bba19b88a6
Allow gl user interfaces to block display device gl rendering. The ui code might want to do that in case it takes a little longer to bring things to screen, for example because we'll hand over a dma-buf to another process (spice will do that). Signed-off-by: Gerd Hoffmann <kraxel@redhat.com> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>