Set up things so that if the INTEL_swap_event extension is not present,
but the driver is known to have good thread support, we use an extra
thread and call glXWaitVideoSync() in the thread. This allows idles
to work properly, even when Mutter is constantly redrawing new frames;
otherwise, without INTEL_swap_event, we'll just block in glXSwapBuffers().
Because the threaded-swap-wait functionality requires XInitThreads(),
and because it isn't clear that it is a win for all applications,
add a API function to conditionally enable it.
Fix the cogl-crate example not to just have a hard-coded dependency
on libX11.
For NVIDIA proprietary drivers, implement sync events with a thread
It's a good guess that the buffer swap will occur at the next vblank,
so use glXWaitVideoSync in a separate thread to deliver a sync event
rather than just letting the client block when frame drawing, which
can signficantly change app logic as compared to the INTEL_swap_event
case.
Fix the get_clock_time() without GLX_OML_sync_control
When we don't have GLX_OML_sync_control, we still can set the
frame presentation time, but we always use the system monotonic time,
so return that from get_clock_time().
Usability of SGI_video_sync is per-display not per-renderer
As previously commented in the code, SGI_video_sync is per-display, rather
than per-renderer. The is_direct flag for the renderer was tested before
it was initialized (per-display) and that resulted in SGI_video_sync
never being used.
Commits 6dbec6f8, 734402e1 and f041b35b introduced memory leaks by
switching to returning copies instead of the original buffers but
forgetting to free those original buffers.
Some error cases were also not freeing the ->prop buffer as they
should.
