Bug 1145345 - Account for a greater variety of rounding errors when comparing coordinates. r=kats

--HG--
extra : source : af3b6caa84116a5f95783ed9262326f4917b6b90

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -372,8 +372,8 @@ static bool IsCloseToVertical(float aAngle, float aThreshold)
 template <typename Units>
 static bool IsZero(const gfx::PointTyped<Units>& aPoint)
 {
-  return FuzzyEqualsMultiplicative(aPoint.x, 0.0f)
-      && FuzzyEqualsMultiplicative(aPoint.y, 0.0f);
+  return FuzzyEqualsAdditive(aPoint.x, 0.0f)
+      && FuzzyEqualsAdditive(aPoint.y, 0.0f);
 }
 
 static inline void LogRendertraceRect(const ScrollableLayerGuid& aGuid, const char* aDesc, const char* aColor, const CSSRect& aRect)

gfx/layers/apz/src/Axis.cpp

@@ -30,6 +30,12 @@
 namespace mozilla {
 namespace layers {
 
+bool FuzzyEqualsCoordinate(float aValue1, float aValue2)
+{
+  return FuzzyEqualsAdditive(aValue1, aValue2, COORDINATE_EPSILON)
+      || FuzzyEqualsMultiplicative(aValue1, aValue2);
+}
+
 extern StaticAutoPtr<ComputedTimingFunction> gVelocityCurveFunction;
 
 Axis::Axis(AsyncPanZoomController* aAsyncPanZoomController)
@@ -180,8 +186,8 @@ void Axis::OverscrollBy(ParentLayerCoord aOverscroll) {
   aOverscroll = ApplyResistance(aOverscroll);
   if (aOverscroll > 0) {
 #ifdef DEBUG
-    if (!FuzzyEqualsAdditive(GetCompositionEnd().value, GetPageEnd().value, COORDINATE_EPSILON)) {
-      nsPrintfCString message("composition end (%f) is not within COORDINATE_EPISLON of page end (%f)\n",
+    if (!FuzzyEqualsCoordinate(GetCompositionEnd().value, GetPageEnd().value)) {
+      nsPrintfCString message("composition end (%f) is not equal (within error) to page end (%f)\n",
                               GetCompositionEnd().value, GetPageEnd().value);
       NS_ASSERTION(false, message.get());
       MOZ_CRASH();
@@ -190,8 +196,8 @@ void Axis::OverscrollBy(ParentLayerCoord aOverscroll) {
     MOZ_ASSERT(mOverscroll >= 0);
   } else if (aOverscroll < 0) {
 #ifdef DEBUG
-    if (!FuzzyEqualsAdditive(GetOrigin().value, GetPageStart().value, COORDINATE_EPSILON)) {
-      nsPrintfCString message("composition origin (%f) is not within COORDINATE_EPISLON of page origin (%f)\n",
+    if (!FuzzyEqualsCoordinate(GetOrigin().value, GetPageStart().value)) {
+      nsPrintfCString message("composition origin (%f) is not equal (within error) to page origin (%f)\n",
                               GetOrigin().value, GetPageStart().value);
       NS_ASSERTION(false, message.get());
       MOZ_CRASH();

gfx/layers/apz/src/Axis.h

@@ -25,6 +25,16 @@ const float EPSILON = 0.0001f;
 // isn't too large.
 const float COORDINATE_EPSILON = 0.01f;
 
+/**
+ * Compare two coordinates for equality, accounting for rounding error.
+ * Use both FuzzyEqualsAdditive() with COORDINATE_EPISLON, which accounts for
+ * things like the error introduced by rounding during a round-trip to app
+ * units, and FuzzyEqualsMultiplicative(), which accounts for accumulated error
+ * due to floating-point operations (which can be larger than COORDINATE_EPISLON
+ * for sufficiently large coordinate values).
+ */
+bool FuzzyEqualsCoordinate(float aValue1, float aValue2);
+
 struct FrameMetrics;
 class AsyncPanZoomController;