Window and Session Manager Functions
Although it is difficult to categorize functions as exclusively for an application,
a window manager, or a session manager, the functions in this chapter are most
often used by window managers and session managers. It is not expected that
these functions will be used by most application programs. Xlib provides
management functions to:
Change the parent of a windowControl the lifetime of a windowManage installed colormapsSet and retrieve the font search pathGrab the serverKill a clientControl the screen saverControl host accessChanging the Parent of a Window
To change a window's parent to another window on the same screen, use
.
There is no way to move a window between screens.
XReparentWindowXReparentWindowDisplay *displayWindow wWindow parentintx, ydisplay
Specifies the connection to the X server.
w
Specifies the window.
parent
Specifies the parent window.
xy
Specify the x and y coordinates(Xy.
If the specified window is mapped,
automatically performs an
UnmapWindow
request on it, removes it from its current position in the hierarchy,
and inserts it as the child of the specified parent.
The window is placed in the stacking order on top with respect to
sibling windows.
After reparenting the specified window,
causes the X server to generate a
ReparentNotify
event.
The override_redirect member returned in this event is
set to the window's corresponding attribute.
Window manager clients usually should ignore this window if this member
is set to
True.
Finally, if the specified window was originally mapped,
the X server automatically performs a
MapWindow
request on it.
The X server performs normal exposure processing on formerly obscured
windows.
The X server might not generate
Expose
events for regions from the initial
UnmapWindow
request that are immediately obscured by the final
MapWindow
request.
A
BadMatch
error results if:
The new parent window is not on the same screen as
the old parent window.
The new parent window is the specified window or an inferior of the
specified window.
The new parent is
InputOnly,
and the window is not.
The specified window has a
ParentRelative
background, and the new parent window is not the same depth as the
specified window.
can generate
BadMatch
and
BadWindow
errors.
Controlling the Lifetime of a Window
The save-set of a client is a list of other clients' windows that,
if they are inferiors of one of the client's windows at connection close,
should not be destroyed and should be remapped if they are unmapped.
For further information about close-connection processing,
see section 2.6.
To allow an application's window to survive when a window manager that
has reparented a window fails,
Xlib provides the save-set functions that you can
use to control the longevity of subwindows
that are normally destroyed when the parent is destroyed.
For example, a window manager that wants to add decoration
to a window by adding a frame might reparent an application's
window.
When the frame is destroyed,
the application's window should not be destroyed
but be returned to its previous place in the window hierarchy.
The X server automatically removes windows from the save-set
when they are destroyed.
To add or remove a window from the client's save-set, use
.
XChangeSaveSetXChangeSaveSetDisplay *displayWindow wint change_modedisplay
Specifies the connection to the X server.
w
Specifies the window (Wi.
change_mode
Specifies the mode.
You can pass
SetModeInsert
or
SetModeDelete.
Depending on the specified mode,
either inserts or deletes the specified window from the client's save-set.
The specified window must have been created by some other client,
or a
BadMatch
error results.
can generate
BadMatch,
BadValue,
and
BadWindow
errors.
To add a window to the client's save-set, use
.
XAddToSaveSetXAddToSaveSetDisplay *displayWindow wdisplay
Specifies the connection to the X server.
w
Specifies the window (Wi.
The
function adds the specified window to the client's save-set.
The specified window must have been created by some other client,
or a
BadMatch
error results.
can generate
BadMatch
and
BadWindow
errors.
To remove a window from the client's save-set, use
.
XRemoveFromSaveSetXRemoveFromSaveSetDisplay *displayWindow wdisplay
Specifies the connection to the X server.
w
Specifies the window (Wi.
The
function removes the specified window from the client's save-set.
The specified window must have been created by some other client,
or a
BadMatch
error results.
can generate
BadMatch
and
BadWindow
errors.
Managing Installed Colormaps
The X server maintains a list of installed colormaps.
Windows using these colormaps are guaranteed to display with
correct colors; windows using other colormaps may or may not display
with correct colors.
