Comment 6 for bug 377090

I think a lot of compositing managers will choose that option (when they have updated frames to display of course). Right now though there's no good way for them to sync all output. They can block on a given pipe's vblank event, but that's racy, since the compositor process may not be woken up in time or may not finish its drawing in time to draw w/o tearing. So we really need glXSwapBuffers to be sync'd automatically, which allows the compositor (or other GL apps) to prepare a whole frame, swap buffers, and then continue rendering the next frame and not worry about tearing at all.