third_party/WebKit/Source/core/frame/VisualViewport.cpp

/*
 * Copyright (C) 2013 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "core/frame/VisualViewport.h"

#include "core/frame/FrameHost.h"
#include "core/frame/FrameView.h"
#include "core/frame/LocalFrame.h"
#include "core/frame/PageScaleConstraints.h"
#include "core/frame/PageScaleConstraintsSet.h"
#include "core/frame/Settings.h"
#include "core/inspector/InspectorInstrumentation.h"
#include "core/layout/TextAutosizer.h"
#include "core/layout/compositing/PaintLayerCompositor.h"
#include "core/loader/FrameLoaderClient.h"
#include "core/page/ChromeClient.h"
#include "core/page/Page.h"
#include "core/page/scrolling/ScrollingCoordinator.h"
#include "platform/Histogram.h"
#include "platform/TraceEvent.h"
#include "platform/geometry/DoubleRect.h"
#include "platform/geometry/FloatSize.h"
#include "platform/graphics/GraphicsLayer.h"
#include "platform/scroll/Scrollbar.h"
#include "platform/scroll/ScrollbarThemeOverlay.h"
#include "public/platform/WebCompositorSupport.h"
#include "public/platform/WebLayer.h"
#include "public/platform/WebLayerTreeView.h"
#include "public/platform/WebScrollbar.h"
#include "public/platform/WebScrollbarLayer.h"
#include <memory>

using blink::WebLayer;
using blink::WebLayerTreeView;
using blink::WebScrollbar;
using blink::WebScrollbarLayer;
using blink::FrameHost;
using blink::GraphicsLayer;

namespace blink {

VisualViewport::VisualViewport(FrameHost& owner)
    : m_frameHost(&owner)
    , m_scale(1)
    , m_topControlsAdjustment(0)
    , m_maxPageScale(-1)
    , m_trackPinchZoomStatsForPage(false)
{
    reset();
}

VisualViewport::~VisualViewport()
{
    sendUMAMetrics();
}

DEFINE_TRACE(VisualViewport)
{
    visitor->trace(m_frameHost);
    ScrollableArea::trace(visitor);
}

void VisualViewport::updateStyleAndLayoutIgnorePendingStylesheets()
{
    if (!mainFrame())
        return;

    if (Document* document = mainFrame()->document())
        document->updateStyleAndLayoutIgnorePendingStylesheets();
}

void VisualViewport::enqueueScrollEvent()
{
    if (!RuntimeEnabledFeatures::visualViewportAPIEnabled())
        return;

    if (Document* document = mainFrame()->document())
        document->enqueueVisualViewportScrollEvent();
}

void VisualViewport::enqueueResizeEvent()
{
    if (!RuntimeEnabledFeatures::visualViewportAPIEnabled())
        return;

    if (Document* document = mainFrame()->document())
        document->enqueueVisualViewportResizeEvent();
}

void VisualViewport::setSize(const IntSize& size)
{
    if (m_size == size)
        return;

    TRACE_EVENT2("blink", "VisualViewport::setSize", "width", size.width(), "height", size.height());
    bool widthDidChange = size.width() != m_size.width();
    m_size = size;

    if (m_innerViewportContainerLayer) {
        m_innerViewportContainerLayer->setSize(FloatSize(m_size));

        // Need to re-compute sizes for the overlay scrollbars.
        initializeScrollbars();
    }

    if (!mainFrame())
        return;

    enqueueResizeEvent();

    bool autosizerNeedsUpdating = widthDidChange
        && mainFrame()->settings()
        && mainFrame()->settings()->textAutosizingEnabled();

    if (autosizerNeedsUpdating) {
        // This needs to happen after setting the m_size member since it'll be read in the update call.
        if (TextAutosizer* textAutosizer = mainFrame()->document()->textAutosizer())
            textAutosizer->updatePageInfoInAllFrames();
    }
}

void VisualViewport::reset()
{
    setScaleAndLocation(1, FloatPoint());
}

void VisualViewport::mainFrameDidChangeSize()
{
    TRACE_EVENT0("blink", "VisualViewport::mainFrameDidChangeSize");

