OpenGL Programming Guide

Appendix DThe OpenGL Extension to the X Window System

Controlling Rendering

Synchronizing Execution

To prevent X requests from executing until any outstanding OpenGL rendering is completed, call glXWaitGL(). Then, any previously issued OpenGL commands are guaranteed to be executed before any X rendering calls made after glXWaitGL(). Although the same result can be achieved with glFinish(), glXWaitGL() doesn't require a round trip to the server and thus is more efficient in cases where the client and server are on separate machines.

To prevent an OpenGL command sequence from executing until any outstanding X requests are completed, use glXWaitX(). This routine guarantees that previously issued X rendering calls are executed before any OpenGL calls made after glXWaitX().

OpenGL Programming Guide