REGRESSION: Google Search (mobile) video thumbnails are too large.

[WebKit-https.git] / Source / WebCore / rendering / RenderLayer.cpp

/*
 * Copyright (C) 2006-2014 Apple Inc. All rights reserved.
 *
 * Portions are Copyright (C) 1998 Netscape Communications Corporation.
 *
 * Other contributors:
 *   Robert O'Callahan <roc+@cs.cmu.edu>
 *   David Baron <dbaron@fas.harvard.edu>
 *   Christian Biesinger <cbiesinger@web.de>
 *   Randall Jesup <rjesup@wgate.com>
 *   Roland Mainz <roland.mainz@informatik.med.uni-giessen.de>
 *   Josh Soref <timeless@mac.com>
 *   Boris Zbarsky <bzbarsky@mit.edu>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * Alternatively, the contents of this file may be used under the terms
 * of either the Mozilla Public License Version 1.1, found at
 * http://www.mozilla.org/MPL/ (the "MPL") or the GNU General Public
 * License Version 2.0, found at http://www.fsf.org/copyleft/gpl.html
 * (the "GPL"), in which case the provisions of the MPL or the GPL are
 * applicable instead of those above.  If you wish to allow use of your
 * version of this file only under the terms of one of those two
 * licenses (the MPL or the GPL) and not to allow others to use your
 * version of this file under the LGPL, indicate your decision by
 * deletingthe provisions above and replace them with the notice and
 * other provisions required by the MPL or the GPL, as the case may be.
 * If you do not delete the provisions above, a recipient may use your
 * version of this file under any of the LGPL, the MPL or the GPL.
 */

#include "config.h"
#include "RenderLayer.h"

#include "AnimationController.h"
#include "BoxShape.h"
#include "CSSPropertyNames.h"
#include "Chrome.h"
#include "Document.h"
#include "DocumentEventQueue.h"
#include "Element.h"
#include "EventHandler.h"
#include "FEColorMatrix.h"
#include "FEMerge.h"
#include "FilterEffectRenderer.h"
#include "FloatConversion.h"
#include "FloatPoint3D.h"
#include "FloatRect.h"
#include "FloatRoundedRect.h"
#include "FlowThreadController.h"
#include "FocusController.h"
#include "Frame.h"
#include "FrameLoader.h"
#include "FrameLoaderClient.h"
#include "FrameSelection.h"
#include "FrameTree.h"
#include "FrameView.h"
#include "Gradient.h"
#include "GraphicsContext.h"
#include "HTMLFormControlElement.h"
#include "HTMLFrameElement.h"
#include "HTMLFrameOwnerElement.h"
#include "HTMLNames.h"
#include "HitTestingTransformState.h"
#include "HitTestRequest.h"
#include "HitTestResult.h"
#include "InspectorInstrumentation.h"
#include "OverflowEvent.h"
#include "OverlapTestRequestClient.h"
#include "Page.h"
#include "PlatformMouseEvent.h"
#include "RenderFlowThread.h"
#include "RenderGeometryMap.h"
#include "RenderInline.h"
#include "RenderIterator.h"
#include "RenderLayerBacking.h"
#include "RenderLayerCompositor.h"
#include "RenderLayerFilterInfo.h"
#include "RenderMarquee.h"
#include "RenderMultiColumnFlowThread.h"
#include "RenderNamedFlowFragment.h"
#include "RenderNamedFlowThread.h"
#include "RenderRegion.h"
#include "RenderReplica.h"
#include "RenderSVGResourceClipper.h"
#include "RenderScrollbar.h"
#include "RenderScrollbarPart.h"
#include "RenderTableCell.h"
#include "RenderTableRow.h"
#include "RenderText.h"
#include "RenderTheme.h"
#include "RenderTreeAsText.h"
#include "RenderView.h"
#include "SVGNames.h"
#include "ScaleTransformOperation.h"
#include "ScrollAnimator.h"
#include "Scrollbar.h"
#include "ScrollbarTheme.h"
#include "ScrollingCoordinator.h"
#include "Settings.h"
#include "ShadowRoot.h"
#include "SourceGraphic.h"
#include "StyleProperties.h"
#include "StyleResolver.h"
#include "TextStream.h"
#include "TransformationMatrix.h"
#include "TranslateTransformOperation.h"
#include <stdio.h>
#include <wtf/StdLibExtras.h>
#include <wtf/text/CString.h>

#if ENABLE(CSS_SCROLL_SNAP)
#include "AxisScrollSnapOffsets.h"
#endif

#define MIN_INTERSECT_FOR_REVEAL 32

namespace WebCore {

using namespace HTMLNames;

bool ClipRect::intersects(const HitTestLocation& hitTestLocation) const
{
    return hitTestLocation.intersects(m_rect);
}

void makeMatrixRenderable(TransformationMatrix& matrix, bool has3DRendering)
{
#if !ENABLE(3D_RENDERING)
    UNUSED_PARAM(has3DRendering);
    matrix.makeAffine();
#else
    if (!has3DRendering)
        matrix.makeAffine();
#endif
}

RenderLayer::RenderLayer(RenderLayerModelObject& rendererLayerModelObject)
    : m_inResizeMode(false)
    , m_scrollDimensionsDirty(true)
    , m_normalFlowListDirty(true)
    , m_hasSelfPaintingLayerDescendant(false)
    , m_hasSelfPaintingLayerDescendantDirty(false)
    , m_hasOutOfFlowPositionedDescendant(false)
    , m_hasOutOfFlowPositionedDescendantDirty(true)
    , m_needsCompositedScrolling(false)
    , m_descendantsAreContiguousInStackingOrder(false)
    , m_isRootLayer(rendererLayerModelObject.isRenderView())
    , m_usedTransparency(false)
    , m_paintingInsideReflection(false)
    , m_inOverflowRelayout(false)
    , m_repaintStatus(NeedsNormalRepaint)
    , m_visibleContentStatusDirty(true)
    , m_hasVisibleContent(false)
    , m_visibleDescendantStatusDirty(false)
    , m_hasVisibleDescendant(false)
    , m_3DTransformedDescendantStatusDirty(true)
    , m_has3DTransformedDescendant(false)
    , m_hasCompositingDescendant(false)
    , m_hasTransformedAncestor(false)
    , m_has3DTransformedAncestor(false)
    , m_indirectCompositingReason(static_cast<unsigned>(IndirectCompositingReason::None))
    , m_viewportConstrainedNotCompositedReason(NoNotCompositedReason)
#if PLATFORM(IOS)
    , m_adjustForIOSCaretWhenScrolling(false)
#endif
#if PLATFORM(IOS)
#if ENABLE(IOS_TOUCH_EVENTS)
    , m_registeredAsTouchEventListenerForScrolling(false)
#endif
    , m_inUserScroll(false)
    , m_requiresScrollBoundsOriginUpdate(false)
#endif
    , m_containsDirtyOverlayScrollbars(false)
    , m_updatingMarqueePosition(false)
#if !ASSERT_DISABLED
    , m_layerListMutationAllowed(true)
#endif
    , m_hasFilterInfo(false)
#if ENABLE(CSS_COMPOSITING)
    , m_blendMode(BlendModeNormal)
    , m_hasNotIsolatedCompositedBlendingDescendants(false)
    , m_hasNotIsolatedBlendingDescendants(false)
    , m_hasNotIsolatedBlendingDescendantsStatusDirty(false)
#endif
    , m_renderer(rendererLayerModelObject)
    , m_parent(nullptr)
    , m_previous(nullptr)
    , m_next(nullptr)
    , m_first(nullptr)
    , m_last(nullptr)
    , m_staticInlinePosition(0)
    , m_staticBlockPosition(0)
    , m_enclosingPaginationLayer(nullptr)
{
    m_isNormalFlowOnly = shouldBeNormalFlowOnly();
    m_isSelfPaintingLayer = shouldBeSelfPaintingLayer();

    // Non-stacking containers should have empty z-order lists. As this is already the case,
    // there is no need to dirty / recompute these lists.
    m_zOrderListsDirty = isStackingContainer();

    ScrollableArea::setConstrainsScrollingToContentEdge(false);

    if (!renderer().firstChild()) {
        m_visibleContentStatusDirty = false;
        m_hasVisibleContent = renderer().style().visibility() == VISIBLE;
    }

    if (Element* element = renderer().element()) {
        // We save and restore only the scrollOffset as the other scroll values are recalculated.
        m_scrollOffset = element->savedLayerScrollOffset();
        if (!m_scrollOffset.isZero())
            scrollAnimator()->setCurrentPosition(FloatPoint(m_scrollOffset.width(), m_scrollOffset.height()));
        element->setSavedLayerScrollOffset(IntSize());
    }
}

RenderLayer::~RenderLayer()
{
    if (inResizeMode() && !renderer().documentBeingDestroyed())
        renderer().frame().eventHandler().resizeLayerDestroyed();

    renderer().view().frameView().removeScrollableArea(this);

    if (!renderer().documentBeingDestroyed()) {
#if ENABLE(IOS_TOUCH_EVENTS)
        unregisterAsTouchEventListenerForScrolling();
#endif
        if (Element* element = renderer().element())
            element->setSavedLayerScrollOffset(m_scrollOffset);
    }

    destroyScrollbar(HorizontalScrollbar);
    destroyScrollbar(VerticalScrollbar);

    if (renderer().frame().page()) {
        if (ScrollingCoordinator* scrollingCoordinator = renderer().frame().page()->scrollingCoordinator())
            scrollingCoordinator->willDestroyScrollableArea(this);
    }

    if (m_reflection)
        removeReflection();

    FilterInfo::remove(*this);

    // Child layers will be deleted by their corresponding render objects, so
    // we don't need to delete them ourselves.

    clearBacking(true);
}

String RenderLayer::name() const
{
    StringBuilder name;
    name.append(renderer().renderName());

    if (Element* element = renderer().element()) {
        name.append(' ');
        name.append(element->tagName());

        if (element->hasID()) {
            name.appendLiteral(" id=\'");
            name.append(element->getIdAttribute());
            name.append('\'');
        }

        if (element->hasClass()) {
            name.appendLiteral(" class=\'");
            for (size_t i = 0; i < element->classNames().size(); ++i) {
                if (i > 0)
                    name.append(' ');
                name.append(element->classNames()[i]);
            }
            name.append('\'');
        }
    }

    if (isReflection())
        name.appendLiteral(" (reflection)");

    return name.toString();
}

RenderLayerCompositor& RenderLayer::compositor() const
{
    return renderer().view().compositor();
}

void RenderLayer::contentChanged(ContentChangeType changeType)
{
    if ((changeType == CanvasChanged || changeType == VideoChanged || changeType == FullScreenChanged || changeType == ImageChanged) && compositor().updateLayerCompositingState(*this))
        compositor().setCompositingLayersNeedRebuild();

    if (m_backing)
        m_backing->contentChanged(changeType);
}

bool RenderLayer::canRender3DTransforms() const
{
    return compositor().canRender3DTransforms();
}

bool RenderLayer::paintsWithFilters() const
{
    // FIXME: Eventually there will be cases where we paint with filters even without accelerated compositing,
    // and this whole function won't be inside the #if below.

    if (!renderer().hasFilter())
        return false;
        
    if (!isComposited())
        return true;

    if (!m_backing || !m_backing->canCompositeFilters())
        return true;

    return false;
}

bool RenderLayer::requiresFullLayerImageForFilters() const 
{
    if (!paintsWithFilters())
        return false;
    FilterEffectRenderer* renderer = filterRenderer();
    return renderer && renderer->hasFilterThatMovesPixels();
}

FilterEffectRenderer* RenderLayer::filterRenderer() const
{
    FilterInfo* filterInfo = FilterInfo::getIfExists(*this);
    return filterInfo ? filterInfo->renderer() : 0;
}

void RenderLayer::updateLayerPositionsAfterLayout(const RenderLayer* rootLayer, UpdateLayerPositionsFlags flags)
{
    RenderGeometryMap geometryMap(UseTransforms);
    if (this != rootLayer)
        geometryMap.pushMappingsToAncestor(parent(), 0);
    updateLayerPositions(&geometryMap, flags);
}

void RenderLayer::updateLayerPositions(RenderGeometryMap* geometryMap, UpdateLayerPositionsFlags flags)
{
    updateLayerPosition(); // For relpositioned layers or non-positioned layers,
                           // we need to keep in sync, since we may have shifted relative
                           // to our parent layer.
    if (geometryMap)
        geometryMap->pushMappingsToAncestor(this, parent());

    // Clear our cached clip rect information.
    clearClipRects();
    
    if (hasOverflowControls()) {
        LayoutSize offsetFromRoot;
        if (geometryMap)
            offsetFromRoot = LayoutSize(toFloatSize(geometryMap->absolutePoint(FloatPoint())));
        else {
            // FIXME: It looks suspicious to call convertToLayerCoords here
            // as canUseConvertToLayerCoords may be true for an ancestor layer.
            offsetFromRoot = offsetFromAncestor(root());
        }
        positionOverflowControls(roundedIntSize(offsetFromRoot));
    }

    updateDescendantDependentFlags();

    if (flags & UpdatePagination)
        updatePagination();
    else
        m_enclosingPaginationLayer = nullptr;
    
    if (m_hasVisibleContent) {
        // FIXME: LayoutState does not work with RenderLayers as there is not a 1-to-1
        // mapping between them and the RenderObjects. It would be neat to enable
        // LayoutState outside the layout() phase and use it here.
        ASSERT(!renderer().view().layoutStateEnabled());

        RenderLayerModelObject* repaintContainer = renderer().containerForRepaint();
        LayoutRect oldRepaintRect = m_repaintRect;
        LayoutRect oldOutlineBox = m_outlineBox;
        computeRepaintRects(repaintContainer, geometryMap);

        // FIXME: Should ASSERT that value calculated for m_outlineBox using the cached offset is the same
        // as the value not using the cached offset, but we can't due to https://bugs.webkit.org/show_bug.cgi?id=37048
        if (flags & CheckForRepaint) {
            if (!renderer().view().printing()) {
                bool didRepaint = false;
                if (m_repaintStatus & NeedsFullRepaint) {
                    renderer().repaintUsingContainer(repaintContainer, oldRepaintRect);
                    if (m_repaintRect != oldRepaintRect) {
                        renderer().repaintUsingContainer(repaintContainer, m_repaintRect);
                        didRepaint = true;
                    }
                } else if (shouldRepaintAfterLayout()) {
                    renderer().repaintAfterLayoutIfNeeded(repaintContainer, oldRepaintRect, oldOutlineBox, &m_repaintRect, &m_outlineBox);
                    didRepaint = true;
                }

                if (didRepaint && renderer().isRenderNamedFlowFragmentContainer()) {
                    // If we just repainted a region, we must also repaint the flow thread since it is the one
                    // doing the actual painting of the flowed content.
                    RenderNamedFlowFragment& region = *downcast<RenderBlockFlow>(renderer()).renderNamedFlowFragment();
                    if (region.isValid())
                        region.flowThread()->layer()->repaintIncludingDescendants();
                }
            }
        }
    } else
        clearRepaintRects();

    m_repaintStatus = NeedsNormalRepaint;
    m_hasTransformedAncestor = flags & SeenTransformedLayer;
    m_has3DTransformedAncestor = flags & Seen3DTransformedLayer;

    // Go ahead and update the reflection's position and size.
    if (m_reflection)
        m_reflection->layout();

    // Clear the IsCompositingUpdateRoot flag once we've found the first compositing layer in this update.
    bool isUpdateRoot = (flags & IsCompositingUpdateRoot);
    if (isComposited())
        flags &= ~IsCompositingUpdateRoot;

    if (renderer().isInFlowRenderFlowThread()) {
        updatePagination();
        flags |= UpdatePagination;
    }

    if (transform()) {
        flags |= SeenTransformedLayer;
        if (!transform()->isAffine())
            flags |= Seen3DTransformedLayer;
    }

    for (RenderLayer* child = firstChild(); child; child = child->nextSibling())
        child->updateLayerPositions(geometryMap, flags);

    if ((flags & UpdateCompositingLayers) && isComposited()) {
        RenderLayerBacking::UpdateAfterLayoutFlags updateFlags = RenderLayerBacking::CompositingChildrenOnly;
        if (flags & NeedsFullRepaintInBacking)
            updateFlags |= RenderLayerBacking::NeedsFullRepaint;
        if (isUpdateRoot)
            updateFlags |= RenderLayerBacking::IsUpdateRoot;
        backing()->updateAfterLayout(updateFlags);
    }
        
