Bug 1165185 - Try to avoid invalidations when scrolling transformed elements. r=roc

gfx/2d/Matrix.h

@@ -13,6 +13,7 @@
 #include <math.h>
 #include "mozilla/Attributes.h"
 #include "mozilla/DebugOnly.h"
+#include "mozilla/FloatingPoint.h"
 
 namespace mozilla {
 namespace gfx {
@@ -857,6 +858,26 @@ public:
            gfx::FuzzyEqual(_43, o._43) && gfx::FuzzyEqual(_44, o._44);
   }
 
+  bool FuzzyEqualsMultiplicative(const Matrix4x4& o) const
+  {
+    return ::mozilla::FuzzyEqualsMultiplicative(_11, o._11) &&
+           ::mozilla::FuzzyEqualsMultiplicative(_12, o._12) &&
+           ::mozilla::FuzzyEqualsMultiplicative(_13, o._13) &&
+           ::mozilla::FuzzyEqualsMultiplicative(_14, o._14) &&
+           ::mozilla::FuzzyEqualsMultiplicative(_21, o._21) &&
+           ::mozilla::FuzzyEqualsMultiplicative(_22, o._22) &&
+           ::mozilla::FuzzyEqualsMultiplicative(_23, o._23) &&
+           ::mozilla::FuzzyEqualsMultiplicative(_24, o._24) &&
+           ::mozilla::FuzzyEqualsMultiplicative(_31, o._31) &&
+           ::mozilla::FuzzyEqualsMultiplicative(_32, o._32) &&
+           ::mozilla::FuzzyEqualsMultiplicative(_33, o._33) &&
+           ::mozilla::FuzzyEqualsMultiplicative(_34, o._34) &&
+           ::mozilla::FuzzyEqualsMultiplicative(_41, o._41) &&
+           ::mozilla::FuzzyEqualsMultiplicative(_42, o._42) &&
+           ::mozilla::FuzzyEqualsMultiplicative(_43, o._43) &&
+           ::mozilla::FuzzyEqualsMultiplicative(_44, o._44);
+  }
+
   bool IsBackfaceVisible() const
   {
     // Inverse()._33 < 0;
@@ -889,6 +910,24 @@ public:
     return *this;
   }
 
+  // Nudge the 3D components to integer so that this matrix will become 2D if
+  // it's very close to already being 2D.
+  // This doesn't change the _41 and _42 components.
+  Matrix4x4 &NudgeTo2D()
+  {
+    NudgeToInteger(&_13);
+    NudgeToInteger(&_14);
+    NudgeToInteger(&_23);
+    NudgeToInteger(&_24);
+    NudgeToInteger(&_31);
+    NudgeToInteger(&_32);
+    NudgeToInteger(&_33);
+    NudgeToInteger(&_34);
+    NudgeToInteger(&_43);
+    NudgeToInteger(&_44);
+    return *this;
+  }
+
   Point4D TransposedVector(int aIndex) const
   {
       MOZ_ASSERT(aIndex >= 0 && aIndex <= 3, "Invalid matrix array index");

gfx/layers/LayerTreeInvalidation.cpp

@@ -136,7 +136,7 @@ struct LayerPropertiesBase : public LayerProperties
   nsIntRegion ComputeChange(NotifySubDocInvalidationFunc aCallback,
                             bool& aGeometryChanged)
   {
-    bool transformChanged = !mTransform.FuzzyEqual(mLayer->GetLocalTransform()) ||
+    bool transformChanged = !mTransform.FuzzyEqualsMultiplicative(mLayer->GetLocalTransform()) ||
                             mLayer->GetPostXScale() != mPostXScale ||
                             mLayer->GetPostYScale() != mPostYScale;
     Layer* otherMask = mLayer->GetMaskLayer();

layout/base/FrameLayerBuilder.cpp

@@ -4630,12 +4630,13 @@ ChooseScaleAndSetTransform(FrameLayerBuilder* aLayerBuilder,
   if (aTransform) {
     // aTransform is applied first, then the scale is applied to the result
     transform = (*aTransform)*transform;
-    // Set any matrix entries close to integers to be those exact integers.
-    // This protects against floating-point inaccuracies causing problems
-    // in the checks below.
-    // We use the fixed epsilon version here because we don't want the nudging
-    // to depend on the scroll position.
-    transform.NudgeToIntegersFixedEpsilon();
+    // Set relevant 3d matrix entries that are close to integers to be those
+    // exact integers. This protects against floating-point inaccuracies
+    // causing problems in the CanDraw2D / Is2D checks below.
+    // We don't nudge all matrix components here. In particular, we don't want to
+    // nudge the X/Y translation components, because those include the scroll
+    // offset, and we don't want scrolling to affect whether we nudge or not.
+    transform.NudgeTo2D();
   }
   Matrix transform2d;
   if (aContainerFrame &&

layout/reftests/backgrounds/vector/empty/reftest.list

@@ -3,11 +3,10 @@
 == wide--contain--height.html ref-wide-empty.html
 == wide--contain--width.html ref-wide-empty.html
 