    // In unit tests we may not have initialized the layer tree.
    if (m_innerViewportScrollLayer)
        m_innerViewportScrollLayer->setSize(FloatSize(contentsSize()));

    clampToBoundaries();
}

FloatSize VisualViewport::visibleSize() const
{
    FloatSize scaledSize(m_size);
    scaledSize.expand(0, m_topControlsAdjustment);
    scaledSize.scale(1 / m_scale);
    return scaledSize;
}

FloatRect VisualViewport::visibleRect() const
{
    return FloatRect(location(), visibleSize());
}

FloatRect VisualViewport::visibleRectInDocument() const
{
    if (!mainFrame() || !mainFrame()->view())
        return FloatRect();

    FloatPoint viewLocation = FloatPoint(mainFrame()->view()->getScrollableArea()->scrollPositionDouble());
    return FloatRect(viewLocation, visibleSize());
}

FloatRect VisualViewport::mainViewToViewportCSSPixels(const FloatRect& rect) const
{
    // Note, this is in CSS Pixels so we don't apply scale.
    FloatRect rectInViewport = rect;
    rectInViewport.moveBy(-location());
    return rectInViewport;
}

FloatPoint VisualViewport::viewportCSSPixelsToRootFrame(const FloatPoint& point) const
{
    // Note, this is in CSS Pixels so we don't apply scale.
    FloatPoint pointInRootFrame = point;
    pointInRootFrame.moveBy(location());
    return pointInRootFrame;
}

void VisualViewport::setLocation(const FloatPoint& newLocation)
{
    setScaleAndLocation(m_scale, newLocation);
}

void VisualViewport::move(const FloatPoint& delta)
{
    setLocation(m_offset + delta);
}

void VisualViewport::move(const FloatSize& delta)
{
    setLocation(m_offset + delta);
}

void VisualViewport::setScale(float scale)
{
    setScaleAndLocation(scale, m_offset);
}

double VisualViewport::scrollLeft()
{
    if (!mainFrame())
        return 0;

    updateStyleAndLayoutIgnorePendingStylesheets();

    return adjustScrollForAbsoluteZoom(visibleRect().x(), mainFrame()->pageZoomFactor());
}

double VisualViewport::scrollTop()
{
    if (!mainFrame())
        return 0;

    updateStyleAndLayoutIgnorePendingStylesheets();

    return adjustScrollForAbsoluteZoom(visibleRect().y(), mainFrame()->pageZoomFactor());
}

double VisualViewport::clientWidth()
{
    if (!mainFrame())
        return 0;

    updateStyleAndLayoutIgnorePendingStylesheets();

    double width = adjustScrollForAbsoluteZoom(visibleSize().width(), mainFrame()->pageZoomFactor());
    return width - mainFrame()->view()->verticalScrollbarWidth();
}

double VisualViewport::clientHeight()
{
    if (!mainFrame())
        return 0;

    updateStyleAndLayoutIgnorePendingStylesheets();

    double height = adjustScrollForAbsoluteZoom(visibleSize().height(), mainFrame()->pageZoomFactor());
    return height - mainFrame()->view()->horizontalScrollbarHeight();
}

double VisualViewport::pageScale()
{
    updateStyleAndLayoutIgnorePendingStylesheets();

    return m_scale;
}

void VisualViewport::setScaleAndLocation(float scale, const FloatPoint& location)
{
    if (!mainFrame())
        return;

    bool valuesChanged = false;

    if (scale != m_scale) {
        m_scale = scale;
        valuesChanged = true;
        frameHost().chromeClient().pageScaleFactorChanged();
        enqueueResizeEvent();
    }

    FloatPoint clampedOffset(clampOffsetToBoundaries(location));

    if (clampedOffset != m_offset) {
        m_offset = clampedOffset;
        scrollAnimator().setCurrentPosition(m_offset);

        // SVG runs with accelerated compositing disabled so no ScrollingCoordinator.
        if (ScrollingCoordinator* coordinator = frameHost().page().scrollingCoordinator())
            coordinator->scrollableAreaScrollLayerDidChange(this);

        if (!frameHost().settings().inertVisualViewport()) {
            if (Document* document = mainFrame()->document())
                document->enqueueScrollEventForNode(document);
        }

        enqueueScrollEvent();

        mainFrame()->loader().client()->didChangeScrollOffset();
        valuesChanged = true;
    }

    if (!valuesChanged)
        return;

