (error) {
- fprintf (stderr, "ERROR: can't open font : %d\n", error->error_code);
- xcb_disconnect (c);
- exit (-1);
- }
-
- cursor = xcb_generate_id (c);
- xcb_create_glyph_cursor (c, cursor, font, font,
- cursor_id, cursor_id + 1,
- 0, 0, 0,
- 0, 0, 0);
-
- gc = xcb_generate_id (c);
- mask = XCB_GC_FOREGROUND | XCB_GC_BACKGROUND | XCB_GC_FONT;
- values_list[0] = screen->black_pixel;
- values_list[1] = screen->white_pixel;
- values_list[2] = font;
- cookie_gc = xcb_create_gc_checked (c, gc, window, mask, values_list);
- error = xcb_request_check (c, cookie_gc);
- if (error) {
- fprintf (stderr, "ERROR: can't create gc : %d\n", error->error_code);
- xcb_disconnect (c);
- exit (-1);
- }
-
- mask = XCB_CW_CURSOR;
- value_list = cursor;
- xcb_change_window_attributes (c, window, mask, &value_list);
-
- xcb_free_cursor (c, cursor);
-
- cookie_font = xcb_close_font_checked (c, font);
- error = xcb_request_check (c, cookie_font);
- if (error) {
- fprintf (stderr, "ERROR: can't close font : %d\n", error->error_code);
- xcb_disconnect (c);
- exit (-1);
- }
-}
-
-int main ()
-{
- xcb_screen_iterator_t screen_iter;
- xcb_connection_t *c;
- const xcb_setup_t *setup;
- xcb_screen_t *screen;
- xcb_generic_event_t *e;
- xcb_generic_error_t *error;
- xcb_void_cookie_t cookie_window;
- xcb_void_cookie_t cookie_map;
- xcb_window_t window;
- uint32_t mask;
- uint32_t values[2];
- int screen_number;
- uint8_t is_hand = 0;
-
- /* getting the connection */
- c = xcb_connect (NULL, &screen_number);
- if (!c) {
- fprintf (stderr, "ERROR: can't connect to an X server\n");
- return -1;
- }
-
- /* getting the current screen */
- setup = xcb_get_setup (c);
-
- screen = NULL;
- screen_iter = xcb_setup_roots_iterator (setup);
- for (; screen_iter.rem != 0; --screen_number, xcb_screen_next (&screen_iter))
- if (screen_number == 0)
- {
- screen = screen_iter.data;
- break;
- }
- if (!screen) {
- fprintf (stderr, "ERROR: can't get the current screen\n");
- xcb_disconnect (c);
- return -1;
- }
-
- /* creating the window */
- window = xcb_generate_id (c);
- mask = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK;
- values[0] = screen->white_pixel;
- values[1] =
- XCB_EVENT_MASK_KEY_RELEASE |
- XCB_EVENT_MASK_BUTTON_PRESS |
- XCB_EVENT_MASK_EXPOSURE |
- XCB_EVENT_MASK_POINTER_MOTION;
- cookie_window = xcb_create_window_checked (c,
- screen->root_depth,
- window, screen->root,
- 20, 200, WIDTH, HEIGHT,
- 0, XCB_WINDOW_CLASS_INPUT_OUTPUT,
- screen->root_visual,
- mask, values);
- cookie_map = xcb_map_window_checked (c, window);
-
- /* error managing */
- error = xcb_request_check (c, cookie_window);
- if (error) {
- fprintf (stderr, "ERROR: can't create window : %d\n", error->error_code);
- xcb_disconnect (c);
- return -1;
- }
- error = xcb_request_check (c, cookie_map);
- if (error) {
- fprintf (stderr, "ERROR: can't map window : %d\n", error->error_code);
- xcb_disconnect (c);
- return -1;
- }
-
- cursor_set (c, screen, window, 68);
-
- xcb_flush(c);
-
- while (1) {
- e = xcb_poll_for_event(c);
- if (e) {
- switch (e->response_type & ~0x80) {
- case XCB_EXPOSE: {
- char *text;
-
- text = "click here to change cursor";
- button_draw (c, screen, window,
- (WIDTH - 7 * strlen(text)) / 2,
- (HEIGHT - 16) / 2, text);
-
- text = "Press ESC key to exit...";
- text_draw (c, screen, window, 10, HEIGHT - 10, text);
- break;
- }
- case XCB_BUTTON_PRESS: {
- xcb_button_press_event_t *ev;
- int length;
-
- ev = (xcb_button_press_event_t *)e;
- length = strlen ("click here to change cursor");
-
- if ((ev->event_x >= (WIDTH - 7 * length) / 2) &&
- (ev->event_x <= ((WIDTH - 7 * length) / 2 + 7 * length + 6)) &&
- (ev->event_y >= (HEIGHT - 16) / 2 - 19) &&
- (ev->event_y <= ((HEIGHT - 16) / 2)))
- is_hand = 1 - is_hand;
-
- is_hand ? cursor_set (c, screen, window, 58) : cursor_set (c, screen, window, 68);
- }
- case XCB_KEY_RELEASE: {
- xcb_key_release_event_t *ev;
-
- ev = (xcb_key_release_event_t *)e;
-
- switch (ev->detail) {
- /* ESC */
- case 9:
- free (e);
- xcb_disconnect (c);
- return 0;
- }
- }
- }
- free (e);
- }
- }
-
- return 0;
-}
-</pre>
- </ol>
- <li class="title"><a name="translation">Translation of basic Xlib functions and macros</a>
- <p>
- The problem when you want to port an Xlib program to XCB is that
- you don't know if the Xlib function that you want to "translate"
- is a X Window one or an Xlib macro. In that section, we describe
- a way to translate the usual functions or macros that Xlib
- provides. It's usually just a member of a structure.
- </p>
- <ol>
- <li class="subtitle"><a name="displaystructure">Members of the Display structure</a>
- <p>
- In this section, we look at how to translate the macros that
- return some members of the <span class="code">Display</span>
- structure. They are obtained by using a function that requires a
- <span class="code">xcb_connection_t *</span> or a member of the
- <span class="code">xcb_setup_t</span> structure
- (via the function <span class="code">xcb_get_setup</span>), or
- a function that requires that structure.
- </p>
- <ol>
- <li class="subtitle"><a name="ConnectionNumber">ConnectionNumber</a>
- <p>
- This number is the file descriptor that connects the client
- to the server. You just have to use that function:
- </p>
- <pre class="code">
-int xcb_get_file_descriptor (xcb_connection_t *c);
-</pre>
- <li class="subtitle"><a name="DefaultScreen"></a>DefaultScreen
- <p>
- That number is not stored by XCB. It is returned in the
- second parameter of the function <span class="code"><a href="#openconn">xcb_connect</a></span>.
- Hence, you have to store it yourself if you want to use
- it. Then, to get the <span class="code">xcb_screen_t</span>
- structure, you have to iterate on the screens.
- The equivalent function of the Xlib's
- <span class="code">ScreenOfDisplay</span> function can be
- found <a href="#ScreenOfDisplay">below</a>. This is also provided in the
- xcb_aux_t library as <span class="code">xcb_aux_get_screen()</span>. OK, here is the
- small piece of code to get that number:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-int screen_default_nbr;
-
-/* you pass the name of the display you want to xcb_connect_t */
-
-c = xcb_connect (display_name, &screen_default_nbr);
-
-/* screen_default_nbr contains now the number of the default screen */
-</pre>
- <li class="subtitle"><a name="QLength"></a>QLength
- <p>
- Not documented yet.
- </p>
- <p>
- However, this points out a basic difference in philosophy between
- Xlib and XCB. Xlib has several functions for filtering and
- manipulating the incoming and outgoing X message queues. XCB
- wishes to hide this as much as possible from the user, which
- allows for more freedom in implementation strategies.
- </p>
- <li class="subtitle"><a name="ScreenCount"></a>ScreenCount
- <p>
- You get the count of screens with the functions
- <span class="code">xcb_get_setup</span>
- and
- <span class="code">xcb_setup_roots_iterator</span>
- (if you need to iterate):
- </p>
- <pre class="code">
-xcb_connection_t *c;
-int screen_count;
-
-/* you init the connection */
-
-screen_count = xcb_setup_roots_iterator (xcb_get_setup (c)).rem;
-
-/* screen_count contains now the count of screens */
-</pre>
- <p>
- If you don't want to iterate over the screens, a better way
- to get that number is to use
- <span class="code">xcb_setup_roots_length_t</span>:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-int screen_count;
-
-/* you init the connection */
-
-screen_count = xcb_setup_roots_length (xcb_get_setup (c));
-
-/* screen_count contains now the count of screens */
-</pre>
- <li class="subtitle"><a name="ServerVendor"></a>ServerVendor
- <p>
- You get the name of the vendor of the server hardware with
- the functions <span class="code">xcb_get_setup</span>
- and
- <span
- class="code">xcb_setup_vendor</span>. Beware
- that, unlike Xlib, the string returned by XCB is not
- necessarily null-terminaled:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-char *vendor = NULL;
-int length;
-
-/* you init the connection */
-length = xcb_setup_vendor_length (xcb_get_setup (c));
-vendor = (char *)malloc (length + 1);
-if (vendor)
-memcpy (vendor, xcb_setup_vendor (xcb_get_setup (c)), length);
-vendor[length] = '\0';
-
-/* vendor contains now the name of the vendor. Must be freed when not used anymore */
-</pre>
- <li class="subtitle"><a name="ProtocolVersion"></a>ProtocolVersion
- <p>
- You get the major version of the protocol in the
- <span class="code">xcb_setup_t</span>
- structure, with the function <span class="code">xcb_get_setup</span>:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-uint16_t protocol_major_version;
-
-/* you init the connection */
-
-protocol_major_version = xcb_get_setup (c)->protocol_major_version;
-
-/* protocol_major_version contains now the major version of the protocol */
-</pre>
- <li class="subtitle"><a name="ProtocolRevision"></a>ProtocolRevision
- <p>
- You get the minor version of the protocol in the
- <span class="code">xcb_setup_t</span>
- structure, with the function <span class="code">xcb_get_setup</span>:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-uint16_t protocol_minor_version;
-
-/* you init the connection */
-
-protocol_minor_version = xcb_get_setup (c)->protocol_minor_version;
-
-/* protocol_minor_version contains now the minor version of the protocol */
-</pre>
- <li class="subtitle"><a name="VendorRelease"></a>VendorRelease
- <p>
- You get the number of the release of the server hardware in the
- <span class="code">xcb_setup_t</span>
- structure, with the function <span class="code">xcb_get_setup</span>:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-uint32_t release_number;
-
-/* you init the connection */
-
-release_number = xcb_get_setup (c)->release_number;
-
-/* release_number contains now the number of the release of the server hardware */
-</pre>
- <li class="subtitle"><a name="DisplayString"></a>DisplayString
- <p>
- The name of the display is not stored in XCB. You have to
- store it by yourself.
- </p>
- <li class="subtitle"><a name="BitmapUnit"></a>BitmapUnit
- <p>
- You get the bitmap scanline unit in the
- <span class="code">xcb_setup_t</span>
- structure, with the function <span class="code">xcb_get_setup</span>:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-uint8_t bitmap_format_scanline_unit;
-
-/* you init the connection */
-
-bitmap_format_scanline_unit = xcb_get_setup (c)->bitmap_format_scanline_unit;
-
-/* bitmap_format_scanline_unit contains now the bitmap scanline unit */
-</pre>
- <li class="subtitle"><a name="BitmapBitOrder"></a>BitmapBitOrder
- <p>
- You get the bitmap bit order in the
- <span class="code">xcb_setup_t</span>
- structure, with the function <span class="code">xcb_get_setup</span>:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-uint8_t bitmap_format_bit_order;
-
-/* you init the connection */
-
-bitmap_format_bit_order = xcb_get_setup (c)->bitmap_format_bit_order;
-
-/* bitmap_format_bit_order contains now the bitmap bit order */
-</pre>
- <li class="subtitle"><a name="BitmapPad"></a>BitmapPad
- <p>
- You get the bitmap scanline pad in the
- <span class="code">xcb_setup_t</span>
- structure, with the function <span class="code">xcb_get_setup</span>:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-uint8_t bitmap_format_scanline_pad;
-
-/* you init the connection */
-
-bitmap_format_scanline_pad = xcb_get_setup (c)->bitmap_format_scanline_pad;
-
-/* bitmap_format_scanline_pad contains now the bitmap scanline pad */
-</pre>
- <li class="subtitle"><a name="ImageByteOrder"></a>ImageByteOrder
- <p>
- You get the image byte order in the
- <span class="code">xcb_setup_t</span>
- structure, with the function <span class="code">xcb_get_setup</span>:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-uint8_t image_byte_order;
-
-/* you init the connection */
-
-image_byte_order = xcb_get_setup (c)->image_byte_order;
-
-/* image_byte_order contains now the image byte order */
-</pre>
- </ol>
- <li class="subtitle"><a name="screenofdisplay">ScreenOfDisplay related functions</a>
- <p>
- in Xlib, <span class="code">ScreenOfDisplay</span> returns a
- <span class="code">Screen</span> structure that contains
- several characteristics of your screen. XCB has a similar
- structure (<span class="code">xcb_screen_t</span>),
- but the way to obtain it is a bit different. With
- Xlib, you just provide the number of the screen and you grab it
- from an array. With XCB, you iterate over all the screens to
- obtain the one you want. The complexity of this operation is
- O(n). So the best is to store this structure if you use
- it often. See <a href="#ScreenOfDisplay">screen_of_display</a> just below.
- </p>
- <p>
- Xlib provides generally two functions to obtain the characteristics
- related to the screen. One with the display and the number of
- the screen, which calls <span class="code">ScreenOfDisplay</span>,
- and the other that uses the <span class="code">Screen</span> structure.
- This might be a bit confusing. As mentioned above, with XCB, it
- is better to store the <span class="code">xcb_screen_t</span>
- structure. Then, you have to read the members of this
- structure. That's why the Xlib functions are put by pairs (or
- more) as, with XCB, you will use the same code.
- </p>
- <ol>
- <li class="subtitle"><a name="ScreenOfDisplay">ScreenOfDisplay</a>
- <p>
- This function returns the Xlib <span class="code">Screen</span>
- structure. With XCB, you iterate over all the screens and
- once you get the one you want, you return it:
- </p>
- <pre class="code"><a name="ScreenOfDisplay"></a>
-xcb_screen_t *screen_of_display (xcb_connection_t *c,
- int screen)
-{
- xcb_screen_iterator_t iter;
-
- iter = xcb_setup_roots_iterator (xcb_get_setup (c));
- for (; iter.rem; --screen, xcb_screen_next (&iter))
- if (screen == 0)
- return iter.data;
-
- return NULL;
-}
-</pre>
- <p>
- As mentioned above, you might want to store the value
- returned by this function.
- </p>
- <p>
- All the functions below will use the result of that
- function, as they just grab a specific member of the
- <span class="code">xcb_screen_t</span> structure.
- </p>
- <li class="subtitle"><a name="DefaultScreenOfDisplay"></a>DefaultScreenOfDisplay
- <p>
- It is the default screen that you obtain when you connect to
- the X server. It suffices to call the <a href="#ScreenOfDisplay">screen_of_display</a>
- function above with the connection and the number of the
- default screen.
- </p>
- <pre class="code">
-xcb_connection_t *c;
-int screen_default_nbr;
-xcb_screen_t *default_screen; /* the returned default screen */
-
-/* you pass the name of the display you want to xcb_connect_t */
-
-c = xcb_connect (display_name, &screen_default_nbr);
-default_screen = screen_of_display (c, screen_default_nbr);
-
-/* default_screen contains now the default root window, or a NULL window if no screen is found */
-</pre>
- <li class="subtitle"><a name="RootWindow">RootWindow / RootWindowOfScreen</a>
- <br>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-xcb_window_t root_window = { 0 }; /* the returned window */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen)
- root_window = screen->root;
-
-/* root_window contains now the root window, or a NULL window if no screen is found */
-</pre>
- <li class="subtitle"><a name="DefaultRootWindow">DefaultRootWindow</a>
- <p>
- It is the root window of the default screen. So, you call
- <a name="ScreenOfDisplay">ScreenOfDisplay</a> with the
- default screen number and you get the
- <a href="#RootWindow">root window</a> as above:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_default_nbr;
-xcb_window_t root_window = { 0 }; /* the returned root window */
-
-/* you pass the name of the display you want to xcb_connect_t */
-
-c = xcb_connect (display_name, &screen_default_nbr);
-screen = screen_of_display (c, screen_default_nbr);
-if (screen)
- root_window = screen->root;
-
-/* root_window contains now the default root window, or a NULL window if no screen is found */
-</pre>
- <li class="subtitle"><a name="DefaultVisual">DefaultVisual / DefaultVisualOfScreen</a>
- <p>
- While a Visual is, in Xlib, a structure, in XCB, there are
- two types: <span class="code">xcb_visualid_t</span>, which is
- the Id of the visual, and <span class="code">xcb_visualtype_t</span>,
- which corresponds to the Xlib Visual. To get the Id of the
- visual of a screen, just get the
- <span class="code">root_visual</span>
- member of a <span class="code">xcb_screen_t</span>:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-xcb_visualid_t root_visual = { 0 }; /* the returned visual Id */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen)
- root_visual = screen->root_visual;
-
-/* root_visual contains now the value of the Id of the visual, or a NULL visual if no screen is found */
-</pre>
- <p>
- To get the <span class="code">xcb_visualtype_t</span>
- structure, it's a bit less easy. You have to get the
- <span class="code">xcb_screen_t</span> structure that you want,
- get its <span class="code">root_visual</span> member,
- then iterate over the <span class="code">xcb_depth_t</span>s
- and the <span class="code">xcb_visualtype_t</span>s, and compare
- the <span class="code">xcb_visualid_t</span> of these <span class="code">xcb_visualtype_t</span>s:
- with <span class="code">root_visual</span>:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-xcb_visualid_t root_visual = { 0 };
-xcb_visualtype_t *visual_type = NULL; /* the returned visual type */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen) {
- xcb_depth_iterator_t depth_iter;
-
- depth_iter = xcb_screen_allowed_depths_iterator (screen);
- for (; depth_iter.rem; xcb_depth_next (&depth_iter)) {
- xcb_visualtype_iterator_t visual_iter;
-
- visual_iter = xcb_depth_visuals_iterator (depth_iter.data);
- for (; visual_iter.rem; xcb_visualtype_next (&visual_iter)) {
- if (screen->root_visual == visual_iter.data->visual_id) {
- visual_type = visual_iter.data;
- break;
- }
- }
- }
-}
-
-/* visual_type contains now the visual structure, or a NULL visual structure if no screen is found */
-</pre>
- <li class="subtitle"><a name="DefaultGC">DefaultGC / DefaultGCOfScreen</a>
- <p>
- This default Graphic Context is just a newly created Graphic
- Context, associated to the root window of a
- <span class="code">xcb_screen_t</span>,
- using the black white pixels of that screen:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-xcb_gcontext_t gc = { 0 }; /* the returned default graphic context */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen) {
- xcb_drawable_t draw;
- uint32_t mask;
- uint32_t values[2];
-
- gc = xcb_generate_id (c);
- draw = screen->root;
- mask = XCB_GC_FOREGROUND | XCB_GC_BACKGROUND;
- values[0] = screen->black_pixel;
- values[1] = screen->white_pixel;
- xcb_create_gc (c, gc, draw, mask, values);
-}
-
-/* gc contains now the default graphic context */
-</pre>
- <li class="subtitle"><a name="BlackPixel">BlackPixel / BlackPixelOfScreen</a>
- <p>
- It is the Id of the black pixel, which is in the structure
- of an <span class="code">xcb_screen_t</span>.
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-uint32_t black_pixel = 0; /* the returned black pixel */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen)
- black_pixel = screen->black_pixel;
-
-/* black_pixel contains now the value of the black pixel, or 0 if no screen is found */
-</pre>
- <li class="subtitle"><a name="WhitePixel">WhitePixel / WhitePixelOfScreen</a>
- <p>
- It is the Id of the white pixel, which is in the structure
- of an <span class="code">xcb_screen_t</span>.
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-uint32_t white_pixel = 0; /* the returned white pixel */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen)
- white_pixel = screen->white_pixel;
-
-/* white_pixel contains now the value of the white pixel, or 0 if no screen is found */
-</pre>
- <li class="subtitle"><a name="DisplayWidth">DisplayWidth / WidthOfScreen</a>
- <p>
- It is the width in pixels of the screen that you want, and
- which is in the structure of the corresponding
- <span class="code">xcb_screen_t</span>.
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-uint32_t width_in_pixels = 0; /* the returned width in pixels */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen)
- width_in_pixels = screen->width_in_pixels;
-
-/* width_in_pixels contains now the width in pixels, or 0 if no screen is found */
-</pre>
- <li class="subtitle"><a name="DisplayHeight">DisplayHeight / HeightOfScreen</a>
- <p>
- It is the height in pixels of the screen that you want, and
- which is in the structure of the corresponding
- <span class="code">xcb_screen_t</span>.
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-uint32_t height_in_pixels = 0; /* the returned height in pixels */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen)
- height_in_pixels = screen->height_in_pixels;
-
-/* height_in_pixels contains now the height in pixels, or 0 if no screen is found */
-</pre>
- <li class="subtitle"><a name="DisplayWidthMM">DisplayWidthMM / WidthMMOfScreen</a>
- <p>
- It is the width in millimeters of the screen that you want, and
- which is in the structure of the corresponding
- <span class="code">xcb_screen_t</span>.
