Source/core/rendering/RenderTableCell.cpp

/* [<][>][^][v][top][bottom][index][help] */
This source file includes following definitions.
m_intrinsicPaddingAfter
willBeRemovedFromTree
parseColSpanFromDOM
parseRowSpanFromDOM
updateColAndRowSpanFlags
colSpanOrRowSpanChanged
logicalWidthFromColumns
computePreferredLogicalWidths
addLayerHitTestRects
computeIntrinsicPadding
updateLogicalWidth
setCellLogicalWidth
layout
paddingTop
paddingBottom
paddingLeft
paddingRight
paddingBefore
paddingAfter
setOverrideLogicalContentHeightFromRowHeight
offsetFromContainer
clippedOverflowRectForRepaint
computeRectForRepaint
cellBaselinePosition
styleDidChange
compareBorders
chooseBorder
hasStartBorderAdjoiningTable
hasEndBorderAdjoiningTable
collapsedStartBorder
computeCollapsedStartBorder
collapsedEndBorder
computeCollapsedEndBorder
collapsedBeforeBorder
computeCollapsedBeforeBorder
collapsedAfterBorder
computeCollapsedAfterBorder
cachedCollapsedLeftBorder
cachedCollapsedRightBorder
cachedCollapsedTopBorder
cachedCollapsedBottomBorder
borderLeft
borderRight
borderTop
borderBottom
borderStart
borderEnd
borderBefore
borderAfter
borderHalfLeft
borderHalfRight
borderHalfTop
borderHalfBottom
borderHalfStart
borderHalfEnd
borderHalfBefore
borderHalfAfter
paint
collapsedBorderStyle
addBorder
nextBorder
addBorderStyle
collectBorderValues
compareBorderValuesForQSort
sortBorderValues
paintCollapsedBorders
paintBackgroundsBehindCell
paintBoxDecorations
paintMask
boxShadowShouldBeAppliedToBackground
scrollbarsChanged
createAnonymous
createAnonymousWithParentRenderer
/*
 * Copyright (C) 1997 Martin Jones (mjones@kde.org)
 *           (C) 1997 Torben Weis (weis@kde.org)
 *           (C) 1998 Waldo Bastian (bastian@kde.org)
 *           (C) 1999 Lars Knoll (knoll@kde.org)
 *           (C) 1999 Antti Koivisto (koivisto@kde.org)
 * Copyright (C) 2003, 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/RenderTableCell.h"

#include "HTMLNames.h"
#include "core/css/StylePropertySet.h"
#include "core/html/HTMLTableCellElement.h"
#include "core/rendering/LayoutRectRecorder.h"
#include "core/rendering/PaintInfo.h"
#include "core/rendering/RenderTableCol.h"
#include "core/rendering/RenderView.h"
#include "core/rendering/SubtreeLayoutScope.h"
#include "core/rendering/style/CollapsedBorderValue.h"
#include "platform/geometry/FloatQuad.h"
#include "platform/geometry/TransformState.h"
#include "platform/graphics/GraphicsContextStateSaver.h"

using namespace std;

namespace WebCore {

using namespace HTMLNames;

struct SameSizeAsRenderTableCell : public RenderBlockFlow {
    unsigned bitfields;
    int paddings[2];
};

COMPILE_ASSERT(sizeof(RenderTableCell) == sizeof(SameSizeAsRenderTableCell), RenderTableCell_should_stay_small);
COMPILE_ASSERT(sizeof(CollapsedBorderValue) == 8, CollapsedBorderValue_should_stay_small);

RenderTableCell::RenderTableCell(Element* element)
    : RenderBlockFlow(element)
    , m_column(unsetColumnIndex)
    , m_cellWidthChanged(false)
    , m_intrinsicPaddingBefore(0)
    , m_intrinsicPaddingAfter(0)
{
    // We only update the flags when notified of DOM changes in colSpanOrRowSpanChanged()
    // so we need to set their initial values here in case something asks for colSpan()/rowSpan() before then.
    updateColAndRowSpanFlags();
}

void RenderTableCell::willBeRemovedFromTree()
{
    RenderBlockFlow::willBeRemovedFromTree();

    section()->setNeedsCellRecalc();
    section()->removeCachedCollapsedBorders(this);
}

unsigned RenderTableCell::parseColSpanFromDOM() const
{
    ASSERT(node());
    if (isHTMLTableCellElement(*node()))
        return min<unsigned>(toHTMLTableCellElement(*node()).colSpan(), maxColumnIndex);
    return 1;
}

unsigned RenderTableCell::parseRowSpanFromDOM() const
{
    ASSERT(node());
    if (isHTMLTableCellElement(*node()))
        return min<unsigned>(toHTMLTableCellElement(*node()).rowSpan(), maxRowIndex);
    return 1;
}

void RenderTableCell::updateColAndRowSpanFlags()
{
    // The vast majority of table cells do not have a colspan or rowspan,
    // so we keep a bool to know if we need to bother reading from the DOM.
    m_hasColSpan = node() && parseColSpanFromDOM() != 1;
    m_hasRowSpan = node() && parseRowSpanFromDOM() != 1;
}

void RenderTableCell::colSpanOrRowSpanChanged()
{
    ASSERT(node());
    ASSERT(isHTMLTableCellElement(*node()));

    updateColAndRowSpanFlags();

