AI 145796: Land the WebKit merge @r42026.

Automated import of CL 145796

1 files changed, 803 insertions, 0 deletions

diff --git a/WebCore/rendering/RenderLayerCompositor.cpp b/WebCore/rendering/RenderLayerCompositor.cpp
new file mode 100644
index 0000000..cbb3df7
--- /dev/null
+++ b/WebCore/rendering/RenderLayerCompositor.cpp
@@ -0,0 +1,803 @@
+/*
+ * Copyright (C) 2009 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 "ChromeClient.h"
+#include "CSSPropertyNames.h"
+#include "Frame.h"
+#include "FrameView.h"
+#include "GraphicsLayer.h"
+#include "HitTestRequest.h"
+#include "HitTestResult.h"
+#include "Page.h"
+#include "RenderLayerBacking.h"
+#include "RenderView.h"
+
+#if PROFILE_LAYER_REBUILD
+#include <wtf/CurrentTime.h>
+#endif
+
+#ifndef NDEBUG
+#include "CString.h"
+#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
+
+namespace WebCore {
+
+struct CompositingState {
+    CompositingState(RenderLayer* compAncestor)
+        : m_subtreeIsCompositing(false)
+        , m_compositingAncestor(compAncestor)
+#ifndef NDEBUG
+        , m_depth(0)
+#endif
+    {
+    }
+    
+    bool m_subtreeIsCompositing;
+    RenderLayer* m_compositingAncestor;
+#ifndef NDEBUG
+    int m_depth;
+#endif
+};
+
+static TransformationMatrix flipTransform()
+{
+    TransformationMatrix flipper;
+    flipper.flipY();
+    return flipper;
+}
+
+RenderLayerCompositor::RenderLayerCompositor(RenderView* renderView)
+    : m_renderView(renderView)
+    , m_rootPlatformLayer(0)
+    , m_compositing(false)
+    , m_rootLayerAttached(false)
+    , m_compositingLayersNeedUpdate(false)
+#if PROFILE_LAYER_REBUILD
+    , m_rootLayerUpdateCount(0)
+#endif // PROFILE_LAYER_REBUILD
+{
+}
+
+RenderLayerCompositor::~RenderLayerCompositor()
+{
+    ASSERT(!m_rootLayerAttached);
+    delete m_rootPlatformLayer;
+}
+
+void RenderLayerCompositor::enableCompositingMode(bool enable /* = true */)
+{
+    if (enable != m_compositing) {
+        m_compositing = enable;
+        
+        // We never go out of compositing mode for a given page,
+        // but if all the layers disappear, we'll just be left with
+        // the empty root layer, which has minimal overhead.
+        if (m_compositing)
+            ensureRootPlatformLayer();
+    }
+}
+
+void RenderLayerCompositor::setCompositingLayersNeedUpdate(bool needUpdate)
+{
+    if (inCompositingMode())
+        m_compositingLayersNeedUpdate = needUpdate;
+}
+
+void RenderLayerCompositor::updateCompositingLayers(RenderLayer* updateRoot)
+{
+    if (!m_compositingLayersNeedUpdate)
+        return;
+
+    ASSERT(inCompositingMode());
+
+    if (!updateRoot) {
+        // Only clear the flag if we're updating the entire hierarchy
+        m_compositingLayersNeedUpdate = false;
+        updateRoot = rootRenderLayer();
+    }
+
+#if PROFILE_LAYER_REBUILD
+    ++m_rootLayerUpdateCount;
+    
+    double startTime = WTF::currentTime();
+#endif        
+
+    // Go through the layers in presentation order, so that we can compute which
+    // RLs need compositing layers.
+    // FIXME: we could maybe do this in one pass, but the parenting logic would be more
+    // complex.
+    {
+        CompositingState compState(updateRoot);
+        computeCompositingRequirements(updateRoot, compState);
+    }
+
+    // Now create and parent the compositing layers.