Xlib provides functions that you can use to install a colormap,
uninstall a colormap, and obtain a list of installed colormaps.
At any time,
there is a subset of the installed maps that is viewed as an ordered list
and is called the required list.
The length of the required list is at most M,
where M is the minimum number of installed colormaps specified for the screen
in the connection setup.
The required list is maintained as follows.
When a colormap is specified to
,
it is added to the head of the list;
the list is truncated at the tail, if necessary, to keep its length to
at most M.
When a colormap is specified to
and it is in the required list,
it is removed from the list.
A colormap is not added to the required list when it is implicitly installed
by the X server,
and the X server cannot implicitly uninstall a colormap that is in the
required list.
To install a colormap, use
.
XInstallColormapXInstallColormapDisplay *displayColormap colormapdisplay
Specifies the connection to the X server.
colormap
Specifies the colormap.
The
function installs the specified colormap for its associated screen.
All windows associated with this colormap immediately display with
true colors.
You associated the windows with this colormap when you created them by calling
,
,
,
or
.
If the specified colormap is not already an installed colormap,
the X server generates a
ColormapNotify
event on each window that has that colormap.
In addition, for every other colormap that is installed as
a result of a call to
,
the X server generates a
ColormapNotify
event on each window that has that colormap.
can generate a
BadColor
error.
To uninstall a colormap, use
.
XUninstallColormapXUninstallColormapDisplay *displayColormap colormapdisplay
Specifies the connection to the X server.
colormap
Specifies the colormap.
The
function removes the specified colormap from the required
list for its screen.
As a result,
the specified colormap might be uninstalled,
and the X server might implicitly install or uninstall additional colormaps.
Which colormaps get installed or uninstalled is server dependent
except that the required list must remain installed.
If the specified colormap becomes uninstalled,
the X server generates a
ColormapNotify
event on each window that has that colormap.
In addition, for every other colormap that is installed or uninstalled as a
result of a call to
,
the X server generates a
ColormapNotify
event on each window that has that colormap.
can generate a
BadColor
error.
To obtain a list of the currently installed colormaps for a given screen, use
.
XListInstalledColormapsColormap *XListInstalledColormapsDisplay *displayWindow wint *num_returndisplay
Specifies the connection to the X server.
w
Specifies the window (Wi.
num_return
Returns the number of currently installed colormaps.
The
function returns a list of the currently installed colormaps for the screen
of the specified window.
The order of the colormaps in the list is not significant
and is no explicit indication of the required list.
When the allocated list is no longer needed,
free it by using
.
can generate a
BadWindow
error.
Setting and Retrieving the Font Search Path
The set of fonts available from a server depends on a font
search path. Xlib provides functions to set and retrieve the
search path for a server.
To set the font search path, use
.
XSetFontPathXSetFontPathDisplay *displaychar **directoriesint ndirsdisplay
Specifies the connection to the X server.
directories
Specifies the directory path used to look for a font.
Setting the path to the empty list restores the default path defined
for the X server.
ndirs
Specifies the number of directories in the path.
The
function defines the directory search path for font lookup.
There is only one search path per X server, not one per client.
The encoding and interpretation of the strings are implementation-dependent,
but typically they specify directories or font servers to be searched
in the order listed.
An X server is permitted to cache font information internally;
for example, it might cache an entire font from a file and not
check on subsequent opens of that font to see if the underlying
font file has changed.
However,
when the font path is changed,
the X server is guaranteed to flush all cached information about fonts
for which there currently are no explicit resource IDs allocated.
The meaning of an error from this request is implementation-dependent.
can generate a
BadValue
error.
To get the current font search path, use
.
XGetFontPathchar **XGetFontPathDisplay *displayint *npaths_returndisplay
Specifies the connection to the X server.
npaths_return
Returns the number of strings in the font path array.
The
function allocates and returns an array of strings containing the search path.
The contents of these strings are implementation-dependent
and are not intended to be interpreted by client applications.
When it is no longer needed,
the data in the font path should be freed by using
.
To free data returned by
,
use
.
