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\s+1\fBUsing Widgets\fP\s-1
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.LP
.XS
Chapter 2 \- Using Widgets
.XE
.IN "using widgets" "" "@DEF@"
Widgets serve as the primary tools for building a user interface or
application environment.  The Athena widget set consists of primitive
widgets that contain no children (for example, a command button) and
composite widgets which may contain one or more widget children (for
example, a Box widget).
.LP
The remaining chapters explain the widgets that are provided
by the Athena widget set.
These user-interface components serve as an interface for
application programmers who do not want to implement their own widgets.
In addition, they serve as a starting point
for those widget programmers who, using the \*(xI mechanisms,
want to implement alternative application programming interfaces.
.LP
This chapter is a brief introduction to widget programming.  The
examples provided use the Athena widgets, though most of the concepts
will apply to all widget sets.  Although there are several programming
interfaces to the \*(tk, only one is described here.  A full
description of the programming interface is provided in the document
\fI\*(xT\fP.
.NH 2
Setting the Locale
.LP
.XS
	Setting the Locale
.XE
If it is desirable that the application take advantage of
internationalization (i18n), you must establish locale with
.PN XtSetLanguageProc
before \fBXtDisplayInitialize\fP or \fBXtAppInitialize\fP
is called.  For full details, please refer to the document
\fI\*(xT\fP, section 2.2. However, the following simplest-case
call is sufficient in many or most applications.
.LP
.IN "internationalization" "" ""
.IN "XtSetLanguageProc" "" "@DEF@"
.IN "locale" "" ""
.Ds
.TA .5i 2i
.ta .5i 2i
	XtSetLanguageProc(NULL, NULL, NULL);
.De
.LP
Most notably, this will affect the Standard C locale, determine which
resource files will be loaded, and what fonts will be required of FontSet
specifications.  In many cases, the addition of this line is the only source change
required to internationalize Xaw programs, and will not disturb the function
of programs in the default "C" locale.
.NH 2
Initializing the Toolkit
.LP
.XS
	Initializing the Toolkit
.XE
You must call a toolkit initialization function before invoking any
other toolkit routines (besides locale setting, above).
.PN XtAppInitialize
opens the X server connection, parses the command line,
and creates an initial widget that will serve as the root of
a tree of widgets created by this application.
.IN "initialization" "" "@DEF@"
.IN "toolkit initialization" "" "@DEF@"
.IN "XtAppInitialize" "" "@DEF@"
.IN "fallback resources" "" "@DEF@"
.FD 0
Widget XtAppInitialize(\fIapp_context_return\fP, \fIapplication_class\fP, \
\fIoptions\fP, \fInum_options\fP,
.ta 2i
	\fIargc_in_out\fP, \fIargv_in_out\fP, \fIfallback_resources\fP, \
\fIargs\fP, \fInum_args\fP)
.br
      XtAppContext *\fIapp_context_return\fP;
.br
      String \fIapplication_class\fP;
.br
      XrmOptionDescRec \fIoptions\fP[];
.br
      Cardinal \fInum_options\fP;
.br
      int *\fIargc_in_out\fP;
.br
      String *\fIargv_in_out\fP[];
.br
      String *\fIfallback_resources\fP;
.br
      ArgList \fIargs\fP;
.br
      Cardinal \fInum_args\fP;
.FN
.IP \fIapp_con_return\fP 1.5i
Returns the application context of this application, if non-NULL.
.IP \fIapplication_class\fP 1.5i
Specifies the class name of this application,
which is usually the generic name for all instances of this application.
A useful convention is to form the class name by capitalizing the
first letter of the application name. For example, the application named
``xman'' has a class name of ``Xman''.
.IP \fIoptions\fP 1.5i
Specifies how to parse the command line for any application-specific
resources.
The options argument is passed as a parameter to
.PN XrmParseCommand .
For further information,
see \fI\*(xL\fP.
.IP \fInum_options\fP 1.5i
Specifies the number of entries in the options list.
.IP \fIargc_in_out\fP 1.5i
Specifies a pointer to the number of command line parameters.
.IP \fIargv_in_out\fP 1.5i
Specifies the command line parameters.
.IP \fIfallback_resources\fP 1.5i
Specifies resource values to be used if the site-wide application class
defaults file cannot be opened, or NULL.
.IP \fIargs\fP 1.5i
Specifies the argument list to use when creating the Application shell.
.IP \fInum_args\fP 1.5i
Specifies the number of arguments in \fIargs\fP.
.LP
This function will remove the command line arguments that the toolkit
reads from \fIargc_in_out\fP, and \fIargv_in_out\fP.  It will then
attempt to open the display.  If the display cannot be opened, an error
message is issued and XtAppInitialize terminates the application.  Once
the display is opened, all resources are read from the locations
specified by the \*(xI.  This function returns an ApplicationShell
widget to be used as the root of the application's widget tree.
