path: root/Source/WebCore/platform/graphics/chromium/cc/CCOcclusionTracker.cpp

/*
 * Copyright (C) 2012 Google 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 AND ITS CONTRIBUTORS "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 OR ITS 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 "cc/CCOcclusionTracker.h"

#include "LayerChromium.h"
#include "cc/CCLayerImpl.h"
#include "cc/CCMathUtil.h"

#include <algorithm>

using namespace std;

namespace WebCore {

template<typename LayerType, typename RenderSurfaceType>
CCOcclusionTrackerBase<LayerType, RenderSurfaceType>::CCOcclusionTrackerBase(IntRect scissorRectInScreenSpace, bool recordMetricsForFrame)
    : m_scissorRectInScreenSpace(scissorRectInScreenSpace)
    , m_overdrawMetrics(CCOverdrawMetrics::create(recordMetricsForFrame))
{
}

template<typename LayerType, typename RenderSurfaceType>
void CCOcclusionTrackerBase<LayerType, RenderSurfaceType>::enterLayer(const CCLayerIteratorPosition<LayerType>& layerIterator)
{
    RenderSurfaceType* renderSurface = layerIterator.targetRenderSurfaceLayer->renderSurface();

    if (layerIterator.representsItself)
        enterTargetRenderSurface(renderSurface);
    else if (layerIterator.representsTargetRenderSurface)
        finishedTargetRenderSurface(layerIterator.currentLayer, renderSurface);
}

template<typename LayerType, typename RenderSurfaceType>
void CCOcclusionTrackerBase<LayerType, RenderSurfaceType>::leaveLayer(const CCLayerIteratorPosition<LayerType>& layerIterator)
{
    RenderSurfaceType* renderSurface = layerIterator.targetRenderSurfaceLayer->renderSurface();

    if (layerIterator.representsItself)
        markOccludedBehindLayer(layerIterator.currentLayer);
    else if (layerIterator.representsContributingRenderSurface)
        leaveToTargetRenderSurface(renderSurface);
}

template<typename LayerType, typename RenderSurfaceType>
void CCOcclusionTrackerBase<LayerType, RenderSurfaceType>::enterTargetRenderSurface(const RenderSurfaceType* newTarget)
{
    if (!m_stack.isEmpty() && m_stack.last().surface == newTarget)
        return;

    const RenderSurfaceType* oldTarget = m_stack.isEmpty() ? 0 : m_stack.last().surface;
    const RenderSurfaceType* oldAncestorThatMovesPixels = !oldTarget ? 0 : oldTarget->nearestAncestorThatMovesPixels();
    const RenderSurfaceType* newAncestorThatMovesPixels = newTarget->nearestAncestorThatMovesPixels();

    m_stack.append(StackObject(newTarget));

    // We copy the screen occlusion into the new RenderSurface subtree, but we never copy in the
    // target occlusion, since we are looking at a new RenderSurface target.

    // If we are entering a subtree that is going to move pixels around, then the occlusion we've computed
    // so far won't apply to the pixels we're drawing here in the same way. We discard the occlusion thus
    // far to be safe, and ensure we don't cull any pixels that are moved such that they become visible.
    bool enteringSubtreeThatMovesPixels = newAncestorThatMovesPixels && newAncestorThatMovesPixels != oldAncestorThatMovesPixels;

    bool copyScreenOcclusionForward = m_stack.size() > 1 && !enteringSubtreeThatMovesPixels;
    if (copyScreenOcclusionForward) {
        int lastIndex = m_stack.size() - 1;
        m_stack[lastIndex].occlusionInScreen = m_stack[lastIndex - 1].occlusionInScreen;
    }
}

static inline bool layerOpacityKnown(const LayerChromium* layer) { return !layer->drawOpacityIsAnimating(); }
static inline bool layerOpacityKnown(const CCLayerImpl*) { return true; }
static inline bool layerTransformsToTargetKnown(const LayerChromium* layer) { return !layer->drawTransformIsAnimating(); }
static inline bool layerTransformsToTargetKnown(const CCLayerImpl*) { return true; }
static inline bool layerTransformsToScreenKnown(const LayerChromium* layer) { return !layer->screenSpaceTransformIsAnimating(); }
static inline bool layerTransformsToScreenKnown(const CCLayerImpl*) { return true; }