    // With all our children positioned, now update our marquee if we need to.
    if (m_marquee) {
        // FIXME: would like to use TemporaryChange<> but it doesn't work with bitfields.
        bool oldUpdatingMarqueePosition = m_updatingMarqueePosition;
        m_updatingMarqueePosition = true;
        m_marquee->updateMarqueePosition();
        m_updatingMarqueePosition = oldUpdatingMarqueePosition;
    }

    if (geometryMap)
        geometryMap->popMappingsToAncestor(parent());
}

LayoutRect RenderLayer::repaintRectIncludingNonCompositingDescendants() const
{
    LayoutRect repaintRect = m_repaintRect;
    for (RenderLayer* child = firstChild(); child; child = child->nextSibling()) {
        // Don't include repaint rects for composited child layers; they will paint themselves and have a different origin.
        if (child->isComposited())
            continue;

        repaintRect.unite(child->repaintRectIncludingNonCompositingDescendants());
    }
    return repaintRect;
}

void RenderLayer::setAncestorChainHasSelfPaintingLayerDescendant()
{
    for (RenderLayer* layer = this; layer; layer = layer->parent()) {
        if (!layer->m_hasSelfPaintingLayerDescendantDirty && layer->hasSelfPaintingLayerDescendant())
            break;

        layer->m_hasSelfPaintingLayerDescendantDirty = false;
        layer->m_hasSelfPaintingLayerDescendant = true;
    }
}

void RenderLayer::dirtyAncestorChainHasSelfPaintingLayerDescendantStatus()
{
    for (RenderLayer* layer = this; layer; layer = layer->parent()) {
        layer->m_hasSelfPaintingLayerDescendantDirty = true;
        // If we have reached a self-painting layer, we know our parent should have a self-painting descendant
        // in this case, there is no need to dirty our ancestors further.
        if (layer->isSelfPaintingLayer()) {
            ASSERT(!parent() || parent()->m_hasSelfPaintingLayerDescendantDirty || parent()->hasSelfPaintingLayerDescendant());
            break;
        }
    }
}

bool RenderLayer::acceleratedCompositingForOverflowScrollEnabled() const
{
    return renderer().frame().settings().acceleratedCompositingForOverflowScrollEnabled();
}

// If we are a stacking container, then this function will determine if our
// descendants for a contiguous block in stacking order. This is required in
// order for an element to be safely promoted to a stacking container. It is safe
// to become a stacking container if this change would not alter the stacking
// order of layers on the page. That can only happen if a non-descendant appear
// between us and our descendants in stacking order. Here's an example:
//
//                                 this
//                                /  |  \.
//                               A   B   C
//                              /\   |   /\.
//                             0 -8  D  2  7
//                                   |
//                                   5
//
// I've labeled our normal flow descendants A, B, C, and D, our stacking
// container descendants with their z indices, and us with 'this' (we're a
// stacking container and our zIndex doesn't matter here). These nodes appear in
// three lists: posZOrder, negZOrder, and normal flow (keep in mind that normal
// flow layers don't overlap). So if we arrange these lists in order we get our
// stacking order:
//
//                     [-8], [A-D], [0, 2, 5, 7]--> pos z-order.
//                       |     |
//        Neg z-order. <-+     +--> Normal flow descendants.
//
// We can then assign new, 'stacking' order indices to these elements as follows:
//
//                     [-8], [A-D], [0, 2, 5, 7]
// 'Stacking' indices:  -1     0     1  2  3  4
//
// Note that the normal flow descendants can share an index because they don't
// stack/overlap. Now our problem becomes very simple: a layer can safely become
// a stacking container if the stacking-order indices of it and its descendants
// appear in a contiguous block in the list of stacking indices. This problem
// can be solved very efficiently by calculating the min/max stacking indices in
// the subtree, and the number stacking container descendants. Once we have this
// information, we know that the subtree's indices form a contiguous block if:
//
//           maxStackIndex - minStackIndex == numSCDescendants
//
// So for node A in the example above we would have:
//   maxStackIndex = 1
//   minStackIndex = -1
//   numSCDecendants = 2
//
// and so,
//       maxStackIndex - minStackIndex == numSCDescendants
//  ===>                      1 - (-1) == 2
//  ===>                             2 == 2
//
//  Since this is true, A can safely become a stacking container.
//  Now, for node C we have:
//
//   maxStackIndex = 4
//   minStackIndex = 0 <-- because C has stacking index 0.
//   numSCDecendants = 2
//
// and so,
//       maxStackIndex - minStackIndex == numSCDescendants
//  ===>                         4 - 0 == 2
//  ===>                             4 == 2
//
// Since this is false, C cannot be safely promoted to a stacking container. This
// happened because of the elements with z-index 5 and 0. Now if 5 had been a
// child of C rather than D, and A had no child with Z index 0, we would have had:
//
//   maxStackIndex = 3
//   minStackIndex = 0 <-- because C has stacking index 0.
//   numSCDecendants = 3
//
// and so,
//       maxStackIndex - minStackIndex == numSCDescendants
//  ===>                         3 - 0 == 3
//  ===>                             3 == 3
//
//  And we would conclude that C could be promoted.
void RenderLayer::updateDescendantsAreContiguousInStackingOrder()
{
    if (!isStackingContext() || !acceleratedCompositingForOverflowScrollEnabled())
        return;

    ASSERT(!m_normalFlowListDirty);
    ASSERT(!m_zOrderListsDirty);

    std::unique_ptr<Vector<RenderLayer*>> posZOrderList;
    std::unique_ptr<Vector<RenderLayer*>> negZOrderList;
    rebuildZOrderLists(StopAtStackingContexts, posZOrderList, negZOrderList);

    // Create a reverse lookup.
    HashMap<const RenderLayer*, int> lookup;

    if (negZOrderList) {
        int stackingOrderIndex = -1;
        size_t listSize = negZOrderList->size();
        for (size_t i = 0; i < listSize; ++i) {
            RenderLayer* currentLayer = negZOrderList->at(listSize - i - 1);
            if (!currentLayer->isStackingContext())
                continue;
            lookup.set(currentLayer, stackingOrderIndex--);
        }
    }

    if (posZOrderList) {
        size_t listSize = posZOrderList->size();
        int stackingOrderIndex = 1;
        for (size_t i = 0; i < listSize; ++i) {
            RenderLayer* currentLayer = posZOrderList->at(i);
            if (!currentLayer->isStackingContext())
                continue;
            lookup.set(currentLayer, stackingOrderIndex++);
        }
    }

    int minIndex = 0;
    int maxIndex = 0;
    int count = 0;
    bool firstIteration = true;
    updateDescendantsAreContiguousInStackingOrderRecursive(lookup, minIndex, maxIndex, count, firstIteration);
}

void RenderLayer::updateDescendantsAreContiguousInStackingOrderRecursive(const HashMap<const RenderLayer*, int>& lookup, int& minIndex, int& maxIndex, int& count, bool firstIteration)
{
    if (isStackingContext() && !firstIteration) {
        if (lookup.contains(this)) {
            minIndex = std::min(minIndex, lookup.get(this));
            maxIndex = std::max(maxIndex, lookup.get(this));
            count++;
        }
        return;
    }

    for (RenderLayer* child = firstChild(); child; child = child->nextSibling()) {
        int childMinIndex = 0;
        int childMaxIndex = 0;
        int childCount = 0;
        child->updateDescendantsAreContiguousInStackingOrderRecursive(lookup, childMinIndex, childMaxIndex, childCount, false);
        if (childCount) {
            count += childCount;
            minIndex = std::min(minIndex, childMinIndex);
            maxIndex = std::max(maxIndex, childMaxIndex);
        }
    }

    if (!isStackingContext()) {
        bool newValue = maxIndex - minIndex == count;
        bool didUpdate = newValue != m_descendantsAreContiguousInStackingOrder;
        m_descendantsAreContiguousInStackingOrder = newValue;
        if (didUpdate)
            updateNeedsCompositedScrolling();
    }
}

void RenderLayer::computeRepaintRects(const RenderLayerModelObject* repaintContainer, const RenderGeometryMap* geometryMap)
{
    ASSERT(!m_visibleContentStatusDirty);

    m_repaintRect = renderer().clippedOverflowRectForRepaint(repaintContainer);
    m_outlineBox = renderer().outlineBoundsForRepaint(repaintContainer, geometryMap);
}


void RenderLayer::computeRepaintRectsIncludingDescendants()
{
    // FIXME: computeRepaintRects() has to walk up the parent chain for every layer to compute the rects.
    // We should make this more efficient.
    // FIXME: it's wrong to call this when layout is not up-to-date, which we do.
    computeRepaintRects(renderer().containerForRepaint());

    for (RenderLayer* layer = firstChild(); layer; layer = layer->nextSibling())
        layer->computeRepaintRectsIncludingDescendants();
}

void RenderLayer::clearRepaintRects()
{
    ASSERT(!m_hasVisibleContent);
    ASSERT(!m_visibleContentStatusDirty);

    m_repaintRect = LayoutRect();
    m_outlineBox = LayoutRect();
}

void RenderLayer::updateLayerPositionsAfterDocumentScroll()
{
    ASSERT(this == renderer().view().layer());

    RenderGeometryMap geometryMap(UseTransforms);
    updateLayerPositionsAfterScroll(&geometryMap);
}

void RenderLayer::updateLayerPositionsAfterOverflowScroll()
{
    RenderGeometryMap geometryMap(UseTransforms);
    if (this != renderer().view().layer())
        geometryMap.pushMappingsToAncestor(parent(), 0);

    // FIXME: why is it OK to not check the ancestors of this layer in order to
    // initialize the HasSeenViewportConstrainedAncestor and HasSeenAncestorWithOverflowClip flags?
    updateLayerPositionsAfterScroll(&geometryMap, IsOverflowScroll);
}

void RenderLayer::updateLayerPositionsAfterScroll(RenderGeometryMap* geometryMap, UpdateLayerPositionsAfterScrollFlags flags)
{
    // FIXME: This shouldn't be needed, but there are some corner cases where
    // these flags are still dirty. Update so that the check below is valid.
    updateDescendantDependentFlags();

    // If we have no visible content and no visible descendants, there is no point recomputing
    // our rectangles as they will be empty. If our visibility changes, we are expected to
    // recompute all our positions anyway.
    if (!m_hasVisibleDescendant && !m_hasVisibleContent)
        return;

    bool positionChanged = updateLayerPosition();
    if (positionChanged)
        flags |= HasChangedAncestor;

    if (geometryMap)
        geometryMap->pushMappingsToAncestor(this, parent());

    if (flags & HasChangedAncestor || flags & HasSeenViewportConstrainedAncestor || flags & IsOverflowScroll)
        clearClipRects();

    if (renderer().style().hasViewportConstrainedPosition())
        flags |= HasSeenViewportConstrainedAncestor;

    if (renderer().hasOverflowClip())
        flags |= HasSeenAncestorWithOverflowClip;

    if (flags & HasSeenViewportConstrainedAncestor
        || (flags & IsOverflowScroll && flags & HasSeenAncestorWithOverflowClip)) {
        // FIXME: We could track the repaint container as we walk down the tree.
        computeRepaintRects(renderer().containerForRepaint(), geometryMap);
    } else {
        // Check that our cached rects are correct.
        ASSERT(m_repaintRect == renderer().clippedOverflowRectForRepaint(renderer().containerForRepaint()));
        ASSERT(m_outlineBox == renderer().outlineBoundsForRepaint(renderer().containerForRepaint(), geometryMap));
    }
    
    for (RenderLayer* child = firstChild(); child; child = child->nextSibling())
        child->updateLayerPositionsAfterScroll(geometryMap, flags);

    // We don't update our reflection as scrolling is a translation which does not change the size()
    // of an object, thus RenderReplica will still repaint itself properly as the layer position was
    // updated above.

    if (m_marquee) {
        bool oldUpdatingMarqueePosition = m_updatingMarqueePosition;
        m_updatingMarqueePosition = true;
        m_marquee->updateMarqueePosition();
        m_updatingMarqueePosition = oldUpdatingMarqueePosition;
    }

    if (geometryMap)
        geometryMap->popMappingsToAncestor(parent());
}

void RenderLayer::positionNewlyCreatedOverflowControls()
{
    if (!backing()->hasUnpositionedOverflowControlsLayers())
        return;

    RenderGeometryMap geometryMap(UseTransforms);
    if (this != renderer().view().layer() && parent())
        geometryMap.pushMappingsToAncestor(parent(), 0);

    LayoutPoint offsetFromRoot = LayoutPoint(geometryMap.absolutePoint(FloatPoint()));
    positionOverflowControls(toIntSize(roundedIntPoint(offsetFromRoot)));
}

#if ENABLE(CSS_COMPOSITING)

void RenderLayer::updateBlendMode()
{
    bool hadBlendMode = m_blendMode != BlendModeNormal;
    if (parent() && hadBlendMode != hasBlendMode()) {
        if (hasBlendMode())
            parent()->updateAncestorChainHasBlendingDescendants();
        else
            parent()->dirtyAncestorChainHasBlendingDescendants();
    }

    BlendMode newBlendMode = renderer().style().blendMode();
    if (newBlendMode != m_blendMode)
        m_blendMode = newBlendMode;
}

void RenderLayer::updateAncestorChainHasBlendingDescendants()
{
    for (auto layer = this; layer; layer = layer->parent()) {
        if (!layer->hasNotIsolatedBlendingDescendantsStatusDirty() && layer->hasNotIsolatedBlendingDescendants())
            break;
        layer->m_hasNotIsolatedBlendingDescendants = true;
        layer->m_hasNotIsolatedBlendingDescendantsStatusDirty = false;

        layer->updateSelfPaintingLayer();

        if (layer->isStackingContext())
            break;
    }
}

void RenderLayer::dirtyAncestorChainHasBlendingDescendants()
{
    for (auto layer = this; layer; layer = layer->parent()) {
        if (layer->hasNotIsolatedBlendingDescendantsStatusDirty())
            break;
        
        layer->m_hasNotIsolatedBlendingDescendantsStatusDirty = true;

        if (layer->isStackingContext())
            break;
    }
}
#endif

void RenderLayer::updateTransform()
{
    // hasTransform() on the renderer is also true when there is transform-style: preserve-3d or perspective set,
    // so check style too.
    bool hasTransform = renderer().hasTransform() && renderer().style().hasTransform();
    bool had3DTransform = has3DTransform();

    bool hadTransform = !!m_transform;
    if (hasTransform != hadTransform) {
        if (hasTransform)
            m_transform = std::make_unique<TransformationMatrix>();
        else
            m_transform = nullptr;
        
        // Layers with transforms act as clip rects roots, so clear the cached clip rects here.
        clearClipRectsIncludingDescendants();
    }
    
    if (hasTransform) {
        RenderBox* box = renderBox();
        ASSERT(box);
        m_transform->makeIdentity();
        box->style().applyTransform(*m_transform, snapRectToDevicePixels(box->borderBoxRect(), box->document().deviceScaleFactor()), RenderStyle::IncludeTransformOrigin);
        makeMatrixRenderable(*m_transform, canRender3DTransforms());
    }

    if (had3DTransform != has3DTransform())
        dirty3DTransformedDescendantStatus();
}

TransformationMatrix RenderLayer::currentTransform(RenderStyle::ApplyTransformOrigin applyOrigin) const
{
    if (!m_transform)
        return TransformationMatrix();

    RenderBox* box = renderBox();
    ASSERT(box);
    FloatRect pixelSnappedBorderRect = snapRectToDevicePixels(box->borderBoxRect(), box->document().deviceScaleFactor());
    if (renderer().style().isRunningAcceleratedAnimation()) {
        TransformationMatrix currTransform;
        RefPtr<RenderStyle> style = renderer().animation().getAnimatedStyleForRenderer(renderer());
        style->applyTransform(currTransform, pixelSnappedBorderRect, applyOrigin);
        makeMatrixRenderable(currTransform, canRender3DTransforms());
        return currTransform;
    }

    // m_transform includes transform-origin, so we need to recompute the transform here.
    if (applyOrigin == RenderStyle::ExcludeTransformOrigin) {
        TransformationMatrix currTransform;
        box->style().applyTransform(currTransform, pixelSnappedBorderRect, RenderStyle::ExcludeTransformOrigin);
        makeMatrixRenderable(currTransform, canRender3DTransforms());
        return currTransform;
    }

    return *m_transform;
}

TransformationMatrix RenderLayer::renderableTransform(PaintBehavior paintBehavior) const
{
    if (!m_transform)
        return TransformationMatrix();
    
    if (paintBehavior & PaintBehaviorFlattenCompositingLayers) {
        TransformationMatrix matrix = *m_transform;
        makeMatrixRenderable(matrix, false /* flatten 3d */);
        return matrix;
    }

    return *m_transform;
}

RenderLayer* RenderLayer::enclosingOverflowClipLayer(IncludeSelfOrNot includeSelf) const
{
    const RenderLayer* layer = (includeSelf == IncludeSelf) ? this : parent();
    while (layer) {
        if (layer->renderer().hasOverflowClip())
            return const_cast<RenderLayer*>(layer);

        layer = layer->parent();
    }
    return 0;
}

// FIXME: This is terrible. Bring back a cached bit for this someday. This crawl is going to slow down all
// painting of content inside paginated layers.
bool RenderLayer::hasCompositedLayerInEnclosingPaginationChain() const
{
    // No enclosing layer means no compositing in the chain.
    if (!m_enclosingPaginationLayer)
        return false;
    
    // If the enclosing layer is composited, we don't have to check anything in between us and that
    // layer.
    if (m_enclosingPaginationLayer->isComposited())
        return true;

    // If we are the enclosing pagination layer, then we can't be composited or we'd have passed the
    // previous check.
    if (m_enclosingPaginationLayer == this)
        return false;