    // FIXME: I suspect that we could return early here if !m_hasColSpan && !m_hasRowSpan.

    setNeedsLayoutAndPrefWidthsRecalc();
    if (parent() && section())
        section()->setNeedsCellRecalc();
}

Length RenderTableCell::logicalWidthFromColumns(RenderTableCol* firstColForThisCell, Length widthFromStyle) const
{
    ASSERT(firstColForThisCell && firstColForThisCell == table()->colElement(col()));
    RenderTableCol* tableCol = firstColForThisCell;

    unsigned colSpanCount = colSpan();
    int colWidthSum = 0;
    for (unsigned i = 1; i <= colSpanCount; i++) {
        Length colWidth = tableCol->style()->logicalWidth();

        // Percentage value should be returned only for colSpan == 1.
        // Otherwise we return original width for the cell.
        if (!colWidth.isFixed()) {
            if (colSpanCount > 1)
                return widthFromStyle;
            return colWidth;
        }

        colWidthSum += colWidth.value();
        tableCol = tableCol->nextColumn();
        // If no next <col> tag found for the span we just return what we have for now.
        if (!tableCol)
            break;
    }

    // Column widths specified on <col> apply to the border box of the cell, see bug 8126.
    // FIXME: Why is border/padding ignored in the negative width case?
    if (colWidthSum > 0)
        return Length(max(0, colWidthSum - borderAndPaddingLogicalWidth().ceil()), Fixed);
    return Length(colWidthSum, Fixed);
}

void RenderTableCell::computePreferredLogicalWidths()
{
    // The child cells rely on the grids up in the sections to do their computePreferredLogicalWidths work.  Normally the sections are set up early, as table
    // cells are added, but relayout can cause the cells to be freed, leaving stale pointers in the sections'
    // grids.  We must refresh those grids before the child cells try to use them.
    table()->recalcSectionsIfNeeded();

    RenderBlockFlow::computePreferredLogicalWidths();
    if (node() && style()->autoWrap()) {
        // See if nowrap was set.
        Length w = styleOrColLogicalWidth();
        const AtomicString& nowrap = toElement(node())->getAttribute(nowrapAttr);
        if (!nowrap.isNull() && w.isFixed())
            // Nowrap is set, but we didn't actually use it because of the
            // fixed width set on the cell.  Even so, it is a WinIE/Moz trait
            // to make the minwidth of the cell into the fixed width.  They do this
            // even in strict mode, so do not make this a quirk.  Affected the top
            // of hiptop.com.
            m_minPreferredLogicalWidth = max<LayoutUnit>(w.value(), m_minPreferredLogicalWidth);
    }
}

void RenderTableCell::addLayerHitTestRects(LayerHitTestRects& layerRects, const RenderLayer* currentLayer, const LayoutPoint& layerOffset, const LayoutRect& containerRect) const
{
    LayoutPoint adjustedLayerOffset = layerOffset;
    // RenderTableCell's location includes the offset of it's containing RenderTableRow, so
    // we need to subtract that again here (as for RenderTableCell::offsetFromContainer.
    if (parent())
        adjustedLayerOffset -= parentBox()->locationOffset();
    RenderBox::addLayerHitTestRects(layerRects, currentLayer, adjustedLayerOffset, containerRect);
}

void RenderTableCell::computeIntrinsicPadding(int rowHeight, SubtreeLayoutScope& layouter)
{
    int oldIntrinsicPaddingBefore = intrinsicPaddingBefore();
    int oldIntrinsicPaddingAfter = intrinsicPaddingAfter();
    int logicalHeightWithoutIntrinsicPadding = pixelSnappedLogicalHeight() - oldIntrinsicPaddingBefore - oldIntrinsicPaddingAfter;

    int intrinsicPaddingBefore = 0;
    switch (style()->verticalAlign()) {
    case SUB:
    case SUPER:
    case TEXT_TOP:
    case TEXT_BOTTOM:
    case LENGTH:
    case BASELINE: {
        LayoutUnit baseline = cellBaselinePosition();
        if (baseline > borderBefore() + paddingBefore())
            intrinsicPaddingBefore = section()->rowBaseline(rowIndex()) - (baseline - oldIntrinsicPaddingBefore);
        break;
    }
    case TOP:
        break;
    case MIDDLE:
        intrinsicPaddingBefore = (rowHeight - logicalHeightWithoutIntrinsicPadding) / 2;
        break;
    case BOTTOM:
        intrinsicPaddingBefore = rowHeight - logicalHeightWithoutIntrinsicPadding;
        break;
    case BASELINE_MIDDLE:
        break;
    }

    int intrinsicPaddingAfter = rowHeight - logicalHeightWithoutIntrinsicPadding - intrinsicPaddingBefore;
    setIntrinsicPaddingBefore(intrinsicPaddingBefore);
    setIntrinsicPaddingAfter(intrinsicPaddingAfter);