static inline bool surfaceOpacityKnown(const RenderSurfaceChromium* surface) { return !surface->drawOpacityIsAnimating(); }
static inline bool surfaceOpacityKnown(const CCRenderSurface*) { return true; }
static inline bool surfaceTransformsToTargetKnown(const RenderSurfaceChromium* surface) { return !surface->targetSurfaceTransformsAreAnimating(); }
static inline bool surfaceTransformsToTargetKnown(const CCRenderSurface*) { return true; }
static inline bool surfaceTransformsToScreenKnown(const RenderSurfaceChromium* surface) { return !surface->screenSpaceTransformsAreAnimating(); }
static inline bool surfaceTransformsToScreenKnown(const CCRenderSurface*) { return true; }

template<typename LayerType, typename RenderSurfaceType>
void CCOcclusionTrackerBase<LayerType, RenderSurfaceType>::finishedTargetRenderSurface(const LayerType* owningLayer, const RenderSurfaceType* finishedTarget)
{
    // FIXME: Remove the owningLayer parameter when we can get all the info from the surface.
    ASSERT(owningLayer->renderSurface() == finishedTarget);

    // Make sure we know about the target surface.
    enterTargetRenderSurface(finishedTarget);

    // If the occlusion within the surface can not be applied to things outside of the surface's subtree, then clear the occlusion here so it won't be used.
    if (owningLayer->maskLayer() || !surfaceOpacityKnown(finishedTarget) || finishedTarget->drawOpacity() < 1 || finishedTarget->filters().hasFilterThatAffectsOpacity()) {
        m_stack.last().occlusionInScreen = Region();
        m_stack.last().occlusionInTarget = Region();
    } else {
        if (!surfaceTransformsToTargetKnown(finishedTarget))
            m_stack.last().occlusionInTarget = Region();
        if (!surfaceTransformsToScreenKnown(finishedTarget))
            m_stack.last().occlusionInScreen = Region();
    }
}

template<typename RenderSurfaceType>
static inline Region transformSurfaceOpaqueRegion(const RenderSurfaceType* surface, const Region& region, const TransformationMatrix& transform)
{
    // Verify that rects within the |surface| will remain rects in its target surface after applying |transform|. If this is true, then
    // apply |transform| to each rect within |region| in order to transform the entire Region.

    bool clipped;
    FloatQuad transformedBoundsQuad = CCMathUtil::mapQuad(transform, FloatQuad(region.bounds()), clipped);
    // FIXME: Find a rect interior to each transformed quad.
    if (clipped || !transformedBoundsQuad.isRectilinear())
        return Region();

    Region transformedRegion;

    Vector<IntRect> rects = region.rects();
    // Clipping has been verified above, so mapRect will give correct results.
    for (size_t i = 0; i < rects.size(); ++i) {
        IntRect transformedRect = enclosedIntRect(transform.mapRect(FloatRect(rects[i])));
        if (!surface->clipRect().isEmpty())
            transformedRect.intersect(surface->clipRect());
        transformedRegion.unite(transformedRect);
    }
    return transformedRegion;
}

static inline void reduceOcclusion(const IntRect& affectedArea, const IntRect& expandedPixel, Region& occlusion)
{
    if (affectedArea.isEmpty())
        return;

    Region affectedOcclusion = intersect(occlusion, affectedArea);
    Vector<IntRect> affectedOcclusionRects = affectedOcclusion.rects();

    occlusion.subtract(affectedArea);
    for (size_t j = 0; j < affectedOcclusionRects.size(); ++j) {
        IntRect& occlusionRect = affectedOcclusionRects[j];

        // Shrink the rect by expanding the non-opaque pixels outside the rect.

