/*
 Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)

 This library is free software; you can redistribute it and/or
 modify it under the terms of the GNU Library General Public
 License as published by the Free Software Foundation; either
 version 2 of the License, or (at your option) any later version.

 This library is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 Library General Public License for more details.

 You should have received a copy of the GNU Library General Public License
 along with this library; see the file COPYING.LIB.  If not, write to
 the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 Boston, MA 02110-1301, USA.
 */

#include "config.h"
#include "TextureMapperLayer.h"

#include "FloatQuad.h"
#include "GraphicsLayerTextureMapper.h"
#include "Region.h"
#include <wtf/MathExtras.h>

namespace WebCore {

class TextureMapperPaintOptions {
public:
    TextureMapperPaintOptions(TextureMapper& textureMapper)
        : textureMapper(textureMapper)
    { }

    TextureMapper& textureMapper;
    TransformationMatrix transform;
    RefPtr<BitmapTexture> surface;
    float opacity { 1 };
    IntSize offset;
};

void TextureMapperLayer::computeTransformsRecursive()
{
    if (m_state.size.isEmpty() && m_state.masksToBounds)
        return;

    // Compute transforms recursively on the way down to leafs.
    TransformationMatrix parentTransform;
    if (m_parent)
        parentTransform = m_parent->m_currentTransform.combinedForChildren();
    else if (m_effectTarget)
        parentTransform = m_effectTarget->m_currentTransform.combined();
    m_currentTransform.combineTransforms(parentTransform);

    m_state.visible = m_state.backfaceVisibility || !m_currentTransform.combined().isBackFaceVisible();

    if (m_parent && m_parent->m_state.preserves3D)
        m_centerZ = m_currentTransform.combined().mapPoint(FloatPoint3D(m_state.size.width() / 2, m_state.size.height() / 2, 0)).z();

    if (m_state.maskLayer)
        m_state.maskLayer->computeTransformsRecursive();
    if (m_state.replicaLayer)
        m_state.replicaLayer->computeTransformsRecursive();
    for (auto* child : m_children) {
        ASSERT(child->m_parent == this);
        child->computeTransformsRecursive();
    }

    // Reorder children if needed on the way back up.
    if (m_state.preserves3D)
        sortByZOrder(m_children);
}

void TextureMapperLayer::paint()
{
    computeTransformsRecursive();

    ASSERT(m_textureMapper);
    TextureMapperPaintOptions options(*m_textureMapper);
    options.textureMapper.bindSurface(0);

    paintRecursive(options);
}

static Color blendWithOpacity(const Color& color, float opacity)
{
    if (color.isOpaque() && opacity == 1.)
        return color;

    return color.colorWithAlphaMultipliedBy(opacity);
}

void TextureMapperLayer::computePatternTransformIfNeeded()
{
    if (!m_patternTransformDirty)
        return;

    m_patternTransformDirty = false;
    m_patternTransform =
        TransformationMatrix::rectToRect(FloatRect(FloatPoint::zero(), m_state.contentsTileSize), FloatRect(FloatPoint::zero(), m_state.contentsRect.size()))
        .multiply(TransformationMatrix().translate(m_state.contentsTilePhase.width() / m_state.contentsRect.width(), m_state.contentsTilePhase.height() / m_state.contentsRect.height()));
}

void TextureMapperLayer::paintSelf(const TextureMapperPaintOptions& options)
{
    if (!m_state.visible || !m_state.contentsVisible)
        return;

