glXWaitGL - complete GL execution prior to subsequent X calls
GL rendering calls made prior to glXWaitGL are guaranteed to be executed
before X rendering calls made after glXWaitGL. Although this same
result can be achieved using glFinish, glXWaitGL 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.
glXWaitGL is ignored if there is no current GLX
context.
glXWaitGL may or may not flush the X 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current context of the calling thread is a window, and that window is no
longer valid.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, glXWaitX, XSync