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-uint32_t width_in_millimeters = 0; /* the returned width in millimeters */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen)
- width_in_millimeters = screen->width_in_millimeters;
-
-/* width_in_millimeters contains now the width in millimeters, or 0 if no screen is found */
-</pre>
- <li class="subtitle"><a name="DisplayHeightMM">DisplayHeightMM / HeightMMOfScreen</a>
- <p>
- It is the height in millimeters of the screen that you want, and
- which is in the structure of the corresponding
- <span class="code">xcb_screen_t</span>.
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-uint32_t height_in_millimeters = 0; /* the returned height in millimeters */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen)
- height_in_millimeters = screen->height_in_millimeters;
-
-/* height_in_millimeters contains now the height in millimeters, or 0 if no screen is found */
-</pre>
- <li class="subtitle"><a name="DisplayPlanes">DisplayPlanes / DefaultDepth / DefaultDepthOfScreen / PlanesOfScreen</a>
- <p>
- It is the depth (in bits) of the root window of the
- screen. You get it from the <span class="code">xcb_screen_t</span> structure.
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-uint8_t root_depth = 0; /* the returned depth of the root window */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen)
- root_depth = screen->root_depth;
-
-/* root_depth contains now the depth of the root window, or 0 if no screen is found */
-</pre>
- <li class="subtitle"><a name="DefaultColormap">DefaultColormap / DefaultColormapOfScreen</a>
- <p>
- This is the default colormap of the screen (and not the
- (default) colormap of the default screen !). As usual, you
- get it from the <span class="code">xcb_screen_t</span> structure:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-xcb_colormap_t default_colormap = { 0 }; /* the returned default colormap */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen)
- default_colormap = screen->default_colormap;
-
-/* default_colormap contains now the default colormap, or a NULL colormap if no screen is found */
-</pre>
- <li class="subtitle"><a name="MinCmapsOfScreen"></a>MinCmapsOfScreen
- <p>
- You get the minimum installed colormaps in the <span class="code">xcb_screen_t</span> structure:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-uint16_t min_installed_maps = 0; /* the returned minimum installed colormaps */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen)
- min_installed_maps = screen->min_installed_maps;
-
-/* min_installed_maps contains now the minimum installed colormaps, or 0 if no screen is found */
-</pre>
- <li class="subtitle"><a name="MaxCmapsOfScreen"></a>MaxCmapsOfScreen
- <p>
- You get the maximum installed colormaps in the <span class="code">xcb_screen_t</span> structure:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-uint16_t max_installed_maps = 0; /* the returned maximum installed colormaps */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen)
- max_installed_maps = screen->max_installed_maps;
-
-/* max_installed_maps contains now the maximum installed colormaps, or 0 if no screen is found */
-</pre>
- <li class="subtitle"><a name="DoesSaveUnders"></a>DoesSaveUnders
- <p>
- You know if <span class="code">save_unders</span> is set,
- by looking in the <span class="code">xcb_screen_t</span> structure:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-uint8_t save_unders = 0; /* the returned value of save_unders */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen)
- save_unders = screen->save_unders;
-
-/* save_unders contains now the value of save_unders, or FALSE if no screen is found */
-</pre>
- <li class="subtitle"><a name="DoesBackingStore"></a>DoesBackingStore
- <p>
- You know the value of <span class="code">backing_stores</span>,
- by looking in the <span class="code">xcb_screen_t</span> structure:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-uint8_t backing_stores = 0; /* the returned value of backing_stores */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen)
- backing_stores = screen->backing_stores;
-
-/* backing_stores contains now the value of backing_stores, or FALSE if no screen is found */
-</pre>
- <li class="subtitle"><a name="EventMaskOfScreen"></a>EventMaskOfScreen
- <p>
- To get the current input masks,
- you look in the <span class="code">xcb_screen_t</span> structure:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_screen_t *screen;
-int screen_nbr;
-uint32_t current_input_masks = 0; /* the returned value of current input masks */
-
-/* you init the connection and screen_nbr */
-
-screen = screen_of_display (c, screen_nbr);
-if (screen)
- current_input_masks = screen->current_input_masks;
-
-/* current_input_masks contains now the value of the current input masks, or FALSE if no screen is found */
-</pre>
- </ol>
- <li class="subtitle"><a name="misc">Miscellaneous macros</a>
- <ol>
- <li class="subtitle"><a name="DisplayOfScreen"></a>DisplayOfScreen
- <p>
- in Xlib, the <span class="code">Screen</span> structure
- stores its associated <span class="code">Display</span>
- structure. This is not the case in the X Window protocol,
- hence, it's also not the case in XCB. So you have to store
- it by yourself.
- </p>
- <li class="subtitle"><a name="DisplayCells"></a>DisplayCells / CellsOfScreen
- <p>
- To get the colormap entries,
- you look in the <span class="code">xcb_visualtype_t</span>
- structure, that you grab like <a class="subsection" href="#DefaultVisual">here</a>:
- </p>
- <pre class="code">
-xcb_connection_t *c;
-xcb_visualtype_t *visual_type;
-uint16_t colormap_entries = 0; /* the returned value of the colormap entries */
-
-/* you init the connection and visual_type */
-
-if (visual_type)
- colormap_entries = visual_type->colormap_entries;
-
-/* colormap_entries contains now the value of the colormap entries, or FALSE if no screen is found */
-</pre>
- </ol>
- </ol>
- </ol>
- </div>
-</body>
-
-</html>
+<!DOCTYPE html public "-//W3C//DTD HTML 4.01 Transitional//EN" +"http://www.w3.org/TR/html4/loose.dtd"> + +<html> + +<head> + <title>Basic Graphics Programming With The XCB Library</title> + <meta http-equiv="content-type" content="text/html; charset=iso-8859-1"> + <link href="xcb.css" rel="stylesheet" type="text/css"> +</head> + +<body> + <div class="title"> + Basic Graphics Programming With The XCB Library + </div> + <div class="toc"> + <ol> + <li><a class="section" href="#intro">Introduction</a> + <li><a class="section" href="#Xmodel">The client and server model of the X window system</a> + <li><a class="section" href="#asynch">GUI programming: the asynchronous model</a> + <li><a class="section" href="#notions">Basic XCB notions</a> + <ol> + <li><a class="subsection" href="#conn">The X Connection</a> + <li><a class="subsection" href="#requestsreplies">Requests and replies: the Xlib killers</a> + <li><a class="subsection" href="#gc">The Graphics Context</a> + <li>Object handles + <li>Memory allocation for XCB structures + <li><a class="subsection" href="#events">Events</a> + </ol> + <li><a class="section" href="#use">Using XCB-based programs</a> + <ol> + <li><a class="subsection" href="#inst">Installation of XCB</a> + <li><a class="subsection" href="#comp">Compiling XCB-based programs</a> + </ol> + <li><a class="section" href="#openconn">Opening and closing the connection to an X server</a> + <li><a class="section" href="#screen">Checking basic information about a connection</a> + <li><a class="section" href="#helloworld">Creating a basic window - the "hello world" program</a> + <li><a class="section" href="#drawing">Drawing in a window</a> + <ol> + <li><a class="subsection" href="#allocgc">Allocating a Graphics Context</a> + <li><a class="subsection" href="#changegc">Changing the attributes of a Graphics Context</a> + <li><a class="subsection" href="#drawingprim">Drawing primitives: point, line, box, circle,...</a> + </ol> + <li><a class="section" href="#xevents">X Events</a> + <ol> + <li><a class="subsection" href="#register">Registering for event types using event masks</a> + <li><a class="subsection" href="#loop">Receiving events: writing the events loop</a> + <li><a class="subsection" href="#expose">Expose events</a> + <li><a class="subsection" href="#userinput">Getting user input</a> + <ol> + <li><a class="subsubsection" href="#mousepressrelease">Mouse button press and release events</a> + <li><a class="subsubsection" href="#mousemvnt">Mouse movement events</a> + <li><a class="subsubsection" href="#mouseenter">Mouse pointer enter and leave events</a> + <li><a class="subsubsection" href="#focus">The keyboard focus</a> + <li><a class="subsubsection" href="#keypress">Keyboard press and release events</a> + </ol> + <li><a class="subsection" href="#eventex">X events: a complete example</a> + </ol> + <li><a class="section" href="#font">Handling text and fonts</a> + <ol> + <li><a class="subsection" href="#fontstruct">The Font structure</a> + <li><a class="subsection" href="#openingfont">Opening a Font</a> + <li><a class="subsection" href="#assigningfont">Assigning a Font to a Graphic Context</a> + <li><a class="subsection" href="#drawingtext">Drawing text in a drawable</a> + <li><a class="subsection" href="#fontcompleteexample">Complete example</a> + </ol> + <li>Windows hierarchy + <ol> + <li>Root, parent and child windows + <li>Events propagation + </ol> + <li><a class="section" href="#wm">Interacting with the window manager</a> + <ol> + <li><a class="subsection" href="#wmprop">Window properties</a> + <li><a class="subsection" href="#wmname">Setting the window name and icon name</a> + <li>Setting preferred window size(s) + <li>Setting miscellaneous window manager hints + <li>Setting an application's icon + <li>Obeying the delete-window protocol + </ol> + <li><a class="section" href="#winop">Simple window operations</a> + <ol> + <li><a class="subsection" href="#winmap">Mapping and unmapping a window</a> + <li><a class="subsection" href="#winconf">Configuring a window</a> + <li><a class="subsection" href="#winmove">Moving a window around the screen</a> + <li><a class="subsection" href="#winsize">Resizing a window</a> + <li><a class="subsection" href="#winstack">Changing windows stacking order: raise and lower</a> + <li>Iconifying and de-iconifying a window + <li><a class="subsection" href="#wingetinfo">Getting informations about a window</a> + </ol> + <li><a class="section" href="#usecolor">Using colors to paint the rainbow</a> + <ol> + <li><a class="subsection" href="#colormap">Color maps</a> + <li><a class="subsection" href="#colormapalloc">Allocating and freeing Color Maps</a> + <li><a class="subsection" href="#alloccolor">Allocating and freeing a color entry</a> + <li>Drawing with a color + </ol> + <li><a class="section" href="#pixmaps">X Bitmaps and Pixmaps</a> + <ol> + <li><a class="subsection" href="#pixmapswhat">What is a X Bitmap ? An X Pixmap ?</a> + <li>Loading a bitmap from a file + <li>Drawing a bitmap in a window + <li><a class="subsection" href="#pixmapscreate">Creating a pixmap</a> + <li><a class="subsection" href="#pixmapsdraw">Drawing a pixmap in a window</a> + <li><a class="subsection" href="#pixmapsfree">Freeing a pixmap</a> + </ol> + <li><a class="subsection" href="#mousecursor">Messing with the mouse cursor</a> + <ol> + <li><a class="subsection" href="#mousecursorcreate">Creating and destroying a mouse cursor</a> + <li><a class="subsection" href="#mousecursorset">Setting a window's mouse cursor</a> + <li><a class="subsection" href="#mousecursorexample">Complete example</a> + </ol> + <li><a class="subsection" href="#translation">Translation of basic Xlib functions and macros</a> + <ol> + <li><a class="subsection" href="#displaystructure">Members of the Display structure</a> + <ol> + <li><a class="subsection" href="#ConnectionNumber">ConnectionNumber</a> + <li><a class="subsection" href="#DefaultScreen">DefaultScreen</a> + <li><a class="subsection" href="#QLength">QLength</a> + <li><a class="subsection" href="#ScreenCount">ScreenCount</a> + <li><a class="subsection" href="#ServerVendor">ServerVendor</a> + <li><a class="subsection" href="#ProtocolVersion">ProtocolVersion</a> + <li><a class="subsection" href="#ProtocolRevision">ProtocolRevision</a> + <li><a class="subsection" href="#VendorRelease">VendorRelease</a> + <li><a class="subsection" href="#DisplayString">DisplayString</a> + <li><a class="subsection" href="#BitmapUnit">BitmapUnit</a> + <li><a class="subsection" href="#BitmapBitOrder">BitmapBitOrder</a> + <li><a class="subsection" href="#BitmapPad">BitmapPad</a> + <li><a class="subsection" href="#ImageByteOrder">ImageByteOrder</a> + </ol> + <li><a class="subsection" href="#screenofdisplay">ScreenOfDisplay related functions</a> + <ol> + <li><a class="subsection" href="#ScreenOfDisplay">ScreenOfDisplay</a> + <li><a class="subsection" href="#DefaultScreenOfDisplay">DefaultScreenOfDisplay</a> + <li><a class="subsection" href="#RootWindow">RootWindow / RootWindowOfScreen</a> + <li><a class="subsection" href="#DefaultRootWindow">DefaultRootWindow</a> + <li><a class="subsection" href="#DefaultVisual">DefaultVisual / DefaultVisualOfScreen</a> + <li><a class="subsection" href="#DefaultGC">DefaultGC / DefaultGCOfScreen</a> + <li><a class="subsection" href="#BlackPixel">BlackPixel / BlackPixelOfScreen</a> + <li><a class="subsection" href="#WhitePixel">WhitePixel / WhitePixelOfScreen</a> + <li><a class="subsection" href="#DisplayWidth">DisplayWidth / WidthOfScreen</a> + <li><a class="subsection" href="#DisplayHeight">DisplayHeight / HeightOfScreen</a> + <li><a class="subsection" href="#DisplayWidthMM">DisplayWidthMM / WidthMMOfScreen</a> + <li><a class="subsection" href="#DisplayHeightMM">DisplayHeightMM / HeightMMOfScreen</a> + <li><a class="subsection" href="#DisplayPlanes">DisplayPlanes / DefaultDepth / DefaultDepthOfScreen / PlanesOfScreen</a> + <li><a class="subsection" href="#DefaultColormap">DefaultColormap / DefaultColormapOfScreen</a> + <li><a class="subsection" href="#MinCmapsOfScreen">MinCmapsOfScreen</a> + <li><a class="subsection" href="#MaxCmapsOfScreen">MaxCmapsOfScreen</a> + <li><a class="subsection" href="#DoesSaveUnders">DoesSaveUnders</a> + <li><a class="subsection" href="#DoesBackingStore">DoesBackingStore</a> + <li><a class="subsection" href="#EventMaskOfScreen">EventMaskOfScreen</a> + </ol> + <li><a class="subsection" href="#misc">Miscellaneaous macros</a> + <ol> + <li><a class="subsection" href="#DisplayOfScreen">DisplayOfScreen</a> + <li><a class="subsection" href="#DisplayCells">DisplayCells / CellsOfScreen</a> + </ol> + </ol> + </ol> + </div> + <div class="section"> + <ol> + <li class="title"><a name="intro">Introduction</a> + <p> + This tutorial is based on the + <a href="http://users.actcom.co.il/~choo/lupg/tutorials/xlib-programming/xlib-programming.html">Xlib Tutorial</a> + written by <a href="mailto:choor at atcom dot co dot il">Guy Keren</a>. The + author allowed me to take some parts of his text, mainly the text which + deals with the X Windows generality. + </p> + <p> + This tutorial is intended for people who want to start to program + with the <a href="http://xcb.freedesktop.org">XCB</a> + library. keep in mind that XCB, like the + <a href="http://tronche.com/gui/x/xlib/introduction">Xlib</a> + library, isn't what most programmers wanting to write X + applications are looking for. They should use a much higher + level GUI toolkit like Motif, + <a href="http://www.lesstif.org">LessTiff</a>, + <a href="http://www.gtk.org">GTK</a>, + <a href="http://www.trolltech.com">QT</a>, + <a href="http://www.enlightenment.org">EWL</a>, + <a href="http://www.enlightenment.org">ETK</a>, or use + <a href="http://cairographics.org">Cairo</a>. + However, + we need to start somewhere. More than this, knowing how things + work down below is never a bad idea. + </p> + <p> + After reading this tutorial, one should be able to write very + simple graphical programs, but not programs with decent user + interfaces. For such programs, one of the previously mentioned + libraries should be used. + </p> + <p> + But what is XCB? Xlib has been + the standard C binding for the <a href="http://www.x.org">X + Window System</a> protocol for many years now. It is an + excellent piece of work, but there are applications for which it + is not ideal, for example: + </p> + <ul> + <li><b>Small platforms</b>: Xlib is a large piece of code, and + it's difficult to make it smaller + <li><b>Latency hiding</b>: Xlib requests requiring a reply are + effectively synchronous: they block until the reply appears, + whether the result is needed immediately or not. + <li><b>Direct access to the protocol</b>: Xlib does quite a + bit of caching, layering, and similar optimizations. While this + is normally a feature, it makes it difficult to simply emit + specified X protocol requests and process specific + responses. + <li><b>Threaded applications</b>: While Xlib does attempt to + support multithreading, the API makes this difficult and + error-prone. + <li><b>New extensions</b>: The Xlib infrastructure provides + limited support for the new creation of X extension client side + code. + </ul> + <p> + For these reasons, among others, XCB, an X C binding, has been + designed to solve the above problems and thus provide a base for + </p> + <ul> + <li>Toolkit implementation. + <li>Direct protocol-level programming. + <li>Lightweight emulation of commonly used portions of the + Xlib API. + </ul> + <br> + <li class="title"><a name="Xmodel">The client and server model of the X window system</a> + <p> + The X Window System was developed with one major goal: + flexibility. The idea was that the way things look is one thing, + but the way things work is another matter. Thus, the lower + levels provide the tools required to draw windows, handle user + input, allow drawing graphics using colors (or black and white + screens), etc. To this point, a decision was made to separate + the system into two parts. A client that decides what to do, and + a server that actually draws on the screen and reads user input + in order to send it to the client for processing. + </p> + <p> + This model is the complete opposite of what is used to when + dealing with clients and servers. In our case, the user sits + near the machine controlled by the server, while the client + might be running on a remote machine. The server controls the + screens, mouse and keyboard. A client may connect to the server, + request that it draws a window (or several windows), and ask the + server to send it any input the user sends to these + windows. Thus, several clients may connect to a single X server + (one might be running mail software, one running a WWW + browser, etc). When input is sent by the user to some window, + the server sends a message to the client controlling this window + for processing. The client decides what to do with this input, + and sends the server requests for drawing in the window. + </p> + <p> + The whole session is carried out using the X message + protocol. This protocol was originally carried over the TCP/IP + protocol suite, allowing the client to run on any machine + connected to the same network that the server is. Later on, the + X servers were extended to allow clients running on the local + machine with more optimized access to the server (note that an X + protocol message may be several hundreds of KB in size), such as + using shared memory, or using Unix domain sockets (a method for + creating a logical channel on a Unix system between two processes). + </p> + <li class="title"><a name="asynch">GUI programming: the asynchronous model</a> + <p> + Unlike conventional computer programs, that carry some serial + nature, a GUI program usually uses an asynchronous programming + model, also known as "event-driven programming". This means that + that program mostly sits idle, waiting for events sent by the X + server, and then acts upon these events. An event may say "The + user pressed the 1st button mouse in spot (x,y)", or "The window + you control needs to be redrawn". In order for the program to be + responsive to the user input, as well as to refresh requests, it + needs to handle each event in a rather short period of time + (e.g. less that 200 milliseconds, as a rule of thumb). + </p> + <p> + This also implies that the program may not perform operations + that might take a long time while handling an event (such as + opening a network connection to some remote server, or + connecting to a database server, or even performing a long file + copy operation). Instead, it needs to perform all these + operations in an asynchronous manner. This may be done by using + various asynchronous models to perform the longish operations, + or by performing them in a different process or thread. + </p> + <p> + So the way a GUI program looks is something like that: + </p> + <ol> + <li>Perform initialization routines. + <li>Connect to the X server. + <li>Perform X-related initialization. + <li>While not finished: + <ol> + <li>Receive the next event from the X server. + <li>Handle the event, possibly sending various drawing + requests to the X server. + <li>If the event was a quit message, exit the loop. + </ol> + <li>Close down the connection to the X server. + <li>Perform cleanup operations. + </ol> + <br> + <li class="title"><a name="notions">Basic XCB notions</a> + <p> + XCB has been created to eliminate the need for + programs to actually implement the X protocol layer. This + library gives a program a very low-level access to any X + server. Since the protocol is standardized, a client using any + implementation of XCB may talk with any X server (the same + occurs for Xlib, of course). We now give a brief description of + the basic XCB notions. They will be detailed later. + </p> + <ol> + <li class="subtitle"><a name="conn">The X Connection</a> + <p> + The major notion of using XCB is the X Connection. This is a + structure representing the connection we