.NH 2
Creating a Widget
.LP
.XS
	Creating a Widget
.XE
.IN "widget creation" "" "@DEF@"
.IN "creating widgets" "" "@DEF@"
.IN "XtRealizeWidget" "" ""
Creating a widget is a three-step process.  First, the widget instance
is allocated, and various instance-specific attributes are set by
using \fBXtCreateWidget\fP.  Second, the widget's parent is informed
of the new child by using \fBXtManageChild\fP.  Finally, X windows are
created for the parent and all its children by using \fBXtRealizeWidget\fP
and specifying the top-most widget. The first two steps can be
combined by using \fBXtCreateManagedWidget\fP.  In addition,
\fBXtRealizeWidget\fP is automatically called when the child becomes
managed if the parent is already realized.
.LP
To allocate, initialize, and manage a widget, use
.PN XtCreateManagedWidget .
.IN "XtCreateManagedWidget" "" "@DEF@"
.FD 0
Widget XtCreateManagedWidget(\fIname\fP, \fIwidget_class\fP, \fIparent\fP, \
\fIargs\fP, \fInum_args\fP)
.br
      String \fIname\fP;
.br
      WidgetClass \fIwidget_class\fP;
.br
      Widget \fIparent\fP;
.br
      ArgList \fIargs\fP;
.br
      Cardinal \fInum_args\fP;
.FN
.IP \fIname\fP 1i
Specifies the instance name for the created widget that is used for retrieving
widget resources.
.IP \fIwidget_class\fP 1i
Specifies the widget class pointer for the created widget.
.IP \fIparent\fP 1i
Specifies the parent widget ID.
.IP \fIargs\fP 1i
Specifies the argument list.  The argument list is a variable-length
list composed of name and value pairs that contain information
pertaining to the specific widget instance being created.  For further
information, see Section 2.7.2.
.IP \fInum_args\fP 1i
Specifies the number of arguments in the argument list.
If the num_args is zero, the argument list is never referenced.
.LP
When a widget instance is successfully created, the widget identifier
is returned to the application.  If an error is encountered, the
.PN XtError
routine is invoked to inform the user of the error.
.IN "XtError" "" ""
.LP
For further information, see \fI\*(xT\fP.
.NH 2
Common Resources
.XS
	Common Resources
.XE
.IN "resource" ""
.LP
Although a widget can have unique arguments that it understands, all
widgets have common arguments that provide some regularity of operation.
The common arguments allow arbitrary widgets to be managed by
higher-level components without regard for the individual widget type.
Widgets will ignore any argument that they do not understand.
.LP
The following resources are retrieved from the argument list
or from the resource database by all of the Athena widgets:
.TS H
lw(1.5i) lw(1i) lw(1i) lw(2i).
_
.sp 3p
.TB
Name	Class	Type	Default Value
.sp 3p
_
.TH
.R
.sp 3p
accelerators	Accelerators	AcceleratorTable	NULL
ancestorSensitive	AncestorSensitive	Boolean	True
background	Background	Pixel	XtDefaultBackground
backgroundPixmap	Pixmap	Pixmap	XtUnspecifiedPixmap
borderColor	BorderColor	Pixel	XtDefaultForeground
borderPixmap	Pixmap	Pixmap	XtUnspecifiedPixmap
borderWidth	BorderWidth	Dimension	1
colormap	Colormap	Colormap	Parent's Colormap
depth	Depth	int	Parent's Depth
destroyCallback	Callback	XtCallbackList	NULL
height	Height	Dimension	\fIwidget dependent\fP
mappedWhenManaged	MappedWhenManaged	Boolean	True
screen	Screen	Screen	Parent's Screen
sensitive	Sensitive	Boolean	True
translations	Translations	TranslationTable	\fIwidget dependent\fP
width	Width	Dimension	\fIwidget dependent\fP
x	Position	Position	0
y	Position	Position	0
.sp 3p
_
.TE
.IN "XtDefaultForeground" "" ""
.IN "XtDefaultBackground" "" ""
.LP
The following additional resources are retrieved from the argument list
or from the resource database by many of the Athena widgets:
.TS H
lw(1.5i) lw(1i) lw(1i) lw(2i).