    InspectorInstrumentation::didUpdateLayout(mainFrame());
    mainFrame()->loader().saveScrollState();

    clampToBoundaries();
}

bool VisualViewport::magnifyScaleAroundAnchor(float magnifyDelta, const FloatPoint& anchor)
{
    const float oldPageScale = scale();
    const float newPageScale = frameHost().chromeClient().clampPageScaleFactorToLimits(
        magnifyDelta * oldPageScale);
    if (newPageScale == oldPageScale)
        return false;
    if (!mainFrame() || !mainFrame()->view())
        return false;

    // Keep the center-of-pinch anchor in a stable position over the course
    // of the magnify.
    FloatPoint anchorAtOldScale = anchor.scaledBy(1.f / oldPageScale);
    FloatPoint anchorAtNewScale = anchor.scaledBy(1.f / newPageScale);
    FloatSize anchorDelta = anchorAtOldScale - anchorAtNewScale;

    // First try to use the anchor's delta to scroll the FrameView.
    FloatSize anchorDeltaUnusedByScroll = anchorDelta;

    // Manually bubble any remaining anchor delta up to the visual viewport.
    FloatPoint newLocation(location() + anchorDeltaUnusedByScroll);
    setScaleAndLocation(newPageScale, newLocation);
    return true;
}

// Modifies the top of the graphics layer tree to add layers needed to support
// the inner/outer viewport fixed-position model for pinch zoom. When finished,
// the tree will look like this (with * denoting added layers):
//
// *rootTransformLayer
//  +- *innerViewportContainerLayer (fixed pos container)
//     +- *overscrollElasticityLayer
//     |   +- *pageScaleLayer
//     |       +- *innerViewportScrollLayer
//     |           +-- overflowControlsHostLayer (root layer) [ owned by PaintLayerCompositor ]
//     |               +-- outerViewportContainerLayer (fixed pos container) [frame container layer in PaintLayerCompositor]
//     |               |   +-- outerViewportScrollLayer [frame scroll layer in PaintLayerCompositor]
//     |               |       +-- content layers ...
//     +- *PageOverlay for InspectorOverlay
//     +- *PageOverlay for ColorOverlay
//     +- horizontalScrollbarLayer [ owned by PaintLayerCompositor ]
//     +- verticalScrollbarLayer [ owned by PaintLayerCompositor ]
//     +- scroll corner (non-overlay only) [ owned by PaintLayerCompositor ]
//
void VisualViewport::attachToLayerTree(GraphicsLayer* currentLayerTreeRoot)
{
    TRACE_EVENT1("blink", "VisualViewport::attachToLayerTree", "currentLayerTreeRoot", (bool)currentLayerTreeRoot);
    if (!currentLayerTreeRoot) {
        if (m_innerViewportScrollLayer)
            m_innerViewportScrollLayer->removeAllChildren();
        return;
    }

    if (currentLayerTreeRoot->parent() && currentLayerTreeRoot->parent() == m_innerViewportScrollLayer.get())
        return;

    if (!m_innerViewportScrollLayer) {
        ASSERT(!m_overlayScrollbarHorizontal
            && !m_overlayScrollbarVertical
            && !m_overscrollElasticityLayer
            && !m_pageScaleLayer
            && !m_innerViewportContainerLayer);

        // FIXME: The root transform layer should only be created on demand.
        m_rootTransformLayer = GraphicsLayer::create(this);
        m_innerViewportContainerLayer = GraphicsLayer::create(this);
        m_overscrollElasticityLayer = GraphicsLayer::create(this);
        m_pageScaleLayer = GraphicsLayer::create(this);
        m_innerViewportScrollLayer = GraphicsLayer::create(this);
        m_overlayScrollbarHorizontal = GraphicsLayer::create(this);
        m_overlayScrollbarVertical = GraphicsLayer::create(this);

        ScrollingCoordinator* coordinator = frameHost().page().scrollingCoordinator();
        ASSERT(coordinator);
        coordinator->setLayerIsContainerForFixedPositionLayers(m_innerViewportScrollLayer.get(), true);