have open with a + given X server. It hides a queue of messages coming from the + server, and a queue of pending requests that our client + intends to send to the server. In XCB, this structure is named + 'xcb_connection_t'. It is analogous to the Xlib Display. + When we open a connection to an X server, the + library returns a pointer to such a structure. Later, we + supply this pointer to any XCB function that should send + messages to the X server or receive messages from this server. + </p> + <li class="subtitle"><a name="requestsreplies">Requests and + replies: the Xlib killers</a> + <p> + To ask for information from the X server, we have to make a request + and ask for a reply. With Xlib, these two tasks are + automatically done: Xlib locks the system, sends a request, + waits for a reply from the X server and unlocks. This is + annoying, especially if one makes a lot of requests to the X + server. Indeed, Xlib has to wait for the end of a reply + before asking for the next request (because of the locks that + Xlib sends). For example, here is a time-line of N=4 + requests/replies with Xlib, with a round-trip latency + <b>T_round_trip</b> that is 5 times long as the time required + to write or read a request/reply (<b>T_write/T_read</b>): + </p> + <pre class="text"> + W-----RW-----RW-----RW-----R +</pre> + <ul> + <li>W: Writing request + <li>-: Stalled, waiting for data + <li>R: Reading reply + </ul> + <p> + The total time is N * (T_write + T_round_trip + T_read). + </p> + <p> + With XCB, we can suppress most of the round-trips as the + requests and the replies are not locked. We usually send a + request, then XCB returns to us a <b>cookie</b>, which is an + identifier. Then, later, we ask for a reply using this + <b>cookie</b> and XCB returns a + pointer to that reply. Hence, with XCB, we can send a lot of + requests, and later in the program, ask for all the replies + when we need them. Here is the time-line for 4 + requests/replies when we use this property of XCB: + </p> + <pre class="text"> + WWWW--RRRR +</pre> + <p> + The total time is N * T_write + max (0, T_round_trip - (N-1) * + T_write) + N * T_read. Which can be considerably faster than + all those Xlib round-trips. + </p> + <p> + Here is a program that computes the time to create 500 atoms + with Xlib and XCB. It shows the Xlib way, the bad XCB way + (which is similar to Xlib) and the good XCB way. On my + computer, XCB is 25 times faster than Xlib. + </p> + <pre class="code"> +#include <stdlib.h> +#include <stdio.h> +#include <string.h> +#include <sys/time.h> + +#include <xcb/xcb.h> + +#include <X11/Xlib.h> + +double +get_time(void) +{ + struct timeval timev; + + gettimeofday(&timev, NULL); + + return (double)timev.tv_sec + (((double)timev.tv_usec) / 1000000); +} + +int +main () +{ + xcb_connection_t *c; + xcb_atom_t *atoms; + xcb_intern_atom_cookie_t *cs; + char **names; + int count; + int i; + double start; + double end; + double diff; + + /* Xlib */ + Display *disp; + Atom *atoms_x; + double diff_x; + + c = xcb_connect (NULL, NULL); + + count = 500; + atoms = (xcb_atom_t *)malloc (count * sizeof (atoms)); + names = (char **)malloc (count * sizeof (char *)); + + /* init names */ + for (i = 0; i < count; ++i) { + char buf[100]; + + sprintf (buf, "NAME%d", i); + names[i] = strdup (buf); + } + + /* bad use */ + start = get_time (); + + for (i = 0; i < count; ++i) + atoms[i] = xcb_intern_atom_reply (c, + xcb_intern_atom (c, + 0, + strlen(names[i]), + names[i]), + NULL)->atom; + + end = get_time (); + diff = end - start; + printf ("bad use time : %f\n", diff); + + /* good use */ + start = get_time (); + + cs = (xcb_intern_atom_cookie_t *) malloc (count * sizeof(xcb_intern_atom_cookie_t)); + for(i = 0; i < count; ++i) + cs[i] = xcb_intern_atom (c, 0, strlen(names[i]), names[i]); + + for(i = 0; i < count; ++i) { + xcb_intern_atom_reply_t *r; + + r = xcb_intern_atom_reply(c, cs[i], 0); + if(r) + atoms[i] = r->atom; + free(r); + } + + end = get_time (); + printf ("good use time : %f\n", end - start); + printf ("ratio : %f\n", diff / (end - start)); + diff = end - start; + + /* free var */ + free (atoms); + free (cs); + + xcb_disconnect (c); + + /* Xlib */ + disp = XOpenDisplay (getenv("DISPLAY")); + + atoms_x = (Atom *)malloc (count * sizeof (atoms_x)); + + start = get_time (); + + for (i = 0; i < count; ++i) + atoms_x[i] = XInternAtom(disp, names[i], 0); + + end = get_time (); + diff_x = end - start; + printf ("Xlib use time : %f\n", diff_x); + printf ("ratio : %f\n", diff_x / diff); + + free (atoms_x); + for (i = 0; i < count; ++i) + free (names[i]); + free (names); + + XCloseDisplay (disp); + + return 0; +} +</pre> + <li class="subtitle"><a name="gc">The Graphic Context</a> + <p> + When we perform various drawing operations (graphics, text, + etc), we may specify various options for controlling how the + data will be drawn (what foreground and background colors to + use, how line edges will be connected, what font to use when + drawing some text, etc). In order to avoid the need to supply + hundreds of parameters to each drawing function, a graphical + context structure is used. We set the various drawing options + in this structure, and then we pass a pointer to this + structure to any drawing routines. This is rather handy, as we + often need to perform several drawing requests with the same + options. Thus, we would initialize a graphical context, set + the desired options, and pass this structure to all drawing + functions. + </p> + <p> + Note that graphic contexts have no client-side structure in + XCB, they're just XIDs. Xlib has a client-side structure + because it caches the GC contents so it can avoid making + redundant requests, but of course XCB doesn't do that. + </p> + <li class="subtitle"><a name="events">Events</a> + <p> + A structure is used to pass events received from the X + server. XCB supports exactly the events specified in the + protocol (33 events). This structure contains the type + of event received (including a bit for whether it came + from the server or another client), as well as the data associated with the + event (e.g. position on the screen where the event was + generated, mouse button associated with the event, region of + the screen associated with a "redraw" event, etc). The way to + read the event's data depends on the event type. + </p> + </ol> + <br> + <li class="title"><a name="use">Using XCB-based programs</a> + <br> + <ol> + <li class="subtitle"><a name="inst">Installation of XCB</a> + <p> + <b>TODO:</b> These instructions are out of date. + Just reference the <a href="http://xcb.freedesktop.org/">main XCB page</a> + so we don't have to maintain these instructions in more than + one place. + </p> + <p> + To build XCB from source, you need to have installed at + least: + </p> + <ul> + <li>pkgconfig 0.15.0 + <li><a href="http://www.gnu.org/software/automake/">automake 1.7</a> + <li><a href="http://www.gnu.org/software/autoconf/">autoconf 2.50</a> + <li><a href="http://www.check.org">check</a> + <li><a href="http://xmlsoft.org/XSLT/">xsltproc</a> + <li><a href="http://www.gnu.org/software/gperf/">gperf 3.0.1</a> + </ul> + <p> + You have to checkout in the git repository the following modules: + </p> + <ul> + <li>Xau from xlibs + <li>xcb-proto + <li>xcb + </ul> + <p> + Note that xcb-proto exists only to install header + files, so typing 'make' or 'make all' will produce the message + "Nothing to be done for 'all'". That's normal. + </p> + <li class="subtitle"><a name="comp">Compiling XCB-based programs</a> + <p> + Compiling XCB-based programs requires linking them with the XCB + library. This is easily done thanks to pkgconfig: + </p> + <pre class="text"> +gcc -Wall prog.c -o prog `pkg-config --cflags --libs xcb` +</pre> + </ol> + <li class="title"><a name="openconn">Opening and closing the connection to an X server</a> + <p> + An X program first needs to open the connection to the X + server. There is a function that opens a connection. It requires + the display name, or NULL. In the latter case, the display name + will be the one in the environment variable DISPLAY. + </p> + <pre class="code"> +<span class="type">xcb_connection_t</span> *xcb_connect (<span class="keyword">const</span> <span class="type">char</span> *displayname, + <span class="type">int</span> *screenp); +</pre> + <p> + The second parameter returns the screen number used for the + connection. The returned structure describes an XCB connection + and is opaque. Here is how the connection can be opened: + </p> + <pre class="code"> +#<span class="include">include</span> <span class="string"><xcb/xcb.h></span> + +<span class="type">int</span> +<span class="function">main</span> () +{ + <span class="type">xcb_connection_t</span> *c; + + /* Open the connection to the X server. Use the DISPLAY environment variable as the default display name */ + c = xcb_connect (NULL, NULL); + + <span class="keyword">return</span> 0; +} +</pre> + <p> + To close a connection, it suffices to use: + </p> + <pre class="code"> +<span class="type">void</span> xcb_disconnect (<span class="type">xcb_connection_t</span> *c); +</pre> + <div class="comp"> + <div class="title"> + Comparison Xlib/XCB + </div> + <div class="xlib"> + <ul> + <li>XOpenDisplay () + </ul> + </div> + <div class="xcb"> + <ul> + <li>xcb_connect () + </ul> + </div> + <div class="xlib"> + <ul> + <li>XCloseDisplay () + </ul> + </div> + <div class="xcb"> + <ul> + <li>xcb_disconnect () + </ul> + </div> + </div> + <br> + <li class="title"><a name="screen">Checking basic information about a connection</a> + <p> + Once we have opened a connection to an X server, we should check some + basic information about it: what screens it has, what is the + size (width and height) of the screen, how many colors it + supports (black and white ? grey scale ?, 256 colors ? more ?), + and so on. We get such information from the xcb_screen_t + structure: + </p> + <pre class="code"> +typedef struct { + xcb_window_t root; + xcb_colormap_t default_colormap; + uint32_t white_pixel; + uint32_t black_pixel; + uint32_t current_input_masks; + uint16_t width_in_pixels; + uint16_t height_in_pixels; + uint16_t width_in_millimeters; + uint16_t height_in_millimeters; + uint16_t min_installed_maps; + uint16_t max_installed_maps; + xcb_visualid_t root_visual; + uint8_t backing_stores; + uint8_t save_unders; + uint8_t root_depth; + uint8_t allowed_depths_len; +} xcb_screen_t; +</pre> + <p> + We could retrieve the first screen of the connection by using the + following function: + </p> + <pre class="code"> +xcb_screen_iterator_t xcb_setup_roots_iterator (xcb_setup_t *R); +</pre> + <p> + Here is a small program that shows how to use this function: + </p> + <pre class="code"> +#include <stdio.h> + +#include <xcb/xcb.h> + +int +main () +{ + xcb_connection_t *c; + xcb_screen_t *screen; + int screen_nbr; + xcb_screen_iterator_t iter; + + /* Open the connection to the X server. Use the DISPLAY environment variable */ + c = xcb_connect (NULL, &screen_nbr); + + /* Get the screen #screen_nbr */ + iter = xcb_setup_roots_iterator (xcb_get_setup (c)); + for (; iter.rem; --screen_nbr, xcb_screen_next (&iter)) + if (screen_nbr == 0) { + screen = iter.data; + break; + } + + printf ("\n"); + printf ("Informations of screen %ld:\n", screen->root); + printf (" width.........: %d\n", screen->width_in_pixels); + printf (" height........: %d\n", screen->height_in_pixels); + printf (" white pixel...: %ld\n", screen->white_pixel); + printf (" black pixel...: %ld\n", screen->black_pixel); + printf ("\n"); + + return 0; +} +</pre> + <li class="title"><a name="helloworld">Creating a basic window - the "hello world" program</a> + <p> + After we got some basic information about our screen, we can + create our first window. In the X Window System, a window is + characterized by an Id. So, in XCB, a window is of type: + </p> + <pre class="code"> +typedef uint32_t xcb_window_t; +</pre> + <p> + We first ask for a new Id for our window, with this function: + </p> + <pre class="code"> +xcb_window_t xcb_generate_id(xcb_connection_t *c); +</pre> + <p> + Then, XCB supplies the following function to create new windows: + </p> + <pre class="code"> +xcb_void_cookie_t xcb_create_window (xcb_connection_t *c, /* Pointer to the xcb_connection_t structure */ + uint8_t depth, /* Depth of the screen */ + xcb_window_t wid, /* Id of the window */ + xcb_window_t parent, /* Id of an existing window that should be the parent of the new window */ + int16_t x, /* X position of the top-left corner of the window (in pixels) */ + int16_t y, /* Y position of the top-left corner of the window (in pixels) */ + uint16_t width, /* Width of the window (in pixels) */ + uint16_t height, /* Height of the window (in pixels) */ + uint16_t border_width, /* Width of the window's border (in pixels) */ + uint16_t _class, + xcb_visualid_t visual, + uint32_t value_mask, + const uint32_t *value_list); +</pre> + <p> + The fact that we created the window does not mean that it will + be drawn on screen. By default, newly created windows are not + mapped on the screen (they are invisible). In order to make our + window visible, we use the function <span class="code">xcb_map_window()</span>, whose + prototype is + </p> + <pre class="code"> +xcb_void_cookie_t xcb_map_window (xcb_connection_t *c, + xcb_window_t window); +</pre> + <p> + Finally, here is a small program to create a window of size + 150x150 pixels, positioned at the top-left corner of the screen: + </p> + <pre class="code"> +#include <unistd.h> /* pause() */ + +#include <xcb/xcb.h> + +int +main () +{ + xcb_connection_t *c; + xcb_screen_t *screen; + xcb_window_t win; + + /* Open the connection to the X server */ + c = xcb_connect (NULL, NULL); + + /* Get the first screen */ + screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data; + + /* Ask for our window's Id */ + win = xcb_generate_id(c); + + /* Create the window */ + xcb_create_window (c, /* Connection */ + XCB_COPY_FROM_PARENT, /* depth (same as root)*/ + win, /* window Id */ + screen->root, /* parent window */ + 0, 0, /* x, y */ + 150, 150, /* width, height */ + 10, /* border_width */ + XCB_WINDOW_CLASS_INPUT_OUTPUT, /* class */ + screen->root_visual, /* visual */ + 0, NULL); /* masks, not used yet */ + + /* Map the window on the screen */ + xcb_map_window (c, win); + + /* Make sure commands are sent before we pause, so window is shown */ + xcb_flush (c); + + pause (); /* hold client until Ctrl-C */ + + return 0; +} +</pre> + <p> + In this code, you see one more function - <span class="code">xcb_flush()</span>, not explained + yet. It is used to flush all the pending requests. More + precisely, there are 2 functions that do such things. The first + one is <span class="code">xcb_flush()</span>: + </p> + <pre class="code"> +int xcb_flush (xcb_connection_t *c); +</pre> + <p> + This function flushes all pending requests to the X server (much + like the <span class="code">fflush()</span> function is used to + flush standard output). The second function is + <span class="code">xcb_aux_sync()</span>: + </p> + <pre class="code"> +int xcb_aux_sync (xcb_connection_t *c); +</pre> + <p> + This functions also flushes all pending requests to the X + server, and then waits until the X server finishing processing + these requests. In a normal program, this will not be necessary + (we'll see why when we get to write a normal X program), but for + now, we put it there. + </p> + <p> + The window that is created by the above code has a non defined + background. This one can be set to a specific color, + thanks to the two last parameters of + <span class="code">xcb_create_window()</span>, which are not + described yet. See the subsections + <a href="#winconf">Configuring a window</a> or + <a href="#winconf">Registering for event types using event masks</a> + for examples on how to use these parameters. In addition, as no + events are handled, you have to make a Ctrl-C to interrupt the + program. + </p> + <p> + <b>TODO</b>: one should tell what these functions return and + about the generic error + </p> + <div class="comp"> + <div class="title"> + Comparison Xlib/XCB + </div> + <div class="xlib"> + <ul> + <li>XCreateWindow () + </ul> + </div> + <div class="xcb"> + <ul> + <li>xcb_generate_id () + <li>xcb_create_window () + </ul> + </div> + </div> + <br> + <li class="title"><a name="drawing">Drawing in a window</a> + <p> + Drawing in a window can be done using various graphical + functions (drawing pixels, lines, rectangles, etc). In order to + draw in a window, we first need to define various general + drawing parameters (what line width to use, which color to draw + with, etc). This is done using a graphical context. + </p> + <ol> + <li class="subtitle"><a name="allocgc">Allocating a Graphics Context</a> + <p> + As we said, a graphical context defines several attributes to + be used with the various drawing functions. For this, we + define a graphical context. We can use more than one graphical + context with a single window, in order to draw in multiple + styles (different colors, different line widths, etc). In XCB, + a Graphics Context is, as a window, characterized by an Id: + </p> + <pre class="code"> +typedef uint32_t xcb_gcontext_t; +</pre> + <p> + We first ask the X server to attribute an Id to our graphic + context with this function: + </p> + <pre class="code"> +xcb_gcontext_t xcb_generate_id (xcb_connection_t *c); +</pre> + <p> + Then, we set the attributes of the graphic context with this function: + </p> + <pre class="code"> +xcb_void_cookie_t xcb_create_gc (xcb_connection_t *c, + xcb_gcontext_t cid, + xcb_drawable_t drawable, + uint32_t value_mask, + const uint32_t *value_list); +</pre> + <p> + We give now an example on how to allocate a graphic context + that specifies that each drawing function that uses it will + draw in foreground with a black color. + </p> + <pre class="code"> +#include <xcb/xcb.h> + +int +main () +{ + xcb_connection_t *c; + xcb_screen_t *screen; + xcb_drawable_t win; + xcb_gcontext_t black; + uint32_t mask; + uint32_t value[1]; + + /* Open the connection to the X server and get the first screen */ + c = xcb_connect (NULL, NULL); + screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data; + + /* Create a black graphic context for drawing in the foreground */ + win = screen->root; + black = xcb_generate_id (c); + mask = XCB_GC_FOREGROUND; + value[0] = screen->black_pixel; + xcb_create_gc (c, black, win, mask, value); + + return 0; +} +</pre> + <p> + Note should be taken regarding the role of "value_mask" and + "value_list" in the prototype of <span class="code">xcb_create_gc()</span>. Since a + graphic context has many attributes, and since we often just + want to define a few of them, we need to be able to tell the + <span class="code">xcb_create_gc()</span> which attributes we + want to set. This is what the "value_mask" parameter is + for. We then use the "value_list" parameter to specify actual + values for the attribute we defined in "value_mask". Thus, for + each constant used in "value_list", we will use the matching + constant in "value_mask". In this case, we define a graphic + context with one attribute: when drawing (a point, a line, + etc), the foreground color will be black. The rest of the + attributes of this graphic context will be set to their + default values. + </p> + <p> + See the next Subsection for more details. + </p> + <div class="comp"> + <div class="title"> + Comparison Xlib/XCB + </div> + <div class="xlib"> + <ul> + <li>XCreateGC () + </ul> + </div> + <div class="xcb"> + <ul> + <li>xcb_generate_id () + <li>xcb_create_gc () + </ul> + </div> + </div> + <br> + <li class="subtitle"><a name="changegc">Changing the attributes of a Graphics Context</a> + <p> + Once we have allocated a Graphic Context, we may need to + change its attributes (for example, changing the foreground + color we use to draw a line, or changing the attributes of the + font we use to display strings. See Subsections Drawing with a + color and + <a href="#assigningfont">Assigning a Font to a Graphic Context</a>). + This is done by using this function: + </p> + <pre class="code"> +xcb_void_cookie_t xcb_change_gc (xcb_connection_t *c, /* The XCB Connection */ + xcb_gcontext_t gc, /* The Graphic Context */ + uint32_t value_mask, /* Components of the Graphic Context that have to be set */ + const uint32_t *value_list); /* Value as specified by value_mask */ +</pre> + <p> + The <span class="code">value_mask</span> parameter could take + any combination of these masks from the xcb_gc_t enumeration: + </p> + <ul> + <li>XCB_GC_FUNCTION + <li>XCB_GC_PLANE_MASK + <li>XCB_GC_FOREGROUND + <li>XCB_GC_BACKGROUND + <li>XCB_GC_LINE_WIDTH + <li>XCB_GC_LINE_STYLE + <li>XCB_GC_CAP_STYLE + <li>XCB_GC_JOIN_STYLE + <li>XCB_GC_FILL_STYLE + <li>XCB_GC_FILL_RULE + <li>XCB_GC_TILE + <li>XCB_GC_STIPPLE + <li>XCB_GC_TILE_STIPPLE_ORIGIN_X + <li>XCB_GC_TILE_STIPPLE_ORIGIN_Y + <li>XCB_GC_FONT + <li>XCB_GC_SUBWINDOW_MODE + <li>XCB_GC_GRAPHICS_EXPOSURES + <li>XCB_GC_CLIP_ORIGIN_X + <li>XCB_GC_CLIP_ORIGIN_Y + <li>XCB_GC_CLIP_MASK + <li>XCB_GC_DASH_OFFSET + <li>XCB_GC_DASH_LIST + <li>XCB_GC_ARC_MODE + </ul> + <p> + It is possible to set several attributes at the same + time (for example setting the attributes of a font and the + color which will be used to display a string), by OR'ing these + values in <span class="code">value_mask</span>. Then + <span class="code">value_list</span> has to be an array which + lists the value for the respective attributes. <b>These values + must be in the same order as masks listed above.</b> See Subsection + Drawing with a color to have an example. + </p> + <p> + <b>TODO</b>: set the links of the 3 subsections, once they will + be written :) + </p> + <p> + <b>TODO</b>: give an example which sets several attributes. + </p> + <li class="subtitle"><a name="drawingprim">Drawing primitives: point, line, box, circle,...