XVisualInfo *visua )

PARAMETERS
       dpy    Specifies the connection to the X server.

       visua  Specifies  the  visual  to  be  queried.   It  is a pointer to an
              XVisualInfo structure, not a visual ID or a pointer to a Visual.

       _param3
              Specifies the visual attribute to be returned.

       _param4
              Returns the requested value.

DESCRIPTION
       glXGetConfig sets _param4 to the _param3 value of windows or GLX pixmaps
       created with respect to visua.  glXGetConfig returns an error code if it
       fails for any reason.  Otherwise, zero is returned.

       _param3 is one of the following:

       GLX_USE_GL            True if OpenGL rendering is supported by this vis‐
                             ual, False otherwise.

       GLX_BUFFER_SIZE       Number  of  bits per color buffer.  For RGBA visu‐
                             als, GLX_BUFFER_SIZE is the sum  of  GLX_RED_SIZE,
                             GLX_GREEN_SIZE, GLX_BLUE_SIZE, and GLX_ALPHA_SIZE.
                             For color index visuals,  GLX_BUFFER_SIZE  is  the
                             size of the color indexes.

       GLX_LEVEL             Frame  buffer  level of the visual.  Level zero is
                             the default frame buffer.  Positive levels  corre‐
                             spond  to  frame  buffers that overlay the default
                             buffer, and negative levels  correspond  to  frame
                             buffers that underlay the default buffer.

       GLX_RGBA              True  if color buffers store red, green, blue, and
                             alpha values.  False if they store color indexes.

       GLX_DOUBLEBUFFER      True if color buffers exist  in  front/back  pairs
                             that can be swapped, False otherwise.

       GLX_STEREO            True  if  color buffers exist in left/right pairs,
                             False otherwise.

       GLX_AUX_BUFFERS       Number of auxiliary color buffers that are  avail‐
                             able.  Zero indicates that no auxiliary color buf‐
                             fers exist.

       GLX_RED_SIZE          Number of bits of red stored in each color buffer.
                             Undefined if GLX_RGBA is False.

                             buffer.

       GLX_ACCUM_GREEN_SIZE  Number of bits of green stored in the accumulation
                             buffer.

       GLX_ACCUM_BLUE_SIZE   Number of bits of blue stored in the  accumulation
                             buffer.

       GLX_ACCUM_ALPHA_SIZE  Number of bits of alpha stored in the accumulation
                             buffer.

       The X protocol allows a single visual ID to be instantiated with differ‐
       ent numbers of bits per pixel.  Windows or GLX pixmaps that will be ren‐
       dered with OpenGL, however, must be instantiated  with  a  color  buffer
       depth of GLX_BUFFER_SIZE.

       Although  a  GLX  implementation can export many visuals that support GL
       rendering, it must support at least one RGBA visual.  This  visual  must
       have  at  least  one color buffer, a stencil buffer of at least 1 bit, a
       depth buffer of at least 12 bits, and  an  accumulation  buffer.   Alpha
       bitplanes  are  optional in this visual.  However, its color buffer size
       must be  as  great  as  that  of  the  deepest  TrueColor,  DirectColor,
       PseudoColor,  or StaticColor visual supported on level zero, and it must
       itself be made available on level zero.

       In addition, if the X server exports a PseudoColor or StaticColor visual
       on  framebuffer  level  0, a color index visual is also required on that
       level.  It must have at least one color buffer, a stencil buffer  of  at
       least  1  bit, and a depth buffer of at least 12 bits.  This visual must
       have as many color bitplanes as the deepest PseudoColor  or  StaticColor
       visual supported on level 0.

       Applications  are  best  written  to select the visual that most closely
       meets their requirements.  Creating windows or GLX pixmaps with unneces‐
       sary buffers can result in reduced rendering performance as well as poor
       resource allocation.

NOTES
       XVisualInfo is defined in Xutil.h.  It is a structure that includes vis‐
       ual, visualID, screen, and depth elements.

ERRORS
       GLX_NO_EXTENSION is returned if dpy does not support the GLX extension.

       GLX_BAD_SCREEN is returned if the screen of visua does not correspond to
       a screen.

       GLX_BAD_ATTRIBUTE is returned if _param3 is not a valid GLX attribute.

       GLX_BAD_VISUAL is returned if visua doesn't support GLX and an attribute
       other than GLX_USE_GL is requested.