[timeline] Account for clock roll backs between frames

If the system clock rolls back between two frames then we need
to account for the change, to avoid stopping the timeline.

The best option, since a roll back can be any arbitrary amount
of milliseconds, is to skip a frame.

Fixes bug:

  http://bugzilla.moblin.org/show_bug.cgi?id=3839

1 files changed, 23 insertions, 10 deletions

diff --git a/clutter/clutter-timeline.c b/clutter/clutter-timeline.c
index e254f4598..7f33395b5 100644
--- a/clutter/clutter-timeline.c
+++ b/clutter/clutter-timeline.c
@@ -56,9 +56,10 @@ struct _ClutterTimelinePrivate
   guint delay;
 
   /* The current amount of elapsed time */
-  gint elapsed_time;
+  gint64 elapsed_time;
+
   /* The elapsed time since the last frame was fired */
-  gint msecs_delta;
+  gint64 msecs_delta;
 
   GHashTable *markers_by_name;
 
@@ -570,9 +571,9 @@ clutter_timeline_do_frame (ClutterTimeline *timeline)
 
   g_object_ref (timeline);
 
-  CLUTTER_TIMESTAMP (SCHEDULER, "Timeline [%p] activated (cur: %d)\n",
+  CLUTTER_TIMESTAMP (SCHEDULER, "Timeline [%p] activated (cur: %ld)\n",
                      timeline,
-                     priv->elapsed_time);
+                     (long) priv->elapsed_time);
 
   /* Advance time */
   if (priv->direction == CLUTTER_TIMELINE_FORWARD)
@@ -637,10 +638,10 @@ clutter_timeline_do_frame (ClutterTimeline *timeline)
        * on the last frame we will still go ahead and send the
        * completed signal */
       CLUTTER_NOTE (SCHEDULER,
-                    "Timeline [%p] completed (cur: %d, tot: %d)",
+                    "Timeline [%p] completed (cur: %ld, tot: %ld)",
                     timeline,
-                    priv->elapsed_time,
-                    priv->msecs_delta);
+                    (long) priv->elapsed_time,
+                    (long) priv->msecs_delta);
 
       if (!priv->loop && priv->is_playing)
         {
@@ -1223,9 +1224,21 @@ clutter_timeline_do_tick (ClutterTimeline *timeline,
     }
   else
     {
-      gint msecs =
-	(tick_time->tv_sec - priv->last_frame_time.tv_sec) * 1000
-        + (tick_time->tv_usec - priv->last_frame_time.tv_usec) / 1000;
+      gint64 msecs;
+
+      msecs = (tick_time->tv_sec - priv->last_frame_time.tv_sec) * 1000
+            + (tick_time->tv_usec - priv->last_frame_time.tv_usec) / 1000;
+
+      /* if the clock rolled back between ticks we need to
+       * account for it; the best course of action, since the
+       * clock roll back can happen by any arbitrary amount
+       * of milliseconds, is to drop a frame here
+       */
+      if (msecs < 0)
+        {
+          priv->last_frame_time = *tick_time;
+          return;
+        }
 
       if (msecs != 0)
 	{