XDoes*() XDoes*()
Name
XDoesBackingStore, XDoesSaveUnders, DoesBackingStore, DoesSaveUnders –
query server support for backing store or save unders.
Synopsis
int XDoesBackingStore(screen)
Screen *screen;
Bool XDoesSaveUnders(screen)
Screen *screen;
Arguments
screen Specifies the appropriate Screen structure.
ReturnsXDoesSaveUnders() returns True or False. XDoesBackingStore() returns
WhenMapped, NotUseful, or Always.
DescriptionXDoesSaveUnders() returns a boolean value indicating whether the screen
supports save unders. If True, the screen supports save unders. If
False, the screen does not support save unders.
XDoesBackingStore() returns a value indicating whether the screen sup‐
ports backing stores. The value returned can be one of WhenMapped,
NotUseful, or Always.
Save unders and backing stores are optional server features controlled
with window attributes. These macros tell you whether the server sup‐
ports them. A "save under" is an area beneath a window (usually a menu
or dialog box) that the server saves, so that when the window is
removed from the screen, the underlying applications do not need to
redraw their windows. This speeds up user response with a slight cost
in increased server memory consumption. A "backing store" is an off-
screen copy of a window, maintained even when the window is not visible
or not mapped. The server uses the copy to redraw the window whenever
that window would otherwise have received an Expose event. This
reduces the load on applications at the expense of a possibly great
increase in server memory usage.
The C language macros DoesSaveUnders() and DoesBackingStore() are
equivalent and slightly more efficient.
See AlsoXChangeWindowAttributes(), XGetWindowAttributes().
Xlib - Macro Equivalents XDoes*()
