Implement incremental paint property tree rebuilding

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

 // Copyright 2015 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/PaintPropertyTreeBuilder.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
 #include "core/layout/LayoutInline.h"
 #include "core/layout/LayoutPart.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/svg/LayoutSVGRoot.h"
+#include "core/paint/FindPropertiesNeedingUpdate.h"
 #include "core/paint/ObjectPaintProperties.h"
 #include "core/paint/PaintLayer.h"
 #include "core/paint/SVGRootPainter.h"
 #include "platform/transforms/TransformationMatrix.h"
 #include "wtf/PtrUtil.h"
 #include <memory>
 
 namespace blink {
 
 namespace {
@@ skipping 41 matching lines @@
   context.current.scroll = context.absolutePosition.scroll =
       context.fixedPosition.scroll = rootScrollNode();
 
   // Ensure scroll tree properties are reset. They will be rebuilt during the
   // tree walk.
   rootScrollNode()->clearMainThreadScrollingReasons();
 
   return context;
 }
 
-const TransformPaintPropertyNode* updateFrameViewPreTranslation(
+void updateFrameViewPreTranslation(
     FrameView& frameView,
     PassRefPtr<const TransformPaintPropertyNode> parent,
     const TransformationMatrix& matrix,
     const FloatPoint3D& origin) {
   DCHECK(!RuntimeEnabledFeatures::rootLayerScrollingEnabled());
-  if (TransformPaintPropertyNode* existingPreTranslation =
-          frameView.preTranslation())
+  if (auto* existingPreTranslation = frameView.preTranslation()) {
     existingPreTranslation->update(std::move(parent), matrix, origin);
-  else
+  } else {
     frameView.setPreTranslation(
         TransformPaintPropertyNode::create(std::move(parent), matrix, origin));
-  return frameView.preTranslation();
+  }
 }
 
-const ClipPaintPropertyNode* updateFrameViewContentClip(
+void updateFrameViewContentClip(
     FrameView& frameView,
     PassRefPtr<const ClipPaintPropertyNode> parent,
     PassRefPtr<const TransformPaintPropertyNode> localTransformSpace,
     const FloatRoundedRect& clipRect) {
   DCHECK(!RuntimeEnabledFeatures::rootLayerScrollingEnabled());
-  if (ClipPaintPropertyNode* existingContentClip = frameView.contentClip())
+  if (auto* existingContentClip = frameView.contentClip()) {
     existingContentClip->update(std::move(parent),
                                 std::move(localTransformSpace), clipRect);
-  else
+  } else {
     frameView.setContentClip(ClipPaintPropertyNode::create(
         std::move(parent), std::move(localTransformSpace), clipRect));
-  return frameView.contentClip();
+  }
 }
 
-const TransformPaintPropertyNode* updateFrameViewScrollTranslation(
+void updateFrameViewScrollTranslation(
     FrameView& frameView,
     PassRefPtr<const TransformPaintPropertyNode> parent,
     const TransformationMatrix& matrix,
     const FloatPoint3D& origin) {
   DCHECK(!RuntimeEnabledFeatures::rootLayerScrollingEnabled());
-  if (TransformPaintPropertyNode* existingScrollTranslation =
-          frameView.scrollTranslation())
+  if (auto* existingScrollTranslation = frameView.scrollTranslation()) {
     existingScrollTranslation->update(std::move(parent), matrix, origin);
-  else
+  } else {
     frameView.setScrollTranslation(
         TransformPaintPropertyNode::create(std::move(parent), matrix, origin));
-  return frameView.scrollTranslation();
+  }
 }
 
-ScrollPaintPropertyNode* updateFrameViewScroll(
+void updateFrameViewScroll(
     FrameView& frameView,
     PassRefPtr<ScrollPaintPropertyNode> parent,
     PassRefPtr<const TransformPaintPropertyNode> scrollOffset,
     const IntSize& clip,
     const IntSize& bounds,
     bool userScrollableHorizontal,
     bool userScrollableVertical) {
   DCHECK(!RuntimeEnabledFeatures::rootLayerScrollingEnabled());
-  if (ScrollPaintPropertyNode* existingScroll = frameView.scroll())
+  if (auto* existingScroll = frameView.scroll()) {
     existingScroll->update(std::move(parent), std::move(scrollOffset), clip,
                            bounds, userScrollableHorizontal,
                            userScrollableVertical);
-  else
+  } else {
     frameView.setScroll(ScrollPaintPropertyNode::create(
         std::move(parent), std::move(scrollOffset), clip, bounds,
         userScrollableHorizontal, userScrollableVertical));
-  return frameView.scroll();
+  }
 }
 
-void PaintPropertyTreeBuilder::buildTreeNodes(
+void PaintPropertyTreeBuilder::updateProperties(
     FrameView& frameView,
     PaintPropertyTreeBuilderContext& context) {
   if (RuntimeEnabledFeatures::rootLayerScrollingEnabled()) {
     LayoutView* layoutView = frameView.layoutView();
     if (!layoutView)
       return;
 
-    TransformationMatrix frameTranslate;
-    frameTranslate.translate(frameView.x() + layoutView->location().x() +
-                                 context.current.paintOffset.x(),
-                             frameView.y() + layoutView->location().y() +
-                                 context.current.paintOffset.y());
-    context.current.transform =
-        layoutView->getMutableForPainting()
-            .ensurePaintProperties()
-            .updatePaintOffsetTranslation(context.current.transform,
-                                          frameTranslate, FloatPoint3D());
+#if DCHECK_IS_ON()
+    auto findObjectPropertiesNeedingUpdateScope =
+        FindObjectPropertiesNeedingUpdateScope::create(*layoutView);
+#endif
+
+    if (layoutView->needsPaintPropertyUpdate()) {
+      TransformationMatrix frameTranslate;
+      frameTranslate.translate(frameView.x() + layoutView->location().x() +
+                                   context.current.paintOffset.x(),
+                               frameView.y() + layoutView->location().y() +
+                                   context.current.paintOffset.y());
+      layoutView->getMutableForPainting()
+          .ensurePaintProperties()
+          .updatePaintOffsetTranslation(context.current.transform,
+                                        frameTranslate, FloatPoint3D());
+    }
+
+    const auto* properties = layoutView->paintProperties();
+    DCHECK(properties && properties->paintOffsetTranslation());
+    context.current.transform = properties->paintOffsetTranslation();
     context.current.paintOffset = LayoutPoint();
     context.current.renderingContextID = 0;
     context.current.shouldFlattenInheritedTransform = true;
     context.absolutePosition = context.current;
     context.containerForAbsolutePosition =
         nullptr;  // This will get set in updateOutOfFlowContext().
     context.fixedPosition = context.current;
     return;
   }
 