    // FIXME: Changing an intrinsic padding shouldn't trigger a relayout as it only shifts the cell inside the row but
    // doesn't change the logical height.
    if (intrinsicPaddingBefore != oldIntrinsicPaddingBefore || intrinsicPaddingAfter != oldIntrinsicPaddingAfter)
        layouter.setNeedsLayout(this);
}

void RenderTableCell::updateLogicalWidth()
{
}

void RenderTableCell::setCellLogicalWidth(int tableLayoutLogicalWidth, SubtreeLayoutScope& layouter)
{
    if (tableLayoutLogicalWidth == logicalWidth())
        return;

    layouter.setNeedsLayout(this);

    if (!table()->selfNeedsLayout() && checkForRepaintDuringLayout())
        repaint();

    setLogicalWidth(tableLayoutLogicalWidth);
    setCellWidthChanged(true);
}

void RenderTableCell::layout()
{
    ASSERT(needsLayout());

    LayoutRectRecorder recorder(*this);

    updateFirstLetter();

    int oldCellBaseline = cellBaselinePosition();
    layoutBlock(cellWidthChanged());

    // If we have replaced content, the intrinsic height of our content may have changed since the last time we laid out. If that's the case the intrinsic padding we used
    // for layout (the padding required to push the contents of the cell down to the row's baseline) is included in our new height and baseline and makes both
    // of them wrong. So if our content's intrinsic height has changed push the new content up into the intrinsic padding and relayout so that the rest of
    // table and row layout can use the correct baseline and height for this cell.
    if (isBaselineAligned() && section()->rowBaseline(rowIndex()) && cellBaselinePosition() > section()->rowBaseline(rowIndex())) {
        int newIntrinsicPaddingBefore = max<LayoutUnit>(0, intrinsicPaddingBefore() - max<LayoutUnit>(0, cellBaselinePosition() - oldCellBaseline));
        setIntrinsicPaddingBefore(newIntrinsicPaddingBefore);
        SubtreeLayoutScope layouter(this);
        layouter.setNeedsLayout(this);
        layoutBlock(cellWidthChanged());
    }

    setCellWidthChanged(false);
}

LayoutUnit RenderTableCell::paddingTop() const
{
    int result = computedCSSPaddingTop();
    if (!isHorizontalWritingMode())
        return result;
    return result + (style()->writingMode() == TopToBottomWritingMode ? intrinsicPaddingBefore() : intrinsicPaddingAfter());
}

LayoutUnit RenderTableCell::paddingBottom() const
{
    int result = computedCSSPaddingBottom();
    if (!isHorizontalWritingMode())
        return result;
    return result + (style()->writingMode() == TopToBottomWritingMode ? intrinsicPaddingAfter() : intrinsicPaddingBefore());
}

LayoutUnit RenderTableCell::paddingLeft() const
{
    int result = computedCSSPaddingLeft();
    if (isHorizontalWritingMode())
        return result;
    return result + (style()->writingMode() == LeftToRightWritingMode ? intrinsicPaddingBefore() : intrinsicPaddingAfter());
}

LayoutUnit RenderTableCell::paddingRight() const
{
    int result = computedCSSPaddingRight();
    if (isHorizontalWritingMode())
        return result;
    return result + (style()->writingMode() == LeftToRightWritingMode ? intrinsicPaddingAfter() : intrinsicPaddingBefore());
}

LayoutUnit RenderTableCell::paddingBefore() const
{
    return static_cast<int>(computedCSSPaddingBefore()) + intrinsicPaddingBefore();
}

LayoutUnit RenderTableCell::paddingAfter() const
{
    return static_cast<int>(computedCSSPaddingAfter()) + intrinsicPaddingAfter();
}

void RenderTableCell::setOverrideLogicalContentHeightFromRowHeight(LayoutUnit rowHeight)
{
    clearIntrinsicPadding();
    setOverrideLogicalContentHeight(max<LayoutUnit>(0, rowHeight - borderAndPaddingLogicalHeight()));
}

LayoutSize RenderTableCell::offsetFromContainer(RenderObject* o, const LayoutPoint& point, bool* offsetDependsOnPoint) const
{
    ASSERT(o == container());