        // The expandedPixel is the IntRect for a single pixel after being
        // expanded by filters on the layer. The original pixel would be
        // IntRect(0, 0, 1, 1), and the expanded pixel is the rect, relative
        // to this original rect, that the original pixel can influence after
        // being filtered.
        // To convert the expandedPixel IntRect back to filter outsets:
        // x = -leftOutset
        // width = leftOutset + rightOutset
        // maxX = x + width = -leftOutset + leftOutset + rightOutset = rightOutset

        // The leftOutset of the filters moves pixels on the right side of
        // the occlusionRect into it, shrinking its right edge.
        int shrinkLeft = occlusionRect.x() == affectedArea.x() ? 0 : expandedPixel.maxX();
        int shrinkTop = occlusionRect.y() == affectedArea.y() ? 0 : expandedPixel.maxY();
        int shrinkRight = occlusionRect.maxX() == affectedArea.maxX() ? 0 : -expandedPixel.x();
        int shrinkBottom = occlusionRect.maxY() == affectedArea.maxY() ? 0 : -expandedPixel.y();

        occlusionRect.move(shrinkLeft, shrinkTop);
        occlusionRect.contract(shrinkLeft + shrinkRight, shrinkTop + shrinkBottom);

        occlusion.unite(occlusionRect);
    }
}

template<typename RenderSurfaceType>
static void reduceOcclusionBelowSurface(RenderSurfaceType* surface, const IntRect& surfaceRect, const TransformationMatrix& surfaceTransform, RenderSurfaceType* surfaceTarget, Region& occlusionInTarget, Region& occlusionInScreen)
{
    if (surfaceRect.isEmpty())
        return;

    IntRect boundsInTarget = enclosingIntRect(CCMathUtil::mapClippedRect(surfaceTransform, FloatRect(surfaceRect)));
    if (!surface->clipRect().isEmpty())
        boundsInTarget.intersect(surface->clipRect());

    int outsetTop, outsetRight, outsetBottom, outsetLeft;
    surface->backgroundFilters().getOutsets(outsetTop, outsetRight, outsetBottom, outsetLeft);

    // The filter can move pixels from outside of the clip, so allow affectedArea to expand outside the clip.
    boundsInTarget.move(-outsetLeft, -outsetTop);
    boundsInTarget.expand(outsetLeft + outsetRight, outsetTop + outsetBottom);

    IntRect boundsInScreen = enclosingIntRect(CCMathUtil::mapClippedRect(surfaceTarget->screenSpaceTransform(), FloatRect(boundsInTarget)));

    IntRect filterOutsetsInTarget(-outsetLeft, -outsetTop, outsetLeft + outsetRight, outsetTop + outsetBottom);
    IntRect filterOutsetsInScreen = enclosingIntRect(CCMathUtil::mapClippedRect(surfaceTarget->screenSpaceTransform(), FloatRect(filterOutsetsInTarget)));

    reduceOcclusion(boundsInTarget, filterOutsetsInTarget, occlusionInTarget);
    reduceOcclusion(boundsInScreen, filterOutsetsInScreen, occlusionInScreen);
}

template<typename LayerType, typename RenderSurfaceType>
void CCOcclusionTrackerBase<LayerType, RenderSurfaceType>::leaveToTargetRenderSurface(const RenderSurfaceType* newTarget)
{
    int lastIndex = m_stack.size() - 1;
    bool surfaceWillBeAtTopAfterPop = m_stack.size() > 1 && m_stack[lastIndex - 1].surface == newTarget;

    // We merge the screen occlusion from the current RenderSurface subtree out to its parent target RenderSurface.
    // The target occlusion can be merged out as well but needs to be transformed to the new target.

    const RenderSurfaceType* oldTarget = m_stack[lastIndex].surface;
    Region oldTargetOcclusionInNewTarget = transformSurfaceOpaqueRegion<RenderSurfaceType>(oldTarget, m_stack[lastIndex].occlusionInTarget, oldTarget->originTransform());
    if (oldTarget->hasReplica() && !oldTarget->replicaHasMask())
        oldTargetOcclusionInNewTarget.unite(transformSurfaceOpaqueRegion<RenderSurfaceType>(oldTarget, m_stack[lastIndex].occlusionInTarget, oldTarget->replicaOriginTransform()));