XFreeFontPathXFreeFontPathchar **listlist
Specifies the array of strings you want to free.
The
function
frees the data allocated by
.
Grabbing the Server
Xlib provides functions that you can use to grab and ungrab the server.
These functions can be used to control processing of output on other
connections by the window system server.
While the server is grabbed,
no processing of requests or close downs on any other connection will occur.
A client closing its connection automatically ungrabs the server.
MenusWindowmanagers
Although grabbing the server is highly discouraged, it is sometimes necessary.
To grab the server, use
.
ServergrabbingGrabbingserverXGrabServerXGrabServerDisplay *displaydisplay
Specifies the connection to the X server.
The
function disables processing of requests and close downs on all other
connections than the one this request arrived on.
You should not grab the X server any more than is absolutely necessary.
To ungrab the server, use
.
XUngrabServerXUngrabServerDisplay *displaydisplay
Specifies the connection to the X server.
The
function restarts processing of requests and close downs on other connections.
You should avoid grabbing the X server as much as possible.
Killing Clients
Xlib provides a function to cause the connection to
a client to be closed and its resources to be destroyed.
To destroy a client, use
.
XKillClientXKillClientDisplay *displayXID resourcedisplay
Specifies the connection to the X server.
resource
Specifies any resource associated with the client that you want to destroy or
AllTemporary.
The
function
forces a close down of the client
that created the resource
if a valid resource is specified.
If the client has already terminated in
either
RetainPermanent
or
RetainTemporary
mode, all of the client's
resources are destroyed.
If
AllTemporary
is specified, the resources of all clients that have terminated in
RetainTemporary
are destroyed (see section 2.5).
This permits implementation of window manager facilities that aid debugging.
A client can set its close-down mode to
RetainTemporary.
If the client then crashes,
its windows would not be destroyed.
The programmer can then inspect the application's window tree
and use the window manager to destroy the zombie windows.
can generate a
BadValue
error.
Controlling the Screen Saver
Xlib provides functions that you can use to set or reset the mode
of the screen saver, to force or activate the screen saver,
or to obtain the current screen saver values.
To set the screen saver mode, use
.
XSetScreenSaverXSetScreenSaverDisplay *displayinttimeout, intervalint prefer_blankingint allow_exposuresdisplay
Specifies the connection to the X server.
timeout
Specifies the timeout, in seconds, until the screen saver turns on.
interval
Specifies the interval, in seconds, between screen saver alterations.
prefer_blanking
Specifies how to enable screen blanking.
You can pass
DontPreferBlanking,
PreferBlanking,
or
DefaultBlanking.
allow_exposures
Specifies the screen save control values.
You can pass
DontAllowExposures,
AllowExposures,
or
DefaultExposures.
Timeout and interval are specified in seconds.
A timeout of 0 disables the screen saver
(but an activated screen saver is not deactivated),
and a timeout of −1 restores the default.
Other negative values generate a
BadValue
error.
If the timeout value is nonzero,
enables the screen saver.
An interval of 0 disables the random-pattern motion.
If no input from devices (keyboard, mouse, and so on) is generated
for the specified number of timeout seconds once the screen saver is enabled,
the screen saver is activated.
For each screen,
if blanking is preferred and the hardware supports video blanking,
the screen simply goes blank.
Otherwise, if either exposures are allowed or the screen can be regenerated
without sending
Expose
events to clients,
the screen is tiled with the root window background tile randomly
re-origined each interval seconds.
Otherwise, the screens' state do not change,
and the screen saver is not activated.
The screen saver is deactivated,
and all screen states are restored at the next
keyboard or pointer input or at the next call to
with mode
ScreenSaverReset.
If the server-dependent screen saver method supports periodic change,
the interval argument serves as a hint about how long the change period
should be, and zero hints that no periodic change should be made.
Examples of ways to change the screen include scrambling the colormap
periodically, moving an icon image around the screen periodically, or tiling
the screen with the root window background tile, randomly re-origined
periodically.
can generate a
BadValue
error.
