Source/core/rendering/RenderView.cpp

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This source file includes following definitions.
m_renderCounterCount
hitTest
hitTest
computeLogicalHeight
updateLogicalWidth
availableLogicalHeight
isChildAllowed
canCenterDialog
positionDialog
positionDialogs
layoutContent
checkLayoutState
layout
mapLocalToContainer
pushMappingToContainer
mapAbsoluteToLocalPoint
computeSelfHitTestRects
paint
rendererObscuresBackground
rootFillsViewportBackground
paintBoxDecorations
shouldRepaint
repaintViewRectangle
repaintViewAndCompositedLayers
computeRectForRepaint
absoluteRects
absoluteQuads
rendererAfterPosition
selectionBounds
repaintSelection
getNextOrPrevRenderObjectBasedOnDirection
setSelection
getSelection
clearSelection
selectionStartEnd
shouldUsePrintingLayout
viewRect
unscaledDocumentRect
rootBackgroundIsEntirelyFixed
backgroundRect
documentRect
viewHeight
viewWidth
viewLogicalHeight
zoomFactor
pushLayoutState
shouldDisableLayoutStateForSubtree
updateHitTestResult
usesCompositing
compositor
setIsInWindow
flowThreadController
pushLayoutStateForCurrentFlowThread
popLayoutStateForCurrentFlowThread
intervalArena
backgroundIsKnownToBeOpaqueInRect
layoutViewportWidth
layoutViewportHeight
/*
 * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
 * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
 *
 * 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 "core/rendering/RenderView.h"

#include "RuntimeEnabledFeatures.h"
#include "core/dom/Document.h"
#include "core/dom/Element.h"
#include "core/frame/LocalFrame.h"
#include "core/html/HTMLDialogElement.h"
#include "core/html/HTMLFrameOwnerElement.h"
#include "core/html/HTMLIFrameElement.h"
#include "core/page/Page.h"
#include "core/rendering/ColumnInfo.h"
#include "core/rendering/FlowThreadController.h"
#include "core/rendering/GraphicsContextAnnotator.h"
#include "core/rendering/HitTestResult.h"
#include "core/rendering/LayoutRectRecorder.h"
#include "core/rendering/RenderFlowThread.h"
#include "core/rendering/RenderGeometryMap.h"
#include "core/rendering/RenderLayer.h"
#include "core/rendering/RenderSelectionInfo.h"
#include "core/rendering/compositing/CompositedLayerMapping.h"
#include "core/rendering/compositing/RenderLayerCompositor.h"
#include "core/svg/SVGDocumentExtensions.h"
#include "platform/geometry/FloatQuad.h"
#include "platform/geometry/TransformState.h"
#include "platform/graphics/GraphicsContext.h"

namespace WebCore {

RenderView::RenderView(Document* document)
    : RenderBlockFlow(document)
    , m_frameView(document->view())
    , m_selectionStart(0)
    , m_selectionEnd(0)
    , m_selectionStartPos(-1)
    , m_selectionEndPos(-1)
    , m_pageLogicalHeight(0)
    , m_pageLogicalHeightChanged(false)
    , m_layoutState(0)
    , m_layoutStateDisableCount(0)
    , m_renderQuoteHead(0)
    , m_renderCounterCount(0)
{
    // init RenderObject attributes
    setInline(false);

    m_minPreferredLogicalWidth = 0;
    m_maxPreferredLogicalWidth = 0;

    setPreferredLogicalWidthsDirty(MarkOnlyThis);

    setPositionState(AbsolutePosition); // to 0,0 :)
}

RenderView::~RenderView()
{
}

bool RenderView::hitTest(const HitTestRequest& request, HitTestResult& result)
{
    return hitTest(request, result.hitTestLocation(), result);
}

bool RenderView::hitTest(const HitTestRequest& request, const HitTestLocation& location, HitTestResult& result)
{
    // We have to recursively update layout/style here because otherwise, when the hit test recurses
    // into a child document, it could trigger a layout on the parent document, which can destroy RenderLayers
    // that are higher up in the call stack, leading to crashes.
    // Note that Document::updateLayout calls its parent's updateLayout.
    // FIXME: It should be the caller's responsibility to ensure an up-to-date layout.
    frameView()->updateLayoutAndStyleIfNeededRecursive();
    return layer()->hitTest(request, location, result);
}

void RenderView::computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit, LogicalExtentComputedValues& computedValues) const
{
    computedValues.m_extent = (!shouldUsePrintingLayout() && m_frameView) ? LayoutUnit(viewLogicalHeight()) : logicalHeight;
}

void RenderView::updateLogicalWidth()
{
    if (!shouldUsePrintingLayout() && m_frameView)
        setLogicalWidth(viewLogicalWidth());
}