    // The enclosing paginated layer is our ancestor and is not composited, so we have to check
    // intermediate layers between us and the enclosing pagination layer. Start with our own layer.
    if (isComposited())
        return true;
    
    // For normal flow layers, we can recur up the layer tree.
    if (isNormalFlowOnly())
        return parent()->hasCompositedLayerInEnclosingPaginationChain();
    
    // Otherwise we have to go up the containing block chain. Find the first enclosing
    // containing block layer ancestor, and check that.
    RenderView* renderView = &renderer().view();
    for (RenderBlock* containingBlock = renderer().containingBlock(); containingBlock && containingBlock != renderView; containingBlock = containingBlock->containingBlock()) {
        if (containingBlock->hasLayer())
            return containingBlock->layer()->hasCompositedLayerInEnclosingPaginationChain();
    }
    return false;
}

void RenderLayer::updatePagination()
{
    m_enclosingPaginationLayer = nullptr;
    
    if (!parent())
        return;
    
    // Each layer that is inside a multicolumn flow thread has to be checked individually and
    // genuinely know if it is going to have to split itself up when painting only its contents (and not any other descendant
    // layers). We track an enclosingPaginationLayer instead of using a simple bit, since we want to be able to get back
    // to that layer easily.
    if (renderer().isInFlowRenderFlowThread()) {
        m_enclosingPaginationLayer = this;
        return;
    }

    if (isNormalFlowOnly()) {
        // Content inside a transform is not considered to be paginated, since we simply
        // paint the transform multiple times in each column, so we don't have to use
        // fragments for the transformed content.
        if (parent()->hasTransform())
            m_enclosingPaginationLayer = nullptr;
        else
            m_enclosingPaginationLayer = parent()->enclosingPaginationLayer(IncludeCompositedPaginatedLayers);
        return;
    }

    // For the new columns code, we want to walk up our containing block chain looking for an enclosing layer. Once
    // we find one, then we just check its pagination status.
    RenderView* renderView = &renderer().view();
    RenderBlock* containingBlock;
    for (containingBlock = renderer().containingBlock(); containingBlock && containingBlock != renderView; containingBlock = containingBlock->containingBlock()) {
        if (containingBlock->hasLayer()) {
            // Content inside a transform is not considered to be paginated, since we simply
            // paint the transform multiple times in each column, so we don't have to use
            // fragments for the transformed content.
            if (containingBlock->layer()->hasTransform())
                m_enclosingPaginationLayer = nullptr;
            else
                m_enclosingPaginationLayer = containingBlock->layer()->enclosingPaginationLayer(IncludeCompositedPaginatedLayers);
            return;
        }
    }
}

bool RenderLayer::canBeStackingContainer() const
{
    if (isStackingContext() || !stackingContainer())
        return true;

    return m_descendantsAreContiguousInStackingOrder;
}

void RenderLayer::setHasVisibleContent()
{ 
    if (m_hasVisibleContent && !m_visibleContentStatusDirty) {
        ASSERT(!parent() || parent()->hasVisibleDescendant());
        return;
    }

    m_visibleContentStatusDirty = false; 
    m_hasVisibleContent = true;
    computeRepaintRects(renderer().containerForRepaint());
    if (!isNormalFlowOnly()) {
        // We don't collect invisible layers in z-order lists if we are not in compositing mode.
        // As we became visible, we need to dirty our stacking containers ancestors to be properly
        // collected. FIXME: When compositing, we could skip this dirtying phase.
        for (RenderLayer* sc = stackingContainer(); sc; sc = sc->stackingContainer()) {
            sc->dirtyZOrderLists();
            if (sc->hasVisibleContent())
                break;
        }
    }

    if (parent())
        parent()->setAncestorChainHasVisibleDescendant();
}

void RenderLayer::dirtyVisibleContentStatus() 
{ 
    m_visibleContentStatusDirty = true; 
    if (parent())
        parent()->dirtyAncestorChainVisibleDescendantStatus();
}

void RenderLayer::dirtyAncestorChainVisibleDescendantStatus()
{
    for (RenderLayer* layer = this; layer; layer = layer->parent()) {
        if (layer->m_visibleDescendantStatusDirty)
            break;

        layer->m_visibleDescendantStatusDirty = true;
    }
}

void RenderLayer::setAncestorChainHasVisibleDescendant()
{
    for (RenderLayer* layer = this; layer; layer = layer->parent()) {
        if (!layer->m_visibleDescendantStatusDirty && layer->hasVisibleDescendant())
            break;

        layer->m_hasVisibleDescendant = true;
        layer->m_visibleDescendantStatusDirty = false;
    }
}

void RenderLayer::updateDescendantDependentFlags(HashSet<const RenderObject*>* outOfFlowDescendantContainingBlocks)
{
    if (m_visibleDescendantStatusDirty || m_hasSelfPaintingLayerDescendantDirty || m_hasOutOfFlowPositionedDescendantDirty || hasNotIsolatedBlendingDescendantsStatusDirty()) {
        bool hasVisibleDescendant = false;
        bool hasSelfPaintingLayerDescendant = false;
        bool hasOutOfFlowPositionedDescendant = false;
#if ENABLE(CSS_COMPOSITING)
        bool hasNotIsolatedBlendingDescendants = false;
#endif

        HashSet<const RenderObject*> childOutOfFlowDescendantContainingBlocks;
        for (RenderLayer* child = firstChild(); child; child = child->nextSibling()) {
            childOutOfFlowDescendantContainingBlocks.clear();
            child->updateDescendantDependentFlags(&childOutOfFlowDescendantContainingBlocks);

            bool childIsOutOfFlowPositioned = child->renderer().isOutOfFlowPositioned();
            if (childIsOutOfFlowPositioned)
                childOutOfFlowDescendantContainingBlocks.add(child->renderer().containingBlock());

            if (outOfFlowDescendantContainingBlocks) {
                HashSet<const RenderObject*>::const_iterator it = childOutOfFlowDescendantContainingBlocks.begin();
                for (; it != childOutOfFlowDescendantContainingBlocks.end(); ++it)
                    outOfFlowDescendantContainingBlocks->add(*it);
            }

            hasVisibleDescendant |= child->m_hasVisibleContent || child->m_hasVisibleDescendant;
            hasSelfPaintingLayerDescendant |= child->isSelfPaintingLayer() || child->hasSelfPaintingLayerDescendant();
            hasOutOfFlowPositionedDescendant |= !childOutOfFlowDescendantContainingBlocks.isEmpty();
#if ENABLE(CSS_COMPOSITING)
            hasNotIsolatedBlendingDescendants |= child->hasBlendMode() || (child->hasNotIsolatedBlendingDescendants() && !child->isolatesBlending());
#endif

            bool allFlagsSet = hasVisibleDescendant && hasSelfPaintingLayerDescendant && hasOutOfFlowPositionedDescendant;
#if ENABLE(CSS_COMPOSITING)
            allFlagsSet &= hasNotIsolatedBlendingDescendants;
#endif
            if (allFlagsSet)
                break;
        }

        if (outOfFlowDescendantContainingBlocks)
            outOfFlowDescendantContainingBlocks->remove(&renderer());

        m_hasVisibleDescendant = hasVisibleDescendant;
        m_visibleDescendantStatusDirty = false;
        m_hasSelfPaintingLayerDescendant = hasSelfPaintingLayerDescendant;
        m_hasSelfPaintingLayerDescendantDirty = false;

        m_hasOutOfFlowPositionedDescendant = hasOutOfFlowPositionedDescendant;
        if (m_hasOutOfFlowPositionedDescendantDirty)
            updateNeedsCompositedScrolling();

        m_hasOutOfFlowPositionedDescendantDirty = false;
#if ENABLE(CSS_COMPOSITING)
        m_hasNotIsolatedBlendingDescendants = hasNotIsolatedBlendingDescendants;
        if (m_hasNotIsolatedBlendingDescendantsStatusDirty) {
            m_hasNotIsolatedBlendingDescendantsStatusDirty = false;
            updateSelfPaintingLayer();
        }
#endif
    }

    if (m_visibleContentStatusDirty) {
        if (renderer().style().visibility() == VISIBLE)
            m_hasVisibleContent = true;
        else {
            // layer may be hidden but still have some visible content, check for this
            m_hasVisibleContent = false;
            RenderObject* r = renderer().firstChild();
            while (r) {
                if (r->style().visibility() == VISIBLE && !r->hasLayer()) {
                    m_hasVisibleContent = true;
                    break;
                }
                RenderObject* child = nullptr;
                if (!r->hasLayer() && (child = r->firstChildSlow()))
                    r = child;
                else if (r->nextSibling())
                    r = r->nextSibling();
                else {
                    do {
                        r = r->parent();
                        if (r == &renderer())
                            r = nullptr;
                    } while (r && !r->nextSibling());
                    if (r)
                        r = r->nextSibling();
                }
            }
        }    
        m_visibleContentStatusDirty = false; 
    }
}

void RenderLayer::dirty3DTransformedDescendantStatus()
{
    RenderLayer* curr = stackingContainer();
    if (curr)
        curr->m_3DTransformedDescendantStatusDirty = true;
        
    // This propagates up through preserve-3d hierarchies to the enclosing flattening layer.
    // Note that preserves3D() creates stacking context, so we can just run up the stacking containers.
    while (curr && curr->preserves3D()) {
        curr->m_3DTransformedDescendantStatusDirty = true;
        curr = curr->stackingContainer();
    }
}

// Return true if this layer or any preserve-3d descendants have 3d.
bool RenderLayer::update3DTransformedDescendantStatus()
{
    if (m_3DTransformedDescendantStatusDirty) {
        m_has3DTransformedDescendant = false;

        updateZOrderLists();

        // Transformed or preserve-3d descendants can only be in the z-order lists, not
        // in the normal flow list, so we only need to check those.
        if (Vector<RenderLayer*>* positiveZOrderList = posZOrderList()) {
            for (unsigned i = 0; i < positiveZOrderList->size(); ++i)
                m_has3DTransformedDescendant |= positiveZOrderList->at(i)->update3DTransformedDescendantStatus();
        }

        // Now check our negative z-index children.
        if (Vector<RenderLayer*>* negativeZOrderList = negZOrderList()) {
            for (unsigned i = 0; i < negativeZOrderList->size(); ++i)
                m_has3DTransformedDescendant |= negativeZOrderList->at(i)->update3DTransformedDescendantStatus();
        }
        
        m_3DTransformedDescendantStatusDirty = false;
    }
    
    // If we live in a 3d hierarchy, then the layer at the root of that hierarchy needs
    // the m_has3DTransformedDescendant set.
    if (preserves3D())
        return has3DTransform() || m_has3DTransformedDescendant;

    return has3DTransform();
}

bool RenderLayer::updateLayerPosition()
{
    LayoutPoint localPoint;
    LayoutSize inlineBoundingBoxOffset; // We don't put this into the RenderLayer x/y for inlines, so we need to subtract it out when done.
    if (renderer().isInline() && is<RenderInline>(renderer())) {
        auto& inlineFlow = downcast<RenderInline>(renderer());
        IntRect lineBox = inlineFlow.linesBoundingBox();
        setSize(lineBox.size());
        inlineBoundingBoxOffset = toLayoutSize(lineBox.location());
        localPoint += inlineBoundingBoxOffset;
    } else if (RenderBox* box = renderBox()) {
        // FIXME: Is snapping the size really needed here for the RenderBox case?
        setSize(box->pixelSnappedSize());
        localPoint += box->topLeftLocationOffset();
    }

    if (!renderer().isOutOfFlowPositioned() && renderer().parent()) {
        // We must adjust our position by walking up the render tree looking for the
        // nearest enclosing object with a layer.
        RenderElement* ancestor = renderer().parent();
        while (ancestor && !ancestor->hasLayer()) {
            if (is<RenderBox>(*ancestor) && !is<RenderTableRow>(*ancestor)) {
                // Rows and cells share the same coordinate space (that of the section).
                // Omit them when computing our xpos/ypos.
                localPoint += downcast<RenderBox>(*ancestor).topLeftLocationOffset();
            }
            ancestor = ancestor->parent();
        }
        if (is<RenderBox>(*ancestor) && is<RenderTableRow>(*ancestor)) {
            // Put ourselves into the row coordinate space.
            localPoint -= downcast<RenderBox>(*ancestor).topLeftLocationOffset();
        }
    }
    
    // Subtract our parent's scroll offset.
    if (renderer().isOutOfFlowPositioned() && enclosingPositionedAncestor()) {
        RenderLayer* positionedParent = enclosingPositionedAncestor();

        // For positioned layers, we subtract out the enclosing positioned layer's scroll offset.
        if (positionedParent->renderer().hasOverflowClip()) {
            LayoutSize offset = positionedParent->scrolledContentOffset();
            localPoint -= offset;
        }
        
        if (renderer().isOutOfFlowPositioned() && positionedParent->renderer().isInFlowPositioned() && is<RenderInline>(positionedParent->renderer())) {
            LayoutSize offset = downcast<RenderInline>(positionedParent->renderer()).offsetForInFlowPositionedInline(&downcast<RenderBox>(renderer()));
            localPoint += offset;
        }
    } else if (parent()) {
        if (parent()->renderer().hasOverflowClip()) {
            IntSize scrollOffset = parent()->scrolledContentOffset();
            localPoint -= scrollOffset;
        }
    }
    
    bool positionOrOffsetChanged = false;
    if (renderer().isInFlowPositioned()) {
        LayoutSize newOffset = downcast<RenderBoxModelObject>(renderer()).offsetForInFlowPosition();
        positionOrOffsetChanged = newOffset != m_offsetForInFlowPosition;
        m_offsetForInFlowPosition = newOffset;
        localPoint.move(m_offsetForInFlowPosition);
    } else {
        m_offsetForInFlowPosition = LayoutSize();
    }

    // FIXME: We'd really like to just get rid of the concept of a layer rectangle and rely on the renderers.
    localPoint -= inlineBoundingBoxOffset;
    
    positionOrOffsetChanged |= location() != localPoint;
    setLocation(localPoint);
    return positionOrOffsetChanged;
}

TransformationMatrix RenderLayer::perspectiveTransform() const
{
    if (!renderer().hasTransform())
        return TransformationMatrix();

    const RenderStyle& style = renderer().style();
    if (!style.hasPerspective())
        return TransformationMatrix();

    // Maybe fetch the perspective from the backing?
    const IntRect borderBox = downcast<RenderBox>(renderer()).pixelSnappedBorderBoxRect();
    const float boxWidth = borderBox.width();
    const float boxHeight = borderBox.height();

    float perspectiveOriginX = floatValueForLength(style.perspectiveOriginX(), boxWidth);
    float perspectiveOriginY = floatValueForLength(style.perspectiveOriginY(), boxHeight);

    // A perspective origin of 0,0 makes the vanishing point in the center of the element.
    // We want it to be in the top-left, so subtract half the height and width.
    perspectiveOriginX -= boxWidth / 2.0f;
    perspectiveOriginY -= boxHeight / 2.0f;
    
    TransformationMatrix t;
    t.translate(perspectiveOriginX, perspectiveOriginY);
    t.applyPerspective(style.perspective());
    t.translate(-perspectiveOriginX, -perspectiveOriginY);
    
    return t;
}

FloatPoint RenderLayer::perspectiveOrigin() const
{
    if (!renderer().hasTransform())
        return FloatPoint();

    const LayoutRect borderBox = downcast<RenderBox>(renderer()).borderBoxRect();
    const RenderStyle& style = renderer().style();

    return FloatPoint(floatValueForLength(style.perspectiveOriginX(), borderBox.width()),
                      floatValueForLength(style.perspectiveOriginY(), borderBox.height()));
}

RenderLayer* RenderLayer::stackingContainer() const
{
    RenderLayer* layer = parent();
    while (layer && !layer->isStackingContainer())
        layer = layer->parent();

    ASSERT(!layer || layer->isStackingContainer());
    return layer;
}

static inline bool isPositionedContainer(RenderLayer* layer)
{
    return layer->isRootLayer() || layer->renderer().isPositioned() || layer->hasTransform();
}

static inline bool isFixedPositionedContainer(RenderLayer* layer)
{
    return layer->isRootLayer() || layer->hasTransform();
}

RenderLayer* RenderLayer::enclosingPositionedAncestor() const
{
    RenderLayer* curr = parent();
    while (curr && !isPositionedContainer(curr))
        curr = curr->parent();

    return curr;
}

static RenderLayer* parentLayerCrossFrame(const RenderLayer* layer)
{
    ASSERT(layer);
    if (layer->parent())
        return layer->parent();

    HTMLFrameOwnerElement* ownerElement = layer->renderer().document().ownerElement();
    if (!ownerElement)
        return nullptr;