    IntRect unoccludedSurfaceRect;
    IntRect unoccludedReplicaRect;
    if (oldTarget->backgroundFilters().hasFilterThatMovesPixels()) {
        unoccludedSurfaceRect = unoccludedContributingSurfaceContentRect(oldTarget, false, oldTarget->contentRect());
        if (oldTarget->hasReplica())
            unoccludedReplicaRect = unoccludedContributingSurfaceContentRect(oldTarget, true, oldTarget->contentRect());
    }

    if (surfaceWillBeAtTopAfterPop) {
        // Merge the top of the stack down.
        m_stack[lastIndex - 1].occlusionInScreen.unite(m_stack[lastIndex].occlusionInScreen);
        m_stack[lastIndex - 1].occlusionInTarget.unite(oldTargetOcclusionInNewTarget);
        m_stack.removeLast();
    } else {
        // Replace the top of the stack with the new pushed surface. Copy the occluded screen region to the top.
        m_stack.last().surface = newTarget;
        m_stack.last().occlusionInTarget = oldTargetOcclusionInNewTarget;
    }

    if (oldTarget->backgroundFilters().hasFilterThatMovesPixels()) {
        reduceOcclusionBelowSurface(oldTarget, unoccludedSurfaceRect, oldTarget->originTransform(), newTarget, m_stack.last().occlusionInTarget, m_stack.last().occlusionInScreen);
        if (oldTarget->hasReplica())
            reduceOcclusionBelowSurface(oldTarget, unoccludedReplicaRect, oldTarget->replicaOriginTransform(), newTarget, m_stack.last().occlusionInTarget, m_stack.last().occlusionInScreen);
    }
}

template<typename LayerType>
static inline TransformationMatrix contentToScreenSpaceTransform(const LayerType* layer)
{
    ASSERT(layerTransformsToScreenKnown(layer));
    IntSize boundsInLayerSpace = layer->bounds();
    IntSize boundsInContentSpace = layer->contentBounds();

    TransformationMatrix transform = layer->screenSpaceTransform();

    if (boundsInContentSpace.isEmpty())
        return transform;

    // Scale from content space to layer space
    transform.scaleNonUniform(boundsInLayerSpace.width() / static_cast<double>(boundsInContentSpace.width()),
                              boundsInLayerSpace.height() / static_cast<double>(boundsInContentSpace.height()));

    return transform;
}

template<typename LayerType>
static inline TransformationMatrix contentToTargetSurfaceTransform(const LayerType* layer)
{
    ASSERT(layerTransformsToTargetKnown(layer));
    IntSize boundsInLayerSpace = layer->bounds();
    IntSize boundsInContentSpace = layer->contentBounds();

    TransformationMatrix transform = layer->drawTransform();

    if (boundsInContentSpace.isEmpty())
        return transform;

    // Scale from content space to layer space
    transform.scaleNonUniform(boundsInLayerSpace.width() / static_cast<double>(boundsInContentSpace.width()),
                              boundsInLayerSpace.height() / static_cast<double>(boundsInContentSpace.height()));

    // The draw transform expects the origin to be in the middle of the layer.
    transform.translate(-boundsInContentSpace.width() / 2.0, -boundsInContentSpace.height() / 2.0);

    return transform;
}

// FIXME: Remove usePaintTracking when paint tracking is on for paint culling.
template<typename LayerType>
static inline void addOcclusionBehindLayer(Region& region, const LayerType* layer, const TransformationMatrix& transform, const Region& opaqueContents, const IntRect& scissorRect, const IntSize& minimumTrackingSize)
{
    ASSERT(layer->visibleLayerRect().contains(opaqueContents.bounds()));

    bool clipped;
    FloatQuad visibleTransformedQuad = CCMathUtil::mapQuad(transform, FloatQuad(layer->visibleLayerRect()), clipped);
    // FIXME: Find a rect interior to each transformed quad.
    if (clipped || !visibleTransformedQuad.isRectilinear())
        return;

    Vector<IntRect> contentRects = opaqueContents.rects();
    // We verify that the possible bounds of this region are not clipped above, so we can use mapRect() safely here.
    for (size_t i = 0; i < contentRects.size(); ++i) {
        IntRect transformedRect = enclosedIntRect(transform.mapRect(FloatRect(contentRects[i])));
        transformedRect.intersect(scissorRect);
        if (transformedRect.width() >= minimumTrackingSize.width() || transformedRect.height() >= minimumTrackingSize.height())
            region.unite(transformedRect);
    }
}

template<typename LayerType, typename RenderSurfaceType>
void CCOcclusionTrackerBase<LayerType, RenderSurfaceType>::markOccludedBehindLayer(const LayerType* layer)
{
    ASSERT(!m_stack.isEmpty());
    ASSERT(layer->targetRenderSurface() == m_stack.last().surface);
    if (m_stack.isEmpty())
        return;

    if (!layerOpacityKnown(layer) || layer->drawOpacity() < 1)
        return;

