From 1b8a2e6d1c30f3c25df6df871801649af50e8553 Mon Sep 17 00:00:00 2001
From: "David Zbarsky
 ext:(%2C%20David%20Baron%20%3Cdbaron%40dbaron.org%3E%2C%20Chris%20Jones%20%3Cjones.chris.g%40gmail.com%3E)"
 <dzbarsky@gmail.com>
Date: Thu, 22 Nov 2012 15:49:06 -0800
Subject: [PATCH] Bug 788409:  When the compositor runs past the end of an
 animation, just fill forwards until the main thread catches up. r=dbaron
 a=blocking-basecamp

---
 gfx/layers/ipc/CompositorParent.cpp |  6 ----
 layout/style/nsAnimationManager.cpp | 45 +++++++++++++++--------------
 layout/style/nsAnimationManager.h   |  4 ++-
 3 files changed, 27 insertions(+), 28 deletions(-)

diff --git a/gfx/layers/ipc/CompositorParent.cpp b/gfx/layers/ipc/CompositorParent.cpp
index 5623c48cc3a..f6c8698d2ec 100644
--- a/gfx/layers/ipc/CompositorParent.cpp
+++ b/gfx/layers/ipc/CompositorParent.cpp
@@ -720,12 +720,6 @@ SampleAnimations(Layer* aLayer, TimeStamp aPoint)
                                                 numIterations,
                                                 animation.direction());
 
-    if (positionInIteration == -1) {
-      animations.RemoveElementAt(i);
-      animationData.RemoveElementAt(i);
-      continue;
-    }
-
     NS_ABORT_IF_FALSE(0.0 <= positionInIteration &&
                       positionInIteration <= 1.0,
                       "position should be in [0-1]");
diff --git a/layout/style/nsAnimationManager.cpp b/layout/style/nsAnimationManager.cpp
index 7d45b82bfbe..a9110587ecb 100644
--- a/layout/style/nsAnimationManager.cpp
+++ b/layout/style/nsAnimationManager.cpp
@@ -54,29 +54,32 @@ ElementAnimations::GetPositionInIteration(TimeStamp aStartTime, TimeStamp aCurre
     currentTimeDuration / aDuration;
   bool dispatchStartOrIteration = false;
   if (currentIterationCount >= aIterationCount) {
-    if (!aAnimation) {
-      // We are on the compositor, so send a signal that the animation is over.
-      // The main thread will fire the animationend event.
-      return -1;
-    }
-    // Dispatch 'animationend' when needed.
-    if (aIsForElement &&
-        aAnimation->mLastNotification !=
-          ElementAnimation::LAST_NOTIFICATION_END) {
-      aAnimation->mLastNotification = ElementAnimation::LAST_NOTIFICATION_END;
-      // XXXdz: if this animation was done on the compositor, we should
-      // invalidate the frame and update style once we start throttling style
-      // updates.
-      AnimationEventInfo ei(aEa->mElement, aAnimation->mName, NS_ANIMATION_END,
-                            currentTimeDuration);
-      aEventsToDispatch->AppendElement(ei);
-    }
+    if (aAnimation) {
+      // Dispatch 'animationend' when needed.
+      if (aIsForElement &&
+          aAnimation->mLastNotification !=
+            ElementAnimation::LAST_NOTIFICATION_END) {
+        aAnimation->mLastNotification = ElementAnimation::LAST_NOTIFICATION_END;
+        // XXXdz: if this animation was done on the compositor, we should
+        // invalidate the frame and update style once we start throttling style
+        // updates.
+        AnimationEventInfo ei(aEa->mElement, aAnimation->mName, NS_ANIMATION_END,
+                              currentTimeDuration);
+        aEventsToDispatch->AppendElement(ei);
+      }
 
-    if (!aAnimation->FillsForwards()) {
-      // No animation data.
-      return -1;
+      if (!aAnimation->FillsForwards()) {
+        // No animation data.
+        return -1;
+      }
+    } else {
+      // If aAnimation is null, that means we're on the compositor
+      // thread.  We want to just keep filling forwards until the main
+      // thread gets around to updating the compositor thread (which
+      // might take a little while).  So just assume we fill fowards and
+      // move on.
     }
-    currentIterationCount = double(aAnimation->mIterationCount);
+    currentIterationCount = aIterationCount;
   } else {
     if (aAnimation && !aAnimation->IsPaused()) {
       aEa->mNeedsRefreshes = true;
diff --git a/layout/style/nsAnimationManager.h b/layout/style/nsAnimationManager.h
index 88da7215e77..330689d86dd 100644
--- a/layout/style/nsAnimationManager.h
+++ b/layout/style/nsAnimationManager.h
@@ -128,7 +128,9 @@ struct ElementAnimations : public mozilla::css::CommonElementAnimationData
   // from the main thread, we need the actual ElementAnimation* in order to 
   // get correct animation-fill behavior and to fire animation events.
   // This function returns -1 for the position if the animation should not be
-  // run (because it is not currently active and has no fill behavior.)
+  // run (because it is not currently active and has no fill behavior), but
+  // only does so if aAnimation is non-null; with a null aAnimation it is an
+  // error to give aCurrentTime < aStartTime, and fill-forwards is assumed.
   static double GetPositionInIteration(TimeStamp aStartTime,
                                        TimeStamp aCurrentTime,
                                        TimeDuration aDuration,