LayoutUnit RenderView::availableLogicalHeight(AvailableLogicalHeightType heightType) const
{
    // If we have columns, then the available logical height is reduced to the column height.
    if (hasColumns())
        return columnInfo()->columnHeight();
    return RenderBlockFlow::availableLogicalHeight(heightType);
}

bool RenderView::isChildAllowed(RenderObject* child, RenderStyle*) const
{
    return child->isBox();
}

static bool canCenterDialog(const RenderStyle* style)
{
    // FIXME: We must center for FixedPosition as well.
    return style->position() == AbsolutePosition && style->hasAutoTopAndBottom();
}

void RenderView::positionDialog(RenderBox* box)
{
    HTMLDialogElement* dialog = toHTMLDialogElement(box->node());
    if (dialog->centeringMode() == HTMLDialogElement::NotCentered)
        return;
    if (dialog->centeringMode() == HTMLDialogElement::Centered) {
        if (canCenterDialog(box->style()))
            box->setY(dialog->centeredPosition());
        return;
    }

    ASSERT(dialog->centeringMode() == HTMLDialogElement::NeedsCentering);
    if (!canCenterDialog(box->style())) {
        dialog->setNotCentered();
        return;
    }
    FrameView* frameView = document().view();
    int scrollTop = frameView->scrollOffset().height();
    int visibleHeight = frameView->visibleContentRect(IncludeScrollbars).height();
    LayoutUnit top = scrollTop;
    if (box->height() < visibleHeight)
        top += (visibleHeight - box->height()) / 2;
    box->setY(top);
    dialog->setCentered(top);
}

void RenderView::positionDialogs()
{
    TrackedRendererListHashSet* positionedDescendants = positionedObjects();
    if (!positionedDescendants)
        return;
    TrackedRendererListHashSet::iterator end = positionedDescendants->end();
    for (TrackedRendererListHashSet::iterator it = positionedDescendants->begin(); it != end; ++it) {
        RenderBox* box = *it;
        if (isHTMLDialogElement(box->node()))
            positionDialog(box);
    }
}

void RenderView::layoutContent()
{
    ASSERT(needsLayout());

    LayoutRectRecorder recorder(*this);
    RenderBlockFlow::layout();

    if (RuntimeEnabledFeatures::dialogElementEnabled())
        positionDialogs();

#ifndef NDEBUG
    checkLayoutState();
#endif
}

#ifndef NDEBUG
void RenderView::checkLayoutState()
{
    if (!RuntimeEnabledFeatures::repaintAfterLayoutEnabled()) {
        ASSERT(layoutDeltaMatches(LayoutSize()));
    }
    ASSERT(!m_layoutStateDisableCount);
    ASSERT(!m_layoutState->next());
}
#endif

void RenderView::layout()
{
    if (!document().paginated())
        setPageLogicalHeight(0);

    if (shouldUsePrintingLayout())
        m_minPreferredLogicalWidth = m_maxPreferredLogicalWidth = logicalWidth();

    SubtreeLayoutScope layoutScope(this);

    // Use calcWidth/Height to get the new width/height, since this will take the full page zoom factor into account.
    bool relayoutChildren = !shouldUsePrintingLayout() && (!m_frameView || width() != viewWidth() || height() != viewHeight());
    if (relayoutChildren) {
        layoutScope.setChildNeedsLayout(this);
        for (RenderObject* child = firstChild(); child; child = child->nextSibling()) {
            if (child->isSVGRoot())
                continue;

            if ((child->isBox() && toRenderBox(child)->hasRelativeLogicalHeight())
                    || child->style()->logicalHeight().isPercent()
                    || child->style()->logicalMinHeight().isPercent()
                    || child->style()->logicalMaxHeight().isPercent())
                layoutScope.setChildNeedsLayout(child);
        }

        if (document().svgExtensions())
            document().accessSVGExtensions().invalidateSVGRootsWithRelativeLengthDescendents(&layoutScope);
    }

    ASSERT(!m_layoutState);
    if (!needsLayout())
        return;

    RootLayoutStateScope rootLayoutStateScope(*this);

    m_pageLogicalHeightChanged = false;

    layoutContent();