-  TransformationMatrix frameTranslate;
-  frameTranslate.translate(frameView.x() + context.current.paintOffset.x(),
-                           frameView.y() + context.current.paintOffset.y());
-  context.current.transform = updateFrameViewPreTranslation(
-      frameView, context.current.transform, frameTranslate, FloatPoint3D());
+#if DCHECK_IS_ON()
+  auto findFrameViewPropertiesNeedingUpdateScope =
+      FindFrameViewPropertiesNeedingUpdateScope::create(&frameView);
+#endif
 
-  FloatRoundedRect contentClip(
-      IntRect(IntPoint(), frameView.visibleContentSize()));
-  context.current.clip = updateFrameViewContentClip(
-      frameView, context.current.clip, frameView.preTranslation(), contentClip);
+  if (frameView.needsPaintPropertyUpdate()) {
+    TransformationMatrix frameTranslate;
+    frameTranslate.translate(frameView.x() + context.current.paintOffset.x(),
+                             frameView.y() + context.current.paintOffset.y());
+    updateFrameViewPreTranslation(frameView, context.current.transform,
+                                  frameTranslate, FloatPoint3D());
 
-  // Record the fixed properties before any scrolling occurs.
-  const auto* fixedTransformNode = context.current.transform;
-  auto* fixedScrollNode = context.current.scroll;
+    FloatRoundedRect contentClip(
+        IntRect(IntPoint(), frameView.visibleContentSize()));
+    updateFrameViewContentClip(frameView, context.current.clip,
+                               frameView.preTranslation(), contentClip);
 
-  ScrollOffset scrollOffset = frameView.scrollOffset();
-  if (frameView.isScrollable() || !scrollOffset.isZero()) {
-    TransformationMatrix frameScroll;
-    frameScroll.translate(-scrollOffset.width(), -scrollOffset.height());
-    context.current.transform = updateFrameViewScrollTranslation(
-        frameView, frameView.preTranslation(), frameScroll, FloatPoint3D());
+    ScrollOffset scrollOffset = frameView.scrollOffset();
+    if (frameView.isScrollable() || !scrollOffset.isZero()) {
+      TransformationMatrix frameScroll;
+      frameScroll.translate(-scrollOffset.width(), -scrollOffset.height());
+      updateFrameViewScrollTranslation(frameView, frameView.preTranslation(),
+                                       frameScroll, FloatPoint3D());
 
-    IntSize scrollClip = frameView.visibleContentSize();
-    IntSize scrollBounds = frameView.contentsSize();
-    bool userScrollableHorizontal =
-        frameView.userInputScrollable(HorizontalScrollbar);
-    bool userScrollableVertical =
-        frameView.userInputScrollable(VerticalScrollbar);
-    context.current.scroll = updateFrameViewScroll(
-        frameView, context.current.scroll, frameView.scrollTranslation(),
-        scrollClip, scrollBounds, userScrollableHorizontal,
-        userScrollableVertical);
-  } else {
-    // Ensure pre-existing properties are cleared when there is no scrolling.
-    frameView.setScrollTranslation(nullptr);
-    frameView.setScroll(nullptr);
+      IntSize scrollClip = frameView.visibleContentSize();
+      IntSize scrollBounds = frameView.contentsSize();
+      bool userScrollableHorizontal =
+          frameView.userInputScrollable(HorizontalScrollbar);
+      bool userScrollableVertical =
+          frameView.userInputScrollable(VerticalScrollbar);
+      updateFrameViewScroll(frameView, context.current.scroll,
+                            frameView.scrollTranslation(), scrollClip,
+                            scrollBounds, userScrollableHorizontal,
+                            userScrollableVertical);
+    } else {
+      // Ensure pre-existing properties are cleared when there is no scrolling.
+      frameView.setScrollTranslation(nullptr);
+      frameView.setScroll(nullptr);
+    }
   }
 
   // Initialize the context for current, absolute and fixed position cases.
   // They are the same, except that scroll translation does not apply to
   // fixed position descendants.
+  const auto* fixedTransformNode = frameView.preTranslation()
+                                       ? frameView.preTranslation()
+                                       : context.current.transform;
+  auto* fixedScrollNode = context.current.scroll;
+  DCHECK(frameView.preTranslation());
+  context.current.transform = frameView.preTranslation();
+  DCHECK(frameView.contentClip());
+  context.current.clip = frameView.contentClip();
+  if (const auto* scrollTranslation = frameView.scrollTranslation())
+    context.current.transform = scrollTranslation;
+  if (auto* scroll = frameView.scroll())
+    context.current.scroll = scroll;
   context.current.paintOffset = LayoutPoint();
   context.current.renderingContextID = 0;
   context.current.shouldFlattenInheritedTransform = true;
   context.absolutePosition = context.current;
   context.containerForAbsolutePosition = nullptr;
   context.fixedPosition = context.current;
   context.fixedPosition.transform = fixedTransformNode;
   context.fixedPosition.scroll = fixedScrollNode;
 
   std::unique_ptr<PropertyTreeState> contentsState(
       new PropertyTreeState(context.current.transform, context.current.clip,
                             context.currentEffect, context.current.scroll));
   frameView.setTotalPropertyTreeStateForContents(std::move(contentsState));
 }
 
 void PaintPropertyTreeBuilder::updatePaintOffsetTranslation(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
   // LayoutView's paint offset is updated in the FrameView property update.
   if (object.isLayoutView()) {
     DCHECK(context.current.paintOffset == LayoutPoint());
     return;
   }
 
