Source/WebCore/rendering/RenderLayerCompositor.cpp - WebKit - Git at Google

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */

 #include "config.h"

 #if USE(ACCELERATED_COMPOSITING)
 #include "RenderLayerCompositor.h"

 #include "AnimationController.h"
 #include "CanvasRenderingContext.h"
 #include "CSSPropertyNames.h"
 #include "Chrome.h"
 #include "ChromeClient.h"
 #include "FlowThreadController.h"
 #include "Frame.h"
 #include "FrameView.h"
 #include "GraphicsLayer.h"
 #include "HTMLCanvasElement.h"
 #include "HTMLIFrameElement.h"
 #include "HTMLNames.h"
 #include "HitTestResult.h"
 #include "InspectorInstrumentation.h"
 #include "Logging.h"
 #include "NodeList.h"
 #include "Page.h"
 #include "RenderEmbeddedObject.h"
 #include "RenderFlowThread.h"
 #include "RenderFullScreen.h"
 #include "RenderGeometryMap.h"
 #include "RenderIFrame.h"
 #include "RenderLayerBacking.h"
 #include "RenderNamedFlowFragment.h"
 #include "RenderReplica.h"
 #include "RenderVideo.h"
 #include "RenderView.h"
 #include "ScrollbarTheme.h"
 #include "ScrollingConstraints.h"
 #include "ScrollingCoordinator.h"
 #include "Settings.h"
 #include "TiledBacking.h"
 #include "TransformState.h"
 #include <wtf/CurrentTime.h>
 #include <wtf/TemporaryChange.h>
 #include <wtf/text/CString.h>
 #include <wtf/text/StringBuilder.h>

 #if ENABLE(PLUGIN_PROXY_FOR_VIDEO)
 #include "HTMLAudioElement.h"
 #include "HTMLMediaElement.h"
 #endif

 #ifndef NDEBUG
 #include "RenderTreeAsText.h"
 #endif

 #if ENABLE(3D_RENDERING)
 // This symbol is used to determine from a script whether 3D rendering is enabled (via 'nm').
 bool WebCoreHas3DRendering = true;
 #endif

 #if !PLATFORM(MAC) && !PLATFORM(IOS)
 #define WTF_USE_COMPOSITING_FOR_SMALL_CANVASES 1
 #endif

 namespace WebCore {

 static const int canvasAreaThresholdRequiringCompositing = 50 * 100;
 // During page loading delay layer flushes up to this many seconds to allow them coalesce, reducing workload.
 static const double throttledLayerFlushDelay = .5;

 using namespace HTMLNames;

 class RenderLayerCompositor::OverlapMap {
     WTF_MAKE_NONCOPYABLE(OverlapMap);
 public:
     OverlapMap()
         : m_geometryMap(UseTransforms)
     {
         // Begin assuming the root layer will be composited so that there is
         // something on the stack. The root layer should also never get an
         // popCompositingContainer call.
         pushCompositingContainer();
     }

     void add(const RenderLayer* layer, const IntRect& bounds)
     {
         // Layers do not contribute to overlap immediately--instead, they will
         // contribute to overlap as soon as their composited ancestor has been
         // recursively processed and popped off the stack.
         ASSERT(m_overlapStack.size() >= 2);
         m_overlapStack[m_overlapStack.size() - 2].append(bounds);
         m_layers.add(layer);
     }

     bool contains(const RenderLayer* layer)
     {
         return m_layers.contains(layer);
     }

     bool overlapsLayers(const IntRect& bounds) const
     {
         return m_overlapStack.last().intersects(bounds);
     }

     bool isEmpty()
     {
         return m_layers.isEmpty();
     }

     void pushCompositingContainer()
     {
         m_overlapStack.append(RectList());
     }

     void popCompositingContainer()
     {
         m_overlapStack[m_overlapStack.size() - 2].append(m_overlapStack.last());
         m_overlapStack.removeLast();
     }

     RenderGeometryMap& geometryMap() { return m_geometryMap; }

 private:
     struct RectList {
         Vector<IntRect> rects;
         IntRect boundingRect;

         void append(const IntRect& rect)
         {
             rects.append(rect);
             boundingRect.unite(rect);
         }

         void append(const RectList& rectList)
         {
             rects.appendVector(rectList.rects);
             boundingRect.unite(rectList.boundingRect);
         }

         bool intersects(const IntRect& rect) const
         {
             if (!rects.size() || !boundingRect.intersects(rect))
                 return false;

             for (unsigned i = 0; i < rects.size(); i++) {
                 if (rects[i].intersects(rect))
                     return true;
             }
             return false;
         }
     };

     Vector<RectList> m_overlapStack;
     HashSet<const RenderLayer*> m_layers;
     RenderGeometryMap m_geometryMap;
 };

 struct CompositingState {
     CompositingState(RenderLayer* compAncestor, bool testOverlap = true)
         : m_compositingAncestor(compAncestor)
         , m_subtreeIsCompositing(false)
         , m_testingOverlap(testOverlap)
 #ifndef NDEBUG
         , m_depth(0)
 #endif
     {
     }

     CompositingState(const CompositingState& other)
         : m_compositingAncestor(other.m_compositingAncestor)
         , m_subtreeIsCompositing(other.m_subtreeIsCompositing)
         , m_testingOverlap(other.m_testingOverlap)
 #ifndef NDEBUG
         , m_depth(other.m_depth + 1)
 #endif
     {
     }

     RenderLayer* m_compositingAncestor;
     bool m_subtreeIsCompositing;
     bool m_testingOverlap;
 #ifndef NDEBUG
     int m_depth;
 #endif
 };


 #if !LOG_DISABLED
 static inline bool compositingLogEnabled()
 {
     return LogCompositing.state == WTFLogChannelOn;
 }
 #endif

 RenderLayerCompositor::RenderLayerCompositor(RenderView& renderView)
     : m_renderView(renderView)
     , m_updateCompositingLayersTimer(this, &RenderLayerCompositor::updateCompositingLayersTimerFired)
     , m_hasAcceleratedCompositing(true)
     , m_compositingTriggers(static_cast<ChromeClient::CompositingTriggerFlags>(ChromeClient::AllTriggers))
     , m_compositedLayerCount(0)
     , m_showDebugBorders(false)
     , m_showRepaintCounter(false)
     , m_acceleratedDrawingEnabled(false)
     , m_reevaluateCompositingAfterLayout(false)
     , m_compositing(false)
     , m_compositingLayersNeedRebuild(false)
     , m_flushingLayers(false)
     , m_shouldFlushOnReattach(false)
     , m_forceCompositingMode(false)
     , m_inPostLayoutUpdate(false)
     , m_isTrackingRepaints(false)
     , m_layersWithTiledBackingCount(0)
     , m_rootLayerAttachment(RootLayerUnattached)
     , m_layerFlushTimer(this, &RenderLayerCompositor::layerFlushTimerFired)
     , m_layerFlushThrottlingEnabled(false)
     , m_layerFlushThrottlingTemporarilyDisabledForInteraction(false)
     , m_hasPendingLayerFlush(false)
     , m_paintRelatedMilestonesTimer(this, &RenderLayerCompositor::paintRelatedMilestonesTimerFired)
 #if !LOG_DISABLED
     , m_rootLayerUpdateCount(0)
     , m_obligateCompositedLayerCount(0)
     , m_secondaryCompositedLayerCount(0)
     , m_obligatoryBackingStoreBytes(0)
     , m_secondaryBackingStoreBytes(0)
 #endif
 {
 }

 RenderLayerCompositor::~RenderLayerCompositor()
 {
     // Take care that the owned GraphicsLayers are deleted first as their destructors may call back here.
     m_clipLayer = nullptr;
     m_scrollLayer = nullptr;
     ASSERT(m_rootLayerAttachment == RootLayerUnattached);
 }

 void RenderLayerCompositor::enableCompositingMode(bool enable /* = true */)
 {
     if (enable != m_compositing) {
         m_compositing = enable;

         if (m_compositing) {
             ensureRootLayer();
             notifyIFramesOfCompositingChange();
         } else
             destroyRootLayer();
     }
 }

 void RenderLayerCompositor::cacheAcceleratedCompositingFlags()
 {
     bool hasAcceleratedCompositing = false;
     bool showDebugBorders = false;
     bool showRepaintCounter = false;
     bool forceCompositingMode = false;
     bool acceleratedDrawingEnabled = false;

     const Settings& settings = m_renderView.frameView().frame().settings();
     hasAcceleratedCompositing = settings.acceleratedCompositingEnabled();

     // We allow the chrome to override the settings, in case the page is rendered
     // on a chrome that doesn't allow accelerated compositing.
     if (hasAcceleratedCompositing) {
         if (Page* page = this->page()) {
             m_compositingTriggers = page->chrome().client().allowedCompositingTriggers();
             hasAcceleratedCompositing = m_compositingTriggers;
         }
     }

     showDebugBorders = settings.showDebugBorders();
     showRepaintCounter = settings.showRepaintCounter();
     forceCompositingMode = settings.forceCompositingMode() && hasAcceleratedCompositing;

     if (forceCompositingMode && m_renderView.document().ownerElement())
         forceCompositingMode = requiresCompositingForScrollableFrame();

     acceleratedDrawingEnabled = settings.acceleratedDrawingEnabled();

     if (hasAcceleratedCompositing != m_hasAcceleratedCompositing || showDebugBorders != m_showDebugBorders || showRepaintCounter != m_showRepaintCounter || forceCompositingMode != m_forceCompositingMode)
         setCompositingLayersNeedRebuild();

     bool debugBordersChanged = m_showDebugBorders != showDebugBorders;
     m_hasAcceleratedCompositing = hasAcceleratedCompositing;
     m_showDebugBorders = showDebugBorders;
     m_showRepaintCounter = showRepaintCounter;
     m_forceCompositingMode = forceCompositingMode;
     m_acceleratedDrawingEnabled = acceleratedDrawingEnabled;

     if (debugBordersChanged) {
         if (m_layerForHorizontalScrollbar)
             m_layerForHorizontalScrollbar->setShowDebugBorder(m_showDebugBorders);

         if (m_layerForVerticalScrollbar)
             m_layerForVerticalScrollbar->setShowDebugBorder(m_showDebugBorders);

         if (m_layerForScrollCorner)
             m_layerForScrollCorner->setShowDebugBorder(m_showDebugBorders);
     }
 }

 bool RenderLayerCompositor::canRender3DTransforms() const
 {
     return hasAcceleratedCompositing() && (m_compositingTriggers & ChromeClient::ThreeDTransformTrigger);
 }

 void RenderLayerCompositor::setCompositingLayersNeedRebuild(bool needRebuild)
 {
     if (inCompositingMode())
         m_compositingLayersNeedRebuild = needRebuild;
 }

 void RenderLayerCompositor::customPositionForVisibleRectComputation(const GraphicsLayer* graphicsLayer, FloatPoint& position) const
 {
     if (graphicsLayer != m_scrollLayer.get())
         return;

     FloatPoint scrollPosition = -position;

     if (m_renderView.frameView().scrollBehaviorForFixedElements() == StickToDocumentBounds)
         scrollPosition = m_renderView.frameView().constrainScrollPositionForOverhang(roundedIntPoint(scrollPosition));

     position = -scrollPosition;
 }

 void RenderLayerCompositor::notifyFlushRequired(const GraphicsLayer* layer)
 {
     scheduleLayerFlush(layer->canThrottleLayerFlush());
 }

 void RenderLayerCompositor::scheduleLayerFlushNow()
 {
     m_hasPendingLayerFlush = false;
     if (Page* page = this->page())
         page->chrome().client().scheduleCompositingLayerFlush();
 }

 void RenderLayerCompositor::scheduleLayerFlush(bool canThrottle)
 {
     ASSERT(!m_flushingLayers);

     if (canThrottle && isThrottlingLayerFlushes()) {
         m_hasPendingLayerFlush = true;
         return;
     }
     scheduleLayerFlushNow();
 }

 void RenderLayerCompositor::flushPendingLayerChanges(bool isFlushRoot)
 {
     // FrameView::flushCompositingStateIncludingSubframes() flushes each subframe,
     // but GraphicsLayer::flushCompositingState() will cross frame boundaries
     // if the GraphicsLayers are connected (the RootLayerAttachedViaEnclosingFrame case).
     // As long as we're not the root of the flush, we can bail.
     if (!isFlushRoot && rootLayerAttachment() == RootLayerAttachedViaEnclosingFrame)
         return;

     if (rootLayerAttachment() == RootLayerUnattached) {
         m_shouldFlushOnReattach = true;
         return;
     }

     FrameView& frameView = m_renderView.frameView();
     AnimationUpdateBlock animationUpdateBlock(&frameView.frame().animation());

     ASSERT(!m_flushingLayers);
     m_flushingLayers = true;

     if (GraphicsLayer* rootLayer = rootGraphicsLayer()) {
         // Having a m_clipLayer indicates that we're doing scrolling via GraphicsLayers.
         IntRect visibleRect = m_clipLayer ? IntRect(IntPoint(), frameView.contentsSize()) : frameView.visibleContentRect();
         rootLayer->flushCompositingState(visibleRect);
     }

     ASSERT(m_flushingLayers);
     m_flushingLayers = false;

     for (auto it = m_viewportConstrainedLayersNeedingUpdate.begin(), end = m_viewportConstrainedLayersNeedingUpdate.end(); it != end; ++it)
         registerOrUpdateViewportConstrainedLayer(**it);
     m_viewportConstrainedLayersNeedingUpdate.clear();

     startLayerFlushTimerIfNeeded();
 }

 void RenderLayerCompositor::didFlushChangesForLayer(RenderLayer& layer, const GraphicsLayer* graphicsLayer)
 {
     if (m_viewportConstrainedLayers.contains(&layer))
         m_viewportConstrainedLayersNeedingUpdate.add(&layer);

     RenderLayerBacking* backing = layer.backing();
     if (backing->backgroundLayerPaintsFixedRootBackground() && graphicsLayer == backing->backgroundLayer())
         fixedRootBackgroundLayerChanged();
 }

 void RenderLayerCompositor::didPaintBacking(RenderLayerBacking*)
 {
     FrameView& frameView = m_renderView.frameView();
     frameView.setLastPaintTime(monotonicallyIncreasingTime());
     if (frameView.milestonesPendingPaint() && !m_paintRelatedMilestonesTimer.isActive())
         m_paintRelatedMilestonesTimer.startOneShot(0);
 }

 void RenderLayerCompositor::didChangeVisibleRect()
 {
     GraphicsLayer* rootLayer = rootGraphicsLayer();
     if (!rootLayer)
         return;

     const FrameView& frameView = m_renderView.frameView();
     IntRect visibleRect = m_clipLayer ? IntRect(IntPoint(), frameView.contentsSize()) : frameView.visibleContentRect();
     if (!rootLayer->visibleRectChangeRequiresFlush(visibleRect))
         return;
     scheduleLayerFlushNow();
 }

 void RenderLayerCompositor::notifyFlushBeforeDisplayRefresh(const GraphicsLayer*)
 {
     if (!m_layerUpdater) {
         PlatformDisplayID displayID = 0;
         if (Page* page = this->page())
             displayID = page->chrome().displayID();

         m_layerUpdater = adoptPtr(new GraphicsLayerUpdater(this, displayID));
     }

     m_layerUpdater->scheduleUpdate();
 }

 void RenderLayerCompositor::flushLayers(GraphicsLayerUpdater*)
 {
     flushPendingLayerChanges(true); // FIXME: deal with iframes
 }

 void RenderLayerCompositor::layerTiledBackingUsageChanged(const GraphicsLayer*, bool usingTiledBacking)
 {
     if (usingTiledBacking)
         ++m_layersWithTiledBackingCount;
     else {
         ASSERT(m_layersWithTiledBackingCount > 0);
         --m_layersWithTiledBackingCount;
     }
 }

 RenderLayerCompositor* RenderLayerCompositor::enclosingCompositorFlushingLayers() const
 {
     for (Frame* frame = &m_renderView.frameView().frame(); frame; frame = frame->tree().parent()) {
         RenderLayerCompositor* compositor = frame->contentRenderer() ? &frame->contentRenderer()->compositor() : 0;
         if (compositor->isFlushingLayers())
             return compositor;
     }

     return 0;
 }

 void RenderLayerCompositor::scheduleCompositingLayerUpdate()
 {
     if (!m_updateCompositingLayersTimer.isActive())
         m_updateCompositingLayersTimer.startOneShot(0);
 }

 void RenderLayerCompositor::updateCompositingLayersTimerFired(Timer<RenderLayerCompositor>*)
 {
     updateCompositingLayers(CompositingUpdateAfterLayout);
 }

 bool RenderLayerCompositor::hasAnyAdditionalCompositedLayers(const RenderLayer& rootLayer) const
 {
     return m_compositedLayerCount > (rootLayer.isComposited() ? 1 : 0);
 }

 void RenderLayerCompositor::updateCompositingLayers(CompositingUpdateType updateType, RenderLayer* updateRoot)
 {
     m_updateCompositingLayersTimer.stop();