</a> + <p> + After we have created a Graphic Context, we can draw on a + window using this Graphic Context, with a set of XCB + functions, collectively called "drawing primitives". Let see + how they are used. + </p> + <p> + To draw a point, or several points, we use + </p> + <pre class="code"> +xcb_void_cookie_t xcb_poly_point (xcb_connection_t *c, /* The connection to the X server */ + uint8_t coordinate_mode, /* Coordinate mode, usually set to XCB_COORD_MODE_ORIGIN */ + xcb_drawable_t drawable, /* The drawable on which we want to draw the point(s) */ + xcb_gcontext_t gc, /* The Graphic Context we use to draw the point(s) */ + uint32_t points_len, /* The number of points */ + const xcb_point_t *points); /* An array of points */ +</pre> + <p> + The <span class="code">coordinate_mode</span> parameter + specifies the coordinate mode. Available values are + </p> + <ul> + <li><span class="code">XCB_COORD_MODE_ORIGIN</span> + <li><span class="code">XCB_COORD_MODE_PREVIOUS</span> + </ul> + <p> + If XCB_COORD_MODE_PREVIOUS is used, then all points but the first one + are relative to the immediately previous point. + </p> + <p> + The <span class="code">xcb_point_t</span> type is just a + structure with two fields (the coordinates of the point): + </p> + <pre class="code"> +typedef struct { + int16_t x; + int16_t y; +} xcb_point_t; +</pre> + <p> + You could see an example in xpoints.c. <b>TODO</b> Set the link. + </p> + <p> + To draw a line, or a polygonal line, we use + </p> + <pre class="code"> +xcb_void_cookie_t xcb_poly_line (xcb_connection_t *c, /* The connection to the X server */ + uint8_t coordinate_mode, /* Coordinate mode, usually set to XCB_COORD_MODE_ORIGIN */ + xcb_drawable_t drawable, /* The drawable on which we want to draw the line(s) */ + xcb_gcontext_t gc, /* The Graphic Context we use to draw the line(s) */ + uint32_t points_len, /* The number of points in the polygonal line */ + const xcb_point_t *points); /* An array of points */ +</pre> + <p> + This function will draw the line between the first and the + second points, then the line between the second and the third + points, and so on. + </p> + <p> + To draw a segment, or several segments, we use + </p> + <pre class="code"> +xcb_void_cookie_t xcb_poly_segment (xcb_connection_t *c, /* The connection to the X server */ + xcb_drawable_t drawable, /* The drawable on which we want to draw the segment(s) */ + xcb_gcontext_t gc, /* The Graphic Context we use to draw the segment(s) */ + uint32_t segments_len, /* The number of segments */ + const xcb_segment_t *segments); /* An array of segments */ +</pre> + <p> + The <span class="code">xcb_segment_t</span> type is just a + structure with four fields (the coordinates of the two points + that define the segment): + </p> + <pre class="code"> +typedef struct { + int16_t x1; + int16_t y1; + int16_t x2; + int16_t y2; +} xcb_segment_t; +</pre> + <p> + To draw a rectangle, or several rectangles, we use + </p> + <pre class="code"> +xcb_void_cookie_t xcb_poly_rectangle (xcb_connection_t *c, /* The connection to the X server */ + xcb_drawable_t drawable, /* The drawable on which we want to draw the rectangle(s) */ + xcb_gcontext_t gc, /* The Graphic Context we use to draw the rectangle(s) */ + uint32_t rectangles_len, /* The number of rectangles */ + const xcb_rectangle_t *rectangles); /* An array of rectangles */ +</pre> + <p> + The <span class="code">xcb_rectangle_t</span> type is just a + structure with four fields (the coordinates of the top-left + corner of the rectangle, and its width and height): + </p> + <pre class="code"> +typedef struct { + int16_t x; + int16_t y; + uint16_t width; + uint16_t height; +} xcb_rectangle_t; +</pre> + <!-- There's no coordinate_mode. Is it normal? --> + <!-- [iano] Yes, it's not in the protocol. --> + <p> + To draw an elliptical arc, or several elliptical arcs, we use + </p> + <pre class="code"> +xcb_void_cookie_t xcb_poly_arc (xcb_connection_t *c, /* The connection to the X server */ + xcb_drawable_t drawable, /* The drawable on which we want to draw the arc(s) */ + xcb_gcontext_t gc, /* The Graphic Context we use to draw the arc(s) */ + uint32_t arcs_len, /* The number of arcs */ + const xcb_arc_t *arcs); /* An array of arcs */ +</pre> + <p> + The <span class="code">xcb_arc_t</span> type is a structure with + six fields: + </p> + <pre class="code"> +typedef struct { + int16_t x; /* Top left x coordinate of the rectangle surrounding the ellipse */ + int16_t y; /* Top left y coordinate of the rectangle surrounding the ellipse */ + uint16_t width; /* Width of the rectangle surrounding the ellipse */ + uint16_t height; /* Height of the rectangle surrounding the ellipse */ + int16_t angle1; /* Angle at which the arc begins */ + int16_t angle2; /* Angle at which the arc ends */ +} xcb_arc_t; +</pre> + <div class="emph"> + <p> + Note: the angles are expressed in units of 1/64 of a degree, + so to have an angle of 90 degrees, starting at 0, + <span class="code">angle1 = 0</span> and + <span class="code">angle2 = 90 << 6</span>. Positive angles + indicate counterclockwise motion, while negative angles + indicate clockwise motion. + </p> + </div> + <!-- I think that (x,y) should be the center of the + ellipse, and (width, height) the radius. It's more logical. --> + <!-- iano: Yes, and I bet some toolkits do that. + But the protocol (and many other graphics APIs) define arcs + by bounding rectangles. --> + <p> + The corresponding function which fill inside the geometrical + object are listed below, without further explanation, as they + are used as the above functions. + </p> + <p> + To Fill a polygon defined by the points given as arguments , + we use + </p> + <pre class="code"> +xcb_void_cookie_t xcb_fill_poly (xcb_connection_t *c, + xcb_drawable_t drawable, + xcb_gcontext_t gc, + uint8_t shape, + uint8_t coordinate_mode, + uint32_t points_len, + const xcb_point_t *points); +</pre> + <p> + The <span class="code">shape</span> parameter specifies a + shape that helps the server to improve performance. Available + values are + </p> + <ul> + <li><span class="code">XCB_POLY_SHAPE_COMPLEX</span> + <li><span class="code">XCB_POLY_SHAPE_NONCONVEX</span> + <li><span class="code">XCB_POLY_SHAPE_CONVEX</span> + </ul> + <p> + To fill one or several rectangles, we use + </p> + <pre class="code"> +xcb_void_cookie_t xcb_poly_fill_rectangle (xcb_connection_t *c, + xcb_drawable_t drawable, + xcb_gcontext_t gc, + uint32_t rectangles_len, + const xcb_rectangle_t *rectangles); +</pre> + <p> + To fill one or several arcs, we use + </p> + <pre class="code"> +xcb_void_cookie_t xcb_poly_fill_arc (xcb_connection_t *c, + xcb_drawable_t drawable, + xcb_gcontext_t gc, + uint32_t arcs_len, + const xcb_arc_t *arcs); +</pre> + <br> + <a name="points.c"></a> + <p> + To illustrate these functions, here is an example that draws + four points, a polygonal line, two segments, two rectangles + and two arcs. Remark that we use events for the first time, as + an introduction to the next section. + </p> + <p> + <b>TODO:</b> Use screen->root_depth for depth parameter. + </p> + <pre class="code"> +#include <stdlib.h> +#include <stdio.h> + +#include <xcb/xcb.h> + +int +main () +{ + xcb_connection_t *c; + xcb_screen_t *screen; + xcb_drawable_t win; + xcb_gcontext_t foreground; + xcb_generic_event_t *e; + uint32_t mask = 0; + uint32_t values[2]; + + /* geometric objects */ + xcb_point_t points[] = { + {10, 10}, + {10, 20}, + {20, 10}, + {20, 20}}; + + xcb_point_t polyline[] = { + {50, 10}, + { 5, 20}, /* rest of points are relative */ + {25,-20}, + {10, 10}}; + + xcb_segment_t segments[] = { + {100, 10, 140, 30}, + {110, 25, 130, 60}}; + + xcb_rectangle_t rectangles[] = { + { 10, 50, 40, 20}, + { 80, 50, 10, 40}}; + + xcb_arc_t arcs[] = { + {10, 100, 60, 40, 0, 90 << 6}, + {90, 100, 55, 40, 0, 270 << 6}}; + + /* Open the connection to the X server */ + c = xcb_connect (NULL, NULL); + + /* Get the first screen */ + screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data; + + /* Create black (foreground) graphic context */ + win = screen->root; + + foreground = xcb_generate_id (c); + mask = XCB_GC_FOREGROUND | XCB_GC_GRAPHICS_EXPOSURES; + values[0] = screen->black_pixel; + values[1] = 0; + xcb_create_gc (c, foreground, win, mask, values); + + /* Ask for our window's Id */ + win = xcb_generate_id(c); + + /* Create the window */ + mask = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK; + values[0] = screen->white_pixel; + values[1] = XCB_EVENT_MASK_EXPOSURE; + xcb_create_window (c, /* Connection */ + XCB_COPY_FROM_PARENT, /* depth */ + win, /* window Id */ + screen->root, /* parent window */ + 0, 0, /* x, y */ + 150, 150, /* width, height */ + 10, /* border_width */ + XCB_WINDOW_CLASS_INPUT_OUTPUT, /* class */ + screen->root_visual, /* visual */ + mask, values); /* masks */ + + /* Map the window on the screen */ + xcb_map_window (c, win); + + + /* We flush the request */ + xcb_flush (c); + + while ((e = xcb_wait_for_event (c))) { + switch (e->response_type & ~0x80) { + case XCB_EXPOSE: { + /* We draw the points */ + xcb_poly_point (c, XCB_COORD_MODE_ORIGIN, win, foreground, 4, points); + + /* We draw the polygonal line */ + xcb_poly_line (c, XCB_COORD_MODE_PREVIOUS, win, foreground, 4, polyline); + + /* We draw the segements */ + xcb_poly_segment (c, win, foreground, 2, segments); + + /* We draw the rectangles */ + xcb_poly_rectangle (c, win, foreground, 2, rectangles); + + /* We draw the arcs */ + xcb_poly_arc (c, win, foreground, 2, arcs); + + /* We flush the request */ + xcb_flush (c); + + break; + } + default: { + /* Unknown event type, ignore it */ + break; + } + } + /* Free the Generic Event */ + free (e); + } + + return 0; +} +</pre> + </ol> + <li class="title"><a name="xevents">X Events</a> + <p> + In an X program, everything is driven by events. Event painting + on the screen is sometimes done as a response to an event (an + <span class="code">Expose</span> event). If part of a program's + window that was hidden, gets exposed (e.g. the window was raised + above other widows), the X server will send an "expose" event to + let the program know it should repaint that part of the + window. User input (key presses, mouse movement, etc) is also + received as a set of events. + </p> + <ol> + <li class="subtitle"><a name="register">Registering for event types using event masks</a> + <p> + During the creation of a window, you should give it what kind + of events it wishes to receive. Thus, you may register for + various mouse (also called pointer) events, keyboard events, + expose events, and so on. This is done for optimizing the + server-to-client connection (i.e. why send a program (that + might even be running at the other side of the globe) an event + it is not interested in ?) + </p> + <p> + In XCB, you use the "value_mask" and "value_list" data in the + <span class="code">xcb_create_window()</span> function to + register for events. Here is how we register for + <span class="code">Expose</span> event when creating a window: + </p> + <pre class="code"> + mask = XCB_CW_EVENT_MASK; + valwin[0] = XCB_EVENT_MASK_EXPOSURE; + win = xcb_generate_id (c); + xcb_create_window (c, depth, win, root->root, + 0, 0, 150, 150, 10, + XCB_WINDOW_CLASS_INPUT_OUTPUT, root->root_visual, + mask, valwin); +</pre> + <p> + <span class="code">XCB_EVENT_MASK_EXPOSURE</span> is a constant defined + in the xcb_event_mask_t enumeration in the "xproto.h" header file. If we wanted to register for several + event types, we can logically "or" them, as follows: + </p> + <pre class="code"> + mask = XCB_CW_EVENT_MASK; + valwin[0] = XCB_EVENT_MASK_EXPOSURE | XCB_EVENT_MASK_BUTTON_PRESS; + win = xcb_generate_id (c); + xcb_create_window (c, depth, win, root->root, + 0, 0, 150, 150, 10, + XCB_WINDOW_CLASS_INPUT_OUTPUT, root->root_visual, + mask, valwin); +</pre> + <p> + This registers for <span class="code">Expose</span> events as + well as for mouse button presses inside the created + window. You should note that a mask may represent several + event sub-types. + </p> + <p> + The values that a mask could take are given + by the <span class="code">xcb_cw_t</span> enumeration: + </p> + <pre class="code"> +typedef enum { + XCB_CW_BACK_PIXMAP = 1L<<0, + XCB_CW_BACK_PIXEL = 1L<<1, + XCB_CW_BORDER_PIXMAP = 1L<<2, + XCB_CW_BORDER_PIXEL = 1L<<3, + XCB_CW_BIT_GRAVITY = 1L<<4, + XCB_CW_WIN_GRAVITY = 1L<<5, + XCB_CW_BACKING_STORE = 1L<<6, + XCB_CW_BACKING_PLANES = 1L<<7, + XCB_CW_BACKING_PIXEL = 1L<<8, + XCB_CW_OVERRIDE_REDIRECT = 1L<<9, + XCB_CW_SAVE_UNDER = 1L<<10, + XCB_CW_EVENT_MASK = 1L<<11, + XCB_CW_DONT_PROPAGATE = 1L<<12, + XCB_CW_COLORMAP = 1L<<13, + XCB_CW_CURSOR = 1L<<14 +} xcb_cw_t; +</pre> + <div class="emph"> + <p>Note: we must be careful when setting the values of the valwin + parameter, as they have to follow the order the + <span class="code">xcb_cw_t</span> enumeration. Here is an + example: + </p> + </div> + <pre class="code"> + mask = XCB_CW_EVENT_MASK | XCB_CW_BACK_PIXMAP; + valwin[0] = XCB_NONE; /* for XCB_CW_BACK_PIXMAP (whose value is 1) */ + valwin[1] = XCB_EVENT_MASK_EXPOSURE | XCB_EVENT_MASK_BUTTON_PRESS; /* for XCB_CW_EVENT_MASK, whose value (2048) */ + /* is greater than the one of XCB_CW_BACK_PIXMAP */ +</pre> + <p> + If the window has already been created, we can use the + <span class="code">xcb_change_window_attributes()</span> function to set + the events that the window will receive. The subsection + <a href="#winconf">Configuring a window</a> shows its + prototype. As an example, here is a piece of code that + configures the window to receive the + <span class="code">Expose</span> and + <span class="code">ButtonPress</span> events: + </p> + <pre class="code"> +const static uint32_t values[] = { XCB_EVENT_MASK_EXPOSURE | XCB_EVENT_MASK_BUTTON_PRESS }; + +/* The connection c and the window win are supposed to be defined */ + +xcb_change_window_attributes (c, win, XCB_CW_EVENT_MASK, values); +</pre> + <div class="emph"> + <p> + Note: A common bug programmers do is adding code to handle new + event types in their program, while forgetting to add the + masks for these events in the creation of the window. Such a + programmer then should sit down for hours debugging his + program, wondering "Why doesn't my program notice that I + released the button?", only to find that they registered for + button press events but not for button release events. + </p> + </div> + <li class="subtitle"><a name="loop">Receiving events: writing the events loop</a> + <p> + After we have registered for the event types we are interested + in, we need to enter a loop of receiving events and handling + them. There are two ways to receive events: a blocking way and + a non-blocking way: + </p> + <ul> + <li> + <span class="code">xcb_wait_for_event (xcb_connection_t *c)</span> + is the blocking way. It waits (so blocks...) until an event is + queued in the X server. Then it retrieves it into a newly + allocated structure (it dequeues it from the queue) and returns + it. This structure has to be freed. The function returns + <span class="code">NULL</span> if an error occurs. + + <br> + <li> + <span class="code">xcb_poll_for_event (xcb_connection_t *c, int + *error)</span> is the non-blocking way. It looks at the event + queue and returns (and dequeues too) an existing event into + a newly allocated structure. This structure has to be + freed. It returns <span class="code">NULL</span> if there is + no event. If an error occurs, the parameter <span + class="code">error</span> will be filled with the error + status. + </ul> + <p> + There are various ways to write such a loop. We present two + ways to write such a loop, with the two functions above. The + first one uses <span class="code">xcb_wait_for_event_t</span>, which + is similar to an event Xlib loop using only <span + class="code">XNextEvent</span>: + </p> + <pre class="code"> + xcb_generic_event_t *e; + + while ((e = xcb_wait_for_event (c))) { + switch (e->response_type & ~0x80) { + case XCB_EXPOSE: { + /* Handle the Expose event type */ + xcb_expose_event_t *ev = (xcb_expose_event_t *)e; + + /* ... */ + + break; + } + case XCB_BUTTON_PRESS: { + /* Handle the ButtonPress event type */ + xcb_button_press_event_t *ev = (xcb_button_press_event_t *)e; + + /* ... */ + + break; + } + default: { + /* Unknown event type, ignore it */ + break; + } + } + /* Free the Generic Event */ + free (e); + } +</pre> + <p> + You will certainly want to use <span + class="code">xcb_poll_for_event(xcb_connection_t *c, int + *error)</span> if, in Xlib, you use <span + class="code">XPending</span> or + <span class="code">XCheckMaskEvent</span>: + </p> + <pre class="code"> + while (XPending (display)) { + XEvent ev; + + XNextEvent(d, &ev); + + /* Manage your event */ + } +</pre> + <p> + Such a loop in XCB looks like: + </p> + <pre class="code"> + xcb_generic_event_t *ev; + + while ((ev = xcb_poll_for_event (conn, 0))) { + /* Manage your event */ + } +</pre> + <p> + The events are managed in the same way as with <span + class="code">xcb_wait_for_event_t</span>. + Obviously, we will need to give the user some way of + terminating the program. This is usually done by handling a + special "quit" event, as we will soon see. + </p> + <div class="comp"> + <div class="title"> + Comparison Xlib/XCB + </div> + <div class="xlib"> + <ul> + <li>XNextEvent () + </ul> + </div> + <div class="xcb"> + <ul> + <li>xcb_wait_for_event () + </ul> + </div> + <div class="xlib"> + <ul> + <li>XPending () + <li>XCheckMaskEvent () + </ul> + </div> + <div class="xcb"> + <ul> + <li>xcb_poll_for_event () + </ul> + </div> + </div> + <br> + <li class="subtitle"><a name="expose">Expose events</a> + <p> + The <span class="code">Expose</span> event is one of the most + basic (and most used) events an application may receive. It + will be sent to us in one of several cases: + </p> + <ul> + <li>A window that covered part of our window has moved + away, exposing part (or all) of our window. + <li>Our window was raised above other windows. + <li>Our window mapped for the first time. + <li>Our window was de-iconified. + </ul> + <p> + You should note the implicit assumption hidden here: the + contents of our window is lost when it is being obscured + (covered) by either windows. One may wonder why the X server + does not save this contents. The answer is: to save + memory. After all, the number of windows on a display at a + given time may be very large, and storing the contents of all + of them might require a lot of memory. Actually, there is a + way to tell the X server to store the contents of a window in + special cases, as we will see later. + </p> + <p> + When we get an <span class="code">Expose</span> event, we + should take the event's data from the members of the following + structure: + </p> + <pre class="code"> +typedef struct { + uint8_t response_type; /* The type of the event, here it is XCB_EXPOSE */ + uint8_t pad0; + uint16_t sequence; + xcb_window_t window; /* The Id of the window that receives the event (in case */ + /* our application registered for events on several windows */ + uint16_t x; /* The x coordinate of the top-left part of the window that needs to be redrawn */ + uint16_t y; /* The y coordinate of the top-left part of the window that needs to be redrawn */ + uint16_t width; /* The width of the part of the window that needs to be redrawn */ + uint16_t height; /* The height of the part of the window that needs to be redrawn */ + uint16_t count; +} xcb_expose_event_t; +</pre> + <li class="subtitle"><a name="userinput">Getting user input</a> + <p> + User input traditionally comes from two sources: the mouse + and the keyboard. Various event types exist to notify us of + user input (a key being presses on the keyboard, a key being + released on the keyboard, the mouse moving over our window, + the mouse entering (or leaving) our window, and so on. + </p> + <ol> + <li class="subsubtitle"><a name="mousepressrelease">Mouse button press and release events</a> + <p> + The first event type we will deal with is a mouse + button-press (or button-release) event in our window. In + order to register to such an event type, we should add one + (or more) of the following masks when we create our window: + </p> + <ul> + <li><span class="code">XCB_EVENT_MASK_BUTTON_PRESS</span>: notify us + of any button that was pressed in one of our windows. + <li><span class="code">XCB_EVENT_MASK_BUTTON_RELEASE</span>: notify us + of any button that was released in one of our windows. + </ul> + <p> + The structure to be checked for in our events loop is the + same for these two events, and is the following: + </p> + <pre class="code"> +typedef struct { + uint8_t response_type; /* The type of the event, here it is xcb_button_press_event_t or xcb_button_release_event_t */ + xcb_button_t detail; + uint16_t sequence; + xcb_timestamp_t time; /* Time, in milliseconds the event took place in */ + xcb_window_t root; + xcb_window_t event; + xcb_window_t child; + int16_t root_x; + int16_t root_y; + int16_t event_x; /* The x coordinate where the mouse has been pressed in the window */ + int16_t event_y; /* The y coordinate where the mouse has been pressed in the window */ + uint16_t state; /* A mask of the buttons (or keys) during the event */ + uint8_t same_screen; +} xcb_button_press_event_t; + +typedef xcb_button_press_event_t xcb_button_release_event_t; +</pre> + <p> + The <span class="code">time</span> field may be used to calculate "double-click" + situations by an application (e.g. if the mouse button was + clicked two times in a duration shorter than a given amount + of time, assume this was a double click). + </p> + <p> + The <span class="code">state</span> field is a mask of the buttons held down during + the event. It is a bitwise OR of any of the following (from the xcb_button_mask_t and + xcb_mod_mask_t enumerations): + </p> + <ul> + <li><span class="code">XCB_BUTTON_MASK_1</span> + <li><span class="code">XCB_BUTTON_MASK_2</span> + <li><span class="code">XCB_BUTTON_MASK_3</span> + <li><span class="code">XCB_BUTTON_MASK_4</span> + <li><span class="code">XCB_BUTTON_MASK_5</span> + <li><span