XdbeGetVisualInfo(3XX1Version 11 (Release XdbeGetVisualInfo(3X11)
NAME
XdbeGetVisualInfo
SYNOPSIS
#include <X11/extensions/Xdbe.h>
XdbeScreenVisualInfo *XdbeGetVisualInfo(
Display *dpy,
Drawable *screen_specifiers,
int *num_screens)
DESCRIPTION
This function returns information about which visuals
support double buffering. The argument num_screens
specifies how many elements there are in the
screen_specifiers list. Each drawable in screen_specifiers
designates a screen for which the supported visuals are
being requested. If num_screens is zero, information for
all screens is requested. In this case, upon return from
this function, num_screens will be set to the number of
screens that were found. If an error occurs, this function
returns NULL, else it returns a pointer to a list of
XdbeScreenVisualInfo structures of length num_screens. The
nth element in the returned list corresponds to the nth
drawable in the screen_specifiers list, unless num_screens
was passed in with the value zero, in which case the nth
element in the returned list corresponds to the nth screen
of the server, starting with screen zero. The
XdbeScreenVisualInfo structure has the following fields:
int count
XdbeVisualInfo *visinfo
count specifies the number of items in visinfo. visinfo
specifies a list of visuals, depths, and performance hints
for this screen.
The XdbeVisualInfo structure has the following fields:
VisualID visual
int depth
int perflevel
visual specifies one visual ID that supports double-
buffering. depth specifies the depth of the visual.
perflevel is a performance hint.
The only operation defined on a perflevel is comparison to a
perflevel of another visual on the same screen. The visual
having the higher perflevel is likely to have better
double-buffering graphics performance than the visual having
the lower perflevel. Nothing can be deduced from the
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XdbeGetVisualInfo(3XX1Version 11 (Release XdbeGetVisualInfo(3X11)
following: the magnitude of the difference of two
perflevels, a perflevel value in isolation, or comparing
perflevels from different servers.
ERRORS
BadDrawable
One or more values passed in screen_specifiers is not a
valid drawable.
SEE ALSO
DBE, XdbeAllocateBackBufferName(), XdbeBeginIdiom(),
XdbeDeallocateBackBufferName(), XdbeEndIdiom(),
XdbeFreeVisualInfo(), XdbeGetBackBufferAttributes(),
XdbeQueryExtension(), XdbeSwapBuffers().
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