    // We apply the following transform to compensate for painting into a surface, and then apply the offset so that the painting fits in the target rect.
    TransformationMatrix transform;
    transform.translate(options.offset.width(), options.offset.height());
    transform.multiply(options.transform);
    transform.multiply(m_currentTransform.combined());

    if (m_state.solidColor.isValid() && !m_state.contentsRect.isEmpty() && m_state.solidColor.isVisible()) {
        options.textureMapper.drawSolidColor(m_state.contentsRect, transform, blendWithOpacity(m_state.solidColor, options.opacity));
        if (m_state.showDebugBorders)
            options.textureMapper.drawBorder(m_state.debugBorderColor, m_state.debugBorderWidth, layerRect(), transform);
        return;
    }

    options.textureMapper.setWrapMode(TextureMapper::StretchWrap);
    options.textureMapper.setPatternTransform(TransformationMatrix());

    if (m_backingStore) {
        FloatRect targetRect = layerRect();
        ASSERT(!targetRect.isEmpty());
        m_backingStore->paintToTextureMapper(options.textureMapper, targetRect, transform, options.opacity);
        if (m_state.showDebugBorders)
            m_backingStore->drawBorder(options.textureMapper, m_state.debugBorderColor, m_state.debugBorderWidth, targetRect, transform);
        // Only draw repaint count for the main backing store.
        if (m_state.showRepaintCounter)
            m_backingStore->drawRepaintCounter(options.textureMapper, m_state.repaintCount, m_state.debugBorderColor, targetRect, transform);
    }

    if (!m_contentsLayer)
        return;

    if (!m_state.contentsTileSize.isEmpty()) {
        computePatternTransformIfNeeded();
        options.textureMapper.setWrapMode(TextureMapper::RepeatWrap);
        options.textureMapper.setPatternTransform(m_patternTransform);
    }

    ASSERT(!layerRect().isEmpty());
    m_contentsLayer->paintToTextureMapper(options.textureMapper, m_state.contentsRect, transform, options.opacity);
    if (m_state.showDebugBorders)
        m_contentsLayer->drawBorder(options.textureMapper, m_state.debugBorderColor, m_state.debugBorderWidth, m_state.contentsRect, transform);
}

void TextureMapperLayer::sortByZOrder(Vector<TextureMapperLayer* >& array)
{
    std::sort(array.begin(), array.end(),
        [](TextureMapperLayer* a, TextureMapperLayer* b) {
            return a->m_centerZ < b->m_centerZ;
        });
}

void TextureMapperLayer::paintSelfAndChildren(const TextureMapperPaintOptions& options)
{
    paintSelf(options);

    if (m_children.isEmpty())
        return;

    bool shouldClip = m_state.masksToBounds && !m_state.preserves3D;
    if (shouldClip) {
        TransformationMatrix clipTransform;
        clipTransform.translate(options.offset.width(), options.offset.height());
        clipTransform.multiply(options.transform);
        clipTransform.multiply(m_currentTransform.combined());
        options.textureMapper.beginClip(clipTransform, layerRect());
    }

    for (auto* child : m_children)
        child->paintRecursive(options);

    if (shouldClip)
        options.textureMapper.endClip();
}

bool TextureMapperLayer::shouldBlend() const
{
    if (m_state.preserves3D)
        return false;

    return m_currentOpacity < 1
        || hasFilters()
        || m_state.maskLayer
        || (m_state.replicaLayer && m_state.replicaLayer->m_state.maskLayer);
}

bool TextureMapperLayer::isVisible() const
{
    if (m_state.size.isEmpty() && (m_state.masksToBounds || m_state.maskLayer || m_children.isEmpty()))
        return false;
    if (!m_state.visible && m_children.isEmpty())
        return false;
    if (!m_state.contentsVisible && m_children.isEmpty())
        return false;
    if (m_currentOpacity < 0.01)
        return false;
    return true;
}

void TextureMapperLayer::paintSelfAndChildrenWithReplica(const TextureMapperPaintOptions& options)
{
    if (m_state.replicaLayer) {
        TextureMapperPaintOptions replicaOptions(options);
        replicaOptions.transform
            .multiply(m_state.replicaLayer->m_currentTransform.combined())
            .multiply(m_currentTransform.combined().inverse().value_or(TransformationMatrix()));
        paintSelfAndChildren(replicaOptions);
    }

    paintSelfAndChildren(options);
}

void TextureMapperLayer::setAnimatedTransform(const TransformationMatrix& matrix)
{
    m_currentTransform.setLocalTransform(matrix);
}

void TextureMapperLayer::setAnimatedOpacity(float opacity)
{
    m_currentOpacity = opacity;
}

