glXGetVideoSyncSGI(3G)	    OpenGL Reference - GLX	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
















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