    LayoutSize offset = RenderBlockFlow::offsetFromContainer(o, point, offsetDependsOnPoint);
    if (parent())
        offset -= parentBox()->locationOffset();

    return offset;
}

LayoutRect RenderTableCell::clippedOverflowRectForRepaint(const RenderLayerModelObject* repaintContainer) const
{
    // If the table grid is dirty, we cannot get reliable information about adjoining cells,
    // so we ignore outside borders. This should not be a problem because it means that
    // the table is going to recalculate the grid, relayout and repaint its current rect, which
    // includes any outside borders of this cell.
    if (!table()->collapseBorders() || table()->needsSectionRecalc())
        return RenderBlockFlow::clippedOverflowRectForRepaint(repaintContainer);

    bool rtl = !styleForCellFlow()->isLeftToRightDirection();
    int outlineSize = style()->outlineSize();
    int left = max(borderHalfLeft(true), outlineSize);
    int right = max(borderHalfRight(true), outlineSize);
    int top = max(borderHalfTop(true), outlineSize);
    int bottom = max(borderHalfBottom(true), outlineSize);
    if ((left && !rtl) || (right && rtl)) {
        if (RenderTableCell* before = table()->cellBefore(this)) {
            top = max(top, before->borderHalfTop(true));
            bottom = max(bottom, before->borderHalfBottom(true));
        }
    }
    if ((left && rtl) || (right && !rtl)) {
        if (RenderTableCell* after = table()->cellAfter(this)) {
            top = max(top, after->borderHalfTop(true));
            bottom = max(bottom, after->borderHalfBottom(true));
        }
    }
    if (top) {
        if (RenderTableCell* above = table()->cellAbove(this)) {
            left = max(left, above->borderHalfLeft(true));
            right = max(right, above->borderHalfRight(true));
        }
    }
    if (bottom) {
        if (RenderTableCell* below = table()->cellBelow(this)) {
            left = max(left, below->borderHalfLeft(true));
            right = max(right, below->borderHalfRight(true));
        }
    }
    LayoutPoint location(max<LayoutUnit>(left, -visualOverflowRect().x()), max<LayoutUnit>(top, -visualOverflowRect().y()));
    LayoutRect r(-location.x(), -location.y(), location.x() + max(width() + right, visualOverflowRect().maxX()), location.y() + max(height() + bottom, visualOverflowRect().maxY()));

    if (!RuntimeEnabledFeatures::repaintAfterLayoutEnabled()) {
        if (RenderView* v = view()) {
            // FIXME: layoutDelta needs to be applied in parts before/after transforms and
            // repaint containers. https://bugs.webkit.org/show_bug.cgi?id=23308
            r.move(v->layoutDelta());
        }
    }
    computeRectForRepaint(repaintContainer, r);
    return r;
}

void RenderTableCell::computeRectForRepaint(const RenderLayerModelObject* repaintContainer, LayoutRect& r, bool fixed) const
{
    if (repaintContainer == this)
        return;
    r.setY(r.y());
    RenderView* v = view();
    if ((!v || !v->layoutStateEnabled() || repaintContainer) && parent())
        r.moveBy(-parentBox()->location()); // Rows are in the same coordinate space, so don't add their offset in.
    RenderBlockFlow::computeRectForRepaint(repaintContainer, r, fixed);
}

LayoutUnit RenderTableCell::cellBaselinePosition() const
{
    // <http://www.w3.org/TR/2007/CR-CSS21-20070719/tables.html#height-layout>: The baseline of a cell is the baseline of
    // the first in-flow line box in the cell, or the first in-flow table-row in the cell, whichever comes first. If there
    // is no such line box or table-row, the baseline is the bottom of content edge of the cell box.
    LayoutUnit firstLineBaseline = firstLineBoxBaseline();
    if (firstLineBaseline != -1)
        return firstLineBaseline;
    return paddingBefore() + borderBefore() + contentLogicalHeight();
}

void RenderTableCell::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle)
{
    ASSERT(style()->display() == TABLE_CELL);
    ASSERT(!row() || row()->rowIndexWasSet());

    RenderBlockFlow::styleDidChange(diff, oldStyle);
    setHasBoxDecorations(true);

    if (parent() && section() && oldStyle && style()->height() != oldStyle->height())
        section()->rowLogicalHeightChanged(rowIndex());

    // Our intrinsic padding pushes us down to align with the baseline of other cells on the row. If our vertical-align
    // has changed then so will the padding needed to align with other cells - clear it so we can recalculate it from scratch.
    if (oldStyle && style()->verticalAlign() != oldStyle->verticalAlign())
        clearIntrinsicPadding();

    // If border was changed, notify table.
    if (parent()) {
        RenderTable* table = this->table();
        if (table && !table->selfNeedsLayout() && !table->normalChildNeedsLayout()&& oldStyle && oldStyle->border() != style()->border())
            table->invalidateCollapsedBorders();
    }
}