        // Set masks to bounds so the compositor doesn't clobber a manually
        // set inner viewport container layer size.
        m_innerViewportContainerLayer->setMasksToBounds(frameHost().settings().mainFrameClipsContent());
        m_innerViewportContainerLayer->setSize(FloatSize(m_size));

        m_innerViewportScrollLayer->platformLayer()->setScrollClipLayer(
            m_innerViewportContainerLayer->platformLayer());
        m_innerViewportScrollLayer->platformLayer()->setUserScrollable(true, true);

        m_rootTransformLayer->addChild(m_innerViewportContainerLayer.get());
        m_innerViewportContainerLayer->addChild(m_overscrollElasticityLayer.get());
        m_overscrollElasticityLayer->addChild(m_pageScaleLayer.get());
        m_pageScaleLayer->addChild(m_innerViewportScrollLayer.get());

        // Ensure this class is set as the scroll layer's ScrollableArea.
        coordinator->scrollableAreaScrollLayerDidChange(this);

        initializeScrollbars();
    }

    m_innerViewportScrollLayer->removeAllChildren();
    m_innerViewportScrollLayer->addChild(currentLayerTreeRoot);
}

void VisualViewport::initializeScrollbars()
{
    // Do nothing if not attached to layer tree yet - will initialize upon attach.
    if (!m_innerViewportContainerLayer)
        return;

    if (visualViewportSuppliesScrollbars()) {
        if (!m_overlayScrollbarHorizontal->parent())
            m_innerViewportContainerLayer->addChild(m_overlayScrollbarHorizontal.get());
        if (!m_overlayScrollbarVertical->parent())
            m_innerViewportContainerLayer->addChild(m_overlayScrollbarVertical.get());
    } else {
        m_overlayScrollbarHorizontal->removeFromParent();
        m_overlayScrollbarVertical->removeFromParent();
    }

    setupScrollbar(WebScrollbar::Horizontal);
    setupScrollbar(WebScrollbar::Vertical);
}

void VisualViewport::setupScrollbar(WebScrollbar::Orientation orientation)
{
    bool isHorizontal = orientation == WebScrollbar::Horizontal;
    GraphicsLayer* scrollbarGraphicsLayer = isHorizontal ?
        m_overlayScrollbarHorizontal.get() : m_overlayScrollbarVertical.get();
    std::unique_ptr<WebScrollbarLayer>& webScrollbarLayer = isHorizontal ?
        m_webOverlayScrollbarHorizontal : m_webOverlayScrollbarVertical;

    ScrollbarThemeOverlay& theme = ScrollbarThemeOverlay::mobileTheme();
    int thumbThickness = theme.thumbThickness();
    int scrollbarThickness = theme.scrollbarThickness(RegularScrollbar);
    int scrollbarMargin = theme.scrollbarMargin();

    if (!webScrollbarLayer) {
        ScrollingCoordinator* coordinator = frameHost().page().scrollingCoordinator();
        ASSERT(coordinator);
        ScrollbarOrientation webcoreOrientation = isHorizontal ? HorizontalScrollbar : VerticalScrollbar;
        webScrollbarLayer = coordinator->createSolidColorScrollbarLayer(webcoreOrientation, thumbThickness, scrollbarMargin, false);

        // The compositor will control the scrollbar's visibility. Set to invisible by defualt
        // so scrollbars don't show up in layout tests.
        webScrollbarLayer->layer()->setOpacity(0);
        scrollbarGraphicsLayer->setContentsToPlatformLayer(webScrollbarLayer->layer());
        scrollbarGraphicsLayer->setDrawsContent(false);
    }

    int xPosition = isHorizontal ? 0 : m_innerViewportContainerLayer->size().width() - scrollbarThickness;
    int yPosition = isHorizontal ? m_innerViewportContainerLayer->size().height() - scrollbarThickness : 0;
    int width = isHorizontal ? m_innerViewportContainerLayer->size().width() - scrollbarThickness : scrollbarThickness;
    int height = isHorizontal ? scrollbarThickness : m_innerViewportContainerLayer->size().height() - scrollbarThickness;

