Bug 1043859 - Expose the APZC overscroll transform as a separate function. r=botond

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -2453,7 +2453,11 @@ bool AsyncPanZoomController::UpdateAnimation(const TimeStamp& aSampleTime,
   return false;
 }
 
-void AsyncPanZoomController::GetOverscrollTransform(Matrix4x4* aTransform) const {
+Matrix4x4 AsyncPanZoomController::GetOverscrollTransform() const {
+  if (!IsOverscrolled()) {
+    return Matrix4x4();
+  }
+
   // The overscroll effect is a uniform stretch along the overscrolled axis,
   // with the edge of the content where we have reached the end of the
   // scrollable area pinned into place.
@@ -2488,8 +2492,8 @@ void AsyncPanZoomController::GetOverscrollTransform(Matrix4x4* aTransform) const
   }
 
   // Combine the transformations into a matrix.
-  *aTransform = Matrix4x4().Scale(scaleX, scaleY, 1)
-                           .PostTranslate(translation.x, translation.y, 0);
+  return Matrix4x4().Scale(scaleX, scaleY, 1)
+                    .PostTranslate(translation.x, translation.y, 0);
 }
 
 bool AsyncPanZoomController::AdvanceAnimations(const TimeStamp& aSampleTime)
@@ -2565,19 +2569,12 @@ bool AsyncPanZoomController::AdvanceAnimations(const TimeStamp& aSampleTime)
 }
 
 void AsyncPanZoomController::SampleContentTransformForFrame(ViewTransform* aOutTransform,
-                                                            ScreenPoint& aScrollOffset,
-                                                            Matrix4x4* aOutOverscrollTransform)
+                                                            ScreenPoint& aScrollOffset)
 {
   ReentrantMonitorAutoEnter lock(mMonitor);
 
   aScrollOffset = mFrameMetrics.GetScrollOffset() * mFrameMetrics.GetZoom();
   *aOutTransform = GetCurrentAsyncTransform();
-
-  // If we are overscrolled, we would like the compositor to apply an
-  // additional transform that produces an overscroll effect.
-  if (aOutOverscrollTransform && IsOverscrolled()) {
-    GetOverscrollTransform(aOutOverscrollTransform);
-  }
 }
 
 ViewTransform AsyncPanZoomController::GetCurrentAsyncTransform() const {

gfx/layers/apz/src/AsyncPanZoomController.h

@@ -166,18 +166,17 @@ public:
   /**
    * Query the transforms that should be applied to the layer corresponding
    * to this APZC due to asynchronous panning and zooming.
-   * This function returns two transforms via out parameters:
-   *   |aOutTransform| is the transform due to regular panning and zooming
-   *   |aOverscrollTransform| is the transform due to overscrolling
-   * The two are separated because some clients want to ignore the overscroll
-   * transform for some purposes (and for convenience to these clients, the
-   * overscroll transform parameter may be nullptr). Clients who do not want
-   * to ignore the overscroll transform should multiply the two transforms
-   * together.
+   * This function returns the async transform via the |aOutTransform|
+   * out parameter.
    */
   void SampleContentTransformForFrame(ViewTransform* aOutTransform,
-                                      ScreenPoint& aScrollOffset,
-                                      Matrix4x4* aOutOverscrollTransform);
+                                      ScreenPoint& aScrollOffset);
+
+  /**
+   * Return a visual effect that reflects this apzc's
+   * overscrolled state, if any.
+   */
+  Matrix4x4 GetOverscrollTransform() const;
 
   /**
    * A shadow layer update has arrived. |aLayerMetrics| is the new FrameMetrics
@@ -595,12 +594,6 @@ private:
    */
   bool ConvertToGecko(const ScreenPoint& aPoint, CSSPoint* aOut);
 
-  /**
-   * Return in |aTransform| a visual effect that reflects this apzc's
-   * overscrolled state, if any.
-   */
-  void GetOverscrollTransform(Matrix4x4* aTransform) const;
-
   enum AxisLockMode {
     FREE,     /* No locking at all */
     STANDARD, /* Default axis locking mode that remains locked until pan ends*/

gfx/layers/composite/AsyncCompositionManager.cpp

@@ -586,11 +586,10 @@ AsyncCompositionManager::ApplyAsyncContentTransformToTree(Layer *aLayer)
     hasAsyncTransform = true;
 
     ViewTransform asyncTransformWithoutOverscroll;
-    Matrix4x4 overscrollTransform;
     ScreenPoint scrollOffset;
     controller->SampleContentTransformForFrame(&asyncTransformWithoutOverscroll,
-                                               scrollOffset,
-                                               &overscrollTransform);
+                                               scrollOffset);
+    Matrix4x4 overscrollTransform = controller->GetOverscrollTransform();
 
     if (!aLayer->IsScrollInfoLayer()) {
       controller->MarkAsyncTransformAppliedToContent();

gfx/tests/gtest/TestAsyncPanZoomController.cpp

@@ -162,10 +162,9 @@ public:
   bool SampleContentTransformForFrame(const TimeStamp& aSampleTime,
                                       ViewTransform* aOutTransform,
                                       ScreenPoint& aScrollOffset) {
-    Matrix4x4 aOverscrollTransform;  // ignored
     bool ret = AdvanceAnimations(aSampleTime);
     AsyncPanZoomController::SampleContentTransformForFrame(
-      aOutTransform, aScrollOffset, &aOverscrollTransform);
+      aOutTransform, aScrollOffset);
     return ret;
   }
 };