Avoid false-positives of paint offset change detection (method 2)

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp

Index: third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
index 34b7942e959e2e6c6f757736832a8ca09f7c4a95..ced31e0017a8c47e82ca52ff038562d1552d2a04 100644
--- a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
@@ -215,17 +215,18 @@ void PaintPropertyTreeBuilder::updateProperties(
   frameView.setTotalPropertyTreeStateForContents(std::move(contentsState));
 }
 
-void PaintPropertyTreeBuilder::updatePaintOffsetTranslation(
+static bool calculatePaintOffsetTranslation(
     const LayoutObject& object,
-    PaintPropertyTreeBuilderContext& context) {
+    const LayoutPoint& paintOffset,
+    IntPoint& roundedPaintOffset,
+    LayoutPoint& fractionalPaintOffset) {
   bool usesPaintOffsetTranslation = false;
   if (RuntimeEnabledFeatures::rootLayerScrollingEnabled() &&
       object.isLayoutView()) {
     // Root layer scrolling always creates a translation node for LayoutView to
     // ensure fixed and absolute contexts use the correct transform space.
     usesPaintOffsetTranslation = true;
-  } else if (object.isBoxModelObject() &&
-             context.current.paintOffset != LayoutPoint()) {
+  } else if (object.isBoxModelObject() && paintOffset != LayoutPoint()) {
     PaintLayer* layer = toLayoutBoxModelObject(object).layer();
     if (layer &&
         layer->paintsWithTransform(GlobalPaintFlattenCompositingLayers))
@@ -239,10 +240,22 @@ void PaintPropertyTreeBuilder::updatePaintOffsetTranslation(
   // called "subpixel accumulation". For more information, see
   // PaintLayer::subpixelAccumulation() and
   // PaintLayerPainter::paintFragmentByApplyingTransform.
-  IntPoint roundedPaintOffset = roundedIntPoint(context.current.paintOffset);
-  LayoutPoint fractionalPaintOffset =
-      LayoutPoint(context.current.paintOffset - roundedPaintOffset);
+  if (usesPaintOffsetTranslation) {
+    roundedPaintOffset = roundedIntPoint(paintOffset);
+    fractionalPaintOffset = LayoutPoint(paintOffset - roundedPaintOffset);
+  }
+
+  return usesPaintOffsetTranslation;
+}
 
+void PaintPropertyTreeBuilder::updatePaintOffsetTranslation(
+    const LayoutObject& object,
+    PaintPropertyTreeBuilderContext& context) {
+  IntPoint roundedPaintOffset;
+  LayoutPoint fractionalPaintOffset;
+  bool usesPaintOffsetTranslation = calculatePaintOffsetTranslation(
+      object, context.current.paintOffset, roundedPaintOffset,
+      fractionalPaintOffset);
   if (object.needsPaintPropertyUpdate() || context.forceSubtreeUpdate) {
     if (usesPaintOffsetTranslation) {
       auto& properties = object.getMutableForPainting().ensurePaintProperties();
@@ -863,7 +876,7 @@ void PaintPropertyTreeBuilder::updateOutOfFlowContext(
   }
 }
 
-void PaintPropertyTreeBuilder::updateContextForBoxPosition(
+void PaintPropertyTreeBuilder::updateContextForLocation(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
   if (!object.isBoxModelObject())
@@ -930,15 +943,29 @@ void PaintPropertyTreeBuilder::updateContextForBoxPosition(
     }
   }
 
+  IntPoint roundedPaintOffset;
+  LayoutPoint paintOffsetAfterTranslation = context.current.paintOffset;
+  if (calculatePaintOffsetTranslation(
+          toLayoutBoxModelObject(object), context.current.paintOffset,
+          roundedPaintOffset, paintOffsetAfterTranslation)) {
+    const auto* properties = object.paintProperties();
+    if (!properties || !properties->paintOffsetTranslation() ||
+        properties->paintOffsetTranslation()->matrix().to2DTranslation() !=
+            FloatSize(roundedPaintOffset.x(), roundedPaintOffset.y()))
+      object.getMutableForPainting().setNeedsPaintPropertyUpdate();
+  }
+
   // Many paint properties depend on paint offset so we force an update of
   // the entire subtree on paint offset changes.
-  if (object.paintOffset() != context.current.paintOffset)
+  if (object.paintOffset() != paintOffsetAfterTranslation)
     context.forceSubtreeUpdate = true;
 }
 
 void PaintPropertyTreeBuilder::updatePropertiesForSelf(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
+  updateContextForLocation(object, context);
+
 #if DCHECK_IS_ON()
   FindObjectPropertiesNeedingUpdateScope checkNeedsUpdateScope(object, context);
 #endif