    // Use the GraphicsLayer to position the scrollbars.
    scrollbarGraphicsLayer->setPosition(IntPoint(xPosition, yPosition));
    scrollbarGraphicsLayer->setSize(FloatSize(width, height));
    scrollbarGraphicsLayer->setContentsRect(IntRect(0, 0, width, height));
}

void VisualViewport::registerLayersWithTreeView(WebLayerTreeView* layerTreeView) const
{
    TRACE_EVENT0("blink", "VisualViewport::registerLayersWithTreeView");
    ASSERT(layerTreeView);

    if (!mainFrame())
        return;

    ASSERT(!frameHost().page().deprecatedLocalMainFrame()->contentLayoutItem().isNull());

    PaintLayerCompositor* compositor = frameHost().page().deprecatedLocalMainFrame()->contentLayoutItem().compositor();
    // Get the outer viewport scroll layer.
    WebLayer* scrollLayer = compositor->scrollLayer() ? compositor->scrollLayer()->platformLayer() : 0;

    m_webOverlayScrollbarHorizontal->setScrollLayer(scrollLayer);
    m_webOverlayScrollbarVertical->setScrollLayer(scrollLayer);

    ASSERT(compositor);
    layerTreeView->registerViewportLayers(
        m_overscrollElasticityLayer->platformLayer(),
        m_pageScaleLayer->platformLayer(),
        m_innerViewportScrollLayer->platformLayer(),
        scrollLayer);
}

bool VisualViewport::visualViewportSuppliesScrollbars() const
{
    return frameHost().settings().viewportEnabled();
}

bool VisualViewport::scrollAnimatorEnabled() const
{
    return frameHost().settings().scrollAnimatorEnabled();
}

void VisualViewport::clearLayersForTreeView(WebLayerTreeView* layerTreeView) const
{
    ASSERT(layerTreeView);

    layerTreeView->clearViewportLayers();
}

HostWindow* VisualViewport::getHostWindow() const
{
    return &frameHost().chromeClient();
}

DoubleRect VisualViewport::visibleContentRectDouble(IncludeScrollbarsInRect) const
{
    return visibleRect();
}

IntRect VisualViewport::visibleContentRect(IncludeScrollbarsInRect scrollbarInclusion) const
{
    return enclosingIntRect(visibleContentRectDouble(scrollbarInclusion));
}

bool VisualViewport::shouldUseIntegerScrollOffset() const
{
    LocalFrame* frame = mainFrame();
    if (frame && frame->settings() && !frame->settings()->preferCompositingToLCDTextEnabled())
        return true;

    return ScrollableArea::shouldUseIntegerScrollOffset();
}

int VisualViewport::scrollSize(ScrollbarOrientation orientation) const
{
    IntSize scrollDimensions = maximumScrollPosition() - minimumScrollPosition();
    return (orientation == HorizontalScrollbar) ? scrollDimensions.width() : scrollDimensions.height();
}

IntPoint VisualViewport::minimumScrollPosition() const
{
    return IntPoint();
}

IntPoint VisualViewport::maximumScrollPosition() const
{
    return flooredIntPoint(maximumScrollPositionDouble());
}

DoublePoint VisualViewport::maximumScrollPositionDouble() const
{
    if (!mainFrame())
        return IntPoint();

    // TODO(bokan): We probably shouldn't be storing the bounds in a float. crbug.com/470718.
    FloatSize frameViewSize(contentsSize());

    if (m_topControlsAdjustment) {
        float minScale = frameHost().pageScaleConstraintsSet().finalConstraints().minimumScale;
        frameViewSize.expand(0, m_topControlsAdjustment / minScale);
    }

    frameViewSize.scale(m_scale);
    frameViewSize = FloatSize(flooredIntSize(frameViewSize));

    FloatSize viewportSize(m_size);
    viewportSize.expand(0, ceilf(m_topControlsAdjustment));

    FloatSize maxPosition = frameViewSize - viewportSize;
    maxPosition.scale(1 / m_scale);
    return DoublePoint(maxPosition);
}

IntPoint VisualViewport::clampDocumentOffsetAtScale(const IntPoint& offset, float scale)
{
    if (!mainFrame() || !mainFrame()->view())
        return IntPoint();

    FrameView* view = mainFrame()->view();

    FloatSize scaledSize(m_size);
    scaledSize.scale(1 / scale);