// The following rules apply for resolving conflicts and figuring out which border
// to use.
// (1) Borders with the 'border-style' of 'hidden' take precedence over all other conflicting
// borders. Any border with this value suppresses all borders at this location.
// (2) Borders with a style of 'none' have the lowest priority. Only if the border properties of all
// the elements meeting at this edge are 'none' will the border be omitted (but note that 'none' is
// the default value for the border style.)
// (3) If none of the styles are 'hidden' and at least one of them is not 'none', then narrow borders
// are discarded in favor of wider ones. If several have the same 'border-width' then styles are preferred
// in this order: 'double', 'solid', 'dashed', 'dotted', 'ridge', 'outset', 'groove', and the lowest: 'inset'.
// (4) If border styles differ only in color, then a style set on a cell wins over one on a row,
// which wins over a row group, column, column group and, lastly, table. It is undefined which color
// is used when two elements of the same type disagree.
static int compareBorders(const CollapsedBorderValue& border1, const CollapsedBorderValue& border2)
{
    // Sanity check the values passed in. The null border have lowest priority.
    if (!border2.exists()) {
        if (!border1.exists())
            return 0;
        return 1;
    }
    if (!border1.exists())
        return -1;

    // Rule #1 above.
    if (border2.style() == BHIDDEN) {
        if (border1.style() == BHIDDEN)
            return 0;
        return -1;
    }
    if (border1.style() == BHIDDEN)
        return 1;

    // Rule #2 above.  A style of 'none' has lowest priority and always loses to any other border.
    if (border2.style() == BNONE) {
        if (border1.style() == BNONE)
            return 0;
        return 1;
    }
    if (border1.style() == BNONE)
        return -1;

    // The first part of rule #3 above. Wider borders win.
    if (border1.width() != border2.width())
        return border1.width() < border2.width() ? -1 : 1;

    // The borders have equal width.  Sort by border style.
    if (border1.style() != border2.style())
        return border1.style() < border2.style() ? -1 : 1;

    // The border have the same width and style.  Rely on precedence (cell over row over row group, etc.)
    if (border1.precedence() == border2.precedence())
        return 0;
    return border1.precedence() < border2.precedence() ? -1 : 1;
}

static CollapsedBorderValue chooseBorder(const CollapsedBorderValue& border1, const CollapsedBorderValue& border2)
{
    const CollapsedBorderValue& border = compareBorders(border1, border2) < 0 ? border2 : border1;
    return border.style() == BHIDDEN ? CollapsedBorderValue() : border;
}

bool RenderTableCell::hasStartBorderAdjoiningTable() const
{
    bool isStartColumn = !col();
    bool isEndColumn = table()->colToEffCol(col() + colSpan() - 1) == table()->numEffCols() - 1;
    bool hasSameDirectionAsTable = hasSameDirectionAs(table());

    // The table direction determines the row direction. In mixed directionality, we cannot guarantee that
    // we have a common border with the table (think a ltr table with rtl start cell).
    return (isStartColumn && hasSameDirectionAsTable) || (isEndColumn && !hasSameDirectionAsTable);
}

bool RenderTableCell::hasEndBorderAdjoiningTable() const
{
    bool isStartColumn = !col();
    bool isEndColumn = table()->colToEffCol(col() + colSpan() - 1) == table()->numEffCols() - 1;
    bool hasSameDirectionAsTable = hasSameDirectionAs(table());

    // The table direction determines the row direction. In mixed directionality, we cannot guarantee that
    // we have a common border with the table (think a ltr table with ltr end cell).
    return (isStartColumn && !hasSameDirectionAsTable) || (isEndColumn && hasSameDirectionAsTable);
}

CollapsedBorderValue RenderTableCell::collapsedStartBorder(IncludeBorderColorOrNot includeColor) const
{
    CollapsedBorderValue result = computeCollapsedStartBorder(includeColor);
    if (includeColor)
        section()->setCachedCollapsedBorder(this, CBSStart, result);
    return result;
}

CollapsedBorderValue RenderTableCell::computeCollapsedStartBorder(IncludeBorderColorOrNot includeColor) const
{
    RenderTable* table = this->table();

    // For the start border, we need to check, in order of precedence:
    // (1) Our start border.
    int startColorProperty = includeColor ? CSSProperty::resolveDirectionAwareProperty(CSSPropertyWebkitBorderStartColor, styleForCellFlow()->direction(), styleForCellFlow()->writingMode()) : 0;
    int endColorProperty = includeColor ? CSSProperty::resolveDirectionAwareProperty(CSSPropertyWebkitBorderEndColor, styleForCellFlow()->direction(), styleForCellFlow()->writingMode()) : 0;
    CollapsedBorderValue result(style()->borderStart(), includeColor ? resolveColor(startColorProperty) : Color(), BCELL);