+  bool usesPaintOffsetTranslation = false;
   if (object.isBoxModelObject() &&
       context.current.paintOffset != LayoutPoint()) {
     // TODO(trchen): Eliminate PaintLayer dependency.
     PaintLayer* layer = toLayoutBoxModelObject(object).layer();
-    if (layer && layer->paintsWithTransform(GlobalPaintNormalPhase)) {
-      // We should use the same subpixel paint offset values for snapping
-      // regardless of whether a transform is present. If there is a transform
-      // we round the paint offset but keep around the residual fractional
-      // component for the transformed content to paint with.  In spv1 this was
-      // 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 (layer && layer->paintsWithTransform(GlobalPaintNormalPhase))
+      usesPaintOffsetTranslation = true;
+  }
 
-      context.current.transform =
-          object.getMutableForPainting()
-              .ensurePaintProperties()
-              .updatePaintOffsetTranslation(
-                  context.current.transform,
-                  TransformationMatrix().translate(roundedPaintOffset.x(),
-                                                   roundedPaintOffset.y()),
-                  FloatPoint3D(),
-                  context.current.shouldFlattenInheritedTransform,
-                  context.current.renderingContextID);
-      context.current.paintOffset = fractionalPaintOffset;
-      return;
+  // We should use the same subpixel paint offset values for snapping
+  // regardless of whether a transform is present. If there is a transform
+  // we round the paint offset but keep around the residual fractional
+  // component for the transformed content to paint with.  In spv1 this was
+  // 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 (object.needsPaintPropertyUpdate()) {
+    if (usesPaintOffsetTranslation) {
+      object.getMutableForPainting()
+          .ensurePaintProperties()
+          .updatePaintOffsetTranslation(
+              context.current.transform,
+              TransformationMatrix().translate(roundedPaintOffset.x(),
+                                               roundedPaintOffset.y()),
+              FloatPoint3D(), context.current.shouldFlattenInheritedTransform,
+              context.current.renderingContextID);
+    } else {
+      if (auto* properties = object.getMutableForPainting().paintProperties())
+        properties->clearPaintOffsetTranslation();
     }
   }
 
-  if (auto* properties = object.getMutableForPainting().paintProperties())
-    properties->clearPaintOffsetTranslation();
+  const auto* properties = object.paintProperties();
+  if (properties && properties->paintOffsetTranslation()) {
+    context.current.transform = properties->paintOffsetTranslation();
+    context.current.paintOffset = fractionalPaintOffset;
+  }
 }
 
 static FloatPoint3D transformOrigin(const LayoutBox& box) {
   const ComputedStyle& style = box.styleRef();
   FloatSize borderBoxSize(box.size());
   return FloatPoint3D(
       floatValueForLength(style.transformOriginX(), borderBoxSize.width()),
       floatValueForLength(style.transformOriginY(), borderBoxSize.height()),
       style.transformOriginZ());
 }
 
 // SVG does not use the general transform update of |updateTransform|, instead
 // creating a transform node for SVG-specific transforms without 3D.
 void PaintPropertyTreeBuilder::updateTransformForNonRootSVG(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
   DCHECK(object.isSVG() && !object.isSVGRoot());
   // SVG (other than SVGForeignObject) does not use paint offset internally.
   DCHECK(object.isSVGForeignObject() ||
          context.current.paintOffset == LayoutPoint());
 
-  // FIXME(pdr): Refactor this so all non-root SVG objects use the same
-  // transform function.
-  const AffineTransform& transform = object.isSVGForeignObject()
-                                         ? object.localSVGTransform()
-                                         : object.localToSVGParentTransform();
+  if (object.needsPaintPropertyUpdate()) {
+    // FIXME(pdr): Refactor this so all non-root SVG objects use the same

[Xianzhu, 2016/10/26 19:21:51]

Nit: s/FIXME/TODO/

[pdr., 2016/10/26 23:10:19]

Done

+    // transform function.
+    const AffineTransform& transform = object.isSVGForeignObject()
+                                           ? object.localSVGTransform()
+                                           : object.localToSVGParentTransform();
+    // FIXME(pdr): Check for the presence of a transform instead of the value.
+    // Checking for an identity matrix will cause the property tree structure
+    // to change during animations if the animation passes through the
+    // identity matrix.
+    if (!transform.isIdentity()) {
+      // The origin is included in the local transform, so leave origin empty.
+      object.getMutableForPainting().ensurePaintProperties().updateTransform(
+          context.current.transform, TransformationMatrix(transform),
+          FloatPoint3D());
+    } else {
+      if (auto* properties = object.getMutableForPainting().paintProperties())
+        properties->clearTransform();
+    }
+  }
 
-  // FIXME(pdr): Check for the presence of a transform instead of the value.
-  // Checking for an identity matrix will cause the property tree structure to
-  // change during animations if the animation passes through the identity
-  // matrix.
-  if (!transform.isIdentity()) {
-    // The origin is included in the local transform, so leave origin empty.
-    context.current.transform =
-        object.getMutableForPainting().ensurePaintProperties().updateTransform(
-            context.current.transform, TransformationMatrix(transform),
-            FloatPoint3D());
+  if (object.paintProperties() && object.paintProperties()->transform()) {
+    context.current.transform = object.paintProperties()->transform();
+    context.current.shouldFlattenInheritedTransform = false;
     context.current.renderingContextID = 0;
-    context.current.shouldFlattenInheritedTransform = false;
-  } else {
-    if (auto* properties = object.getMutableForPainting().paintProperties())
-      properties->clearTransform();
   }
 }
 
 void PaintPropertyTreeBuilder::updateTransform(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
   if (object.isSVG() && !object.isSVGRoot()) {
     updateTransformForNonRootSVG(object, context);
     return;
   }
 
