Bug 1193062 - Make AllowScrollHandoff work for both ScrollWheelInput and PanGestureInput blocks. r=kats

--HG--
extra : commitid : DwBaXlllNDK
extra : rebase_source : f5f76749edd625b925cacda5627c40c7633c4609
extra : histedit_source : 6ba23a9269071eec6c08baab31a36532c9e143d6

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -1534,10 +1534,9 @@ AsyncPanZoomController::CanScroll(Layer::ScrollDirection aDirection) const
 }
 
 bool
-AsyncPanZoomController::AllowScrollHandoffInWheelTransaction() const
+AsyncPanZoomController::AllowScrollHandoffInCurrentBlock() const
 {
-  WheelBlockState* block = mInputQueue->CurrentWheelBlock();
-  return block->AllowScrollHandoff();
+  return mInputQueue->AllowScrollHandoff();
 }
 
 nsEventStatus AsyncPanZoomController::OnScrollWheel(const ScrollWheelInput& aEvent)
@@ -2093,22 +2092,17 @@ bool AsyncPanZoomController::AttemptScroll(const ParentLayerPoint& aStartPoint,
     return true;
   }
 
-  // If in a wheel transaction that has not ended, we drop overscroll.
-  if (aOverscrollHandoffState.mScrollSource == ScrollSource::Wheel &&
-      !AllowScrollHandoffInWheelTransaction())
-  {
-    return true;
-  }
-
-  // If there is overscroll, first try to hand it off to an APZC later
-  // in the handoff chain to consume (either as a normal scroll or as
-  // overscroll).
-  // Note: "+ overscroll" rather than "- overscroll" because "overscroll"
-  // is what's left of "displacement", and "displacement" is "start - end".
-  ++aOverscrollHandoffState.mChainIndex;
-  if (CallDispatchScroll(aEndPoint + overscroll, aEndPoint,
-                         aOverscrollHandoffState)) {
-    return true;
+  if (AllowScrollHandoffInCurrentBlock()) {
+    // If there is overscroll, first try to hand it off to an APZC later
+    // in the handoff chain to consume (either as a normal scroll or as
+    // overscroll).
+    // Note: "+ overscroll" rather than "- overscroll" because "overscroll"
+    // is what's left of "displacement", and "displacement" is "start - end".
+    ++aOverscrollHandoffState.mChainIndex;
+    if (CallDispatchScroll(aEndPoint + overscroll, aEndPoint,
+                           aOverscrollHandoffState)) {
+      return true;
+    }
   }
 
   // If there is no APZC later in the handoff chain that accepted the

gfx/layers/apz/src/AsyncPanZoomController.h

@@ -894,8 +894,8 @@ private:
 
   void StartSmoothScroll(ScrollSource aSource);
 
-  // Returns whether overscroll is allowed during a wheel event.
-  bool AllowScrollHandoffInWheelTransaction() const;
+  // Returns whether overscroll is allowed during an event.
+  bool AllowScrollHandoffInCurrentBlock() const;
 
   /* ===================================================================
    * The functions and members in this section are used to make ancestor chains

gfx/layers/apz/src/InputQueue.cpp

@@ -405,6 +405,19 @@ InputQueue::HasReadyTouchBlock() const
          mInputBlockQueue[0]->IsReadyForHandling();
 }
 
+bool
+InputQueue::AllowScrollHandoff() const
+{
+  MOZ_ASSERT(CurrentBlock());
+  if (CurrentBlock()->AsWheelBlock()) {
+    return CurrentBlock()->AsWheelBlock()->AllowScrollHandoff();
+  }
+  if (CurrentBlock()->AsPanGestureBlock()) {
+    return CurrentBlock()->AsPanGestureBlock()->AllowScrollHandoff();
+  }
+  return true;
+}
+
 void
 InputQueue::ScheduleMainThreadTimeout(const nsRefPtr<AsyncPanZoomController>& aTarget, uint64_t aInputBlockId) {
   INPQ_LOG("scheduling main thread timeout for target %p\n", aTarget.get());

gfx/layers/apz/src/InputQueue.h

@@ -102,6 +102,10 @@ public:
    * Remove all input blocks from the input queue.
    */
   void Clear();
+  /**
+   * Whether the current pending block allows scroll handoff.
+   */
+  bool AllowScrollHandoff() const;
 
 private:
   ~InputQueue();