class="code">XCB_MOD_MASK_SHIFT</span> + <li><span class="code">XCB_MOD_MASK_LOCK</span> + <li><span class="code">XCB_MOD_MASK_CONTROL</span> + <li><span class="code">XCB_MOD_MASK_1</span> + <li><span class="code">XCB_MOD_MASK_2</span> + <li><span class="code">XCB_MOD_MASK_3</span> + <li><span class="code">XCB_MOD_MASK_4</span> + <li><span class="code">XCB_MOD_MASK_5</span> + </ul> + <p> + Their names are self explanatory, where the first 5 refer to + the mouse buttons that are being pressed, while the rest + refer to various "special keys" that are being pressed (Mod1 + is usually the 'Alt' key or the 'Meta' key). + </p> + <p> + <b>TODO:</b> Problem: it seems that the state does not + change when clicking with various buttons. + </p> + <li class="subsubtitle"><a name="mousemvnt">Mouse movement events</a> + <p> + Similar to mouse button press and release events, we also + can be notified of various mouse movement events. These can + be split into two families. One is of mouse pointer + movement while no buttons are pressed, and the second is a + mouse pointer motion while one (or more) of the buttons are + pressed (this is sometimes called "a mouse drag operation", + or just "dragging"). The following event masks may be added + during the creation of our window: + </p> + <ul> + <li><span class="code">XCB_EVENT_MASK_POINTER_MOTION</span>: events of + the pointer moving in one of the windows controlled by our + application, while no mouse button is held pressed. + <li><span class="code">XCB_EVENT_MASK_BUTTON_MOTION</span>: Events of + the pointer moving while one or more of the mouse buttons + is held pressed. + <li><span class="code">XCB_EVENT_MASK_BUTTON_1_MOTION</span>: same as + <span class="code">XCB_EVENT_MASK_BUTTON_MOTION</span>, but only when + the 1st mouse button is held pressed. + <li><span class="code">XCB_EVENT_MASK_BUTTON_2_MOTION</span>, + <span class="code">XCB_EVENT_MASK_BUTTON_3_MOTION</span>, + <span class="code">XCB_EVENT_MASK_BUTTON_4_MOTION</span>, + <span class="code">XCB_EVENT_MASK_BUTTON_5_MOTION</span>: same as + <span class="code">XCB_EVENT_MASK_BUTTON_1_MOTION</span>, but + respectively for 2nd, 3rd, 4th and 5th mouse button. + </ul> + <p> + The structure to be checked for in our events loop is the + same for these events, and is the following: + </p> + <pre class="code"> +typedef struct { + uint8_t response_type; /* The type of the event */ + uint8_t detail; + uint16_t sequence; + xcb_timestamp_t time; /* Time, in milliseconds the event took place in */ + xcb_window_t root; + xcb_window_t event; + xcb_window_t child; + int16_t root_x; + int16_t root_y; + int16_t event_x; /* The x coordinate of the mouse when the event was generated */ + int16_t event_y; /* The y coordinate of the mouse when the event was generated */ + uint16_t state; /* A mask of the buttons (or keys) during the event */ + uint8_t same_screen; +} xcb_motion_notify_event_t; +</pre> + <li class="subsubtitle"><a name="mouseenter">Mouse pointer enter and leave events</a> + <p> + Another type of event that applications might be interested + in, is a mouse pointer entering a window the program + controls, or leaving such a window. Some programs use these + events to show the user that the application is now in + focus. In order to register for such an event type, we + should add one (or more) of the following masks when we + create our window: + </p> + <ul> + <li><span class="code">xcb_event_enter_window_t</span>: notify us + when the mouse pointer enters any of our controlled + windows. + <li><span class="code">xcb_event_leave_window_t</span>: notify us + when the mouse pointer leaves any of our controlled + windows. + </ul> + <p> + The structure to be checked for in our events loop is the + same for these two events, and is the following: + </p> + <pre class="code"> +typedef struct { + uint8_t response_type; /* The type of the event */ + uint8_t detail; + uint16_t sequence; + xcb_timestamp_t time; /* Time, in milliseconds the event took place in */ + xcb_window_t root; + xcb_window_t event; + xcb_window_t child; + int16_t root_x; + int16_t root_y; + int16_t event_x; /* The x coordinate of the mouse when the event was generated */ + int16_t event_y; /* The y coordinate of the mouse when the event was generated */ + uint16_t state; /* A mask of the buttons (or keys) during the event */ + uint8_t mode; /* The number of mouse button that was clicked */ + uint8_t same_screen_focus; +} xcb_enter_notify_event_t; + +typedef xcb_enter_notify_event_t xcb_leave_notify_event_t; +</pre> + <li class="subsubtitle"><a name="focus">The keyboard focus</a> + <p> + There may be many windows on a screen, but only a single + keyboard attached to them. How does the X server then know + which window should be sent a given keyboard input ? This is + done using the keyboard focus. Only a single window on the + screen may have the keyboard focus at a given time. There + is a XCB function that allows a program to set the keyboard + focus to a given window. The user can usually set the + keyboard focus using the window manager (often by clicking + on the title bar of the desired window). Once our window + has the keyboard focus, every key press or key release will + cause an event to be sent to our program (if it regsitered + for these event types...). + </p> + <li class="subsubtitle"><a name="keypress">Keyboard press and release events</a> + <p> + If a window controlled by our program currently holds the + keyboard focus, it can receive key press and key release + events. So, we should add one (or more) of the following + masks when we create our window: + </p> + <ul> + <li><span class="code">XCB_EVENT_MASK_KEY_PRESS</span>: notify us when + a key was pressed while any of our controlled windows had + the keyboard focus. + <li><span class="code">XCB_EVENT_MASK_KEY_RELEASE</span>: notify us + when a key was released while any of our controlled + windows had the keyboard focus. + </ul> + <p> + The structure to be checked for in our events loop is the + same for these two events, and is the following: + </p> + <pre class="code"> +typedef struct { + uint8_t response_type; /* The type of the event */ + xcb_keycode_t detail; + uint16_t sequence; + xcb_timestamp_t time; /* Time, in milliseconds the event took place in */ + xcb_window_t root; + xcb_window_t event; + xcb_window_t child; + int16_t root_x; + int16_t root_y; + int16_t event_x; + int16_t event_y; + uint16_t state; + uint8_t same_screen; +} xcb_key_press_event_t; + +typedef xcb_key_press_event_t xcb_key_release_event_t; +</pre> + <p> + The <span class="code">detail</span> field refers to the + physical key on the keyboard. + </p> + <p> + <b>TODO:</b> Talk about getting the ASCII code from the key code. + </p> + </ol> + <li class="subtitle"><a name="eventex">X events: a complete example</a> + <p> + As an example for handling events, we show a program that + creates a window, enters an events loop and checks for all the + events described above, and writes on the terminal the relevant + characteristics of the event. With this code, it should be + easy to add drawing operations, like those which have been + described above. + </p> + <pre class="code"> +#include <stdlib.h> +#include <stdio.h> + +#include <xcb/xcb.h> + +void +print_modifiers (uint32_t mask) +{ + const char **mod, *mods[] = { + "Shift", "Lock", "Ctrl", "Alt", + "Mod2", "Mod3", "Mod4", "Mod5", + "Button1", "Button2", "Button3", "Button4", "Button5" + }; + printf ("Modifier mask: "); + for (mod = mods ; mask; mask >>= 1, mod++) + if (mask & 1) + printf(*mod); + putchar ('\n'); +} + +int +main () +{ + xcb_connection_t *c; + xcb_screen_t *screen; + xcb_window_t win; + xcb_generic_event_t *e; + uint32_t mask = 0; + uint32_t values[2]; + + /* Open the connection to the X server */ + c = xcb_connect (NULL, NULL); + + /* Get the first screen */ + screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data; + + /* Ask for our window's Id */ + win = xcb_generate_id (c); + + /* Create the window */ + mask = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK; + values[0] = screen->white_pixel; + values[1] = XCB_EVENT_MASK_EXPOSURE | XCB_EVENT_MASK_BUTTON_PRESS | + XCB_EVENT_MASK_BUTTON_RELEASE | XCB_EVENT_MASK_POINTER_MOTION | + XCB_EVENT_MASK_ENTER_WINDOW | XCB_EVENT_MASK_LEAVE_WINDOW | + XCB_EVENT_MASK_KEY_PRESS | XCB_EVENT_MASK_KEY_RELEASE; + xcb_create_window (c, /* Connection */ + 0, /* depth */ + win, /* window Id */ + screen->root, /* parent window */ + 0, 0, /* x, y */ + 150, 150, /* width, height */ + 10, /* border_width */ + XCB_WINDOW_CLASS_INPUT_OUTPUT, /* class */ + screen->root_visual, /* visual */ + mask, values); /* masks */ + + /* Map the window on the screen */ + xcb_map_window (c, win); + + xcb_flush (c); + + while ((e = xcb_wait_for_event (c))) { + switch (e->response_type & ~0x80) { + case XCB_EXPOSE: { + xcb_expose_event_t *ev = (xcb_expose_event_t *)e; + + printf ("Window %ld exposed. Region to be redrawn at location (%d,%d), with dimension (%d,%d)\n", + ev->window, ev->x, ev->y, ev->width, ev->height); + break; + } + case XCB_BUTTON_PRESS: { + xcb_button_press_event_t *ev = (xcb_button_press_event_t *)e; + print_modifiers(ev->state); + + switch (ev->detail) { + case 4: + printf ("Wheel Button up in window %ld, at coordinates (%d,%d)\n", + ev->event, ev->event_x, ev->event_y); + break; + case 5: + printf ("Wheel Button down in window %ld, at coordinates (%d,%d)\n", + ev->event, ev->event_x, ev->event_y); + break; + default: + printf ("Button %d pressed in window %ld, at coordinates (%d,%d)\n", + ev->detail, ev->event, ev->event_x, ev->event_y); + } + break; + } + case XCB_BUTTON_RELEASE: { + xcb_button_release_event_t *ev = (xcb_button_release_event_t *)e; + print_modifiers(ev->state); + + printf ("Button %d released in window %ld, at coordinates (%d,%d)\n", + ev->detail, ev->event, ev->event_x, ev->event_y); + break; + } + case XCB_MOTION_NOTIFY: { + xcb_motion_notify_event_t *ev = (xcb_motion_notify_event_t *)e; + + printf ("Mouse moved in window %ld, at coordinates (%d,%d)\n", + ev->event, ev->event_x, ev->event_y); + break; + } + case XCB_ENTER_NOTIFY: { + xcb_enter_notify_event_t *ev = (xcb_enter_notify_event_t *)e; + + printf ("Mouse entered window %ld, at coordinates (%d,%d)\n", + ev->event, ev->event_x, ev->event_y); + break; + } + case XCB_LEAVE_NOTIFY: { + xcb_leave_notify_event_t *ev = (xcb_leave_notify_event_t *)e; + + printf ("Mouse left window %ld, at coordinates (%d,%d)\n", + ev->event, ev->event_x, ev->event_y); + break; + } + case XCB_KEY_PRESS: { + xcb_key_press_event_t *ev = (xcb_key_press_event_t *)e; + print_modifiers(ev->state); + + printf ("Key pressed in window %ld\n", + ev->event); + break; + } + case XCB_KEY_RELEASE: { + xcb_key_release_event_t *ev = (xcb_key_release_event_t *)e; + print_modifiers(ev->state); + + printf ("Key released in window %ld\n", + ev->event); + break; + } + default: + /* Unknown event type, ignore it */ + printf("Unknown event: %d\n", e->response_type); + break; + } + /* Free the Generic Event */ + free (e); + } + + return 0; +} +</pre> + </ol> + <li class="title"><a name="font">Handling text and fonts</a> + <p> + Besides drawing graphics on a window, we often want to draw + text. Text strings have two major properties: the characters to + be drawn and the font with which they are drawn. In order to + draw text, we need to first request the X server to load a + font. We then assign a font to a Graphic Context, and finally, we + draw the text in a window, using the Graphic Context. + </p> + <ol> + <li class="subtitle"><a name="fontstruct">The Font structure</a> + <p> + In order to support flexible fonts, a font type is + defined. You know what ? It's an Id: + </p> + <pre class="code"> +typedef uint32_t xcb_font_t; +</pre> + <p> + It is used to contain information about a font, and is passed + to several functions that handle fonts selection and text drawing. + We ask the X server to attribute an Id to our font with the + function: + </p> + <pre class="code"> +xcb_font_t xcb_generate_id (xcb_connection_t *c); +</pre> + <br> + <li class="subtitle"><a name="openingfont">Opening a Font</a> + <p> + To open a font, we use the following function: + </p> + <pre class="code"> +xcb_void_cookie_t xcb_open_font (xcb_connection_t *c, + xcb_font_t fid, + uint16_t name_len, + const char *name); +</pre> + <p> + The <span class="code">fid</span> parameter is the font Id + defined by <span class="code">xcb_generate_id()</span> (see + above). The <span class="code">name</span> parameter is the + name of the font you want to open. Use the command + <span class="code">xlsfonts</span> in a terminal to know which + are the fonts available on your computer. The parameter + <span class="code">name_len</span> is the length of the name + of the font (given by <span class="code">strlen()</span>). + </p> + <li class="subtitle"><a name="assigningfont">Assigning a Font to a Graphic Context</a> + <p> + Once a font is opened, you have to create a Graphic Context + that will contain the informations about the color of the + foreground and the background used when you draw a text in a + Drawable. Here is an exemple of a Graphic Context that will + allow us to draw an opened font with a black foreground and a + white background: + </p> + <pre class="code"> + /* + * c is the connection + * screen is the screen where the window is displayed + * window is the window in which we will draw the text + * font is the opened font + */ + + uint32_t value_list[3]; + xcb_gcontext_t gc; + uint32_t mask; + + gc = xcb_generate_id (c); + mask = XCB_GC_FOREGROUND | XCB_GC_BACKGROUND | XCB_GC_FONT; + value_list[0] = screen->black_pixel; + value_list[1] = screen->white_pixel; + value_list[2] = font; + xcb_create_gc (c, gc, window, mask, value_list); + + /* The font is not needed anymore, so we close it */ + xcb_close_font (c, font); +</pre> + <li class="subtitle"><a name="drawingtext">Drawing text in a drawable</a> + <p> + To draw a text in a drawable, we use the following function: + </p> + <pre class="code"> +xcb_void_cookie_t xcb_image_text_8 (xcb_connection_t *c, + uint8_t string_len, + xcb_drawable_t drawable, + xcb_gcontext_t gc, + int16_t x, + int16_t y, + const char *string); +</pre> + <p> + The <span class="code">string</span> parameter is the text to + draw. The location of the drawing is given by the parameters + <span class="code">x</span> and <span class="code">y</span>. + The base line of the text is exactly the parameter + <span class="code">y</span>. + </p> + <li class="subtitle"><a name="fontcompleteexample">Complete example</a> + <p> + This example draw a text at 10 pixels (for the base line) of + the bottom of a window. Pressing the Esc key exits the program. + </p> + <pre class="code"> +#include <stdlib.h> +#include <stdio.h> +#include <string.h> + +#include <xcb/xcb.h> + +#define WIDTH 300 +#define HEIGHT 100 + + + +static xcb_gc_t gc_font_get (xcb_connection_t *c, + xcb_screen_t *screen, + xcb_window_t window, + const char *font_name); + +static void text_draw (xcb_connection_t *c, + xcb_screen_t *screen, + xcb_window_t window, + int16_t x1, + int16_t y1, + const char *label); + +static void +text_draw (xcb_connection_t *c, + xcb_screen_t *screen, + xcb_window_t window, + int16_t x1, + int16_t y1, + const char *label) +{ + xcb_void_cookie_t cookie_gc; + xcb_void_cookie_t cookie_text; + xcb_generic_error_t *error; + xcb_gcontext_t gc; + uint8_t length; + + length = strlen (label); + + gc = gc_font_get(c, screen, window, "7x13"); + + cookie_text = xcb_image_text_8_checked (c, length, window, gc, + x1, + y1, label); + error = xcb_request_check (c, cookie_text); + if (error) { + fprintf (stderr, "ERROR: can't paste text : %d\n", error->error_code); + xcb_disconnect (c); + exit (-1); + } + + cookie_gc = xcb_free_gc (c, gc); + error = xcb_request_check (c, cookie_gc); + if (error) { + fprintf (stderr, "ERROR: can't free gc : %d\n", error->error_code); + xcb_disconnect (c); + exit (-1); + } +} + +static xcb_gc_t +gc_font_get (xcb_connection_t *c, + xcb_screen_t *screen, + xcb_window_t window, + const char *font_name) +{ + uint32_t value_list[3]; + xcb_void_cookie_t cookie_font; + xcb_void_cookie_t cookie_gc; + xcb_generic_error_t *error; + xcb_font_t font; + xcb_gcontext_t gc; + uint32_t mask; + + font = xcb_generate_id (c); + cookie_font = xcb_open_font_checked (c, font, + strlen (font_name), + font_name); + + error = xcb_request_check (c, cookie_font); + if (error) { + fprintf (stderr, "ERROR: can't open font : %d\n", error->error_code); + xcb_disconnect (c); + return -1; + } + + gc = xcb_generate_id (c); + mask = XCB_GC_FOREGROUND | XCB_GC_BACKGROUND | XCB_GC_FONT; + value_list[0] = screen->black_pixel; + value_list[1] = screen->white_pixel; + value_list[2] = font; + cookie_gc = xcb_create_gc_checked (c, gc, window, mask, value_list); + error = xcb_request_check (c, cookie_gc); + if (error) { + fprintf (stderr, "ERROR: can't create gc : %d\n", error->error_code); + xcb_disconnect (c); + exit (-1); + } + + cookie_font = xcb_close_font_checked (c, font); + error = xcb_request_check (c, cookie_font); + if (error) { + fprintf (stderr, "ERROR: can't close font : %d\n", error->error_code); + xcb_disconnect (c); + exit (-1); + } + + return gc; +} + +int main () +{ + xcb_screen_iterator_t screen_iter; + xcb_connection_t *c; + const xcb_setup_t *setup; + xcb_screen_t *screen; + xcb_generic_event_t *e; + xcb_generic_error_t *error; + xcb_void_cookie_t cookie_window; + xcb_void_cookie_t cookie_map; + xcb_window_t window; + uint32_t mask; + uint32_t values[2]; + int screen_number; + + /* getting the connection */ + c = xcb_connect (NULL, &screen_number); + if (!c) { + fprintf (stderr, "ERROR: can't connect to an X server\n"); + return -1; + } + + /* getting the current screen */ + setup = xcb_get_setup (c); + + screen = NULL; + screen_iter = xcb_setup_roots_iterator (setup); + for (; screen_iter.rem != 0; --screen_number, xcb_screen_next (&screen_iter)) + if (screen_number == 0) + { + screen = screen_iter.data; + break; + } + if (!screen) { + fprintf (stderr, "ERROR: can't get the current screen\n"); + xcb_disconnect (c); + return -1; + } + + /* creating the window */ + window = xcb_generate_id (c); + mask = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK; + values[0] = screen->white_pixel; + values[1] = + XCB_EVENT_MASK_KEY_RELEASE | + XCB_EVENT_MASK_BUTTON_PRESS | + XCB_EVENT_MASK_EXPOSURE | + XCB_EVENT_MASK_POINTER_MOTION; + cookie_window = xcb_create_window_checked (c, + screen->root_depth, + window, screen->root, + 20, 200, WIDTH, HEIGHT, + 0, XCB_WINDOW_CLASS_INPUT_OUTPUT, + screen->root_visual, + mask, values); + cookie_map = xcb_map_window_checked (c, window); + + /* error managing */ + error = xcb_request_check (c, cookie_window); + if (error) { + fprintf (stderr, "ERROR: can't create window : %d\n", error->error_code); + xcb_disconnect (c); + return -1; + } + error = xcb_request_check (c, cookie_map); + if (error) { + fprintf (stderr, "ERROR: can't map window : %d\n", error->error_code); + xcb_disconnect (c); + return -1; + } + + xcb_flush(c); + + while (1) { + e = xcb_poll_for_event(c); + if (e) { + switch (e->response_type & ~0x80) { + case XCB_EXPOSE: { + char *text; + + text = "Press ESC key to exit..."; + text_draw (c, screen, window, 10, HEIGHT - 10, text); + break; + } + case XCB_KEY_RELEASE: { + xcb_key_release_event_t *ev; + + ev = (xcb_key_release_event_t *)e; + + switch (ev->detail) { + /* ESC */ + case 9: + free (e); + xcb_disconnect (c); + return 0; + } + } + } + free (e); + } + } + + return 0; +} +</pre> + </ol> + <li class="title"><a name="wm">Interacting with the window manager</a> + <p> + After we have seen how to create windows and draw on them, we + take one step back, and look at how our windows are interacting + with their environment (the full screen and the other + windows). First of all, our application needs to interact with + the window manager. The window manager is responsible to + decorating drawn windows (i.e. adding a frame, an iconify + button, a system menu, a title bar, etc), as well as handling + icons shown when windows are being iconified. It also handles + ordering of windows on the screen, and other administrative + tasks. We need to give it various hints as to how we want it to + treat our application's windows. + </p> + <ol> + <li class="subtitle"><a name="wmprop">Window properties</a> + <p> + Many of the parameters communicated to the window manager are + passed using data called "properties". These properties are + attached by the X server to different windows, and are stored + in a format that makes it possible to read them from different + machines that may use different architectures (remember that + an X client program may run on a remote machine). + </p> + <p> + The property and its type (a string, an integer, etc) are + Id. Their type are <span class="code">xcb_atom_t</span>: + </p> + <pre class="code"> +typedef uint32_t xcb_atom_t; +</pre> + <p> + To change the property of a window, we use the following + function: + </p> + <pre class="code"> +xcb_void_cookie_t xcb_change_property (xcb_connection_t *c, /* Connection to the X server */ + uint8_t mode, /* Property mode */ + xcb_window_t window, /* Window */ + xcb_atom_t property, /* Property to change */ + xcb_atom_t type, /* Type of the property */ + uint8_t format, /* Format of the property (8, 16, 32) */ + uint32_t data_len, /* Length of the data parameter */ + const void *data); /* Data */ +</pre> + <p> + The <span class="code">mode</span> parameter coud be one of + the following values (defined in enumeration xcb_prop_mode_t in + the xproto.h header file): + </p> + <ul> + <li>XCB_PROP_MODE_REPLACE + <li>XCB_PROP_MODE_PREPEND + <li>XCB_PROP_MODE_APPEND + </ul> + <br> + <li class="subtitle"><a name="wmname">Setting the window name and icon name</a> + <p> + The first thing we want to do would be to set the name for our + window. This is done using the + <span class="code">xcb_change_property()</span> function. This + name may be used by the window manager as the title of the + window (in the title bar), in a task list, etc. The property + atom to use to set the name of a window is + <span class="code">WM_NAME</span> (and + <span class="code">WM_ICON_NAME</span> for the iconified + window) and its type is <span class="code">STRING</span>. Here + is an example of utilization: + </p> + <pre class="code"> +#include <string.h> + +#include <xcb/xcb.h> +#include <xcb/xcb_atom.h> + +int +main () +{ + xcb_connection_t *c; + xcb_screen_t *screen; + xcb_window_t win; + char *title = "Hello World !"; + char *title_icon = "Hello World ! (iconified)"; + + + + /* Open the connection to the X server */ + c = xcb_connect (NULL, NULL); + + /* Get the first screen */ + screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data; + + /* Ask for our window's Id */ + win = xcb_generate_id (c); + + /* Create the window */ + xcb_create_window (c, /* Connection */ + 0, /* depth */ + win, /* window Id */ + screen->root, /* parent window */ + 0, 0, /* x, y */ + 250, 150, /* width, height */ + 10, /* border_width */ + XCB_WINDOW_CLASS_INPUT_OUTPUT, /* class */ + screen->root_visual, /* visual */ + 0, NULL); /* masks, not used */ + + /* Set the title of the window */ + xcb_change_property (c, XCB_PROP_MODE_REPLACE, win, + WM_NAME, STRING, 8, + strlen (title), title); + + /* Set the title of the window icon */ + xcb_change_property (c, XCB_PROP_MODE_REPLACE, win, + WM_ICON_NAME, STRING, 8, + strlen(title_icon), title_icon); + + /* Map the window on the screen */ + xcb_map_window (c, win); + + xcb_flush (c); + + while (1) {} + + return 0; +} +</pre> + <div class="emph"> + <p>Note: the use of the atoms needs our program to be compiled + and linked against xcb_atom, so that we have to use + </p> + </div> + <pre class="text"> +gcc prog.c -o prog `pkg-config --cflags --libs xcb_atom` +</pre> + <div class="emph"> + <p> + for the program to compile fine. + </p> + </div> + </ol> + <li class="title"><a name="winop">Simple window operations</a> + <p> + One more thing we can do to our window is manipulate them on the + screen (resize them, move them, raise or lower them, iconify + them, and so on). Some window operations functions are supplied + by XCB for this purpose. + </p> + <ol> + <li class="subtitle"><a name="winmap">Mapping and un-mapping a window</a> + <p> + The first pair of operations we can apply on a window is + mapping it, or un-mapping it. Mapping a window causes the + window to appear on the screen, as we have seen in our simple + window program example. Un-mapping it causes it to be removed + from the screen (although the window as a logical entity still + exists). This gives the effect of making a window hidden + (unmapped) and shown again (mapped). For example, if we have a + dialog box window in our program, instead of creating it every + time the user asks to open it, we can create the window once, + in an un-mapped mode, and when the user asks to open it, we + simply map the window on the screen. When the user clicked the + 'OK' or 'Cancel' button, we simply un-map the window. This is + much faster than creating and destroying the window, however, + the cost is wasted resources, both on the client side, and on + the X server side. + </p> + <p> + To map a window, you use the following function: + </p> + <pre class="code"> +xcb_void_cookie_t xcb_map_window (xcb_connection_t *c, + xcb_window_t window); +</pre> + <p> + To have a simple example, see the <a href="#helloworld">example</a> + above. The mapping operation will cause an + <span class="code">Expose</span> event to be sent to our + application, unless the window is completely covered by other + windows. + </p> + <p> + Un-mapping a window is also simple. You use the function + </p> + <pre class="code"> +xcb_void_cookie_t xcb_unmap_window (xcb_connection_t *c, + xcb_window_t window); +</pre> + <p> + The utilization of this function is the same as + <span class="code">xcb_map_window()</span>. + </p> + <li class="subtitle"><a name="winconf">Configuring a window</a> + <p> + As we have seen when we have created our first window, in the + X Events subsection, we can set some attributes for the window + (that is, the position, the size, the events the window will + receive, etc). If we want to modify them, but the window is + already created, we can change them by using the following + function: + </p> + <pre class="code"> +xcb_void_cookie_t xcb_configure_window (xcb_connection_t *c, /* The connection to the X server*/ + xcb_window_t window, /* The window to configure */ + uint16_t value_mask, /* The mask */ + const uint32_t *value_list); /* The values to set */ +</pre> + <p> + We set the <span class="code">value_mask</span> to one or + several mask values that are in the xcb_config_window_t enumeration in the xproto.h header: + </p> + <ul> + <li><span class="code">XCB_CONFIG_WINDOW_X</span>: new x coordinate of the window's top left corner + <li><span class="code">XCB_CONFIG_WINDOW_Y</span>: new y coordinate of the window's top left corner + <li><span class="code">XCB_CONFIG_WINDOW_WIDTH</span>: new width of the window + <li><span class="code">XCB_CONFIG_WINDOW_HEIGHT</span>: new height of the window + <li><span class="code">XCB_CONFIG_WINDOW_BORDER_WIDTH</span>: new width of the border of the window + <li><span class="code">XCB_CONFIG_WINDOW_SIBLING</span> + <li><span class="code">XCB_CONFIG_WINDOW_STACK_MODE</span>: the new stacking order + </ul> + <p> + We then give to <span class="code">value_mask</span> the new + value. We now describe how to use + <span class="code">xcb_configure_window_t</span> in some useful + situations. + </p> + <li class="subtitle"><a name="winmove">Moving a window around the screen</a> + <p> + An operation we might want to do with windows is to move them + to a different location. This can be done like this: + </p> + <pre class="code"> +const static uint32_t values[] = { 10, 20 }; + +/* The connection c and the window win are supposed to be defined */ + +/* Move the window to coordinates x = 10 and y = 20 */ +xcb_configure_window (c, win, XCB_CONFIG_WINDOW_X | XCB_CONFIG_WINDOW_Y, values); +</pre> + <p> + Note that when the window is moved, it might get partially + exposed or partially hidden by other windows, and thus we + might get <span class="code">Expose</span> events due to this + operation. + </p> + <li class="subtitle"><a name="winsize">Resizing a window</a> + <p> + Yet another operation we can do is to change the size of a + window. This is done using the following code: + </p> + <pre class="code"> +const static uint32_t values[] = { 200, 300 }; + +/* The connection c and the window win are supposed to be defined */ + +/* Resize the window to width = 10 and height = 20 */ +xcb_configure_window (c, win, XCB_CONFIG_WINDOW_WIDTH | XCB_CONFIG_WINDOW_HEIGHT, values); +</pre> + <p> + We can also combine the move and resize operations using one + single call to <span class="code">xcb_configure_window_t</span>: + </p> + <pre class="code"> +const static uint32_t values[] = { 10, 20, 200, 300 }; + +/* The connection c and the window win are supposed to be defined */ + +/* Move the window to coordinates x = 10 and y = 20 */ +/* and resize the window to width = 10 and height = 20 */ +xcb_configure_window (c, win, XCB_CONFIG_WINDOW_X | XCB_CONFIG_WINDOW_Y | XCB_CONFIG_WINDOW_WIDTH | XCB_CONFIG_WINDOW_HEIGHT, values); +</pre> + <li class="subtitle"><a name="winstack">Changing windows stacking order: raise and lower</a> + <p> + Until now, we changed properties of a single window. We'll see + that there are properties that relate to the window and other + windows. One of them is the stacking order. That is, the order + in which the windows are layered on top of each other. The + front-most window is said to be on the top of the stack, while + the back-most window is at the bottom of the stack. Here is + how to manipulate our windows stack order: + </p> + <pre class="code"> +const static uint32_t values[] = { XCB_STACK_MODE_ABOVE }; + +/* The connection c and the window win are supposed to be defined */ + +/* Move the window on the top of the stack */ +xcb_configure_window (c, win, XCB_CONFIG_WINDOW_STACK_MODE, values); +</pre> + <pre class="code"> +const static uint32_t values[] = { XCB_STACK_MODE_BELOW }; + +/* The connection c and the window win are supposed to be defined */ + +/* Move the window on the bottom of the stack */ +xcb_configure_window (c, win, XCB_CONFIG_WINDOW_STACK_MODE, values); +</pre> + <li class="subtitle"><a name="wingetinfo">Getting information about a window</a> + <p> + Just like we can set various attributes of our windows, we can + also ask the X server supply the current values of these + attributes. For example, we can check where a window is + located on the screen, what is its current size, whether it is + mapped or not, etc. The structure that contains some of this + information is + </p> + <pre class="code"> +typedef struct { + uint8_t response_type; + uint8_t depth; /* depth of the window */ + uint16_t sequence; + uint32_t length; + xcb_window_t root; /* Id of the root window *> + int16_t x; /* X coordinate of the window's location */ + int16_t y; /* Y coordinate of the window's location */ + uint16_t width; /* Width of the window */ + uint16_t height; /* Height of the window */ + uint16_t border_width; /* Width of the window's border */ +} xcb_get_geometry_reply_t; +</pre> + <p> + XCB fill this structure with two functions: + </p> + <pre class="code"> +xcb_get_geometry_cookie_t xcb_get_geometry (xcb_connection_t *c, + xcb_drawable_t drawable); +xcb_get_geometry_reply_t *xcb_get_geometry_reply (xcb_connection_t *c, + xcb_get_geometry_cookie_t cookie, + xcb_generic_error_t **e); +</pre> + <p> + You use them as follows: + </p> + <pre class="code"> + xcb_connection_t *c; + xcb_drawable_t win; + xcb_get_geometry_reply_t *geom; + + /* You initialize c and win */ + + geom = xcb_get_geometry_reply (c, xcb_get_geometry (c, win), NULL); + + /* Do something with the fields of geom */ + + free (geom); +</pre> + <p> + Remark that you have to free the structure, as + <span class="code">xcb_get_geometry_reply_t</span> allocates a + newly one. + </p> + <p> + One problem is that the returned location of the window is + relative to its parent window. This makes these coordinates + rather useless for any window manipulation functions, like + moving it on the screen. In order to overcome this problem, we + need to take a two-step operation. First, we find out the Id + of the parent window of our window. We then translate the + above relative coordinates to the screen coordinates. + </p> + <p> + To get the Id of the parent window, we need this structure: + </p> + <pre class="code"> +typedef struct { + uint8_t response_type; + uint8_t pad0; + uint16_t sequence; + uint32_t length; + xcb_window_t root; + xcb_window_t parent; /* Id of the parent window */ + uint16_t children_len; + uint8_t pad1[14]; +} xcb_query_tree_reply_t; +</pre> + <p> + To fill this structure, we use these two functions: + </p> + <pre class="code"> +xcb_query_tree_cookie_t xcb_query_tree (xcb_connection_t *c, + xcb_window_t window); +xcb_query_tree_reply_t *xcb_query_tree_reply (xcb_connection_t *c, + xcb_query_tree_cookie_t cookie, + xcb_generic_error_t **e); +</pre> + <p> + The translated coordinates will be found in this structure: + </p> + <pre class="code"> +typedef struct { + uint8_t response_type; + uint8_t same_screen; + uint16_t sequence; + uint32_t length; + xcb_window_t child; + uint16_t dst_x; /* Translated x coordinate */ + uint16_t dst_y; /* Translated y coordinate */ +} xcb_translate_coordinates_reply_t; +</pre> + <p> + As usual, we need two functions to fill this structure: + </p> + <pre class="code"> +xcb_translate_coordinates_cookie_t xcb_translate_coordinates (xcb_connection_t *c, + xcb_window_t src_window, + xcb_window_t dst_window, + int16_t src_x, + int16_t src_y); +xcb_translate_coordinates_reply_t *xcb_translate_coordinates_reply (xcb_connection_t *c, + xcb_translate_coordinates_cookie_t cookie, + xcb_generic_error_t **e); +</pre> + <p> + We use them as follows: + </p> + <pre class="code"> + xcb_connection_t *c; + xcb_drawable_t win; + xcb_get_geometry_reply_t *geom; + xcb_query_tree_reply_t *tree; + xcb_translate_coordinates_reply_t *trans; + + /* You initialize c and win */ + + geom = xcb_get_geometry_reply (c, xcb_get_geometry (c, win), NULL); + if (!geom) + return 0; + + tree = xcb_query_tree_reply (c, xcb_query_tree (c, win), NULL); + if (!tree) + return 0; + + trans = xcb_translate_coordinates_reply (c, + xcb_translate_coordinates (c, + win, + tree->parent, + geom->x, geom->y), + NULL); + if (!trans) + return 0; + + /* the translated coordinates are in trans->dst_x and trans->dst_y */ + + free (trans); + free (tree); + free (geom); +</pre> + <p> + Of course, as for <span class="code">geom</span>, + <span class="code">tree</span> and + <span class="code">trans</span> have to be freed. + </p> + <p> + The work is a bit hard, but XCB is a very low-level library. + </p> + <p> + <b>TODO:</b> the utilization of these functions should be a + prog, which displays the coordinates of the window. + </p> + <p> + There is another structure that gives informations about our window: + </p> + <pre class="code"> +typedef struct { + uint8_t response_type; + uint8_t backing_store; + uint16_t sequence; + uint32_t length; + xcb_visualid_t visual; /* Visual of the window */ + uint16_t _class; + uint8_t bit_gravity; + uint8_t win_gravity; + uint32_t backing_planes; + uint32_t backing_pixel; + uint8_t save_under; + uint8_t map_is_installed; + uint8_t map_state; /* Map state of the window */ + uint8_t override_redirect; + xcb_colormap_t colormap; /* Colormap of the window */ + uint32_t all_event_masks; + uint32_t your_event_mask; + uint16_t do_not_propagate_mask; +} xcb_get_window_attributes_reply_t; +</pre> + <p> + XCB supplies these two functions to fill it: + </p> + <pre class="code"> +xcb_get_window_attributes_cookie_t xcb_get_window_attributes (xcb_connection_t *c, + xcb_window_t window); +xcb_get_window_attributes_reply_t *xcb_get_window_attributes_reply (xcb_connection_t *c, + xcb_get_window_attributes_cookie_t cookie, + xcb_generic_error_t **e); +</pre> + <p> + You use them as follows: + </p> + <pre class="code"> + xcb_connection_t *c; + xcb_drawable_t win; + xcb_get_window_attributes_reply_t *attr; + + /* You initialize c and win */ + + attr = xcb_get_window_attributes_reply (c, xcb_get_window_attributes (c, win), NULL); + + if (!attr) + return 0; + + /* Do something with the fields of attr */ + + free (attr); +</pre> + <p> + As for <span class="code">geom</span>, + <span class="code">attr</span> has to be freed. + </p> + </ol> + <li class="title"><a name="usecolor">Using colors to paint the rainbow</a> + <p> + Up until now, all our painting operation were done using black + and white. We will (finally) see now how to draw using colors. + </p> + <ol> + <li class="subtitle"><a name="colormap">Color maps</a> + <p> + In the beginning, there were not enough colors. Screen + controllers could only support a limited number of colors + simultaneously (initially 2, then 4, 16 and 256). Because of + this, an application could not just ask to draw in a "light + purple-red" color, and expect that color to be available. Each + application allocated the colors it needed, and when all the + color entries (4, 16, 256 colors) were in use, the next color + allocation would fail. + </p> + <p> + Thus, the notion of "a color map" was introduced. A color map + is a table whose size is the same as the number of + simultaneous colors a given screen controller. Each entry + contained the RGB (Red, Green and Blue) values of a different + color (all colors can be drawn using some combination of red, + green and blue). When an application wants to draw on the + screen, it does not specify which color to use. Rather, it + specifies which color entry of some color map to be used + during this drawing. Change the value in this color map entry + and the drawing will use a different color. + </p> + <p> + In order to be able to draw using colors that got something to + do with what the programmer intended, color map allocation + functions are supplied. You could ask to allocate entry for a + color with a set of RGB values. If one already existed, you + would get its index in the table. If none existed, and the + table was not full, a new cell would be allocated to contain + the given RGB values, and its index returned. If the table was + full, the procedure would fail. You could then ask to get a + color map entry with a color that is closest to the one you + were asking for. This would mean that the actual drawing on + the screen would be done using colors similar to what you + wanted, but not the same. + </p> + <p> + On today's more modern screens where one runs an X server with + support for 16 million colors, this limitation looks a little + silly, but remember that there are still older computers with + older graphics cards out there. Using color map, support for + these screen becomes transparent to you. On a display + supporting 16 million colors, any color entry allocation + request would succeed. On a display supporting a limited + number of colors, some color allocation requests would return + similar colors. It won't look as good, but your application + would still work. + </p> + <li class="subtitle"><a name="colormapalloc">Allocating and freeing Color Maps</a> + <p> + When you draw using XCB, you can choose to use the standard + color map of the screen your window is displayed on, or you + can allocate a new color map and apply it to a window. In the + latter case, each time the mouse moves onto your window, the + screen color map will be replaced by your window's color map, + and you'll see all the other windows on screen change their + colors into something quite bizzare. In fact, this is the + effect you get with X applications that use the "-install" + command line option. + </p> + <p> + In XCB, a color map is (as often in X) an Id: + </p> + <pre class="code"> +typedef uint32_t xcb_colormap_t; +</pre> + <p> + In order to access the screen's default color map, you just + have to retrieve the <span class="code">default_colormap</span> + field of the <span class="code">xcb_screen_t</span> structure + (see Section + <a href="#screen">Checking basic information about a connection</a>): + </p> + <pre class="code"> +#include <stdio.h> + +#include <xcb/xcb.h> + +int +main () +{ + xcb_connection_t *c; + xcb_screen_t *screen; + xcb_colormap_t colormap; + + /* Open the connection to the X server and get the first screen */ + c = xcb_connect (NULL, NULL); + screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data; + + colormap = screen->default_colormap; + + return 0; +} +</pre> + <p> + This will return the color map used by default on the first + screen (again, remember that an X server may support several + different screens, each of which might have its own resources). + </p> + <p> + The other option, that of allocating a new colormap, works as + follows. We first ask the X server to give an Id to our color + map, with this function: + </p> + <pre class="code"> +xcb_colormap_t xcb_generate_id (xcb_connection_t *c); +</pre> + <p> + Then, we create the color map with + </p> + <pre class="code"> +xcb_void_cookie_t xcb_create_colormap (xcb_connection_t *c, /* Pointer to the xcb_connection_t structure */ + uint8_t alloc, /* Colormap entries to be allocated (AllocNone or AllocAll) */ + xcb_colormap_t mid, /* Id of the color map */ + xcb_window_t window, /* Window on whose screen the colormap will be created */ + xcb_visualid_t visual); /* Id of the visual supported by the screen */ +</pre> + <p> + Here is an example of creation of a new color map: + </p> + <pre class="code"> +#include <xcb/xcb.h> + +int +main () +{ + xcb_connection_t *c; + xcb_screen_t *screen; + xcb_window_t win; + xcb_colormap_t cmap + + /* Open the connection to the X server and get the first screen */ + c = xcb_connect (NULL, NULL); + screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data; + + /* We create the window win here*/ + + cmap = xcb_generate_id (c); + xcb_create_colormap (c, XCB_COLORMAP_ALLOC_NONE, cmap, win, screen->root_visual); + + return 0; +} +</pre> + <p> + Note that the window parameter is only used to allow the X + server to create the color map for the given screen. We can + then use this color map for any window drawn on the same screen. + </p> + <p> + To free a color map, it suffices to use this function: + </p> + <pre class="code"> +xcb_void_cookie_t xcb_free_colormap (xcb_connection_t *c, /* The connection */ + xcb_colormap_t cmap); /* The color map */ +</pre> + <div class="comp"> + <div class="title"> + Comparison Xlib/XCB + </div> + <div class="xlib"> + <ul> + <li>XCreateColormap () + </ul> + </div> + <div class="xcb"> + <ul> + <li>xcb_generate_id () + <li>xcb_create_colormap () + </ul> + </div> + <div class="xlib"> + <ul> + <li>XFreeColormap () + </ul> + </div> + <div class="xcb"> + <ul> + <li>xcb_free_colormap () + </ul> + </div> + </div> + <br> + <li class="subtitle"><a name="alloccolor">Allocating and freeing a color entry</a> + <p> + Once we got access to some color map, we can start allocating + colors. The informations related to a color are stored in the + following structure: + </p> + <pre class="code"> +typedef struct { + uint8_t response_type; + uint8_t pad0; + uint16_t sequence; + uint32_t length; + uint16_t red; /* The red component */ + uint16_t green; /* The green component */ + uint16_t blue; /* The blue component */ + uint8_t pad1[2]; + uint32_t pixel; /* The entry in the color map, supplied by the X server */ +} xcb_alloc_color_reply_t; +</pre> + <p> + XCB supplies these two functions to fill it: + </p> + <pre class="code"> +xcb_alloc_color_cookie_t xcb_alloc_color (xcb_connection_t *c, + xcb_colormap_t cmap, + uint16_t red, + uint16_t green, + uint16_t blue); +xcb_alloc_color_reply_t *xcb_alloc_color_reply (xcb_connection_t *c, + xcb_alloc_color_cookie_t cookie, + xcb_generic_error_t **e); +</pre> + <p> + The fuction <span class="code">xcb_alloc_color()</span> takes the + 3 RGB components as parameters (red, green and blue). Here is an + example of using these functions: + </p> + <pre class="code"> +#include <malloc.h> + +#include <xcb/xcb.h> + +int +main () +{ + xcb_connection_t *c; + xcb_screen_t *screen; + xcb_window_t win; + xcb_colormap_t cmap; + xcb_alloc_color_reply_t *rep; + + /* Open the connection to the X server and get the first screen */ + c = xcb_connect (NULL, NULL); + screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data; + + /* We create the window win here*/ + + cmap = xcb_generate_id (c); + xcb_create_colormap (c, XCB_COLORMAP_ALLOC_NONE, cmap, win, screen->root_visual); + + rep = xcb_alloc_color_reply (c, xcb_alloc_color (c, cmap, 65535, 0, 0), NULL); + + if (!rep) + return 0; + + /* Do something with r->pixel or the components */ + + free (rep); + + return 0; +} +</pre> + <p> + As <span class="code">xcb_alloc_color_reply()</span> allocates + memory, you have to free <span class="code">rep</span>. + </p> + <p> + <b>TODO</b>: Talk about freeing colors. + </p> + </ol> + <li class="title"><a name="pixmaps">X Bitmaps and Pixmaps</a> + <p> + One thing many so-called "Multi-Media" applications need to do, + is display images. In the X world, this is done using bitmaps + and pixmaps. We have already seen some usage of them when + setting an icon for our application. Lets study them further, + and see how to draw these images inside a window, along side the + simple graphics and text we have seen so far. + </p> + <p> + One thing to note before delving further, is that XCB (nor Xlib) + supplies no means of manipulating popular image formats, such as + gif, png, jpeg or tiff. It is up to the programmer (or to higher + level graphics libraries) to translate these image formats into + formats that the X server is familiar with (x bitmaps and x + pixmaps). + </p> + <ol> + <li class="subtitle"><a name="pixmapswhat">What is a X Bitmap? An X Pixmap?