_
.sp 3p
.TB
Name	Class	Type	Default Value
.sp 3p
_
.TH
.R
.sp 3p
callback	Callback	XtCallbackList	NULL
cursor	Cursor	Cursor	\fIwidget dependent\fP
foreground	Foreground	Pixel	XtDefaultForeground
insensitiveBorder	Insensitive	Pixmap	GreyPixmap
.sp 3p
_
.TE
.IN "XtDefaultForeground" "" ""
.NH 2
Resource Conversions
.XS
	Resource Conversions
.XE
.IN "conversions" "" "@DEF@"
.IN "string conversions" "" "@DEF@"
.IN "type conversions" "" "@DEF@"
.LP
Most resources in the Athena widget set have a converter registered that
will translate the string in a resource file to the correct internal
representation.  While some are obvious (string to integer, for example),
others need specific mention of the allowable values.  Three general
converters are described here:
.IP \(bu 5
Cursor
.IP \(bu 5
Pixel
.IP \(bu 5
Bitmap
.LP
Many widgets have defined special converters that apply only to that
widget.  When these occur, the documentation section for that widget
will describe the converter.
.NH 3
Cursor Conversion
.IN "conversions" "ColorCursor" "@DEF@"
.IN "conversions" "Cursor" "@DEF@"
.IN "cursor" "" ""
.LP
The value for the \fBcursorName\fP resource is specified in the resource
database as a string, and is of the following forms:
.IP \(bu 5
A standard X cursor name from \fB< X11/cursorfont.h >\fP.
The names in \fBcursorfont.h\fP each describe a specific cursor.  The
resource names for these cursors are exactly like the names in this file
except the \fBXC_\fP is not used.  The cursor definition \fBXC_gumby\fP
has a resource name of \fBgumby\fP.
.IP \(bu 5
Glyphs, as in \fIFONT font-name glyph-index [[ font-name ] glyph-index ]\fP.
The first font and glyph specify the cursor source pixmap.
The second font and glyph specify the cursor mask pixmap.
The mask font defaults to the source font,
and the mask glyph index defaults to the source glyph index.
.IP \(bu 5
A relative or absolute file name.
If a relative or absolute file name is specified, that file is used to
create the source pixmap.  Then the string "Mask" is appended to
locate the cursor mask pixmap.  If the "Mask" file does not exist, the
suffix "msk" is tried.  If "msk" fails, no cursor mask will be used.
If the filename does not start with '/' or './' the the bitmap
file path is used (see section 2.4.3).
.NH 3
Pixel Conversion
.LP
.IN "conversions" "Pixel" "@DEF@"
.IN "pixel" "" ""
.IN "rgb.txt" "" ""
.IN "XtDefaultForeground" "" ""
.IN "XtDefaultBackground" "" ""
The string-to-pixel converter takes any name that is acceptable to
XParseColor (see \fI\*(xL\fP).  In addition this routine understands
the special toolkit symbols `XtDefaultForeground' and
`XtDefaultBackground', described in \fI\*(xT\fP.  In short the acceptable
pixel names are:
.IP \(bu 5
Any color name for the rgb.txt file (typically in the directory
/usr/lib/X11 on POSIX systems).
.IP \(bu 5
A numeric specification of the form #<red><green><blue> where these
numeric values are hexadecimal digits (both upper and lower case).
.IP \(bu 5
The special strings `XtDefaultForeground' and `XtDefaultBackground'
.NH 3
Bitmap Conversion
.IN "bitmap conversions" "" "@DEF@"
.IN "conversions" "Bitmap" "@DEF@"
.IN "bitmapFilePath" "" "@DEF@"
.IN "BitmapFilePath" "" "@DEF@"
.IN "/usr/include/X11/bitmaps" "" ""
.LP
The string-to-bitmap converter attempts to locate a file containing
bitmap data whose name is specified by the input string.  If the file
name is relative (i.e. does not begin with / or ./), the directories to
be searched are specified in the \fBbitmapFilePath\fP resource--class
\fBBitmapFilePath\fP.  This resource specifies a colon (:) separated
list of directories that will be searched for the named bitmap or
cursor glyph (see section 2.4.1).  The \fBbitmapFilePath\fP resource is
global to the application, and may \fBnot\fP be specified differently
for each widget that wishes to convert a cursor to bitmap.  In addition
to the directories specified in the \fBbitmapFilePath\fP resource a
default directory is searched.  When using POSIX the default
directory is
.PN /usr/include/X11/bitmaps .
.NH 2
Realizing a Widget
.LP
.XS
	Realizing a Widget
.XE
.IN "realizing widgets" "" "@DEF@"
The
.PN XtRealizeWidget
function performs two tasks:
.IP \(bu 5
Calculates the geometry constraints of all managed descendants
of this widget.  The actual calculation is put off until realize time
for performance reasons.
.IP \(bu 5
Creates an X window for the widget and, if it is a composite widget,
realizes each of its managed children.
.IN "XtRealizeWidget" "" "@DEF@"
.FD 0
void XtRealizeWidget(\fIw\fP)
.br
      Widget \fIw\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget.
