NAME
glXChooseVisual - return a visual that matches specified
attributes
C SPECIFICATION
XVisualInfo* glXChooseVisual( Display *dpy,
int screen,
int *attribList )
delim $$
PARAMETERS
dpy Specifies the connection to the X server.
screen Specifies the screen number.
attribList Specifies a list of Boolean attributes and
integer attribute/value pairs. The last attri-
bute must be None.
DESCRIPTION
glXChooseVisual returns a pointer to an XVisualInfo struc-
ture describing the visual that best meets a minimum specif-
ication. The Boolean GLX attributes of the visual that is
returned will match the specified values, and the integer
GLX attributes will meet or exceed the specified minimum
values. If all other attributes are equivalent, then
TrueColor and PseudoColor visuals have priority over
DirectColor and StaticColor visuals, respectively. If no
conforming visual exists, NULL is returned. To free the
data returned by this function, use XFree.
All Boolean GLX attributes default to False except
GLX_USE_GL, which defaults to True. All integer GLX attri-
butes default to zero. Default specifications are super-
seded by attributes included in attribList. Boolean attri-
butes included in attribList are understood to be True.
Integer attributes are followed immediately by the
corresponding desired or minimum value. The list must be
terminated with None.
The interpretations of the various GLX visual attributes are
as follows:
GLX_USE_GL Ignored. Only visuals that can be
rendered with GLX are considered.
GLX_BUFFER_SIZE Must be followed by a nonnegative
integer that indicates the desired
color index buffer size. The smallest
index buffer of at least the specified
size is preferred. Ignored if
GLX_RGBA is asserted.
GLX_LEVEL Must be followed by an integer
buffer-level specification. This
specification is honored exactly.
Buffer level zero corresponds to the
default frame buffer of the display.
Buffer level one is the first overlay
frame buffer, level two the second
overlay frame buffer, and so on.
Negative buffer levels correspond to
underlay frame buffers.
GLX_RGBA If present, only TrueColor and
DirectColor visuals are considered.
Otherwise, only PseudoColor and Sta-
ticColor visuals are considered.
GLX_DOUBLEBUFFER If present, only double-buffered visu-
als are considered. Otherwise, only
single-buffered visuals are con-
sidered.
GLX_STEREO If present, only stereo visuals are
considered. Otherwise, only monos-
copic visuals are considered.
GLX_AUX_BUFFERS Must be followed by a nonnegative
integer that indicates the desired
number of auxiliary buffers. Visuals
with the smallest number of auxiliary
buffers that meets or exceeds the
specified number are preferred.
GLX_RED_SIZE Must be followed by a nonnegative
minimum size specification. If this
value is zero, the smallest available
red buffer is preferred. Otherwise,
the largest available red buffer of at
least the minimum size is preferred.
GLX_GREEN_SIZE Must be followed by a nonnegative
minimum size specification. If this
value is zero, the smallest available
green buffer is preferred. Otherwise,
the largest available green buffer of
at least the minimum size is pre-
ferred.
GLX_BLUE_SIZE Must be followed by a nonnegative
minimum size specification. If this
value is zero, the smallest available
blue buffer is preferred. Otherwise,
the largest available blue buffer of
at least the minimum size is pre-
ferred.
GLX_ALPHA_SIZE Must be followed by a nonnegative
minimum size specification. If this
value is zero, the smallest available
alpha buffer is preferred. Otherwise,
the largest available alpha buffer of
at least the minimum size is pre-
ferred.
GLX_DEPTH_SIZE Must be followed by a nonnegative
minimum size specification. If this
value is zero, visuals with no depth
buffer are preferred. Otherwise, the
largest available depth buffer of at
least the minimum size is preferred.
GLX_STENCIL_SIZE Must be followed by a nonnegative
integer that indicates the desired
number of stencil bitplanes. The
smallest stencil buffer of at least
the specified size is preferred. If
the desired value is zero, visuals
with no stencil buffer are preferred.
GLX_ACCUM_RED_SIZE Must be followed by a nonnegative
minimum size specification. If this
value is zero, visuals with no red
accumulation buffer are preferred.
Otherwise, the largest possible red
accumulation buffer of at least the
minimum size is preferred.
GLX_ACCUM_GREEN_SIZE Must be followed by a nonnegative
minimum size specification. If this
value is zero, visuals with no green
accumulation buffer are preferred.
Otherwise, the largest possible green
accumulation buffer of at least the
minimum size is preferred.
GLX_ACCUM_BLUE_SIZE Must be followed by a nonnegative
minimum size specification. If this
value is zero, visuals with no blue
accumulation buffer are preferred.
Otherwise, the largest possible blue
accumulation buffer of at least the
minimum size is preferred.
GLX_ACCUM_ALPHA_SIZE Must be followed by a nonnegative
minimum size specification. If this
value is zero, visuals with no alpha
accumulation buffer are preferred.
Otherwise, the largest possible alpha
accumulation buffer of at least the
minimum size is preferred.
EXAMPLES
attribList =
{GLX_RGBA, GLX_RED_SIZE, 4, GLX_GREEN_SIZE, 4,
GLX_BLUE_SIZE, 4, None};
Specifies a single-buffered RGB visual in the normal frame
buffer, not an overlay or underlay buffer. The returned
visual supports at least four bits each of red, green, and
blue, and possibly no bits of alpha. It does not support
color index mode, double-buffering, or stereo display. It
may or may not have one or more auxiliary color buffers, a
depth buffer, a stencil buffer, or an accumulation buffer.
NOTES
XVisualInfo is defined in Xutil.h. It is a structure that
includes visual, visualID, screen, and depth elements.
glXChooseVisual is implemented as a client-side utility
using only XGetVisualInfo and glXGetConfig. Calls to these
two routines can be used to implement selection algorithms
other than the generic one implemented by glXChooseVisual.
GLX implementers are strongly discouraged, but not pros-
cribed, from changing the selection algorithm used by
glXChooseVisual. Therefore, selections may change from
release to release of the client-side library.
There is no direct filter for picking only visuals that sup-
port GLXPixmaps. GLXPixmaps are supported for visuals whose
GLX_BUFFER_SIZE. is one of the Pixmap depths supported by
the X server.
ERRORS
NULL is returned if an undefined GLX attribute is encoun-
tered in attribList.
SEE ALSO
glXCreateContext, glXGetConfig
Acknowledgement and Disclaimer