Bug 951793 - Add a few utility functions to expose the overscroll behavior in relevant places in APZ. r=kats

MozReview-Commit-ID: 4wFfUY5p6J5

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -3929,6 +3929,11 @@ const FrameMetrics& AsyncPanZoomController::GetFrameMetrics() const {
   return mFrameMetrics;
 }
 
+const ScrollMetadata& AsyncPanZoomController::GetScrollMetadata() const {
+  mRecursiveMutex.AssertCurrentThreadIn();
+  return mScrollMetadata;
+}
+
 APZCTreeManager* AsyncPanZoomController::GetApzcTreeManager() const {
   mRecursiveMutex.AssertNotCurrentThreadIn();
   return mTreeManager;

gfx/layers/apz/src/AsyncPanZoomController.h

@@ -668,6 +668,12 @@ protected:
    */
   const FrameMetrics& GetFrameMetrics() const;
 
+  /**
+   * Gets the current scroll metadata. This is *not* the Gecko copy stored in
+   * the layers code/
+   */
+  const ScrollMetadata& GetScrollMetadata() const;
+
   /**
    * Gets the pointer to the apzc tree manager. All the access to tree manager
    * should be made via this method and not via private variable since this method

gfx/layers/apz/src/Axis.cpp

@@ -491,6 +491,21 @@ const FrameMetrics& Axis::GetFrameMetrics() const {
   return mAsyncPanZoomController->GetFrameMetrics();
 }
 
+const ScrollMetadata& Axis::GetScrollMetadata() const {
+  return mAsyncPanZoomController->GetScrollMetadata();
+}
+
+bool Axis::OverscrollBehaviorAllowsHandoff() const {
+  // Scroll handoff is a "non-local" overscroll behavior, so it's allowed
+  // with "auto" and disallowed with "contain" and "none".
+  return GetOverscrollBehavior() == OverscrollBehavior::Auto;
+}
+
+bool Axis::OverscrollBehaviorAllowsOverscrollEffect() const {
+  // An overscroll effect is a "local" overscroll behavior, so it's allowed
+  // with "auto" and "contain" and disallowed with "none".
+  return GetOverscrollBehavior() != OverscrollBehavior::None;
+}
 
 AxisX::AxisX(AsyncPanZoomController* aAsyncPanZoomController)
   : Axis(aAsyncPanZoomController)
@@ -528,6 +543,11 @@ const char* AxisX::Name() const
   return "X";
 }
 
+OverscrollBehavior AxisX::GetOverscrollBehavior() const
+{
+  return GetScrollMetadata().GetOverscrollBehavior().mBehaviorX;
+}
+
 AxisY::AxisY(AsyncPanZoomController* aAsyncPanZoomController)
   : Axis(aAsyncPanZoomController)
 {
@@ -564,5 +584,10 @@ const char* AxisY::Name() const
   return "Y";
 }
 
+OverscrollBehavior AxisY::GetOverscrollBehavior() const
+{
+  return GetScrollMetadata().GetOverscrollBehavior().mBehaviorY;
+}
+
 } // namespace layers
 } // namespace mozilla

gfx/layers/apz/src/Axis.h

@@ -249,6 +249,9 @@ public:
 
   ParentLayerCoord GetPos() const { return mPos; }
 
+  bool OverscrollBehaviorAllowsHandoff() const;
+  bool OverscrollBehaviorAllowsOverscrollEffect() const;
+
   virtual ParentLayerCoord GetPointOffset(const ParentLayerPoint& aPoint) const = 0;
   virtual ParentLayerCoord GetRectLength(const ParentLayerRect& aRect) const = 0;
   virtual ParentLayerCoord GetRectOffset(const ParentLayerRect& aRect) const = 0;
@@ -286,6 +289,9 @@ protected:
   nsTArray<std::pair<uint32_t, float> > mVelocityQueue;
 
   const FrameMetrics& GetFrameMetrics() const;
+  const ScrollMetadata& GetScrollMetadata() const;
+
+  virtual OverscrollBehavior GetOverscrollBehavior() const = 0;
 
   // Adjust a requested overscroll amount for resistance, yielding a smaller
   // actual overscroll amount.
@@ -307,6 +313,8 @@ public:
   virtual CSSToParentLayerScale GetScaleForAxis(const CSSToParentLayerScale2D& aScale) const override;
   virtual ScreenPoint MakePoint(ScreenCoord aCoord) const override;
   virtual const char* Name() const override;
+private:
+  virtual OverscrollBehavior GetOverscrollBehavior() const override;
 };
 
 class AxisY : public Axis {
@@ -318,6 +326,8 @@ public:
   virtual CSSToParentLayerScale GetScaleForAxis(const CSSToParentLayerScale2D& aScale) const override;
   virtual ScreenPoint MakePoint(ScreenCoord aCoord) const override;
   virtual const char* Name() const override;
+private:
+  virtual OverscrollBehavior GetOverscrollBehavior() const override;
 };
 
 } // namespace layers