TransformationMatrix TextureMapperLayer::replicaTransform()
{
    return TransformationMatrix(m_state.replicaLayer->m_currentTransform.combined()).multiply(m_currentTransform.combined().inverse().value_or(TransformationMatrix()));
}

void TextureMapperLayer::setAnimatedFilters(const FilterOperations& filters)
{
    m_currentFilters = filters;
}

static void resolveOverlaps(Region& newRegion, Region& overlapRegion, Region& nonOverlapRegion)
{
    Region newOverlapRegion(newRegion);
    newOverlapRegion.intersect(nonOverlapRegion);
    nonOverlapRegion.subtract(newOverlapRegion);
    overlapRegion.unite(newOverlapRegion);
    newRegion.subtract(overlapRegion);
    nonOverlapRegion.unite(newRegion);
}

void TextureMapperLayer::computeOverlapRegions(Region& overlapRegion, Region& nonOverlapRegion, ResolveSelfOverlapMode mode)
{
    if (!m_state.visible || !m_state.contentsVisible)
        return;

    FloatRect boundingRect;
    if (m_backingStore || m_state.masksToBounds || m_state.maskLayer || hasFilters())
        boundingRect = layerRect();
    else if (m_contentsLayer || m_state.solidColor.isVisible())
        boundingRect = m_state.contentsRect;

    if (m_currentFilters.hasOutsets()) {
        FilterOutsets outsets = m_currentFilters.outsets();
        IntRect unfilteredTargetRect(boundingRect);
        boundingRect.move(std::max(0, -outsets.left()), std::max(0, -outsets.top()));
        boundingRect.expand(outsets.left() + outsets.right(), outsets.top() + outsets.bottom());
        boundingRect.unite(unfilteredTargetRect);
    }

    TransformationMatrix replicaMatrix;
    if (m_state.replicaLayer) {
        replicaMatrix = replicaTransform();
        boundingRect.unite(replicaMatrix.mapRect(boundingRect));
    }

    boundingRect = m_currentTransform.combined().mapRect(boundingRect);

    // Count all masks and filters as overlap layers.
    if (hasFilters() || m_state.maskLayer || (m_state.replicaLayer && m_state.replicaLayer->m_state.maskLayer)) {
        Region newOverlapRegion(enclosingIntRect(boundingRect));
        nonOverlapRegion.subtract(newOverlapRegion);
        overlapRegion.unite(newOverlapRegion);
        return;
    }

    Region newOverlapRegion;
    Region newNonOverlapRegion(enclosingIntRect(boundingRect));

    if (!m_state.masksToBounds) {
        for (auto* child : m_children)
            child->computeOverlapRegions(newOverlapRegion, newNonOverlapRegion, ResolveSelfOverlapIfNeeded);
    }

    if (m_state.replicaLayer) {
        newOverlapRegion.unite(replicaMatrix.mapRect(newOverlapRegion.bounds()));
        Region replicaRegion(replicaMatrix.mapRect(newNonOverlapRegion.bounds()));
        resolveOverlaps(replicaRegion, newOverlapRegion, newNonOverlapRegion);
    }

    if ((mode != ResolveSelfOverlapAlways) && shouldBlend()) {
        newNonOverlapRegion.unite(newOverlapRegion);
        newOverlapRegion = Region();
    }

    overlapRegion.unite(newOverlapRegion);
    resolveOverlaps(newNonOverlapRegion, overlapRegion, nonOverlapRegion);
}

void TextureMapperLayer::paintUsingOverlapRegions(const TextureMapperPaintOptions& options)
{
    Region overlapRegion;
    Region nonOverlapRegion;
    computeOverlapRegions(overlapRegion, nonOverlapRegion, ResolveSelfOverlapAlways);
    if (overlapRegion.isEmpty()) {
        paintSelfAndChildrenWithReplica(options);
        return;
    }