-  const ComputedStyle& style = object.styleRef();
-  if (object.isBox() && (style.hasTransform() || style.preserves3D())) {
-    TransformationMatrix matrix;
-    style.applyTransform(matrix, toLayoutBox(object).size(),
-                         ComputedStyle::ExcludeTransformOrigin,
-                         ComputedStyle::IncludeMotionPath,
-                         ComputedStyle::IncludeIndependentTransformProperties);
-    FloatPoint3D origin = transformOrigin(toLayoutBox(object));
+  if (object.needsPaintPropertyUpdate()) {
+    const ComputedStyle& style = object.styleRef();
+    if (object.isBox() && (style.hasTransform() || style.preserves3D())) {
+      TransformationMatrix matrix;
+      style.applyTransform(
+          matrix, toLayoutBox(object).size(),
+          ComputedStyle::ExcludeTransformOrigin,
+          ComputedStyle::IncludeMotionPath,
+          ComputedStyle::IncludeIndependentTransformProperties);
 
-    unsigned renderingContextID = context.current.renderingContextID;
-    unsigned renderingContextIDForChildren = 0;
-    bool flattensInheritedTransform =
-        context.current.shouldFlattenInheritedTransform;
-    bool childrenFlattenInheritedTransform = true;
-
-    // TODO(trchen): transform-style should only be respected if a PaintLayer
-    // is created.
-    if (style.preserves3D()) {
+      // TODO(trchen): transform-style should only be respected if a PaintLayer
+      // is created.
       // If a node with transform-style: preserve-3d does not exist in an
       // existing rendering context, it establishes a new one.
-      if (!renderingContextID)
+      unsigned renderingContextID = context.current.renderingContextID;
+      if (style.preserves3D() && !renderingContextID)
         renderingContextID = PtrHash<const LayoutObject>::hash(&object);
-      renderingContextIDForChildren = renderingContextID;
-      childrenFlattenInheritedTransform = false;
+
+      object.getMutableForPainting().ensurePaintProperties().updateTransform(
+          context.current.transform, matrix,
+          transformOrigin(toLayoutBox(object)),
+          context.current.shouldFlattenInheritedTransform, renderingContextID);
+    } else {
+      if (auto* properties = object.getMutableForPainting().paintProperties())
+        properties->clearTransform();
     }
+  }
 
-    context.current.transform =
-        object.getMutableForPainting().ensurePaintProperties().updateTransform(
-            context.current.transform, matrix, origin,
-            flattensInheritedTransform, renderingContextID);
-    context.current.renderingContextID = renderingContextIDForChildren;
-    context.current.shouldFlattenInheritedTransform =
-        childrenFlattenInheritedTransform;
-  } else {
-    if (auto* properties = object.getMutableForPainting().paintProperties())
-      properties->clearTransform();
+  const auto* properties = object.paintProperties();
+  if (properties && properties->transform()) {
+    context.current.transform = properties->transform();
+    unsigned renderingContextID = properties->transform()->renderingContextID();
+    if (context.current.renderingContextID != renderingContextID) {
+      context.current.renderingContextID = renderingContextID;
+      context.current.shouldFlattenInheritedTransform = false;
+    } else {
+      context.current.renderingContextID = 0;
+      context.current.shouldFlattenInheritedTransform = true;
+    }
   }
 }
 
 void PaintPropertyTreeBuilder::updateEffect(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
   const ComputedStyle& style = object.styleRef();
 
   if (!style.isStackingContext()) {
-    if (ObjectPaintProperties* properties =
-            object.getMutableForPainting().paintProperties())
-      properties->clearEffect();
+    if (object.needsPaintPropertyUpdate()) {
+      if (auto* properties = object.getMutableForPainting().paintProperties())
+        properties->clearEffect();
+    }
     return;
   }
 
-  // TODO(trchen): Can't omit effect node if we have 3D children.
-  // TODO(trchen): Can't omit effect node if we have blending children.
-  bool effectNodeNeeded = false;
+  if (object.needsPaintPropertyUpdate()) {
+    // TODO(trchen): Can't omit effect node if we have 3D children.
+    // TODO(trchen): Can't omit effect node if we have blending children.
+    bool effectNodeNeeded = false;
 
-  float opacity = style.opacity();
-  if (opacity != 1.0f)
-    effectNodeNeeded = true;
+    float opacity = style.opacity();
+    if (opacity != 1.0f)
+      effectNodeNeeded = true;
 
-  CompositorFilterOperations filter;
-  if (object.isSVG() && !object.isSVGRoot()) {
-    // TODO(trchen): SVG caches filters in SVGResources. Implement it.
-  } else if (PaintLayer* layer = toLayoutBoxModelObject(object).layer()) {
-    // TODO(trchen): Eliminate PaintLayer dependency.
-    filter = layer->createCompositorFilterOperationsForFilter(style);
+    CompositorFilterOperations filter;
+    if (object.isSVG() && !object.isSVGRoot()) {
+      // TODO(trchen): SVG caches filters in SVGResources. Implement it.
+    } else if (PaintLayer* layer = toLayoutBoxModelObject(object).layer()) {
+      // TODO(trchen): Eliminate PaintLayer dependency.
+      filter = layer->createCompositorFilterOperationsForFilter(style);
+    }
+
+    const ClipPaintPropertyNode* outputClip = rootClipNode();
+    // The CSS filter spec didn't specify how filters interact with overflow
+    // clips. The implementation here mimics the old Blink/WebKit behavior for
+    // backward compatibility.
+    // Basically the output of the filter will be affected by clips that applies
+    // to the current element. The descendants that paints into the input of the
+    // filter ignores any clips collected so far. For example:
+    // <div style="overflow:scroll">
+    //   <div style="filter:blur(1px);">
+    //     <div>A</div>
+    //     <div style="position:absolute;">B</div>
+    //   </div>
+    // </div>
+    // In this example "A" should be clipped if the filter was not present.
+    // With the filter, "A" will be rastered without clipping, but instead
+    // the blurred result will be clipped.
+    // On the other hand, "B" should not be clipped because the overflow clip is
+    // not in its containing block chain, but as the filter output will be
+    // clipped, so a blurred "B" may still be invisible.
+    if (!filter.isEmpty()) {
+      effectNodeNeeded = true;
+      outputClip = context.current.clip;
+
+      // TODO(trchen): A filter may contain spatial operations such that an
+      // output pixel may depend on an input pixel outside of the output clip.
+      // We should generate a special clip node to represent this expansion.
+    }
+
+    if (effectNodeNeeded) {
+      object.getMutableForPainting().ensurePaintProperties().updateEffect(
+          context.currentEffect, context.current.transform, outputClip,
+          std::move(filter), opacity);
+    } else {
+      if (auto* properties = object.getMutableForPainting().paintProperties())
+        properties->clearEffect();
+    }
   }
 
