glXGetVideoSyncSGI(3G)

NAME
     glXGetVideoSyncSGI - obtain value of vertical retrace counter


C SPECIFICATION
     int glXGetVideoSyncSGI( unsigned int *count )


PARAMETERS
     count  Pointer to variable which receives the value of the vertical
            retrace counter of the graphics pipeline associated with the
            current context.


DESCRIPTION
     glXGetVideoSyncSGI is part of the SGI_video_sync extension.  This
     extension provides a way to synchronize with the video frame rate of a
     monitor (in the case of an interlaced display, the synchronization is
     actually with the field rate).

     A vertical retrace precedes the display of each video frame.  The kernel
     maintains a 32-bit unsigned integer counter for each graphics pipe in the
     system.  This counter is initialized via the /usr/gfx/gfxinit command,
     and incremented upon each vertical retrace.  Since all the video output
     channels of a graphics pipe must be genlocked, one counter suffices for
     all the monitors driven by a pipe.

     A process can query or sleep on the counter of the graphics pipe
     associated with its current OpenGL rendering context, provided that the
     rendering context is direct.  (See glXCreateContext.)

     If the current context is direct, glXGetVideoSyncSGI places the value of
     the vertical retrace counter in the location referenced by count, then
     returns zero.  Otherwise, glXGetVideoSyncSGI returns GLX_BAD_CONTEXT_SGI.



SEE ALSO
     glXWaitVideoSyncSGI, glXCreateContext, glXQueryVersion, glGetString