Bug 1201330 - Keep scroll handler induced layer activity active until the scroll frame becomes inactive. r=roc

layout/base/ActiveLayerTracker.cpp

@@ -97,6 +97,13 @@ public:
   // Previous scale due to the CSS transform property.
   Maybe<gfxSize> mPreviousTransformScale;
 
+  // The scroll frame during for which we most recently received a call to
+  // NotifyAnimatedFromScrollHandler.
+  nsWeakFrame mAnimatingScrollHandlerFrame;
+  // The set of activities that were triggered during
+  // mAnimatingScrollHandlerFrame's scroll event handler.
+  EnumSet<ActivityIndex> mScrollHandlerInducedActivity;
+
   // Number of restyle operations detected
   uint8_t mRestyleCounts[ACTIVITY_COUNT];
   bool mContentActive;
@@ -109,12 +116,20 @@ public:
   LayerActivityTracker()
     : nsExpirationTracker<LayerActivity,4>(GENERATION_MS,
                                            "LayerActivityTracker")
+    , mDestroying(false)
   {}
   ~LayerActivityTracker() {
+    mDestroying = true;
     AgeAllGenerations();
   }
 
   virtual void NotifyExpired(LayerActivity* aObject);
+
+public:
+  nsWeakFrame mCurrentScrollHandlerFrame;
+
+private:
+  bool mDestroying;
 };
 
 static LayerActivityTracker* gLayerActivityTracker = nullptr;
@@ -133,6 +148,13 @@ NS_DECLARE_FRAME_PROPERTY(LayerActivityProperty, DeleteValue<LayerActivity>)
 void
 LayerActivityTracker::NotifyExpired(LayerActivity* aObject)
 {
+  if (!mDestroying && aObject->mAnimatingScrollHandlerFrame.IsAlive()) {
+    // Reset the restyle counts, but let the layer activity survive.
+    PodArrayZero(aObject->mRestyleCounts);
+    MarkUsed(aObject);
+    return;
+  }
+
   RemoveObject(aObject);
 
   nsIFrame* f = aObject->mFrame;
@@ -294,6 +316,27 @@ ActiveLayerTracker::NotifyAnimated(nsIFrame* aFrame, nsCSSProperty aProperty)
   mutationCount = 0xFF;
 }
 
+/* static */ void
+ActiveLayerTracker::NotifyAnimatedFromScrollHandler(nsIFrame* aFrame, nsCSSProperty aProperty,
+                                                    nsIFrame* aScrollFrame)
+{
+  if (aFrame->PresContext() != aScrollFrame->PresContext()) {
+    // Don't allow cross-document dependencies.
+    return;
+  }
+  LayerActivity* layerActivity = GetLayerActivityForUpdate(aFrame);
+  LayerActivity::ActivityIndex activityIndex = LayerActivity::GetActivityIndexForProperty(aProperty);
+
+  if (layerActivity->mAnimatingScrollHandlerFrame.GetFrame() != aScrollFrame) {
+    // Discard any activity of a different scroll frame. We only track the
+    // most recent scroll handler induced activity.
+    layerActivity->mScrollHandlerInducedActivity.clear();
+    layerActivity->mAnimatingScrollHandlerFrame = aScrollFrame;
+  }
+
+  layerActivity->mScrollHandlerInducedActivity += activityIndex;
+}
+
 static bool
 IsPresContextInScriptAnimationCallback(nsPresContext* aPresContext)
 {
@@ -310,10 +353,14 @@ IsPresContextInScriptAnimationCallback(nsPresContext* aPresContext)
 ActiveLayerTracker::NotifyInlineStyleRuleModified(nsIFrame* aFrame,
                                                   nsCSSProperty aProperty)
 {
-  if (!IsPresContextInScriptAnimationCallback(aFrame->PresContext())) {
-    return;
+  if (IsPresContextInScriptAnimationCallback(aFrame->PresContext())) {
+    NotifyAnimated(aFrame, aProperty);
+  }
+  if (gLayerActivityTracker &&
+      gLayerActivityTracker->mCurrentScrollHandlerFrame.IsAlive()) {
+    NotifyAnimatedFromScrollHandler(aFrame, aProperty,
+      gLayerActivityTracker->mCurrentScrollHandlerFrame.GetFrame());
   }
-  NotifyAnimated(aFrame, aProperty);
 }
 
 /* static */ bool
@@ -322,6 +369,29 @@ ActiveLayerTracker::IsStyleMaybeAnimated(nsIFrame* aFrame, nsCSSProperty aProper
   return IsStyleAnimated(nullptr, aFrame, aProperty);
 }
 