+    {
+        CompositingState compState(updateRoot);
+        rebuildCompositingLayerTree(updateRoot, compState);
+    }
+    
+#if PROFILE_LAYER_REBUILD
+    double endTime = WTF::currentTime();
+    if (!updateRoot)
+        fprintf(stderr, "Update %d: computeCompositingRequirements for the world took %fms\n"
+                    m_rootLayerUpdateCount, 1000.0 * (endTime - startTime));
+#endif
+    ASSERT(updateRoot || !m_compositingLayersNeedUpdate);
+}
+
+bool RenderLayerCompositor::updateLayerCompositingState(RenderLayer* layer, StyleDifference diff)
+{
+    bool needsLayer = needsToBeComposited(layer);
+    bool layerChanged = false;
+
+    RenderBoxModelObject* repaintContainer = 0;
+    IntRect repaintRect;
+
+    if (needsLayer) {
+        enableCompositingMode();
+        if (!layer->backing()) {
+            // Get the repaint container before we make backing for this layer
+            repaintContainer = layer->renderer()->containerForRepaint();
+            repaintRect = calculateCompositedBounds(layer, repaintContainer ? repaintContainer->layer() : layer->root());
+
+            layer->ensureBacking();
+            layerChanged = true;
+        }
+    } else {
+        if (layer->backing()) {
+            layer->clearBacking();
+            // Get the repaint container now that we've cleared the backing
+            repaintContainer = layer->renderer()->containerForRepaint();
+            repaintRect = calculateCompositedBounds(layer, repaintContainer ? repaintContainer->layer() : layer->root());
+            layerChanged = true;
+        }
+    }
+    
+    if (layerChanged) {
+        // Invalidate the destination into which this layer used to render.
+        layer->renderer()->repaintUsingContainer(repaintContainer, repaintRect);
+
+        if (!repaintContainer || 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();
+        }
+    }
+
+    if (!needsLayer)
+        return layerChanged;
+
+    if (layer->backing()->updateGraphicsLayers(needsContentsCompositingLayer(layer),
+                                               clippedByAncestor(layer),
+                                               clipsCompositingDescendants(layer),
+                                               diff >= StyleDifferenceRepaint))
+        layerChanged = true;
+
+    return layerChanged;
+}
+
+// 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.
+IntRect RenderLayerCompositor::calculateCompositedBounds(const RenderLayer* layer, const RenderLayer* ancestorLayer, IntRect* layerBoundingBox)
+{
+    IntRect boundingBoxRect, unionBounds;
+    boundingBoxRect = unionBounds = layer->localBoundingBox();
+    
+    ASSERT(layer->isStackingContext() || (!layer->m_posZOrderList || layer->m_posZOrderList->size() == 0));
+
+    Vector<RenderLayer*>* negZOrderList = layer->negZOrderList();
+    if (negZOrderList) {
+        for (Vector<RenderLayer*>::iterator it = negZOrderList->begin(); it != negZOrderList->end(); ++it) {
+            RenderLayer* curLayer = (*it);
+            if (!curLayer->isComposited()) {
+                IntRect childUnionBounds = calculateCompositedBounds(curLayer, layer);
+                unionBounds.unite(childUnionBounds);
+            }
+        }
+    }
+
+    Vector<RenderLayer*>* posZOrderList = layer->posZOrderList();
+    if (posZOrderList) {
+        for (Vector<RenderLayer*>::iterator it = posZOrderList->begin(); it != posZOrderList->end(); ++it) {
+            RenderLayer* curLayer = (*it);
+            if (!curLayer->isComposited()) {
+                IntRect childUnionBounds = calculateCompositedBounds(curLayer, layer);
+                unionBounds.unite(childUnionBounds);
+            }
+        }
+    }
+
+    Vector<RenderLayer*>* normalFlowList = layer->normalFlowList();
+    if (normalFlowList) {
+        for (Vector<RenderLayer*>::iterator it = normalFlowList->begin(); it != normalFlowList->end(); ++it) {
+            RenderLayer* curLayer = (*it);
+            if (!curLayer->isComposited()) {
+                IntRect curAbsBounds = calculateCompositedBounds(curLayer, layer);
+                unionBounds.unite(curAbsBounds);
+            }
+        }
+    }
+
+    if (!layer->isComposited() && layer->transform()) {
+        TransformationMatrix* affineTrans = layer->transform();
+        boundingBoxRect = affineTrans->mapRect(boundingBoxRect);
+        unionBounds = affineTrans->mapRect(unionBounds);
+    }
+
+    int ancestorRelX = 0, ancestorRelY = 0;
+    layer->convertToLayerCoords(ancestorLayer, ancestorRelX, ancestorRelY);
+    unionBounds.move(ancestorRelX, ancestorRelY);
+
+    if (layerBoundingBox) {
+        boundingBoxRect.move(ancestorRelX, ancestorRelY);
+        *layerBoundingBox = boundingBoxRect;
+    }
+    
+    return unionBounds;
+}
+
+void RenderLayerCompositor::layerWasAdded(RenderLayer* /*parent*/, RenderLayer* /*child*/)
+{
+    setCompositingLayersNeedUpdate();
+}
+
+void RenderLayerCompositor::layerWillBeRemoved(RenderLayer* parent, RenderLayer* child)
+{
+    if (child->isComposited())
+        setCompositingParent(child, 0);
+    
+    // If the document is being torn down (document's renderer() is null), then there's
+    // no need to do any layer updating.
