video_sync



This extension provides a means for synchronization with the video frame rate of a monitor.

A video counter is maintained, and incremented at each vertical retrace interval. 

	int glXGetVideoSyncSGI(GLuint *count);
	int glXWaitVideoSyncSGI(GLuint divisor, 
				GLuint remainder, 
				GLuint *count);
glxWaitVideoSyncSGI() puts the calling process to to sleep until
(C mod D) = R