     // Compositing layers will be updated in Document::implicitClose() if suppressed here.
     if (!m_renderView.document().visualUpdatesAllowed())
         return;

     // Avoid updating the layers with old values. Compositing layers will be updated after the layout is finished.
     if (m_renderView.needsLayout())
         return;

     if (m_forceCompositingMode && !m_compositing)
         enableCompositingMode(true);

     if (!m_reevaluateCompositingAfterLayout && !m_compositing)
         return;

     AnimationUpdateBlock animationUpdateBlock(&m_renderView.frameView().frame().animation());

     TemporaryChange<bool> postLayoutChange(m_inPostLayoutUpdate, true);

     bool checkForHierarchyUpdate = m_reevaluateCompositingAfterLayout;
     bool needGeometryUpdate = false;

     switch (updateType) {
     case CompositingUpdateAfterStyleChange:
     case CompositingUpdateAfterLayout:
     case CompositingUpdateOnHitTest:
         checkForHierarchyUpdate = true;
         break;
     case CompositingUpdateOnScroll:
         checkForHierarchyUpdate = true; // Overlap can change with scrolling, so need to check for hierarchy updates.

         needGeometryUpdate = true;
         break;
     case CompositingUpdateOnCompositedScroll:
         needGeometryUpdate = true;
         break;
     }

     if (!checkForHierarchyUpdate && !needGeometryUpdate)
         return;

     bool needHierarchyUpdate = m_compositingLayersNeedRebuild;
     bool isFullUpdate = !updateRoot;

     // Only clear the flag if we're updating the entire hierarchy.
     m_compositingLayersNeedRebuild = false;
     updateRoot = &rootRenderLayer();

     if (isFullUpdate && updateType == CompositingUpdateAfterLayout)
         m_reevaluateCompositingAfterLayout = false;

 #if !LOG_DISABLED
     double startTime = 0;
     if (compositingLogEnabled()) {
         ++m_rootLayerUpdateCount;
         startTime = monotonicallyIncreasingTime();
     }
 #endif

     if (checkForHierarchyUpdate) {
         if (isFullUpdate)
             updateRenderFlowThreadLayersIfNeeded();
         // Go through the layers in presentation order, so that we can compute which RenderLayers need compositing layers.
         // FIXME: we could maybe do this and the hierarchy udpate in one pass, but the parenting logic would be more complex.
         CompositingState compState(updateRoot);
         bool layersChanged = false;
         bool saw3DTransform = false;
         OverlapMap overlapTestRequestMap;
         computeCompositingRequirements(nullptr, *updateRoot, &overlapTestRequestMap, compState, layersChanged, saw3DTransform);
         needHierarchyUpdate |= layersChanged;
     }

 #if !LOG_DISABLED
     if (compositingLogEnabled() && isFullUpdate && (needHierarchyUpdate || needGeometryUpdate)) {
         m_obligateCompositedLayerCount = 0;
         m_secondaryCompositedLayerCount = 0;
         m_obligatoryBackingStoreBytes = 0;
         m_secondaryBackingStoreBytes = 0;

         Frame& frame = m_renderView.frameView().frame();
         bool isMainFrame = !m_renderView.document().ownerElement();
         LOG(Compositing, "\nUpdate %d of %s.\n", m_rootLayerUpdateCount, isMainFrame ? "main frame" : frame.tree().uniqueName().string().utf8().data());
     }
 #endif

     if (needHierarchyUpdate) {
         // Update the hierarchy of the compositing layers.
         Vector<GraphicsLayer*> childList;
         rebuildCompositingLayerTree(*updateRoot, childList, 0);

         // Host the document layer in the RenderView's root layer.
         if (isFullUpdate) {
             // Even when childList is empty, don't drop out of compositing mode if there are
             // composited layers that we didn't hit in our traversal (e.g. because of visibility:hidden).
             if (childList.isEmpty() && !hasAnyAdditionalCompositedLayers(*updateRoot))
                 destroyRootLayer();
             else
                 m_rootContentLayer->setChildren(childList);
         }
     } else if (needGeometryUpdate) {
         // We just need to do a geometry update. This is only used for position:fixed scrolling;
         // most of the time, geometry is updated via RenderLayer::styleChanged().
         updateLayerTreeGeometry(*updateRoot, 0);
     }

 #if !LOG_DISABLED
     if (compositingLogEnabled() && isFullUpdate && (needHierarchyUpdate || needGeometryUpdate)) {
         double endTime = monotonicallyIncreasingTime();
         LOG(Compositing, "Total layers   primary   secondary   obligatory backing (KB)   secondary backing(KB)   total backing (KB)  update time (ms)\n");

         LOG(Compositing, "%8d %11d %9d %20.2f %22.2f %22.2f %18.2f\n",
             m_obligateCompositedLayerCount + m_secondaryCompositedLayerCount, m_obligateCompositedLayerCount,
             m_secondaryCompositedLayerCount, m_obligatoryBackingStoreBytes / 1024, m_secondaryBackingStoreBytes / 1024, (m_obligatoryBackingStoreBytes + m_secondaryBackingStoreBytes) / 1024, 1000.0 * (endTime - startTime));
     }
 #endif
     ASSERT(updateRoot || !m_compositingLayersNeedRebuild);

     if (!hasAcceleratedCompositing())
         enableCompositingMode(false);

     // Inform the inspector that the layer tree has changed.
     InspectorInstrumentation::layerTreeDidChange(page());
 }

 void RenderLayerCompositor::updateRenderFlowThreadLayersIfNeeded()
 {
     if (m_renderView.hasRenderNamedFlowThreads())
         m_renderView.flowThreadController().updateRenderFlowThreadLayersIfNeeded();
 }

 void RenderLayerCompositor::layerBecameNonComposited(const RenderLayer& layer)
 {
     // Inform the inspector that the given RenderLayer was destroyed.
     InspectorInstrumentation::renderLayerDestroyed(page(), &layer);

     ASSERT(m_compositedLayerCount > 0);
     --m_compositedLayerCount;
 }

 #if !LOG_DISABLED
 void RenderLayerCompositor::logLayerInfo(const RenderLayer& layer, int depth)
 {
     if (!compositingLogEnabled())
         return;

     RenderLayerBacking* backing = layer.backing();
     if (requiresCompositingLayer(layer) || layer.isRootLayer()) {
         ++m_obligateCompositedLayerCount;
         m_obligatoryBackingStoreBytes += backing->backingStoreMemoryEstimate();
     } else {
         ++m_secondaryCompositedLayerCount;
         m_secondaryBackingStoreBytes += backing->backingStoreMemoryEstimate();
     }

     StringBuilder logString;
     logString.append(String::format("%*p %dx%d %.2fKB", 12 + depth * 2, &layer,
         backing->compositedBounds().width().round(), backing->compositedBounds().height().round(),
         backing->backingStoreMemoryEstimate() / 1024));

     logString.append(" (");
     logString.append(logReasonsForCompositing(layer));
     logString.append(") ");

     if (backing->graphicsLayer()->contentsOpaque() || backing->paintsIntoCompositedAncestor()) {
         logString.append('[');
         if (backing->graphicsLayer()->contentsOpaque())
             logString.append("opaque");
         if (backing->paintsIntoCompositedAncestor())
             logString.append("paints into ancestor");
         logString.append("] ");
     }

     logString.append(layer.name());

     LOG(Compositing, "%s", logString.toString().utf8().data());
 }
 #endif

 bool RenderLayerCompositor::updateBacking(RenderLayer& layer, CompositingChangeRepaint shouldRepaint)
 {
     bool layerChanged = false;
     RenderLayer::ViewportConstrainedNotCompositedReason viewportConstrainedNotCompositedReason = RenderLayer::NoNotCompositedReason;

     if (needsToBeComposited(layer, &viewportConstrainedNotCompositedReason)) {
         enableCompositingMode();

         if (!layer.backing()) {
             // If we need to repaint, do so before making backing
             if (shouldRepaint == CompositingChangeRepaintNow)
                 repaintOnCompositingChange(layer);

             layer.ensureBacking();

             // At this time, the ScrollingCoordinator only supports the top-level frame.
             if (layer.isRootLayer() && !m_renderView.document().ownerElement()) {
                 layer.backing()->attachToScrollingCoordinatorWithParent(0);
                 if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
                     scrollingCoordinator->frameViewRootLayerDidChange(&m_renderView.frameView());
 #if ENABLE(RUBBER_BANDING)
                 if (Page* page = this->page()) {
                     updateLayerForHeader(page->headerHeight());
                     updateLayerForFooter(page->footerHeight());
                 }
 #endif
                 if (mainFrameBackingIsTiledWithMargin())
                     m_rootContentLayer->setMasksToBounds(false);
             }

             // This layer and all of its descendants have cached repaints rects that are relative to
             // the repaint container, so change when compositing changes; we need to update them here.
             if (layer.parent())
                 layer.computeRepaintRectsIncludingDescendants();

             layerChanged = true;
         }
     } else {
         if (layer.backing()) {
             // If we're removing backing on a reflection, clear the source GraphicsLayer's pointer to
             // its replica GraphicsLayer. In practice this should never happen because reflectee and reflection
             // are both either composited, or not composited.
             if (layer.isReflection()) {
                 RenderLayer* sourceLayer = toRenderLayerModelObject(layer.renderer().parent())->layer();
                 if (RenderLayerBacking* backing = sourceLayer->backing()) {
                     ASSERT(backing->graphicsLayer()->replicaLayer() == layer.backing()->graphicsLayer());
                     backing->graphicsLayer()->setReplicatedByLayer(0);
                 }
             }

             removeViewportConstrainedLayer(layer);

             layer.clearBacking();
             layerChanged = true;

             // This layer and all of its descendants have cached repaints rects that are relative to
             // the repaint container, so change when compositing changes; we need to update them here.
             layer.computeRepaintRectsIncludingDescendants();

             // If we need to repaint, do so now that we've removed the backing
             if (shouldRepaint == CompositingChangeRepaintNow)
                 repaintOnCompositingChange(layer);
         }
     }

 #if ENABLE(VIDEO)
     if (layerChanged && layer.renderer().isVideo()) {
         // If it's a video, give the media player a chance to hook up to the layer.
         toRenderVideo(layer.renderer()).acceleratedRenderingStateChanged();
     }
 #endif

     if (layerChanged && layer.renderer().isWidget()) {
         RenderLayerCompositor* innerCompositor = frameContentsCompositor(toRenderWidget(&layer.renderer()));
         if (innerCompositor && innerCompositor->inCompositingMode())
             innerCompositor->updateRootLayerAttachment();
     }

     if (layerChanged)
         layer.clearClipRectsIncludingDescendants(PaintingClipRects);

     // If a fixed position layer gained/lost a backing or the reason not compositing it changed,
     // the scrolling coordinator needs to recalculate whether it can do fast scrolling.
     if (layer.renderer().style().position() == FixedPosition) {
         if (layer.viewportConstrainedNotCompositedReason() != viewportConstrainedNotCompositedReason) {
             layer.setViewportConstrainedNotCompositedReason(viewportConstrainedNotCompositedReason);
             layerChanged = true;
         }
         if (layerChanged) {
             if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
                 scrollingCoordinator->frameViewFixedObjectsDidChange(&m_renderView.frameView());
         }
     } else
         layer.setViewportConstrainedNotCompositedReason(RenderLayer::NoNotCompositedReason);

     if (layer.backing())
         layer.backing()->updateDebugIndicators(m_showDebugBorders, m_showRepaintCounter);

     return layerChanged;
 }

 bool RenderLayerCompositor::updateLayerCompositingState(RenderLayer& layer, CompositingChangeRepaint shouldRepaint)
 {
     bool layerChanged = updateBacking(layer, shouldRepaint);

     // See if we need content or clipping layers. Methods called here should assume
     // that the compositing state of descendant layers has not been updated yet.
     if (layer.backing() && layer.backing()->updateGraphicsLayerConfiguration())
         layerChanged = true;

     return layerChanged;
 }

 void RenderLayerCompositor::repaintOnCompositingChange(RenderLayer& layer)
 {
     // If the renderer is not attached yet, no need to repaint.
     if (&layer.renderer() != &m_renderView && !layer.renderer().parent())
         return;

     RenderLayerModelObject* repaintContainer = layer.renderer().containerForRepaint();
     if (!repaintContainer)
         repaintContainer = &m_renderView;

     layer.repaintIncludingNonCompositingDescendants(repaintContainer);
     if (repaintContainer == &m_renderView) {
         // The contents of this layer may be moving between the window
         // and a GraphicsLayer, so we need to make sure the window system
         // synchronizes those changes on the screen.
         m_renderView.frameView().setNeedsOneShotDrawingSynchronization();
     }
 }

 // This method assumes that layout is up-to-date, unlike repaintOnCompositingChange().
 void RenderLayerCompositor::repaintInCompositedAncestor(RenderLayer& layer, const LayoutRect& rect)
 {
     RenderLayer* compositedAncestor = layer.enclosingCompositingLayerForRepaint(ExcludeSelf);
     if (compositedAncestor) {
         ASSERT(compositedAncestor->backing());

         LayoutPoint offset;
         layer.convertToLayerCoords(compositedAncestor, offset);

         LayoutRect repaintRect = rect;
         repaintRect.moveBy(offset);

         compositedAncestor->setBackingNeedsRepaintInRect(repaintRect);
     }

     // The contents of this layer may be moving from a GraphicsLayer to the window,
     // so we need to make sure the window system synchronizes those changes on the screen.
     if (compositedAncestor == m_renderView.layer())
         m_renderView.frameView().setNeedsOneShotDrawingSynchronization();
 }

 // The bounds of the GraphicsLayer created for a compositing layer is the union of the bounds of all the descendant
 // RenderLayers that are rendered by the composited RenderLayer.
 LayoutRect RenderLayerCompositor::calculateCompositedBounds(const RenderLayer& layer, const RenderLayer& ancestorLayer) const
 {
     if (!canBeComposited(layer))
         return LayoutRect();
     return layer.calculateLayerBounds(&ancestorLayer, nullptr, RenderLayer::DefaultCalculateLayerBoundsFlags | RenderLayer::ExcludeHiddenDescendants | RenderLayer::DontConstrainForMask);
 }

 void RenderLayerCompositor::layerWasAdded(RenderLayer&, RenderLayer&)
 {
     setCompositingLayersNeedRebuild();
 }

 void RenderLayerCompositor::layerWillBeRemoved(RenderLayer& parent, RenderLayer& child)
 {
     if (!child.isComposited() || parent.renderer().documentBeingDestroyed())
         return;

     removeViewportConstrainedLayer(child);
     repaintInCompositedAncestor(child, child.backing()->compositedBounds());

     setCompositingParent(child, nullptr);
     setCompositingLayersNeedRebuild();
 }

 RenderLayer* RenderLayerCompositor::enclosingNonStackingClippingLayer(const RenderLayer& layer) const
 {
     for (RenderLayer* parent = layer.parent(); parent; parent = parent->parent()) {
         if (parent->isStackingContainer())
             return nullptr;
         if (parent->renderer().hasClipOrOverflowClip())
             return parent;
     }
     return nullptr;
 }

 void RenderLayerCompositor::addToOverlapMap(OverlapMap& overlapMap, RenderLayer& layer, IntRect& layerBounds, bool& boundsComputed)
 {
     if (layer.isRootLayer())
         return;

     if (!boundsComputed) {
         // FIXME: If this layer's overlap bounds include its children, we don't need to add its
         // children's bounds to the overlap map.
         layerBounds = enclosingIntRect(overlapMap.geometryMap().absoluteRect(layer.overlapBounds()));
         // Empty rects never intersect, but we need them to for the purposes of overlap testing.
         if (layerBounds.isEmpty())
             layerBounds.setSize(IntSize(1, 1));
         boundsComputed = true;
     }

