GLXCHOOSEVISUAL(3G)

NAME
glXChooseVisual - return a visual that matches specified attributes

C SPECIFICATION
XVisualInfo* glXChooseVisual( Display *dpy,
	int screen,
	int *attribList )

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 describing 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 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 attributes default to zero. Default specifications are superseded by attributes included in attribList. 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 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 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 visuals 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 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 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 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 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 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 encountered in attribList.

SEE ALSO
glXCreateContext, glXGetConfig