    // (2) The end border of the preceding cell.
    RenderTableCell* cellBefore = table->cellBefore(this);
    if (cellBefore) {
        CollapsedBorderValue cellBeforeAdjoiningBorder = CollapsedBorderValue(cellBefore->borderAdjoiningCellAfter(this), includeColor ? cellBefore->resolveColor(endColorProperty) : Color(), BCELL);
        // |result| should be the 2nd argument as |cellBefore| should win in case of equality per CSS 2.1 (Border conflict resolution, point 4).
        result = chooseBorder(cellBeforeAdjoiningBorder, result);
        if (!result.exists())
            return result;
    }

    bool startBorderAdjoinsTable = hasStartBorderAdjoiningTable();
    if (startBorderAdjoinsTable) {
        // (3) Our row's start border.
        result = chooseBorder(result, CollapsedBorderValue(row()->borderAdjoiningStartCell(this), includeColor ? parent()->resolveColor(startColorProperty) : Color(), BROW));
        if (!result.exists())
            return result;

        // (4) Our row group's start border.
        result = chooseBorder(result, CollapsedBorderValue(section()->borderAdjoiningStartCell(this), includeColor ? section()->resolveColor(startColorProperty) : Color(), BROWGROUP));
        if (!result.exists())
            return result;
    }

    // (5) Our column and column group's start borders.
    bool startColEdge;
    bool endColEdge;
    if (RenderTableCol* colElt = table->colElement(col(), &startColEdge, &endColEdge)) {
        if (colElt->isTableColumnGroup() && startColEdge) {
            // The |colElt| is a column group and is also the first colgroup (in case of spanned colgroups).
            result = chooseBorder(result, CollapsedBorderValue(colElt->borderAdjoiningCellStartBorder(this), includeColor ? colElt->resolveColor(startColorProperty) : Color(), BCOLGROUP));
            if (!result.exists())
                return result;
        } else if (!colElt->isTableColumnGroup()) {
            // We first consider the |colElt| and irrespective of whether it is a spanned col or not, we apply
            // its start border. This is as per HTML5 which states that: "For the purposes of the CSS table model,
            // the col element is expected to be treated as if it was present as many times as its span attribute specifies".
            result = chooseBorder(result, CollapsedBorderValue(colElt->borderAdjoiningCellStartBorder(this), includeColor ? colElt->resolveColor(startColorProperty) : Color(), BCOL));
            if (!result.exists())
                return result;
            // Next, apply the start border of the enclosing colgroup but only if it is adjacent to the cell's edge.
            if (RenderTableCol* enclosingColumnGroup = colElt->enclosingColumnGroupIfAdjacentBefore()) {
                result = chooseBorder(result, CollapsedBorderValue(enclosingColumnGroup->borderAdjoiningCellStartBorder(this), includeColor ? enclosingColumnGroup->resolveColor(startColorProperty) : Color(), BCOLGROUP));
                if (!result.exists())
                    return result;
            }
        }
    }

    // (6) The end border of the preceding column.
    if (cellBefore) {
        if (RenderTableCol* colElt = table->colElement(col() - 1, &startColEdge, &endColEdge)) {
            if (colElt->isTableColumnGroup() && endColEdge) {
                // The element is a colgroup and is also the last colgroup (in case of spanned colgroups).
                result = chooseBorder(CollapsedBorderValue(colElt->borderAdjoiningCellAfter(this), includeColor ? colElt->resolveColor(endColorProperty) : Color(), BCOLGROUP), result);
                if (!result.exists())
                    return result;
            } else if (colElt->isTableColumn()) {
                // Resolve the collapsing border against the col's border ignoring any 'span' as per HTML5.
                result = chooseBorder(CollapsedBorderValue(colElt->borderAdjoiningCellAfter(this), includeColor ? colElt->resolveColor(endColorProperty) : Color(), BCOL), result);
                if (!result.exists())
                    return result;
                // Next, if the previous col has a parent colgroup then its end border should be applied
                // but only if it is adjacent to the cell's edge.
                if (RenderTableCol* enclosingColumnGroup = colElt->enclosingColumnGroupIfAdjacentAfter()) {
                    result = chooseBorder(CollapsedBorderValue(enclosingColumnGroup->borderAdjoiningCellEndBorder(this), includeColor ? enclosingColumnGroup->resolveColor(endColorProperty) : Color(), BCOLGROUP), result);
                    if (!result.exists())
                        return result;
                }
            }
        }
    }

    if (startBorderAdjoinsTable) {
        // (7) The table's start border.
        result = chooseBorder(result, CollapsedBorderValue(table->tableStartBorderAdjoiningCell(this), includeColor ? table->resolveColor(startColorProperty) : Color(), BTABLE));
        if (!result.exists())
            return result;
    }

    return result;
}

CollapsedBorderValue RenderTableCell::collapsedEndBorder(IncludeBorderColorOrNot includeColor) const
{
    CollapsedBorderValue result = computeCollapsedEndBorder(includeColor);
    if (includeColor)
        section()->setCachedCollapsedBorder(this, CBSEnd, result);
    return result;
}