     IntRect clipRect = pixelSnappedIntRect(layer.backgroundClipRect(RenderLayer::ClipRectsContext(&rootRenderLayer(), 0, AbsoluteClipRects)).rect()); // FIXME: Incorrect for CSS regions.
     const Settings& settings = m_renderView.frameView().frame().settings();
     if (!settings.delegatesPageScaling())
         clipRect.scale(pageScaleFactor());
     clipRect.intersect(layerBounds);
     overlapMap.add(&layer, clipRect);
 }

 void RenderLayerCompositor::addToOverlapMapRecursive(OverlapMap& overlapMap, RenderLayer& layer, RenderLayer* ancestorLayer)
 {
     if (!canBeComposited(layer) || overlapMap.contains(&layer))
         return;

     // A null ancestorLayer is an indication that 'layer' has already been pushed.
     if (ancestorLayer)
         overlapMap.geometryMap().pushMappingsToAncestor(&layer, ancestorLayer);

     IntRect bounds;
     bool haveComputedBounds = false;
     addToOverlapMap(overlapMap, layer, bounds, haveComputedBounds);

 #if !ASSERT_DISABLED
     LayerListMutationDetector mutationChecker(&layer);
 #endif

     if (layer.isStackingContainer()) {
         if (Vector<RenderLayer*>* negZOrderList = layer.negZOrderList()) {
             for (size_t i = 0, size = negZOrderList->size(); i < size; ++i)
                 addToOverlapMapRecursive(overlapMap, *negZOrderList->at(i), &layer);
         }
     }

     if (Vector<RenderLayer*>* normalFlowList = layer.normalFlowList()) {
         for (size_t i = 0, size = normalFlowList->size(); i < size; ++i)
             addToOverlapMapRecursive(overlapMap, *normalFlowList->at(i), &layer);
     }

     if (layer.isStackingContainer()) {
         if (Vector<RenderLayer*>* posZOrderList = layer.posZOrderList()) {
             for (size_t i = 0, size = posZOrderList->size(); i < size; ++i)
                 addToOverlapMapRecursive(overlapMap, *posZOrderList->at(i), &layer);
         }
     }

     if (ancestorLayer)
         overlapMap.geometryMap().popMappingsToAncestor(ancestorLayer);
 }

 //  Recurse through the layers in z-index and overflow order (which is equivalent to painting order)
 //  For the z-order children of a compositing layer:
 //      If a child layers has a compositing layer, then all subsequent layers must
 //      be compositing in order to render above that layer.
 //
 //      If a child in the negative z-order list is compositing, then the layer itself
 //      must be compositing so that its contents render over that child.
 //      This implies that its positive z-index children must also be compositing.
 //
 void RenderLayerCompositor::computeCompositingRequirements(RenderLayer* ancestorLayer, RenderLayer& layer, OverlapMap* overlapMap, CompositingState& compositingState, bool& layersChanged, bool& descendantHas3DTransform)
 {
     layer.updateDescendantDependentFlags();
     layer.updateLayerListsIfNeeded();

     if (layer.isFlowThreadCollectingGraphicsLayersUnderRegions()) {
         RenderFlowThread& flowThread = toRenderFlowThread(layer.renderer());
         layer.setHasCompositingDescendant(flowThread.hasCompositingRegionDescendant());

         // Before returning, we need to update the lists of all child layers. This is required because,
         // if this flow thread will not be painted (for instance because of having no regions, or only invalid regions),
         // the child layers will never have their lists updated (which would normally happen during painting).
         layer.updateDescendantsLayerListsIfNeeded(true);

         return;
     }

     if (overlapMap)
         overlapMap->geometryMap().pushMappingsToAncestor(&layer, ancestorLayer);

     // Clear the flag
     layer.setHasCompositingDescendant(false);

     RenderLayer::IndirectCompositingReason compositingReason = compositingState.m_subtreeIsCompositing ? RenderLayer::IndirectCompositingForStacking : RenderLayer::NoIndirectCompositingReason;

     bool haveComputedBounds = false;
     IntRect absBounds;
     if (overlapMap && !overlapMap->isEmpty() && compositingState.m_testingOverlap) {
         // If we're testing for overlap, we only need to composite if we overlap something that is already composited.
         absBounds = enclosingIntRect(overlapMap->geometryMap().absoluteRect(layer.overlapBounds()));

         // Empty rects never intersect, but we need them to for the purposes of overlap testing.
         if (absBounds.isEmpty())
             absBounds.setSize(IntSize(1, 1));
         haveComputedBounds = true;
         compositingReason = overlapMap->overlapsLayers(absBounds) ? RenderLayer::IndirectCompositingForOverlap : RenderLayer::NoIndirectCompositingReason;
     }

 #if ENABLE(VIDEO)
     // Video is special. It's the only RenderLayer type that can both have
     // RenderLayer children and whose children can't use its backing to render
     // into. These children (the controls) always need to be promoted into their
     // own layers to draw on top of the accelerated video.
     if (compositingState.m_compositingAncestor && compositingState.m_compositingAncestor->renderer().isVideo())
         compositingReason = RenderLayer::IndirectCompositingForOverlap;
 #endif

     layer.setIndirectCompositingReason(compositingReason);

     // The children of this layer don't need to composite, unless there is
     // a compositing layer among them, so start by inheriting the compositing
     // ancestor with m_subtreeIsCompositing set to false.
     CompositingState childState(compositingState);
     childState.m_subtreeIsCompositing = false;

     bool willBeComposited = needsToBeComposited(layer);
     if (willBeComposited) {
         // Tell the parent it has compositing descendants.
         compositingState.m_subtreeIsCompositing = true;
         // This layer now acts as the ancestor for kids.
         childState.m_compositingAncestor = &layer;

         if (overlapMap)
             overlapMap->pushCompositingContainer();
         // This layer is going to be composited, so children can safely ignore the fact that there's an
         // animation running behind this layer, meaning they can rely on the overlap map testing again.
         childState.m_testingOverlap = true;
     }

 #if !ASSERT_DISABLED
     LayerListMutationDetector mutationChecker(&layer);
 #endif

     bool anyDescendantHas3DTransform = false;

     if (layer.isStackingContainer()) {
         if (Vector<RenderLayer*>* negZOrderList = layer.negZOrderList()) {
             for (size_t i = 0, size = negZOrderList->size(); i < size; ++i) {
                 computeCompositingRequirements(&layer, *negZOrderList->at(i), overlapMap, childState, layersChanged, anyDescendantHas3DTransform);

                 // If we have to make a layer for this child, make one now so we can have a contents layer
                 // (since we need to ensure that the -ve z-order child renders underneath our contents).
                 if (!willBeComposited && childState.m_subtreeIsCompositing) {
                     // make layer compositing
                     layer.setIndirectCompositingReason(RenderLayer::IndirectCompositingForBackgroundLayer);
                     childState.m_compositingAncestor = &layer;
                     if (overlapMap)
                         overlapMap->pushCompositingContainer();
                     // This layer is going to be composited, so children can safely ignore the fact that there's an
                     // animation running behind this layer, meaning they can rely on the overlap map testing again
                     childState.m_testingOverlap = true;
                     willBeComposited = true;
                 }
             }
         }
     }

     if (layer.renderer().isRenderNamedFlowFragmentContainer()) {
         // We are going to collect layers from the RenderFlowThread into the GraphicsLayer of the parent of the
         // anonymous RenderRegion, but first we need to make sure that the parent itself of the region is going to
         // have a composited layer. We only want to make regions composited when there's an actual layer that we
         // need to move to that region.
         computeRegionCompositingRequirements(toRenderBlockFlow(layer.renderer()).renderNamedFlowFragment(), overlapMap, childState, layersChanged, anyDescendantHas3DTransform);
     }


     if (Vector<RenderLayer*>* normalFlowList = layer.normalFlowList()) {
         for (size_t i = 0, size = normalFlowList->size(); i < size; ++i)
             computeCompositingRequirements(&layer, *normalFlowList->at(i), overlapMap, childState, layersChanged, anyDescendantHas3DTransform);
     }

     if (layer.isStackingContainer()) {
         if (Vector<RenderLayer*>* posZOrderList = layer.posZOrderList()) {
             for (size_t i = 0, size = posZOrderList->size(); i < size; ++i)
                 computeCompositingRequirements(&layer, *posZOrderList->at(i), overlapMap, childState, layersChanged, anyDescendantHas3DTransform);
         }
     }

     // If we just entered compositing mode, the root will have become composited (as long as accelerated compositing is enabled).
     if (layer.isRootLayer()) {
         if (inCompositingMode() && m_hasAcceleratedCompositing)
             willBeComposited = true;
     }

     ASSERT(willBeComposited == needsToBeComposited(layer));

     // All layers (even ones that aren't being composited) need to get added to
     // the overlap map. Layers that do not composite will draw into their
     // compositing ancestor's backing, and so are still considered for overlap.
     if (overlapMap && childState.m_compositingAncestor && !childState.m_compositingAncestor->isRootLayer())
         addToOverlapMap(*overlapMap, layer, absBounds, haveComputedBounds);

     // Now check for reasons to become composited that depend on the state of descendant layers.
     RenderLayer::IndirectCompositingReason indirectCompositingReason;
     if (!willBeComposited && canBeComposited(layer)
         && requiresCompositingForIndirectReason(layer.renderer(), childState.m_subtreeIsCompositing, anyDescendantHas3DTransform, indirectCompositingReason)) {
         layer.setIndirectCompositingReason(indirectCompositingReason);
         childState.m_compositingAncestor = &layer;
         if (overlapMap) {
             overlapMap->pushCompositingContainer();
             addToOverlapMapRecursive(*overlapMap, layer);
         }
         willBeComposited = true;
     }

     ASSERT(willBeComposited == needsToBeComposited(layer));
     if (layer.reflectionLayer()) {
         // FIXME: Shouldn't we call computeCompositingRequirements to handle a reflection overlapping with another renderer?
         layer.reflectionLayer()->setIndirectCompositingReason(willBeComposited ? RenderLayer::IndirectCompositingForStacking : RenderLayer::NoIndirectCompositingReason);
     }

     // Subsequent layers in the parent stacking context also need to composite.
     if (childState.m_subtreeIsCompositing)
         compositingState.m_subtreeIsCompositing = true;

     // Set the flag to say that this SC has compositing children.
     layer.setHasCompositingDescendant(childState.m_subtreeIsCompositing);

     // setHasCompositingDescendant() may have changed the answer to needsToBeComposited() when clipping,
     // so test that again.
     bool isCompositedClippingLayer = canBeComposited(layer) && clipsCompositingDescendants(layer);

     // Turn overlap testing off for later layers if it's already off, or if we have an animating transform.
     // Note that if the layer clips its descendants, there's no reason to propagate the child animation to the parent layers. That's because
     // we know for sure the animation is contained inside the clipping rectangle, which is already added to the overlap map.
     if ((!childState.m_testingOverlap && !isCompositedClippingLayer) || isRunningAcceleratedTransformAnimation(layer.renderer()))
         compositingState.m_testingOverlap = false;

     if (isCompositedClippingLayer) {
         if (!willBeComposited) {
             childState.m_compositingAncestor = &layer;
             if (overlapMap) {
                 overlapMap->pushCompositingContainer();
                 addToOverlapMapRecursive(*overlapMap, layer);
             }
             willBeComposited = true;
          }
     }

     if (overlapMap && childState.m_compositingAncestor == &layer && !layer.isRootLayer())
         overlapMap->popCompositingContainer();

     // If we're back at the root, and no other layers need to be composited, and the root layer itself doesn't need
     // to be composited, then we can drop out of compositing mode altogether. However, don't drop out of compositing mode
     // if there are composited layers that we didn't hit in our traversal (e.g. because of visibility:hidden).
     if (layer.isRootLayer() && !childState.m_subtreeIsCompositing && !requiresCompositingLayer(layer) && !m_forceCompositingMode && !hasAnyAdditionalCompositedLayers(layer)) {
         enableCompositingMode(false);
         willBeComposited = false;
     }

     // If the layer is going into compositing mode, repaint its old location.
     ASSERT(willBeComposited == needsToBeComposited(layer));
     if (!layer.isComposited() && willBeComposited)
         repaintOnCompositingChange(layer);

     // Update backing now, so that we can use isComposited() reliably during tree traversal in rebuildCompositingLayerTree().
     if (updateBacking(layer, CompositingChangeRepaintNow))
         layersChanged = true;

     if (layer.reflectionLayer() && updateLayerCompositingState(*layer.reflectionLayer(), CompositingChangeRepaintNow))
         layersChanged = true;

     descendantHas3DTransform |= anyDescendantHas3DTransform || layer.has3DTransform();

     if (overlapMap)
         overlapMap->geometryMap().popMappingsToAncestor(ancestorLayer);
 }

 void RenderLayerCompositor::computeRegionCompositingRequirements(RenderNamedFlowFragment* region, OverlapMap* overlapMap, CompositingState& childState, bool& layersChanged, bool& anyDescendantHas3DTransform)
 {
     if (!region->isValid())
         return;

     RenderFlowThread* flowThread = region->flowThread();

     if (overlapMap)
         overlapMap->geometryMap().pushRenderFlowThread(flowThread);

     if (const RenderLayerList* layerList = flowThread->getLayerListForRegion(region)) {
         for (size_t i = 0, listSize = layerList->size(); i < listSize; ++i) {
             RenderLayer& curLayer = *layerList->at(i);
             ASSERT(flowThread->regionForCompositedLayer(curLayer) == region);
             computeCompositingRequirements(flowThread->layer(), curLayer, overlapMap, childState, layersChanged, anyDescendantHas3DTransform);
         }
     }

     if (overlapMap)
         overlapMap->geometryMap().popMappingsToAncestor(region->layerOwner());
 }

 void RenderLayerCompositor::setCompositingParent(RenderLayer& childLayer, RenderLayer* parentLayer)
 {
     ASSERT(!parentLayer || childLayer.ancestorCompositingLayer() == parentLayer);
     ASSERT(childLayer.isComposited());

     // It's possible to be called with a parent that isn't yet composited when we're doing
     // partial updates as required by painting or hit testing. Just bail in that case;
     // we'll do a full layer update soon.
     if (!parentLayer || !parentLayer->isComposited())
         return;

     if (parentLayer) {
         GraphicsLayer* hostingLayer = parentLayer->backing()->parentForSublayers();
         GraphicsLayer* hostedLayer = childLayer.backing()->childForSuperlayers();

         hostingLayer->addChild(hostedLayer);
     } else
         childLayer.backing()->childForSuperlayers()->removeFromParent();
 }

 void RenderLayerCompositor::removeCompositedChildren(RenderLayer& layer)
 {
     ASSERT(layer.isComposited());

     layer.backing()->parentForSublayers()->removeAllChildren();
 }

 #if ENABLE(VIDEO)
 bool RenderLayerCompositor::canAccelerateVideoRendering(RenderVideo& video) const
 {
     if (!m_hasAcceleratedCompositing)
         return false;

     return video.supportsAcceleratedRendering();
 }
 #endif

 void RenderLayerCompositor::rebuildCompositingLayerTree(RenderLayer& layer, Vector<GraphicsLayer*>& childLayersOfEnclosingLayer, int depth)
 {
     // Make the layer compositing if necessary, and set up clipping and content layers.
     // Note that we can only do work here that is independent of whether the descendant layers
     // have been processed. computeCompositingRequirements() will already have done the repaint if necessary.