</a> + <p> + An X bitmap is a two-color image stored in a format specific + to the X window system. When stored in a file, the bitmap data + looks like a C source file. It contains variables defining the + width and the height of the bitmap, an array containing the + bit values of the bitmap (the size of the array is + (width+7)/8*height and the bit and byte order are LSB), and + an optional hot-spot location (that will + be explained later, when discussing mouse cursors). + </p> + <p> + An X pixmap is a format used to stored images in the memory of + an X server. This format can store both black and white images + (such as x bitmaps) as well as color images. It is the only + image format supported by the X protocol, and any image to be + drawn on screen, should be first translated into this format. + </p> + <p> + In actuality, an X pixmap can be thought of as a window that + does not appear on the screen. Many graphics operations that + work on windows, will also work on pixmaps. Indeed, the type + of X pixmap in XCB is an Id like a window: + </p> + <pre class="code"> +typedef uint32_t xcb_pixmap_t; +</pre> + <p> + Like Xlib, there is no difference between a Drawable, a Window + or a Pixmap: + </p> + <pre class="code"> +typedef uint32_t xcb_drawable_t; +</pre> + <p> + in order to avoid confusion between a window and a pixmap. The + operations that will work the same on a window or a pixmap + will require a <span class="code">xcb_drawable_t</span> + </p> + <div class="emph"> + <p> + Remark: In Xlib, there is no specific difference between a + <span class="code">Drawable</span>, a + <span class="code">Pixmap</span> or a + <span class="code">Window</span>: all are 32 bit long + integer. XCB wraps all these different IDs in structures to + provide some measure of type-safety. + </p> + </div> + <li class="subtitle"><a name="pixmapscreate">Creating a pixmap</a> + <p> + Sometimes we want to create an un-initialized pixmap, so we + can later draw into it. This is useful for image drawing + programs (creating a new empty canvas will cause the creation + of a new pixmap on which the drawing can be stored). It is + also useful when reading various image formats: we load the + image data into memory, create a pixmap on the server, and + then draw the decoded image data onto that pixmap. + </p> + <p> + To create a new pixmap, we first ask the X server to give an + Id to our pixmap, with this function: + </p> + <pre class="code"> +xcb_pixmap_t xcb_generate_id (xcb_connection_t *c); +</pre> + <p> + Then, XCB supplies the following function to create new pixmaps: + </p> + <pre class="code"> +xcb_void_cookie_t xcb_create_pixmap (xcb_connection_t *c, /* Pointer to the xcb_connection_t structure */ + uint8_t depth, /* Depth of the screen */ + xcb_pixmap_t pid, /* Id of the pixmap */ + xcb_drawable_t drawable, + uint16_t width, /* Width of the window (in pixels) */ + uint16_t height); /* Height of the window (in pixels) */ +</pre> + <p> + <b>TODO</b>: Explain the drawable parameter, and give an + example (like <a href="xpoints.c">xpoints.c</a>) + </p> + <li class="subtitle"><a name="pixmapsdraw"></a>Drawing a pixmap in a window + <p> + Once we got a handle to a pixmap, we can draw it on some + window, using the following function: + </p> + <pre class="code"> +xcb_void_cookie_t xcb_copy_area (xcb_connection_t *c, /* Pointer to the xcb_connection_t structure */ + xcb_drawable_t src_drawable, /* The Drawable we want to paste */ + xcb_drawable_t dst_drawable, /* The Drawable on which we copy the previous Drawable */ + xcb_gcontext_t gc, /* A Graphic Context */ + int16_t src_x, /* Top left x coordinate of the region we want to copy */ + int16_t src_y, /* Top left y coordinate of the region we want to copy */ + int16_t dst_x, /* Top left x coordinate of the region where we want to copy */ + int16_t dst_y, /* Top left y coordinate of the region where we want to copy */ + uint16_t width, /* Width of the region we want to copy */ + uint16_t height); /* Height of the region we want to copy */ +</pre> + <p> + As you can see, we could copy the whole pixmap, as well as + only a given rectangle of the pixmap. This is useful to + optimize the drawing speed: we could copy only what we have + modified in the pixmap. + </p> + <p> + <b>One important note should be made</b>: it is possible to + create pixmaps with different depths on the same screen. When + we perform copy operations (a pixmap onto a window, etc), we + should make sure that both source and target have the same + depth. If they have a different depth, the operation would + fail. The exception to this is if we copy a specific bit plane + of the source pixmap using the + <span class="code">xcb_copy_plane_t</span> function. In such an + event, we can copy a specific plane to the target window (in + actuality, setting a specific bit in the color of each pixel + copied). This can be used to generate strange graphic effects + in a window, but that is beyond the scope of this tutorial. + </p> + <li class="subtitle"><a name="pixmapsfree"></a>Freeing a pixmap + <p> + Finally, when we are done using a given pixmap, we should free + it, in order to free resources of the X server. This is done + using this function: + </p> + <pre class="code"> +xcb_void_cookie_t xcb_free_pixmap (xcb_connection_t *c, /* Pointer to the xcb_connection_t structure */ + xcb_pixmap_t pixmap); /* A given pixmap */ +</pre> + <p> + Of course, after having freed it, we must not try accessing + the pixmap again. + </p> + <p> + <b>TODO</b>: Give an example, or a link to xpoints.c + </p> + </ol> + <li class="title"><a name="mousecursor">Messing with the mouse cursor</a> + <p> + It it possible to modify the shape of the mouse pointer (also + called the X pointer) when in certain states, as we otfen see in + programs. For example, a busy application would often display + the sand clock over its main window, to give the user a visual + hint that he should wait. Let's see how we can change the mouse + cursor of our windows. + </p> + <ol> + <li class="subtitle"><a name="mousecursorcreate">Creating and destroying a mouse cursor</a> + <p> + There are two methods for creating cursors. One of them is by + using a set of predefined cursors, that are supplied by the X + server, the other is by using a user-supplied bitmap. + </p> + <p> + In the first method, we use a special font named "cursor", and + the function <span class="code">xcb_create_glyph_cursor</span>: + </p> + <pre class="code"> +xcb_void_cookie_t xcb_create_glyph_cursor (xcb_connection_t *c, + xcb_cursor_t cid, + xcb_font_t source_font, /* font for the source glyph */ + xcb_font_t mask_font, /* font for the mask glyph or XCB_NONE */ + uint16_t source_char, /* character glyph for the source */ + uint16_t mask_char, /* character glyph for the mask */ + uint16_t fore_red, /* red value for the foreground of the source */ + uint16_t fore_green, /* green value for the foreground of the source */ + uint16_t fore_blue, /* blue value for the foreground of the source */ + uint16_t back_red, /* red value for the background of the source */ + uint16_t back_green, /* green value for the background of the source */ + uint16_t back_blue) /* blue value for the background of the source */ +</pre> + <p> + <b>TODO</b>: Describe <span class="code">source_char</span> + and <span class="code">mask_char</span>, for example by giving + an example on how to get the values. There is a list there: + <a href="http://tronche.com/gui/x/xlib/appendix/b/">X Font Cursors</a> + </p> + <p> + So we first open that font (see <a href="#loadfont">Loading a Font</a>) + and create the new cursor. As for every X ressource, we have to + ask for an X id with <span class="code">xcb_generate_id</span> + first: + </p> + <pre class="code"> +xcb_font_t font; +xcb_cursor_t cursor; + +/* The connection is set */ + +font = xcb_generate_id (conn); +xcb_open_font (conn, font, strlen ("cursor"), "cursor"); + +cursor = xcb_generate_id (conn); +xcb_create_glyph_cursor (conn, cursor, font, font, + 58, 58 + 1, + 0, 0, 0, + 0, 0, 0); +</pre> + <p> + We have created the cursor "right hand" by specifying 58 to + the <span class="code">source_fon</span>t argument and 58 + 1 + to the <span class="code">mask_font</span>. + </p> + <p> + The cursor is destroyed by using the function + </p> + <pre class="code"> +xcb_void_cookie_t xcb_free_cursor (xcb_connection_t *c, + xcb_cursor_t cursor); +</pre> + <p> + In the second method, we create a new cursor by using a pair + of pixmaps, with depth of one (that is, two colors + pixmaps). One pixmap defines the shape of the cursor, while + the other works as a mask, specifying which pixels of the + cursor will be actually drawn. The rest of the pixels will be + transparent. + </p> + <p> + <b>TODO</b>: give an example. + </p> + <li class="subtitle"><a name="mousecursorset">Setting a window's mouse cursor</a> + <p> + Once the cursor is created, we can modify the cursor of our + window by using <span class="code">xcb_change_window_attributes</span> + and using the <span class="code">XCB_CWCURSOR</span> attribute: + </p> + <pre class="code"> +uint32_t mask; +uint32_t value_list; + +/* The connection and window are set */ +/* The cursor is already created */ + +mask = XCB_CWCURSOR; +value_list = cursor; +xcb_change_window_attributes (conn, window, mask, &value_list); +</pre> + <p> + Of course, the cursor and the font must be freed. + </p> + <li class="subtitle"><a name="mousecursorexample">Complete example</a> + <p> + The following example displays a window with a + button. When entering the window, the window cursor is changed + to an arrow. When clicking once on the button, the cursor is + changed to a hand. When clicking again on the button, the + cursor window gets back to the arrow. The Esc key exits the + application. + </p> + <pre class="code"> +#include <stdlib.h> +#include <stdio.h> +#include <string.h> + +#include <xcb/xcb.h> + +#define WIDTH 300 +#define HEIGHT 150 + + + +static xcb_gc_t gc_font_get (xcb_connection_t *c, + xcb_screen_t *screen, + xcb_window_t window, + const char *font_name); + +static void button_draw (xcb_connection_t *c, + xcb_screen_t *screen, + xcb_window_t window, + int16_t x1, + int16_t y1, + const char *label); + +static void text_draw (xcb_connection_t *c, + xcb_screen_t *screen, + xcb_window_t window, + int16_t x1, + int16_t y1, + const char *label); + +static void cursor_set (xcb_connection_t *c, + xcb_screen_t *screen, + xcb_window_t window, + int cursor_id); + + +static void +button_draw (xcb_connection_t *c, + xcb_screen_t *screen, + xcb_window_t window, + int16_t x1, + int16_t y1, + const char *label) +{ + xcb_point_t points[5]; + xcb_void_cookie_t cookie_gc; + xcb_void_cookie_t cookie_line; + xcb_void_cookie_t cookie_text; + xcb_generic_error_t *error; + xcb_gcontext_t gc; + int16_t width; + int16_t height; + uint8_t length; + int16_t inset; + + length = strlen (label); + inset = 2; + + gc = gc_font_get(c, screen, window, "7x13"); + + width = 7 * length + 2 * (inset + 1); + height = 13 + 2 * (inset + 1); + points[0].x = x1; + points[0].y = y1; + points[1].x = x1 + width; + points[1].y = y1; + points[2].x = x1 + width; + points[2].y = y1 - height; + points[3].x = x1; + points[3].y = y1 - height; + points[4].x = x1; + points[4].y = y1; + cookie_line = xcb_poly_line_checked (c, XCB_COORD_MODE_ORIGIN, + window, gc, 5, points); + + error = xcb_request_check (c, cookie_line); + if (error) { + fprintf (stderr, "ERROR: can't draw lines : %d\n", error->error_code); + xcb_disconnect (c); + exit (-1); + } + + cookie_text = xcb_image_text_8_checked (c, length, window, gc, + x1 + inset + 1, + y1 - inset - 1, label); + error = xcb_request_check (c, cookie_text); + if (error) { + fprintf (stderr, "ERROR: can't paste text : %d\n", error->error_code); + xcb_disconnect (c); + exit (-1); + } + + cookie_gc = xcb_free_gc (c, gc); + error = xcb_request_check (c, cookie_gc); + if (error) { + fprintf (stderr, "ERROR: can't free gc : %d\n", error->error_code); + xcb_disconnect (c); + exit (-1); + } +} + +static void +text_draw (xcb_connection_t *c, + xcb_screen_t *screen, + xcb_window_t window, + int16_t x1, + int16_t y1, + const char *label) +{ + xcb_void_cookie_t cookie_gc; + xcb_void_cookie_t cookie_text; + xcb_generic_error_t *error; + xcb_gcontext_t gc; + uint8_t length; + + length = strlen (label); + + gc = gc_font_get(c, screen, window, "7x13"); + + cookie_text = xcb_image_text_8_checked (c, length, window, gc, + x1, + y1, label); + error = xcb_request_check (c, cookie_text); + if (error) { + fprintf (stderr, "ERROR: can't paste text : %d\n", error->error_code); + xcb_disconnect (c); + exit (-1); + } + + cookie_gc = xcb_free_gc (c, gc); + error = xcb_request_check (c, cookie_gc); + if (error) { + fprintf (stderr, "ERROR: can't free gc : %d\n", error->error_code); + xcb_disconnect (c); + exit (-1); + } +} + +static xcb_gc_t +gc_font_get (xcb_connection_t *c, + xcb_screen_t *screen, + xcb_window_t window, + const char *font_name) +{ + uint32_t value_list[3]; + xcb_void_cookie_t cookie_font; + xcb_void_cookie_t cookie_gc; + xcb_generic_error_t *error; + xcb_font_t font; + xcb_gcontext_t gc; + uint32_t mask; + + font = xcb_generate_id (c); + cookie_font = xcb_open_font_checked (c, font, + strlen (font_name), + font_name); + + error = xcb_request_check (c, cookie_font); + if (error) { + fprintf (stderr, "ERROR: can't open font : %d\n", error->error_code); + xcb_disconnect (c); + return -1; + } + + gc = xcb_generate_id (c); + mask = XCB_GC_FOREGROUND | XCB_GC_BACKGROUND | XCB_GC_FONT; + value_list[0] = screen->black_pixel; + value_list[1] = screen->white_pixel; + value_list[2] = font; + cookie_gc = xcb_create_gc_checked (c, gc, window, mask, value_list); + error = xcb_request_check (c, cookie_gc); + if (error) { + fprintf (stderr, "ERROR: can't create gc : %d\n", error->error_code); + xcb_disconnect (c); + exit (-1); + } + + cookie_font = xcb_close_font_checked (c, font); + error = xcb_request_check (c, cookie_font); + if (error) { + fprintf (stderr, "ERROR: can't close font : %d\n", error->error_code); + xcb_disconnect (c); + exit (-1); + } + + return gc; +} + +static void +cursor_set (xcb_connection_t *c, + xcb_screen_t *screen, + xcb_window_t window, + int cursor_id) +{ + uint32_t values_list[3]; + xcb_void_cookie_t cookie_font; + xcb_void_cookie_t cookie_gc; + xcb_generic_error_t *error; + xcb_font_t font; + xcb_cursor_t cursor; + xcb_gcontext_t gc; + uint32_t mask; + uint32_t value_list; + + font = xcb_generate_id (c); + cookie_font = xcb_open_font_checked (c, font, + strlen ("cursor"), + "cursor"); + error = xcb_request_check (c, cookie_font); + if (error) { + fprintf (stderr, "ERROR: can't open font : %d\n", error->error_code); + xcb_disconnect (c); + exit (-1); + } + + cursor = xcb_generate_id (c); + xcb_create_glyph_cursor (c, cursor, font, font, + cursor_id, cursor_id + 1, + 0, 0, 0, + 0, 0, 0); + + gc = xcb_generate_id (c); + mask = XCB_GC_FOREGROUND | XCB_GC_BACKGROUND | XCB_GC_FONT; + values_list[0] = screen->black_pixel; + values_list[1] = screen->white_pixel; + values_list[2] = font; + cookie_gc = xcb_create_gc_checked (c, gc, window, mask, values_list); + error = xcb_request_check (c, cookie_gc); + if (error) { + fprintf (stderr, "ERROR: can't create gc : %d\n", error->error_code); + xcb_disconnect (c); + exit (-1); + } + + mask = XCB_CW_CURSOR; + value_list = cursor; + xcb_change_window_attributes (c, window, mask, &value_list); + + xcb_free_cursor (c, cursor); + + cookie_font = xcb_close_font_checked (c, font); + error = xcb_request_check (c, cookie_font); + if (error) { + fprintf (stderr, "ERROR: can't close font : %d\n", error->error_code); + xcb_disconnect (c); + exit (-1); + } +} + +int main () +{ + xcb_screen_iterator_t screen_iter; + xcb_connection_t *c; + const xcb_setup_t *setup; + xcb_screen_t *screen; + xcb_generic_event_t *e; + xcb_generic_error_t *error; + xcb_void_cookie_t cookie_window; + xcb_void_cookie_t cookie_map; + xcb_window_t window; + uint32_t mask; + uint32_t values[2]; + int screen_number; + uint8_t is_hand = 0; + + /* getting the connection */ + c = xcb_connect (NULL, &screen_number); + if (!c) { + fprintf (stderr, "ERROR: can't connect to an X server\n"); + return -1; + } + + /* getting the current screen */ + setup = xcb_get_setup (c); + + screen = NULL; + screen_iter = xcb_setup_roots_iterator (setup); + for (; screen_iter.rem != 0; --screen_number, xcb_screen_next (&screen_iter)) + if (screen_number == 0) + { + screen = screen_iter.data; + break; + } + if (!screen) { + fprintf (stderr, "ERROR: can't get the current screen\n"); + xcb_disconnect (c); + return -1; + } + + /* creating the window */ + window = xcb_generate_id (c); + mask = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK; + values[0] = screen->white_pixel; + values[1] = + XCB_EVENT_MASK_KEY_RELEASE | + XCB_EVENT_MASK_BUTTON_PRESS | + XCB_EVENT_MASK_EXPOSURE | + XCB_EVENT_MASK_POINTER_MOTION; + cookie_window = xcb_create_window_checked (c, + screen->root_depth, + window, screen->root, + 20, 200, WIDTH, HEIGHT, + 0, XCB_WINDOW_CLASS_INPUT_OUTPUT, + screen->root_visual, + mask, values); + cookie_map = xcb_map_window_checked (c, window); + + /* error managing */ + error = xcb_request_check (c, cookie_window); + if (error) { + fprintf (stderr, "ERROR: can't create window : %d\n", error->error_code); + xcb_disconnect (c); + return -1; + } + error = xcb_request_check (c, cookie_map); + if (error) { + fprintf (stderr, "ERROR: can't map window : %d\n", error->error_code); + xcb_disconnect (c); + return -1; + } + + cursor_set (c, screen, window, 68); + + xcb_flush(c); + + while (1) { + e = xcb_poll_for_event(c); + if (e) { + switch (e->response_type & ~0x80) { + case XCB_EXPOSE: { + char *text; + + text = "click here to change cursor"; + button_draw (c, screen, window, + (WIDTH - 7 * strlen(text)) / 2, + (HEIGHT - 16) / 2, text); + + text = "Press ESC key to exit..."; + text_draw (c, screen, window, 10, HEIGHT - 10, text); + break; + } + case XCB_BUTTON_PRESS: { + xcb_button_press_event_t *ev; + int length; + + ev = (xcb_button_press_event_t *)e; + length = strlen ("click here to change cursor"); + + if ((ev->event_x >= (WIDTH - 7 * length) / 2) && + (ev->event_x <= ((WIDTH - 7 * length) / 2 + 7 * length + 6)) && + (ev->event_y >= (HEIGHT - 16) / 2 - 19) && + (ev->event_y <= ((HEIGHT - 16) / 2))) + is_hand = 1 - is_hand; + + is_hand ? cursor_set (c, screen, window, 58) : cursor_set (c, screen, window, 68); + } + case XCB_KEY_RELEASE: { + xcb_key_release_event_t *ev; + + ev = (xcb_key_release_event_t *)e; + + switch (ev->detail) { + /* ESC */ + case 9: + free (e); + xcb_disconnect (c); + return 0; + } + } + } + free (e); + } + } + + return 0; +} +</pre> + </ol> + <li class="title"><a name="translation">Translation of basic Xlib functions and macros</a> + <p> + The problem when you want to port an Xlib program to XCB is that + you don't know if the Xlib function that you want to "translate" + is a X Window one or an Xlib macro. In that section, we describe + a way to translate the usual functions or macros that Xlib + provides. It's usually just a member of a structure. + </p> + <ol> + <li class="subtitle"><a name="displaystructure">Members of the Display structure</a> + <p> + In this section, we look at how to translate the macros that + return some members of the <span class="code">Display</span> + structure. They are obtained by using a function that requires a + <span class="code">xcb_connection_t *</span> or a member of the + <span class="code">xcb_setup_t</span> structure + (via the function <span class="code">xcb_get_setup</span>), or + a function that requires that structure. + </p> + <ol> + <li class="subtitle"><a name="ConnectionNumber">ConnectionNumber</a> + <p> + This number is the file descriptor that connects the client + to the server. You just have to use that function: + </p> + <pre