#ifndef NDEBUG
    checkLayoutState();
#endif
    clearNeedsLayout();
}

void RenderView::mapLocalToContainer(const RenderLayerModelObject* repaintContainer, TransformState& transformState, MapCoordinatesFlags mode, bool* wasFixed) const
{
    ASSERT_UNUSED(wasFixed, !wasFixed || *wasFixed == static_cast<bool>(mode & IsFixed));

    if (!repaintContainer && mode & UseTransforms && shouldUseTransformFromContainer(0)) {
        TransformationMatrix t;
        getTransformFromContainer(0, LayoutSize(), t);
        transformState.applyTransform(t);
    }

    if (mode & IsFixed && m_frameView)
        transformState.move(m_frameView->scrollOffsetForFixedPosition());

    if (repaintContainer == this)
        return;

    if (mode & TraverseDocumentBoundaries) {
        if (RenderObject* parentDocRenderer = frame()->ownerRenderer()) {
            transformState.move(-frame()->view()->scrollOffset());
            if (parentDocRenderer->isBox())
                transformState.move(toLayoutSize(toRenderBox(parentDocRenderer)->contentBoxRect().location()));
            parentDocRenderer->mapLocalToContainer(repaintContainer, transformState, mode, wasFixed);
            return;
        }
    }

    // If a container was specified, and was not 0 or the RenderView,
    // then we should have found it by now.
    ASSERT_ARG(repaintContainer, !repaintContainer);
}

const RenderObject* RenderView::pushMappingToContainer(const RenderLayerModelObject* ancestorToStopAt, RenderGeometryMap& geometryMap) const
{
    LayoutSize offsetForFixedPosition;
    LayoutSize offset;
    RenderObject* container = 0;

    if (m_frameView)
        offsetForFixedPosition = m_frameView->scrollOffsetForFixedPosition();

    if (geometryMap.mapCoordinatesFlags() & TraverseDocumentBoundaries) {
        if (RenderPart* parentDocRenderer = frame()->ownerRenderer()) {
            offset = -m_frameView->scrollOffset();
            offset += toLayoutSize(parentDocRenderer->contentBoxRect().location());
            container = parentDocRenderer;
        }
    }

    // If a container was specified, and was not 0 or the RenderView, then we
    // should have found it by now unless we're traversing to a parent document.
    ASSERT_ARG(ancestorToStopAt, !ancestorToStopAt || ancestorToStopAt == this || container);

    if ((!ancestorToStopAt || container) && shouldUseTransformFromContainer(container)) {
        TransformationMatrix t;
        getTransformFromContainer(container, LayoutSize(), t);
        geometryMap.push(this, t, false, false, false, true, offsetForFixedPosition);
    } else {
        geometryMap.push(this, offset, false, false, false, false, offsetForFixedPosition);
    }

    return container;
}

void RenderView::mapAbsoluteToLocalPoint(MapCoordinatesFlags mode, TransformState& transformState) const
{
    if (mode & IsFixed && m_frameView)
        transformState.move(m_frameView->scrollOffsetForFixedPosition());

    if (mode & UseTransforms && shouldUseTransformFromContainer(0)) {
        TransformationMatrix t;
        getTransformFromContainer(0, LayoutSize(), t);
        transformState.applyTransform(t);
    }
}

void RenderView::computeSelfHitTestRects(Vector<LayoutRect>& rects, const LayoutPoint&) const
{
    // Record the entire size of the contents of the frame. Note that we don't just
    // use the viewport size (containing block) here because we want to ensure this includes
    // all children (so we can avoid walking them explicitly).
    rects.append(LayoutRect(LayoutPoint::zero(), frameView()->contentsSize()));
}

void RenderView::paint(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
{
    // If we ever require layout but receive a paint anyway, something has gone horribly wrong.
    ASSERT(!needsLayout());
    // RenderViews should never be called to paint with an offset not on device pixels.
    ASSERT(LayoutPoint(IntPoint(paintOffset.x(), paintOffset.y())) == paintOffset);

    ANNOTATE_GRAPHICS_CONTEXT(paintInfo, this);

    // This avoids painting garbage between columns if there is a column gap.
    if (m_frameView && style()->isOverflowPaged())
        paintInfo.context->fillRect(paintInfo.rect, m_frameView->baseBackgroundColor());

    paintObject(paintInfo, paintOffset);
}

static inline bool rendererObscuresBackground(RenderBox* rootBox)
{
    ASSERT(rootBox);
    RenderStyle* style = rootBox->style();
    if (style->visibility() != VISIBLE
        || style->opacity() != 1
        || style->hasFilter()
        || style->hasTransform())
        return false;

    if (rootBox->compositingState() == PaintsIntoOwnBacking)
        return false;

    const RenderObject* rootRenderer = rootBox->rendererForRootBackground();
    if (rootRenderer->style()->backgroundClip() == TextFillBox)
        return false;

    return true;
}

bool RenderView::rootFillsViewportBackground(RenderBox* rootBox) const
{
    ASSERT(rootBox);
    // CSS Boxes always fill the viewport background (see paintRootBoxFillLayers)
    if (!rootBox->isSVG())
        return true;