    RenderElement* ownerRenderer = ownerElement->renderer();
    if (!ownerRenderer)
        return nullptr;

    return ownerRenderer->enclosingLayer();
}

RenderLayer* RenderLayer::enclosingScrollableLayer() const
{
    for (RenderLayer* nextLayer = parentLayerCrossFrame(this); nextLayer; nextLayer = parentLayerCrossFrame(nextLayer)) {
        if (is<RenderBox>(nextLayer->renderer()) && downcast<RenderBox>(nextLayer->renderer()).canBeScrolledAndHasScrollableArea())
            return nextLayer;
    }

    return nullptr;
}

IntRect RenderLayer::scrollableAreaBoundingBox() const
{
    return renderer().absoluteBoundingBoxRect();
}

bool RenderLayer::isRubberBandInProgress() const
{
#if ENABLE(RUBBER_BANDING)
    if (!scrollsOverflow())
        return false;

    if (ScrollAnimator* scrollAnimator = existingScrollAnimator())
        return scrollAnimator->isRubberBandInProgress();
#endif

    return false;
}

bool RenderLayer::forceUpdateScrollbarsOnMainThreadForPerformanceTesting() const
{
    Page* page = renderer().frame().page();
    return page && page->settings().forceUpdateScrollbarsOnMainThreadForPerformanceTesting();
}

RenderLayer* RenderLayer::enclosingTransformedAncestor() const
{
    RenderLayer* curr = parent();
    while (curr && !curr->isRootLayer() && !curr->transform())
        curr = curr->parent();

    return curr;
}

static inline const RenderLayer* compositingContainer(const RenderLayer* layer)
{
    return layer->isNormalFlowOnly() ? layer->parent() : layer->stackingContainer();
}

inline bool RenderLayer::shouldRepaintAfterLayout() const
{
    if (m_repaintStatus == NeedsNormalRepaint)
        return true;

    // Composited layers that were moved during a positioned movement only
    // layout, don't need to be repainted. They just need to be recomposited.
    ASSERT(m_repaintStatus == NeedsFullRepaintForPositionedMovementLayout);
    return !isComposited() || backing()->paintsIntoCompositedAncestor();
}

static bool compositedWithOwnBackingStore(const RenderLayer* layer)
{
    return layer->isComposited() && !layer->backing()->paintsIntoCompositedAncestor();
}

RenderLayer* RenderLayer::enclosingCompositingLayer(IncludeSelfOrNot includeSelf) const
{
    if (includeSelf == IncludeSelf && isComposited())
        return const_cast<RenderLayer*>(this);

    for (const RenderLayer* curr = compositingContainer(this); curr; curr = compositingContainer(curr)) {
        if (curr->isComposited())
            return const_cast<RenderLayer*>(curr);
    }
         
    return 0;
}

RenderLayer* RenderLayer::enclosingCompositingLayerForRepaint(IncludeSelfOrNot includeSelf) const
{
    if (includeSelf == IncludeSelf && isComposited() && !backing()->paintsIntoCompositedAncestor())
        return const_cast<RenderLayer*>(this);

    for (const RenderLayer* curr = compositingContainer(this); curr; curr = compositingContainer(curr)) {
        if (compositedWithOwnBackingStore(curr))
            return const_cast<RenderLayer*>(curr);
    }
         
    return 0;
}

RenderLayer* RenderLayer::enclosingFilterLayer(IncludeSelfOrNot includeSelf) const
{
    const RenderLayer* curr = (includeSelf == IncludeSelf) ? this : parent();
    for (; curr; curr = curr->parent()) {
        if (curr->requiresFullLayerImageForFilters())
            return const_cast<RenderLayer*>(curr);
    }
    
    return 0;
}

RenderLayer* RenderLayer::enclosingFilterRepaintLayer() const
{
    for (const RenderLayer* curr = this; curr; curr = curr->parent()) {
        if ((curr != this && curr->requiresFullLayerImageForFilters()) || compositedWithOwnBackingStore(curr) || curr->isRootLayer())
            return const_cast<RenderLayer*>(curr);
    }
    return 0;
}

void RenderLayer::setFilterBackendNeedsRepaintingInRect(const LayoutRect& rect)
{
    if (rect.isEmpty())
        return;
    
    LayoutRect rectForRepaint = rect;
    renderer().style().filterOutsets().expandRect(rectForRepaint);

    FilterInfo& filterInfo = FilterInfo::get(*this);
    filterInfo.expandDirtySourceRect(rectForRepaint);
    
    RenderLayer* parentLayer = enclosingFilterRepaintLayer();
    ASSERT(parentLayer);
    FloatQuad repaintQuad(rectForRepaint);
    LayoutRect parentLayerRect = renderer().localToContainerQuad(repaintQuad, &parentLayer->renderer()).enclosingBoundingBox();

    if (parentLayer->isComposited()) {
        if (!parentLayer->backing()->paintsIntoWindow()) {
            parentLayer->setBackingNeedsRepaintInRect(parentLayerRect);
            return;
        }
        // If the painting goes to window, redirect the painting to the parent RenderView.
        parentLayer = renderer().view().layer();
        parentLayerRect = renderer().localToContainerQuad(repaintQuad, &parentLayer->renderer()).enclosingBoundingBox();
    }

    if (parentLayer->paintsWithFilters()) {
        parentLayer->setFilterBackendNeedsRepaintingInRect(parentLayerRect);
        return;        
    }
    
    if (parentLayer->isRootLayer()) {
        downcast<RenderView>(parentLayer->renderer()).repaintViewRectangle(parentLayerRect);
        return;
    }
    
    ASSERT_NOT_REACHED();
}

bool RenderLayer::hasAncestorWithFilterOutsets() const
{
    for (const RenderLayer* curr = this; curr; curr = curr->parent()) {
        if (curr->renderer().style().hasFilterOutsets())
            return true;
    }
    return false;
}

RenderLayer* RenderLayer::clippingRootForPainting() const
{
    if (isComposited())
        return const_cast<RenderLayer*>(this);

    const RenderLayer* current = this;
    while (current) {
        if (current->isRootLayer())
            return const_cast<RenderLayer*>(current);

        current = compositingContainer(current);
        ASSERT(current);
        if (current->transform() || compositedWithOwnBackingStore(current))
            return const_cast<RenderLayer*>(current);
    }

    ASSERT_NOT_REACHED();
    return 0;
}

LayoutPoint RenderLayer::absoluteToContents(const LayoutPoint& absolutePoint) const
{
    // We don't use convertToLayerCoords because it doesn't know about transforms
    return LayoutPoint(renderer().absoluteToLocal(absolutePoint, UseTransforms));
}

bool RenderLayer::cannotBlitToWindow() const
{
    if (isTransparent() || hasReflection() || hasTransform())
        return true;
    if (!parent())
        return false;
    return parent()->cannotBlitToWindow();
}

RenderLayer* RenderLayer::transparentPaintingAncestor()
{
    if (isComposited())
        return 0;

    for (RenderLayer* curr = parent(); curr; curr = curr->parent()) {
        if (curr->isComposited())
            return 0;
        if (curr->isTransparent())
            return curr;
    }
    return 0;
}

enum TransparencyClipBoxBehavior {
    PaintingTransparencyClipBox,
    HitTestingTransparencyClipBox
};

enum TransparencyClipBoxMode {
    DescendantsOfTransparencyClipBox,
    RootOfTransparencyClipBox
};

static LayoutRect transparencyClipBox(const RenderLayer&, const RenderLayer* rootLayer, TransparencyClipBoxBehavior, TransparencyClipBoxMode, PaintBehavior = 0);

static void expandClipRectForRegionAndReflection(LayoutRect& clipRect, const RenderLayer& layer, const RenderLayer* rootLayer,
    TransparencyClipBoxBehavior transparencyBehavior, PaintBehavior paintBehavior)
{
    // If this is a region, then the painting is actually done by its flow thread's layer.
    if (layer.renderer().isRenderNamedFlowFragmentContainer()) {
        RenderBlockFlow& regionContainer = downcast<RenderBlockFlow>(layer.renderer());
        RenderNamedFlowFragment& region = *regionContainer.renderNamedFlowFragment();
        RenderLayer* flowThreadLayer = region.flowThread()->layer();
        if (flowThreadLayer && (!layer.reflection() || layer.reflectionLayer() != flowThreadLayer)) {
            LayoutRect flowThreadClipRect = transparencyClipBox(*flowThreadLayer, rootLayer, transparencyBehavior, DescendantsOfTransparencyClipBox, paintBehavior);
            LayoutSize moveOffset = (regionContainer.contentBoxRect().location() + layer.offsetFromAncestor(flowThreadLayer)) - region.flowThreadPortionRect().location();
            flowThreadClipRect.move(moveOffset);
            
            clipRect.unite(flowThreadClipRect);
        }
    }
}

static void expandClipRectForDescendantsAndReflection(LayoutRect& clipRect, const RenderLayer& layer, const RenderLayer* rootLayer,
    TransparencyClipBoxBehavior transparencyBehavior, PaintBehavior paintBehavior)
{
    // If we have a mask, then the clip is limited to the border box area (and there is
    // no need to examine child layers).
    if (!layer.renderer().hasMask()) {
        // Note: we don't have to walk z-order lists since transparent elements always establish
        // a stacking container. This means we can just walk the layer tree directly.
        for (RenderLayer* curr = layer.firstChild(); curr; curr = curr->nextSibling()) {
            if (!layer.reflection() || layer.reflectionLayer() != curr)
                clipRect.unite(transparencyClipBox(*curr, rootLayer, transparencyBehavior, DescendantsOfTransparencyClipBox, paintBehavior));
        }
    }

    expandClipRectForRegionAndReflection(clipRect, layer, rootLayer, transparencyBehavior, paintBehavior);

    // If we have a reflection, then we need to account for that when we push the clip.  Reflect our entire
    // current transparencyClipBox to catch all child layers.
    // FIXME: Accelerated compositing will eventually want to do something smart here to avoid incorporating this
    // size into the parent layer.
    if (layer.renderer().hasReflection()) {
        LayoutSize delta = layer.offsetFromAncestor(rootLayer);
        clipRect.move(-delta);
        clipRect.unite(layer.renderBox()->reflectedRect(clipRect));
        clipRect.move(delta);
    }
}

static LayoutRect transparencyClipBox(const RenderLayer& layer, const RenderLayer* rootLayer, TransparencyClipBoxBehavior transparencyBehavior,
    TransparencyClipBoxMode transparencyMode, PaintBehavior paintBehavior)
{
    // FIXME: Although this function completely ignores CSS-imposed clipping, we did already intersect with the
    // paintDirtyRect, and that should cut down on the amount we have to paint.  Still it
    // would be better to respect clips.
    
    if (rootLayer != &layer && ((transparencyBehavior == PaintingTransparencyClipBox && layer.paintsWithTransform(paintBehavior))
        || (transparencyBehavior == HitTestingTransparencyClipBox && layer.hasTransform()))) {
        // The best we can do here is to use enclosed bounding boxes to establish a "fuzzy" enough clip to encompass
        // the transformed layer and all of its children.
        RenderLayer::PaginationInclusionMode mode = transparencyBehavior == HitTestingTransparencyClipBox ? RenderLayer::IncludeCompositedPaginatedLayers : RenderLayer::ExcludeCompositedPaginatedLayers;
        const RenderLayer* paginationLayer = transparencyMode == DescendantsOfTransparencyClipBox ? layer.enclosingPaginationLayer(mode) : 0;
        const RenderLayer* rootLayerForTransform = paginationLayer ? paginationLayer : rootLayer;
        LayoutSize delta = layer.offsetFromAncestor(rootLayerForTransform);

        TransformationMatrix transform;
        transform.translate(delta.width(), delta.height());
        transform = transform * *layer.transform();

        // We don't use fragment boxes when collecting a transformed layer's bounding box, since it always
        // paints unfragmented.
        LayoutRect clipRect = layer.boundingBox(&layer);
        expandClipRectForDescendantsAndReflection(clipRect, layer, &layer, transparencyBehavior, paintBehavior);
        layer.renderer().style().filterOutsets().expandRect(clipRect);
        LayoutRect result = transform.mapRect(clipRect);
        if (!paginationLayer)
            return result;
        
        // We have to break up the transformed extent across our columns.
        // Split our box up into the actual fragment boxes that render in the columns/pages and unite those together to
        // get our true bounding box.
        auto& enclosingFlowThread = downcast<RenderFlowThread>(paginationLayer->renderer());
        result = enclosingFlowThread.fragmentsBoundingBox(result);
        result.move(paginationLayer->offsetFromAncestor(rootLayer));
        return result;
    }
    
    LayoutRect clipRect = layer.boundingBox(rootLayer, layer.offsetFromAncestor(rootLayer), transparencyBehavior == HitTestingTransparencyClipBox ? RenderLayer::UseFragmentBoxesIncludingCompositing : RenderLayer::UseFragmentBoxesExcludingCompositing);
    expandClipRectForDescendantsAndReflection(clipRect, layer, rootLayer, transparencyBehavior, paintBehavior);
    layer.renderer().style().filterOutsets().expandRect(clipRect);

    return clipRect;
}

static LayoutRect paintingExtent(const RenderLayer& currentLayer, const RenderLayer* rootLayer, const LayoutRect& paintDirtyRect, PaintBehavior paintBehavior)
{
    return intersection(transparencyClipBox(currentLayer, rootLayer, PaintingTransparencyClipBox, RootOfTransparencyClipBox, paintBehavior), paintDirtyRect);
}

void RenderLayer::beginTransparencyLayers(GraphicsContext* context, const LayerPaintingInfo& paintingInfo, const LayoutRect& dirtyRect)
{
    if (context->paintingDisabled() || (paintsWithTransparency(paintingInfo.paintBehavior) && m_usedTransparency))
        return;

    RenderLayer* ancestor = transparentPaintingAncestor();
    if (ancestor)
        ancestor->beginTransparencyLayers(context, paintingInfo, dirtyRect);
    
    if (paintsWithTransparency(paintingInfo.paintBehavior)) {
        m_usedTransparency = true;
        context->save();
        LayoutRect adjustedClipRect = paintingExtent(*this, paintingInfo.rootLayer, dirtyRect, paintingInfo.paintBehavior);
        adjustedClipRect.move(paintingInfo.subpixelAccumulation);
        FloatRect pixelSnappedClipRect = snapRectToDevicePixels(adjustedClipRect, renderer().document().deviceScaleFactor());
        context->clip(pixelSnappedClipRect);

#if ENABLE(CSS_COMPOSITING)
        if (hasBlendMode())
            context->setCompositeOperation(context->compositeOperation(), blendMode());
#endif

        context->beginTransparencyLayer(renderer().opacity());

#if ENABLE(CSS_COMPOSITING)
        if (hasBlendMode())
            context->setCompositeOperation(context->compositeOperation(), BlendModeNormal);
#endif

#ifdef REVEAL_TRANSPARENCY_LAYERS
        context->setFillColor(Color(0.0f, 0.0f, 0.5f, 0.2f), ColorSpaceDeviceRGB);
        context->fillRect(pixelSnappedClipRect);
#endif
    }
}

#if PLATFORM(IOS)
void RenderLayer::willBeDestroyed()
{
    if (RenderLayerBacking* layerBacking = backing())
        layerBacking->layerWillBeDestroyed();
}
#endif

void RenderLayer::addChild(RenderLayer* child, RenderLayer* beforeChild)
{
    RenderLayer* prevSibling = beforeChild ? beforeChild->previousSibling() : lastChild();
    if (prevSibling) {
        child->setPreviousSibling(prevSibling);
        prevSibling->setNextSibling(child);
        ASSERT(prevSibling != child);
    } else
        setFirstChild(child);

    if (beforeChild) {
        beforeChild->setPreviousSibling(child);
        child->setNextSibling(beforeChild);
        ASSERT(beforeChild != child);
    } else
        setLastChild(child);

    child->setParent(this);

    if (child->isNormalFlowOnly())
        dirtyNormalFlowList();

    if (!child->isNormalFlowOnly() || child->firstChild()) {
        // Dirty the z-order list in which we are contained. The stackingContainer() can be null in the
        // case where we're building up generated content layers. This is ok, since the lists will start
        // off dirty in that case anyway.
        child->dirtyStackingContainerZOrderLists();
    }

    child->updateDescendantDependentFlags();
    if (child->m_hasVisibleContent || child->m_hasVisibleDescendant)
        setAncestorChainHasVisibleDescendant();

    if (child->isSelfPaintingLayer() || child->hasSelfPaintingLayerDescendant())
        setAncestorChainHasSelfPaintingLayerDescendant();

    if (child->renderer().isOutOfFlowPositioned() || child->hasOutOfFlowPositionedDescendant())
        setAncestorChainHasOutOfFlowPositionedDescendant(child->renderer().containingBlock());

#if ENABLE(CSS_COMPOSITING)
    if (child->hasBlendMode() || (child->hasNotIsolatedBlendingDescendants() && !child->isolatesBlending()))
        updateAncestorChainHasBlendingDescendants();
#endif

    compositor().layerWasAdded(*this, *child);
}

RenderLayer* RenderLayer::removeChild(RenderLayer* oldChild)
{
    if (!renderer().documentBeingDestroyed())
        compositor().layerWillBeRemoved(*this, *oldChild);

