OpenGL man pages
glXWaitX - complete X execution prior to subsequent OpenGL calls
void glXWaitX( void )
X rendering calls made prior to glXWaitX are guaranteed to be executed
before OpenGL rendering calls made after glXWaitX. Although this 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 OpenGL stream.
GLXBadCurrentWindow is generated if the drawable associated with the
current context of the calling thread is a window, and that window is no
glFinish, glFlush, glXWaitGL, XSync
Fri Dec 6 11:18:03 EST 1996
Look here for legal stuff: Legal