.LP
For further information about this function,
see the \fI\*(xT\fP.
.NH 2
Processing Events
.LP
.XS
	Processing Events
.XE
.IN "events" "" ""
.IN "XtAppInitialize" "" ""
Now that the application has created, managed and realized its
widgets, it is ready to process the events that will be delivered by the
X Server to this client.  A function call that will process the
events is \fBXtAppMainLoop\fP.
.IN "XtAppMainLoop" "" "@DEF@"
.FD 0
void XtAppMainLoop(\fIapp_context\fP)
.br
      XtAppContext \fIapp_context\fP;
.FN
.IP \fIapp_context\fP 1i
Specifies the application context of this application.  The value is
normally returned by \fBXtAppInitialize\fP.
.LP
This function never returns: it is an infinite loop that processes the
X events.  User input can be handled through callback procedures and
application defined action routines.  More details are provided in
\fI\*(xT\fP.
.NH 2
Standard Widget Manipulation Functions
.XS
	Standard Widget Manipulation Functions
.XE
.LP
After a widget has been created, a client can interact with that
widget by calling one of the standard widget manipulation routines
provided by the \*(xI, or a widget class-specific manipulation routine.
.LP
The \*(xI provide generic routines to give the application programmer
access to a set of standard widget functions.  The common widget
routines let an application or composite widget perform the following
operations on widgets without requiring explicit knowledge of the widget
type.
.IP \(bu 5
Control the mapping of widget windows
.IP \(bu 5
Destroy a widget instance
.IP \(bu 5
Obtain an argument value
.IP \(bu 5
Set an argument value
.NH 3
Mapping Widgets
.LP
By default,
widget windows are mapped (made viewable) automatically by
\fBXtRealizeWidget\fP.  This behavior can be disabled by using
\fBXtSetMappedWhenManaged\fP, making the client responsible for calling
\fBXtMapWidget\fP to make the widget viewable.
.IN "XtSetMappedWhenManaged" "" "@DEF@"
.IN "XtMapWidget" "" ""
.IN "XtRealizeWidget" "" ""
.FD 0
void XtSetMappedWhenManaged(\fIw\fP, \fImap_when_managed\fP)
.br
      Widget \fIw\fP;
.br
      Boolean \fImap_when_managed\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget.
.IP \fImap_when_managed\fP 1i
Specifies the new value.
If map_when_managed is \fBTrue\fP, the widget is mapped automatically
when it is realized.  If map_when_managed is \fBFalse\fP, the client
must call
.PN XtMapWidget
or make a second call to
.PN XtSetMappedWhenManaged
to cause the child window to be mapped.
.LP
.sp
The definition for
.PN XtMapWidget
is:
.IN "XtMapWidget" "" "@DEF@"
.FD 0
void XtMapWidget(\fIw\fP)
.br
     Widget \fIw\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget.
.LP
When you are creating several children in sequence for a previously
realized common parent it is generally more efficient to construct a
list of children as they are created (using \fBXtCreateWidget\fP) and
then use \fBXtManageChildren\fP to request that their parent managed
them all at once.  By managing a list of children at one time, the
parent can avoid wasteful duplication of geometry processing and the
associated ``screen flash''.
.IN "XtManageChildren" "" "@DEF@"
.IN "XtCreateWidget" "" ""
.FD 0
void XtManageChildren(\fIchildren\fP, \fInum_children\fP)
.br
      WidgetList \fIchildren\fP;
.br
      Cardinal \fInum_children\fP;
.FN
.IP \fIchildren\fP 1i
Specifies a list of children to add.
.IP \fInum_children\fP 1i
Specifies the number of children to add.
.LP
If the parent is already visible on the screen, it is especially
important to batch updates so that the minimum amount of visible window
reconfiguration is performed.
.LP
For further information about these functions,
see the \fI\*(xT\fP.
.NH 3
Destroying Widgets
.LP
To destroy a widget instance of any type, use
.PN XtDestroyWidget .
.IN "XtDestroyWidget" "" "@DEF@"
.FD 0
void XtDestroyWidget(\fIw\fP)
.br
      Widget \fIw\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget.
.LP
.PN XtDestroyWidget
destroys the widget and recursively destroys any children that it may have,
including the windows created by its children.
After calling
.PN XtDestroyWidget ,
no further references should be made to the widget or any children
that the destroyed widget may have had.
.NH 3
Retrieving Widget Resource Values
.LP
To retrieve the current value of a resource attribute associated
with a widget instance, use
.PN XtGetValues .
.IN "XtGetValues" "" "@DEF@"
.FD 0
void XtGetValues(\fIw\fP, \fIargs\fP, \fInum_args\fP)
.br
      Widget \fIw\fP;
.br
      ArgList \fIargs\fP;
.br
      Cardinal \fInum_args\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget.
