glXChooseVisual
GLXCHOOSEVISUAL() GLXCHOOSEVISUAL()
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 attribute must be None.
DESCRIPTION
glXChooseVisual returns a pointer to an XVisualInfo structure describ-
ing the visual that best meets a minimum specification. 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 speci-
fied 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 attributes default to zero.
Default specifications are superseded by attributes included in attri-
bList. Boolean attributes included in attribList are understood to be
True. Integer attributes and enumerated type 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 fol-
lows:
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 speci-
fied 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
main 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 visu-
als are considered. Otherwise, only PseudoColor
and StaticColor visuals are considered.
GLX_DOUBLEBUFFER If present, only double-buffered visuals are
considered. Otherwise, only single-buffered
visuals are considered.
GLX_STEREO If present, only stereo visuals are considered.
Otherwise, only monoscopic visuals are consid-
ered.
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 preferred.
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 preferred.
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 preferred.
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 bit-
planes. 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 pre-
ferred.
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 accumula-
tion buffer of at least the minimum size is pre-
ferred.
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 accumula-
tion buffer of at least the minimum size is pre-
ferred.
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 accumula-
tion buffer of at least the minimum size is pre-
ferred.
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 dis-
play. 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 proscribed, 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 support GLX-
Pixmaps. 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 encountered in
attribList.
SEE ALSO
glXCreateContext, glXGetConfig
GLXCHOOSEVISUAL()