     // Do not iterate the RenderFlowThread directly. We are going to collect composited layers as part of regions.
     if (layer.isFlowThreadCollectingGraphicsLayersUnderRegions())
         return;

     RenderLayerBacking* layerBacking = layer.backing();
     if (layerBacking) {
         // The compositing state of all our children has been updated already, so now
         // we can compute and cache the composited bounds for this layer.
         layerBacking->updateCompositedBounds();

         if (RenderLayer* reflection = layer.reflectionLayer()) {
             if (reflection->backing())
                 reflection->backing()->updateCompositedBounds();
         }

         if (layerBacking->updateGraphicsLayerConfiguration())
             layerBacking->updateDebugIndicators(m_showDebugBorders, m_showRepaintCounter);

         layerBacking->updateGraphicsLayerGeometry();

         if (!layer.parent())
             updateRootLayerPosition();

 #if !LOG_DISABLED
         logLayerInfo(layer, depth);
 #else
         UNUSED_PARAM(depth);
 #endif
         if (layerBacking->hasUnpositionedOverflowControlsLayers())
             layer.positionNewlyCreatedOverflowControls();
     }

     // If this layer has backing, then we are collecting its children, otherwise appending
     // to the compositing child list of an enclosing layer.
     Vector<GraphicsLayer*> layerChildren;
     Vector<GraphicsLayer*>& childList = layerBacking ? layerChildren : childLayersOfEnclosingLayer;

 #if !ASSERT_DISABLED
     LayerListMutationDetector mutationChecker(&layer);
 #endif

     if (layer.isStackingContainer()) {
         if (Vector<RenderLayer*>* negZOrderList = layer.negZOrderList()) {
             for (size_t i = 0, size = negZOrderList->size(); i < size; ++i)
                 rebuildCompositingLayerTree(*negZOrderList->at(i), childList, depth + 1);
         }

         // If a negative z-order child is compositing, we get a foreground layer which needs to get parented.
         if (layerBacking && layerBacking->foregroundLayer())
             childList.append(layerBacking->foregroundLayer());
     }

     if (layer.renderer().isRenderNamedFlowFragmentContainer())
         rebuildRegionCompositingLayerTree(toRenderBlockFlow(layer.renderer()).renderNamedFlowFragment(), layerChildren, depth + 1);

     if (Vector<RenderLayer*>* normalFlowList = layer.normalFlowList()) {
         for (size_t i = 0, size = normalFlowList->size(); i < size; ++i)
             rebuildCompositingLayerTree(*normalFlowList->at(i), childList, depth + 1);
     }

     if (layer.isStackingContainer()) {
         if (Vector<RenderLayer*>* posZOrderList = layer.posZOrderList()) {
             for (size_t i = 0, size = posZOrderList->size(); i < size; ++i)
                 rebuildCompositingLayerTree(*posZOrderList->at(i), childList, depth + 1);
         }
     }

     if (layerBacking) {
         bool parented = false;
         if (layer.renderer().isWidget())
             parented = parentFrameContentLayers(toRenderWidget(&layer.renderer()));

         if (!parented)
             layerBacking->parentForSublayers()->setChildren(layerChildren);

         // If the layer has a clipping layer the overflow controls layers will be siblings of the clipping layer.
         // Otherwise, the overflow control layers are normal children.
         if (!layerBacking->hasClippingLayer() && !layerBacking->hasScrollingLayer()) {
             if (GraphicsLayer* overflowControlLayer = layerBacking->layerForHorizontalScrollbar()) {
                 overflowControlLayer->removeFromParent();
                 layerBacking->parentForSublayers()->addChild(overflowControlLayer);
             }

             if (GraphicsLayer* overflowControlLayer = layerBacking->layerForVerticalScrollbar()) {
                 overflowControlLayer->removeFromParent();
                 layerBacking->parentForSublayers()->addChild(overflowControlLayer);
             }

             if (GraphicsLayer* overflowControlLayer = layerBacking->layerForScrollCorner()) {
                 overflowControlLayer->removeFromParent();
                 layerBacking->parentForSublayers()->addChild(overflowControlLayer);
             }
         }

         childLayersOfEnclosingLayer.append(layerBacking->childForSuperlayers());
     }
 }

 void RenderLayerCompositor::rebuildRegionCompositingLayerTree(RenderNamedFlowFragment* region, Vector<GraphicsLayer*>& childList, int depth)
 {
     if (!region->isValid())
         return;

     RenderFlowThread* flowThread = region->flowThread();
     ASSERT(flowThread->collectsGraphicsLayersUnderRegions());
     if (const RenderLayerList* layerList = flowThread->getLayerListForRegion(region)) {
         for (size_t i = 0, listSize = layerList->size(); i < listSize; ++i) {
             RenderLayer& curLayer = *layerList->at(i);
             ASSERT(flowThread->regionForCompositedLayer(curLayer) == region);
             rebuildCompositingLayerTree(curLayer, childList, depth + 1);
         }
     }
 }

 void RenderLayerCompositor::frameViewDidChangeLocation(const IntPoint& contentsOffset)
 {
     if (m_overflowControlsHostLayer)
         m_overflowControlsHostLayer->setPosition(contentsOffset);
 }

 void RenderLayerCompositor::frameViewDidChangeSize()
 {
     if (m_clipLayer) {
         const FrameView& frameView = m_renderView.frameView();
         m_clipLayer->setSize(frameView.unscaledVisibleContentSize());

         frameViewDidScroll();
         updateOverflowControlsLayers();

 #if ENABLE(RUBBER_BANDING)
         if (m_layerForOverhangAreas)
             m_layerForOverhangAreas->setSize(frameView.frameRect().size());
 #endif
     }
 }

 bool RenderLayerCompositor::hasCoordinatedScrolling() const
 {
     ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator();
     return scrollingCoordinator && scrollingCoordinator->coordinatesScrollingForFrameView(&m_renderView.frameView());
 }

 void RenderLayerCompositor::frameViewDidScroll()
 {
     if (!m_scrollLayer)
         return;

     // If there's a scrolling coordinator that manages scrolling for this frame view,
     // it will also manage updating the scroll layer position.
     if (hasCoordinatedScrolling()) {
         // We have to schedule a flush in order for the main TiledBacking to update its tile coverage.
         scheduleLayerFlushNow();
         return;
     }

     FrameView& frameView = m_renderView.frameView();
     IntPoint scrollPosition = frameView.scrollPosition();

     const Settings& settings = m_renderView.frameView().frame().settings();
     if (settings.compositedScrollingForFramesEnabled()) {
         if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
             scrollingCoordinator->scrollableAreaScrollLayerDidChange(&frameView);
     }

     m_scrollLayer->setPosition(FloatPoint(-scrollPosition.x(), -scrollPosition.y()));

     if (GraphicsLayer* fixedBackgroundLayer = fixedRootBackgroundLayer())
         fixedBackgroundLayer->setPosition(IntPoint(frameView.scrollOffsetForFixedPosition()));
 }

 void RenderLayerCompositor::frameViewDidAddOrRemoveScrollbars()
 {
     updateOverflowControlsLayers();
 }

 void RenderLayerCompositor::frameViewDidLayout()
 {
     RenderLayerBacking* renderViewBacking = m_renderView.layer()->backing();
     if (renderViewBacking)
         renderViewBacking->adjustTiledBackingCoverage();
 }

 void RenderLayerCompositor::rootFixedBackgroundsChanged()
 {
     RenderLayerBacking* renderViewBacking = m_renderView.layer()->backing();
     if (renderViewBacking && renderViewBacking->usingTiledBacking())
         setCompositingLayersNeedRebuild();
 }

 void RenderLayerCompositor::scrollingLayerDidChange(RenderLayer& layer)
 {
     if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
         scrollingCoordinator->scrollableAreaScrollLayerDidChange(&layer);
 }

 void RenderLayerCompositor::fixedRootBackgroundLayerChanged()
 {
     if (m_renderView.documentBeingDestroyed())
         return;

     if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator()) {
         RenderLayerBacking* renderViewBacking = m_renderView.layer()->backing();
         if (!renderViewBacking)
             return;

         scrollingCoordinator->updateScrollingNode(renderViewBacking->scrollLayerID(), scrollLayer(), fixedRootBackgroundLayer());
     }
 }

 String RenderLayerCompositor::layerTreeAsText(LayerTreeFlags flags)
 {
     updateCompositingLayers(CompositingUpdateAfterLayout);

     if (!m_rootContentLayer)
         return String();

     flushPendingLayerChanges(true);

     LayerTreeAsTextBehavior layerTreeBehavior = LayerTreeAsTextBehaviorNormal;
     if (flags & LayerTreeFlagsIncludeDebugInfo)
         layerTreeBehavior |= LayerTreeAsTextDebug;
     if (flags & LayerTreeFlagsIncludeVisibleRects)
         layerTreeBehavior |= LayerTreeAsTextIncludeVisibleRects;
     if (flags & LayerTreeFlagsIncludeTileCaches)
         layerTreeBehavior |= LayerTreeAsTextIncludeTileCaches;
     if (flags & LayerTreeFlagsIncludeRepaintRects)
         layerTreeBehavior |= LayerTreeAsTextIncludeRepaintRects;
     if (flags & LayerTreeFlagsIncludePaintingPhases)
         layerTreeBehavior |= LayerTreeAsTextIncludePaintingPhases;
     if (flags & LayerTreeFlagsIncludeContentLayers)
         layerTreeBehavior |= LayerTreeAsTextIncludeContentLayers;

     // We skip dumping the scroll and clip layers to keep layerTreeAsText output
     // similar between platforms.
     String layerTreeText = m_rootContentLayer->layerTreeAsText(layerTreeBehavior);

     // Dump an empty layer tree only if the only composited layer is the main frame's tiled backing,
     // so that tests expecting us to drop out of accelerated compositing when there are no layers succeed.
     if (!hasAnyAdditionalCompositedLayers(rootRenderLayer()) && mainFrameBackingIsTiled() && !(layerTreeBehavior & LayerTreeAsTextIncludeTileCaches))
         layerTreeText = "";

     // The true root layer is not included in the dump, so if we want to report
     // its repaint rects, they must be included here.
     if (flags & LayerTreeFlagsIncludeRepaintRects) {
         String layerTreeTextWithRootRepaintRects = m_renderView.frameView().trackedRepaintRectsAsText();
         layerTreeTextWithRootRepaintRects.append(layerTreeText);
         return layerTreeTextWithRootRepaintRects;
     }

     return layerTreeText;
 }

 RenderLayerCompositor* RenderLayerCompositor::frameContentsCompositor(RenderWidget* renderer)
 {
     if (Document* contentDocument = renderer->frameOwnerElement().contentDocument()) {
         if (RenderView* view = contentDocument->renderView())
             return &view->compositor();
     }
     return 0;
 }

 bool RenderLayerCompositor::parentFrameContentLayers(RenderWidget* renderer)
 {
     RenderLayerCompositor* innerCompositor = frameContentsCompositor(renderer);
     if (!innerCompositor || !innerCompositor->inCompositingMode() || innerCompositor->rootLayerAttachment() != RootLayerAttachedViaEnclosingFrame)
         return false;

     RenderLayer* layer = renderer->layer();
     if (!layer->isComposited())
         return false;

     RenderLayerBacking* backing = layer->backing();
     GraphicsLayer* hostingLayer = backing->parentForSublayers();
     GraphicsLayer* rootLayer = innerCompositor->rootGraphicsLayer();
     if (hostingLayer->children().size() != 1 || hostingLayer->children()[0] != rootLayer) {
         hostingLayer->removeAllChildren();
         hostingLayer->addChild(rootLayer);
     }
     return true;
 }

 // This just updates layer geometry without changing the hierarchy.
 void RenderLayerCompositor::updateLayerTreeGeometry(RenderLayer& layer, int depth)
 {
     // FIXME: fixed positioned elements inside a named flow are not composited yet.
     if (layer.isOutOfFlowRenderFlowThread())
         return;

     if (RenderLayerBacking* layerBacking = layer.backing()) {
         // The compositing state of all our children has been updated already, so now
         // we can compute and cache the composited bounds for this layer.
         layerBacking->updateCompositedBounds();

         if (RenderLayer* reflection = layer.reflectionLayer()) {
             if (reflection->backing())
                 reflection->backing()->updateCompositedBounds();
         }

         layerBacking->updateGraphicsLayerConfiguration();
         layerBacking->updateGraphicsLayerGeometry();

         if (!layer.parent())
             updateRootLayerPosition();

 #if !LOG_DISABLED
         logLayerInfo(layer, depth);
 #else
         UNUSED_PARAM(depth);
 #endif
     }

 #if !ASSERT_DISABLED
     LayerListMutationDetector mutationChecker(&layer);
 #endif

     if (layer.isStackingContainer()) {
         if (Vector<RenderLayer*>* negZOrderList = layer.negZOrderList()) {
             for (size_t i = 0, size = negZOrderList->size(); i < size; ++i)
                 updateLayerTreeGeometry(*negZOrderList->at(i), depth + 1);
         }
     }

     if (Vector<RenderLayer*>* normalFlowList = layer.normalFlowList()) {
         for (size_t i = 0, size = normalFlowList->size(); i < size; ++i)
             updateLayerTreeGeometry(*normalFlowList->at(i), depth + 1);
     }

     if (layer.isStackingContainer()) {
         if (Vector<RenderLayer*>* posZOrderList = layer.posZOrderList()) {
             for (size_t i = 0, size = posZOrderList->size(); i < size; ++i)
                 updateLayerTreeGeometry(*posZOrderList->at(i), depth + 1);
         }
     }
 }

 // Recurs down the RenderLayer tree until its finds the compositing descendants of compositingAncestor and updates their geometry.
 void RenderLayerCompositor::updateCompositingDescendantGeometry(RenderLayer& compositingAncestor, RenderLayer& layer, bool compositedChildrenOnly)
 {
     if (&layer != &compositingAncestor) {
         if (RenderLayerBacking* layerBacking = layer.backing()) {
             layerBacking->updateCompositedBounds();

             if (RenderLayer* reflection = layer.reflectionLayer()) {
                 if (reflection->backing())
                     reflection->backing()->updateCompositedBounds();
             }

             layerBacking->updateGraphicsLayerGeometry();
             if (compositedChildrenOnly)
                 return;
         }
     }

     if (layer.reflectionLayer())
         updateCompositingDescendantGeometry(compositingAncestor, *layer.reflectionLayer(), compositedChildrenOnly);

     if (!layer.hasCompositingDescendant())
         return;

 #if !ASSERT_DISABLED
     LayerListMutationDetector mutationChecker(&layer);
 #endif

     if (layer.isStackingContainer()) {
         if (Vector<RenderLayer*>* negZOrderList = layer.negZOrderList()) {
             size_t listSize = negZOrderList->size();
             for (size_t i = 0; i < listSize; ++i)
                 updateCompositingDescendantGeometry(compositingAncestor, *negZOrderList->at(i), compositedChildrenOnly);
         }
     }

     if (Vector<RenderLayer*>* normalFlowList = layer.normalFlowList()) {
         size_t listSize = normalFlowList->size();
         for (size_t i = 0; i < listSize; ++i)
             updateCompositingDescendantGeometry(compositingAncestor, *normalFlowList->at(i), compositedChildrenOnly);
     }

     if (layer.isStackingContainer()) {
         if (Vector<RenderLayer*>* posZOrderList = layer.posZOrderList()) {
             size_t listSize = posZOrderList->size();
             for (size_t i = 0; i < listSize; ++i)
                 updateCompositingDescendantGeometry(compositingAncestor, *posZOrderList->at(i), compositedChildrenOnly);
         }
     }
 }


 void RenderLayerCompositor::repaintCompositedLayers(const IntRect* absRect)
 {
     recursiveRepaintLayer(rootRenderLayer(), absRect);
 }

 void RenderLayerCompositor::recursiveRepaintLayer(RenderLayer& layer, const IntRect* rect)
 {
     // FIXME: This method does not work correctly with transforms.
     if (layer.isComposited() && !layer.backing()->paintsIntoCompositedAncestor()) {
         if (rect)
             layer.setBackingNeedsRepaintInRect(*rect);
         else
             layer.setBackingNeedsRepaint();
     }

 #if !ASSERT_DISABLED
     LayerListMutationDetector mutationChecker(&layer);
 #endif

     if (layer.hasCompositingDescendant()) {
         if (Vector<RenderLayer*>* negZOrderList = layer.negZOrderList()) {
             for (size_t i = 0, size = negZOrderList->size(); i < size; ++i) {
                 RenderLayer& childLayer = *negZOrderList->at(i);
                 if (rect) {
                     IntRect childRect(*rect);
                     childLayer.convertToPixelSnappedLayerCoords(&layer, childRect);
                     recursiveRepaintLayer(childLayer, &childRect);
                 } else
                     recursiveRepaintLayer(childLayer);
             }
         }

         if (Vector<RenderLayer*>* posZOrderList = layer.posZOrderList()) {
             for (size_t i = 0, size = posZOrderList->size(); i < size; ++i) {
                 RenderLayer& childLayer = *posZOrderList->at(i);
                 if (rect) {
                     IntRect childRect(*rect);
                     childLayer.convertToPixelSnappedLayerCoords(&layer, childRect);
                     recursiveRepaintLayer(childLayer, &childRect);
                 } else
                     recursiveRepaintLayer(childLayer);
             }
         }
     }
     if (Vector<RenderLayer*>* normalFlowList = layer.normalFlowList()) {
         for (size_t i = 0, size = normalFlowList->size(); i < size; ++i) {
             RenderLayer& childLayer = *normalFlowList->at(i);
             if (rect) {
                 IntRect childRect(*rect);
                 childLayer.convertToPixelSnappedLayerCoords(&layer, childRect);
                 recursiveRepaintLayer(childLayer, &childRect);
             } else
                 recursiveRepaintLayer(childLayer);
         }
     }
 }