+static bool
+CheckScrollInducedActivity(LayerActivity* aLayerActivity,
+                           LayerActivity::ActivityIndex aActivityIndex,
+                           nsDisplayListBuilder* aBuilder)
+{
+  if (!aLayerActivity->mScrollHandlerInducedActivity.contains(aActivityIndex) ||
+      !aLayerActivity->mAnimatingScrollHandlerFrame.IsAlive()) {
+    return false;
+  }
+
+  nsIScrollableFrame* scrollFrame =
+    do_QueryFrame(aLayerActivity->mAnimatingScrollHandlerFrame.GetFrame());
+  if (scrollFrame && (!aBuilder || scrollFrame->IsScrollingActive(aBuilder))) {
+    return true;
+  }
+
+  // The scroll frame has been destroyed or has become inactive. Clear it from
+  // the layer activity so that it can expire.
+  aLayerActivity->mAnimatingScrollHandlerFrame = nullptr;
+  aLayerActivity->mScrollHandlerInducedActivity.clear();
+  return false;
+}
+
 /* static */ bool
 ActiveLayerTracker::IsStyleAnimated(nsDisplayListBuilder* aBuilder,
                                     nsIFrame* aFrame, nsCSSProperty aProperty)
@@ -340,7 +410,11 @@ ActiveLayerTracker::IsStyleAnimated(nsDisplayListBuilder* aBuilder,
 
   LayerActivity* layerActivity = GetLayerActivity(aFrame);
   if (layerActivity) {
-    if (layerActivity->RestyleCountForProperty(aProperty) >= 2) {
+    LayerActivity::ActivityIndex activityIndex = LayerActivity::GetActivityIndexForProperty(aProperty);
+    if (layerActivity->mRestyleCounts[activityIndex] >= 2) {
+      return true;
+    }
+    if (CheckScrollInducedActivity(layerActivity, activityIndex, aBuilder)) {
       return true;
     }
   }
@@ -458,6 +532,15 @@ ActiveLayerTracker::IsContentActive(nsIFrame* aFrame)
   return layerActivity && layerActivity->mContentActive;
 }
 
+/* static */ void
+ActiveLayerTracker::SetCurrentScrollHandlerFrame(nsIFrame* aFrame)
+{
+  if (!gLayerActivityTracker) {
+    gLayerActivityTracker = new LayerActivityTracker();
+  }
+  gLayerActivityTracker->mCurrentScrollHandlerFrame = aFrame;
+}
+
 /* static */ void
 ActiveLayerTracker::Shutdown()
 {

layout/base/ActiveLayerTracker.h

@@ -49,6 +49,12 @@ public:
    * Any such marking will time out after a short period.
    */
   static void NotifyAnimated(nsIFrame* aFrame, nsCSSProperty aProperty);
+  /**
+   * Notify aFrame as being known to have an animation of aProperty through an
+   * inline style modification during aScrollFrame's scroll event handler.
+   */
+  static void NotifyAnimatedFromScrollHandler(nsIFrame* aFrame, nsCSSProperty aProperty,
+                                              nsIFrame* aScrollFrame);
   /**
    * Notify that a property in the inline style rule of aFrame's element
    * has been modified.
@@ -107,6 +113,13 @@ public:
    * Return true if this frame's content is still marked as active.
    */
   static bool IsContentActive(nsIFrame* aFrame);
+
+  /**
+   * Called before and after a scroll event handler is executed, with the
+   * scrollframe or nullptr, respectively. This acts as a hint to treat
+   * inline style changes during the handler differently.
+   */
+  static void SetCurrentScrollHandlerFrame(nsIFrame* aFrame);
 };
 
 } // namespace mozilla

layout/generic/nsGfxScrollFrame.cpp

@@ -4206,6 +4206,7 @@ ScrollFrameHelper::FireScrollEvent()
 {
   mScrollEvent.Forget();
 
+  ActiveLayerTracker::SetCurrentScrollHandlerFrame(mOuter);
   WidgetGUIEvent event(true, eScroll, nullptr);
   nsEventStatus status = nsEventStatus_eIgnore;
   nsIContent* content = mOuter->GetContent();
@@ -4223,6 +4224,7 @@ ScrollFrameHelper::FireScrollEvent()
     event.mFlags.mBubbles = false;
     EventDispatcher::Dispatch(content, prescontext, &event, nullptr, &status);
   }
+  ActiveLayerTracker::SetCurrentScrollHandlerFrame(nullptr);
 }
 
 void

mfbt/EnumSet.h

@@ -127,6 +127,14 @@ public:
     return result;
   }
 
+  /**
+   * Clear
+   */
+  void clear()
+  {
+    mBitField = 0;
+  }
+
   /**
    * Intersection
    */