CollapsedBorderValue RenderTableCell::computeCollapsedEndBorder(IncludeBorderColorOrNot includeColor) const
{
    RenderTable* table = this->table();
    // Note: We have to use the effective column information instead of whether we have a cell after as a table doesn't
    // have to be regular (any row can have less cells than the total cell count).
    bool isEndColumn = table->colToEffCol(col() + colSpan() - 1) == table->numEffCols() - 1;

    // For end border, we need to check, in order of precedence:
    // (1) Our end border.
    int startColorProperty = includeColor ? CSSProperty::resolveDirectionAwareProperty(CSSPropertyWebkitBorderStartColor, styleForCellFlow()->direction(), styleForCellFlow()->writingMode()) : 0;
    int endColorProperty = includeColor ? CSSProperty::resolveDirectionAwareProperty(CSSPropertyWebkitBorderEndColor, styleForCellFlow()->direction(), styleForCellFlow()->writingMode()) : 0;
    CollapsedBorderValue result = CollapsedBorderValue(style()->borderEnd(), includeColor ? resolveColor(endColorProperty) : Color(), BCELL);

    // (2) The start border of the following cell.
    if (!isEndColumn) {
        if (RenderTableCell* cellAfter = table->cellAfter(this)) {
            CollapsedBorderValue cellAfterAdjoiningBorder = CollapsedBorderValue(cellAfter->borderAdjoiningCellBefore(this), includeColor ? cellAfter->resolveColor(startColorProperty) : Color(), BCELL);
            result = chooseBorder(result, cellAfterAdjoiningBorder);
            if (!result.exists())
                return result;
        }
    }

    bool endBorderAdjoinsTable = hasEndBorderAdjoiningTable();
    if (endBorderAdjoinsTable) {
        // (3) Our row's end border.
        result = chooseBorder(result, CollapsedBorderValue(row()->borderAdjoiningEndCell(this), includeColor ? parent()->resolveColor(endColorProperty) : Color(), BROW));
        if (!result.exists())
            return result;

        // (4) Our row group's end border.
        result = chooseBorder(result, CollapsedBorderValue(section()->borderAdjoiningEndCell(this), includeColor ? section()->resolveColor(endColorProperty) : Color(), BROWGROUP));
        if (!result.exists())
            return result;
    }

    // (5) Our column and column group's end borders.
    bool startColEdge;
    bool endColEdge;
    if (RenderTableCol* colElt = table->colElement(col() + colSpan() - 1, &startColEdge, &endColEdge)) {
        if (colElt->isTableColumnGroup() && endColEdge) {
            // The element is a colgroup and is also the last colgroup (in case of spanned colgroups).
            result = chooseBorder(result, CollapsedBorderValue(colElt->borderAdjoiningCellEndBorder(this), includeColor ? colElt->resolveColor(endColorProperty) : Color(), BCOLGROUP));
            if (!result.exists())
                return result;
        } else if (!colElt->isTableColumnGroup()) {
            // First apply the end border of the column irrespective of whether it is spanned or not. This is as per
            // HTML5 which states that: "For the purposes of the CSS table model, the col element is expected to be
            // treated as if it was present as many times as its span attribute specifies".
            result = chooseBorder(result, CollapsedBorderValue(colElt->borderAdjoiningCellEndBorder(this), includeColor ? colElt->resolveColor(endColorProperty) : Color(), BCOL));
            if (!result.exists())
                return result;
            // Next, if it has a parent colgroup then we apply its end border but only if it is adjacent to the cell.
            if (RenderTableCol* enclosingColumnGroup = colElt->enclosingColumnGroupIfAdjacentAfter()) {
                result = chooseBorder(result, CollapsedBorderValue(enclosingColumnGroup->borderAdjoiningCellEndBorder(this), includeColor ? enclosingColumnGroup->resolveColor(endColorProperty) : Color(), BCOLGROUP));
                if (!result.exists())
                    return result;
            }
        }
    }

    // (6) The start border of the next column.
    if (!isEndColumn) {
        if (RenderTableCol* colElt = table->colElement(col() + colSpan(), &startColEdge, &endColEdge)) {
            if (colElt->isTableColumnGroup() && startColEdge) {
                // This case is a colgroup without any col, we only compute it if it is adjacent to the cell's edge.
                result = chooseBorder(result, CollapsedBorderValue(colElt->borderAdjoiningCellBefore(this), includeColor ? colElt->resolveColor(startColorProperty) : Color(), BCOLGROUP));
                if (!result.exists())
                    return result;
            } else if (colElt->isTableColumn()) {
                // Resolve the collapsing border against the col's border ignoring any 'span' as per HTML5.
                result = chooseBorder(result, CollapsedBorderValue(colElt->borderAdjoiningCellBefore(this), includeColor ? colElt->resolveColor(startColorProperty) : Color(), BCOL));
                if (!result.exists())
                    return result;
                // If we have a parent colgroup, resolve the border only if it is adjacent to the cell.
                if (RenderTableCol* enclosingColumnGroup = colElt->enclosingColumnGroupIfAdjacentBefore()) {
                    result = chooseBorder(result, CollapsedBorderValue(enclosingColumnGroup->borderAdjoiningCellStartBorder(this), includeColor ? enclosingColumnGroup->resolveColor(startColorProperty) : Color(), BCOLGROUP));
                    if (!result.exists())
                        return result;
                }
            }
        }
    }