    // Having both overlap and non-overlap regions carries some overhead. Avoid it if the overlap area
    // is big anyway.
    if (overlapRegion.bounds().size().area() > nonOverlapRegion.bounds().size().area()) {
        overlapRegion.unite(nonOverlapRegion);
        nonOverlapRegion = Region();
    }

    nonOverlapRegion.translate(options.offset);
    Vector<IntRect> rects = nonOverlapRegion.rects();

    for (auto& rect : rects) {
        if (!rect.intersects(options.textureMapper.clipBounds()))
            continue;

        options.textureMapper.beginClip(TransformationMatrix(), rect);
        paintSelfAndChildrenWithReplica(options);
        options.textureMapper.endClip();
    }

    rects = overlapRegion.rects();
    static const size_t OverlapRegionConsolidationThreshold = 4;
    if (nonOverlapRegion.isEmpty() && rects.size() > OverlapRegionConsolidationThreshold) {
        rects.clear();
        rects.append(overlapRegion.bounds());
    }

    IntSize maxTextureSize = options.textureMapper.maxTextureSize();
    IntRect adjustedClipBounds(options.textureMapper.clipBounds());
    adjustedClipBounds.move(-options.offset);
    for (auto& rect : rects) {
        for (int x = rect.x(); x < rect.maxX(); x += maxTextureSize.width()) {
            for (int y = rect.y(); y < rect.maxY(); y += maxTextureSize.height()) {
                IntRect tileRect(IntPoint(x, y), maxTextureSize);
                tileRect.intersect(rect);
                if (!tileRect.intersects(adjustedClipBounds))
                    continue;

                paintWithIntermediateSurface(options, tileRect);
            }
        }
    }
}

void TextureMapperLayer::applyMask(const TextureMapperPaintOptions& options)
{
    options.textureMapper.setMaskMode(true);
    paintSelf(options);
    options.textureMapper.setMaskMode(false);
}

PassRefPtr<BitmapTexture> TextureMapperLayer::paintIntoSurface(const TextureMapperPaintOptions& options, const IntSize& size)
{
    RefPtr<BitmapTexture> surface = options.textureMapper.acquireTextureFromPool(size, BitmapTexture::SupportsAlpha | BitmapTexture::FBOAttachment);
    TextureMapperPaintOptions paintOptions(options);
    paintOptions.surface = surface;
    options.textureMapper.bindSurface(surface.get());
    paintSelfAndChildren(paintOptions);
    if (m_state.maskLayer)
        m_state.maskLayer->applyMask(options);
    surface = surface->applyFilters(options.textureMapper, m_currentFilters);
    options.textureMapper.bindSurface(surface.get());
    return surface.release();
}

static void commitSurface(const TextureMapperPaintOptions& options, PassRefPtr<BitmapTexture> surface, const IntRect& rect, float opacity)
{
    options.textureMapper.bindSurface(options.surface.get());
    TransformationMatrix targetTransform;
    targetTransform.translate(options.offset.width(), options.offset.height());
    targetTransform.multiply(options.transform);
    options.textureMapper.drawTexture(*surface.get(), rect, targetTransform, opacity);
}

void TextureMapperLayer::paintWithIntermediateSurface(const TextureMapperPaintOptions& options, const IntRect& rect)
{
    RefPtr<BitmapTexture> replicaSurface;
    RefPtr<BitmapTexture> mainSurface;
    TextureMapperPaintOptions paintOptions(options);
    paintOptions.offset = -IntSize(rect.x(), rect.y());
    paintOptions.opacity = 1;
    paintOptions.transform = TransformationMatrix();
    if (m_state.replicaLayer) {
        paintOptions.transform = replicaTransform();
        replicaSurface = paintIntoSurface(paintOptions, rect.size());
        paintOptions.transform = TransformationMatrix();
        if (m_state.replicaLayer->m_state.maskLayer)
            m_state.replicaLayer->m_state.maskLayer->applyMask(paintOptions);
    }