    return rootBox->frameRect().contains(frameRect());
}

void RenderView::paintBoxDecorations(PaintInfo& paintInfo, const LayoutPoint&)
{
    // Check to see if we are enclosed by a layer that requires complex painting rules.  If so, we cannot blit
    // when scrolling, and we need to use slow repaints.  Examples of layers that require this are transparent layers,
    // layers with reflections, or transformed layers.
    // FIXME: This needs to be dynamic.  We should be able to go back to blitting if we ever stop being inside
    // a transform, transparency layer, etc.
    Element* elt;
    for (elt = document().ownerElement(); view() && elt && elt->renderer(); elt = elt->document().ownerElement()) {
        RenderLayer* layer = elt->renderer()->enclosingLayer();
        if (layer->cannotBlitToWindow()) {
            frameView()->setCannotBlitToWindow();
            break;
        }

        if (layer->enclosingCompositingLayerForRepaint()) {
            frameView()->setCannotBlitToWindow();
            break;
        }
    }

    if (document().ownerElement() || !view())
        return;

    if (paintInfo.skipRootBackground())
        return;

    bool shouldPaintBackground = true;
    Node* documentElement = document().documentElement();
    if (RenderBox* rootBox = documentElement ? toRenderBox(documentElement->renderer()) : 0)
        shouldPaintBackground = !rootFillsViewportBackground(rootBox) || !rendererObscuresBackground(rootBox);

    // If painting will entirely fill the view, no need to fill the background.
    if (!shouldPaintBackground)
        return;

    // This code typically only executes if the root element's visibility has been set to hidden,
    // if there is a transform on the <html>, or if there is a page scale factor less than 1.
    // Only fill with the base background color (typically white) if we're the root document,
    // since iframes/frames with no background in the child document should show the parent's background.
    if (frameView()->isTransparent()) // FIXME: This needs to be dynamic.  We should be able to go back to blitting if we ever stop being transparent.
        frameView()->setCannotBlitToWindow(); // The parent must show behind the child.
    else {
        Color baseColor = frameView()->baseBackgroundColor();
        if (baseColor.alpha()) {
            CompositeOperator previousOperator = paintInfo.context->compositeOperation();
            paintInfo.context->setCompositeOperation(CompositeCopy);
            paintInfo.context->fillRect(paintInfo.rect, baseColor);
            paintInfo.context->setCompositeOperation(previousOperator);
        } else {
            paintInfo.context->clearRect(paintInfo.rect);
        }
    }
}

bool RenderView::shouldRepaint(const LayoutRect& rect) const
{
    if (document().printing())
        return false;
    return m_frameView && !rect.isEmpty();
}

void RenderView::repaintViewRectangle(const LayoutRect& ur) const
{
    if (!shouldRepaint(ur))
        return;

    // We always just invalidate the root view, since we could be an iframe that is clipped out
    // or even invisible.
    Element* elt = document().ownerElement();
    if (!elt)
        m_frameView->repaintContentRectangle(pixelSnappedIntRect(ur));
    else if (RenderBox* obj = elt->renderBox()) {
        LayoutRect vr = viewRect();
        LayoutRect r = intersection(ur, vr);

        // Subtract out the contentsX and contentsY offsets to get our coords within the viewing
        // rectangle.
        r.moveBy(-vr.location());

        // FIXME: Hardcoded offsets here are not good.
        r.moveBy(obj->contentBoxRect().location());
        obj->repaintRectangle(r);
    }
}

void RenderView::repaintViewAndCompositedLayers()
{
    repaint();

    // The only way we know how to hit these ASSERTS below this point is via the Chromium OS login screen.
    DisableCompositingQueryAsserts disabler;

    if (compositor()->inCompositingMode())
        compositor()->repaintCompositedLayers();
}

void RenderView::computeRectForRepaint(const RenderLayerModelObject* repaintContainer, LayoutRect& rect, bool fixed) const
{
    // If a container was specified, and was not 0 or the RenderView,
    // then we should have found it by now.
    ASSERT_ARG(repaintContainer, !repaintContainer || repaintContainer == this);

    if (document().printing())
        return;

    if (style()->isFlippedBlocksWritingMode()) {
        // We have to flip by hand since the view's logical height has not been determined.  We
        // can use the viewport width and height.
        if (style()->isHorizontalWritingMode())
            rect.setY(viewHeight() - rect.maxY());
        else
            rect.setX(viewWidth() - rect.maxX());
    }

    if (fixed && m_frameView) {
        rect.move(m_frameView->scrollOffsetForFixedPosition());
        // If we have a pending scroll, invalidate the previous scroll position.
        if (!m_frameView->pendingScrollDelta().isZero()) {
            rect.move(-m_frameView->pendingScrollDelta());
        }
    }