+    if (parent->renderer()->documentBeingDestroyed())
+        return;
+
+    RenderLayer* compLayer = parent->enclosingCompositingLayer();
+    if (compLayer) {
+        IntRect ancestorRect = calculateCompositedBounds(child, compLayer);
+        compLayer->setBackingNeedsRepaintInRect(ancestorRect);
+        // 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.
+        m_renderView->frameView()->setNeedsOneShotDrawingSynchronization();
+    }
+
+    setCompositingLayersNeedUpdate();
+}
+
+RenderLayer* RenderLayerCompositor::enclosingNonStackingClippingLayer(const RenderLayer* layer) const
+{
+    for (RenderLayer* curr = layer->parent(); curr != 0; curr = curr->parent()) {
+        if (curr->isStackingContext())
+            return 0;
+
+        if (curr->renderer()->hasOverflowClip())
+            return curr;
+    }
+    return 0;
+}
+
+//  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* layer, struct CompositingState& ioCompState)
+{
+    layer->updateLayerPosition();
+    layer->updateZOrderLists();
+    layer->updateNormalFlowList();
+    
+    // Clear the flag
+    layer->setHasCompositingDescendant(false);
+    layer->setMustOverlayCompositedLayers(ioCompState.m_subtreeIsCompositing);
+    
+    const bool isCompositingLayer = needsToBeComposited(layer);
+    ioCompState.m_subtreeIsCompositing = isCompositingLayer;
+
+    CompositingState childState = ioCompState;
+    if (isCompositingLayer)
+        childState.m_compositingAncestor = layer;
+
+    // The children of this stacking context don't need to composite, unless there is
+    // a compositing layer among them, so start by assuming false.
+    childState.m_subtreeIsCompositing = false;
+
+#ifndef NDEBUG
+    ++childState.m_depth;
+#endif
+
+    if (layer->isStackingContext()) {
+        ASSERT(!layer->m_zOrderListsDirty);
+        Vector<RenderLayer*>* negZOrderList = layer->negZOrderList();
+        if (negZOrderList && negZOrderList->size() > 0) {
+            for (Vector<RenderLayer*>::const_iterator it = negZOrderList->begin(); it != negZOrderList->end(); ++it) {
+                RenderLayer* curLayer = (*it);
+                computeCompositingRequirements(curLayer, childState);
+
+                // 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 (childState.m_subtreeIsCompositing) {
+                    // make |this| compositing
+                    layer->setMustOverlayCompositedLayers(true);
+                    childState.m_compositingAncestor = layer;
+                }
+            }
+        }
+    }
+    
+    ASSERT(!layer->m_normalFlowListDirty);
+    Vector<RenderLayer*>* normalFlowList = layer->normalFlowList();
+    if (normalFlowList && normalFlowList->size() > 0) {
+        for (Vector<RenderLayer*>::const_iterator it = normalFlowList->begin(); it != normalFlowList->end(); ++it) {
+            RenderLayer* curLayer = (*it);
+            computeCompositingRequirements(curLayer, childState);
+        }
+    }
+
+    if (layer->isStackingContext()) {
+        Vector<RenderLayer*>* posZOrderList = layer->posZOrderList();
+        if (posZOrderList && posZOrderList->size() > 0) {
+            for (Vector<RenderLayer*>::const_iterator it = posZOrderList->begin(); it != posZOrderList->end(); ++it) {
+                RenderLayer* curLayer = (*it);
+                computeCompositingRequirements(curLayer, childState);
+            }
+        }
+    }
+
+    // If we have a software transform, and we have layers under us, we need to also
+    // be composited. Also, if we have opacity < 1, then we need to be a layer so that
+    // the child layers are opaque, then rendered with opacity on this layer.
