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 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.
