[Bug 79223] extra vsync when reading back pixels in xbmc

https://bugs.freedesktop.org/show_bug.cgi?id=79223

--- Comment #2 from Pierre Ossman pierre-bugzilla@ossman.eu --- Ok, so it is glReadPixels() that is waiting for vsync. I added some measurements around that call and it is definitely where the delay happens.

For good measure I removed the mapping (step 2) and the extra render (step 4). So it does seem that glReadPixels() is simply broken and isn't doing the nice asynchronous read is it supposed to.

Oddly enough I could not reproduce the problem with a simple test program. So there is something else required to provoke the issue.

Ideas?