The description of glXWaitX says "X rendering calls made prior to glXWaitX are
guaranteed to be executed before GL rendering calls made after glXWaitX", but
glXWaitX is currently a no-op when direct rendering unless the current
drawable is a window and single buffered. In situations where
dri2_copy_drawable is used it performs the required X server round trip.
At one point in history glXWaitX called XSync with direct rendering:
It seems XSync should be used when dri2_copy_drawable is not necessary.
There is some discussion in this thread:
Perhaps LastKnownRequestProcessed NextRequest can be used to determine whether
the XSync is necessary. They could also detect that the XSync is not necessary after dri2_copy_drawable.
glxWaitGL looks like a no-op in similar situations.
I wonder whether at least a glFlush is required here.
applegl and indirect contexts appear to support glXWaitX/GL.
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