Move LayoutObject::m_previousPosition... into a global map in ObjectPaintInvalidator

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

 // 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.
 
 #include "core/paint/ObjectPaintInvalidator.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/layout/LayoutBlockFlow.h"
 #include "core/layout/LayoutView.h"
@@ skipping 15 matching lines @@
 }
 
 static void setPreviousSelectionVisualRect(const LayoutObject& object,
                                            const LayoutRect& rect) {
   if (rect.isEmpty())
     selectionVisualRectMap().remove(&object);
   else
     selectionVisualRectMap().set(&object, rect);
 }
 
+typedef HashMap<const LayoutObject*, LayoutPoint> LocationInBackingMap;
+static LocationInBackingMap& locationInBackingMap() {
+  DEFINE_STATIC_LOCAL(LocationInBackingMap, map, ());
+  return map;
+}
+
 void ObjectPaintInvalidator::objectWillBeDestroyed(const LayoutObject& object) {
   selectionVisualRectMap().remove(&object);
+  locationInBackingMap().remove(&object);
 }
 
 // TODO(trchen): Use std::function<void, LayoutObject&> when available.
 template <typename LayoutObjectTraversalFunctor>
 void traverseNonCompositingDescendantsInPaintOrder(
     const LayoutObject&,
     const LayoutObjectTraversalFunctor&);
 
 template <typename LayoutObjectTraversalFunctor>
 void traverseNonCompositingDescendantsBelongingToAncestorPaintInvalidationContainer(
@@ skipping 315 matching lines @@
     m_object.invalidateDisplayItemClients(PaintInvalidationRectangle);
 
   return dirtyRectOnBacking;
 }
 
 void ObjectPaintInvalidator::slowSetPaintingLayerNeedsRepaint() {
   if (PaintLayer* paintingLayer = m_object.paintingLayer())
     paintingLayer->setNeedsRepaint();
 }
 
+LayoutPoint ObjectPaintInvalidator::previousLocationInBacking() const {
+  // TODO(wangxianzhu): Use a bit in LayoutObject to indicate whether the object
+  // has previous location in the map to avoid unnecessary map lookup.
+  auto it = locationInBackingMap().find(&m_object);

[chrishtr, 2016/11/04 18:20:07]

This lookup will be slow. How slow?

I think you should address the TODO in this patch to avoid making things slower.

[Xianzhu, 2016/11/04 19:11:03]

Done.

+  if (it == locationInBackingMap().end())
+    return m_object.previousVisualRect().location();
+  return it->value;
+}
+
+void ObjectPaintInvalidator::setPreviousLocationInBacking(
+    const LayoutPoint& location) {
+  // TODO(wangxianzhu): Use a bit in LayoutObject to indicate whether the object
+  // has previous location in the map to avoid unnecessary map lookup.
+  if (location == m_object.previousVisualRect().location())
+    locationInBackingMap().remove(&m_object);
+  else
+    locationInBackingMap().set(&m_object, location);
+}
+
 void ObjectPaintInvalidatorWithContext::fullyInvalidatePaint(
     PaintInvalidationReason reason,
     const LayoutRect& oldVisualRect,
     const LayoutRect& newVisualRect) {
   // The following logic avoids invalidating twice if one set of bounds contains
   // the other.
   if (!newVisualRect.contains(oldVisualRect)) {
     LayoutRect invalidationRect = oldVisualRect;
     invalidatePaintUsingContainer(*m_context.paintInvalidationContainer,
                                   invalidationRect, reason);
@@ skipping 134 matching lines @@
 
   m_context.paintingLayer->setNeedsRepaint();
   m_object.invalidateDisplayItemClients(reason);
   return reason;
 }
 
 DisablePaintInvalidationStateAsserts::DisablePaintInvalidationStateAsserts()
     : m_disabler(&gDisablePaintInvalidationStateAsserts, true) {}
 
 }  // namespace blink