Bug 1049109 - Clear overscroll along entire handoff chain at end of pinch. r=kats

gfx/layers/apz/src/APZCTreeManager.cpp

@@ -902,10 +902,6 @@ APZCTreeManager::DispatchScroll(AsyncPanZoomController* aPrev,
     return false;
   }
 
-  if (next->GetGuid().mLayersId != aPrev->GetGuid().mLayersId) {
-    NS_WARNING("Handing off scroll across a layer tree boundary; may need to revise approach to bug 1031067");
-  }
-
   // Convert the start and end points from |aPrev|'s coordinate space to
   // |next|'s coordinate space. Since |aPrev| may be the same as |next|
   // (if |aPrev| is the APZC that is initiating the scroll and there is no

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -1316,8 +1316,14 @@ nsEventStatus AsyncPanZoomController::OnScaleEnd(const PinchGestureInput& aEvent
     // that into a pinch by increasing the span sufficiently. In such a case,
     // there is no snap-back animation to get us out of overscroll, so we need
     // to get out of it somehow.
-    mX.ClearOverscroll();
-    mY.ClearOverscroll();
+    // Moreover, in cases of scroll handoff, the overscroll can be on an APZC
+    // further up in the handoff chain rather than on the current APZC, so
+    // we need to clear overscroll along the entire handoff chain.
+    if (HasReadyTouchBlock()) {
+      CurrentTouchBlock()->GetOverscrollHandoffChain()->ClearOverscroll();
+    } else {
+      ClearOverscroll();
+    }
 
     ScheduleComposite();
     RequestContentRepaint();
@@ -1897,14 +1903,19 @@ void AsyncPanZoomController::CancelAnimation() {
   // preempt normal mechanisms for relieving overscroll, so we need to clear
   // overscroll here.
   if (mX.IsOverscrolled() || mY.IsOverscrolled()) {
-    mX.ClearOverscroll();
-    mY.ClearOverscroll();
+    ClearOverscroll();
     RequestContentRepaint();
     ScheduleComposite();
     UpdateSharedCompositorFrameMetrics();
   }
 }
 
+void AsyncPanZoomController::ClearOverscroll() {
+  ReentrantMonitorAutoEnter lock(mMonitor);
+  mX.ClearOverscroll();
+  mY.ClearOverscroll();
+}
+
 void AsyncPanZoomController::SetCompositorParent(CompositorParent* aCompositorParent) {
   mCompositorParent = aCompositorParent;
 }

gfx/layers/apz/src/AsyncPanZoomController.h

@@ -288,12 +288,15 @@ public:
   void StartAnimation(AsyncPanZoomAnimation* aAnimation);
 
   /**
-   * Cancels any currently running animation. Note that all this does is set the
-   * state of the AsyncPanZoomController back to NOTHING, but it is the
-   * animation's responsibility to check this before advancing.
+   * Cancels any currently running animation.
    */
   void CancelAnimation();
 
+  /**
+   * Clear any overscroll on this APZC.
+   */
+  void ClearOverscroll();
+
   /**
    * Returns allowed touch behavior for the given point on the scrollable layer.
    * Internally performs a kind of hit testing based on the regions constructed

gfx/layers/apz/src/OverscrollHandoffChain.cpp

@@ -61,21 +61,30 @@ OverscrollHandoffChain::IndexOf(const AsyncPanZoomController* aApzc) const
 }
 
 void
-OverscrollHandoffChain::FlushRepaints() const
+OverscrollHandoffChain::ForEachApzc(APZCMethod aMethod) const
 {
   MOZ_ASSERT(Length() > 0);
   for (uint32_t i = 0; i < Length(); ++i) {
-    mChain[i]->FlushRepaintForOverscrollHandoff();
+    (mChain[i]->*aMethod)();
   }
 }
 
+void
+OverscrollHandoffChain::FlushRepaints() const
+{
+  ForEachApzc(&AsyncPanZoomController::FlushRepaintForOverscrollHandoff);
+}
+
 void
 OverscrollHandoffChain::CancelAnimations() const
 {
-  MOZ_ASSERT(Length() > 0);
-  for (uint32_t i = 0; i < Length(); ++i) {
-    mChain[i]->CancelAnimation();
-  }
+  ForEachApzc(&AsyncPanZoomController::CancelAnimation);
+}
+
+void
+OverscrollHandoffChain::ClearOverscroll() const
+{
+  ForEachApzc(&AsyncPanZoomController::ClearOverscroll);
 }
 
 void

gfx/layers/apz/src/OverscrollHandoffChain.h

@@ -94,6 +94,9 @@ public:
   // Cancel animations all the way up the chain.
   void CancelAnimations() const;
 
+  // Clear overscroll all the way up the chain.
+  void ClearOverscroll() const;
+
   // Snap back the APZC that is overscrolled, if any.
   void SnapBackOverscrolledApzc() const;
 
@@ -102,6 +105,9 @@ public:
   bool CanBePanned(const AsyncPanZoomController* aApzc) const;
 private:
   std::vector<nsRefPtr<AsyncPanZoomController>> mChain;
+
+  typedef void (AsyncPanZoomController::*APZCMethod)();
+  void ForEachApzc(APZCMethod aMethod) const;
 };
 
 // Don't pollute other files with this macro for now.