 RenderLayer& RenderLayerCompositor::rootRenderLayer() const
 {
     return *m_renderView.layer();
 }

 GraphicsLayer* RenderLayerCompositor::rootGraphicsLayer() const
 {
     if (m_overflowControlsHostLayer)
         return m_overflowControlsHostLayer.get();
     return m_rootContentLayer.get();
 }

 GraphicsLayer* RenderLayerCompositor::scrollLayer() const
 {
     return m_scrollLayer.get();
 }

 #if ENABLE(RUBBER_BANDING)
 GraphicsLayer* RenderLayerCompositor::headerLayer() const
 {
     return m_layerForHeader.get();
 }

 GraphicsLayer* RenderLayerCompositor::footerLayer() const
 {
     return m_layerForFooter.get();
 }
 #endif

 TiledBacking* RenderLayerCompositor::pageTiledBacking() const
 {
     RenderLayerBacking* renderViewBacking = m_renderView.layer()->backing();
     return renderViewBacking ? renderViewBacking->tiledBacking() : nullptr;
 }

 void RenderLayerCompositor::setIsInWindow(bool isInWindow)
 {
     if (TiledBacking* tiledBacking = pageTiledBacking())
         tiledBacking->setIsInWindow(isInWindow);

     if (!inCompositingMode())
         return;

     if (isInWindow) {
         if (m_rootLayerAttachment != RootLayerUnattached)
             return;

         RootLayerAttachment attachment = shouldPropagateCompositingToEnclosingFrame() ? RootLayerAttachedViaEnclosingFrame : RootLayerAttachedViaChromeClient;
         attachRootLayer(attachment);
     } else {
         if (m_rootLayerAttachment == RootLayerUnattached)
             return;

         detachRootLayer();
     }
 }

 void RenderLayerCompositor::clearBackingForLayerIncludingDescendants(RenderLayer& layer)
 {
     if (layer.isComposited()) {
         removeViewportConstrainedLayer(layer);
         layer.clearBacking();
     }

     for (RenderLayer* childLayer = layer.firstChild(); childLayer; childLayer = childLayer->nextSibling())
         clearBackingForLayerIncludingDescendants(*childLayer);
 }

 void RenderLayerCompositor::clearBackingForAllLayers()
 {
     clearBackingForLayerIncludingDescendants(*m_renderView.layer());
 }

 void RenderLayerCompositor::updateRootLayerPosition()
 {
     if (m_rootContentLayer) {
         const IntRect& documentRect = m_renderView.documentRect();
         m_rootContentLayer->setSize(documentRect.size());
         m_rootContentLayer->setPosition(FloatPoint(documentRect.x(), documentRect.y() + m_renderView.frameView().headerHeight()));
     }
     if (m_clipLayer)
         m_clipLayer->setSize(m_renderView.frameView().unscaledVisibleContentSize());

 #if ENABLE(RUBBER_BANDING)
     if (m_contentShadowLayer) {
         m_contentShadowLayer->setPosition(m_rootContentLayer->position());

         FloatSize rootContentLayerSize = m_rootContentLayer->size();
         if (m_contentShadowLayer->size() != rootContentLayerSize) {
             m_contentShadowLayer->setSize(rootContentLayerSize);
             ScrollbarTheme::theme()->setUpContentShadowLayer(m_contentShadowLayer.get());
         }
     }

     updateLayerForTopOverhangArea(m_layerForTopOverhangArea != nullptr);
     updateLayerForBottomOverhangArea(m_layerForBottomOverhangArea != nullptr);
     updateLayerForHeader(m_layerForHeader != nullptr);
     updateLayerForFooter(m_layerForFooter != nullptr);
 #endif
 }

 bool RenderLayerCompositor::has3DContent() const
 {
     return layerHas3DContent(rootRenderLayer());
 }

 bool RenderLayerCompositor::allowsIndependentlyCompositedFrames(const FrameView* view)
 {
 #if PLATFORM(MAC)
     // frames are only independently composited in Mac pre-WebKit2.
     return view->platformWidget();
 #else
     UNUSED_PARAM(view);
 #endif
     return false;
 }

 bool RenderLayerCompositor::shouldPropagateCompositingToEnclosingFrame() const
 {
     // Parent document content needs to be able to render on top of a composited frame, so correct behavior
     // is to have the parent document become composited too. However, this can cause problems on platforms that
     // use native views for frames (like Mac), so disable that behavior on those platforms for now.
     HTMLFrameOwnerElement* ownerElement = m_renderView.document().ownerElement();
     RenderElement* renderer = ownerElement ? ownerElement->renderer() : 0;

     // If we are the top-level frame, don't propagate.
     if (!ownerElement)
         return false;

     if (!allowsIndependentlyCompositedFrames(&m_renderView.frameView()))
         return true;

     if (!renderer || !renderer->isWidget())
         return false;

     // On Mac, only propagate compositing if the frame is overlapped in the parent
     // document, or the parent is already compositing, or the main frame is scaled.
     Page* page = this->page();
     if (page && page->pageScaleFactor() != 1)
         return true;

     RenderWidget* frameRenderer = toRenderWidget(renderer);
     if (frameRenderer->widget()) {
         ASSERT(frameRenderer->widget()->isFrameView());
         FrameView* view = toFrameView(frameRenderer->widget());
         if (view->isOverlappedIncludingAncestors() || view->hasCompositingAncestor())
             return true;
     }

     return false;
 }

 bool RenderLayerCompositor::needsToBeComposited(const RenderLayer& layer, RenderLayer::ViewportConstrainedNotCompositedReason* viewportConstrainedNotCompositedReason) const
 {
     if (!canBeComposited(layer))
         return false;

     return requiresCompositingLayer(layer, viewportConstrainedNotCompositedReason) || layer.mustCompositeForIndirectReasons() || (inCompositingMode() && layer.isRootLayer());
 }

 // Note: this specifies whether the RL needs a compositing layer for intrinsic reasons.
 // Use needsToBeComposited() to determine if a RL actually needs a compositing layer.
 // static
 bool RenderLayerCompositor::requiresCompositingLayer(const RenderLayer& layer, RenderLayer::ViewportConstrainedNotCompositedReason* viewportConstrainedNotCompositedReason) const
 {
     auto renderer = &layer.renderer();

     // The compositing state of a reflection should match that of its reflected layer.
     if (layer.isReflection())
         renderer = toRenderLayerModelObject(renderer->parent()); // The RenderReplica's parent is the object being reflected.

     // The root layer always has a compositing layer, but it may not have backing.
     return requiresCompositingForTransform(*renderer)
         || requiresCompositingForVideo(*renderer)
         || requiresCompositingForCanvas(*renderer)
         || requiresCompositingForPlugin(*renderer)
         || requiresCompositingForFrame(*renderer)
         || (canRender3DTransforms() && renderer->style().backfaceVisibility() == BackfaceVisibilityHidden)
         || clipsCompositingDescendants(*renderer->layer())
         || requiresCompositingForAnimation(*renderer)
         || requiresCompositingForFilters(*renderer)
         || requiresCompositingForPosition(*renderer, *renderer->layer(), viewportConstrainedNotCompositedReason)
         || requiresCompositingForOverflowScrolling(*renderer->layer())
         || requiresCompositingForBlending(*renderer);
 }

 bool RenderLayerCompositor::canBeComposited(const RenderLayer& layer) const
 {
     if (m_hasAcceleratedCompositing && layer.isSelfPaintingLayer()) {
         if (!layer.isInsideFlowThread())
             return true;

         // CSS Regions flow threads do not need to be composited as we use composited RenderRegions
         // to render the background of the RenderFlowThread.
         if (layer.isRenderFlowThread())
             return false;

         // A faster way of saying layer.enclosingFlowThreadLayer()->isFlowThreadCollectingGraphicsLayersUnderRegions()
         return layer.isInsideOutOfFlowThread();
     }
     return false;
 }

 bool RenderLayerCompositor::requiresOwnBackingStore(const RenderLayer& layer, const RenderLayer* compositingAncestorLayer, const IntRect& layerCompositedBoundsInAncestor, const IntRect& ancestorCompositedBounds) const
 {
     auto& renderer = layer.renderer();

     if (compositingAncestorLayer
         && !(compositingAncestorLayer->backing()->graphicsLayer()->drawsContent()
             || compositingAncestorLayer->backing()->paintsIntoWindow()
             || compositingAncestorLayer->backing()->paintsIntoCompositedAncestor()))
         return true;

     if (layer.isRootLayer()
         || layer.transform() // note: excludes perspective and transformStyle3D.
         || requiresCompositingForVideo(renderer)
         || requiresCompositingForCanvas(renderer)
         || requiresCompositingForPlugin(renderer)
         || requiresCompositingForFrame(renderer)
         || (canRender3DTransforms() && renderer.style().backfaceVisibility() == BackfaceVisibilityHidden)
         || requiresCompositingForAnimation(renderer)
         || requiresCompositingForFilters(renderer)
         || requiresCompositingForBlending(renderer)
         || requiresCompositingForPosition(renderer, layer)
         || requiresCompositingForOverflowScrolling(layer)
         || renderer.isTransparent()
         || renderer.hasMask()
         || renderer.hasReflection()
         || renderer.hasFilter())
         return true;


     if (layer.mustCompositeForIndirectReasons()) {
         RenderLayer::IndirectCompositingReason reason = layer.indirectCompositingReason();
         return reason == RenderLayer::IndirectCompositingForOverlap
             || reason == RenderLayer::IndirectCompositingForStacking
             || reason == RenderLayer::IndirectCompositingForBackgroundLayer
             || reason == RenderLayer::IndirectCompositingForGraphicalEffect
             || reason == RenderLayer::IndirectCompositingForPreserve3D; // preserve-3d has to create backing store to ensure that 3d-transformed elements intersect.
     }

     if (!ancestorCompositedBounds.contains(layerCompositedBoundsInAncestor))
         return true;

     return false;
 }

 CompositingReasons RenderLayerCompositor::reasonsForCompositing(const RenderLayer& layer) const
 {
     CompositingReasons reasons = CompositingReasonNone;

     if (!layer.isComposited())
         return reasons;

     auto renderer = &layer.renderer();
     if (layer.isReflection())
         renderer = toRenderLayerModelObject(renderer->parent());

     if (requiresCompositingForTransform(*renderer))
         reasons |= CompositingReason3DTransform;

     if (requiresCompositingForVideo(*renderer))
         reasons |= CompositingReasonVideo;
     else if (requiresCompositingForCanvas(*renderer))
         reasons |= CompositingReasonCanvas;
     else if (requiresCompositingForPlugin(*renderer))
         reasons |= CompositingReasonPlugin;
     else if (requiresCompositingForFrame(*renderer))
         reasons |= CompositingReasonIFrame;

     if ((canRender3DTransforms() && renderer->style().backfaceVisibility() == BackfaceVisibilityHidden))
         reasons |= CompositingReasonBackfaceVisibilityHidden;

     if (clipsCompositingDescendants(*renderer->layer()))
         reasons |= CompositingReasonClipsCompositingDescendants;

     if (requiresCompositingForAnimation(*renderer))
         reasons |= CompositingReasonAnimation;

     if (requiresCompositingForFilters(*renderer))
         reasons |= CompositingReasonFilters;

     if (requiresCompositingForPosition(*renderer, *renderer->layer()))
         reasons |= renderer->style().position() == FixedPosition ? CompositingReasonPositionFixed : CompositingReasonPositionSticky;

     if (requiresCompositingForOverflowScrolling(*renderer->layer()))
         reasons |= CompositingReasonOverflowScrollingTouch;

     if (renderer->layer()->indirectCompositingReason() == RenderLayer::IndirectCompositingForStacking)
         reasons |= CompositingReasonStacking;
     else if (renderer->layer()->indirectCompositingReason() == RenderLayer::IndirectCompositingForOverlap)
         reasons |= CompositingReasonOverlap;
     else if (renderer->layer()->indirectCompositingReason() == RenderLayer::IndirectCompositingForBackgroundLayer)
         reasons |= CompositingReasonNegativeZIndexChildren;
     else if (renderer->layer()->indirectCompositingReason() == RenderLayer::IndirectCompositingForGraphicalEffect) {
         if (renderer->layer()->transform())
             reasons |= CompositingReasonTransformWithCompositedDescendants;

         if (renderer->isTransparent())
             reasons |= CompositingReasonOpacityWithCompositedDescendants;

         if (renderer->hasMask())
             reasons |= CompositingReasonMaskWithCompositedDescendants;

         if (renderer->hasReflection())
             reasons |= CompositingReasonReflectionWithCompositedDescendants;

         if (renderer->hasFilter())
             reasons |= CompositingReasonFilterWithCompositedDescendants;

         if (renderer->hasBlendMode())
             reasons |= CompositingReasonBlendingWithCompositedDescendants;
     } else if (renderer->layer()->indirectCompositingReason() == RenderLayer::IndirectCompositingForPerspective)
         reasons |= CompositingReasonPerspective;
     else if (renderer->layer()->indirectCompositingReason() == RenderLayer::IndirectCompositingForPreserve3D)
         reasons |= CompositingReasonPreserve3D;

     if (inCompositingMode() && renderer->layer()->isRootLayer())
         reasons |= CompositingReasonRoot;

     return reasons;
 }

 #if !LOG_DISABLED
 const char* RenderLayerCompositor::logReasonsForCompositing(const RenderLayer& layer)
 {
     CompositingReasons reasons = reasonsForCompositing(layer);

     if (reasons & CompositingReason3DTransform)
         return "3D transform";

     if (reasons & CompositingReasonVideo)
         return "video";
     else if (reasons & CompositingReasonCanvas)
         return "canvas";
     else if (reasons & CompositingReasonPlugin)
         return "plugin";
     else if (reasons & CompositingReasonIFrame)
         return "iframe";

     if (reasons & CompositingReasonBackfaceVisibilityHidden)
         return "backface-visibility: hidden";

     if (reasons & CompositingReasonClipsCompositingDescendants)
         return "clips compositing descendants";

     if (reasons & CompositingReasonAnimation)
         return "animation";

     if (reasons & CompositingReasonFilters)
         return "filters";

     if (reasons & CompositingReasonPositionFixed)
         return "position: fixed";

     if (reasons & CompositingReasonPositionSticky)
         return "position: sticky";

     if (reasons & CompositingReasonOverflowScrollingTouch)
         return "-webkit-overflow-scrolling: touch";

     if (reasons & CompositingReasonStacking)
         return "stacking";

     if (reasons & CompositingReasonOverlap)
         return "overlap";

     if (reasons & CompositingReasonNegativeZIndexChildren)
         return "negative z-index children";

     if (reasons & CompositingReasonTransformWithCompositedDescendants)
         return "transform with composited descendants";

     if (reasons & CompositingReasonOpacityWithCompositedDescendants)
         return "opacity with composited descendants";

     if (reasons & CompositingReasonMaskWithCompositedDescendants)
         return "mask with composited descendants";

     if (reasons & CompositingReasonReflectionWithCompositedDescendants)
         return "reflection with composited descendants";

     if (reasons & CompositingReasonFilterWithCompositedDescendants)
         return "filter with composited descendants";

     if (reasons & CompositingReasonBlendingWithCompositedDescendants)
         return "blending with composited descendants";

     if (reasons & CompositingReasonPerspective)
         return "perspective";

     if (reasons & CompositingReasonPreserve3D)
         return "preserve-3d";

     if (reasons & CompositingReasonRoot)
         return "root";

     return "";
 }
 #endif

 // Return true if the given layer has some ancestor in the RenderLayer hierarchy that clips,
 // up to the enclosing compositing ancestor. This is required because compositing layers are parented
 // according to the z-order hierarchy, yet clipping goes down the renderer hierarchy.
 // Thus, a RenderLayer can be clipped by a RenderLayer that is an ancestor in the renderer hierarchy,
 // but a sibling in the z-order hierarchy.
 bool RenderLayerCompositor::clippedByAncestor(RenderLayer& layer) const
 {
     if (!layer.isComposited() || !layer.parent())
         return false;

     RenderLayer* compositingAncestor = layer.ancestorCompositingLayer();
     if (!compositingAncestor)
         return false;