.IP \fIargs\fP 1i
Specifies a variable-length argument list of name and \fBaddress\fP
pairs that contain the resource name and the address into which the
resource value is stored.
.IP \fInum_args\fP 1i
Specifies the number of arguments in the argument list.
.LP
The arguments and values passed in the argument list are dependent on
the widget. Note that the caller is responsible for providing space
into which the returned resource value is copied; the \fBArgList\fP
contains a pointer to this storage (e.g. x and y must be
allocated as Position).  For further information, see the \fI\*(xT\fP.
.NH 3
Modifying Widget Resource Values
.LP
To modify the current value of a resource attribute associated with a
widget instance, use
.PN XtSetValues .
.IN "XtSetValues" "" "@DEF@"
.FD 0
void XtSetValues(\fIw\fP, \fIargs\fP, \fInum_args\fP)
.br
      Widget \fIw\fP;
.br
      ArgList \fIargs\fP;
.br
      Cardinal \fInum_args\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget.
.IP \fIargs\fP 1i
Specifies an array of name and \fBvalue\fP pairs that contain the
arguments to be modified and their new values.
.IP \fInum_args\fP 1i
Specifies the number of arguments in the argument list.
.LP
The arguments and values that are passed will depend on the widget
being modified.  Some widgets may not allow certain resources to be
modified after the widget instance has been created or realized.
No notification is given if any part of a \fBXtSetValues\fP request is
ignored.
.LP
For further information about these functions, see the \fI\*(xT\fP.
.IN "XtGetValues" "" ""
.IN "XtSetValues" "" ""
.NT
The argument list entry for
.PN XtGetValues
specifies the address to which the caller wants the value copied.  The
argument list entry for
.PN XtSetValues ,
however, contains the new value itself, if the size of value is less than
sizeof(XtArgVal) (architecture dependent, but at least sizeof(long));
otherwise, it is a pointer to the value.  String resources are always
passed as pointers, regardless of the length of the string.
.NE
.NH 2
Using the Client Callback Interface
.LP
.XS
	Using the Client Callback Interface
.XE
.IN "callbacks" "" ""
Widgets can communicate changes in their state to their clients
by means of a callback facility.
The format for a client's callback handler is:
.IN "CallbackProc" "" "@DEF@"
.FD 0
void \fICallbackProc\fP(\fIw\fP, \fIclient_data\fP, \fIcall_data\fP)
.br
      Widget \fIw\fP;
.br
      XtPointer \fIclient_data\fP;
.br
      XtPointer \fIcall_data\fP;
.FN
.IP \fIw\fP 1i
Specifies widget for which the callback is registered.
.IP \fIclient_data\fP 1i
Specifies arbitrary client-supplied data that the widget should pass
back to the client when the widget executes the client's callback
procedure.  This is a way for the client registering the callback to
also register client-specific data: a pointer to additional information
about the widget, a reason for invoking the callback, and so on. If no
additional information is necessary, NULL may be passed as this argument.
This field is also frequently known as the \fIclosure\fP.
.IP \fIcall_data\fP 1i
Specifies any callback-specific data the widget wants to pass to the client.
For example, when Scrollbar executes its \fBjumpProc\fP callback list,
it passes the current position of the thumb in \fIcall_data\fP.
.LP
Callbacks can be registered either by creating an argument containing
the callback list described below or by using the special convenience
routines \fBXtAddCallback\fP and \fBXtAddCallbacks\fP.  When the widget
is created, a pointer to a list of callback procedure and data pairs can
be passed in the argument list to
.PN XtCreateWidget .
The list is of type
.PN XtCallbackList :
.IN "XtCallbackProc"
.IN "XtAddCallbacks"
.IN "XtAddCallback"
.IN "XtCallbackList" "" "@DEF@"
.IN "XtCallbackRec" "" "@DEF@"
.LP
.Ds 0
.TA .5i 3i
.ta .5i 3i
typedef struct {
	XtCallbackProc callback;
	XtPointer closure;
} XtCallbackRec, *XtCallbackList;
.De
.LP
The callback list must be allocated and initialized before calling
.PN XtCreateWidget .
.IN "XtCreateWidget"
The end of the list is identified by an entry containing NULL in
callback and closure.  Once the widget is created, the client can change
or de-allocate this list; the widget itself makes no further reference
to it.  The closure field contains the client_data passed to the
callback when the callback list is executed.
.LP
The second method for registering callbacks is to use
.PN XtAddCallback
after the widget has been created.