    Region opaqueContents = layer->visibleContentOpaqueRegion();
    if (opaqueContents.isEmpty())
        return;

    IntRect scissorInTarget = layerScissorRectInTargetSurface(layer);
    if (layerTransformsToTargetKnown(layer))
        addOcclusionBehindLayer<LayerType>(m_stack.last().occlusionInTarget, layer, contentToTargetSurfaceTransform<LayerType>(layer), opaqueContents, scissorInTarget, m_minimumTrackingSize);

    // We must clip the occlusion within the layer's scissorInTarget within screen space as well. If the scissor rect can't be moved to screen space and
    // remain rectilinear, then we don't add any occlusion in screen space.

    if (layerTransformsToScreenKnown(layer)) {
        TransformationMatrix targetToScreenTransform = m_stack.last().surface->screenSpaceTransform();
        bool clipped;
        FloatQuad scissorInScreenQuad = CCMathUtil::mapQuad(targetToScreenTransform, FloatQuad(FloatRect(scissorInTarget)), clipped);
        // FIXME: Find a rect interior to the transformed scissor quad.
        if (clipped || !scissorInScreenQuad.isRectilinear())
            return;
        IntRect scissorInScreenRect = intersection(m_scissorRectInScreenSpace, enclosedIntRect(scissorInScreenQuad.boundingBox()));
        addOcclusionBehindLayer<LayerType>(m_stack.last().occlusionInScreen, layer, contentToScreenSpaceTransform<LayerType>(layer), opaqueContents, scissorInScreenRect, m_minimumTrackingSize);
    }
}

static inline bool testContentRectOccluded(const IntRect& contentRect, const TransformationMatrix& contentSpaceTransform, const IntRect& scissorRect, const Region& occlusion)
{
    FloatRect transformedRect = CCMathUtil::mapClippedRect(contentSpaceTransform, FloatRect(contentRect));
    // Take the enclosingIntRect, as we want to include partial pixels in the test.
    IntRect targetRect = intersection(enclosingIntRect(transformedRect), scissorRect);
    return targetRect.isEmpty() || occlusion.contains(targetRect);
}

template<typename LayerType, typename RenderSurfaceType>
bool CCOcclusionTrackerBase<LayerType, RenderSurfaceType>::occluded(const LayerType* layer, const IntRect& contentRect) const
{
    ASSERT(!m_stack.isEmpty());
    if (m_stack.isEmpty())
        return false;
    if (contentRect.isEmpty())
        return true;

    ASSERT(layer->targetRenderSurface() == m_stack.last().surface);

    if (layerTransformsToScreenKnown(layer) && testContentRectOccluded(contentRect, contentToScreenSpaceTransform<LayerType>(layer), m_scissorRectInScreenSpace, m_stack.last().occlusionInScreen))
        return true;
    if (layerTransformsToTargetKnown(layer) && testContentRectOccluded(contentRect, contentToTargetSurfaceTransform<LayerType>(layer), layerScissorRectInTargetSurface(layer), m_stack.last().occlusionInTarget))
        return true;
    return false;
}

// Determines what portion of rect, if any, is unoccluded (not occluded by region). If
// the resulting unoccluded region is not rectangular, we return a rect containing it.
static inline IntRect rectSubtractRegion(const IntRect& rect, const Region& region)
{
    Region rectRegion(rect);
    rectRegion.subtract(region);
    return rectRegion.bounds();
}

static inline IntRect computeUnoccludedContentRect(const IntRect& contentRect, const TransformationMatrix& contentSpaceTransform, const IntRect& scissorRect, const Region& occlusion)
{
    if (!contentSpaceTransform.isInvertible())
        return contentRect;