    // remove the child
    if (oldChild->previousSibling())
        oldChild->previousSibling()->setNextSibling(oldChild->nextSibling());
    if (oldChild->nextSibling())
        oldChild->nextSibling()->setPreviousSibling(oldChild->previousSibling());

    if (m_first == oldChild)
        m_first = oldChild->nextSibling();
    if (m_last == oldChild)
        m_last = oldChild->previousSibling();

    if (oldChild->isNormalFlowOnly())
        dirtyNormalFlowList();
    if (!oldChild->isNormalFlowOnly() || oldChild->firstChild()) { 
        // Dirty the z-order list in which we are contained.  When called via the
        // reattachment process in removeOnlyThisLayer, the layer may already be disconnected
        // from the main layer tree, so we need to null-check the |stackingContainer| value.
        oldChild->dirtyStackingContainerZOrderLists();
    }

    if (oldChild->renderer().isOutOfFlowPositioned() || oldChild->hasOutOfFlowPositionedDescendant())
        dirtyAncestorChainHasOutOfFlowPositionedDescendantStatus();

    oldChild->setPreviousSibling(0);
    oldChild->setNextSibling(0);
    oldChild->setParent(0);
    
    oldChild->updateDescendantDependentFlags();
    if (oldChild->m_hasVisibleContent || oldChild->m_hasVisibleDescendant)
        dirtyAncestorChainVisibleDescendantStatus();

    if (oldChild->isSelfPaintingLayer() || oldChild->hasSelfPaintingLayerDescendant())
        dirtyAncestorChainHasSelfPaintingLayerDescendantStatus();

#if ENABLE(CSS_COMPOSITING)
    if (oldChild->hasBlendMode() || (oldChild->hasNotIsolatedBlendingDescendants() && !oldChild->isolatesBlending()))
        dirtyAncestorChainHasBlendingDescendants();
#endif

    return oldChild;
}

void RenderLayer::removeOnlyThisLayer()
{
    if (!m_parent)
        return;

    // Mark that we are about to lose our layer. This makes render tree
    // walks ignore this layer while we're removing it.
    renderer().setHasLayer(false);

    compositor().layerWillBeRemoved(*m_parent, *this);

    // Dirty the clip rects.
    clearClipRectsIncludingDescendants();

    RenderLayer* nextSib = nextSibling();

    // Remove the child reflection layer before moving other child layers.
    // The reflection layer should not be moved to the parent.
    if (reflection())
        removeChild(reflectionLayer());

    // Now walk our kids and reattach them to our parent.
    RenderLayer* current = m_first;
    while (current) {
        RenderLayer* next = current->nextSibling();
        removeChild(current);
        m_parent->addChild(current, nextSib);
        current->setRepaintStatus(NeedsFullRepaint);
        // updateLayerPositions depends on hasLayer() already being false for proper layout.
        ASSERT(!renderer().hasLayer());
        current->updateLayerPositions(0); // FIXME: use geometry map.
        current = next;
    }

    // Remove us from the parent.
    m_parent->removeChild(this);
    renderer().destroyLayer();
}

void RenderLayer::insertOnlyThisLayer()
{
    if (!m_parent && renderer().parent()) {
        // We need to connect ourselves when our renderer() has a parent.
        // Find our enclosingLayer and add ourselves.
        RenderLayer* parentLayer = renderer().parent()->enclosingLayer();
        ASSERT(parentLayer);
        RenderLayer* beforeChild = parentLayer->reflectionLayer() != this ? renderer().parent()->findNextLayer(parentLayer, &renderer()) : 0;
        parentLayer->addChild(this, beforeChild);
    }

    // Remove all descendant layers from the hierarchy and add them to the new position.
    for (auto& child : childrenOfType<RenderElement>(renderer()))
        child.moveLayers(m_parent, this);

    // Clear out all the clip rects.
    clearClipRectsIncludingDescendants();
}

void RenderLayer::convertToPixelSnappedLayerCoords(const RenderLayer* ancestorLayer, IntPoint& roundedLocation, ColumnOffsetAdjustment adjustForColumns) const
{
    LayoutPoint location = convertToLayerCoords(ancestorLayer, roundedLocation, adjustForColumns);
    roundedLocation = roundedIntPoint(location);
}

// Returns the layer reached on the walk up towards the ancestor.
static inline const RenderLayer* accumulateOffsetTowardsAncestor(const RenderLayer* layer, const RenderLayer* ancestorLayer, LayoutPoint& location, RenderLayer::ColumnOffsetAdjustment adjustForColumns)
{
    ASSERT(ancestorLayer != layer);

    const RenderLayerModelObject& renderer = layer->renderer();
    EPosition position = renderer.style().position();

    // FIXME: Special casing RenderFlowThread so much for fixed positioning here is not great.
    RenderFlowThread* fixedFlowThreadContainer = position == FixedPosition ? renderer.flowThreadContainingBlock() : 0;
    if (fixedFlowThreadContainer && !fixedFlowThreadContainer->isOutOfFlowPositioned())
        fixedFlowThreadContainer = nullptr;

    // FIXME: Positioning of out-of-flow(fixed, absolute) elements collected in a RenderFlowThread
    // may need to be revisited in a future patch.
    // If the fixed renderer is inside a RenderFlowThread, we should not compute location using localToAbsolute,
    // since localToAbsolute maps the coordinates from named flow to regions coordinates and regions can be
    // positioned in a completely different place in the viewport (RenderView).
    if (position == FixedPosition && !fixedFlowThreadContainer && (!ancestorLayer || ancestorLayer == renderer.view().layer())) {
        // If the fixed layer's container is the root, just add in the offset of the view. We can obtain this by calling
        // localToAbsolute() on the RenderView.
        FloatPoint absPos = renderer.localToAbsolute(FloatPoint(), IsFixed);
        location += LayoutSize(absPos.x(), absPos.y());
        return ancestorLayer;
    }

    // For the fixed positioned elements inside a render flow thread, we should also skip the code path below
    // Otherwise, for the case of ancestorLayer == rootLayer and fixed positioned element child of a transformed
    // element in render flow thread, we will hit the fixed positioned container before hitting the ancestor layer.
    if (position == FixedPosition && !fixedFlowThreadContainer) {
        // For a fixed layers, we need to walk up to the root to see if there's a fixed position container
        // (e.g. a transformed layer). It's an error to call offsetFromAncestor() across a layer with a transform,
        // so we should always find the ancestor at or before we find the fixed position container.
        RenderLayer* fixedPositionContainerLayer = nullptr;
        bool foundAncestor = false;
        for (RenderLayer* currLayer = layer->parent(); currLayer; currLayer = currLayer->parent()) {
            if (currLayer == ancestorLayer)
                foundAncestor = true;

            if (isFixedPositionedContainer(currLayer)) {
                fixedPositionContainerLayer = currLayer;
                ASSERT_UNUSED(foundAncestor, foundAncestor);
                break;
            }
        }
        
        ASSERT(fixedPositionContainerLayer); // We should have hit the RenderView's layer at least.

        if (fixedPositionContainerLayer != ancestorLayer) {
            LayoutSize fixedContainerCoords = layer->offsetFromAncestor(fixedPositionContainerLayer);
            LayoutSize ancestorCoords = ancestorLayer->offsetFromAncestor(fixedPositionContainerLayer);
            location += (fixedContainerCoords - ancestorCoords);
            return ancestorLayer;
        }
    }

    if (position == FixedPosition && fixedFlowThreadContainer) {
        ASSERT(ancestorLayer);
        if (ancestorLayer->isOutOfFlowRenderFlowThread()) {
            location += toLayoutSize(layer->location());
            return ancestorLayer;
        }

        if (ancestorLayer == renderer.view().layer()) {
            // Add location in flow thread coordinates.
            location += toLayoutSize(layer->location());

            // Add flow thread offset in view coordinates since the view may be scrolled.
            FloatPoint absPos = renderer.view().localToAbsolute(FloatPoint(), IsFixed);
            location += LayoutSize(absPos.x(), absPos.y());
            return ancestorLayer;
        }
    }

    RenderLayer* parentLayer;
    if (position == AbsolutePosition || position == FixedPosition) {
        // Do what enclosingPositionedAncestor() does, but check for ancestorLayer along the way.
        parentLayer = layer->parent();
        bool foundAncestorFirst = false;
        while (parentLayer) {
            // RenderFlowThread is a positioned container, child of RenderView, positioned at (0,0).
            // This implies that, for out-of-flow positioned elements inside a RenderFlowThread,
            // we are bailing out before reaching root layer.
            if (isPositionedContainer(parentLayer))
                break;

            if (parentLayer == ancestorLayer) {
                foundAncestorFirst = true;
                break;
            }

            parentLayer = parentLayer->parent();
        }

        // We should not reach RenderView layer past the RenderFlowThread layer for any
        // children of the RenderFlowThread.
        if (renderer.flowThreadContainingBlock() && !layer->isOutOfFlowRenderFlowThread())
            ASSERT(parentLayer != renderer.view().layer());

        if (foundAncestorFirst) {
            // Found ancestorLayer before the abs. positioned container, so compute offset of both relative
            // to enclosingPositionedAncestor and subtract.
            RenderLayer* positionedAncestor = parentLayer->enclosingPositionedAncestor();
            LayoutSize thisCoords = layer->offsetFromAncestor(positionedAncestor);
            LayoutSize ancestorCoords = ancestorLayer->offsetFromAncestor(positionedAncestor);
            location += (thisCoords - ancestorCoords);
            return ancestorLayer;
        }
    } else
        parentLayer = layer->parent();
    
    if (!parentLayer)
        return 0;

    location += toLayoutSize(layer->location());

    if (adjustForColumns == RenderLayer::AdjustForColumns) {
        if (RenderLayer* parentLayer = layer->parent()) {
            if (is<RenderMultiColumnFlowThread>(parentLayer->renderer())) {
                RenderRegion* region = downcast<RenderMultiColumnFlowThread>(parentLayer->renderer()).physicalTranslationFromFlowToRegion(location);
                if (region)
                    location.moveBy(region->topLeftLocation() + -parentLayer->renderBox()->topLeftLocation());
            }
        }
    }

    return parentLayer;
}

LayoutPoint RenderLayer::convertToLayerCoords(const RenderLayer* ancestorLayer, const LayoutPoint& location, ColumnOffsetAdjustment adjustForColumns) const
{
    if (ancestorLayer == this)
        return location;

    const RenderLayer* currLayer = this;
    LayoutPoint locationInLayerCoords = location;
    while (currLayer && currLayer != ancestorLayer)
        currLayer = accumulateOffsetTowardsAncestor(currLayer, ancestorLayer, locationInLayerCoords, adjustForColumns);
    return locationInLayerCoords;
}

LayoutSize RenderLayer::offsetFromAncestor(const RenderLayer* ancestorLayer) const
{
    return toLayoutSize(convertToLayerCoords(ancestorLayer, LayoutPoint()));
}

#if PLATFORM(IOS)
bool RenderLayer::hasAcceleratedTouchScrolling() const
{
#if ENABLE(ACCELERATED_OVERFLOW_SCROLLING)
    if (!scrollsOverflow())
        return false;

    Settings* settings = renderer().document().settings();
    // FIXME: settings should not be null at this point. If you find a reliable way to hit this assertion, please file a bug.
    // See <rdar://problem/10266101>.
    ASSERT(settings);

    return renderer().style().useTouchOverflowScrolling() || (settings && settings->alwaysUseAcceleratedOverflowScroll());
#else
    return false;
#endif
}

bool RenderLayer::hasTouchScrollableOverflow() const
{
    return hasAcceleratedTouchScrolling() && (hasScrollableHorizontalOverflow() || hasScrollableVerticalOverflow());
}

#if ENABLE(TOUCH_EVENTS)
bool RenderLayer::handleTouchEvent(const PlatformTouchEvent& touchEvent)
{
    // If we have accelerated scrolling, let the scrolling be handled outside of WebKit.
    if (hasTouchScrollableOverflow())
        return false;

    return ScrollableArea::handleTouchEvent(touchEvent);
}
#endif
#endif // PLATFORM(IOS)

#if ENABLE(IOS_TOUCH_EVENTS)
void RenderLayer::registerAsTouchEventListenerForScrolling()
{
    if (!renderer().element() || m_registeredAsTouchEventListenerForScrolling)
        return;
    
    renderer().document().addTouchEventListener(renderer().element());
    m_registeredAsTouchEventListenerForScrolling = true;
}

void RenderLayer::unregisterAsTouchEventListenerForScrolling()
{
    if (!renderer().element() || !m_registeredAsTouchEventListenerForScrolling)
        return;

    renderer().document().removeTouchEventListener(renderer().element());
    m_registeredAsTouchEventListenerForScrolling = false;
}
#endif // ENABLE(IOS_TOUCH_EVENTS)

bool RenderLayer::usesCompositedScrolling() const
{
    return isComposited() && backing()->scrollingLayer();
}

bool RenderLayer::needsCompositedScrolling() const
{
    return m_needsCompositedScrolling;
}

void RenderLayer::updateNeedsCompositedScrolling()
{
    bool oldNeedsCompositedScrolling = m_needsCompositedScrolling;

    if (!renderer().view().frameView().containsScrollableArea(this))
        m_needsCompositedScrolling = false;
    else {
        bool forceUseCompositedScrolling = acceleratedCompositingForOverflowScrollEnabled()
            && canBeStackingContainer()
            && !hasOutOfFlowPositionedDescendant();

#if !PLATFORM(IOS) && ENABLE(ACCELERATED_OVERFLOW_SCROLLING)
        m_needsCompositedScrolling = forceUseCompositedScrolling || renderer().style().useTouchOverflowScrolling();
#else
        // On iOS we don't want to opt into accelerated composited scrolling, which creates scroll bar
        // layers in WebCore, because we use UIKit to composite our scroll bars.
        m_needsCompositedScrolling = forceUseCompositedScrolling;
#endif
    }

    if (oldNeedsCompositedScrolling != m_needsCompositedScrolling) {
        updateSelfPaintingLayer();
        if (isStackingContainer())
            dirtyZOrderLists();
        else
            clearZOrderLists();

        dirtyStackingContainerZOrderLists();

        compositor().setShouldReevaluateCompositingAfterLayout();
        compositor().setCompositingLayersNeedRebuild();
    }
}

static inline int adjustedScrollDelta(int beginningDelta) {
    // This implemention matches Firefox's.
    // http://mxr.mozilla.org/firefox/source/toolkit/content/widgets/browser.xml#856.
    const int speedReducer = 12;

    int adjustedDelta = beginningDelta / speedReducer;
    if (adjustedDelta > 1)
        adjustedDelta = static_cast<int>(adjustedDelta * sqrt(static_cast<double>(adjustedDelta))) - 1;
    else if (adjustedDelta < -1)
        adjustedDelta = static_cast<int>(adjustedDelta * sqrt(static_cast<double>(-adjustedDelta))) + 1;

    return adjustedDelta;
}

static inline IntSize adjustedScrollDelta(const IntSize& delta)
{
    return IntSize(adjustedScrollDelta(delta.width()), adjustedScrollDelta(delta.height()));
}

void RenderLayer::panScrollFromPoint(const IntPoint& sourcePoint)
{
    IntPoint lastKnownMousePosition = renderer().frame().eventHandler().lastKnownMousePosition();
    
    // We need to check if the last known mouse position is out of the window. When the mouse is out of the window, the position is incoherent
    static IntPoint previousMousePosition;
    if (lastKnownMousePosition.x() < 0 || lastKnownMousePosition.y() < 0)
        lastKnownMousePosition = previousMousePosition;
    else
        previousMousePosition = lastKnownMousePosition;

    IntSize delta = lastKnownMousePosition - sourcePoint;

    if (abs(delta.width()) <= ScrollView::noPanScrollRadius) // at the center we let the space for the icon
        delta.setWidth(0);
    if (abs(delta.height()) <= ScrollView::noPanScrollRadius)
        delta.setHeight(0);

    scrollByRecursively(adjustedScrollDelta(delta), ScrollOffsetClamped);
}

void RenderLayer::scrollByRecursively(const IntSize& delta, ScrollOffsetClamping clamp, ScrollableArea** scrolledArea)
{
    if (delta.isZero())
        return;

    bool restrictedByLineClamp = false;
    if (renderer().parent())
        restrictedByLineClamp = !renderer().parent()->style().lineClamp().isNone();

    if (renderer().hasOverflowClip() && !restrictedByLineClamp) {
        IntSize newScrollOffset = scrollOffset() + delta;
        scrollToOffset(newScrollOffset, clamp);
        if (scrolledArea)
            *scrolledArea = this;

        // If this layer can't do the scroll we ask the next layer up that can scroll to try
        IntSize remainingScrollOffset = newScrollOffset - scrollOffset();
        if (!remainingScrollOffset.isZero() && renderer().parent()) {
            if (RenderLayer* scrollableLayer = enclosingScrollableLayer())
                scrollableLayer->scrollByRecursively(remainingScrollOffset, clamp, scrolledArea);

            renderer().frame().eventHandler().updateAutoscrollRenderer();
        }
    } else {
        // If we are here, we were called on a renderer that can be programmatically scrolled, but doesn't
        // have an overflow clip. Which means that it is a document node that can be scrolled.
        renderer().view().frameView().scrollBy(delta);
        if (scrolledArea)
            *scrolledArea = &renderer().view().frameView();