.IN "XtAddCallback" "" "@DEF@"
.FD 0
void XtAddCallback(\fIw\fP, \fIcallback_name, \fP\fIcallback\fP, \
\fIclient_data\fP)
.br
      Widget \fIw\fP;
.br
      String \fIcallback_name\fP;
.br
      XtCallbackProc \fIcallback\fP;
.br
      XtPointer \fIclient_data\fP;
.FN
.IP \fIw\fP 1i
Specifies the widget to add the callback to.
.IP \fIcallback_name\fP 1i
Specifies the callback list within the widget to append to.
.IP \fIcallback\fP 1i
Specifies the callback procedure to add.
.IP \fIclient_data\fP 1i
Specifies the data to be passed to the callback when it is invoked.
.LP
.PN XtAddCallback
adds the specified callback to the list for the named widget.
.LP
All widgets provide a callback list named
.PN destroyCallback
.IN "destroyCallback" "" "@DEF@"
where clients can register procedures that are to be executed when the
widget is destroyed.  The destroy callbacks are executed when the widget
or an ancestor is destroyed.  The \fIcall_data\fP argument is unused for
destroy callbacks.
.NH 2
Programming Considerations
.LP
.XS
	Programming Considerations
.XE
This section provides some guidelines on how to set up an application
program that uses the \*(tk.
.NH 3
Writing Applications
.LP
.IN "writing applications"
.IN "StringDefs.h"
.IN "Intrinsic.h"
When writing an application that uses the X Toolkit,
you should make sure that your application performs the following:
.IP 1. 5
Include
.Pn < X11/Intrinsic.h >
in your application programs.
This header file automatically includes
.Pn < X11/Xlib.h >,
so all Xlib functions also are defined.
It may also be necessary to include \fB< X11/StringDefs.h >\fP when setting
up argument lists, as many of the XtN\fIsomething\fP definitions are
only defined in this file.
.IP 2. 5
Include the widget-specific header files for each widget type
that you need to use.
For example,
.Pn < X11/Xaw/Label.h >
and
.Pn < X11/Xaw/Command.h >.
.IP 3. 5
Call the
.PN XtAppInitialize
.IN "XtAppInitialize"
function before invoking any other toolkit or Xlib functions.
For further information,
see Section 2.1 and the \fI\*(xT\fP.
.IP 4. 5
To pass attributes to the widget creation routines that will override
any site or user customizations, set up argument lists.  In this
document, a list of valid argument names is provided in the discussion
of each widget.  The names each have a global symbol defined that begins
with \fBXtN\fP to help catch spelling errors.  For example,
\fBXtNlabel\fP is defined for the \fBlabel\fP resource of many widgets.
.IN "XtN" "" "@DEF@"
.IP
For further information, see Section 2.9.2.2.
.IP 5. 5
When the argument list is set up, create the widget with the
\fBXtCreateManagedWidget\fP function.  For further information, see
Section 2.2 and the \fI\*(xT\fP.
.IN "XtCreateManagedWidget"
.IP 6. 5
If the widget has any callback routines, set by the
.PN XtNcallback
argument or the
.PN XtAddCallback
function, declare these routines within the application.
.IN "XtAddCallback"
.IP 7. 5
After creating the initial widget hierarchy, windows must be created
for each widget by calling
.PN XtRealizeWidget
on the top level widget.
.IN "XtRealizeWidget"
.IP 8. 5
Most applications now sit in a loop processing events using
.PN XtAppMainLoop ,
for example:
.IN "XtAppMainLoop"
.IP
.Ds 0
XtCreateManagedWidget(\fIname\fP, \fIclass\fP, \fIparent\fP, \fIargs\fP, \fInum_args\fP);
XtRealizeWidget(\fIshell\fP);
XtAppMainLoop(\fIapp_context\fP);
.De
.IP
For information about this function, see the \fI\*(xT\fP.
.IP 9. 5
Link your application with
.PN libXaw
(the Athena widgets),
.PN libXmu
(miscellaneous utilities),
.PN libXt
(the \*(tk \*(xI),
.PN libSM
(Session Management),
.PN libICE
(Inter-Client Exchange),
.PN libXext
(the extension library needed for the shape extension code which allows
rounded Command buttons), and
.PN libX11
(the core X library).
The following provides a sample command line:
.IN "libXaw"
.IN "libXmu"
.IN "libXt"
.IN "libSM"
.IN "libICE"
.IN "libXext"
.IN "libX11"
.IN "linking applications"
.IN "compiling applications"
.IP
.Ds 0
cc -o \fIapplication\fP \fIapplication\fP.c \-lXaw \-lXmu \-lXt \
\-lSM \-lICE \-lXext \-lX11
.De
.NH 3
Changing Resource Values
.IN "resource" ""
.LP
The \*(xI support two methods of changing the default resource
values; the resource manager, and an argument list passed into
XtCreateWidget.  While resources values will get updated no matter
which method you use, the two methods provide slightly different
functionality.
