[mutter] MetaRendererNative: Wait for the last flip callback before flipping

[Rui Matos <rtcm src gnome org>]

commit 227187f1f115bbea8a1a2d51da5641b3816fdb61
Author: Jonas Ådahl <jadahl gmail com>
Date:   Wed Nov 23 22:41:22 2016 +0800

    MetaRendererNative: Wait for the last flip callback before flipping
    
    We might still end up in swap-buffer without the previous flip callback
    having been invoked. This can happen if there are two monitors, and we
    manage to draw before having all monitor flip callbacks invoked.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=774923

 src/backends/native/meta-renderer-native.c |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)
---
diff --git a/src/backends/native/meta-renderer-native.c b/src/backends/native/meta-renderer-native.c
index e0d2877..c1b0840 100644
--- a/src/backends/native/meta-renderer-native.c
+++ b/src/backends/native/meta-renderer-native.c
@@ -800,12 +800,22 @@ meta_onscreen_native_swap_buffers_with_damage (CoglOnscreen *onscreen,
   MetaRendererNative *renderer_native = egl_renderer->platform;
   CoglOnscreenEGL *egl_onscreen = onscreen->winsys;
   MetaOnscreenNative *onscreen_native = egl_onscreen->platform;
+  MetaBackend *backend = meta_get_backend ();
+  MetaMonitorManager *monitor_manager =
+    meta_backend_get_monitor_manager (backend);
+  MetaMonitorManagerKms *monitor_manager_kms =
+    META_MONITOR_MANAGER_KMS (monitor_manager);
   CoglFrameInfo *frame_info;
 
   frame_info = g_queue_peek_tail (&onscreen->pending_frame_infos);
   frame_info->global_frame_counter = renderer_native->frame_counter;
 
-  g_warn_if_fail (!onscreen_native->pending_queue_swap_notify);
+  /*
+   * Wait for the flip callback before continuing, as we might have started the
+   * animation earlier due to the animation being driven by some other monitor.
+   */
+  while (onscreen_native->pending_flips)
+    meta_monitor_manager_kms_wait_for_flip (monitor_manager_kms);
 
   parent_vtable->onscreen_swap_buffers_with_damage (onscreen,
                                                     rectangles,