class="code"> +int xcb_get_file_descriptor (xcb_connection_t *c); +</pre> + <li class="subtitle"><a name="DefaultScreen"></a>DefaultScreen + <p> + That number is not stored by XCB. It is returned in the + second parameter of the function <span class="code"><a href="#openconn">xcb_connect</a></span>. + Hence, you have to store it yourself if you want to use + it. Then, to get the <span class="code">xcb_screen_t</span> + structure, you have to iterate on the screens. + The equivalent function of the Xlib's + <span class="code">ScreenOfDisplay</span> function can be + found <a href="#ScreenOfDisplay">below</a>. This is also provided in the + xcb_aux_t library as <span class="code">xcb_aux_get_screen()</span>. OK, here is the + small piece of code to get that number: + </p> + <pre class="code"> +xcb_connection_t *c; +int screen_default_nbr; + +/* you pass the name of the display you want to xcb_connect_t */ + +c = xcb_connect (display_name, &screen_default_nbr); + +/* screen_default_nbr contains now the number of the default screen */ +</pre> + <li class="subtitle"><a name="QLength"></a>QLength + <p> + Not documented yet. + </p> + <p> + However, this points out a basic difference in philosophy between + Xlib and XCB. Xlib has several functions for filtering and + manipulating the incoming and outgoing X message queues. XCB + wishes to hide this as much as possible from the user, which + allows for more freedom in implementation strategies. + </p> + <li class="subtitle"><a name="ScreenCount"></a>ScreenCount + <p> + You get the count of screens with the functions + <span class="code">xcb_get_setup</span> + and + <span class="code">xcb_setup_roots_iterator</span> + (if you need to iterate): + </p> + <pre class="code"> +xcb_connection_t *c; +int screen_count; + +/* you init the connection */ + +screen_count = xcb_setup_roots_iterator (xcb_get_setup (c)).rem; + +/* screen_count contains now the count of screens */ +</pre> + <p> + If you don't want to iterate over the screens, a better way + to get that number is to use + <span class="code">xcb_setup_roots_length_t</span>: + </p> + <pre class="code"> +xcb_connection_t *c; +int screen_count; + +/* you init the connection */ + +screen_count = xcb_setup_roots_length (xcb_get_setup (c)); + +/* screen_count contains now the count of screens */ +</pre> + <li class="subtitle"><a name="ServerVendor"></a>ServerVendor + <p> + You get the name of the vendor of the server hardware with + the functions <span class="code">xcb_get_setup</span> + and + <span + class="code">xcb_setup_vendor</span>. Beware + that, unlike Xlib, the string returned by XCB is not + necessarily null-terminaled: + </p> + <pre class="code"> +xcb_connection_t *c; +char *vendor = NULL; +int length; + +/* you init the connection */ +length = xcb_setup_vendor_length (xcb_get_setup (c)); +vendor = (char *)malloc (length + 1); +if (vendor) +memcpy (vendor, xcb_setup_vendor (xcb_get_setup (c)), length); +vendor[length] = '\0'; + +/* vendor contains now the name of the vendor. Must be freed when not used anymore */ +</pre> + <li class="subtitle"><a name="ProtocolVersion"></a>ProtocolVersion + <p> + You get the major version of the protocol in the + <span class="code">xcb_setup_t</span> + structure, with the function <span class="code">xcb_get_setup</span>: + </p> + <pre class="code"> +xcb_connection_t *c; +uint16_t protocol_major_version; + +/* you init the connection */ + +protocol_major_version = xcb_get_setup (c)->protocol_major_version; + +/* protocol_major_version contains now the major version of the protocol */ +</pre> + <li class="subtitle"><a name="ProtocolRevision"></a>ProtocolRevision + <p> + You get the minor version of the protocol in the + <span class="code">xcb_setup_t</span> + structure, with the function <span class="code">xcb_get_setup</span>: + </p> + <pre class="code"> +xcb_connection_t *c; +uint16_t protocol_minor_version; + +/* you init the connection */ + +protocol_minor_version = xcb_get_setup (c)->protocol_minor_version; + +/* protocol_minor_version contains now the minor version of the protocol */ +</pre> + <li class="subtitle"><a name="VendorRelease"></a>VendorRelease + <p> + You get the number of the release of the server hardware in the + <span class="code">xcb_setup_t</span> + structure, with the function <span class="code">xcb_get_setup</span>: + </p> + <pre class="code"> +xcb_connection_t *c; +uint32_t release_number; + +/* you init the connection */ + +release_number = xcb_get_setup (c)->release_number; + +/* release_number contains now the number of the release of the server hardware */ +</pre> + <li class="subtitle"><a name="DisplayString"></a>DisplayString + <p> + The name of the display is not stored in XCB. You have to + store it by yourself. + </p> + <li class="subtitle"><a name="BitmapUnit"></a>BitmapUnit + <p> + You get the bitmap scanline unit in the + <span class="code">xcb_setup_t</span> + structure, with the function <span class="code">xcb_get_setup</span>: + </p> + <pre class="code"> +xcb_connection_t *c; +uint8_t bitmap_format_scanline_unit; + +/* you init the connection */ + +bitmap_format_scanline_unit = xcb_get_setup (c)->bitmap_format_scanline_unit; + +/* bitmap_format_scanline_unit contains now the bitmap scanline unit */ +</pre> + <li class="subtitle"><a name="BitmapBitOrder"></a>BitmapBitOrder + <p> + You get the bitmap bit order in the + <span class="code">xcb_setup_t</span> + structure, with the function <span class="code">xcb_get_setup</span>: + </p> + <pre class="code"> +xcb_connection_t *c; +uint8_t bitmap_format_bit_order; + +/* you init the connection */ + +bitmap_format_bit_order = xcb_get_setup (c)->bitmap_format_bit_order; + +/* bitmap_format_bit_order contains now the bitmap bit order */ +</pre> + <li class="subtitle"><a name="BitmapPad"></a>BitmapPad + <p> + You get the bitmap scanline pad in the + <span class="code">xcb_setup_t</span> + structure, with the function <span class="code">xcb_get_setup</span>: + </p> + <pre class="code"> +xcb_connection_t *c; +uint8_t bitmap_format_scanline_pad; + +/* you init the connection */ + +bitmap_format_scanline_pad = xcb_get_setup (c)->bitmap_format_scanline_pad; + +/* bitmap_format_scanline_pad contains now the bitmap scanline pad */ +</pre> + <li class="subtitle"><a name="ImageByteOrder"></a>ImageByteOrder + <p> + You get the image byte order in the + <span class="code">xcb_setup_t</span> + structure, with the function <span class="code">xcb_get_setup</span>: + </p> + <pre class="code"> +xcb_connection_t *c; +uint8_t image_byte_order; + +/* you init the connection */ + +image_byte_order = xcb_get_setup (c)->image_byte_order; + +/* image_byte_order contains now the image byte order */ +</pre> + </ol> + <li class="subtitle"><a name="screenofdisplay">ScreenOfDisplay related functions</a> + <p> + in Xlib, <span class="code">ScreenOfDisplay</span> returns a + <span class="code">Screen</span> structure that contains + several characteristics of your screen. XCB has a similar + structure (<span class="code">xcb_screen_t</span>), + but the way to obtain it is a bit different. With + Xlib, you just provide the number of the screen and you grab it + from an array. With XCB, you iterate over all the screens to + obtain the one you want. The complexity of this operation is + O(n). So the best is to store this structure if you use + it often. See <a href="#ScreenOfDisplay">screen_of_display</a> just below. + </p> + <p> + Xlib provides generally two functions to obtain the characteristics + related to the screen. One with the display and the number of + the screen, which calls <span class="code">ScreenOfDisplay</span>, + and the other that uses the <span class="code">Screen</span> structure. + This might be a bit confusing. As mentioned above, with XCB, it + is better to store the <span class="code">xcb_screen_t</span> + structure. Then, you have to read the members of this + structure. That's why the Xlib functions are put by pairs (or + more) as, with XCB, you will use the same code. + </p> + <ol> + <li class="subtitle"><a name="ScreenOfDisplay">ScreenOfDisplay</a> + <p> + This function returns the Xlib <span class="code">Screen</span> + structure. With XCB, you iterate over all the screens and + once you get the one you want, you return it: + </p> + <pre class="code"><a name="ScreenOfDisplay"></a> +xcb_screen_t *screen_of_display (xcb_connection_t *c, + int screen) +{ + xcb_screen_iterator_t iter; + + iter = xcb_setup_roots_iterator (xcb_get_setup (c)); + for (; iter.rem; --screen, xcb_screen_next (&iter)) + if (screen == 0) + return iter.data; + + return NULL; +} +</pre> + <p> + As mentioned above, you might want to store the value + returned by this function. + </p> + <p> + All the functions below will use the result of that + function, as they just grab a specific member of the + <span class="code">xcb_screen_t</span> structure. + </p> + <li class="subtitle"><a name="DefaultScreenOfDisplay"></a>DefaultScreenOfDisplay + <p> + It is the default screen that you obtain when you connect to + the X server. It suffices to call the <a href="#ScreenOfDisplay">screen_of_display</a> + function above with the connection and the number of the + default screen. + </p> + <pre class="code"> +xcb_connection_t *c; +int screen_default_nbr; +xcb_screen_t *default_screen; /* the returned default screen */ + +/* you pass the name of the display you want to xcb_connect_t */ + +c = xcb_connect (display_name, &screen_default_nbr); +default_screen = screen_of_display (c, screen_default_nbr); + +/* default_screen contains now the default root window, or a NULL window if no screen is found */ +</pre> + <li class="subtitle"><a name="RootWindow">RootWindow / RootWindowOfScreen</a> + <br> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +xcb_window_t root_window = { 0 }; /* the returned window */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) + root_window = screen->root; + +/* root_window contains now the root window, or a NULL window if no screen is found */ +</pre> + <li class="subtitle"><a name="DefaultRootWindow">DefaultRootWindow</a> + <p> + It is the root window of the default screen. So, you call + <a name="ScreenOfDisplay">ScreenOfDisplay</a> with the + default screen number and you get the + <a href="#RootWindow">root window</a> as above: + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_default_nbr; +xcb_window_t root_window = { 0 }; /* the returned root window */ + +/* you pass the name of the display you want to xcb_connect_t */ + +c = xcb_connect (display_name, &screen_default_nbr); +screen = screen_of_display (c, screen_default_nbr); +if (screen) + root_window = screen->root; + +/* root_window contains now the default root window, or a NULL window if no screen is found */ +</pre> + <li class="subtitle"><a name="DefaultVisual">DefaultVisual / DefaultVisualOfScreen</a> + <p> + While a Visual is, in Xlib, a structure, in XCB, there are + two types: <span class="code">xcb_visualid_t</span>, which is + the Id of the visual, and <span class="code">xcb_visualtype_t</span>, + which corresponds to the Xlib Visual. To get the Id of the + visual of a screen, just get the + <span class="code">root_visual</span> + member of a <span class="code">xcb_screen_t</span>: + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +xcb_visualid_t root_visual = { 0 }; /* the returned visual Id */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) + root_visual = screen->root_visual; + +/* root_visual contains now the value of the Id of the visual, or a NULL visual if no screen is found */ +</pre> + <p> + To get the <span class="code">xcb_visualtype_t</span> + structure, it's a bit less easy. You have to get the + <span class="code">xcb_screen_t</span> structure that you want, + get its <span class="code">root_visual</span> member, + then iterate over the <span class="code">xcb_depth_t</span>s + and the <span class="code">xcb_visualtype_t</span>s, and compare + the <span class="code">xcb_visualid_t</span> of these <span class="code">xcb_visualtype_t</span>s: + with <span class="code">root_visual</span>: + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +xcb_visualid_t root_visual = { 0 }; +xcb_visualtype_t *visual_type = NULL; /* the returned visual type */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) { + xcb_depth_iterator_t depth_iter; + + depth_iter = xcb_screen_allowed_depths_iterator (screen); + for (; depth_iter.rem; xcb_depth_next (&depth_iter)) { + xcb_visualtype_iterator_t visual_iter; + + visual_iter = xcb_depth_visuals_iterator (depth_iter.data); + for (; visual_iter.rem; xcb_visualtype_next (&visual_iter)) { + if (screen->root_visual == visual_iter.data->visual_id) { + visual_type = visual_iter.data; + break; + } + } + } +} + +/* visual_type contains now the visual structure, or a NULL visual structure if no screen is found */ +</pre> + <li class="subtitle"><a name="DefaultGC">DefaultGC / DefaultGCOfScreen</a> + <p> + This default Graphic Context is just a newly created Graphic + Context, associated to the root window of a + <span class="code">xcb_screen_t</span>, + using the black white pixels of that screen: + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +xcb_gcontext_t gc = { 0 }; /* the returned default graphic context */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) { + xcb_drawable_t draw; + uint32_t mask; + uint32_t values[2]; + + gc = xcb_generate_id (c); + draw = screen->root; + mask = XCB_GC_FOREGROUND | XCB_GC_BACKGROUND; + values[0] = screen->black_pixel; + values[1] = screen->white_pixel; + xcb_create_gc (c, gc, draw, mask, values); +} + +/* gc contains now the default graphic context */ +</pre> + <li class="subtitle"><a name="BlackPixel">BlackPixel / BlackPixelOfScreen</a> + <p> + It is the Id of the black pixel, which is in the structure + of an <span class="code">xcb_screen_t</span>. + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +uint32_t black_pixel = 0; /* the returned black pixel */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) + black_pixel = screen->black_pixel; + +/* black_pixel contains now the value of the black pixel, or 0 if no screen is found */ +</pre> + <li class="subtitle"><a name="WhitePixel">WhitePixel / WhitePixelOfScreen</a> + <p> + It is the Id of the white pixel, which is in the structure + of an <span class="code">xcb_screen_t</span>. + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +uint32_t white_pixel = 0; /* the returned white pixel */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) + white_pixel = screen->white_pixel; + +/* white_pixel contains now the value of the white pixel, or 0 if no screen is found */ +</pre> + <li class="subtitle"><a name="DisplayWidth">DisplayWidth / WidthOfScreen</a> + <p> + It is the width in pixels of the screen that you want, and + which is in the structure of the corresponding + <span class="code">xcb_screen_t</span>. + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +uint32_t width_in_pixels = 0; /* the returned width in pixels */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) + width_in_pixels = screen->width_in_pixels; + +/* width_in_pixels contains now the width in pixels, or 0 if no screen is found */ +</pre> + <li class="subtitle"><a name="DisplayHeight">DisplayHeight / HeightOfScreen</a> + <p> + It is the height in pixels of the screen that you want, and + which is in the structure of the corresponding + <span class="code">xcb_screen_t</span>. + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +uint32_t height_in_pixels = 0; /* the returned height in pixels */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) + height_in_pixels = screen->height_in_pixels; + +/* height_in_pixels contains now the height in pixels, or 0 if no screen is found */ +</pre> + <li class="subtitle"><a name="DisplayWidthMM">DisplayWidthMM / WidthMMOfScreen</a> + <p> + It is the width in millimeters of the screen that you want, and + which is in the structure of the corresponding + <span class="code">xcb_screen_t</span>. + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +uint32_t width_in_millimeters = 0; /* the returned width in millimeters */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) + width_in_millimeters = screen->width_in_millimeters; + +/* width_in_millimeters contains now the width in millimeters, or 0 if no screen is found */ +</pre> + <li class="subtitle"><a name="DisplayHeightMM">DisplayHeightMM / HeightMMOfScreen</a> + <p> + It is the height in millimeters of the screen that you want, and + which is in the structure of the corresponding + <span class="code">xcb_screen_t</span>. + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +uint32_t height_in_millimeters = 0; /* the returned height in millimeters */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) + height_in_millimeters = screen->height_in_millimeters; + +/* height_in_millimeters contains now the height in millimeters, or 0 if no screen is found */ +</pre> + <li class="subtitle"><a name="DisplayPlanes">DisplayPlanes / DefaultDepth / DefaultDepthOfScreen / PlanesOfScreen</a> + <p> + It is the depth (in bits) of the root window of the + screen. You get it from the <span class="code">xcb_screen_t</span> structure. + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +uint8_t root_depth = 0; /* the returned depth of the root window */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) + root_depth = screen->root_depth; + +/* root_depth contains now the depth of the root window, or 0 if no screen is found */ +</pre> + <li class="subtitle"><a name="DefaultColormap">DefaultColormap / DefaultColormapOfScreen</a> + <p> + This is the default colormap of the screen (and not the + (default) colormap of the default screen !). As usual, you + get it from the <span class="code">xcb_screen_t</span> structure: + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +xcb_colormap_t default_colormap = { 0 }; /* the returned default colormap */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) + default_colormap = screen->default_colormap; + +/* default_colormap contains now the default colormap, or a NULL colormap if no screen is found */ +</pre> + <li class="subtitle"><a name="MinCmapsOfScreen"></a>MinCmapsOfScreen + <p> + You get the minimum installed colormaps in the <span class="code">xcb_screen_t</span> structure: + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +uint16_t min_installed_maps = 0; /* the returned minimum installed colormaps */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) + min_installed_maps = screen->min_installed_maps; + +/* min_installed_maps contains now the minimum installed colormaps, or 0 if no screen is found */ +</pre> + <li class="subtitle"><a name="MaxCmapsOfScreen"></a>MaxCmapsOfScreen + <p> + You get the maximum installed colormaps in the <span class="code">xcb_screen_t</span> structure: + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +uint16_t max_installed_maps = 0; /* the returned maximum installed colormaps */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) + max_installed_maps = screen->max_installed_maps; + +/* max_installed_maps contains now the maximum installed colormaps, or 0 if no screen is found */ +</pre> + <li class="subtitle"><a name="DoesSaveUnders"></a>DoesSaveUnders + <p> + You know if <span class="code">save_unders</span> is set, + by looking in the <span class="code">xcb_screen_t</span> structure: + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +uint8_t save_unders = 0; /* the returned value of save_unders */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) + save_unders = screen->save_unders; + +/* save_unders contains now the value of save_unders, or FALSE if no screen is found */ +</pre> + <li class="subtitle"><a name="DoesBackingStore"></a>DoesBackingStore + <p> + You know the value of <span class="code">backing_stores</span>, + by looking in the <span class="code">xcb_screen_t</span> structure: + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +uint8_t backing_stores = 0; /* the returned value of backing_stores */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) + backing_stores = screen->backing_stores; + +/* backing_stores contains now the value of backing_stores, or FALSE if no screen is found */ +</pre> + <li class="subtitle"><a name="EventMaskOfScreen"></a>EventMaskOfScreen + <p> + To get the current input masks, + you look in the <span class="code">xcb_screen_t</span> structure: + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_screen_t *screen; +int screen_nbr; +uint32_t current_input_masks = 0; /* the returned value of current input masks */ + +/* you init the connection and screen_nbr */ + +screen = screen_of_display (c, screen_nbr); +if (screen) + current_input_masks = screen->current_input_masks; + +/* current_input_masks contains now the value of the current input masks, or FALSE if no screen is found */ +</pre> + </ol> + <li class="subtitle"><a name="misc">Miscellaneous macros</a> + <ol> + <li class="subtitle"><a name="DisplayOfScreen"></a>DisplayOfScreen + <p> + in Xlib, the <span class="code">Screen</span> structure + stores its associated <span class="code">Display</span> + structure. This is not the case in the X Window protocol, + hence, it's also not the case in XCB. So you have to store + it by yourself. + </p> + <li class="subtitle"><a name="DisplayCells"></a>DisplayCells / CellsOfScreen + <p> + To get the colormap entries, + you look in the <span class="code">xcb_visualtype_t</span> + structure, that you grab like <a class="subsection" href="#DefaultVisual">here</a>: + </p> + <pre class="code"> +xcb_connection_t *c; +xcb_visualtype_t *visual_type; +uint16_t colormap_entries = 0; /* the returned value of the colormap entries */ + +/* you init the connection and visual_type */ + +if (visual_type) + colormap_entries = visual_type->colormap_entries; + +/* colormap_entries contains now the value of the colormap entries, or FALSE if no screen is found */ +</pre> + </ol> + </ol> + </ol> + </div> +</body> + +</html> |