.IP "Resource Manager" 1.5i
This method picks up resource definitions described in \fI\*(xL\fP from
many different locations at run time.  The locations most important to
the application programmer are the \fIfallback resources\fP and the
\fIapp-defaults\fP file, (see \fI\*(xT\fP for the complete list).
Since these resource are loaded at run time, they can be overridden by
the user, allowing an application to be customized to fit the
particular needs of each individual user.  These values can also be
modified without the need to rebuild the application, allowing rapid
prototyping of user interfaces.  Application programmers should use
resources in preference to hard-coded values whenever possible.
.IP "Argument Lists" 1.5i
The values passed into the widget at creation time via an argument list
cannot be modified by the user, and allow no opportunity for
customization.  It is used to set resources that cannot be specified as
strings (e.g. callback lists) or resources that should not be
overridden (e.g. window depth) by the user.
.NH 4
Specifying Resources
.LP
It is important for all X Toolkit application programmers to
understand how to use the X Resource Manager to specify resources for
widgets in an X application.  This section will describe the most common
methods used to specify these resources, and how to use the X Resource
manager.
.IN "xrdb"
.IP \fBXrdb\fP 1.5i
The \fBxrdb\fP utility may be used to load a file containing
resources into the X server.   Once the resources are loaded, the
resources will affect any new applications started on the display that
they were loaded onto.
.IN "application defaults"
.IN "app-defaults"
.IN "/usr/lib/X11/app-defaults"
.IP "\fBApplication Defaults\fP" 1.5i
The application defaults (app-defaults) file (normally in
/usr/lib/X11/app-defaults/\fIclassname\fP) for an application is loaded
whenever the application is started.
.LP
The resource specification has two colon-separated parts, a name, and
a value.  The \fIvalue\fP is a string whose format is dependent on the
resource specified by \fIname\fP.  \fIName\fP is constructed by
appending a resource name to a full widget name.
.LP
The full widget name is a list of the name of every ancestor of the
desired widget separated by periods (.).  Each widget also has a class
associated with it.  A class is a type of widget (e.g. Label or
Scrollbar or Box).  Notice that class names, by convention, begin with
capital letters and instance names begin with lower case letters.  The
class of any widget may be used in place of its name in a resource
specification.  Here are a few examples:
.IP xman.form.button1 1.5i
This is a fully specified resource name, and will affect only widgets
called button1 that are children of widgets called form that are
children of
applications named xman.  (Note that while typically two widgets that
are siblings will have different names, it is not prohibited.)

.IP Xman.Form.Command 1.5i
This will match any Command widget that is a child of a Form widget
that is itself a child of an application of class \fIXman\fP.
.IP Xman.Form.button1 1.5i
This is a mixed resource name with both widget names and classes specified.
.LP
This syntax allows an application programmer to specify any widget
in the widget tree.  To match more than one widget (for example a user
may want to make all Command buttons blue), use an asterisk (*)
instead of a period.  When an asterisk is used, any number of widgets
(including zero) may exist between the two widget names. For example:
.IP Xman*Command 1.5i
This matches all Command widgets in the Xman application.
.IP Foo*button1 1.5i
This matches any widget in the Foo application that is named \fIbutton1\fP.
.LP
The root of all application widget trees is the widget returned by
\fBXtAppInitialize\fP.  Even though this is actually an
ApplicationShell widget, the toolkit replaces its widget class with the
class name of the application.  The name of this widget is either
the name used to invoke the application (\fBargv[0]\fP) or the name of
the application specified using the standard \fI-name\fP command line
option supported by the \*(xI.
.LP
The last step in constructing the resource name is to append the name of
the resource with either a period or asterisk to the full or partial
widget name already constructed.
.IP *foreground:Blue 2.25i
Specifies that all widgets in all applications will have a foreground
color of blue.
.IP Xman*borderWidth:10 2.25i
Specifies that all widgets in an application whose class is Xman will
have a border width of 10 (pixels).
.IP xman.form.button1.label:Testing 2.25i
Specifies that a particular widget in the xman application will have a
label named \fITesting\fP.
.LP
An exclamation point (!) in the first column of a line indicates
that the rest of the line should be treated as a comment.
.LP
\fBFinal Words\fP
.LP
The Resource manager is a powerful tool that can be used very
effectively to customize \*(tk applications at run time by either the
application programmer or the user.  Some final points to note:
.IP \(bu 5
An application programmer may add new resources to their
application.  These resources are associated with the global
application, and not any particular widget.  The \*(tk function used for
adding the application resources is \fBXtGetApplicationResources\fP.