    IntPoint visualViewportMax = flooredIntPoint(FloatSize(contentsSize()) - scaledSize);
    IntPoint max = view->maximumScrollPosition() + visualViewportMax;
    IntPoint min = view->minimumScrollPosition(); // VisualViewportMin should be (0, 0)

    IntPoint clamped = offset;
    clamped = clamped.shrunkTo(max);
    clamped = clamped.expandedTo(min);
    return clamped;
}

void VisualViewport::setTopControlsAdjustment(float adjustment)
{
    m_topControlsAdjustment = adjustment;
}

IntRect VisualViewport::scrollableAreaBoundingBox() const
{
    // This method should return the bounding box in the parent view's coordinate
    // space; however, VisualViewport technically isn't a child of any Frames.
    // Nonetheless, the VisualViewport always occupies the entire main frame so just
    // return that.
    LocalFrame* frame = mainFrame();

    if (!frame || !frame->view())
        return IntRect();

    return frame->view()->frameRect();
}

IntSize VisualViewport::contentsSize() const
{
    LocalFrame* frame = mainFrame();

    if (!frame || !frame->view())
        return IntSize();

    return frame->view()->visibleContentRect(IncludeScrollbars).size();
}

void VisualViewport::setScrollOffset(const DoublePoint& offset, ScrollType)
{
    setLocation(toFloatPoint(offset));
}

GraphicsLayer* VisualViewport::layerForContainer() const
{
    return m_innerViewportContainerLayer.get();
}

GraphicsLayer* VisualViewport::layerForScrolling() const
{
    return m_innerViewportScrollLayer.get();
}

GraphicsLayer* VisualViewport::layerForHorizontalScrollbar() const
{
    return m_overlayScrollbarHorizontal.get();
}

GraphicsLayer* VisualViewport::layerForVerticalScrollbar() const
{
    return m_overlayScrollbarVertical.get();
}

IntRect VisualViewport::computeInterestRect(const GraphicsLayer*, const IntRect&) const
{
    return IntRect();
}

void VisualViewport::paintContents(const GraphicsLayer*, GraphicsContext&, GraphicsLayerPaintingPhase, const IntRect&) const
{
}

LocalFrame* VisualViewport::mainFrame() const
{
    return frameHost().page().mainFrame() && frameHost().page().mainFrame()->isLocalFrame() ? frameHost().page().deprecatedLocalMainFrame() : 0;
}

Widget* VisualViewport::getWidget()
{
    return mainFrame()->view();
}

FloatPoint VisualViewport::clampOffsetToBoundaries(const FloatPoint& offset)
{
    FloatPoint clampedOffset(offset);
    clampedOffset = clampedOffset.shrunkTo(FloatPoint(maximumScrollPositionDouble()));
    clampedOffset = clampedOffset.expandedTo(FloatPoint(minimumScrollPositionDouble()));
    return clampedOffset;
}

void VisualViewport::clampToBoundaries()
{
    setLocation(m_offset);
}

FloatRect VisualViewport::viewportToRootFrame(const FloatRect& rectInViewport) const
{
    FloatRect rectInRootFrame = rectInViewport;
    rectInRootFrame.scale(1 / scale());
    rectInRootFrame.moveBy(location());
    return rectInRootFrame;
}

IntRect VisualViewport::viewportToRootFrame(const IntRect& rectInViewport) const
{
    // FIXME: How to snap to pixels?
    return enclosingIntRect(viewportToRootFrame(FloatRect(rectInViewport)));
}

FloatRect VisualViewport::rootFrameToViewport(const FloatRect& rectInRootFrame) const
{
    FloatRect rectInViewport = rectInRootFrame;
    rectInViewport.moveBy(-location());
    rectInViewport.scale(scale());
    return rectInViewport;
}

IntRect VisualViewport::rootFrameToViewport(const IntRect& rectInRootFrame) const
{
    // FIXME: How to snap to pixels?
    return enclosingIntRect(rootFrameToViewport(FloatRect(rectInRootFrame)));
}

FloatPoint VisualViewport::viewportToRootFrame(const FloatPoint& pointInViewport) const
{
    FloatPoint pointInRootFrame = pointInViewport;
    pointInRootFrame.scale(1 / scale(), 1 / scale());
    pointInRootFrame.moveBy(location());
    return pointInRootFrame;
}