     // If the compositingAncestor clips, that will be taken care of by clipsCompositingDescendants(),
     // so we only care about clipping between its first child that is our ancestor (the computeClipRoot),
     // and layer.
     RenderLayer* computeClipRoot = nullptr;
     RenderLayer* parent = &layer;
     while (parent) {
         RenderLayer* next = parent->parent();
         if (next == compositingAncestor) {
             computeClipRoot = parent;
             break;
         }
         parent = next;
     }

     if (!computeClipRoot || computeClipRoot == &layer)
         return false;

     return layer.backgroundClipRect(RenderLayer::ClipRectsContext(computeClipRoot, 0, TemporaryClipRects)).rect() != PaintInfo::infiniteRect(); // FIXME: Incorrect for CSS regions.
 }

 // Return true if the given layer is a stacking context and has compositing child
 // layers that it needs to clip. In this case we insert a clipping GraphicsLayer
 // into the hierarchy between this layer and its children in the z-order hierarchy.
 bool RenderLayerCompositor::clipsCompositingDescendants(const RenderLayer& layer) const
 {
     return layer.hasCompositingDescendant() && layer.renderer().hasClipOrOverflowClip();
 }

 bool RenderLayerCompositor::requiresCompositingForScrollableFrame() const
 {
     // Need this done first to determine overflow.
     ASSERT(!m_renderView.needsLayout());
     HTMLFrameOwnerElement* ownerElement = m_renderView.document().ownerElement();
     if (!ownerElement)
         return false;

     if (!(m_compositingTriggers & ChromeClient::ScrollableInnerFrameTrigger))
         return false;

     return m_renderView.frameView().isScrollable();
 }

 bool RenderLayerCompositor::requiresCompositingForTransform(RenderLayerModelObject& renderer) const
 {
     if (!(m_compositingTriggers & ChromeClient::ThreeDTransformTrigger))
         return false;

     // Note that we ask the renderer if it has a transform, because the style may have transforms,
     // but the renderer may be an inline that doesn't suppport them.
     return renderer.hasTransform() && renderer.style().transform().has3DOperation();
 }

 bool RenderLayerCompositor::requiresCompositingForVideo(RenderLayerModelObject& renderer) const
 {
     if (!(m_compositingTriggers & ChromeClient::VideoTrigger))
         return false;
 #if ENABLE(VIDEO)
     if (renderer.isVideo()) {
         RenderVideo& video = toRenderVideo(renderer);
         return (video.requiresImmediateCompositing() || video.shouldDisplayVideo()) && canAccelerateVideoRendering(video);
     }
 #if ENABLE(PLUGIN_PROXY_FOR_VIDEO)
     if (renderer.isWidget()) {
         if (!m_hasAcceleratedCompositing)
             return false;

         Element* element = renderer.element();
         if (!element || (!isHTMLVideoElement(element) && !isHTMLAudioElement(element)))
             return false;

         HTMLMediaElement* mediaElement = toHTMLMediaElement(element);
         return mediaElement->player() ? mediaElement->player()->supportsAcceleratedRendering() : false;
     }
 #endif // ENABLE(PLUGIN_PROXY_FOR_VIDEO)
 #else
     UNUSED_PARAM(renderer);
 #endif
     return false;
 }

 bool RenderLayerCompositor::requiresCompositingForCanvas(RenderLayerModelObject& renderer) const
 {
     if (!(m_compositingTriggers & ChromeClient::CanvasTrigger))
         return false;

     if (renderer.isCanvas()) {
         HTMLCanvasElement* canvas = toHTMLCanvasElement(renderer.element());
 #if USE(COMPOSITING_FOR_SMALL_CANVASES)
         bool isCanvasLargeEnoughToForceCompositing = true;
 #else
         bool isCanvasLargeEnoughToForceCompositing = canvas->size().area() >= canvasAreaThresholdRequiringCompositing;
 #endif
         return canvas->renderingContext() && canvas->renderingContext()->isAccelerated() && (canvas->renderingContext()->is3d() || isCanvasLargeEnoughToForceCompositing);
     }

     return false;
 }

 bool RenderLayerCompositor::requiresCompositingForPlugin(RenderLayerModelObject& renderer) const
 {
     if (!(m_compositingTriggers & ChromeClient::PluginTrigger))
         return false;

     bool composite = renderer.isEmbeddedObject() && toRenderEmbeddedObject(&renderer)->allowsAcceleratedCompositing();
     if (!composite)
         return false;

     m_reevaluateCompositingAfterLayout = true;

     RenderWidget& pluginRenderer = *toRenderWidget(&renderer);
     // If we can't reliably know the size of the plugin yet, don't change compositing state.
     if (pluginRenderer.needsLayout())
         return pluginRenderer.hasLayer() && pluginRenderer.layer()->isComposited();

     // Don't go into compositing mode if height or width are zero, or size is 1x1.
     IntRect contentBox = pixelSnappedIntRect(pluginRenderer.contentBoxRect());
     return contentBox.height() * contentBox.width() > 1;
 }

 bool RenderLayerCompositor::requiresCompositingForFrame(RenderLayerModelObject& renderer) const
 {
     if (!renderer.isWidget())
         return false;

     RenderWidget& frameRenderer = *toRenderWidget(&renderer);

     if (!frameRenderer.requiresAcceleratedCompositing())
         return false;

     m_reevaluateCompositingAfterLayout = true;

     RenderLayerCompositor* innerCompositor = frameContentsCompositor(&frameRenderer);
     if (!innerCompositor || !innerCompositor->shouldPropagateCompositingToEnclosingFrame())
         return false;

     // If we can't reliably know the size of the iframe yet, don't change compositing state.
     if (!frameRenderer.parent() || frameRenderer.needsLayout())
         return frameRenderer.hasLayer() && frameRenderer.layer()->isComposited();

     // Don't go into compositing mode if height or width are zero.
     return !pixelSnappedIntRect(frameRenderer.contentBoxRect()).isEmpty();
 }

 bool RenderLayerCompositor::requiresCompositingForAnimation(RenderLayerModelObject& renderer) const
 {
     if (!(m_compositingTriggers & ChromeClient::AnimationTrigger))
         return false;

     AnimationController& animController = renderer.animation();
     return (animController.isRunningAnimationOnRenderer(&renderer, CSSPropertyOpacity)
             && (inCompositingMode() || (m_compositingTriggers & ChromeClient::AnimatedOpacityTrigger)))
 #if ENABLE(CSS_FILTERS)
 #if !PLATFORM(MAC) || (!PLATFORM(IOS) && __MAC_OS_X_VERSION_MIN_REQUIRED >= 1080)
             // <rdar://problem/10907251> - WebKit2 doesn't support CA animations of CI filters on Lion and below
             || animController.isRunningAnimationOnRenderer(&renderer, CSSPropertyWebkitFilter)
 #endif // !PLATFORM(MAC) || (!PLATFORM(IOS) && __MAC_OS_X_VERSION_MIN_REQUIRED >= 1080)
 #endif // CSS_FILTERS
             || animController.isRunningAnimationOnRenderer(&renderer, CSSPropertyWebkitTransform);
 }

 bool RenderLayerCompositor::requiresCompositingForIndirectReason(RenderLayerModelObject& renderer, bool hasCompositedDescendants, bool has3DTransformedDescendants, RenderLayer::IndirectCompositingReason& reason) const
 {
     RenderLayer& layer = *toRenderBoxModelObject(renderer).layer();

     // When a layer has composited descendants, some effects, like 2d transforms, filters, masks etc must be implemented
     // via compositing so that they also apply to those composited descendants.
     if (hasCompositedDescendants && (layer.transform() || renderer.createsGroup() || renderer.hasReflection() || renderer.isRenderNamedFlowFragmentContainer())) {
         reason = RenderLayer::IndirectCompositingForGraphicalEffect;
         return true;
     }

     // A layer with preserve-3d or perspective only needs to be composited if there are descendant layers that
     // will be affected by the preserve-3d or perspective.
     if (has3DTransformedDescendants) {
         if (renderer.style().transformStyle3D() == TransformStyle3DPreserve3D) {
             reason = RenderLayer::IndirectCompositingForPreserve3D;
             return true;
         }

         if (renderer.style().hasPerspective()) {
             reason = RenderLayer::IndirectCompositingForPerspective;
             return true;
         }
     }

     reason = RenderLayer::NoIndirectCompositingReason;
     return false;
 }

 bool RenderLayerCompositor::requiresCompositingForFilters(RenderLayerModelObject& renderer) const
 {
 #if ENABLE(CSS_FILTERS)
     if (!(m_compositingTriggers & ChromeClient::FilterTrigger))
         return false;

     return renderer.hasFilter();
 #else
     UNUSED_PARAM(renderer);
     return false;
 #endif
 }

 bool RenderLayerCompositor::requiresCompositingForBlending(RenderLayerModelObject& renderer) const
 {
 #if ENABLE(CSS_COMPOSITING)
     return renderer.hasBlendMode();
 #else
     UNUSED_PARAM(renderer);
     return false;
 #endif
 }

 static bool isViewportConstrainedFixedOrStickyLayer(const RenderLayer& layer)
 {
     if (layer.renderer().isStickyPositioned())
         return !layer.enclosingOverflowClipLayer(ExcludeSelf);

     if (layer.renderer().style().position() != FixedPosition)
         return false;

     for (RenderLayer* stackingContainer = layer.stackingContainer(); stackingContainer; stackingContainer = stackingContainer->stackingContainer()) {
         if (stackingContainer->isComposited() && stackingContainer->renderer().style().position() == FixedPosition)
             return false;
     }

     return true;
 }

 bool RenderLayerCompositor::requiresCompositingForPosition(RenderLayerModelObject& renderer, const RenderLayer& layer, RenderLayer::ViewportConstrainedNotCompositedReason* viewportConstrainedNotCompositedReason) const
 {
     // position:fixed elements that create their own stacking context (e.g. have an explicit z-index,
     // opacity, transform) can get their own composited layer. A stacking context is required otherwise
     // z-index and clipping will be broken.
     if (!renderer.isPositioned())
         return false;

     EPosition position = renderer.style().position();
     bool isFixed = renderer.isOutOfFlowPositioned() && position == FixedPosition;
     if (isFixed && !layer.isStackingContainer())
         return false;

     bool isSticky = renderer.isInFlowPositioned() && position == StickyPosition;
     if (!isFixed && !isSticky)
         return false;

     // FIXME: acceleratedCompositingForFixedPositionEnabled should probably be renamed acceleratedCompositingForViewportConstrainedPositionEnabled().
     const Settings& settings = m_renderView.frameView().frame().settings();
     if (!settings.acceleratedCompositingForFixedPositionEnabled())
         return false;

     if (isSticky)
         return hasCoordinatedScrolling() && isViewportConstrainedFixedOrStickyLayer(layer);

     auto container = renderer.container();
     // If the renderer is not hooked up yet then we have to wait until it is.
     if (!container) {
         m_reevaluateCompositingAfterLayout = true;
         return false;
     }

     // Don't promote fixed position elements that are descendants of a non-view container, e.g. transformed elements.
     // They will stay fixed wrt the container rather than the enclosing frame.
     if (container != &m_renderView) {
         if (viewportConstrainedNotCompositedReason)
             *viewportConstrainedNotCompositedReason = RenderLayer::NotCompositedForNonViewContainer;
         return false;
     }

     // Subsequent tests depend on layout. If we can't tell now, just keep things the way they are until layout is done.
     if (!m_inPostLayoutUpdate) {
         m_reevaluateCompositingAfterLayout = true;
         return layer.isComposited();
     }

     bool paintsContent = layer.isVisuallyNonEmpty() || layer.hasVisibleDescendant();
     if (!paintsContent) {
         if (viewportConstrainedNotCompositedReason)
             *viewportConstrainedNotCompositedReason = RenderLayer::NotCompositedForNoVisibleContent;
         return false;
     }

     // Fixed position elements that are invisible in the current view don't get their own layer.
     LayoutRect viewBounds = m_renderView.frameView().viewportConstrainedVisibleContentRect();
     LayoutRect layerBounds = layer.calculateLayerBounds(&layer, 0, RenderLayer::UseLocalClipRectIfPossible | RenderLayer::IncludeLayerFilterOutsets | RenderLayer::UseFragmentBoxes
         | RenderLayer::ExcludeHiddenDescendants | RenderLayer::DontConstrainForMask | RenderLayer::IncludeCompositedDescendants);
     // Map to m_renderView to ignore page scale.
     FloatRect absoluteBounds = layer.renderer().localToContainerQuad(FloatRect(layerBounds), &m_renderView).boundingBox();
     if (!viewBounds.intersects(enclosingIntRect(absoluteBounds))) {
         if (viewportConstrainedNotCompositedReason)
             *viewportConstrainedNotCompositedReason = RenderLayer::NotCompositedForBoundsOutOfView;
         return false;
     }

     return true;
 }

 bool RenderLayerCompositor::requiresCompositingForOverflowScrolling(const RenderLayer& layer) const
 {
     return layer.needsCompositedScrolling();
 }

 bool RenderLayerCompositor::isRunningAcceleratedTransformAnimation(RenderLayerModelObject& renderer) const
 {
     if (!(m_compositingTriggers & ChromeClient::AnimationTrigger))
         return false;

     return renderer.animation().isRunningAnimationOnRenderer(&renderer, CSSPropertyWebkitTransform);
 }

 // If an element has negative z-index children, those children render in front of the
 // layer background, so we need an extra 'contents' layer for the foreground of the layer
 // object.
 bool RenderLayerCompositor::needsContentsCompositingLayer(const RenderLayer& layer) const
 {
     return layer.hasNegativeZOrderList();
 }

 bool RenderLayerCompositor::requiresScrollLayer(RootLayerAttachment attachment) const
 {
     // This applies when the application UI handles scrolling, in which case RenderLayerCompositor doesn't need to manage it.
     if (m_renderView.frameView().delegatesScrolling())
         return false;

     // We need to handle our own scrolling if we're:
     return !m_renderView.frameView().platformWidget() // viewless (i.e. non-Mac, or Mac in WebKit2)
         || attachment == RootLayerAttachedViaEnclosingFrame; // a composited frame on Mac
 }

 static void paintScrollbar(Scrollbar* scrollbar, GraphicsContext& context, const IntRect& clip)
 {
     if (!scrollbar)
         return;

     context.save();
     const IntRect& scrollbarRect = scrollbar->frameRect();
     context.translate(-scrollbarRect.x(), -scrollbarRect.y());
     IntRect transformedClip = clip;
     transformedClip.moveBy(scrollbarRect.location());
     scrollbar->paint(&context, transformedClip);
     context.restore();
 }

 void RenderLayerCompositor::paintContents(const GraphicsLayer* graphicsLayer, GraphicsContext& context, GraphicsLayerPaintingPhase, const IntRect& clip)
 {
     if (graphicsLayer == layerForHorizontalScrollbar())
         paintScrollbar(m_renderView.frameView().horizontalScrollbar(), context, clip);
     else if (graphicsLayer == layerForVerticalScrollbar())
         paintScrollbar(m_renderView.frameView().verticalScrollbar(), context, clip);
     else if (graphicsLayer == layerForScrollCorner()) {
         const IntRect& scrollCorner = m_renderView.frameView().scrollCornerRect();
         context.save();
         context.translate(-scrollCorner.x(), -scrollCorner.y());
         IntRect transformedClip = clip;
         transformedClip.moveBy(scrollCorner.location());
         m_renderView.frameView().paintScrollCorner(&context, transformedClip);
         context.restore();
     }
 }

 bool RenderLayerCompositor::supportsFixedRootBackgroundCompositing() const
 {
     RenderLayerBacking* renderViewBacking = m_renderView.layer()->backing();
     return renderViewBacking && renderViewBacking->usingTiledBacking();
 }

 bool RenderLayerCompositor::needsFixedRootBackgroundLayer(const RenderLayer& layer) const
 {
     if (&layer != m_renderView.layer())
         return false;

     return supportsFixedRootBackgroundCompositing() && m_renderView.rootBackgroundIsEntirelyFixed();
 }