+    if (childState.m_subtreeIsCompositing &&
+        (layer->renderer()->hasTransform() || layer->renderer()->style()->opacity() < 1))
+        layer->setMustOverlayCompositedLayers(true);
+
+    // Subsequent layers in the parent stacking context also need to composite.
+    if (childState.m_subtreeIsCompositing)
+        ioCompState.m_subtreeIsCompositing = true;
+
+    // Set the flag to say that this SC has compositing children.
+    // this can affect the answer to needsToBeComposited() when clipping,
+    // but that's ok here.
+    layer->setHasCompositingDescendant(childState.m_subtreeIsCompositing);
+}
+
+void RenderLayerCompositor::setCompositingParent(RenderLayer* childLayer, RenderLayer* parentLayer)
+{
+    ASSERT(childLayer->isComposited());
+    ASSERT(!parentLayer || parentLayer->isComposited());
+    
+    if (parentLayer) {
+        GraphicsLayer* hostingLayer = parentLayer->backing()->parentForSublayers();
+        GraphicsLayer* hostedLayer = childLayer->backing()->childForSuperlayers();
+        
+        hostingLayer->addChild(hostedLayer);
+    } else
+        childLayer->backing()->childForSuperlayers()->removeFromParent();
+    
+    // FIXME: setCompositingParent() is only called at present by rebuildCompositingLayerTree(),
+    // which calls updateGraphicsLayerGeometry via updateLayerCompositingState(), so this should
+    // be optimized.
+    if (parentLayer)
+        childLayer->backing()->updateGraphicsLayerGeometry();
+}
+
+void RenderLayerCompositor::removeCompositedChildren(RenderLayer* layer)
+{
+    ASSERT(layer->isComposited());
+
+    GraphicsLayer* hostingLayer = layer->backing()->parentForSublayers();
+    hostingLayer->removeAllChildren();
+}
+
+void RenderLayerCompositor::parentInRootLayer(RenderLayer* layer)
+{
+    ASSERT(layer->isComposited());
+
+    GraphicsLayer* layerAnchor = layer->backing()->childForSuperlayers();
+
+    if (layerAnchor->parent() != m_rootPlatformLayer) {
+        layerAnchor->removeFromParent();
+        if (m_rootPlatformLayer)
+            m_rootPlatformLayer->addChild(layerAnchor);
+    }
+}
+
+void RenderLayerCompositor::rebuildCompositingLayerTree(RenderLayer* layer, struct CompositingState& ioCompState)
+{
+    updateLayerCompositingState(layer, StyleDifferenceEqual);
+
+    // host the document layer in the RenderView's root layer
+    if (layer->isRootLayer())
+        parentInRootLayer(layer);
+
+    CompositingState childState = ioCompState;
+    if (layer->isComposited())
+        childState.m_compositingAncestor = layer;
+
+#ifndef NDEBUG
+    ++childState.m_depth;
+#endif
+
+    RenderLayerBacking* layerBacking = layer->backing();
+    
+    // FIXME: make this more incremental
+    if (layer->isComposited()) {
+        layerBacking->parentForSublayers()->removeAllChildren();
+        layerBacking->updateInternalHierarchy();
+    }
+    
+    // The children of this stacking context don't need to composite, unless there is
+    // a compositing layer among them, so start by assuming false.