    if (replicaSurface && options.opacity == 1) {
        commitSurface(options, replicaSurface, rect, 1);
        replicaSurface = nullptr;
    }

    mainSurface = paintIntoSurface(paintOptions, rect.size());
    if (replicaSurface) {
        options.textureMapper.bindSurface(replicaSurface.get());
        options.textureMapper.drawTexture(*mainSurface.get(), FloatRect(FloatPoint::zero(), rect.size()));
        mainSurface = replicaSurface;
    }

    commitSurface(options, mainSurface, rect, options.opacity);
}

void TextureMapperLayer::paintRecursive(const TextureMapperPaintOptions& options)
{
    if (!isVisible())
        return;

    TextureMapperPaintOptions paintOptions(options);
    paintOptions.opacity *= m_currentOpacity;

    if (!shouldBlend()) {
        paintSelfAndChildrenWithReplica(paintOptions);
        return;
    }

    paintUsingOverlapRegions(paintOptions);
}

TextureMapperLayer::~TextureMapperLayer()
{
    for (auto* child : m_children)
        child->m_parent = nullptr;

    removeFromParent();

    if (m_effectTarget) {
        if (m_effectTarget->m_state.maskLayer == this)
            m_effectTarget->m_state.maskLayer = nullptr;
        if (m_effectTarget->m_state.replicaLayer == this)
            m_effectTarget->m_state.replicaLayer = nullptr;
    }
}

#if !USE(COORDINATED_GRAPHICS)
void TextureMapperLayer::setChildren(const Vector<GraphicsLayer*>& newChildren)
{
    removeAllChildren();
    for (auto* child : newChildren)
        addChild(&downcast<GraphicsLayerTextureMapper>(child)->layer());
}
#endif

void TextureMapperLayer::setChildren(const Vector<TextureMapperLayer*>& newChildren)
{
    removeAllChildren();
    for (auto* child : newChildren)
        addChild(child);
}

void TextureMapperLayer::addChild(TextureMapperLayer* childLayer)
{
    ASSERT(childLayer != this);

    if (childLayer->m_parent)
        childLayer->removeFromParent();

    childLayer->m_parent = this;
    m_children.append(childLayer);
}

void TextureMapperLayer::removeFromParent()
{
    if (m_parent) {
        size_t index = m_parent->m_children.find(this);
        ASSERT(index != notFound);
        m_parent->m_children.remove(index);
    }

    m_parent = nullptr;
}

void TextureMapperLayer::removeAllChildren()
{
    auto oldChildren = WTFMove(m_children);
    for (auto* child : oldChildren)
        child->m_parent = nullptr;
}

void TextureMapperLayer::setMaskLayer(TextureMapperLayer* maskLayer)
{
    if (maskLayer)
        maskLayer->m_effectTarget = this;
    m_state.maskLayer = maskLayer;
}

void TextureMapperLayer::setReplicaLayer(TextureMapperLayer* replicaLayer)
{
    if (replicaLayer)
        replicaLayer->m_effectTarget = this;
    m_state.replicaLayer = replicaLayer;
}

void TextureMapperLayer::setPosition(const FloatPoint& position)
{
    m_state.pos = position;
    m_currentTransform.setPosition(adjustedPosition());
}

void TextureMapperLayer::setSize(const FloatSize& size)
{
    m_state.size = size;
    m_currentTransform.setSize(size);
}

void TextureMapperLayer::setAnchorPoint(const FloatPoint3D& anchorPoint)
{
    m_state.anchorPoint = anchorPoint;
    m_currentTransform.setAnchorPoint(anchorPoint);
}

void TextureMapperLayer::setPreserves3D(bool preserves3D)
{
    m_state.preserves3D = preserves3D;
    m_currentTransform.setFlattening(!preserves3D);
}

void TextureMapperLayer::setTransform(const TransformationMatrix& transform)
{
    m_state.transform = transform;
    m_currentTransform.setLocalTransform(transform);
}

