Bug 1457586 - Simplify Axis::UpdateWithTouchAtDevicePoint() by removing the aAdditionalDelta parameter. r=mstange

MozReview-Commit-ID: CBBPhfRkl97

Depends on D7653

Differential Revision: https://phabricator.services.mozilla.com/D7654

--HG--
extra : moz-landing-system : lando

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -1501,8 +1501,8 @@ nsEventStatus AsyncPanZoomController::OnScale(const PinchGestureInput& aEvent) {
   // UpdateWithTouchAtDevicePoint() acquires the tree lock, so
   // it cannot be called while the mRecursiveMutex lock is held.
   if (!allowZoom) {
-    mX.UpdateWithTouchAtDevicePoint(aEvent.mLocalFocusPoint.x, 0, aEvent.mTime);
-    mY.UpdateWithTouchAtDevicePoint(aEvent.mLocalFocusPoint.y, 0, aEvent.mTime);
+    mX.UpdateWithTouchAtDevicePoint(aEvent.mLocalFocusPoint.x, aEvent.mTime);
+    mY.UpdateWithTouchAtDevicePoint(aEvent.mLocalFocusPoint.y, aEvent.mTime);
   }
 
   if (!gfxPrefs::APZAllowZooming()) {
@@ -2453,8 +2453,14 @@ nsEventStatus AsyncPanZoomController::OnPan(const PanGestureInput& aEvent, bool
   // size and position. We need to do so even if this is a momentum pan (i.e.
   // aFingersOnTouchpad == false); in that case the "with touch" part is not
   // really appropriate, so we may want to rethink this at some point.
-  mX.UpdateWithTouchAtDevicePoint(aEvent.mLocalPanStartPoint.x, logicalPanDisplacement.x, aEvent.mTime);
-  mY.UpdateWithTouchAtDevicePoint(aEvent.mLocalPanStartPoint.y, logicalPanDisplacement.y, aEvent.mTime);
+  // Note that we have to make all simulated positions relative to
+  // Axis::GetPos(), because the current position is an invented position, and
+  // because resetting the position to the mouse position (e.g.
+  // aEvent.mLocalStartPoint) would mess up velocity calculation. (This is
+  // the only caller of UpdateWithTouchAtDevicePoint() for pan events, so
+  // there is no risk of other calls resetting the position.)
+  mX.UpdateWithTouchAtDevicePoint(mX.GetPos() + logicalPanDisplacement.x, aEvent.mTime);
+  mY.UpdateWithTouchAtDevicePoint(mY.GetPos() + logicalPanDisplacement.y, aEvent.mTime);
 
   HandlePanningUpdate(physicalPanDisplacement);
 
@@ -2891,8 +2897,8 @@ AsyncPanZoomController::StartPanning(const ParentLayerPoint& aStartPoint) {
 
 void AsyncPanZoomController::UpdateWithTouchAtDevicePoint(const MultiTouchInput& aEvent) {
   ParentLayerPoint point = GetFirstTouchPoint(aEvent);
-  mX.UpdateWithTouchAtDevicePoint(point.x, 0, aEvent.mTime);
-  mY.UpdateWithTouchAtDevicePoint(point.y, 0, aEvent.mTime);
+  mX.UpdateWithTouchAtDevicePoint(point.x, aEvent.mTime);
+  mY.UpdateWithTouchAtDevicePoint(point.y, aEvent.mTime);
 }
 
 bool AsyncPanZoomController::AttemptScroll(ParentLayerPoint& aStartPoint,

gfx/layers/apz/src/Axis.cpp

@@ -71,7 +71,7 @@ float Axis::ToLocalVelocity(float aVelocityInchesPerMs) const {
   return localVelocity.Length();
 }
 
-void Axis::UpdateWithTouchAtDevicePoint(ParentLayerCoord aPos, ParentLayerCoord aAdditionalDelta, uint32_t aTimestampMs) {
+void Axis::UpdateWithTouchAtDevicePoint(ParentLayerCoord aPos, uint32_t aTimestampMs) {
   // mVelocityQueue is controller-thread only
   APZThreadUtils::AssertOnControllerThread();
 
@@ -88,7 +88,7 @@ void Axis::UpdateWithTouchAtDevicePoint(ParentLayerCoord aPos, ParentLayerCoord
     return;
   }
 
-  float newVelocity = mAxisLocked ? 0.0f : (float)(mVelocitySamplePos - aPos + aAdditionalDelta) / (float)(aTimestampMs - mVelocitySampleTimeMs);
+  float newVelocity = mAxisLocked ? 0.0f : (float)(mVelocitySamplePos - aPos) / (float)(aTimestampMs - mVelocitySampleTimeMs);
 
   newVelocity = ApplyFlingCurveToVelocity(newVelocity);
 

gfx/layers/apz/src/Axis.h

@@ -46,11 +46,11 @@ public:
   /**
    * Notify this Axis that a new touch has been received, including a timestamp
    * for when the touch was received. This triggers a recalculation of velocity.
-   * This can also used for pan gesture events. For those events, the "touch"
-   * location is stationary and the scroll displacement is passed in as
-   * aAdditionalDelta.
+   * This can also used for pan gesture events. For those events, |aPos| is
+   * an invented position corresponding to the mouse position plus any
+   * accumulated displacements over the course of the pan gesture.
    */
-  void UpdateWithTouchAtDevicePoint(ParentLayerCoord aPos, ParentLayerCoord aAdditionalDelta, uint32_t aTimestampMs);
+  void UpdateWithTouchAtDevicePoint(ParentLayerCoord aPos, uint32_t aTimestampMs);
 
 protected:
   float ApplyFlingCurveToVelocity(float aVelocity) const;
@@ -251,6 +251,13 @@ public:
   virtual const char* Name() const = 0;
 
 protected:
+  // A position along the axis, used during input event processing to
+  // track velocities (and for touch gestures, to track the length of
+  // the gesture). For touch events, this represents the position of
+  // the finger (or in the case of two-finger scrolling, the midpoint
+  // of the two fingers). For pan gesture events, this represents an
+  // invented position corresponding to the mouse position at the start
+  // of the pan, plus deltas representing the displacement of the pan.
   ParentLayerCoord mPos;
 
   // mVelocitySampleTimeMs and mVelocitySamplePos are the time and position