To force the screen saver on or off, use
.
XForceScreenSaverXForceScreenSaverDisplay *displayint modedisplay
Specifies the connection to the X server.
mode
Specifies the mode that is to be applied.
You can pass
ScreenSaverActive
or
ScreenSaverReset.
If the specified mode is
ScreenSaverActive
and the screen saver currently is deactivated,
activates the screen saver even if the screen saver had been disabled
with a timeout of zero.
If the specified mode is
ScreenSaverReset
and the screen saver currently is enabled,
deactivates the screen saver if it was activated,
and the activation timer is reset to its initial state
(as if device input had been received).
can generate a
BadValue
error.
To activate the screen saver, use
.
XActivateScreenSaverXActivateScreenSaverDisplay *displaydisplay
Specifies the connection to the X server.
To reset the screen saver, use
.
XResetScreenSaverXResetScreenSaverDisplay *displaydisplay
Specifies the connection to the X server.
To get the current screen saver values, use
.
XGetScreenSaverXGetScreenSaverDisplay *displayint*timeout_return, *interval_returnint *prefer_blanking_returnint *allow_exposures_returndisplay
Specifies the connection to the X server.
timeout_return
Returns the timeout, in seconds, until the screen saver turns on.
interval_return
Returns the interval between screen saver invocations.
prefer_blanking_return
Returns the current screen blanking preference
(DontPreferBlanking,
PreferBlanking,
or
DefaultBlanking).
allow_exposures_return
Returns the current screen save control value
(DontAllowExposures,
AllowExposures,
or
DefaultExposures).
Controlling Host Access
This section discusses how to:
Add, get, or remove hosts from the access control list
Change, enable, or disable access
Access control listAuthentication
X does not provide any protection on a per-window basis.
If you find out the resource ID of a resource, you can manipulate it.
To provide some minimal level of protection, however,
connections are permitted only from machines you trust.
This is adequate on single-user workstations but obviously
breaks down on timesharing machines.
Although provisions exist in the X protocol for proper connection
authentication, the lack of a standard authentication server
leaves host-level access control as the only common mechanism.
Default Protection
The initial set of hosts allowed to open connections typically consists of:
The host the window system is running on.
On POSIX-conformant systems, each host listed in the
/etc/X?.hosts
file.
The ? indicates the number of the
display.
Files/etc/X?.hosts
This file should consist of host names separated by newlines.
DECnet nodes must terminate in :: to distinguish them from Internet hosts.
If a host is not in the access control list when the access control
mechanism is enabled and if the host attempts to establish a connection,
the server refuses the connection.
To change the access list,
the client must reside on the same host as the server and/or must
have been granted permission in the initial authorization at connection
setup.
Servers also can implement other access control policies in addition to
or in place of this host access facility.
For further information about other access control implementations,
see ``X Window System Protocol.''
Adding, Getting, or Removing Hosts
Xlib provides functions that you can use to add, get, or remove hosts
from the access control list.
All the host access control functions use the
XHostAddress
structure, which contains:
XHostAddress
typedef struct {
int family; /* for example FamilyInternet */
int length; /* length of address, in bytes */
char *address; /* pointer to where to find the address */
} XHostAddress;
The family member specifies which protocol address family to use
(for example, TCP/IP or DECnet) and can be
FamilyInternet,
FamilyInternet6,
FamilyServerInterpreted,
FamilyDECnet,
or
FamilyChaos.
The length member specifies the length of the address in bytes.
The address member specifies a pointer to the address.
For TCP/IP, the address should be in network byte order.
For IP version 4 addresses, the family should be FamilyInternet
and the length should be 4 bytes. For IP version 6 addresses, the
family should be FamilyInternet6 and the length should be 16 bytes.
For the DECnet family,
the server performs no automatic swapping on the address bytes.
A Phase IV address is 2 bytes long.
The first byte contains the least significant 8 bits of the node number.
The second byte contains the most significant 2 bits of the
node number in the least significant 2 bits of the byte
and the area in the most significant 6 bits of the byte.