 GraphicsLayer* RenderLayerCompositor::fixedRootBackgroundLayer() const
 {
     // Get the fixed root background from the RenderView layer's backing.
     RenderLayer* viewLayer = m_renderView.layer();
     if (!viewLayer)
         return nullptr;

     if (viewLayer->isComposited() && viewLayer->backing()->backgroundLayerPaintsFixedRootBackground())
         return viewLayer->backing()->backgroundLayer();

     return nullptr;
 }

 static void resetTrackedRepaintRectsRecursive(GraphicsLayer& graphicsLayer)
 {
     graphicsLayer.resetTrackedRepaints();

     for (size_t i = 0, size = graphicsLayer.children().size(); i < size; ++i)
         resetTrackedRepaintRectsRecursive(*graphicsLayer.children()[i]);

     if (GraphicsLayer* replicaLayer = graphicsLayer.replicaLayer())
         resetTrackedRepaintRectsRecursive(*replicaLayer);

     if (GraphicsLayer* maskLayer = graphicsLayer.maskLayer())
         resetTrackedRepaintRectsRecursive(*maskLayer);
 }

 void RenderLayerCompositor::resetTrackedRepaintRects()
 {
     if (GraphicsLayer* rootLayer = rootGraphicsLayer())
         resetTrackedRepaintRectsRecursive(*rootLayer);
 }

 void RenderLayerCompositor::setTracksRepaints(bool tracksRepaints)
 {
     m_isTrackingRepaints = tracksRepaints;
 }

 bool RenderLayerCompositor::isTrackingRepaints() const
 {
     return m_isTrackingRepaints;
 }

 float RenderLayerCompositor::deviceScaleFactor() const
 {
     Page* page = this->page();
     return page ? page->deviceScaleFactor() : 1;
 }

 float RenderLayerCompositor::pageScaleFactor() const
 {
     Page* page = this->page();
     return page ? page->pageScaleFactor() : 1;
 }

 float RenderLayerCompositor::contentsScaleMultiplierForNewTiles(const GraphicsLayer*) const
 {
     return 1;
 }

 void RenderLayerCompositor::didCommitChangesForLayer(const GraphicsLayer*) const
 {
     // Nothing to do here yet.
 }

 bool RenderLayerCompositor::keepLayersPixelAligned() const
 {
     // When scaling, attempt to align compositing layers to pixel boundaries.
     return true;
 }

 bool RenderLayerCompositor::mainFrameBackingIsTiled() const
 {
     RenderLayer* layer = m_renderView.layer();
     if (!layer)
         return false;

     RenderLayerBacking* backing = layer->backing();
     if (!backing)
         return false;

     return backing->usingTiledBacking();
 }

 bool RenderLayerCompositor::mainFrameBackingIsTiledWithMargin() const
 {
     RenderLayer* layer = m_renderView.layer();
     if (!layer)
         return false;

     RenderLayerBacking* backing = layer->backing();
     if (!backing)
         return false;

     return backing->tiledBackingHasMargin();
 }

 bool RenderLayerCompositor::shouldCompositeOverflowControls() const
 {
     FrameView& frameView = m_renderView.frameView();

     if (frameView.platformWidget())
         return false;

     if (mainFrameBackingIsTiled())
         return true;

     if (!frameView.hasOverlayScrollbars())
         return false;

     return true;
 }

 bool RenderLayerCompositor::requiresHorizontalScrollbarLayer() const
 {
     return shouldCompositeOverflowControls() && m_renderView.frameView().horizontalScrollbar();
 }

 bool RenderLayerCompositor::requiresVerticalScrollbarLayer() const
 {
     return shouldCompositeOverflowControls() && m_renderView.frameView().verticalScrollbar();
 }

 bool RenderLayerCompositor::requiresScrollCornerLayer() const
 {
     return shouldCompositeOverflowControls() && m_renderView.frameView().isScrollCornerVisible();
 }

 #if ENABLE(RUBBER_BANDING)
 bool RenderLayerCompositor::requiresOverhangAreasLayer() const
 {
     // We don't want a layer if this is a subframe.
     if (m_renderView.document().ownerElement())
         return false;

     // We do want a layer if we're using tiled drawing and can scroll.
     if (mainFrameBackingIsTiled() && m_renderView.frameView().hasOpaqueBackground() && !m_renderView.frameView().prohibitsScrolling())
         return true;

     return false;
 }

 bool RenderLayerCompositor::requiresContentShadowLayer() const
 {
     // We don't want a layer if this is a subframe.
     if (m_renderView.document().ownerElement())
         return false;

 #if PLATFORM(MAC)
     if (viewHasTransparentBackground())
         return false;

     // On Mac, we want a content shadow layer if we're using tiled drawing and can scroll.
     if (mainFrameBackingIsTiled() && !m_renderView.frameView().prohibitsScrolling())
         return true;
 #endif

     return false;
 }

 GraphicsLayer* RenderLayerCompositor::updateLayerForTopOverhangArea(bool wantsLayer)
 {
     if (m_renderView.document().ownerElement())
         return 0;

     if (!wantsLayer) {
         if (m_layerForTopOverhangArea) {
             m_layerForTopOverhangArea->removeFromParent();
             m_layerForTopOverhangArea = nullptr;
         }
         return 0;
     }

     if (!m_layerForTopOverhangArea) {
         m_layerForTopOverhangArea = GraphicsLayer::create(graphicsLayerFactory(), this);
 #ifndef NDEBUG
         m_layerForTopOverhangArea->setName("top overhang area");
 #endif
         m_scrollLayer->addChildBelow(m_layerForTopOverhangArea.get(), m_rootContentLayer.get());
     }

     return m_layerForTopOverhangArea.get();
 }

 GraphicsLayer* RenderLayerCompositor::updateLayerForBottomOverhangArea(bool wantsLayer)
 {
     if (m_renderView.document().ownerElement())
         return 0;

     if (!wantsLayer) {
         if (m_layerForBottomOverhangArea) {
             m_layerForBottomOverhangArea->removeFromParent();
             m_layerForBottomOverhangArea = nullptr;
         }
         return 0;
     }

     if (!m_layerForBottomOverhangArea) {
         m_layerForBottomOverhangArea = GraphicsLayer::create(graphicsLayerFactory(), this);
 #ifndef NDEBUG
         m_layerForBottomOverhangArea->setName("bottom overhang area");
 #endif
         m_scrollLayer->addChildBelow(m_layerForBottomOverhangArea.get(), m_rootContentLayer.get());
     }

     m_layerForBottomOverhangArea->setPosition(FloatPoint(0, m_rootContentLayer->size().height() + m_renderView.frameView().headerHeight() + m_renderView.frameView().footerHeight()));
     return m_layerForBottomOverhangArea.get();
 }

 GraphicsLayer* RenderLayerCompositor::updateLayerForHeader(bool wantsLayer)
 {
     if (m_renderView.document().ownerElement())
         return 0;

     if (!wantsLayer) {
         if (m_layerForHeader) {
             m_layerForHeader->removeFromParent();
             m_layerForHeader = nullptr;

             // The ScrollingTree knows about the header layer, and the position of the root layer is affected
             // by the header layer, so if we remove the header, we need to tell the scrolling tree.
             if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
                 scrollingCoordinator->frameViewRootLayerDidChange(&m_renderView.frameView());
         }
         return 0;
     }

     if (!m_layerForHeader) {
         m_layerForHeader = GraphicsLayer::create(graphicsLayerFactory(), this);
 #ifndef NDEBUG
         m_layerForHeader->setName("header");
 #endif
         m_scrollLayer->addChildBelow(m_layerForHeader.get(), m_rootContentLayer.get());
         m_renderView.frameView().addPaintPendingMilestones(DidFirstFlushForHeaderLayer);
     }

     m_layerForHeader->setPosition(FloatPoint());
     m_layerForHeader->setAnchorPoint(FloatPoint3D());
     m_layerForHeader->setSize(FloatSize(m_renderView.frameView().visibleWidth(), m_renderView.frameView().headerHeight()));

     if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
         scrollingCoordinator->frameViewRootLayerDidChange(&m_renderView.frameView());

     if (Page* page = this->page())
         page->chrome().client().didAddHeaderLayer(m_layerForHeader.get());

     return m_layerForHeader.get();
 }

 GraphicsLayer* RenderLayerCompositor::updateLayerForFooter(bool wantsLayer)
 {
     if (m_renderView.document().ownerElement())
         return 0;

     if (!wantsLayer) {
         if (m_layerForFooter) {
             m_layerForFooter->removeFromParent();
             m_layerForFooter = nullptr;

             // The ScrollingTree knows about the footer layer, and the total scrollable size is affected
             // by the footer layer, so if we remove the footer, we need to tell the scrolling tree.
             if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
                 scrollingCoordinator->frameViewRootLayerDidChange(&m_renderView.frameView());
         }
         return 0;
     }

     if (!m_layerForFooter) {
         m_layerForFooter = GraphicsLayer::create(graphicsLayerFactory(), this);
 #ifndef NDEBUG
         m_layerForFooter->setName("footer");
 #endif
         m_scrollLayer->addChildBelow(m_layerForFooter.get(), m_rootContentLayer.get());
     }

     m_layerForFooter->setPosition(FloatPoint(0, m_rootContentLayer->size().height() + m_renderView.frameView().headerHeight()));
     m_layerForFooter->setAnchorPoint(FloatPoint3D());
     m_layerForFooter->setSize(FloatSize(m_renderView.frameView().visibleWidth(), m_renderView.frameView().footerHeight()));

     if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
         scrollingCoordinator->frameViewRootLayerDidChange(&m_renderView.frameView());

     if (Page* page = this->page())
         page->chrome().client().didAddFooterLayer(m_layerForFooter.get());

     return m_layerForFooter.get();
 }

 #endif

 bool RenderLayerCompositor::viewHasTransparentBackground(Color* backgroundColor) const
 {
     if (m_renderView.frameView().isTransparent()) {
         if (backgroundColor)
             *backgroundColor = Color(); // Return an invalid color.
         return true;
     }

     Color documentBackgroundColor = m_renderView.frameView().documentBackgroundColor();
     if (!documentBackgroundColor.isValid())
         documentBackgroundColor = Color::white;

     if (backgroundColor)
         *backgroundColor = documentBackgroundColor;

     return documentBackgroundColor.hasAlpha();
 }

 void RenderLayerCompositor::updateOverflowControlsLayers()
 {
 #if ENABLE(RUBBER_BANDING)
     if (requiresOverhangAreasLayer()) {
         if (!m_layerForOverhangAreas) {
             m_layerForOverhangAreas = GraphicsLayer::create(graphicsLayerFactory(), this);
 #ifndef NDEBUG
             m_layerForOverhangAreas->setName("overhang areas");
 #endif
             m_layerForOverhangAreas->setDrawsContent(false);
             m_layerForOverhangAreas->setSize(m_renderView.frameView().frameRect().size());

             ScrollbarTheme::theme()->setUpOverhangAreasLayerContents(m_layerForOverhangAreas.get(), this->page()->chrome().client().underlayColor());

             // We want the overhang areas layer to be positioned below the frame contents,
             // so insert it below the clip layer.
             m_overflowControlsHostLayer->addChildBelow(m_layerForOverhangAreas.get(), m_clipLayer.get());
         }
     } else if (m_layerForOverhangAreas) {
         m_layerForOverhangAreas->removeFromParent();
         m_layerForOverhangAreas = nullptr;
     }

     if (requiresContentShadowLayer()) {
         if (!m_contentShadowLayer) {
             m_contentShadowLayer = GraphicsLayer::create(graphicsLayerFactory(), this);
 #ifndef NDEBUG
             m_contentShadowLayer->setName("content shadow");
 #endif
             m_contentShadowLayer->setSize(m_rootContentLayer->size());
             m_contentShadowLayer->setPosition(m_rootContentLayer->position());
             ScrollbarTheme::theme()->setUpContentShadowLayer(m_contentShadowLayer.get());

             m_scrollLayer->addChildBelow(m_contentShadowLayer.get(), m_rootContentLayer.get());
         }
     } else if (m_contentShadowLayer) {
         m_contentShadowLayer->removeFromParent();
         m_contentShadowLayer = nullptr;
     }
 #endif

     if (requiresHorizontalScrollbarLayer()) {
         if (!m_layerForHorizontalScrollbar) {
             m_layerForHorizontalScrollbar = GraphicsLayer::create(graphicsLayerFactory(), this);
             m_layerForHorizontalScrollbar->setShowDebugBorder(m_showDebugBorders);
 #ifndef NDEBUG
             m_layerForHorizontalScrollbar->setName("horizontal scrollbar container");

 #endif
 #if PLATFORM(MAC) && USE(CA)
             m_layerForHorizontalScrollbar->setAcceleratesDrawing(acceleratedDrawingEnabled());
 #endif
             m_overflowControlsHostLayer->addChild(m_layerForHorizontalScrollbar.get());

             if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
                 scrollingCoordinator->scrollableAreaScrollbarLayerDidChange(&m_renderView.frameView(), HorizontalScrollbar);
         }
     } else if (m_layerForHorizontalScrollbar) {
         m_layerForHorizontalScrollbar->removeFromParent();
         m_layerForHorizontalScrollbar = nullptr;

         if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
             scrollingCoordinator->scrollableAreaScrollbarLayerDidChange(&m_renderView.frameView(), HorizontalScrollbar);
     }

     if (requiresVerticalScrollbarLayer()) {
         if (!m_layerForVerticalScrollbar) {
             m_layerForVerticalScrollbar = GraphicsLayer::create(graphicsLayerFactory(), this);
             m_layerForVerticalScrollbar->setShowDebugBorder(m_showDebugBorders);
 #ifndef NDEBUG
             m_layerForVerticalScrollbar->setName("vertical scrollbar container");
 #endif
 #if PLATFORM(MAC) && USE(CA)
             m_layerForVerticalScrollbar->setAcceleratesDrawing(acceleratedDrawingEnabled());
 #endif
             m_overflowControlsHostLayer->addChild(m_layerForVerticalScrollbar.get());

             if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
                 scrollingCoordinator->scrollableAreaScrollbarLayerDidChange(&m_renderView.frameView(), VerticalScrollbar);
         }
     } else if (m_layerForVerticalScrollbar) {
         m_layerForVerticalScrollbar->removeFromParent();
         m_layerForVerticalScrollbar = nullptr;

         if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
             scrollingCoordinator->scrollableAreaScrollbarLayerDidChange(&m_renderView.frameView(), VerticalScrollbar);
     }

     if (requiresScrollCornerLayer()) {
         if (!m_layerForScrollCorner) {
             m_layerForScrollCorner = GraphicsLayer::create(graphicsLayerFactory(), this);
             m_layerForScrollCorner->setShowDebugBorder(m_showDebugBorders);
 #ifndef NDEBUG
             m_layerForScrollCorner->setName("scroll corner");
 #endif
 #if PLATFORM(MAC) && USE(CA)
             m_layerForScrollCorner->setAcceleratesDrawing(acceleratedDrawingEnabled());
 #endif
             m_overflowControlsHostLayer->addChild(m_layerForScrollCorner.get());
         }
     } else if (m_layerForScrollCorner) {
         m_layerForScrollCorner->removeFromParent();
         m_layerForScrollCorner = nullptr;
     }

     m_renderView.frameView().positionScrollbarLayers();
 }

 void RenderLayerCompositor::ensureRootLayer()
 {
     RootLayerAttachment expectedAttachment = shouldPropagateCompositingToEnclosingFrame() ? RootLayerAttachedViaEnclosingFrame : RootLayerAttachedViaChromeClient;
     if (expectedAttachment == m_rootLayerAttachment)
          return;

     if (!m_rootContentLayer) {
         m_rootContentLayer = GraphicsLayer::create(graphicsLayerFactory(), this);
 #ifndef NDEBUG
         m_rootContentLayer->setName("content root");
 #endif
         IntRect overflowRect = m_renderView.pixelSnappedLayoutOverflowRect();
         m_rootContentLayer->setSize(FloatSize(overflowRect.maxX(), overflowRect.maxY()));
         m_rootContentLayer->setPosition(FloatPoint());

         // Need to clip to prevent transformed content showing outside this frame
         m_rootContentLayer->setMasksToBounds(true);
     }

     if (requiresScrollLayer(expectedAttachment)) {
         if (!m_overflowControlsHostLayer) {
             ASSERT(!m_scrollLayer);
             ASSERT(!m_clipLayer);

             // Create a layer to host the clipping layer and the overflow controls layers.
             m_overflowControlsHostLayer = GraphicsLayer::create(graphicsLayerFactory(), this);
 #ifndef NDEBUG
             m_overflowControlsHostLayer->setName("overflow controls host");
 #endif

             // Create a clipping layer if this is an iframe
             m_clipLayer = GraphicsLayer::create(graphicsLayerFactory(), this);
 #ifndef NDEBUG
             m_clipLayer->setName("frame clipping");
 #endif
             m_clipLayer->setMasksToBounds(true);

             m_scrollLayer = GraphicsLayer::create(graphicsLayerFactory(), this);
 #ifndef NDEBUG
             m_scrollLayer->setName("frame scrolling");
 #endif
             if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
                 scrollingCoordinator->setLayerIsContainerForFixedPositionLayers(m_scrollLayer.get(), true);