-  const ClipPaintPropertyNode* outputClip = rootClipNode();
-  // The CSS filter spec didn't specify how filters interact with overflow
-  // clips. The implementation here mimics the old Blink/WebKit behavior for
-  // backward compatibility.
-  // Basically the output of the filter will be affected by clips that applies
-  // to the current element. The descendants that paints into the input of the
-  // filter ignores any clips collected so far. For example:
-  // <div style="overflow:scroll">
-  //   <div style="filter:blur(1px);">
-  //     <div>A</div>
-  //     <div style="position:absolute;">B</div>
-  //   </div>
-  // </div>
-  // In this example "A" should be clipped if the filter was not present.
-  // With the filter, "A" will be rastered without clipping, but instead
-  // the blurred result will be clipped.
-  // On the other hand, "B" should not be clipped because the overflow clip is
-  // not in its containing block chain, but as the filter output will be
-  // clipped, so a blurred "B" may still be invisible.
-  if (!filter.isEmpty()) {
-    effectNodeNeeded = true;
-    outputClip = context.current.clip;
-
-    // TODO(trchen): A filter may contain spatial operations such that an output
-    // pixel may depend on an input pixel outside of the output clip. Need to
-    // generate special clip node to hint how to expand clip / cull rect.
+  const auto* properties = object.paintProperties();
+  if (properties && properties->effect()) {
+    context.currentEffect = properties->effect();
+    // TODO(pdr): Once the expansion clip node is created above, it should be
+    // used here to update all current clip nodes;
     const ClipPaintPropertyNode* expansionHint = context.current.clip;
     context.current.clip = context.absolutePosition.clip =
         context.fixedPosition.clip = expansionHint;
   }
-
-  if (!effectNodeNeeded) {
-    if (ObjectPaintProperties* properties =
-            object.getMutableForPainting().paintProperties())
-      properties->clearEffect();
-    return;
-  }
-
-  context.currentEffect =
-      object.getMutableForPainting().ensurePaintProperties().updateEffect(
-          context.currentEffect, context.current.transform, outputClip,
-          std::move(filter), opacity);
 }
 
 void PaintPropertyTreeBuilder::updateCssClip(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
-  if (object.hasClip()) {
-    // Create clip node for descendants that are not fixed position.
-    // We don't have to setup context.absolutePosition.clip here because this
-    // object must be a container for absolute position descendants, and will
-    // copy from in-flow context later at updateOutOfFlowContext() step.
-    DCHECK(object.canContainAbsolutePositionObjects());
-    LayoutRect clipRect =
-        toLayoutBox(object).clipRect(context.current.paintOffset);
-    context.current.clip =
-        object.getMutableForPainting().ensurePaintProperties().updateCssClip(
-            context.current.clip, context.current.transform,
-            FloatRoundedRect(FloatRect(clipRect)));
-    return;
+  if (object.needsPaintPropertyUpdate()) {
+    if (object.hasClip()) {
+      // Create clip node for descendants that are not fixed position.
+      // We don't have to setup context.absolutePosition.clip here because this
+      // object must be a container for absolute position descendants, and will
+      // copy from in-flow context later at updateOutOfFlowContext() step.
+      DCHECK(object.canContainAbsolutePositionObjects());
+      LayoutRect clipRect =
+          toLayoutBox(object).clipRect(context.current.paintOffset);
+      object.getMutableForPainting().ensurePaintProperties().updateCssClip(
+          context.current.clip, context.current.transform,
+          FloatRoundedRect(FloatRect(clipRect)));
+    } else {
+      if (auto* properties = object.getMutableForPainting().paintProperties())
+        properties->clearCssClip();
+    }
   }
 
-  if (auto* properties = object.getMutableForPainting().paintProperties())
-    properties->clearCssClip();
+  const auto* properties = object.paintProperties();
+  if (properties && properties->cssClip())
+    context.current.clip = properties->cssClip();
 }
 
 void PaintPropertyTreeBuilder::updateLocalBorderBoxContext(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
-  // Avoid adding an ObjectPaintProperties for non-boxes to save memory, since
-  // we don't need them at the moment.
-  if (!object.isBox() && !object.hasLayer())
-    return;
-
-  std::unique_ptr<ObjectPaintProperties::PropertyTreeStateWithOffset>
-      borderBoxContext =
-          wrapUnique(new ObjectPaintProperties::PropertyTreeStateWithOffset(
-              context.current.paintOffset,
-              PropertyTreeState(context.current.transform, context.current.clip,
-                                context.currentEffect,
-                                context.current.scroll)));
-  object.getMutableForPainting()
-      .ensurePaintProperties()
-      .setLocalBorderBoxProperties(std::move(borderBoxContext));
+  if (object.needsPaintPropertyUpdate()) {
+    // Avoid adding an ObjectPaintProperties for non-boxes to save memory, since
+    // we don't need them at the moment.
+    if (!object.isBox() && !object.hasLayer()) {
+      if (auto* properties = object.getMutableForPainting().paintProperties())
+        properties->clearLocalBorderBoxProperties();
+    } else {
+      std::unique_ptr<ObjectPaintProperties::PropertyTreeStateWithOffset>
+          borderBoxContext =
+              wrapUnique(new ObjectPaintProperties::PropertyTreeStateWithOffset(
+                  context.current.paintOffset,
+                  PropertyTreeState(context.current.transform,
+                                    context.current.clip, context.currentEffect,
+                                    context.current.scroll)));
+      object.getMutableForPainting()
+          .ensurePaintProperties()
+          .setLocalBorderBoxProperties(std::move(borderBoxContext));
+    }
+  }
 }
 