For the ServerInterpreted family, the length is ignored and the address
member is a pointer to a
XServerInterpretedAddress
structure, which contains:
XServerInterpretedAddress
typedef struct {
int typelength; /* length of type string, in bytes */
int valuelength; /* length of value string, in bytes */
char *type; /* pointer to where to find the type string */
char *value; /* pointer to where to find the address */
} XServerInterpretedAddress;
The type and value members point to strings representing the type and value of
the server interpreted entry. These strings may not be NULL-terminated so care
should be used when accessing them. The typelength and valuelength members
specify the length in byte of the type and value strings.
To add a single host, use
.
XAddHostXAddHostDisplay *displayXHostAddress *hostdisplay
Specifies the connection to the X server.
host
Specifies the host that is to be (Ho.
The
function adds the specified host to the access control list for that display.
The server must be on the same host as the client issuing the command, or a
BadAccess
error results.
can generate
BadAccess
and
BadValue
errors.
To add multiple hosts at one time, use
.
XAddHostsXAddHostsDisplay *displayXHostAddress *hostsint num_hostsdisplay
Specifies the connection to the X server.
hosts
Specifies each host that is to be (Ho.
num_hosts
Specifies the number of hosts.
The
function adds each specified host to the access control list for that display.
The server must be on the same host as the client issuing the command, or a
BadAccess
error results.
can generate
BadAccess
and
BadValue
errors.
To obtain a host list, use
.
XListHostsXHostAddress *XListHostsDisplay *displayint *nhosts_returnBool *state_returndisplay
Specifies the connection to the X server.
nhosts_return
Returns the number of hosts currently in the access control list.
state_return
Returns the state of the access control.
The
function returns the current access control list as well as whether the use
of the list at connection setup was enabled or disabled.
allows a program to find out what machines can make connections.
It also returns a pointer to a list of host structures that
were allocated by the function.
When no longer needed,
this memory should be freed by calling
.
To remove a single host, use
.
XRemoveHostXRemoveHostDisplay *displayXHostAddress *hostdisplay
Specifies the connection to the X server.
host
Specifies the host that is to be (Ho.
The
function removes the specified host from the access control list
for that display.
The server must be on the same host as the client process, or a
BadAccess
error results.
If you remove your machine from the access list,
you can no longer connect to that server,
and this operation cannot be reversed unless you reset the server.
can generate
BadAccess
and
BadValue
errors.
To remove multiple hosts at one time, use
.
XRemoveHostsXRemoveHostsDisplay *displayXHostAddress *hostsint num_hostsdisplay
Specifies the connection to the X server.
hosts
Specifies each host that is to be (Ho.
num_hosts
Specifies the number of hosts.
The
function removes each specified host from the access control list for that
display.
The X server must be on the same host as the client process, or a
BadAccess
error results.
If you remove your machine from the access list,
you can no longer connect to that server,
and this operation cannot be reversed unless you reset the server.
can generate
BadAccess
and
BadValue
errors.
Changing, Enabling, or Disabling Access Control
Xlib provides functions that you can use to enable, disable,
or change access control.
For these functions to execute successfully,
the client application must reside on the same host as the X server
and/or have been given permission in the initial authorization
at connection setup.
To change access control, use
.
XSetAccessControlXSetAccessControlDisplay *displayint modedisplay
Specifies the connection to the X server.
mode
Specifies the mode.
You can pass
EnableAccess
or
DisableAccess.
The
function either enables or disables the use of the access control list
at each connection setup.
can generate
BadAccess
and
BadValue
errors.
To enable access control, use
.
XEnableAccessControlXEnableAccessControlDisplay *displaydisplay
Specifies the connection to the X server.
The
function enables the use of the access control list at each connection setup.
can generate a
BadAccess
error.
To disable access control, use
.
XDisableAccessControlXDisableAccessControlDisplay *displaydisplay
Specifies the connection to the X server.
The
function disables the use of the access control list at each connection setup.
can generate a
BadAccess
error.