+    childState.m_subtreeIsCompositing = false;
+
+    if (layer->isStackingContext()) {
+        ASSERT(!layer->m_zOrderListsDirty);
+
+        Vector<RenderLayer*>* negZOrderList = layer->negZOrderList();
+        if (negZOrderList && negZOrderList->size() > 0) {
+            for (Vector<RenderLayer*>::const_iterator it = negZOrderList->begin(); it != negZOrderList->end(); ++it) {
+                RenderLayer* curLayer = (*it);
+                rebuildCompositingLayerTree(curLayer, childState);
+                if (curLayer->isComposited())
+                    setCompositingParent(curLayer, childState.m_compositingAncestor);
+            }
+        }
+
+        if (layerBacking && layerBacking->contentsLayer()) {
+            // we only have a contents layer if we have an m_layer
+            layerBacking->contentsLayer()->removeFromParent();
+
+            GraphicsLayer* hostingLayer = layerBacking->clippingLayer() ? layerBacking->clippingLayer() : layerBacking->graphicsLayer();
+            hostingLayer->addChild(layerBacking->contentsLayer());
+        }
+    }
+
+    ASSERT(!layer->m_normalFlowListDirty);
+    Vector<RenderLayer*>* normalFlowList = layer->normalFlowList();
+    if (normalFlowList && normalFlowList->size() > 0) {
+        for (Vector<RenderLayer*>::iterator it = normalFlowList->begin(); it != normalFlowList->end(); ++it) {
+            RenderLayer* curLayer = (*it);
+            rebuildCompositingLayerTree(curLayer, childState);
+            if (curLayer->isComposited())
+                setCompositingParent(curLayer, childState.m_compositingAncestor);
+        }
+    }
+    
+    if (layer->isStackingContext()) {
+        Vector<RenderLayer*>* posZOrderList = layer->posZOrderList();
+        if (posZOrderList && posZOrderList->size() > 0) {
+            for (Vector<RenderLayer*>::const_iterator it = posZOrderList->begin(); it != posZOrderList->end(); ++it) {
+                RenderLayer* curLayer = (*it);
+                rebuildCompositingLayerTree(curLayer, childState);
+                if (curLayer->isComposited())
+                    setCompositingParent(curLayer, childState.m_compositingAncestor);
+            }
+        }
+    }
+}
+
+void RenderLayerCompositor::repaintCompositedLayersAbsoluteRect(const IntRect& absRect)
+{
+    recursiveRepaintLayerRect(rootRenderLayer(), absRect);
+}
+
+void RenderLayerCompositor::recursiveRepaintLayerRect(RenderLayer* layer, const IntRect& rect)
+{
+    if (layer->isComposited())
+        layer->setBackingNeedsRepaintInRect(rect);
+
+    if (layer->hasCompositingDescendant()) {
+        Vector<RenderLayer*>* negZOrderList = layer->negZOrderList();
+        if (negZOrderList) {
+            for (Vector<RenderLayer*>::iterator it = negZOrderList->begin(); it != negZOrderList->end(); ++it) {
+                RenderLayer* curLayer = (*it);
+                int x = 0, y = 0;
+                curLayer->convertToLayerCoords(layer, x, y);
+                IntRect childRect(rect);
+                childRect.move(-x, -y);
+                recursiveRepaintLayerRect(curLayer, childRect);
+            }
+        }
+
+        Vector<RenderLayer*>* posZOrderList = layer->posZOrderList();
+        if (posZOrderList) {
+            for (Vector<RenderLayer*>::iterator it = posZOrderList->begin(); it != posZOrderList->end(); ++it) {
+                RenderLayer* curLayer = (*it);
+                int x = 0, y = 0;
+                curLayer->convertToLayerCoords(layer, x, y);
+                IntRect childRect(rect);
+                childRect.move(-x, -y);
+                recursiveRepaintLayerRect(curLayer, childRect);