.IN "XtGetApplicationResources"
.IP \(bu 5
Be careful when creating resource files.  Since widgets will
ignore resources that they do not understand, any spelling
errors will cause a resource to have no effect.
.IP \(bu 5
Only one resource line will match any given resource.  There is a set
of precedence rules, which take the following general stance.
.ta 10n
.IP "" 5
\(bu	More specific overrides less specific, thus period always overrides asterisk.
.IP "" 5
\(bu	Names on the left are more specific and override names on the right.
.IP "" 5
\(bu	When resource specifications are exactly the same, user defaults
.br
	will override program defaults.
.LP
For a complete explanation of the rules of precedence, and
other specific topics see \fI\*(xT\fP and \fI\*(xL\fP.
.NH 4
Creating Argument Lists
.IN "argument lists" "" "@DEF@"
.LP
To set up an argument list for the inline specification of widget attributes,
you may use any of the four approaches discussed in this section.
Each resource name has a global symbol associated with it.  This
global symbol has the form XtN\fIresource name\fP.  For example, the
symbol for ``foreground'' is \fBXtNforeground\fP. For further information,
see the \fI\*(xT\fP.
.LP
Argument are specified by using the following structure:
.IN "ArgList" "" "@DEF@"
.IN "Arg" "" "@DEF@"
.LP
.Ds 0
.TA .5i 1.5i
.ta .5i 1.5i
typedef struct {
	String name;
	XtArgVal value;
} Arg, *ArgList;
.De
.LP
The first approach is to statically initialize the argument list.
For example:
.LP
.Ds 0
.TA .5i
.ta .5i
static Arg arglist[] = {
	{XtNwidth, (XtArgVal) 400},
	{XtNheight, (XtArgVal) 300},
};
.De
.LP
This approach is convenient for lists that do not need to be computed
at runtime and makes adding or deleting new elements easy.
The
.IN "XtNumber"
.PN XtNumber
macro is used to compute the number of elements in the argument list,
preventing simple programming errors:
.LP
.Ds
XtCreateWidget(\fIname\fP, \fIclass\fP, \fIparent\fP, \fIarglist\fP, XtNumber(\fIarglist\fP));
.De
.IN "XtSetArg" "" "@DEF@"
.LP
The second approach is to use the
.PN XtSetArg
macro.
For example:
.LP
.Ds 0
.TA .5i
.ta .5i
Arg arglist[10];
XtSetArg(arglist[1], XtNwidth, 400);
XtSetArg(arglist[2], XtNheight, 300);
.De
.LP
To make it easier to insert and delete entries,
you also can use a variable index:
.LP
.Ds 0
.TA .5i
.ta .5i
Arg arglist[10];
Cardinal i=0;
XtSetArg(arglist[i], XtNwidth,  400);       i++;
XtSetArg(arglist[i], XtNheight, 300);       i++;
.De
.LP
The i variable can then be used as the argument list count in the widget
create function.
In this example,
.IN "XtNumber"
.PN XtNumber
would return 10, not 2, and therefore is not useful.
.NT
You should not use auto-increment or auto-decrement
within the first argument to
.PN XtSetArg .
As it is currently implemented,
.PN XtSetArg
is a macro that dereferences the first argument twice.
.NE
.LP
The third approach is to individually set the elements of the
argument list array:
.LP
.Ds 0
.TA .5i
.ta .5i
Arg arglist[10];
arglist[0].name  = XtNwidth;
arglist[0].value = (XtArgVal) 400;
arglist[1].name  = XtNheight;
arglist[1].value = (XtArgVal) 300;
.De
.LP
Note that in this example, as in the previous example,
.IN "XtNumber"
.PN XtNumber
would return 10, not 2, and therefore would not be useful.
.LP
The fourth approach is to use a mixture of the first and third approaches:
you can statically define the argument list but modify some entries at runtime.
For example:
.LP
.Ds 0
.TA .5i
.ta .5i
static Arg arglist[] = {
	{XtNwidth, (XtArgVal) 400},
	{XtNheight, (XtArgVal) NULL},
};
arglist[1].value = (XtArgVal) 300;
.De
.LP
In this example,
.IN "XtNumber"
.PN XtNumber
can be used, as in the first approach, for easier code maintenance.
.NH 2
Example Programs
.XS
	Example Programs
.XE
.IN "examples"
.LP
The best way to understand how to use any programming library is by
trying some simple examples.  A collection of example programs that
introduces each of the widgets in that Athena widget set, as well as many
important toolkit programming concepts, is available in the X11R6
release as distributed by the X Consortium.  It can be found in the
distribution directory \fBcontrib/examples/mit/Xaw\fP, but see your
site administrator for the exact location of these files on your system.
See the README file from that directory for a guide to the examples.