void TextureMapperLayer::setChildrenTransform(const TransformationMatrix& childrenTransform)
{
    m_state.childrenTransform = childrenTransform;
    m_currentTransform.setChildrenTransform(childrenTransform);
}

void TextureMapperLayer::setContentsRect(const FloatRect& contentsRect)
{
    if (contentsRect == m_state.contentsRect)
        return;
    m_state.contentsRect = contentsRect;
    m_patternTransformDirty = true;
}

void TextureMapperLayer::setContentsTileSize(const FloatSize& size)
{
    if (size == m_state.contentsTileSize)
        return;
    m_state.contentsTileSize = size;
    m_patternTransformDirty = true;
}

void TextureMapperLayer::setContentsTilePhase(const FloatSize& phase)
{
    if (phase == m_state.contentsTilePhase)
        return;
    m_state.contentsTilePhase = phase;
    m_patternTransformDirty = true;
}

void TextureMapperLayer::setMasksToBounds(bool masksToBounds)
{
    m_state.masksToBounds = masksToBounds;
}

void TextureMapperLayer::setDrawsContent(bool drawsContent)
{
    m_state.drawsContent = drawsContent;
}

void TextureMapperLayer::setContentsVisible(bool contentsVisible)
{
    m_state.contentsVisible = contentsVisible;
}

void TextureMapperLayer::setContentsOpaque(bool contentsOpaque)
{
    m_state.contentsOpaque = contentsOpaque;
}

void TextureMapperLayer::setBackfaceVisibility(bool backfaceVisibility)
{
    m_state.backfaceVisibility = backfaceVisibility;
}

void TextureMapperLayer::setOpacity(float opacity)
{
    m_state.opacity = opacity;
}

void TextureMapperLayer::setSolidColor(const Color& color)
{
    m_state.solidColor = color;
}

void TextureMapperLayer::setFilters(const FilterOperations& filters)
{
    m_state.filters = filters;
}

void TextureMapperLayer::setDebugVisuals(bool showDebugBorders, const Color& debugBorderColor, float debugBorderWidth, bool showRepaintCounter)
{
    m_state.showDebugBorders = showDebugBorders;
    m_state.debugBorderColor = debugBorderColor;
    m_state.debugBorderWidth = debugBorderWidth;
    m_state.showRepaintCounter = showRepaintCounter;
}

void TextureMapperLayer::setRepaintCount(int repaintCount)
{
    m_state.repaintCount = repaintCount;
}

void TextureMapperLayer::setContentsLayer(TextureMapperPlatformLayer* platformLayer)
{
    m_contentsLayer = platformLayer;
}

void TextureMapperLayer::setAnimations(const TextureMapperAnimations& animations)
{
    m_animations = animations;
}

void TextureMapperLayer::setFixedToViewport(bool fixedToViewport)
{
    m_fixedToViewport = fixedToViewport;
}

void TextureMapperLayer::setBackingStore(PassRefPtr<TextureMapperBackingStore> backingStore)
{
    m_backingStore = backingStore;
}

bool TextureMapperLayer::descendantsOrSelfHaveRunningAnimations() const
{
    if (m_animations.hasRunningAnimations())
        return true;

    return std::any_of(m_children.begin(), m_children.end(),
        [](TextureMapperLayer* child) {
            return child->descendantsOrSelfHaveRunningAnimations();
        });
}

void TextureMapperLayer::applyAnimationsRecursively()
{
    syncAnimations();
    for (auto* child : m_children)
        child->applyAnimationsRecursively();
}

void TextureMapperLayer::syncAnimations()
{
    m_animations.apply(*this);
    if (!m_animations.hasActiveAnimationsOfType(AnimatedPropertyTransform))
        m_currentTransform.setLocalTransform(m_state.transform);
    if (!m_animations.hasActiveAnimationsOfType(AnimatedPropertyOpacity))
        m_currentOpacity = m_state.opacity;

    if (!m_animations.hasActiveAnimationsOfType(AnimatedPropertyFilter))
        m_currentFilters = m_state.filters;
}