 // TODO(trchen): Remove this once we bake the paint offset into frameRect.
 void PaintPropertyTreeBuilder::updateScrollbarPaintOffset(
     const LayoutObject& object,
     const PaintPropertyTreeBuilderContext& context) {
+  if (!object.needsPaintPropertyUpdate())
+    return;
+
   IntPoint roundedPaintOffset = roundedIntPoint(context.current.paintOffset);
   if (roundedPaintOffset != IntPoint() && object.isBoxModelObject()) {
     if (PaintLayerScrollableArea* scrollableArea =
             toLayoutBoxModelObject(object).getScrollableArea()) {
       if (scrollableArea->horizontalScrollbar() ||
           scrollableArea->verticalScrollbar()) {
         auto paintOffset = TransformationMatrix().translate(
             roundedPaintOffset.x(), roundedPaintOffset.y());
         object.getMutableForPainting()
             .ensurePaintProperties()
             .updateScrollbarPaintOffset(context.current.transform, paintOffset,
                                         FloatPoint3D());
         return;
       }
     }
   }
 
   if (auto* properties = object.getMutableForPainting().paintProperties())
     properties->clearScrollbarPaintOffset();
 }
 
 void PaintPropertyTreeBuilder::updateMainThreadScrollingReasons(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
+  // TODO(pdr): Mark properties as needing an update for main thread scroll
+  // reasons and ensure reason changes are propagated to ancestors to account
+  // for the parent walk below.
   if (context.current.scroll &&
-      !object.document().settings()->threadedScrollingEnabled())
+      !object.document().settings()->threadedScrollingEnabled()) {
     context.current.scroll->addMainThreadScrollingReasons(
         MainThreadScrollingReason::kThreadedScrollingDisabled);
+  }
 
   if (object.isBackgroundAttachmentFixedObject()) {
     auto* scrollNode = context.current.scroll;
     while (
         scrollNode &&
         !scrollNode->hasMainThreadScrollingReasons(
             MainThreadScrollingReason::kHasBackgroundAttachmentFixedObjects)) {
       scrollNode->addMainThreadScrollingReasons(
           MainThreadScrollingReason::kHasBackgroundAttachmentFixedObjects);
       scrollNode = scrollNode->parent();
     }
   }
 }
 
 void PaintPropertyTreeBuilder::updateOverflowClip(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
   if (!object.isBox())
     return;
   const LayoutBox& box = toLayoutBox(object);
+  if (object.needsPaintPropertyUpdate()) {
+    // The <input> elements can't have contents thus CSS overflow property
+    // doesn't apply.  However for layout purposes we do generate child layout
+    // objects for them, e.g. button label.  We should clip the overflow from
+    // those children. This is called control clip and we technically treat them
+    // like overflow clip.
+    LayoutRect clipRect;
+    if (box.hasControlClip()) {
+      clipRect = box.controlClipRect(context.current.paintOffset);
+    } else if (box.hasOverflowClip() || box.styleRef().containsPaint() ||
+               (box.isSVGRoot() &&
+                toLayoutSVGRoot(box).shouldApplyViewportClip())) {
+      clipRect = LayoutRect(pixelSnappedIntRect(
+          box.overflowClipRect(context.current.paintOffset)));
+    } else {
+      if (auto* properties = object.getMutableForPainting().paintProperties()) {
+        properties->clearInnerBorderRadiusClip();
+        properties->clearOverflowClip();
+      }
+      return;
+    }
 
-  // The <input> elements can't have contents thus CSS overflow property doesn't
-  // apply.  However for layout purposes we do generate child layout objects for
-  // them, e.g. button label.  We should clip the overflow from those children.
-  // This is called control clip and we technically treat them like overflow
-  // clip.
-  LayoutRect clipRect;
-  if (box.hasControlClip()) {
-    clipRect = box.controlClipRect(context.current.paintOffset);
-  } else if (box.hasOverflowClip() || box.styleRef().containsPaint() ||
-             (box.isSVGRoot() &&
-              toLayoutSVGRoot(box).shouldApplyViewportClip())) {
-    clipRect = LayoutRect(
-        pixelSnappedIntRect(box.overflowClipRect(context.current.paintOffset)));
-  } else {
-    if (auto* properties = object.getMutableForPainting().paintProperties()) {
+    const auto* currentClip = context.current.clip;
+    if (box.styleRef().hasBorderRadius()) {
+      auto innerBorder = box.styleRef().getRoundedInnerBorderFor(
+          LayoutRect(context.current.paintOffset, box.size()));
+      object.getMutableForPainting()
+          .ensurePaintProperties()
+          .updateInnerBorderRadiusClip(context.current.clip,
+                                       context.current.transform, innerBorder);
+      currentClip = object.paintProperties()->innerBorderRadiusClip();
+    } else if (auto* properties =
+                   object.getMutableForPainting().paintProperties()) {
       properties->clearInnerBorderRadiusClip();
-      properties->clearOverflowClip();
     }
-    return;
+
+    object.getMutableForPainting().ensurePaintProperties().updateOverflowClip(
+        currentClip, context.current.transform,
+        FloatRoundedRect(FloatRect(clipRect)));
   }
 
-  if (box.styleRef().hasBorderRadius()) {
-    auto innerBorder = box.styleRef().getRoundedInnerBorderFor(
-        LayoutRect(context.current.paintOffset, box.size()));
-    context.current.clip =
-        object.getMutableForPainting()
-            .ensurePaintProperties()
-            .updateInnerBorderRadiusClip(
-                context.current.clip, context.current.transform, innerBorder);
-  } else if (auto* properties =
-                 object.getMutableForPainting().paintProperties()) {
-    properties->clearInnerBorderRadiusClip();
-  }
-
-  context.current.clip =
-      object.getMutableForPainting().ensurePaintProperties().updateOverflowClip(
-          context.current.clip, context.current.transform,
-          FloatRoundedRect(FloatRect(clipRect)));
+  const auto* properties = object.paintProperties();
+  if (properties && properties->overflowClip())
+    context.current.clip = properties->overflowClip();
 }
 