+            }
+        }
+        
+        Vector<RenderLayer*>* normalFlowList = layer->normalFlowList();
+        if (normalFlowList) {
+            for (Vector<RenderLayer*>::iterator it = normalFlowList->begin(); it != normalFlowList->end(); ++it) {
+                RenderLayer* curLayer = (*it);
+                int x = 0, y = 0;
+                curLayer->convertToLayerCoords(layer, x, y);
+                IntRect childRect(rect);
+                childRect.move(-x, -y);
+                recursiveRepaintLayerRect(curLayer, childRect);
+            }
+        }
+    }
+}
+
+RenderLayer* RenderLayerCompositor::rootRenderLayer() const
+{
+    return m_renderView->layer();
+}
+
+GraphicsLayer* RenderLayerCompositor::rootPlatformLayer() const
+{
+    return m_rootPlatformLayer;
+}
+
+void RenderLayerCompositor::didMoveOnscreen()
+{
+    if (!m_rootPlatformLayer)
+        return;
+
+    Frame* frame = m_renderView->frameView()->frame();
+    Page* page = frame ? frame->page() : 0;
+    if (!page)
+        return;
+
+    page->chrome()->client()->attachRootGraphicsLayer(frame, m_rootPlatformLayer);
+    m_rootLayerAttached = true;
+}
+
+void RenderLayerCompositor::willMoveOffscreen()
+{
+    if (!m_rootPlatformLayer || !m_rootLayerAttached)
+        return;
+
+    Frame* frame = m_renderView->frameView()->frame();
+    Page* page = frame ? frame->page() : 0;
+    if (!page)
+        return;
+
+    page->chrome()->client()->attachRootGraphicsLayer(frame, 0);
+    m_rootLayerAttached = false;
+}
+
+void RenderLayerCompositor::updateRootLayerPosition()
+{
+    if (m_rootPlatformLayer)
+        m_rootPlatformLayer->setSize(FloatSize(m_renderView->docWidth(), m_renderView->docHeight()));
+}
+
+bool RenderLayerCompositor::has3DContent() const
+{
+    return layerHas3DContent(rootRenderLayer());
+}
+
+bool RenderLayerCompositor::needsToBeComposited(const RenderLayer* layer) const
+{
+    return requiresCompositingLayer(layer) || layer->mustOverlayCompositedLayers();
+}
+
+#define VERBOSE_COMPOSITINGLAYER    0
+
+// 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) const
+{
+    // FIXME: cache the result of these tests?
+#if VERBOSE_COMPOSITINGLAYER
+    bool gotReason = false;
+
+    if (!gotReason && inCompositingMode() && layer->isRootLayer()) {
+        fprintf(stderr, "RenderLayer %p requires compositing layer because: it's the document root\n", layer);
+        gotReason = true;
+    }
+    
+    if (!gotReason && requiresCompositingForTransform(layer->renderer())) {
+        fprintf(stderr, "RenderLayer %p requires compositing layer because: it has 3d transform, perspective, backface, or animating transform\n", layer);
+        gotReason = true;
+    }
+
+    if (!gotReason && layer->renderer()->style()->backfaceVisibility() == BackfaceVisibilityHidden) {
+        fprintf(stderr, "RenderLayer %p requires compositing layer because: it has backface-visibility: hidden\n", layer);
+        gotReason = true;
+    }
+
+    if (!gotReason && clipsCompositingDescendants(layer)) {
+        fprintf(stderr, "RenderLayer %p requires compositing layer because: it has overflow clip\n", layer);
+        gotReason = true;
+    }
+
+    if (!gotReason && requiresCompositingForAnimation(layer->renderer())) {
+        fprintf(stderr, "RenderLayer %p requires compositing layer because: it has a running transition for opacity or transform\n", layer);
+        gotReason = true;
+    }
+    
+    if (!gotReason)
+        fprintf(stderr, "RenderLayer %p does not require compositing layer\n", layer);
+#endif
+
+    // The root layer always has a compositing layer, but it may not have backing.