-# These tests fail because of integer overflow; see bug 894555.
-fails == tall--cover--height.html ref-tall-lime.html
-fails == tall--cover--width.html ref-tall-lime.html
-fails == wide--cover--height.html ref-wide-lime.html
-fails == wide--cover--width.html ref-wide-lime.html
+== tall--cover--height.html ref-tall-lime.html
+== tall--cover--width.html ref-tall-lime.html
+== wide--cover--height.html ref-wide-lime.html
+== wide--cover--width.html ref-wide-lime.html
 
 == zero-height-ratio-contain.html ref-tall-empty.html
 == zero-height-ratio-cover.html ref-tall-empty.html

layout/reftests/invalidation/fractional-transform-1.html

@@ -0,0 +1,36 @@
+<!DOCTYPE html>
+<html lang="en" class="reftest-wait">
+<meta charset="utf-8">
+<title>Scrolling shouldn't invalidate either rect.</title>
+
+<style>
+body {
+  margin: 0;
+  height: 5000px;
+}
+</style>
+
+<body>
+
+<svg width="768" height="1000">
+
+  <g transform="translate(0 -2000.3234)">
+    <rect x="100" y="2300" height="50" width="50" fill="grey" class="reftest-no-paint"/>
+  </g>
+
+  <g transform="translate(0 -4000.6468)">
+    <rect x="200" y="4300" height="50" width="50" fill="grey" class="reftest-no-paint"/>
+  </g>
+
+</svg>
+
+<script>
+
+document.documentElement.scrollTop = 177;
+
+window.addEventListener("MozReftestInvalidate", function (e) {
+  document.documentElement.scrollTop = 30;
+  document.documentElement.removeAttribute("class");
+});
+
+</script>

layout/reftests/invalidation/fractional-transform-2.html

@@ -0,0 +1,32 @@
+<!DOCTYPE html>
+<html lang="en" class="reftest-wait">
+<meta charset="utf-8">
+<title>Scrolling shouldn't invalidate the square.</title>
+
+<style>
+body {
+  margin: 0;
+  height: 5000px;
+}
+</style>
+
+<body>
+
+<svg width="768" height="1000">
+
+  <g transform="translate(0 112.152992)">
+    <rect x="100" y="650" height="50" width="50" fill="grey" class="reftest-no-paint"/>
+  </g>
+
+</svg>
+
+<script>
+
+document.documentElement.scrollTop = 709;
+
+window.addEventListener("MozReftestInvalidate", function (e) {
+  document.documentElement.scrollTop = 617;
+  document.documentElement.removeAttribute("class");
+});
+
+</script>

layout/reftests/invalidation/fractional-transform-3.html

@@ -0,0 +1,32 @@
+<!DOCTYPE html>
+<html lang="en" class="reftest-wait">
+<meta charset="utf-8">
+<title>Scrolling shouldn't invalidate the square.</title>
+
+<style>
+body {
+  margin: 0;
+  height: 5000px;
+}
+</style>
+
+<body>
+
+<svg width="768" height="1000">
+
+  <g transform="translate(0 0.999948799610138)">
+    <rect x="100" y="100" height="50" width="50" fill="grey" class="reftest-no-paint"/>
+  </g>
+
+</svg>
+
+<script>
+
+document.documentElement.scrollTop = 11;
+
+window.addEventListener("MozReftestInvalidate", function (e) {
+  document.documentElement.scrollTop = 51;
+  document.documentElement.removeAttribute("class");
+});
+
+</script>

layout/reftests/invalidation/reftest.list

@@ -67,3 +67,6 @@ pref(layout.animated-image-layers.enabled,true) skip-if(Android||gtkWidget) == t
 fuzzy-if(gtkWidget,2,4) == image-scrolling-zoom-1.html image-scrolling-zoom-1-ref.html
 != image-scrolling-zoom-1-ref.html image-scrolling-zoom-1-notref.html
 != fast-scrolling.html about:blank
+!= fractional-transform-1.html about:blank
+!= fractional-transform-2.html about:blank
+!= fractional-transform-3.html about:blank

mfbt/FloatingPoint.h

@@ -401,6 +401,13 @@ FuzzyEqualsMultiplicative(T aValue1, T aValue2,
                           T aEpsilon = detail::FuzzyEqualsEpsilon<T>::value())
 {
   static_assert(IsFloatingPoint<T>::value, "floating point type required");
+
+  // Short-circuit the common case in order to avoid the expensive operations
+  // below.
+  if (aValue1 == aValue2) {
+    return true;
+  }
+
   // can't use std::min because of bug 965340
   T smaller = Abs(aValue1) < Abs(aValue2) ? Abs(aValue1) : Abs(aValue2);
   return Abs(aValue1 - aValue2) <= aEpsilon * smaller;