 static FloatPoint perspectiveOrigin(const LayoutBox& box) {
   const ComputedStyle& style = box.styleRef();
   FloatSize borderBoxSize(box.size());
   return FloatPoint(
       floatValueForLength(style.perspectiveOriginX(), borderBoxSize.width()),
       floatValueForLength(style.perspectiveOriginY(), borderBoxSize.height()));
 }
 
 void PaintPropertyTreeBuilder::updatePerspective(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
-  const ComputedStyle& style = object.styleRef();
-  if (!object.isBox() || !style.hasPerspective()) {
-    if (auto* properties = object.getMutableForPainting().paintProperties())
-      properties->clearPerspective();
-    return;
-  }
-
-  // The perspective node must not flatten (else nothing will get
-  // perspective), but it should still extend the rendering context as most
-  // transform nodes do.
-  TransformationMatrix matrix =
-      TransformationMatrix().applyPerspective(style.perspective());
-  FloatPoint3D origin = perspectiveOrigin(toLayoutBox(object)) +
-                        toLayoutSize(context.current.paintOffset);
-  context.current.transform =
+  if (object.needsPaintPropertyUpdate()) {
+    const ComputedStyle& style = object.styleRef();
+    if (object.isBox() && style.hasPerspective()) {
+      // The perspective node must not flatten (else nothing will get
+      // perspective), but it should still extend the rendering context as
+      // most transform nodes do.
+      TransformationMatrix matrix =
+          TransformationMatrix().applyPerspective(style.perspective());
+      FloatPoint3D origin = perspectiveOrigin(toLayoutBox(object)) +
+                            toLayoutSize(context.current.paintOffset);
       object.getMutableForPainting().ensurePaintProperties().updatePerspective(
           context.current.transform, matrix, origin,
           context.current.shouldFlattenInheritedTransform,
           context.current.renderingContextID);
-  context.current.shouldFlattenInheritedTransform = false;
+    } else {
+      if (auto* properties = object.getMutableForPainting().paintProperties())
+        properties->clearPerspective();
+    }
+  }
+
+  const auto* properties = object.paintProperties();
+  if (properties && properties->perspective()) {
+    context.current.transform = properties->perspective();
+    context.current.shouldFlattenInheritedTransform = false;
+  }
 }
 
 void PaintPropertyTreeBuilder::updateSvgLocalToBorderBoxTransform(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
   if (!object.isSVGRoot())
     return;
 
-  AffineTransform transformToBorderBox =
-      SVGRootPainter(toLayoutSVGRoot(object))
-          .transformToPixelSnappedBorderBox(context.current.paintOffset);
-
-  // The paint offset is included in |transformToBorderBox| so SVG does not need
-  // to handle paint offset internally.
-  context.current.paintOffset = LayoutPoint();
-
-  if (transformToBorderBox.isIdentity()) {
-    if (auto* properties = object.getMutableForPainting().paintProperties())
-      properties->clearSvgLocalToBorderBoxTransform();
-    return;
-  }
-
-  context.current.transform =
+  if (object.needsPaintPropertyUpdate()) {
+    AffineTransform transformToBorderBox =
+        SVGRootPainter(toLayoutSVGRoot(object))
+            .transformToPixelSnappedBorderBox(context.current.paintOffset);
+    if (!transformToBorderBox.isIdentity()) {
       object.getMutableForPainting()
           .ensurePaintProperties()
           .updateSvgLocalToBorderBoxTransform(
               context.current.transform, transformToBorderBox, FloatPoint3D());
-  context.current.shouldFlattenInheritedTransform = false;
-  context.current.renderingContextID = 0;
+    } else {
+      if (auto* properties = object.getMutableForPainting().paintProperties())
+        properties->clearSvgLocalToBorderBoxTransform();
+    }
+  }
+
+  const auto* properties = object.paintProperties();
+  if (properties && properties->svgLocalToBorderBoxTransform()) {
+    context.current.transform = properties->svgLocalToBorderBoxTransform();
+    context.current.shouldFlattenInheritedTransform = false;
+    context.current.renderingContextID = 0;
+  }
+  // The paint offset is included in |transformToBorderBox| so SVG does not need
+  // to handle paint offset internally.
+  context.current.paintOffset = LayoutPoint();
 }
 
 void PaintPropertyTreeBuilder::updateScrollAndScrollTranslation(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
-  if (object.hasOverflowClip()) {
-    const LayoutBox& box = toLayoutBox(object);
-    const PaintLayerScrollableArea* scrollableArea = box.getScrollableArea();
-    IntSize scrollOffset = box.scrolledContentOffset();
-    if (!scrollOffset.isZero() || scrollableArea->scrollsOverflow()) {
-      TransformationMatrix matrix = TransformationMatrix().translate(
-          -scrollOffset.width(), -scrollOffset.height());
-      context.current.transform =
-          object.getMutableForPainting()
-              .ensurePaintProperties()
-              .updateScrollTranslation(
-                  context.current.transform, matrix, FloatPoint3D(),
-                  context.current.shouldFlattenInheritedTransform,
-                  context.current.renderingContextID);
+  if (object.needsPaintPropertyUpdate()) {
+    if (object.hasOverflowClip()) {
+      const LayoutBox& box = toLayoutBox(object);
+      const PaintLayerScrollableArea* scrollableArea = box.getScrollableArea();
+      IntSize scrollOffset = box.scrolledContentOffset();
+      if (!scrollOffset.isZero() || scrollableArea->scrollsOverflow()) {
+        TransformationMatrix matrix = TransformationMatrix().translate(
+            -scrollOffset.width(), -scrollOffset.height());
+        object.getMutableForPainting()
+            .ensurePaintProperties()
+            .updateScrollTranslation(
+                context.current.transform, matrix, FloatPoint3D(),
+                context.current.shouldFlattenInheritedTransform,
+                context.current.renderingContextID);
 
