[SPInvalidation] Handle pixel-snapping of paint invalidation rects

third_party/WebKit/Source/core/paint/PaintInvalidator.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PaintInvalidator_h
 #define PaintInvalidator_h
 
 #include "platform/geometry/LayoutRect.h"
 #include "platform/graphics/paint/GeometryMapper.h"
 #include "wtf/Vector.h"
@@ skipping 54 matching lines @@
   // stacked contents' paint invalidation containers differ.
   const LayoutBoxModelObject* paintInvalidationContainerForStackedContents =
       nullptr;
 
   PaintLayer* paintingLayer = nullptr;
 
   LayoutRect oldBounds;
   LayoutRect newBounds;
   LayoutPoint oldLocation;
   LayoutPoint newLocation;
+  bool oldBoundsCoversExtraPixels = false;
+  bool newBoundsCoversExtraPixels = false;
 };
 
 class PaintInvalidator {
  public:
   void invalidatePaintIfNeeded(FrameView&, PaintInvalidatorContext&);
   void invalidatePaintIfNeeded(const LayoutObject&, PaintInvalidatorContext&);
 
   // Process objects needing paint invalidation on the next frame.
   // See the definition of PaintInvalidationDelayedFull for more details.
   void processPendingDelayedPaintInvalidations();
 
  private:
   LayoutRect mapLocalRectToPaintInvalidationBacking(
       const LayoutObject&,
       const FloatRect&,
-      const PaintInvalidatorContext&);
+      const PaintInvalidatorContext&,
+      bool& coversExtraPixels);
   LayoutRect computePaintInvalidationRectInBacking(

[pdr., 2016/10/26 05:25:12]

Returning through both a return value and an out-param is a little confusing.
WDYT of making them both out-params, or returning something like:
struct PaintInvalidationRectInBacking {
    LayoutRect rect;
    bool coversExtraPixels;
}

[Xianzhu, 2016/10/26 18:32:31]

Done.

       const LayoutObject&,
-      const PaintInvalidatorContext&);
+      const PaintInvalidatorContext&,
+      bool& coversExtraPixels);
   LayoutPoint computeLocationFromPaintInvalidationBacking(
       const LayoutObject&,
       const PaintInvalidatorContext&);
   void updatePaintingLayer(const LayoutObject&, PaintInvalidatorContext&);
   void updateContext(const LayoutObject&, PaintInvalidatorContext&);
 
   Vector<const LayoutObject*> m_pendingDelayedPaintInvalidations;
   GeometryMapper m_geometryMapper;
 };
 
 }  // namespace blink
 
 #endif  // PaintInvalidator_h