    // Apply our transform if we have one (because of full page zooming).
    if (!repaintContainer && layer() && layer()->transform())
        rect = layer()->transform()->mapRect(rect);
}

void RenderView::absoluteRects(Vector<IntRect>& rects, const LayoutPoint& accumulatedOffset) const
{
    rects.append(pixelSnappedIntRect(accumulatedOffset, layer()->size()));
}

void RenderView::absoluteQuads(Vector<FloatQuad>& quads, bool* wasFixed) const
{
    if (wasFixed)
        *wasFixed = false;
    quads.append(FloatRect(FloatPoint(), layer()->size()));
}

static RenderObject* rendererAfterPosition(RenderObject* object, unsigned offset)
{
    if (!object)
        return 0;

    RenderObject* child = object->childAt(offset);
    return child ? child : object->nextInPreOrderAfterChildren();
}

IntRect RenderView::selectionBounds(bool clipToVisibleContent) const
{
    typedef HashMap<RenderObject*, OwnPtr<RenderSelectionInfo> > SelectionMap;
    SelectionMap selectedObjects;

    RenderObject* os = m_selectionStart;
    RenderObject* stop = rendererAfterPosition(m_selectionEnd, m_selectionEndPos);
    while (os && os != stop) {
        if ((os->canBeSelectionLeaf() || os == m_selectionStart || os == m_selectionEnd) && os->selectionState() != SelectionNone) {
            // Blocks are responsible for painting line gaps and margin gaps. They must be examined as well.
            selectedObjects.set(os, adoptPtr(new RenderSelectionInfo(os, clipToVisibleContent)));
            RenderBlock* cb = os->containingBlock();
            while (cb && !cb->isRenderView()) {
                OwnPtr<RenderSelectionInfo>& blockInfo = selectedObjects.add(cb, nullptr).storedValue->value;
                if (blockInfo)
                    break;
                blockInfo = adoptPtr(new RenderSelectionInfo(cb, clipToVisibleContent));
                cb = cb->containingBlock();
            }
        }

        os = os->nextInPreOrder();
    }

    // Now create a single bounding box rect that encloses the whole selection.
    LayoutRect selRect;
    SelectionMap::iterator end = selectedObjects.end();
    for (SelectionMap::iterator i = selectedObjects.begin(); i != end; ++i) {
        RenderSelectionInfo* info = i->value.get();
        // RenderSelectionInfo::rect() is in the coordinates of the repaintContainer, so map to page coordinates.
        LayoutRect currRect = info->rect();
        if (RenderLayerModelObject* repaintContainer = info->repaintContainer()) {
            FloatQuad absQuad = repaintContainer->localToAbsoluteQuad(FloatRect(currRect));
            currRect = absQuad.enclosingBoundingBox();
        }
        selRect.unite(currRect);
    }
    return pixelSnappedIntRect(selRect);
}

void RenderView::repaintSelection() const
{
    HashSet<RenderBlock*> processedBlocks;

    RenderObject* end = rendererAfterPosition(m_selectionEnd, m_selectionEndPos);
    for (RenderObject* o = m_selectionStart; o && o != end; o = o->nextInPreOrder()) {
        if (!o->canBeSelectionLeaf() && o != m_selectionStart && o != m_selectionEnd)
            continue;
        if (o->selectionState() == SelectionNone)
            continue;

        RenderSelectionInfo(o, true).repaint();

        // Blocks are responsible for painting line gaps and margin gaps. They must be examined as well.
        for (RenderBlock* block = o->containingBlock(); block && !block->isRenderView(); block = block->containingBlock()) {
            if (!processedBlocks.add(block).isNewEntry)
                break;
            RenderSelectionInfo(block, true).repaint();
        }
    }
}

// When exploring the RenderTree looking for the nodes involved in the Selection, sometimes it's
// required to change the traversing direction because the "start" position is below the "end" one.
static inline RenderObject* getNextOrPrevRenderObjectBasedOnDirection(const RenderObject* o, const RenderObject* stop, bool& continueExploring, bool& exploringBackwards)
{
    RenderObject* next;
    if (exploringBackwards) {
        next = o->previousInPreOrder();
        continueExploring = next && !(next)->isRenderView();
    } else {
        next = o->nextInPreOrder();
        continueExploring = next && next != stop;
        exploringBackwards = !next && (next != stop);
        if (exploringBackwards) {
            next = stop->previousInPreOrder();
            continueExploring = next && !next->isRenderView();
        }
    }

    return next;
}

void RenderView::setSelection(RenderObject* start, int startPos, RenderObject* end, int endPos, SelectionRepaintMode blockRepaintMode)
{
    // This code makes no assumptions as to if the rendering tree is up to date or not
    // and will not try to update it. Currently clearSelection calls this
    // (intentionally) without updating the rendering tree as it doesn't care.
    // Other callers may want to force recalc style before calling this.