bool TextureMapperLayer::isAncestorFixedToViewport() const
{
    for (TextureMapperLayer* parent = m_parent; parent; parent = parent->m_parent) {
        if (parent->m_fixedToViewport)
            return true;
    }

    return false;
}

void TextureMapperLayer::setScrollPositionDeltaIfNeeded(const FloatSize& delta)
{
    // delta is the difference between the scroll offset in the ui process and the scroll offset
    // in the web process. We add this delta to the position of fixed layers, to make
    // sure that they do not move while scrolling. We need to reset this delta to fixed layers
    // that have an ancestor which is also a fixed layer, because the delta will be added to the ancestor.
    if (isAncestorFixedToViewport())
        m_scrollPositionDelta = FloatSize();
    else
        m_scrollPositionDelta = delta;
    m_currentTransform.setPosition(adjustedPosition());
}

template<class HitTestCondition> TextureMapperLayer* TextureMapperLayer::hitTest(const FloatPoint& point, HitTestCondition condition)
{
    if (!m_state.visible || !m_state.contentsVisible)
        return 0;

    TextureMapperLayer* result = 0;
    for (int i = m_children.size() - 1; !result && i >= 0; --i)
        result = m_children[i]->hitTest(point, condition);

    if (result)
        return result;

    return condition(this, point) ? this : 0;
}

bool TextureMapperLayer::scrollableLayerHitTestCondition(TextureMapperLayer* layer, const FloatPoint& point)
{
    // scrolling layer's m_parent->m_parent, the parent of the scrolling layes, is the one that defines the
    // rectangle to be used for hit testing.
    if (!layer->isScrollable() || !layer->m_parent || !layer->m_parent->m_parent)
        return false;

    TextureMapperLayer* parentLayer = layer->m_parent->m_parent;
    FloatRect rect = parentLayer->layerRect();
    return parentLayer->m_currentTransform.combined().mapQuad(rect).containsPoint(point);
}

TextureMapperLayer* TextureMapperLayer::findScrollableContentsLayerAt(const FloatPoint& point)
{
    return hitTest(point, &TextureMapperLayer::scrollableLayerHitTestCondition);
}

FloatSize TextureMapperLayer::mapScrollOffset(const FloatSize& offset)
{
    double zeroX, zeroY, offsetX, offsetY;
    TransformationMatrix transform = m_currentTransform.combined().inverse().value_or(TransformationMatrix());
    transform.map(0, 0, zeroX, zeroY);
    transform.map(offset.width(), offset.height(), offsetX, offsetY);
    return FloatSize(offsetX - zeroX, offsetY - zeroY);
}

void TextureMapperLayer::commitScrollOffset(const FloatSize& offset)
{
    FloatSize fullOffset = m_accumulatedScrollOffsetFractionalPart + offset;

    int intWidth = round(fullOffset.width());
    int intHeight = round(fullOffset.height());

    // m_accumulatedScrollOffsetFractionalPart holds the fractional part of the user scroll offset that
    // has not yet been synced with the web process because the web process expects an IntSize.
    m_accumulatedScrollOffsetFractionalPart = FloatSize(fullOffset.width() - intWidth, fullOffset.height() - intHeight);

    m_scrollClient->commitScrollOffset(m_id, IntSize(intWidth, intHeight));
}

void TextureMapperLayer::scrollBy(const FloatSize& offset)
{
    if (!isScrollable() || !m_scrollClient || offset.isZero())
        return;

    FloatSize scrollOffset = mapScrollOffset(offset);
    m_userScrollOffset += scrollOffset;

    m_currentTransform.setPosition(adjustedPosition());
    commitScrollOffset(scrollOffset);
}

void TextureMapperLayer::didCommitScrollOffset(const IntSize& offset)
{
    m_userScrollOffset = FloatSize(m_userScrollOffset.width() - offset.width(), m_userScrollOffset.height() - offset.height());
    m_currentTransform.setPosition(adjustedPosition());
}

}