+    return (inCompositingMode() && layer->isRootLayer()) ||
+             requiresCompositingForTransform(layer->renderer()) ||
+             layer->renderer()->style()->backfaceVisibility() == BackfaceVisibilityHidden ||
+             clipsCompositingDescendants(layer) ||
+             requiresCompositingForAnimation(layer->renderer());
+}
+
+// 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 = 0;
+    RenderLayer* curr = layer;
+    while (curr) {
+        RenderLayer* next = curr->parent();
+        if (next == compositingAncestor) {
+            computeClipRoot = curr;
+            break;
+        }
+        curr = next;
+    }
+    
+    if (!computeClipRoot || computeClipRoot == layer)
+        return false;
+
+    ClipRects parentRects;
+    layer->parentClipRects(computeClipRoot, parentRects, true);
+
+    return parentRects.overflowClipRect() != ClipRects::infiniteRect();
+}
+
+// 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
+{
+    // FIXME: need to look at hasClip() too eventually
+    return layer->hasCompositingDescendant() &&
+           layer->renderer()->hasOverflowClip();
+}
+
+bool RenderLayerCompositor::requiresCompositingForTransform(RenderObject* renderer)
+{
+    RenderStyle* style = renderer->style();
+    // 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() && (style->transform().has3DOperation() || style->transformStyle3D() == TransformStyle3DPreserve3D || style->hasPerspective());
+}
+
+bool RenderLayerCompositor::requiresCompositingForAnimation(RenderObject* renderer)
+{
+    AnimationController* animController = renderer->animation();
+    if (animController)
+        return animController->isAnimatingPropertyOnRenderer(renderer, CSSPropertyOpacity) ||
+               animController->isAnimatingPropertyOnRenderer(renderer, CSSPropertyWebkitTransform);
+    return false;
+}
+
+// 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->m_negZOrderList && layer->m_negZOrderList->size() > 0);
+}
+
+void RenderLayerCompositor::ensureRootPlatformLayer()
+{
+    if (m_rootPlatformLayer)
+        return;
+
+    m_rootPlatformLayer = GraphicsLayer::createGraphicsLayer(0);
+    m_rootPlatformLayer->setSize(FloatSize(m_renderView->docWidth(), m_renderView->docHeight()));
+    m_rootPlatformLayer->setPosition(FloatPoint(0, 0));
+
+    if (GraphicsLayer::graphicsContextsFlipped())
+        m_rootPlatformLayer->setChildrenTransform(flipTransform());
+
+    // Need to clip to prevent transformed content showing outside this frame
+    m_rootPlatformLayer->setMasksToBounds(true);
+    
+    didMoveOnscreen();
+}
+
+bool RenderLayerCompositor::layerHas3DContent(const RenderLayer* layer) const
+{
+    const RenderStyle* style = layer->renderer()->style();
+
+    if (style && 
+        (style->transformStyle3D() == TransformStyle3DPreserve3D ||
+         style->hasPerspective() ||
+         style->transform().has3DOperation()))
+        return true;
+
+    if (layer->isStackingContext()) {
+        Vector<RenderLayer*>* negZOrderList = layer->negZOrderList();
+        if (negZOrderList) {
+            for (Vector<RenderLayer*>::iterator it = negZOrderList->begin(); it != negZOrderList->end(); ++it) {
+                RenderLayer* curLayer = (*it);
+                if (layerHas3DContent(curLayer))
+                    return true;
+            }
+        }
+
+        Vector<RenderLayer*>* posZOrderList = layer->posZOrderList();
+        if (posZOrderList) {
+            for (Vector<RenderLayer*>::iterator it = posZOrderList->begin(); it != posZOrderList->end(); ++it) {
+                RenderLayer* curLayer = (*it);
+                if (layerHas3DContent(curLayer))
+                    return true;
+            }
+        }
+    }
+
+    Vector<RenderLayer*>* normalFlowList = layer->normalFlowList();
+    if (normalFlowList) {
+        for (Vector<RenderLayer*>::iterator it = normalFlowList->begin(); it != normalFlowList->end(); ++it) {
+            RenderLayer* curLayer = (*it);
+            if (layerHas3DContent(curLayer))
+                return true;
+        }
+    }
+    return false;
+}
+
+} // namespace WebCore
+
+#endif // USE(ACCELERATED_COMPOSITING)
+