glXWaitX - complete X execution prior to subsequent GL calls
X rendering calls made prior to glXWaitX are guaranteed to be executed
before GL rendering calls made after glXWaitX. Although the same result
can be achieved using XSync, glXWaitX does not require a round
trip to the server, and it is therefore more efficient in cases where client
and server are on separate machines.
glXWaitX is ignored if there is no current GLX context.
glXWaitX may or may not flush the GL stream.
GLXBadCurrentWindow is generated if the drawable associated with the
current context of the calling thread is a window, and that window is no
longer valid.
glFinish, glFlush, glXWaitGL, XSync