Bug 1016035 - Make the threshold in AxisPhysicsMSDModel::IsFinished controllable by the caller. r=kip

gfx/layers/AxisPhysicsMSDModel.cpp

@@ -70,30 +70,23 @@ AxisPhysicsMSDModel::SetDestination(double aDestination)
 }
 
 bool
-AxisPhysicsMSDModel::IsFinished()
+AxisPhysicsMSDModel::IsFinished(double aSmallestVisibleIncrement)
 {
   // In order to satisfy the condition of reaching the destination, the distance
   // between the simulation position and the destination must be less than
-  // kFinishDistance while the speed is simultaneously less than
-  // kFinishVelocity.  This enables an under-damped system to overshoot the
+  // aSmallestVisibleIncrement while the speed is simultaneously less than
+  // finishVelocity.  This enables an under-damped system to overshoot the
   // destination when desired without prematurely triggering the finished state.
-
-  // As the number of app units per css pixel is 60 and retina / HiDPI displays
-  // may display two pixels for every css pixel, setting kFinishDistance to 30.0
-  // ensures that there will be no perceptable shift in position at the end
-  // of the animation.
-  const double kFinishDistance = 30.0;
-
-  // If kFinishVelocity is set too low, the animation may end long after
+  // If finishVelocity is set too low, the animation may end long after
   // oscillation has finished, resulting in unnecessary processing.
   // If set too high, the animation may prematurely terminate when expected
   // to overshoot the destination in an under-damped system.
-  // 60.0 was selected through experimentation that revealed that a
-  // critically damped system will terminate within 100ms.
-  const double kFinishVelocity = 60.0;
+  // aSmallestVisibleIncrement * 2 was selected through experimentation that
+  // revealed that a critically damped system will terminate within 100ms.
+  const double finishVelocity = aSmallestVisibleIncrement * 2;
 
-  return fabs(mDestination - GetPosition ()) < kFinishDistance
-    && fabs(GetVelocity()) <= kFinishVelocity;
+  return fabs(mDestination - GetPosition ()) < aSmallestVisibleIncrement
+    && fabs(GetVelocity()) <= finishVelocity;
 }
 
 } // namespace layers

gfx/layers/AxisPhysicsMSDModel.h

@@ -38,7 +38,7 @@ public:
    * Returns true when the position is close to the destination and the
    * velocity is low.
    */
-  bool IsFinished();
+  bool IsFinished(double aSmallestVisibleIncrement);
 
 protected:
   virtual double Acceleration(const State &aState);

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -695,7 +695,10 @@ public:
    * or false if the smooth scroll has ended.
    */
   bool DoSample(FrameMetrics& aFrameMetrics, const TimeDuration& aDelta) {
-    if (mXAxisModel.IsFinished() && mYAxisModel.IsFinished()) {
+    nsPoint oneParentLayerPixel =
+      CSSPoint::ToAppUnits(ParentLayerPoint(1, 1) / aFrameMetrics.GetZoom());
+    if (mXAxisModel.IsFinished(oneParentLayerPixel.x) &&
+        mYAxisModel.IsFinished(oneParentLayerPixel.y)) {
       return false;
     }
 
@@ -712,12 +715,12 @@ public:
 
     // Keep the velocity updated for the Axis class so that any animations
     // chained off of the smooth scroll will inherit it.
-    if (mXAxisModel.IsFinished()) {
+    if (mXAxisModel.IsFinished(oneParentLayerPixel.x)) {
       mApzc.mX.SetVelocity(0);
     } else {
       mApzc.mX.SetVelocity(velocity.x);
     }
-    if (mYAxisModel.IsFinished()) {
+    if (mYAxisModel.IsFinished(oneParentLayerPixel.y)) {
       mApzc.mY.SetVelocity(0);
     } else {
       mApzc.mY.SetVelocity(velocity.y);

layout/generic/nsGfxScrollFrame.cpp

@@ -1474,7 +1474,8 @@ public:
                        const nsPoint &aInitialDestination,
                        const nsSize &aInitialVelocity,
                        const nsRect &aRange,
-                       const mozilla::TimeStamp &aStartTime)
+                       const mozilla::TimeStamp &aStartTime,
+                       nsPresContext* aPresContext)
     : mXAxisModel(aInitialPosition.x, aInitialDestination.x,
                   aInitialVelocity.width,
                   gfxPrefs::ScrollBehaviorSpringConstant(),
@@ -1486,6 +1487,7 @@ public:
     , mRange(aRange)
     , mLastRefreshTime(aStartTime)
     , mCallee(nullptr)
+    , mOneDevicePixelInAppUnits(aPresContext->DevPixelsToAppUnits(1))
   {
   }
 
@@ -1542,7 +1544,8 @@ public:
 
   bool IsFinished()
   {
-    return mXAxisModel.IsFinished() && mYAxisModel.IsFinished();
+    return mXAxisModel.IsFinished(mOneDevicePixelInAppUnits) &&
+           mYAxisModel.IsFinished(mOneDevicePixelInAppUnits);
   }
 
   virtual void WillRefresh(mozilla::TimeStamp aTime) override {
@@ -1595,6 +1598,7 @@ private:
   nsRect mRange;
   mozilla::TimeStamp mLastRefreshTime;
   ScrollFrameHelper *mCallee;
+  nscoord mOneDevicePixelInAppUnits;
 };
 
 // AsyncScroll has ref counting.
@@ -2069,7 +2073,7 @@ ScrollFrameHelper::ScrollToWithOrigin(nsPoint aScrollPosition,
         mAsyncSmoothMSDScroll =
           new AsyncSmoothMSDScroll(GetScrollPosition(), mDestination,
                                    currentVelocity, GetScrollRangeForClamping(),
-                                   now);
+                                   now, presContext);
 
         if (!mAsyncSmoothMSDScroll->SetRefreshObserver(this)) {
           // Observer setup failed. Scroll the normal way.