    // Make sure both our start and end objects are defined.
    // Check www.msnbc.com and try clicking around to find the case where this happened.
    if ((start && !end) || (end && !start))
        return;

    // Just return if the selection hasn't changed.
    if (m_selectionStart == start && m_selectionStartPos == startPos &&
        m_selectionEnd == end && m_selectionEndPos == endPos)
        return;

    // Record the old selected objects.  These will be used later
    // when we compare against the new selected objects.
    int oldStartPos = m_selectionStartPos;
    int oldEndPos = m_selectionEndPos;

    // Objects each have a single selection rect to examine.
    typedef HashMap<RenderObject*, OwnPtr<RenderSelectionInfo> > SelectedObjectMap;
    SelectedObjectMap oldSelectedObjects;
    SelectedObjectMap newSelectedObjects;

    // Blocks contain selected objects and fill gaps between them, either on the left, right, or in between lines and blocks.
    // In order to get the repaint rect right, we have to examine left, middle, and right rects individually, since otherwise
    // the union of those rects might remain the same even when changes have occurred.
    typedef HashMap<RenderBlock*, OwnPtr<RenderBlockSelectionInfo> > SelectedBlockMap;
    SelectedBlockMap oldSelectedBlocks;
    SelectedBlockMap newSelectedBlocks;

    RenderObject* os = m_selectionStart;
    RenderObject* stop = rendererAfterPosition(m_selectionEnd, m_selectionEndPos);
    bool exploringBackwards = false;
    bool continueExploring = os && (os != stop);
    while (continueExploring) {
        if ((os->canBeSelectionLeaf() || os == m_selectionStart || os == m_selectionEnd) && os->selectionState() != SelectionNone) {
            // Blocks are responsible for painting line gaps and margin gaps.  They must be examined as well.
            oldSelectedObjects.set(os, adoptPtr(new RenderSelectionInfo(os, true)));
            if (blockRepaintMode == RepaintNewXOROld) {
                RenderBlock* cb = os->containingBlock();
                while (cb && !cb->isRenderView()) {
                    OwnPtr<RenderBlockSelectionInfo>& blockInfo = oldSelectedBlocks.add(cb, nullptr).storedValue->value;
                    if (blockInfo)
                        break;
                    blockInfo = adoptPtr(new RenderBlockSelectionInfo(cb));
                    cb = cb->containingBlock();
                }
            }
        }

        os = getNextOrPrevRenderObjectBasedOnDirection(os, stop, continueExploring, exploringBackwards);
    }

    // Now clear the selection.
    SelectedObjectMap::iterator oldObjectsEnd = oldSelectedObjects.end();
    for (SelectedObjectMap::iterator i = oldSelectedObjects.begin(); i != oldObjectsEnd; ++i)
        i->key->setSelectionStateIfNeeded(SelectionNone);

    // set selection start and end
    m_selectionStart = start;
    m_selectionStartPos = startPos;
    m_selectionEnd = end;
    m_selectionEndPos = endPos;

    // Update the selection status of all objects between m_selectionStart and m_selectionEnd
    if (start && start == end)
        start->setSelectionStateIfNeeded(SelectionBoth);
    else {
        if (start)
            start->setSelectionStateIfNeeded(SelectionStart);
        if (end)
            end->setSelectionStateIfNeeded(SelectionEnd);
    }

    RenderObject* o = start;
    stop = rendererAfterPosition(end, endPos);

    while (o && o != stop) {
        if (o != start && o != end && o->canBeSelectionLeaf())
            o->setSelectionStateIfNeeded(SelectionInside);
        o = o->nextInPreOrder();
    }

    if (blockRepaintMode != RepaintNothing)
        layer()->clearBlockSelectionGapsBounds();