        // FIXME: If we didn't scroll the whole way, do we want to try looking at the frames ownerElement? 
        // https://bugs.webkit.org/show_bug.cgi?id=28237
    }
}

IntSize RenderLayer::clampScrollOffset(const IntSize& scrollOffset) const
{
    RenderBox* box = renderBox();
    ASSERT(box);

    int maxX = scrollWidth() - box->pixelSnappedClientWidth();
    int maxY = scrollHeight() - box->pixelSnappedClientHeight();

    int x = std::max(std::min(scrollOffset.width(), maxX), 0);
    int y = std::max(std::min(scrollOffset.height(), maxY), 0);
    return IntSize(x, y);
}

void RenderLayer::scrollToOffset(const IntSize& scrollOffset, ScrollOffsetClamping clamp)
{
    IntSize newScrollOffset = clamp == ScrollOffsetClamped ? clampScrollOffset(scrollOffset) : scrollOffset;
    if (newScrollOffset != this->scrollOffset())
        scrollToOffsetWithoutAnimation(IntPoint(newScrollOffset));
}

void RenderLayer::scrollTo(int x, int y)
{
    RenderBox* box = renderBox();
    if (!box)
        return;

    if (box->style().overflowX() != OMARQUEE) {
        // Ensure that the dimensions will be computed if they need to be (for overflow:hidden blocks).
        if (m_scrollDimensionsDirty)
            computeScrollDimensions();
#if PLATFORM(IOS)
        if (adjustForIOSCaretWhenScrolling()) {
            int maxX = scrollWidth() - box->clientWidth();
            if (x > maxX - caretWidth) {
                x += caretWidth;
                if (x <= caretWidth)
                    x = 0;
            } else if (x < m_scrollOffset.width() - caretWidth)
                x -= caretWidth;
        }
#endif
    }
    
    // FIXME: Eventually, we will want to perform a blit.  For now never
    // blit, since the check for blitting is going to be very
    // complicated (since it will involve testing whether our layer
    // is either occluded by another layer or clipped by an enclosing
    // layer or contains fixed backgrounds, etc.).
    IntSize newScrollOffset = IntSize(x - scrollOrigin().x(), y - scrollOrigin().y());
    if (m_scrollOffset == newScrollOffset) {
#if PLATFORM(IOS)
        if (m_requiresScrollBoundsOriginUpdate)
            updateCompositingLayersAfterScroll();
#endif
        return;
    }
    
    IntPoint oldPosition = IntPoint(m_scrollOffset);
    m_scrollOffset = newScrollOffset;

    InspectorInstrumentation::willScrollLayer(&renderer().frame());

    RenderView& view = renderer().view();

    // Update the positions of our child layers (if needed as only fixed layers should be impacted by a scroll).
    // We don't update compositing layers, because we need to do a deep update from the compositing ancestor.
    bool inLayout = view.frameView().isInLayout();
    if (!inLayout) {
        // If we're in the middle of layout, we'll just update layers once layout has finished.
        updateLayerPositionsAfterOverflowScroll();
        // Update regions, scrolling may change the clip of a particular region.
#if ENABLE(DASHBOARD_SUPPORT)
        view.frameView().updateAnnotatedRegions();
#endif
        view.frameView().updateWidgetPositions();

        if (!m_updatingMarqueePosition) {
            // Avoid updating compositing layers if, higher on the stack, we're already updating layer
            // positions. Updating layer positions requires a full walk of up-to-date RenderLayers, and
            // in this case we're still updating their positions; we'll update compositing layers later
            // when that completes.
            updateCompositingLayersAfterScroll();
        }

#if PLATFORM(IOS) && ENABLE(TOUCH_EVENTS)
        renderer().document().dirtyTouchEventRects();
#endif
    }

    Frame& frame = renderer().frame();
    RenderLayerModelObject* repaintContainer = renderer().containerForRepaint();
    // The caret rect needs to be invalidated after scrolling
    frame.selection().setCaretRectNeedsUpdate();

    FloatQuad quadForFakeMouseMoveEvent = FloatQuad(m_repaintRect);
    if (repaintContainer)
        quadForFakeMouseMoveEvent = repaintContainer->localToAbsoluteQuad(quadForFakeMouseMoveEvent);
    frame.eventHandler().dispatchFakeMouseMoveEventSoonInQuad(quadForFakeMouseMoveEvent);

    bool requiresRepaint = true;
    if (compositor().inCompositingMode() && usesCompositedScrolling())
        requiresRepaint = false;

    // Just schedule a full repaint of our object.
    if (requiresRepaint)
        renderer().repaintUsingContainer(repaintContainer, m_repaintRect);

    // Schedule the scroll and scroll-related DOM events.
    if (Element* element = renderer().element()) {
        element->document().eventQueue().enqueueOrDispatchScrollEvent(*element);
        element->document().sendWillRevealEdgeEventsIfNeeded(oldPosition, IntPoint(newScrollOffset), visibleContentRect(), contentsSize(), element);
    }

    InspectorInstrumentation::didScrollLayer(&frame);
    if (scrollsOverflow())
        view.frameView().didChangeScrollOffset();

    view.frameView().resumeVisibleImageAnimationsIncludingSubframes();
}

static inline bool frameElementAndViewPermitScroll(HTMLFrameElementBase* frameElementBase, FrameView* frameView) 
{
    // If scrollbars aren't explicitly forbidden, permit scrolling.
    if (frameElementBase && frameElementBase->scrollingMode() != ScrollbarAlwaysOff)
        return true;

    // If scrollbars are forbidden, user initiated scrolls should obviously be ignored.
    if (frameView->wasScrolledByUser())
        return false;

    // Forbid autoscrolls when scrollbars are off, but permits other programmatic scrolls,
    // like navigation to an anchor.
    return !frameView->frame().eventHandler().autoscrollInProgress();
}

void RenderLayer::scrollRectToVisible(const LayoutRect& rect, const ScrollAlignment& alignX, const ScrollAlignment& alignY)
{
    RenderLayer* parentLayer = nullptr;
    LayoutRect newRect = rect;

    // We may end up propagating a scroll event. It is important that we suspend events until 
    // the end of the function since they could delete the layer or the layer's renderer().
    FrameView& frameView = renderer().view().frameView();

    bool restrictedByLineClamp = false;
    if (renderer().parent()) {
        parentLayer = renderer().parent()->enclosingLayer();
        restrictedByLineClamp = !renderer().parent()->style().lineClamp().isNone();
    }

    if (renderer().hasOverflowClip() && !restrictedByLineClamp) {
        // Don't scroll to reveal an overflow layer that is restricted by the -webkit-line-clamp property.
        // This will prevent us from revealing text hidden by the slider in Safari RSS.
        RenderBox* box = renderBox();
        ASSERT(box);
        LayoutRect localExposeRect(box->absoluteToLocalQuad(FloatQuad(FloatRect(rect)), UseTransforms).boundingBox());
        LayoutRect layerBounds(0, 0, box->clientWidth(), box->clientHeight());
        LayoutRect r = getRectToExpose(layerBounds, layerBounds, localExposeRect, alignX, alignY);

        IntSize clampedScrollOffset = clampScrollOffset(scrollOffset() + toIntSize(roundedIntRect(r).location()));
        if (clampedScrollOffset != scrollOffset()) {
            IntSize oldScrollOffset = scrollOffset();
            scrollToOffset(clampedScrollOffset);
            IntSize scrollOffsetDifference = scrollOffset() - oldScrollOffset;
            localExposeRect.move(-scrollOffsetDifference);
            newRect = LayoutRect(box->localToAbsoluteQuad(FloatQuad(FloatRect(localExposeRect)), UseTransforms).boundingBox());
        }
    } else if (!parentLayer && renderer().isBox() && renderBox()->canBeProgramaticallyScrolled()) {
        HTMLFrameOwnerElement* ownerElement = renderer().document().ownerElement();

        if (ownerElement && ownerElement->renderer()) {
            HTMLFrameElementBase* frameElementBase = nullptr;

            if (is<HTMLFrameElementBase>(*ownerElement))
                frameElementBase = downcast<HTMLFrameElementBase>(ownerElement);

            if (frameElementAndViewPermitScroll(frameElementBase, &frameView)) {
                LayoutRect viewRect = frameView.visibleContentRect(LegacyIOSDocumentVisibleRect);
                LayoutRect exposeRect = getRectToExpose(viewRect, viewRect, rect, alignX, alignY);

                int xOffset = roundToInt(exposeRect.x());
                int yOffset = roundToInt(exposeRect.y());
                // Adjust offsets if they're outside of the allowable range.
                xOffset = std::max(0, std::min(frameView.contentsWidth(), xOffset));
                yOffset = std::max(0, std::min(frameView.contentsHeight(), yOffset));

                frameView.setScrollPosition(IntPoint(xOffset, yOffset));
                if (frameView.safeToPropagateScrollToParent()) {
                    parentLayer = ownerElement->renderer()->enclosingLayer();
                    // FIXME: This doesn't correctly convert the rect to
                    // absolute coordinates in the parent.
                    newRect.setX(rect.x() - frameView.scrollX() + frameView.x());
                    newRect.setY(rect.y() - frameView.scrollY() + frameView.y());
                } else
                    parentLayer = nullptr;
            }
        } else {
#if !PLATFORM(IOS)
            LayoutRect viewRect = frameView.visibleContentRect();
            LayoutRect visibleRectRelativeToDocument = viewRect;
            IntSize documentScrollOffsetRelativeToScrollableAreaOrigin = frameView.documentScrollOffsetRelativeToScrollableAreaOrigin();
            visibleRectRelativeToDocument.setLocation(IntPoint(documentScrollOffsetRelativeToScrollableAreaOrigin.width(), documentScrollOffsetRelativeToScrollableAreaOrigin.height()));
#else
            LayoutRect viewRect = frameView.unobscuredContentRect();
            LayoutRect visibleRectRelativeToDocument = viewRect;
#endif

            LayoutRect r = getRectToExpose(viewRect, visibleRectRelativeToDocument, rect, alignX, alignY);
                
            frameView.setScrollPosition(roundedIntPoint(r.location()));

            // This is the outermost view of a web page, so after scrolling this view we
            // scroll its container by calling Page::scrollRectIntoView.
            // This only has an effect on the Mac platform in applications
            // that put web views into scrolling containers, such as Mac OS X Mail.
            // The canAutoscroll function in EventHandler also knows about this.
            if (Page* page = frameView.frame().page())
                page->chrome().scrollRectIntoView(snappedIntRect(rect));
        }
    }
    
    if (renderer().frame().eventHandler().autoscrollInProgress())
        parentLayer = enclosingScrollableLayer();

    if (parentLayer)
        parentLayer->scrollRectToVisible(newRect, alignX, alignY);
}

void RenderLayer::updateCompositingLayersAfterScroll()
{
    if (compositor().inCompositingMode()) {
        // Our stacking container is guaranteed to contain all of our descendants that may need
        // repositioning, so update compositing layers from there.
        if (RenderLayer* compositingAncestor = stackingContainer()->enclosingCompositingLayer()) {
            if (usesCompositedScrolling() && !hasOutOfFlowPositionedDescendant())
                compositor().updateCompositingLayers(CompositingUpdateOnCompositedScroll, compositingAncestor);
            else
                compositor().updateCompositingLayers(CompositingUpdateOnScroll, compositingAncestor);
        }
    }
}

LayoutRect RenderLayer::getRectToExpose(const LayoutRect &visibleRect, const LayoutRect &visibleRectRelativeToDocument, const LayoutRect &exposeRect, const ScrollAlignment& alignX, const ScrollAlignment& alignY)
{
    // Determine the appropriate X behavior.
    ScrollBehavior scrollX;
    LayoutRect exposeRectX(exposeRect.x(), visibleRect.y(), exposeRect.width(), visibleRect.height());
    LayoutUnit intersectWidth = intersection(visibleRect, exposeRectX).width();
    if (intersectWidth == exposeRect.width() || intersectWidth >= MIN_INTERSECT_FOR_REVEAL)
        // If the rectangle is fully visible, use the specified visible behavior.
        // If the rectangle is partially visible, but over a certain threshold,
        // then treat it as fully visible to avoid unnecessary horizontal scrolling
        scrollX = ScrollAlignment::getVisibleBehavior(alignX);
    else if (intersectWidth == visibleRect.width()) {
        // If the rect is bigger than the visible area, don't bother trying to center. Other alignments will work.
        scrollX = ScrollAlignment::getVisibleBehavior(alignX);
        if (scrollX == alignCenter)
            scrollX = noScroll;
    } else if (intersectWidth > 0)
        // If the rectangle is partially visible, but not above the minimum threshold, use the specified partial behavior
        scrollX = ScrollAlignment::getPartialBehavior(alignX);
    else
        scrollX = ScrollAlignment::getHiddenBehavior(alignX);
    // If we're trying to align to the closest edge, and the exposeRect is further right
    // than the visibleRect, and not bigger than the visible area, then align with the right.
    if (scrollX == alignToClosestEdge && exposeRect.maxX() > visibleRect.maxX() && exposeRect.width() < visibleRect.width())
        scrollX = alignRight;

    // Given the X behavior, compute the X coordinate.
    LayoutUnit x;
    if (scrollX == noScroll) 
        x = visibleRect.x();
    else if (scrollX == alignRight)
        x = exposeRect.maxX() - visibleRect.width();
    else if (scrollX == alignCenter)
        x = exposeRect.x() + (exposeRect.width() - visibleRect.width()) / 2;
    else
        x = exposeRect.x();

    // Determine the appropriate Y behavior.
    ScrollBehavior scrollY;
    LayoutRect exposeRectY(visibleRect.x(), exposeRect.y(), visibleRect.width(), exposeRect.height());
    LayoutUnit intersectHeight = intersection(visibleRectRelativeToDocument, exposeRectY).height();
    if (intersectHeight == exposeRect.height())
        // If the rectangle is fully visible, use the specified visible behavior.
        scrollY = ScrollAlignment::getVisibleBehavior(alignY);
    else if (intersectHeight == visibleRect.height()) {
        // If the rect is bigger than the visible area, don't bother trying to center. Other alignments will work.
        scrollY = ScrollAlignment::getVisibleBehavior(alignY);
        if (scrollY == alignCenter)
            scrollY = noScroll;
    } else if (intersectHeight > 0)
        // If the rectangle is partially visible, use the specified partial behavior
        scrollY = ScrollAlignment::getPartialBehavior(alignY);
    else
        scrollY = ScrollAlignment::getHiddenBehavior(alignY);
    // If we're trying to align to the closest edge, and the exposeRect is further down
    // than the visibleRect, and not bigger than the visible area, then align with the bottom.
    if (scrollY == alignToClosestEdge && exposeRect.maxY() > visibleRect.maxY() && exposeRect.height() < visibleRect.height())
        scrollY = alignBottom;

    // Given the Y behavior, compute the Y coordinate.
    LayoutUnit y;
    if (scrollY == noScroll) 
        y = visibleRect.y();
    else if (scrollY == alignBottom)
        y = exposeRect.maxY() - visibleRect.height();
    else if (scrollY == alignCenter)
        y = exposeRect.y() + (exposeRect.height() - visibleRect.height()) / 2;
    else
        y = exposeRect.y();

    return LayoutRect(LayoutPoint(x, y), visibleRect.size());
}

void RenderLayer::autoscroll(const IntPoint& position)
{
    IntPoint currentDocumentPosition = renderer().view().frameView().windowToContents(position);
    scrollRectToVisible(LayoutRect(currentDocumentPosition, LayoutSize(1, 1)), ScrollAlignment::alignToEdgeIfNeeded, ScrollAlignment::alignToEdgeIfNeeded);
}

bool RenderLayer::canResize() const
{
    // We need a special case for <iframe> because they never have
    // hasOverflowClip(). However, they do "implicitly" clip their contents, so
    // we want to allow resizing them also.
    return (renderer().hasOverflowClip() || renderer().isRenderIFrame()) && renderer().style().resize() != RESIZE_NONE;
}

void RenderLayer::resize(const PlatformMouseEvent& evt, const LayoutSize& oldOffset)
{
    // FIXME: This should be possible on generated content but is not right now.
    if (!inResizeMode() || !canResize() || !renderer().element())
        return;

    // FIXME: The only case where renderer->element()->renderer() != renderer is with continuations. Do they matter here?
    // If they do it would still be better to deal with them explicitly.
    Element* element = renderer().element();
    auto* renderer = downcast<RenderBox>(element->renderer());

    Document& document = element->document();
    if (!document.frame()->eventHandler().mousePressed())
        return;

    float zoomFactor = renderer->style().effectiveZoom();

    LayoutSize newOffset = offsetFromResizeCorner(document.view()->windowToContents(evt.position()));
    newOffset.setWidth(newOffset.width() / zoomFactor);
    newOffset.setHeight(newOffset.height() / zoomFactor);
    
    LayoutSize currentSize = LayoutSize(renderer->width() / zoomFactor, renderer->height() / zoomFactor);
    LayoutSize minimumSize = element->minimumSizeForResizing().shrunkTo(currentSize);
    element->setMinimumSizeForResizing(minimumSize);
    