-      IntSize scrollClip = scrollableArea->visibleContentRect().size();
-      IntSize scrollBounds = scrollableArea->contentsSize();
-      bool userScrollableHorizontal =
-          scrollableArea->userInputScrollable(HorizontalScrollbar);
-      bool userScrollableVertical =
-          scrollableArea->userInputScrollable(VerticalScrollbar);
-      context.current.scroll =
-          object.getMutableForPainting().ensurePaintProperties().updateScroll(
-              context.current.scroll, context.current.transform, scrollClip,
-              scrollBounds, userScrollableHorizontal, userScrollableVertical);
-
-      context.current.shouldFlattenInheritedTransform = false;
-      return;
+        IntSize scrollClip = scrollableArea->visibleContentRect().size();
+        IntSize scrollBounds = scrollableArea->contentsSize();
+        bool userScrollableHorizontal =
+            scrollableArea->userInputScrollable(HorizontalScrollbar);
+        bool userScrollableVertical =
+            scrollableArea->userInputScrollable(VerticalScrollbar);
+        object.getMutableForPainting().ensurePaintProperties().updateScroll(
+            context.current.scroll,
+            object.paintProperties()->scrollTranslation(), scrollClip,
+            scrollBounds, userScrollableHorizontal, userScrollableVertical);
+      } else {
+        // Ensure pre-existing properties are cleared when there is no
+        // scrolling.
+        auto* properties = object.getMutableForPainting().paintProperties();
+        if (properties) {
+          properties->clearScrollTranslation();
+          properties->clearScroll();
+        }
+      }
     }
   }
 
-  if (auto* properties = object.getMutableForPainting().paintProperties()) {
-    properties->clearScrollTranslation();
-    properties->clearScroll();
+  if (object.paintProperties() && object.paintProperties()->scroll()) {
+    context.current.transform = object.paintProperties()->scrollTranslation();
+    const auto* scroll = object.paintProperties()->scroll();
+    // TODO(pdr): Remove this const cast.
+    context.current.scroll = const_cast<ScrollPaintPropertyNode*>(scroll);
+    context.current.shouldFlattenInheritedTransform = false;
   }
 }
 
 void PaintPropertyTreeBuilder::updateOutOfFlowContext(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
   if (object.canContainAbsolutePositionObjects()) {
     context.absolutePosition = context.current;
     context.containerForAbsolutePosition = &object;
   }
@@ skipping 19 matching lines @@
     // absolute position container. However for fixed-position descendants we
     // need to insert the clip here if we are not a containing block ancestor of
     // them.
     auto* cssClip = object.getMutableForPainting().paintProperties()->cssClip();
 
     // Before we actually create anything, check whether in-flow context and
     // fixed-position context has exactly the same clip. Reuse if possible.
     if (context.fixedPosition.clip == cssClip->parent()) {
       context.fixedPosition.clip = cssClip;
     } else {
-      context.fixedPosition.clip =
-          object.getMutableForPainting()
-              .ensurePaintProperties()
-              .updateCssClipFixedPosition(
-                  context.fixedPosition.clip,
-                  const_cast<TransformPaintPropertyNode*>(
-                      cssClip->localTransformSpace()),
-                  cssClip->clipRect());
+      if (object.needsPaintPropertyUpdate()) {
+        object.getMutableForPainting()
+            .ensurePaintProperties()
+            .updateCssClipFixedPosition(context.fixedPosition.clip,
+                                        const_cast<TransformPaintPropertyNode*>(
+                                            cssClip->localTransformSpace()),
+                                        cssClip->clipRect());
+      }
+      const auto* properties = object.paintProperties();
+      if (properties && properties->cssClipFixedPosition())
+        context.fixedPosition.clip = properties->cssClipFixedPosition();
       return;
     }
   }
 
-  if (auto* properties = object.getMutableForPainting().paintProperties())
-    properties->clearCssClipFixedPosition();
+  if (object.needsPaintPropertyUpdate()) {
+    if (auto* properties = object.getMutableForPainting().paintProperties())
+      properties->clearCssClipFixedPosition();
+  }
 }
 
 // Override ContainingBlockContext based on the properties of a containing block
 // that was previously walked in a subtree other than the current subtree being
 // walked. Used for out-of-flow positioned descendants of multi-column spanner
 // when the containing block is not in the normal tree walk order.
 // For example:
 // <div id="columns" style="columns: 2">
 //   <div id="relative" style="position: relative">
 //     <div id="spanner" style="column-span: all">
@@ skipping 104 matching lines @@
     // Similar adjustment is done in LayoutTableCell::offsetFromContainer().
     if (boxModelObject.isTableCell()) {
       LayoutObject* parentRow = boxModelObject.parent();
       ASSERT(parentRow && parentRow->isTableRow());
       context.current.paintOffset.moveBy(
           -toLayoutBox(parentRow)->topLeftLocation());
     }
   }
 }
 
-void PaintPropertyTreeBuilder::buildTreeNodesForSelf(
+void PaintPropertyTreeBuilder::updatePropertiesForSelf(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
   if (!object.isBoxModelObject() && !object.isSVG())
     return;
 
+#if DCHECK_IS_ON()
+  auto findObjectPropertiesNeedingUpdateScope =
+      FindObjectPropertiesNeedingUpdateScope::create(object);
+#endif
+
   deriveBorderBoxFromContainerContext(object, context);
 
   updatePaintOffsetTranslation(object, context);
   updateTransform(object, context);
   updateEffect(object, context);
   updateCssClip(object, context);
   updateLocalBorderBoxContext(object, context);
   updateScrollbarPaintOffset(object, context);
   updateMainThreadScrollingReasons(object, context);
 }
 
-void PaintPropertyTreeBuilder::buildTreeNodesForChildren(
+void PaintPropertyTreeBuilder::updatePropertiesForChildren(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
   if (!object.isBoxModelObject() && !object.isSVG())
     return;
 
+#if DCHECK_IS_ON()
+  auto findObjectPropertiesNeedingUpdateScope =
+      FindObjectPropertiesNeedingUpdateScope::create(object);
+#endif
+
   updateOverflowClip(object, context);
   updatePerspective(object, context);
   updateSvgLocalToBorderBoxTransform(object, context);
   updateScrollAndScrollTranslation(object, context);
   updateOutOfFlowContext(object, context);
 }
 
 }  // namespace blink