    // Take the enclosingIntRect at each step, as we want to contain any unoccluded partial pixels in the resulting IntRect.
    FloatRect transformedRect = CCMathUtil::mapClippedRect(contentSpaceTransform, FloatRect(contentRect));
    IntRect shrunkRect = rectSubtractRegion(intersection(enclosingIntRect(transformedRect), scissorRect), occlusion);
    IntRect unoccludedRect = enclosingIntRect(CCMathUtil::projectClippedRect(contentSpaceTransform.inverse(), FloatRect(shrunkRect)));
    // The rect back in content space is a bounding box and may extend outside of the original contentRect, so clamp it to the contentRectBounds.
    return intersection(unoccludedRect, contentRect);
}

template<typename LayerType, typename RenderSurfaceType>
IntRect CCOcclusionTrackerBase<LayerType, RenderSurfaceType>::unoccludedContentRect(const LayerType* layer, const IntRect& contentRect) const
{
    ASSERT(!m_stack.isEmpty());
    if (m_stack.isEmpty())
        return contentRect;
    if (contentRect.isEmpty())
        return contentRect;

    ASSERT(layer->targetRenderSurface() == m_stack.last().surface);

    // We want to return a rect that contains all the visible parts of |contentRect| in both screen space and in the target surface.
    // So we find the visible parts of |contentRect| in each space, and take the intersection.

    IntRect unoccludedInScreen = contentRect;
    if (layerTransformsToScreenKnown(layer))
        unoccludedInScreen = computeUnoccludedContentRect(contentRect, contentToScreenSpaceTransform<LayerType>(layer), m_scissorRectInScreenSpace, m_stack.last().occlusionInScreen);

    if (unoccludedInScreen.isEmpty())
        return unoccludedInScreen;

    IntRect unoccludedInTarget = contentRect;
    if (layerTransformsToTargetKnown(layer))
        unoccludedInTarget = computeUnoccludedContentRect(contentRect, contentToTargetSurfaceTransform<LayerType>(layer), layerScissorRectInTargetSurface(layer), m_stack.last().occlusionInTarget);

    return intersection(unoccludedInScreen, unoccludedInTarget);
}

template<typename LayerType, typename RenderSurfaceType>
IntRect CCOcclusionTrackerBase<LayerType, RenderSurfaceType>::unoccludedContributingSurfaceContentRect(const RenderSurfaceType* surface, bool forReplica, const IntRect& contentRect) const
{
    ASSERT(!m_stack.isEmpty());
    // This should be called while the contributing render surface is still considered the current target in the occlusion tracker.
    ASSERT(surface == m_stack.last().surface);

    // A contributing surface doesn't get occluded by things inside its own surface, so only things outside the surface can occlude it. That occlusion is
    // found just below the top of the stack (if it exists).
    if (m_stack.size() < 2)
        return contentRect;
    if (contentRect.isEmpty())
        return contentRect;

    const StackObject& secondLast = m_stack[m_stack.size() - 2];

    IntRect surfaceClipRect = surface->clipRect();
    if (surfaceClipRect.isEmpty()) {
        const RenderSurfaceType* targetSurface = secondLast.surface;
        surfaceClipRect = intersection(targetSurface->contentRect(), enclosingIntRect(surface->drawableContentRect()));
    }

    const TransformationMatrix& transformToScreen = forReplica ? surface->replicaScreenSpaceTransform() : surface->screenSpaceTransform();
    const TransformationMatrix& transformToTarget = forReplica ? surface->replicaOriginTransform() : surface->originTransform();

    IntRect unoccludedInScreen = contentRect;
    if (surfaceTransformsToScreenKnown(surface))
        unoccludedInScreen = computeUnoccludedContentRect(contentRect, transformToScreen, m_scissorRectInScreenSpace, secondLast.occlusionInScreen);

    if (unoccludedInScreen.isEmpty())
        return unoccludedInScreen;

    IntRect unoccludedInTarget = contentRect;
    if (surfaceTransformsToTargetKnown(surface))
        unoccludedInTarget = computeUnoccludedContentRect(contentRect, transformToTarget, surfaceClipRect, secondLast.occlusionInTarget);

    return intersection(unoccludedInScreen, unoccludedInTarget);
}

template<typename LayerType, typename RenderSurfaceType>
IntRect CCOcclusionTrackerBase<LayerType, RenderSurfaceType>::layerScissorRectInTargetSurface(const LayerType* layer) const
{
    const RenderSurfaceType* targetSurface = m_stack.last().surface;
    FloatRect totalScissor = targetSurface->contentRect();
    if (layer->usesLayerClipping())
        totalScissor.intersect(layer->clipRect());
    return enclosingIntRect(totalScissor);
}