    LayoutSize adjustedOldOffset = LayoutSize(oldOffset.width() / zoomFactor, oldOffset.height() / zoomFactor);
    if (renderer->style().shouldPlaceBlockDirectionScrollbarOnLogicalLeft()) {
        newOffset.setWidth(-newOffset.width());
        adjustedOldOffset.setWidth(-adjustedOldOffset.width());
    }
    
    LayoutSize difference = (currentSize + newOffset - adjustedOldOffset).expandedTo(minimumSize) - currentSize;

    StyledElement* styledElement = downcast<StyledElement>(element);
    bool isBoxSizingBorder = renderer->style().boxSizing() == BORDER_BOX;

    EResize resize = renderer->style().resize();
    if (resize != RESIZE_VERTICAL && difference.width()) {
        if (is<HTMLFormControlElement>(*element)) {
            // Make implicit margins from the theme explicit (see <http://bugs.webkit.org/show_bug.cgi?id=9547>).
            styledElement->setInlineStyleProperty(CSSPropertyMarginLeft, renderer->marginLeft() / zoomFactor, CSSPrimitiveValue::CSS_PX);
            styledElement->setInlineStyleProperty(CSSPropertyMarginRight, renderer->marginRight() / zoomFactor, CSSPrimitiveValue::CSS_PX);
        }
        LayoutUnit baseWidth = renderer->width() - (isBoxSizingBorder ? LayoutUnit() : renderer->horizontalBorderAndPaddingExtent());
        baseWidth = baseWidth / zoomFactor;
        styledElement->setInlineStyleProperty(CSSPropertyWidth, roundToInt(baseWidth + difference.width()), CSSPrimitiveValue::CSS_PX);
    }

    if (resize != RESIZE_HORIZONTAL && difference.height()) {
        if (is<HTMLFormControlElement>(*element)) {
            // Make implicit margins from the theme explicit (see <http://bugs.webkit.org/show_bug.cgi?id=9547>).
            styledElement->setInlineStyleProperty(CSSPropertyMarginTop, renderer->marginTop() / zoomFactor, CSSPrimitiveValue::CSS_PX);
            styledElement->setInlineStyleProperty(CSSPropertyMarginBottom, renderer->marginBottom() / zoomFactor, CSSPrimitiveValue::CSS_PX);
        }
        LayoutUnit baseHeight = renderer->height() - (isBoxSizingBorder ? LayoutUnit() : renderer->verticalBorderAndPaddingExtent());
        baseHeight = baseHeight / zoomFactor;
        styledElement->setInlineStyleProperty(CSSPropertyHeight, roundToInt(baseHeight + difference.height()), CSSPrimitiveValue::CSS_PX);
    }

    document.updateLayout();

    // FIXME (Radar 4118564): We should also autoscroll the window as necessary to keep the point under the cursor in view.
}

int RenderLayer::scrollSize(ScrollbarOrientation orientation) const
{
    Scrollbar* scrollbar = ((orientation == HorizontalScrollbar) ? m_hBar : m_vBar).get();
    return scrollbar ? (scrollbar->totalSize() - scrollbar->visibleSize()) : 0;
}

void RenderLayer::setScrollOffset(const IntPoint& offset)
{
    scrollTo(offset.x(), offset.y());
}

int RenderLayer::scrollPosition(Scrollbar* scrollbar) const
{
    if (scrollbar->orientation() == HorizontalScrollbar)
        return scrollXOffset();
    if (scrollbar->orientation() == VerticalScrollbar)
        return scrollYOffset();
    return 0;
}

IntPoint RenderLayer::scrollPosition() const
{
    return IntPoint(m_scrollOffset);
}

IntPoint RenderLayer::minimumScrollPosition() const
{
    return -scrollOrigin();
}

IntPoint RenderLayer::maximumScrollPosition() const
{
    // FIXME: m_scrollSize may not be up-to-date if m_scrollDimensionsDirty is true.
    return -scrollOrigin() + roundedIntSize(m_scrollSize) - visibleContentRectIncludingScrollbars(ContentsVisibleRect).size();
}

IntRect RenderLayer::visibleContentRectInternal(VisibleContentRectIncludesScrollbars scrollbarInclusion, VisibleContentRectBehavior) const
{
    int verticalScrollbarWidth = 0;
    int horizontalScrollbarHeight = 0;
    if (showsOverflowControls() && scrollbarInclusion == IncludeScrollbars) {
        verticalScrollbarWidth = (verticalScrollbar() && !verticalScrollbar()->isOverlayScrollbar()) ? verticalScrollbar()->width() : 0;
        horizontalScrollbarHeight = (horizontalScrollbar() && !horizontalScrollbar()->isOverlayScrollbar()) ? horizontalScrollbar()->height() : 0;
    }
    
    return IntRect(scrollPosition(), IntSize(std::max(0, m_layerSize.width() - verticalScrollbarWidth), std::max(0, m_layerSize.height() - horizontalScrollbarHeight)));
}

IntSize RenderLayer::overhangAmount() const
{
#if ENABLE(RUBBER_BANDING)
    if (!renderer().frame().settings().rubberBandingForSubScrollableRegionsEnabled())
        return IntSize();

    IntSize stretch;

    int physicalScrollY = scrollPosition().y() + scrollOrigin().y();
    if (physicalScrollY < 0)
        stretch.setHeight(physicalScrollY);
    else if (scrollableContentsSize().height() && physicalScrollY > scrollableContentsSize().height() - visibleHeight())
        stretch.setHeight(physicalScrollY - (scrollableContentsSize().height() - visibleHeight()));

    int physicalScrollX = scrollPosition().x() + scrollOrigin().x();
    if (physicalScrollX < 0)
        stretch.setWidth(physicalScrollX);
    else if (scrollableContentsSize().width() && physicalScrollX > scrollableContentsSize().width() - visibleWidth())
        stretch.setWidth(physicalScrollX - (scrollableContentsSize().width() - visibleWidth()));

    return stretch;
#else
    return IntSize();
#endif
}

bool RenderLayer::isActive() const
{
    Page* page = renderer().frame().page();
    return page && page->focusController().isActive();
}

static int cornerStart(const RenderLayer* layer, int minX, int maxX, int thickness)
{
    if (layer->renderer().style().shouldPlaceBlockDirectionScrollbarOnLogicalLeft())
        return minX + layer->renderer().style().borderLeftWidth();
    return maxX - thickness - layer->renderer().style().borderRightWidth();
}

static LayoutRect cornerRect(const RenderLayer* layer, const LayoutRect& bounds)
{
    int horizontalThickness;
    int verticalThickness;
    if (!layer->verticalScrollbar() && !layer->horizontalScrollbar()) {
        // FIXME: This isn't right.  We need to know the thickness of custom scrollbars
        // even when they don't exist in order to set the resizer square size properly.
        horizontalThickness = ScrollbarTheme::theme()->scrollbarThickness();
        verticalThickness = horizontalThickness;
    } else if (layer->verticalScrollbar() && !layer->horizontalScrollbar()) {
        horizontalThickness = layer->verticalScrollbar()->width();
        verticalThickness = horizontalThickness;
    } else if (layer->horizontalScrollbar() && !layer->verticalScrollbar()) {
        verticalThickness = layer->horizontalScrollbar()->height();
        horizontalThickness = verticalThickness;
    } else {
        horizontalThickness = layer->verticalScrollbar()->width();
        verticalThickness = layer->horizontalScrollbar()->height();
    }
    return LayoutRect(cornerStart(layer, bounds.x(), bounds.maxX(), horizontalThickness),
        bounds.maxY() - verticalThickness - layer->renderer().style().borderBottomWidth(),
        horizontalThickness, verticalThickness);
}

IntRect RenderLayer::scrollCornerRect() const
{
    // We have a scrollbar corner when a scrollbar is visible and not filling the entire length of the box.
    // This happens when:
    // (a) A resizer is present and at least one scrollbar is present
    // (b) Both scrollbars are present.
    bool hasHorizontalBar = horizontalScrollbar();
    bool hasVerticalBar = verticalScrollbar();
    bool hasResizer = renderer().style().resize() != RESIZE_NONE;
    if ((hasHorizontalBar && hasVerticalBar) || (hasResizer && (hasHorizontalBar || hasVerticalBar)))
        return snappedIntRect(cornerRect(this, renderBox()->borderBoxRect()));
    return IntRect();
}

static LayoutRect resizerCornerRect(const RenderLayer* layer, const LayoutRect& bounds)
{
    ASSERT(layer->renderer().isBox());
    if (layer->renderer().style().resize() == RESIZE_NONE)
        return LayoutRect();
    return cornerRect(layer, bounds);
}

LayoutRect RenderLayer::scrollCornerAndResizerRect() const
{
    RenderBox* box = renderBox();
    if (!box)
        return LayoutRect();
    LayoutRect scrollCornerAndResizer = scrollCornerRect();
    if (scrollCornerAndResizer.isEmpty())
        scrollCornerAndResizer = resizerCornerRect(this, box->borderBoxRect());
    return scrollCornerAndResizer;
}

bool RenderLayer::isScrollCornerVisible() const
{
    ASSERT(renderer().isBox());
    return !scrollCornerRect().isEmpty();
}

IntRect RenderLayer::convertFromScrollbarToContainingView(const Scrollbar* scrollbar, const IntRect& scrollbarRect) const
{
    IntRect rect = scrollbarRect;
    rect.move(scrollbarOffset(scrollbar));

    return renderer().view().frameView().convertFromRendererToContainingView(&renderer(), rect);
}

IntRect RenderLayer::convertFromContainingViewToScrollbar(const Scrollbar* scrollbar, const IntRect& parentRect) const
{
    IntRect rect = renderer().view().frameView().convertFromContainingViewToRenderer(&renderer(), parentRect);
    rect.move(-scrollbarOffset(scrollbar));
    return rect;
}

IntPoint RenderLayer::convertFromScrollbarToContainingView(const Scrollbar* scrollbar, const IntPoint& scrollbarPoint) const
{
    IntPoint point = scrollbarPoint;
    point.move(scrollbarOffset(scrollbar));
    return renderer().view().frameView().convertFromRendererToContainingView(&renderer(), point);
}

IntPoint RenderLayer::convertFromContainingViewToScrollbar(const Scrollbar* scrollbar, const IntPoint& parentPoint) const
{
    IntPoint point = renderer().view().frameView().convertFromContainingViewToRenderer(&renderer(), parentPoint);
    point.move(-scrollbarOffset(scrollbar));
    return point;
}

IntSize RenderLayer::visibleSize() const
{
    if (!renderer().isBox())
        return IntSize();

    return IntSize(renderBox()->pixelSnappedClientWidth(), renderBox()->pixelSnappedClientHeight());
}

IntSize RenderLayer::contentsSize() const
{
    return IntSize(scrollWidth(), scrollHeight());
}

IntSize RenderLayer::scrollableContentsSize() const
{
    IntSize contentsSize = this->contentsSize();

    if (!hasScrollableHorizontalOverflow())
        contentsSize.setWidth(std::min(contentsSize.width(), visibleSize().width()));

    if (!hasScrollableVerticalOverflow())
        contentsSize.setHeight(std::min(contentsSize.height(), visibleSize().height()));

    return contentsSize;
}

bool RenderLayer::shouldSuspendScrollAnimations() const
{
    return renderer().view().frameView().shouldSuspendScrollAnimations();
}

#if PLATFORM(IOS)
void RenderLayer::didStartScroll()
{
    if (Page* page = renderer().frame().page())
        page->chrome().client().didStartOverflowScroll();
}

void RenderLayer::didEndScroll()
{
    if (Page* page = renderer().frame().page())
        page->chrome().client().didEndOverflowScroll();
}
    
void RenderLayer::didUpdateScroll()
{
    // Send this notification when we scroll, since this is how we keep selection updated.
    if (Page* page = renderer().frame().page())
        page->chrome().client().didLayout(ChromeClient::Scroll);
}
#endif

IntPoint RenderLayer::lastKnownMousePosition() const
{
    return renderer().frame().eventHandler().lastKnownMousePosition();
}

bool RenderLayer::isHandlingWheelEvent() const
{
    return renderer().frame().eventHandler().isHandlingWheelEvent();
}

IntRect RenderLayer::rectForHorizontalScrollbar(const IntRect& borderBoxRect) const
{
    if (!m_hBar)
        return IntRect();

    const RenderBox* box = renderBox();
    const IntRect& scrollCorner = scrollCornerRect();

    return IntRect(horizontalScrollbarStart(borderBoxRect.x()),
        borderBoxRect.maxY() - box->borderBottom() - m_hBar->height(),
        borderBoxRect.width() - (box->borderLeft() + box->borderRight()) - scrollCorner.width(),
        m_hBar->height());
}

IntRect RenderLayer::rectForVerticalScrollbar(const IntRect& borderBoxRect) const
{
    if (!m_vBar)
        return IntRect();

    const RenderBox* box = renderBox();
    const IntRect& scrollCorner = scrollCornerRect();

    return IntRect(verticalScrollbarStart(borderBoxRect.x(), borderBoxRect.maxX()),
        borderBoxRect.y() + box->borderTop(),
        m_vBar->width(),
        borderBoxRect.height() - (box->borderTop() + box->borderBottom()) - scrollCorner.height());
}

LayoutUnit RenderLayer::verticalScrollbarStart(int minX, int maxX) const
{
    const RenderBox* box = renderBox();
    if (renderer().style().shouldPlaceBlockDirectionScrollbarOnLogicalLeft())
        return minX + box->borderLeft();
    return maxX - box->borderRight() - m_vBar->width();
}

LayoutUnit RenderLayer::horizontalScrollbarStart(int minX) const
{
    const RenderBox* box = renderBox();
    int x = minX + box->borderLeft();
    if (renderer().style().shouldPlaceBlockDirectionScrollbarOnLogicalLeft())
        x += m_vBar ? m_vBar->width() : roundToInt(resizerCornerRect(this, box->borderBoxRect()).width());
    return x;
}

IntSize RenderLayer::scrollbarOffset(const Scrollbar* scrollbar) const
{
    RenderBox* box = renderBox();

    if (scrollbar == m_vBar.get())
        return IntSize(verticalScrollbarStart(0, box->width()), box->borderTop());

    if (scrollbar == m_hBar.get())
        return IntSize(horizontalScrollbarStart(0), box->height() - box->borderBottom() - scrollbar->height());
    
    ASSERT_NOT_REACHED();
    return IntSize();
}

void RenderLayer::invalidateScrollbarRect(Scrollbar* scrollbar, const IntRect& rect)
{
    if (!showsOverflowControls())
        return;

    if (scrollbar == m_vBar.get()) {
        if (GraphicsLayer* layer = layerForVerticalScrollbar()) {
            layer->setNeedsDisplayInRect(rect);
            return;
        }
    } else {
        if (GraphicsLayer* layer = layerForHorizontalScrollbar()) {
            layer->setNeedsDisplayInRect(rect);
            return;
        }
    }

    IntRect scrollRect = rect;
    RenderBox* box = renderBox();
    ASSERT(box);
    // If we are not yet inserted into the tree, there is no need to repaint.
    if (!box->parent())
        return;

    if (scrollbar == m_vBar.get())
        scrollRect.move(verticalScrollbarStart(0, box->width()), box->borderTop());
    else
        scrollRect.move(horizontalScrollbarStart(0), box->height() - box->borderBottom() - scrollbar->height());
    LayoutRect repaintRect = scrollRect;
    renderBox()->flipForWritingMode(repaintRect);
    renderer().repaintRectangle(repaintRect);
}

void RenderLayer::invalidateScrollCornerRect(const IntRect& rect)
{
    if (!showsOverflowControls())
        return;

    if (GraphicsLayer* layer = layerForScrollCorner()) {
        layer->setNeedsDisplayInRect(rect);
        return;
    }

    if (m_scrollCorner)
        m_scrollCorner->repaintRectangle(rect);
    if (m_resizer)
        m_resizer->repaintRectangle(rect);
}

static inline RenderElement* rendererForScrollbar(RenderLayerModelObject& renderer)
{
    if (Element* element = renderer.element()) {
        if (ShadowRoot* shadowRoot = element->containingShadowRoot()) {
            if (shadowRoot->type() == ShadowRoot::UserAgentShadowRoot)
                return shadowRoot->hostElement()->renderer();
        }
    }

    return &renderer;
}

PassRefPtr<Scrollbar> RenderLayer::createScrollbar(ScrollbarOrientation orientation)
{
    RefPtr<Scrollbar> widget;
    RenderElement* actualRenderer = rendererForScrollbar(renderer());
    bool hasCustomScrollbarStyle = actualRenderer->isBox() && actualRenderer->style().hasPseudoStyle(SCROLLBAR);
    if (hasCustomScrollbarStyle)
        widget = RenderScrollbar::createCustomScrollbar(this, orientation, actualRenderer->element());
    else {
        widget = Scrollbar::createNativeScrollbar(this, orientation, RegularScrollbar);
        didAddScrollbar(widget.get(), orientation);
    }
    renderer().view().frameView().addChild(widget.get());
    return widget.release();
}

void RenderLayer::destroyScrollbar(ScrollbarOrientation orientation)
{
    RefPtr<Scrollbar>& scrollbar = orientation == HorizontalScrollbar ? m_hBar : m_vBar;
    if (!scrollbar)
        return;

    if (!scrollbar->isCustomScrollbar())
        willRemoveScrollbar(scrollbar.get(), orientation);

    scrollbar->removeFromParent();
    scrollbar->disconnectFromScrollableArea();
    scrollbar = nullptr;
}

bool RenderLayer::scrollsOverflow() const
{
    if (!is<RenderBox>(renderer()))
        return false;

    return downcast<RenderBox>(renderer()).scrollsOverflow();
}

void RenderLayer::setHasHorizontalScrollbar(bool hasScrollbar)
{
    if (hasScrollbar == hasHorizontalScrollbar())
        return;

    if (hasScrollbar) {
        m_hBar = createScrollbar(HorizontalScrollbar);
#if ENABLE(RUBBER_BANDING)
        ScrollElasticity elasticity = scrollsOverflow() && renderer().frame().settings().rubberBandingForSubScrollableRegionsEnabled() ? ScrollElasticityAutomatic : ScrollElasticityNone;
        ScrollableArea::setHorizontalScrollElasticity(elasticity);
#endif
    } else {
        destroyScrollbar(HorizontalScrollbar);
#if ENABLE(RUBBER_BANDING)
        ScrollableArea::setHorizontalScrollElasticity(ScrollElasticityNone);
#endif
    }