             // Hook them up
             m_overflowControlsHostLayer->addChild(m_clipLayer.get());
             m_clipLayer->addChild(m_scrollLayer.get());
             m_scrollLayer->addChild(m_rootContentLayer.get());

             frameViewDidChangeSize();
             frameViewDidScroll();
         }
     } else {
         if (m_overflowControlsHostLayer) {
             m_overflowControlsHostLayer = nullptr;
             m_clipLayer = nullptr;
             m_scrollLayer = nullptr;
         }
     }

     // Check to see if we have to change the attachment
     if (m_rootLayerAttachment != RootLayerUnattached)
         detachRootLayer();

     attachRootLayer(expectedAttachment);
 }

 void RenderLayerCompositor::destroyRootLayer()
 {
     if (!m_rootContentLayer)
         return;

     detachRootLayer();

 #if ENABLE(RUBBER_BANDING)
     if (m_layerForOverhangAreas) {
         m_layerForOverhangAreas->removeFromParent();
         m_layerForOverhangAreas = nullptr;
     }
 #endif

     if (m_layerForHorizontalScrollbar) {
         m_layerForHorizontalScrollbar->removeFromParent();
         m_layerForHorizontalScrollbar = nullptr;
         if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
             scrollingCoordinator->scrollableAreaScrollbarLayerDidChange(&m_renderView.frameView(), HorizontalScrollbar);
         if (Scrollbar* horizontalScrollbar = m_renderView.frameView().verticalScrollbar())
             m_renderView.frameView().invalidateScrollbar(horizontalScrollbar, IntRect(IntPoint(0, 0), horizontalScrollbar->frameRect().size()));
     }

     if (m_layerForVerticalScrollbar) {
         m_layerForVerticalScrollbar->removeFromParent();
         m_layerForVerticalScrollbar = nullptr;
         if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
             scrollingCoordinator->scrollableAreaScrollbarLayerDidChange(&m_renderView.frameView(), VerticalScrollbar);
         if (Scrollbar* verticalScrollbar = m_renderView.frameView().verticalScrollbar())
             m_renderView.frameView().invalidateScrollbar(verticalScrollbar, IntRect(IntPoint(0, 0), verticalScrollbar->frameRect().size()));
     }

     if (m_layerForScrollCorner) {
         m_layerForScrollCorner = nullptr;
         m_renderView.frameView().invalidateScrollCorner(m_renderView.frameView().scrollCornerRect());
     }

     if (m_overflowControlsHostLayer) {
         m_overflowControlsHostLayer = nullptr;
         m_clipLayer = nullptr;
         m_scrollLayer = nullptr;
     }
     ASSERT(!m_scrollLayer);
     m_rootContentLayer = nullptr;

     m_layerUpdater = nullptr;
 }

 void RenderLayerCompositor::attachRootLayer(RootLayerAttachment attachment)
 {
     if (!m_rootContentLayer)
         return;

     switch (attachment) {
         case RootLayerUnattached:
             ASSERT_NOT_REACHED();
             break;
         case RootLayerAttachedViaChromeClient: {
             Frame& frame = m_renderView.frameView().frame();
             Page* page = frame.page();
             if (!page)
                 return;

             page->chrome().client().attachRootGraphicsLayer(&frame, rootGraphicsLayer());
             break;
         }
         case RootLayerAttachedViaEnclosingFrame: {
             // The layer will get hooked up via RenderLayerBacking::updateGraphicsLayerConfiguration()
             // for the frame's renderer in the parent document.
             m_renderView.document().ownerElement()->scheduleSetNeedsStyleRecalc(SyntheticStyleChange);
             break;
         }
     }

     m_rootLayerAttachment = attachment;
     rootLayerAttachmentChanged();

     if (m_shouldFlushOnReattach) {
         scheduleLayerFlushNow();
         m_shouldFlushOnReattach = false;
     }
 }

 void RenderLayerCompositor::detachRootLayer()
 {
     if (!m_rootContentLayer || m_rootLayerAttachment == RootLayerUnattached)
         return;

     switch (m_rootLayerAttachment) {
     case RootLayerAttachedViaEnclosingFrame: {
         // The layer will get unhooked up via RenderLayerBacking::updateGraphicsLayerConfiguration()
         // for the frame's renderer in the parent document.
         if (m_overflowControlsHostLayer)
             m_overflowControlsHostLayer->removeFromParent();
         else
             m_rootContentLayer->removeFromParent();

         if (HTMLFrameOwnerElement* ownerElement = m_renderView.document().ownerElement())
             ownerElement->scheduleSetNeedsStyleRecalc(SyntheticStyleChange);
         break;
     }
     case RootLayerAttachedViaChromeClient: {
         Frame& frame = m_renderView.frameView().frame();
         Page* page = frame.page();
         if (!page)
             return;

         page->chrome().client().attachRootGraphicsLayer(&frame, 0);
     }
     break;
     case RootLayerUnattached:
         break;
     }

     m_rootLayerAttachment = RootLayerUnattached;
     rootLayerAttachmentChanged();
 }

 void RenderLayerCompositor::updateRootLayerAttachment()
 {
     ensureRootLayer();
 }

 void RenderLayerCompositor::rootLayerAttachmentChanged()
 {
     // The attachment can affect whether the RenderView layer's paintsIntoWindow() behavior,
     // so call updateGraphicsLayerGeometry() to udpate that.
     RenderLayer* layer = m_renderView.layer();
     if (RenderLayerBacking* backing = layer ? layer->backing() : 0)
         backing->updateDrawsContent();
 }

 // IFrames are special, because we hook compositing layers together across iframe boundaries
 // when both parent and iframe content are composited. So when this frame becomes composited, we have
 // to use a synthetic style change to get the iframes into RenderLayers in order to allow them to composite.
 void RenderLayerCompositor::notifyIFramesOfCompositingChange()
 {
     Frame& frame = m_renderView.frameView().frame();

     for (Frame* child = frame.tree().firstChild(); child; child = child->tree().traverseNext(&frame)) {
         if (child->document() && child->document()->ownerElement())
             child->document()->ownerElement()->scheduleSetNeedsStyleRecalc(SyntheticStyleChange);
     }

     // Compositing also affects the answer to RenderIFrame::requiresAcceleratedCompositing(), so
     // we need to schedule a style recalc in our parent document.
     if (HTMLFrameOwnerElement* ownerElement = m_renderView.document().ownerElement())
         ownerElement->scheduleSetNeedsStyleRecalc(SyntheticStyleChange);
 }

 bool RenderLayerCompositor::layerHas3DContent(const RenderLayer& layer) const
 {
     const RenderStyle& style = layer.renderer().style();

     if (style.transformStyle3D() == TransformStyle3DPreserve3D || style.hasPerspective() || style.transform().has3DOperation())
         return true;

     const_cast<RenderLayer&>(layer).updateLayerListsIfNeeded();

 #if !ASSERT_DISABLED
     LayerListMutationDetector mutationChecker(const_cast<RenderLayer*>(&layer));
 #endif

     if (layer.isStackingContainer()) {
         if (Vector<RenderLayer*>* negZOrderList = layer.negZOrderList()) {
             for (size_t i = 0, size = negZOrderList->size(); i < size; ++i) {
                 if (layerHas3DContent(*negZOrderList->at(i)))
                     return true;
             }
         }

         if (Vector<RenderLayer*>* posZOrderList = layer.posZOrderList()) {
             for (size_t i = 0, size = posZOrderList->size(); i < size; ++i) {
                 if (layerHas3DContent(*posZOrderList->at(i)))
                     return true;
             }
         }
     }

     if (Vector<RenderLayer*>* normalFlowList = layer.normalFlowList()) {
         for (size_t i = 0, size = normalFlowList->size(); i < size; ++i) {
             if (layerHas3DContent(*normalFlowList->at(i)))
                 return true;
         }
     }

     return false;
 }

 void RenderLayerCompositor::deviceOrPageScaleFactorChanged()
 {
     // Start at the RenderView's layer, since that's where the scale is applied.
     RenderLayer* viewLayer = m_renderView.layer();
     if (!viewLayer->isComposited())
         return;

     if (GraphicsLayer* rootLayer = viewLayer->backing()->childForSuperlayers())
         rootLayer->noteDeviceOrPageScaleFactorChangedIncludingDescendants();
 }

 void RenderLayerCompositor::updateViewportConstraintStatus(RenderLayer& layer)
 {
     if (isViewportConstrainedFixedOrStickyLayer(layer))
         addViewportConstrainedLayer(layer);
     else
         removeViewportConstrainedLayer(layer);
 }

 void RenderLayerCompositor::addViewportConstrainedLayer(RenderLayer& layer)
 {
     m_viewportConstrainedLayers.add(&layer);
     registerOrUpdateViewportConstrainedLayer(layer);
 }

 void RenderLayerCompositor::removeViewportConstrainedLayer(RenderLayer& layer)
 {
     if (!m_viewportConstrainedLayers.contains(&layer))
         return;

     unregisterViewportConstrainedLayer(layer);
     m_viewportConstrainedLayers.remove(&layer);
     m_viewportConstrainedLayersNeedingUpdate.remove(&layer);
 }

 FixedPositionViewportConstraints RenderLayerCompositor::computeFixedViewportConstraints(RenderLayer& layer) const
 {
     ASSERT(layer.isComposited());

     LayoutRect viewportRect = m_renderView.frameView().viewportConstrainedVisibleContentRect();

     FixedPositionViewportConstraints constraints;

     GraphicsLayer* graphicsLayer = layer.backing()->graphicsLayer();

     constraints.setLayerPositionAtLastLayout(graphicsLayer->position());
     constraints.setViewportRectAtLastLayout(viewportRect);

     const RenderStyle& style = layer.renderer().style();
     if (!style.left().isAuto())
         constraints.addAnchorEdge(ViewportConstraints::AnchorEdgeLeft);

     if (!style.right().isAuto())
         constraints.addAnchorEdge(ViewportConstraints::AnchorEdgeRight);

     if (!style.top().isAuto())
         constraints.addAnchorEdge(ViewportConstraints::AnchorEdgeTop);

     if (!style.bottom().isAuto())
         constraints.addAnchorEdge(ViewportConstraints::AnchorEdgeBottom);

     // If left and right are auto, use left.
     if (style.left().isAuto() && style.right().isAuto())
         constraints.addAnchorEdge(ViewportConstraints::AnchorEdgeLeft);

     // If top and bottom are auto, use top.
     if (style.top().isAuto() && style.bottom().isAuto())
         constraints.addAnchorEdge(ViewportConstraints::AnchorEdgeTop);

     return constraints;
 }

 StickyPositionViewportConstraints RenderLayerCompositor::computeStickyViewportConstraints(RenderLayer& layer) const
 {
     ASSERT(layer.isComposited());
     // We should never get here for stickies constrained by an enclosing clipping layer.
     ASSERT(!layer.enclosingOverflowClipLayer(ExcludeSelf));

     LayoutRect viewportRect = m_renderView.frameView().viewportConstrainedVisibleContentRect();

     RenderBoxModelObject& renderer = toRenderBoxModelObject(layer.renderer());

     StickyPositionViewportConstraints constraints;
     renderer.computeStickyPositionConstraints(constraints, viewportRect);

     GraphicsLayer* graphicsLayer = layer.backing()->graphicsLayer();

     constraints.setLayerPositionAtLastLayout(graphicsLayer->position());
     constraints.setStickyOffsetAtLastLayout(renderer.stickyPositionOffset());

     return constraints;
 }

 static RenderLayerBacking* nearestScrollingCoordinatorAncestor(RenderLayer& layer)
 {
     RenderLayer* ancestor = layer.parent();
     while (ancestor) {
         if (RenderLayerBacking* backing = ancestor->backing()) {
             if (backing->scrollLayerID() && !ancestor->scrollsOverflow())
                 return backing;
         }
         ancestor = ancestor->parent();
     }

     return nullptr;
 }

 void RenderLayerCompositor::registerOrUpdateViewportConstrainedLayer(RenderLayer& layer)
 {
     // FIXME: We should support sticky position here! And we should eventuall support fixed/sticky elements
     // that are inside non-main frames once we get non-main frames scrolling with the ScrollingCoordinator.
     if (m_renderView.document().ownerElement())
         return;

     ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator();
     if (!scrollingCoordinator)
         return;

     // FIXME: rename to supportsViewportConstrainedPositionLayers()?
     if (!scrollingCoordinator->supportsFixedPositionLayers() || !layer.parent())
         return;

     ASSERT(m_viewportConstrainedLayers.contains(&layer));
     ASSERT(layer.isComposited());

     RenderLayerBacking* backing = layer.backing();
     if (!backing)
         return;

     ScrollingNodeID nodeID = backing->scrollLayerID();
     RenderLayerBacking* parent = nearestScrollingCoordinatorAncestor(layer);
     if (!parent)
         return;

     // Always call this even if the backing is already attached because the parent may have changed.
     backing->attachToScrollingCoordinatorWithParent(parent);
     nodeID = backing->scrollLayerID();

     if (layer.renderer().isStickyPositioned())
         scrollingCoordinator->updateViewportConstrainedNode(nodeID, computeStickyViewportConstraints(layer), backing->graphicsLayer());
     else
         scrollingCoordinator->updateViewportConstrainedNode(nodeID, computeFixedViewportConstraints(layer), backing->graphicsLayer());
 }

 void RenderLayerCompositor::unregisterViewportConstrainedLayer(RenderLayer& layer)
 {
     ASSERT(m_viewportConstrainedLayers.contains(&layer));

     if (RenderLayerBacking* backing = layer.backing())
         backing->detachFromScrollingCoordinator();
 }

 void RenderLayerCompositor::windowScreenDidChange(PlatformDisplayID displayID)
 {
     if (m_layerUpdater)
         m_layerUpdater->screenDidChange(displayID);
 }

 ScrollingCoordinator* RenderLayerCompositor::scrollingCoordinator() const
 {
     if (Page* page = this->page())
         return page->scrollingCoordinator();

     return 0;
 }

 GraphicsLayerFactory* RenderLayerCompositor::graphicsLayerFactory() const
 {
     if (Page* page = this->page())
         return page->chrome().client().graphicsLayerFactory();

     return 0;
 }

 Page* RenderLayerCompositor::page() const
 {
     return m_renderView.frameView().frame().page();
 }

 void RenderLayerCompositor::setLayerFlushThrottlingEnabled(bool enabled)
 {
     m_layerFlushThrottlingEnabled = enabled;
     if (m_layerFlushThrottlingEnabled)
         return;
     m_layerFlushTimer.stop();
     if (!m_hasPendingLayerFlush)
         return;
     scheduleLayerFlushNow();
 }

 void RenderLayerCompositor::disableLayerFlushThrottlingTemporarilyForInteraction()
 {
     if (m_layerFlushThrottlingTemporarilyDisabledForInteraction)
         return;
     m_layerFlushThrottlingTemporarilyDisabledForInteraction = true;
 }

 bool RenderLayerCompositor::isThrottlingLayerFlushes() const
 {
     if (!m_layerFlushThrottlingEnabled)
         return false;
     if (!m_layerFlushTimer.isActive())
         return false;
     if (m_layerFlushThrottlingTemporarilyDisabledForInteraction)
         return false;
     return true;
 }

 void RenderLayerCompositor::startLayerFlushTimerIfNeeded()
 {
     m_layerFlushThrottlingTemporarilyDisabledForInteraction = false;
     m_layerFlushTimer.stop();
     if (!m_layerFlushThrottlingEnabled)
         return;
     m_layerFlushTimer.startOneShot(throttledLayerFlushDelay);
 }

 void RenderLayerCompositor::layerFlushTimerFired(Timer<RenderLayerCompositor>*)
 {
     if (!m_hasPendingLayerFlush)
         return;
     scheduleLayerFlushNow();
 }

 void RenderLayerCompositor::paintRelatedMilestonesTimerFired(Timer<RenderLayerCompositor>*)
 {
     Frame& frame = m_renderView.frameView().frame();
     Page* page = frame.page();
     if (!page)
         return;

     // If the layer tree is frozen, we'll paint when it's unfrozen and schedule the timer again.
     if (page->chrome().client().layerTreeStateIsFrozen())
         return;

     m_renderView.frameView().firePaintRelatedMilestones();
 }

 } // namespace WebCore

 #endif // USE(ACCELERATED_COMPOSITING)