// Declare the possible functions here for the linker.
template CCOcclusionTrackerBase<LayerChromium, RenderSurfaceChromium>::CCOcclusionTrackerBase(IntRect scissorRectInScreenSpace, bool recordMetricsForFrame);
template void CCOcclusionTrackerBase<LayerChromium, RenderSurfaceChromium>::enterLayer(const CCLayerIteratorPosition<LayerChromium>&);
template void CCOcclusionTrackerBase<LayerChromium, RenderSurfaceChromium>::leaveLayer(const CCLayerIteratorPosition<LayerChromium>&);
template void CCOcclusionTrackerBase<LayerChromium, RenderSurfaceChromium>::enterTargetRenderSurface(const RenderSurfaceChromium* newTarget);
template void CCOcclusionTrackerBase<LayerChromium, RenderSurfaceChromium>::finishedTargetRenderSurface(const LayerChromium* owningLayer, const RenderSurfaceChromium* finishedTarget);
template void CCOcclusionTrackerBase<LayerChromium, RenderSurfaceChromium>::leaveToTargetRenderSurface(const RenderSurfaceChromium* newTarget);
template void CCOcclusionTrackerBase<LayerChromium, RenderSurfaceChromium>::markOccludedBehindLayer(const LayerChromium*);
template bool CCOcclusionTrackerBase<LayerChromium, RenderSurfaceChromium>::occluded(const LayerChromium*, const IntRect& contentRect) const;
template IntRect CCOcclusionTrackerBase<LayerChromium, RenderSurfaceChromium>::unoccludedContentRect(const LayerChromium*, const IntRect& contentRect) const;
template IntRect CCOcclusionTrackerBase<LayerChromium, RenderSurfaceChromium>::unoccludedContributingSurfaceContentRect(const RenderSurfaceChromium*, bool forReplica, const IntRect& contentRect) const;
template IntRect CCOcclusionTrackerBase<LayerChromium, RenderSurfaceChromium>::layerScissorRectInTargetSurface(const LayerChromium*) const;

template CCOcclusionTrackerBase<CCLayerImpl, CCRenderSurface>::CCOcclusionTrackerBase(IntRect scissorRectInScreenSpace, bool recordMetricsForFrame);
template void CCOcclusionTrackerBase<CCLayerImpl, CCRenderSurface>::enterLayer(const CCLayerIteratorPosition<CCLayerImpl>&);
template void CCOcclusionTrackerBase<CCLayerImpl, CCRenderSurface>::leaveLayer(const CCLayerIteratorPosition<CCLayerImpl>&);
template void CCOcclusionTrackerBase<CCLayerImpl, CCRenderSurface>::enterTargetRenderSurface(const CCRenderSurface* newTarget);
template void CCOcclusionTrackerBase<CCLayerImpl, CCRenderSurface>::finishedTargetRenderSurface(const CCLayerImpl* owningLayer, const CCRenderSurface* finishedTarget);
template void CCOcclusionTrackerBase<CCLayerImpl, CCRenderSurface>::leaveToTargetRenderSurface(const CCRenderSurface* newTarget);
template void CCOcclusionTrackerBase<CCLayerImpl, CCRenderSurface>::markOccludedBehindLayer(const CCLayerImpl*);
template bool CCOcclusionTrackerBase<CCLayerImpl, CCRenderSurface>::occluded(const CCLayerImpl*, const IntRect& contentRect) const;
template IntRect CCOcclusionTrackerBase<CCLayerImpl, CCRenderSurface>::unoccludedContentRect(const CCLayerImpl*, const IntRect& contentRect) const;
template IntRect CCOcclusionTrackerBase<CCLayerImpl, CCRenderSurface>::unoccludedContributingSurfaceContentRect(const CCRenderSurface*, bool forReplica, const IntRect& contentRect) const;
template IntRect CCOcclusionTrackerBase<CCLayerImpl, CCRenderSurface>::layerScissorRectInTargetSurface(const CCLayerImpl*) const;


} // namespace WebCore
#endif // USE(ACCELERATED_COMPOSITING)