    // Now that the selection state has been updated for the new objects, walk them again and
    // put them in the new objects list.
    o = start;
    exploringBackwards = false;
    continueExploring = o && (o != stop);
    while (continueExploring) {
        if ((o->canBeSelectionLeaf() || o == start || o == end) && o->selectionState() != SelectionNone) {
            newSelectedObjects.set(o, adoptPtr(new RenderSelectionInfo(o, true)));
            RenderBlock* cb = o->containingBlock();
            while (cb && !cb->isRenderView()) {
                OwnPtr<RenderBlockSelectionInfo>& blockInfo = newSelectedBlocks.add(cb, nullptr).storedValue->value;
                if (blockInfo)
                    break;
                blockInfo = adoptPtr(new RenderBlockSelectionInfo(cb));
                cb = cb->containingBlock();
            }
        }

        o = getNextOrPrevRenderObjectBasedOnDirection(o, stop, continueExploring, exploringBackwards);
    }

    if (!m_frameView || blockRepaintMode == RepaintNothing)
        return;

    // Have any of the old selected objects changed compared to the new selection?
    for (SelectedObjectMap::iterator i = oldSelectedObjects.begin(); i != oldObjectsEnd; ++i) {
        RenderObject* obj = i->key;
        RenderSelectionInfo* newInfo = newSelectedObjects.get(obj);
        RenderSelectionInfo* oldInfo = i->value.get();
        if (!newInfo || oldInfo->rect() != newInfo->rect() || oldInfo->state() != newInfo->state() ||
            (m_selectionStart == obj && oldStartPos != m_selectionStartPos) ||
            (m_selectionEnd == obj && oldEndPos != m_selectionEndPos)) {
            oldInfo->repaint();
            if (newInfo) {
                newInfo->repaint();
                newSelectedObjects.remove(obj);
            }
        }
    }

    // Any new objects that remain were not found in the old objects dict, and so they need to be updated.
    SelectedObjectMap::iterator newObjectsEnd = newSelectedObjects.end();
    for (SelectedObjectMap::iterator i = newSelectedObjects.begin(); i != newObjectsEnd; ++i)
        i->value->repaint();

    // Have any of the old blocks changed?
    SelectedBlockMap::iterator oldBlocksEnd = oldSelectedBlocks.end();
    for (SelectedBlockMap::iterator i = oldSelectedBlocks.begin(); i != oldBlocksEnd; ++i) {
        RenderBlock* block = i->key;
        RenderBlockSelectionInfo* newInfo = newSelectedBlocks.get(block);
        RenderBlockSelectionInfo* oldInfo = i->value.get();
        if (!newInfo || oldInfo->rects() != newInfo->rects() || oldInfo->state() != newInfo->state()) {
            oldInfo->repaint();
            if (newInfo) {
                newInfo->repaint();
                newSelectedBlocks.remove(block);
            }
        }
    }

    // Any new blocks that remain were not found in the old blocks dict, and so they need to be updated.
    SelectedBlockMap::iterator newBlocksEnd = newSelectedBlocks.end();
    for (SelectedBlockMap::iterator i = newSelectedBlocks.begin(); i != newBlocksEnd; ++i)
        i->value->repaint();
}

void RenderView::getSelection(RenderObject*& startRenderer, int& startOffset, RenderObject*& endRenderer, int& endOffset) const
{
    startRenderer = m_selectionStart;
    startOffset = m_selectionStartPos;
    endRenderer = m_selectionEnd;
    endOffset = m_selectionEndPos;
}

void RenderView::clearSelection()
{
    layer()->repaintBlockSelectionGaps();
    setSelection(0, -1, 0, -1, RepaintNewMinusOld);
}

void RenderView::selectionStartEnd(int& startPos, int& endPos) const
{
    startPos = m_selectionStartPos;
    endPos = m_selectionEndPos;
}

bool RenderView::shouldUsePrintingLayout() const
{
    if (!document().printing() || !m_frameView)
        return false;
    return m_frameView->frame().shouldUsePrintingLayout();
}

LayoutRect RenderView::viewRect() const
{
    if (shouldUsePrintingLayout())
        return LayoutRect(LayoutPoint(), size());
    if (m_frameView)
        return m_frameView->visibleContentRect();
    return LayoutRect();
}

IntRect RenderView::unscaledDocumentRect() const
{
    LayoutRect overflowRect(layoutOverflowRect());
    flipForWritingMode(overflowRect);
    return pixelSnappedIntRect(overflowRect);
}

bool RenderView::rootBackgroundIsEntirelyFixed() const
{
    RenderObject* rootObject = document().documentElement() ? document().documentElement()->renderer() : 0;
    if (!rootObject)
        return false;

    RenderObject* rootRenderer = rootObject->rendererForRootBackground();
    return rootRenderer->hasEntirelyFixedBackground();
}

LayoutRect RenderView::backgroundRect(RenderBox* backgroundRenderer) const
{
    if (!hasColumns())
        return unscaledDocumentRect();

