Bug 1659124 - Avoid passing non-CSS points to IsZero as it may return false when it should return true. r=botond

IsZero() is changed to take a CSSPoint parameter instead of any
point type, to avoid accidentally re-introducing the issue.

Differential Revision: https://phabricator.services.mozilla.com/D145173

gfx/layers/apz/src/APZCTreeManager.cpp

@@ -2718,7 +2718,8 @@ ParentLayerPoint APZCTreeManager::DispatchFling(
     residualVelocity += current->AttemptFling(transformedHandoffState);
 
     // If there's no residual velocity, there's nothing more to hand off.
-    if (IsZero(residualVelocity)) {
+    if (current->Metrics().GetZoom() == CSSToParentLayerScale(0) ||
+        IsZero(residualVelocity / current->Metrics().GetZoom())) {
       return ParentLayerPoint();
     }
 

gfx/layers/apz/src/APZUtils.h

@@ -76,8 +76,7 @@ inline bool ScrollSourceAllowsOverscroll(ScrollSource aSource) {
 // isn't too large.
 const float COORDINATE_EPSILON = 0.02f;
 
-template <typename Units>
-static bool IsZero(const gfx::PointTyped<Units>& aPoint) {
+inline bool IsZero(const CSSPoint& aPoint) {
   return FuzzyEqualsAdditive(aPoint.x, 0.0f, COORDINATE_EPSILON) &&
          FuzzyEqualsAdditive(aPoint.y, 0.0f, COORDINATE_EPSILON);
 }

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -2265,6 +2265,16 @@ bool AsyncPanZoomController::IsContentOfHonouredTargetRightToLeft(
   return Metrics().IsHorizontalContentRightToLeft();
 }
 
+bool AsyncPanZoomController::IsZero(const ParentLayerPoint& aPoint) const {
+  const auto zoom = Metrics().GetZoom();
+
+  if (zoom == CSSToParentLayerScale(0)) {
+    return true;
+  }
+
+  return layers::IsZero(aPoint / zoom);
+}
+
 bool AsyncPanZoomController::AllowScrollHandoffInCurrentBlock() const {
   bool result = mInputQueue->AllowScrollHandoff();
   if (!StaticPrefs::apz_allow_immediate_handoff()) {

gfx/layers/apz/src/AsyncPanZoomController.h

@@ -580,6 +580,8 @@ class AsyncPanZoomController {
   // @see mozilla::WheelDeltaAdjustmentStrategy
   bool IsContentOfHonouredTargetRightToLeft(bool aHonoursRoot) const;
 
+  bool IsZero(const ParentLayerPoint& aPoint) const;
+
  protected:
   // Protected destructor, to discourage deletion outside of Release():
   virtual ~AsyncPanZoomController();

gfx/layers/apz/src/GenericFlingAnimation.h

@@ -100,6 +100,11 @@ class GenericFlingAnimation : public AsyncPanZoomAnimation,
    */
   virtual bool DoSample(FrameMetrics& aFrameMetrics,
                         const TimeDuration& aDelta) override {
+    CSSToParentLayerScale zoom(aFrameMetrics.GetZoom());
+    if (zoom == CSSToParentLayerScale(0)) {
+      return false;
+    }
+
     ParentLayerPoint velocity;
     ParentLayerPoint offset;
     FlingPhysics::Sample(aDelta, &velocity, &offset);
@@ -107,7 +112,7 @@ class GenericFlingAnimation : public AsyncPanZoomAnimation,
     mApzc.SetVelocityVector(velocity);
 
     // If we shouldn't continue the fling, let's just stop and repaint.
-    if (IsZero(velocity)) {
+    if (IsZero(velocity / zoom)) {
       FLING_LOG("%p ending fling animation. overscrolled=%d\n", &mApzc,
                 mApzc.IsOverscrolled());
       // This APZC or an APZC further down the handoff chain may be be
@@ -137,7 +142,7 @@ class GenericFlingAnimation : public AsyncPanZoomAnimation,
     }
 
     // The fling may have caused us to reach the end of our scroll range.
-    if (!IsZero(overscroll)) {
+    if (!IsZero(overscroll / zoom)) {
       // Hand off the fling to the next APZC in the overscroll handoff chain.
 
       // We may have reached the end of the scroll range along one axis but
@@ -176,7 +181,7 @@ class GenericFlingAnimation : public AsyncPanZoomAnimation,
       // as well. (This fling and the handed-off fling will run concurrently.)
       // Note that AdjustDisplacement() will have zeroed out the velocity
       // along the axes where we're overscrolled.
-      return !IsZero(mApzc.GetVelocityVector());
+      return !IsZero(mApzc.GetVelocityVector() / zoom);
     }
 
     return true;

gfx/layers/apz/src/GenericScrollAnimation.cpp

@@ -79,7 +79,7 @@ bool GenericScrollAnimation::DoSample(FrameMetrics& aFrameMetrics,
   if (finished) {
     mApzc.mX.SetVelocity(0);
     mApzc.mY.SetVelocity(0);
-  } else if (!IsZero(displacement)) {
+  } else if (!IsZero(displacement / zoom)) {
     // Convert velocity from AppUnits/Seconds to ParentLayerCoords/Milliseconds
     nsSize velocity = mAnimationPhysics->VelocityAt(now);
     ParentLayerPoint velocityPL =
@@ -99,7 +99,7 @@ bool GenericScrollAnimation::DoSample(FrameMetrics& aFrameMetrics,
   // then end the animation early. Note that the initial displacement could be 0
   // if the compositor ran very quickly (<1ms) after the animation was created.
   // When that happens we want to make sure the animation continues.
-  if (!IsZero(displacement) && IsZero(adjustedOffset)) {
+  if (!IsZero(displacement / zoom) && IsZero(adjustedOffset / zoom)) {
     // Nothing more to do - end the animation.
     return false;
   }

gfx/layers/apz/src/SmoothMsdScrollAnimation.cpp

@@ -79,7 +79,7 @@ bool SmoothMsdScrollAnimation::DoSample(FrameMetrics& aFrameMetrics,
   // layout.css.scroll-behavior.damping-ratio preference is set to less than 1
   // (underdamped) or if a smooth scroll inherits velocity from a fling
   // gesture.
-  if (!IsZero(overscroll)) {
+  if (!IsZero(overscroll / zoom)) {
     // Hand off a fling with the remaining momentum to the next APZC in the
     // overscroll handoff chain.