Avoid tree walks when computing RenderLayer::scrollParent

Source/core/rendering/RenderLayer.h

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 340 matching lines @@
     void* operator new(size_t);
     // Only safe to call from RenderLayerModelObject::destroyLayer()
     void operator delete(void*);
 
     CompositingState compositingState() const;
 
     // This returns true if our document is in a phase of its lifestyle during which
     // compositing state may legally be read.
     bool isAllowedToQueryCompositingState() const;
 
+    // This returns true if our current phase is the compositing update.
+    bool isInCompositingUpdate() const;
+
     CompositedLayerMappingPtr compositedLayerMapping() const;
     CompositedLayerMappingPtr ensureCompositedLayerMapping();
 
     // NOTE: If you are using hasCompositedLayerMapping to determine the state of compositing for this layer,
     // (and not just to do bookkeeping related to the mapping like, say, allocating or deallocating a mapping),
     // then you may have incorrect logic. Use compositingState() instead.
     bool hasCompositedLayerMapping() const { return m_compositedLayerMapping.get(); }
     void clearCompositedLayerMapping(bool layerBeingDestroyed = false);
 
     CompositedLayerMapping* groupedMapping() const { return m_groupedMapping; }
@@ skipping 101 matching lines @@
 
     RenderLayerBlendInfo& blendInfo() { return m_blendInfo; }
 
     void setOffsetFromSquashingLayerOrigin(IntSize offset) { m_compositingProperties.offsetFromSquashingLayerOrigin = offset; }
     IntSize offsetFromSquashingLayerOrigin() const { return m_compositingProperties.offsetFromSquashingLayerOrigin; }
 
     bool scrollsOverflow() const;
 
     bool hasDirectReasonsForCompositing() const { return compositingReasons() & CompositingReasonComboAllDirectReasons; }
 
+    void clearAncestorDependentPropertyCache();
+
 private:
+    struct AncestorDependentPropertyCache {
+        AncestorDependentPropertyCache();
+        RenderLayer* ancestorCompositedScrollingLayer;
+        RenderLayer* scrollParent;
+
+        bool ancestorCompositedScrollingLayerDirty;
+        bool scrollParentDirty;
+    };
+
+    void ensureAncestorDependentPropertyCache() const;
+
     bool hasOverflowControls() const;
 
     void setIsUnclippedDescendant(bool isUnclippedDescendant) { m_isUnclippedDescendant = isUnclippedDescendant; }
 
     void setAncestorChainHasSelfPaintingLayerDescendant();
     void dirtyAncestorChainHasSelfPaintingLayerDescendantStatus();
 
     void setAncestorChainHasOutOfFlowPositionedDescendant();
     void dirtyAncestorChainHasOutOfFlowPositionedDescendantStatus();
 
@@ skipping 78 matching lines @@
 
     bool hitTestContents(const HitTestRequest&, HitTestResult&, const LayoutRect& layerBounds, const HitTestLocation&, HitTestFilter) const;
     bool hitTestContentsForFragments(const LayerFragments&, const HitTestRequest&, HitTestResult&, const HitTestLocation&, HitTestFilter, bool& insideClipRect) const;
     RenderLayer* hitTestTransformedLayerInFragments(RenderLayer* rootLayer, RenderLayer* containerLayer, const HitTestRequest&, HitTestResult&,
         const LayoutRect& hitTestRect, const HitTestLocation&, const HitTestingTransformState* = 0, double* zOffset = 0);
 
     bool childBackgroundIsKnownToBeOpaqueInRect(const LayoutRect&) const;
 
     bool shouldBeSelfPaintingLayer() const;
 
-private:
     // FIXME: We should only create the stacking node if needed.
     bool requiresStackingNode() const { return true; }
     void updateStackingNode();
 
     void updateReflectionInfo(const RenderStyle*);
 
     // FIXME: We could lazily allocate our ScrollableArea based on style properties ('overflow', ...)
     // but for now, we are always allocating it for RenderBox as it's safer.
     bool requiresScrollableArea() const { return renderBox(); }
     void updateScrollableArea();
@@ skipping 31 matching lines @@
     bool lostGroupedMapping() const { return m_compositingProperties.lostGroupedMapping; }
     void setLostGroupedMapping(bool b) { m_compositingProperties.lostGroupedMapping = b; }
 
     void setCompositingReasons(CompositingReasons);
     CompositingReasons compositingReasons() const { return m_compositingProperties.compositingReasons; }
 
     friend class CompositedLayerMapping;
     friend class RenderLayerCompositor;
     friend class RenderLayerModelObject;
 
-private:
     LayerType m_layerType;
 
     // Self-painting layer is an optimization where we avoid the heavy RenderLayer painting
     // machinery for a RenderLayer allocated only to handle the overflow clip case.
     // FIXME(crbug.com/332791): Self-painting layer should be merged into the overflow-only concept.
     unsigned m_isSelfPaintingLayer : 1;
 
     // If have no self-painting descendants, we don't have to walk our children during painting. This can lead to
     // significant savings, especially if the tree has lots of non-self-painting layers grouped together (e.g. table cells).
     unsigned m_hasSelfPaintingLayerDescendant : 1;
@@ skipping 105 matching lines @@
         IntSize offsetFromSquashingLayerOrigin;
     };
 
     CompositingProperties m_compositingProperties;
 
     IntRect m_blockSelectionGapsBounds;
 
     OwnPtr<CompositedLayerMapping> m_compositedLayerMapping;
     OwnPtr<RenderLayerScrollableArea> m_scrollableArea;
 
+    mutable OwnPtr<AncestorDependentPropertyCache> m_ancestorDependentPropertyCache;
+
     CompositedLayerMapping* m_groupedMapping;
 
     RenderLayerRepainter m_repainter;
     RenderLayerClipper m_clipper; // FIXME: Lazily allocate?
     OwnPtr<RenderLayerStackingNode> m_stackingNode;
     OwnPtr<RenderLayerReflectionInfo> m_reflectionInfo;
     RenderLayerBlendInfo m_blendInfo;
 };
 
 } // namespace WebCore
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showLayerTree(const WebCore::RenderLayer*);
 void showLayerTree(const WebCore::RenderObject*);
 #endif
 
 #endif // RenderLayer_h