Only update composited scrolling state when necessary

Source/WebCore/rendering/RenderView.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2006 Apple Computer, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 21 matching lines @@
 
 class FlowThreadController;
 class RenderLayerCompositor;
 class RenderQuote;
 class RenderWidget;
 
 #if ENABLE(CSS_SHADERS) && USE(3D_GRAPHICS)
 class CustomFilterGlobalContext;
 #endif
 
+enum CompositedScrollingUpdateMode {
+    UpdateNeedsCompositedScrolling,
+    UpdateDescendantsAreContiguousInStackingOrder
+};
+
+// This object allows postponing calls to RenderLayer::updateNeedsCompositedScrolling
+// while any instance is in scope. When the last instance is destructed, all
+// updates are processed. This allows us to postpone updates during layer list
+// updates. (If we didn't postpone the updates, they would cause errors since
+// they require clean lists).
+struct ScopedCompositedScrollingUpdater {

[jamesr, 2013/04/09 21:10:00]

in particular this class seems very hacky

+    ScopedCompositedScrollingUpdater(RenderView*);
+    ScopedCompositedScrollingUpdater(RenderLayer*, CompositedScrollingUpdateMode);
+    ~ScopedCompositedScrollingUpdater();
+private:
+    RenderView* m_renderView;
+};
+
 class RenderView : public RenderBlock {
 public:
+    friend struct ScopedCompositedScrollingUpdater;
+
     explicit RenderView(Document*);
     virtual ~RenderView();
 
     bool hitTest(const HitTestRequest&, HitTestResult&);
     bool hitTest(const HitTestRequest&, const HitTestLocation&, HitTestResult&);
 
     virtual const char* renderName() const OVERRIDE { return "RenderView"; }
 
     virtual bool isRenderView() const OVERRIDE { return true; }
 
@@ skipping 153 matching lines @@
     void setRenderQuoteHead(RenderQuote* head) { m_renderQuoteHead = head; }
     RenderQuote* renderQuoteHead() const { return m_renderQuoteHead; }
 
     // FIXME: This is a work around because the current implementation of counters
     // requires walking the entire tree repeatedly and most pages don't actually use either
     // feature so we shouldn't take the performance hit when not needed. Long term we should
     // rewrite the counter and quotes code.
     void addRenderCounter() { m_renderCounterCount++; }
     void removeRenderCounter() { ASSERT(m_renderCounterCount > 0); m_renderCounterCount--; }
     bool hasRenderCounters() { return m_renderCounterCount; }
-    
+
+    void cancelScheduledCompositedScrollingUpdatesForLayer(RenderLayer*);
+
     virtual void addChild(RenderObject* newChild, RenderObject* beforeChild = 0) OVERRIDE;
 
 protected:
     virtual void mapLocalToContainer(const RenderLayerModelObject* repaintContainer, TransformState&, MapCoordinatesFlags = ApplyContainerFlip, bool* wasFixed = 0) const OVERRIDE;
     virtual const RenderObject* pushMappingToContainer(const RenderLayerModelObject* ancestorToStopAt, RenderGeometryMap&) const OVERRIDE;
     virtual void mapAbsoluteToLocalPoint(MapCoordinatesFlags, TransformState&) const;
     virtual bool requiresColumns(int desiredColumnCount) const OVERRIDE;
     
 private:
     bool initializeLayoutState(LayoutState&);
@@ skipping 81 matching lines @@
     RenderWidgetSet m_widgets;
 
 private:
     bool shouldUsePrintingLayout() const;
 
     LayoutUnit m_pageLogicalHeight;
     bool m_pageLogicalHeightChanged;
     LayoutState* m_layoutState;
     unsigned m_layoutStateDisableCount;
     OwnPtr<RenderLayerCompositor> m_compositor;
+
+    unsigned m_scopedCompositedScrollingUpdatersCount;
+    HashSet<RenderLayer*> m_pendingCompositedScrollingUpdates;
+    HashSet<RenderLayer*> m_pendingContiguityUpdates;
+
 #if ENABLE(CSS_SHADERS) && USE(3D_GRAPHICS)
     OwnPtr<CustomFilterGlobalContext> m_customFilterGlobalContext;
 #endif
     OwnPtr<FlowThreadController> m_flowThreadController;
     RefPtr<IntervalArena> m_intervalArena;
 
     RenderQuote* m_renderQuoteHead;
     unsigned m_renderCounterCount;
 };
 
@@ skipping 110 matching lines @@
     RenderObject::FlowThreadState m_flowThreadState;
     bool m_fragmenting;
 #ifndef NDEBUG
     LayoutState* m_layoutState;
 #endif
 };
 
 } // namespace WebCore
 
 #endif // RenderView_h