static void wait_vsync(void)
{
   // I guess we have to wait for flip to have taken place before another flip can be queued up.
   if (waiting_for_flip)
      wait_flip();

   queue_flip(); // Sets waiting_for_flip = true;

   if (!gbm_surface_has_free_buffers(g_gbm_surface)) // We have to wait for this flip to finish.
      wait_flip();
}