FloatPoint VisualViewport::rootFrameToViewport(const FloatPoint& pointInRootFrame) const
{
    FloatPoint pointInViewport = pointInRootFrame;
    pointInViewport.moveBy(-location());
    pointInViewport.scale(scale(), scale());
    return pointInViewport;
}

IntPoint VisualViewport::viewportToRootFrame(const IntPoint& pointInViewport) const
{
    // FIXME: How to snap to pixels?
    return flooredIntPoint(FloatPoint(viewportToRootFrame(FloatPoint(pointInViewport))));
}

IntPoint VisualViewport::rootFrameToViewport(const IntPoint& pointInRootFrame) const
{
    // FIXME: How to snap to pixels?
    return flooredIntPoint(FloatPoint(rootFrameToViewport(FloatPoint(pointInRootFrame))));
}

void VisualViewport::startTrackingPinchStats()
{
    if (!mainFrame())
        return;

    Document* document = mainFrame()->document();
    if (!document)
        return;

    if (!document->url().protocolIsInHTTPFamily())
        return;

    m_trackPinchZoomStatsForPage = !shouldDisableDesktopWorkarounds();
}

void VisualViewport::userDidChangeScale()
{
    if (!m_trackPinchZoomStatsForPage)
        return;

    m_maxPageScale = std::max(m_maxPageScale, m_scale);
}

void VisualViewport::sendUMAMetrics()
{
    if (m_trackPinchZoomStatsForPage) {
        bool didScale = m_maxPageScale > 0;

        DEFINE_STATIC_LOCAL(EnumerationHistogram, didScaleHistogram, ("Viewport.DidScalePage", 2));
        didScaleHistogram.count(didScale ? 1 : 0);

        if (didScale) {
            int zoomPercentage = floor(m_maxPageScale * 100);

            // See the PageScaleFactor enumeration in histograms.xml for the bucket ranges.
            int bucket = floor(zoomPercentage / 25.f);

            DEFINE_STATIC_LOCAL(EnumerationHistogram, maxScaleHistogram, ("Viewport.MaxPageScale", 21));
            maxScaleHistogram.count(bucket);
        }
    }

    m_maxPageScale = -1;
    m_trackPinchZoomStatsForPage = false;
}

bool VisualViewport::shouldDisableDesktopWorkarounds() const
{
    if (!mainFrame() || !mainFrame()->view())
        return false;

    if (!mainFrame()->settings()->viewportEnabled())
        return false;

    // A document is considered adapted to small screen UAs if one of these holds:
    // 1. The author specified viewport has a constrained width that is equal to
    //    the initial viewport width.
    // 2. The author has disabled viewport zoom.
    const PageScaleConstraints& constraints = frameHost().pageScaleConstraintsSet().pageDefinedConstraints();

    return mainFrame()->view()->layoutSize().width() == m_size.width()
        || (constraints.minimumScale == constraints.maximumScale && constraints.minimumScale != -1);
}

CompositorAnimationTimeline* VisualViewport::compositorAnimationTimeline() const
{
    ScrollingCoordinator* c = frameHost().page().scrollingCoordinator();
    return c ? c->compositorAnimationTimeline() : nullptr;
}

String VisualViewport::debugName(const GraphicsLayer* graphicsLayer) const
{
    String name;
    if (graphicsLayer == m_innerViewportContainerLayer.get()) {
        name = "Inner Viewport Container Layer";
    } else if (graphicsLayer == m_overscrollElasticityLayer.get()) {
        name =  "Overscroll Elasticity Layer";
    } else if (graphicsLayer == m_pageScaleLayer.get()) {
        name =  "Page Scale Layer";
    } else if (graphicsLayer == m_innerViewportScrollLayer.get()) {
        name =  "Inner Viewport Scroll Layer";
    } else if (graphicsLayer == m_overlayScrollbarHorizontal.get()) {
        name =  "Overlay Scrollbar Horizontal Layer";
    } else if (graphicsLayer == m_overlayScrollbarVertical.get()) {
        name =  "Overlay Scrollbar Vertical Layer";
    } else if (graphicsLayer == m_rootTransformLayer.get()) {
        name =  "Root Transform Layer";
    } else {
        ASSERT_NOT_REACHED();
    }

    return name;
}

} // namespace blink