    // Destroying or creating one bar can cause our scrollbar corner to come and go.  We need to update the opposite scrollbar's style.
    if (m_hBar)
        m_hBar->styleChanged();
    if (m_vBar)
        m_vBar->styleChanged();

    // Force an update since we know the scrollbars have changed things.
#if ENABLE(DASHBOARD_SUPPORT)
    if (renderer().document().hasAnnotatedRegions())
        renderer().document().setAnnotatedRegionsDirty(true);
#endif
}

void RenderLayer::setHasVerticalScrollbar(bool hasScrollbar)
{
    if (hasScrollbar == hasVerticalScrollbar())
        return;

    if (hasScrollbar) {
        m_vBar = createScrollbar(VerticalScrollbar);
#if ENABLE(RUBBER_BANDING)
        ScrollElasticity elasticity = scrollsOverflow() && renderer().frame().settings().rubberBandingForSubScrollableRegionsEnabled() ? ScrollElasticityAutomatic : ScrollElasticityNone;
        ScrollableArea::setVerticalScrollElasticity(elasticity);
#endif
    } else {
        destroyScrollbar(VerticalScrollbar);
#if ENABLE(RUBBER_BANDING)
        ScrollableArea::setVerticalScrollElasticity(ScrollElasticityNone);
#endif
    }

     // Destroying or creating one bar can cause our scrollbar corner to come and go.  We need to update the opposite scrollbar's style.
    if (m_hBar)
        m_hBar->styleChanged();
    if (m_vBar)
        m_vBar->styleChanged();

    // Force an update since we know the scrollbars have changed things.
#if ENABLE(DASHBOARD_SUPPORT)
    if (renderer().document().hasAnnotatedRegions())
        renderer().document().setAnnotatedRegionsDirty(true);
#endif
}

ScrollableArea* RenderLayer::enclosingScrollableArea() const
{
    if (RenderLayer* scrollableLayer = enclosingScrollableLayer())
        return scrollableLayer;

    // FIXME: We should return the frame view here (or possibly an ancestor frame view,
    // if the frame view isn't scrollable.
    return 0;
}

bool RenderLayer::isScrollableOrRubberbandable()
{
    return renderer().isScrollableOrRubberbandableBox();
}

bool RenderLayer::hasScrollableOrRubberbandableAncestor()
{
    for (RenderLayer* nextLayer = parentLayerCrossFrame(this); nextLayer; nextLayer = parentLayerCrossFrame(nextLayer)) {
        if (nextLayer->isScrollableOrRubberbandable())
            return true;
    }

    return false;
}

#if ENABLE(CSS_SCROLL_SNAP)
void RenderLayer::updateSnapOffsets()
{
    // FIXME: Extend support beyond HTMLElements.
    if (!is<HTMLElement>(enclosingElement()) || !enclosingElement()->renderBox())
        return;

    RenderBox* box = enclosingElement()->renderBox();
    updateSnapOffsetsForScrollableArea(*this, *downcast<HTMLElement>(enclosingElement()), *box, box->style());
}
#endif

int RenderLayer::verticalScrollbarWidth(OverlayScrollbarSizeRelevancy relevancy) const
{
    if (!m_vBar
        || !showsOverflowControls()
        || (m_vBar->isOverlayScrollbar() && (relevancy == IgnoreOverlayScrollbarSize || !m_vBar->shouldParticipateInHitTesting())))
        return 0;

    return m_vBar->width();
}

int RenderLayer::horizontalScrollbarHeight(OverlayScrollbarSizeRelevancy relevancy) const
{
    if (!m_hBar
        || !showsOverflowControls()
        || (m_hBar->isOverlayScrollbar() && (relevancy == IgnoreOverlayScrollbarSize || !m_hBar->shouldParticipateInHitTesting())))
        return 0;

    return m_hBar->height();
}

IntSize RenderLayer::offsetFromResizeCorner(const IntPoint& absolutePoint) const
{
    // Currently the resize corner is either the bottom right corner or the bottom left corner.
    // FIXME: This assumes the location is 0, 0. Is this guaranteed to always be the case?
    IntSize elementSize = size();
    if (renderer().style().shouldPlaceBlockDirectionScrollbarOnLogicalLeft())
        elementSize.setWidth(0);
    IntPoint resizerPoint = IntPoint(elementSize);
    IntPoint localPoint = roundedIntPoint(absoluteToContents(absolutePoint));
    return localPoint - resizerPoint;
}

bool RenderLayer::hasOverflowControls() const
{
    return m_hBar || m_vBar || m_scrollCorner || renderer().style().resize() != RESIZE_NONE;
}

void RenderLayer::positionOverflowControls(const IntSize& offsetFromRoot)
{
    if (!m_hBar && !m_vBar && !canResize())
        return;
    
    RenderBox* box = renderBox();
    if (!box)
        return;

    const IntRect borderBox = box->pixelSnappedBorderBoxRect();
    const IntRect& scrollCorner = scrollCornerRect();
    IntRect absBounds(borderBox.location() + offsetFromRoot, borderBox.size());
    if (m_vBar) {
        IntRect vBarRect = rectForVerticalScrollbar(borderBox);
        vBarRect.move(offsetFromRoot);
        m_vBar->setFrameRect(vBarRect);
    }
    
    if (m_hBar) {
        IntRect hBarRect = rectForHorizontalScrollbar(borderBox);
        hBarRect.move(offsetFromRoot);
        m_hBar->setFrameRect(hBarRect);
    }
    
    if (m_scrollCorner)
        m_scrollCorner->setFrameRect(scrollCorner);
    if (m_resizer)
        m_resizer->setFrameRect(resizerCornerRect(this, borderBox));

    if (isComposited())
        backing()->positionOverflowControlsLayers();
}

int RenderLayer::scrollWidth() const
{
    ASSERT(renderBox());
    if (m_scrollDimensionsDirty)
        const_cast<RenderLayer*>(this)->computeScrollDimensions();
    // FIXME: This should use snappedIntSize() instead with absolute coordinates.
    return roundToInt(m_scrollSize.width());
}

int RenderLayer::scrollHeight() const
{
    ASSERT(renderBox());
    if (m_scrollDimensionsDirty)
        const_cast<RenderLayer*>(this)->computeScrollDimensions();
    // FIXME: This should use snappedIntSize() instead with absolute coordinates.
    return roundToInt(m_scrollSize.height());
}

LayoutUnit RenderLayer::overflowTop() const
{
    RenderBox* box = renderBox();
    LayoutRect overflowRect(box->layoutOverflowRect());
    box->flipForWritingMode(overflowRect);
    return overflowRect.y();
}

LayoutUnit RenderLayer::overflowBottom() const
{
    RenderBox* box = renderBox();
    LayoutRect overflowRect(box->layoutOverflowRect());
    box->flipForWritingMode(overflowRect);
    return overflowRect.maxY();
}

LayoutUnit RenderLayer::overflowLeft() const
{
    RenderBox* box = renderBox();
    LayoutRect overflowRect(box->layoutOverflowRect());
    box->flipForWritingMode(overflowRect);
    return overflowRect.x();
}

LayoutUnit RenderLayer::overflowRight() const
{
    RenderBox* box = renderBox();
    LayoutRect overflowRect(box->layoutOverflowRect());
    box->flipForWritingMode(overflowRect);
    return overflowRect.maxX();
}

void RenderLayer::computeScrollDimensions()
{
    RenderBox* box = renderBox();
    ASSERT(box);

    m_scrollDimensionsDirty = false;

    m_scrollSize.setWidth(overflowRight() - overflowLeft());
    m_scrollSize.setHeight(overflowBottom() - overflowTop());

    int scrollableLeftOverflow = overflowLeft() - box->borderLeft();
    int scrollableTopOverflow = overflowTop() - box->borderTop();
    setScrollOrigin(IntPoint(-scrollableLeftOverflow, -scrollableTopOverflow));
}

bool RenderLayer::hasScrollableHorizontalOverflow() const
{
    return hasHorizontalOverflow() && renderBox()->scrollsOverflowX();
}

bool RenderLayer::hasScrollableVerticalOverflow() const
{
    return hasVerticalOverflow() && renderBox()->scrollsOverflowY();
}

bool RenderLayer::hasHorizontalOverflow() const
{
    ASSERT(!m_scrollDimensionsDirty);

    return scrollWidth() > renderBox()->pixelSnappedClientWidth();
}

bool RenderLayer::hasVerticalOverflow() const
{
    ASSERT(!m_scrollDimensionsDirty);

    return scrollHeight() > renderBox()->pixelSnappedClientHeight();
}

static bool styleRequiresScrollbar(const RenderStyle& style, ScrollbarOrientation axis)
{
    EOverflow overflow = axis == ScrollbarOrientation::HorizontalScrollbar ? style.overflowX() : style.overflowY();
    bool overflowScrollActsLikeAuto = overflow == OSCROLL && !style.hasPseudoStyle(SCROLLBAR) && ScrollbarTheme::theme()->usesOverlayScrollbars();
    return overflow == OSCROLL && !overflowScrollActsLikeAuto;
}

static bool styleDefinesAutomaticScrollbar(const RenderStyle& style, ScrollbarOrientation axis)
{
    EOverflow overflow = axis == ScrollbarOrientation::HorizontalScrollbar ? style.overflowX() : style.overflowY();
    bool overflowScrollActsLikeAuto = overflow == OSCROLL && !style.hasPseudoStyle(SCROLLBAR) && ScrollbarTheme::theme()->usesOverlayScrollbars();
    return overflow == OAUTO || overflow == OOVERLAY || overflowScrollActsLikeAuto;
}

void RenderLayer::updateScrollbarsAfterLayout()
{
    RenderBox* box = renderBox();
    ASSERT(box);

    // List box parts handle the scrollbars by themselves so we have nothing to do.
    if (box->style().appearance() == ListboxPart)
        return;

    bool hasHorizontalOverflow = this->hasHorizontalOverflow();
    bool hasVerticalOverflow = this->hasVerticalOverflow();

    // If overflow requires a scrollbar, then we just need to enable or disable.
    if (styleRequiresScrollbar(renderer().style(), HorizontalScrollbar))
        m_hBar->setEnabled(hasHorizontalOverflow);
    if (styleRequiresScrollbar(renderer().style(), VerticalScrollbar))
        m_vBar->setEnabled(hasVerticalOverflow);

    // Scrollbars with auto behavior may need to lay out again if scrollbars got added or removed.
    bool autoHorizontalScrollBarChanged = box->hasHorizontalScrollbarWithAutoBehavior() && (hasHorizontalScrollbar() != hasHorizontalOverflow);
    bool autoVerticalScrollBarChanged = box->hasVerticalScrollbarWithAutoBehavior() && (hasVerticalScrollbar() != hasVerticalOverflow);

    if (autoHorizontalScrollBarChanged || autoVerticalScrollBarChanged) {
        if (box->hasHorizontalScrollbarWithAutoBehavior())
            setHasHorizontalScrollbar(hasHorizontalOverflow);
        if (box->hasVerticalScrollbarWithAutoBehavior())
            setHasVerticalScrollbar(hasVerticalOverflow);

        updateSelfPaintingLayer();

        // Force an update since we know the scrollbars have changed things.
#if ENABLE(DASHBOARD_SUPPORT)
        if (renderer().document().hasAnnotatedRegions())
            renderer().document().setAnnotatedRegionsDirty(true);
#endif

        renderer().repaint();

        if (renderer().style().overflowX() == OAUTO || renderer().style().overflowY() == OAUTO) {
            if (!m_inOverflowRelayout) {
                // Our proprietary overflow: overlay value doesn't trigger a layout.
                m_inOverflowRelayout = true;
                renderer().setNeedsLayout(MarkOnlyThis);
                if (is<RenderBlock>(renderer())) {
                    RenderBlock& block = downcast<RenderBlock>(renderer());
                    block.scrollbarsChanged(autoHorizontalScrollBarChanged, autoVerticalScrollBarChanged);
                    block.layoutBlock(true);
                } else
                    renderer().layout();
                m_inOverflowRelayout = false;
            }
        }
    }

    // Set up the range (and page step/line step).
    if (m_hBar) {
        int clientWidth = box->pixelSnappedClientWidth();
        int pageStep = Scrollbar::pageStep(clientWidth);
        m_hBar->setSteps(Scrollbar::pixelsPerLineStep(), pageStep);
        m_hBar->setProportion(clientWidth, m_scrollSize.width().round());
    }
    if (m_vBar) {
        int clientHeight = box->pixelSnappedClientHeight();
        int pageStep = Scrollbar::pageStep(clientHeight);
        m_vBar->setSteps(Scrollbar::pixelsPerLineStep(), pageStep);
        m_vBar->setProportion(clientHeight, m_scrollSize.height().round());
    }

    updateScrollableAreaSet(hasScrollableHorizontalOverflow() || hasScrollableVerticalOverflow());
}

void RenderLayer::updateScrollInfoAfterLayout()
{
    RenderBox* box = renderBox();
    if (!box)
        return;

    m_scrollDimensionsDirty = true;
    IntSize originalScrollOffset = scrollOffset();

    computeScrollDimensions();

    if (box->style().overflowX() != OMARQUEE && !isRubberBandInProgress()) {
        // Layout may cause us to be at an invalid scroll position. In this case we need
        // to pull our scroll offsets back to the max (or push them up to the min).
        IntSize clampedScrollOffset = clampScrollOffset(scrollOffset());
#if PLATFORM(IOS)
        // FIXME: This looks wrong. The caret adjust mode should only be enabled on editing related entry points.
        // This code was added to fix an issue where the text insertion point would always be drawn on the right edge
        // of a text field whose content overflowed its bounds. See <rdar://problem/15579797> for more details.
        setAdjustForIOSCaretWhenScrolling(true);
#endif
        if (clampedScrollOffset != scrollOffset())
            scrollToOffset(clampedScrollOffset);

#if PLATFORM(IOS)
        setAdjustForIOSCaretWhenScrolling(false);
#endif
    }

    updateScrollbarsAfterLayout();

    if (originalScrollOffset != scrollOffset())
        scrollToOffsetWithoutAnimation(IntPoint(scrollOffset()));

    // Composited scrolling may need to be enabled or disabled if the amount of overflow changed.
    if (compositor().updateLayerCompositingState(*this))
        compositor().setCompositingLayersNeedRebuild();

#if ENABLE(CSS_SCROLL_SNAP)
    // FIXME: Ensure that offsets are also updated in case of programmatic style changes.
    // https://bugs.webkit.org/show_bug.cgi?id=135964
    updateSnapOffsets();
#if PLATFORM(MAC)
    if (existingScrollAnimator())
        scrollAnimator()->updateScrollAnimatorsAndTimers();
#endif
#endif
}

bool RenderLayer::overflowControlsIntersectRect(const IntRect& localRect) const
{
    const IntRect borderBox = renderBox()->pixelSnappedBorderBoxRect();

    if (rectForHorizontalScrollbar(borderBox).intersects(localRect))
        return true;

    if (rectForVerticalScrollbar(borderBox).intersects(localRect))
        return true;

    if (scrollCornerRect().intersects(localRect))
        return true;
    
    if (resizerCornerRect(this, borderBox).intersects(localRect))
        return true;

    return false;
}

bool RenderLayer::showsOverflowControls() const
{
#if PLATFORM(IOS)
    // Don't render (custom) scrollbars if we have accelerated scrolling.
    if (hasAcceleratedTouchScrolling())
        return false;
#endif

    return true;
}

void RenderLayer::paintOverflowControls(GraphicsContext* context, const IntPoint& paintOffset, const IntRect& damageRect, bool paintingOverlayControls)
{