    ColumnInfo* columnInfo = this->columnInfo();
    LayoutRect backgroundRect(0, 0, columnInfo->desiredColumnWidth(), columnInfo->columnHeight() * columnInfo->columnCount());
    if (!isHorizontalWritingMode())
        backgroundRect = backgroundRect.transposedRect();
    backgroundRenderer->flipForWritingMode(backgroundRect);

    return backgroundRect;
}

IntRect RenderView::documentRect() const
{
    FloatRect overflowRect(unscaledDocumentRect());
    if (hasTransform())
        overflowRect = layer()->currentTransform().mapRect(overflowRect);
    return IntRect(overflowRect);
}

int RenderView::viewHeight(IncludeScrollbarsInRect scrollbarInclusion) const
{
    int height = 0;
    if (!shouldUsePrintingLayout() && m_frameView)
        height = m_frameView->layoutSize(scrollbarInclusion).height();

    return height;
}

int RenderView::viewWidth(IncludeScrollbarsInRect scrollbarInclusion) const
{
    int width = 0;
    if (!shouldUsePrintingLayout() && m_frameView)
        width = m_frameView->layoutSize(scrollbarInclusion).width();

    return width;
}

int RenderView::viewLogicalHeight() const
{
    return style()->isHorizontalWritingMode() ? viewHeight(ExcludeScrollbars) : viewWidth(ExcludeScrollbars);
}

float RenderView::zoomFactor() const
{
    return m_frameView->frame().pageZoomFactor();
}

void RenderView::pushLayoutState(RenderObject& root)
{
    ASSERT(m_layoutStateDisableCount == 0);
    ASSERT(m_layoutState == 0);

    pushLayoutStateForCurrentFlowThread(root);
    m_layoutState = new LayoutState(root);
}

bool RenderView::shouldDisableLayoutStateForSubtree(RenderObject& renderer) const
{
    RenderObject* o = &renderer;
    while (o) {
        if (o->shouldDisableLayoutState())
            return true;
        o = o->container();
    }
    return false;
}

void RenderView::updateHitTestResult(HitTestResult& result, const LayoutPoint& point)
{
    if (result.innerNode())
        return;

    Node* node = document().documentElement();
    if (node) {
        result.setInnerNode(node);
        if (!result.innerNonSharedNode())
            result.setInnerNonSharedNode(node);

        LayoutPoint adjustedPoint = point;
        offsetForContents(adjustedPoint);

        result.setLocalPoint(adjustedPoint);
    }
}

bool RenderView::usesCompositing() const
{
    return m_compositor && m_compositor->inCompositingMode();
}

RenderLayerCompositor* RenderView::compositor()
{
    if (!m_compositor)
        m_compositor = adoptPtr(new RenderLayerCompositor(*this));

    return m_compositor.get();
}

void RenderView::setIsInWindow(bool isInWindow)
{
    if (m_compositor)
        m_compositor->setIsInWindow(isInWindow);
}

FlowThreadController* RenderView::flowThreadController()
{
    if (!m_flowThreadController)
        m_flowThreadController = FlowThreadController::create();

    return m_flowThreadController.get();
}

void RenderView::pushLayoutStateForCurrentFlowThread(const RenderObject& object)
{
    if (!m_flowThreadController)
        return;

    RenderFlowThread* currentFlowThread = m_flowThreadController->currentRenderFlowThread();
    if (!currentFlowThread)
        return;

    currentFlowThread->pushFlowThreadLayoutState(object);
}

void RenderView::popLayoutStateForCurrentFlowThread()
{
    if (!m_flowThreadController)
        return;

    RenderFlowThread* currentFlowThread = m_flowThreadController->currentRenderFlowThread();
    if (!currentFlowThread)
        return;

    currentFlowThread->popFlowThreadLayoutState();
}

IntervalArena* RenderView::intervalArena()
{
    if (!m_intervalArena)
        m_intervalArena = IntervalArena::create();
    return m_intervalArena.get();
}

bool RenderView::backgroundIsKnownToBeOpaqueInRect(const LayoutRect&) const
{
    // FIXME: Remove this main frame check. Same concept applies to subframes too.
    if (!m_frameView || !m_frameView->isMainFrame())
        return false;

    return m_frameView->hasOpaqueBackground();
}

double RenderView::layoutViewportWidth() const
{
    float scale = m_frameView ? m_frameView->frame().pageZoomFactor() : 1;
    return viewWidth(IncludeScrollbars) / scale;
}

double RenderView::layoutViewportHeight() const
{
    float scale = m_frameView ? m_frameView->frame().pageZoomFactor() : 1;
    return viewHeight(IncludeScrollbars) / scale;
}

} // namespace WebCore
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root/Source/core/rendering/RenderView.cpp

DEFINITIONS