    if (endBorderAdjoinsTable) {
        // (7) The table's end border.
        result = chooseBorder(result, CollapsedBorderValue(table->tableEndBorderAdjoiningCell(this), includeColor ? table->resolveColor(endColorProperty) : Color(), BTABLE));
        if (!result.exists())
            return result;
    }

    return result;
}

CollapsedBorderValue RenderTableCell::collapsedBeforeBorder(IncludeBorderColorOrNot includeColor) const
{
    CollapsedBorderValue result = computeCollapsedBeforeBorder(includeColor);
    if (includeColor)
        section()->setCachedCollapsedBorder(this, CBSBefore, result);
    return result;
}

CollapsedBorderValue RenderTableCell::computeCollapsedBeforeBorder(IncludeBorderColorOrNot includeColor) const
{
    RenderTable* table = this->table();

    // For before border, we need to check, in order of precedence:
    // (1) Our before border.
    int beforeColorProperty = includeColor ? CSSProperty::resolveDirectionAwareProperty(CSSPropertyWebkitBorderBeforeColor, styleForCellFlow()->direction(), styleForCellFlow()->writingMode()) : 0;
    int afterColorProperty = includeColor ? CSSProperty::resolveDirectionAwareProperty(CSSPropertyWebkitBorderAfterColor, styleForCellFlow()->direction(), styleForCellFlow()->writingMode()) : 0;
    CollapsedBorderValue result = CollapsedBorderValue(style()->borderBefore(), includeColor ? resolveColor(beforeColorProperty) : Color(), BCELL);

    RenderTableCell* prevCell = table->cellAbove(this);
    if (prevCell) {
        // (2) A before cell's after border.
        result = chooseBorder(CollapsedBorderValue(prevCell->style()->borderAfter(), includeColor ? prevCell->resolveColor(afterColorProperty) : Color(), BCELL), result);
        if (!result.exists())
            return result;
    }

    // (3) Our row's before border.
    result = chooseBorder(result, CollapsedBorderValue(parent()->style()->borderBefore(), includeColor ? parent()->resolveColor(beforeColorProperty) : Color(), BROW));
    if (!result.exists())
        return result;

    // (4) The previous row's after border.
    if (prevCell) {
        RenderObject* prevRow = 0;
        if (prevCell->section() == section())
            prevRow = parent()->previousSibling();
        else
            prevRow = prevCell->section()->lastChild();

        if (prevRow) {
            result = chooseBorder(CollapsedBorderValue(prevRow->style()->borderAfter(), includeColor ? prevRow->resolveColor(afterColorProperty) : Color(), BROW), result);
            if (!result.exists())
                return result;
        }
    }

    // Now check row groups.
    RenderTableSection* currSection = section();
    if (!rowIndex()) {
        // (5) Our row group's before border.
        result = chooseBorder(result, CollapsedBorderValue(currSection->style()->borderBefore(), includeColor ? currSection->resolveColor(beforeColorProperty) : Color(), BROWGROUP));
        if (!result.exists())
            return result;

        // (6) Previous row group's after border.
        currSection = table->sectionAbove(currSection, SkipEmptySections);
        if (currSection) {
            result = chooseBorder(CollapsedBorderValue(currSection->style()->borderAfter(), includeColor ? currSection->resolveColor(afterColorProperty) : Color(), BROWGROUP), result);
            if (!result.exists())
                return result;
        }
    }

    if (!currSection) {
        // (8) Our column and column group's before borders.
        RenderTableCol* colElt = table->colElement(col());
        if (colElt) {
            result = chooseBorder(result, CollapsedBorderValue(colElt->style()->borderBefore(), includeColor ? colElt->resolveColor(beforeColorProperty) : Color(), BCOL));
            if (!result.exists())
                return result;
            if (RenderTableCol* enclosingColumnGroup = colElt->enclosingColumnGroup()) {
                result = chooseBorder(result, CollapsedBorderValue(enclosingColumnGroup->style()->borderBefore(), includeColor ? enclosingColumnGroup->resolveColor(beforeColorProperty) : Color(), BCOLGROUP));
                if (!result.exists())
                    return result;
            }
        }

        // (9) The table's before border.
        result = chooseBorder(result, CollapsedBorderValue(table->style()->borderBefore(), includeColor ? table->resolveColor(beforeColorProperty) : Color(), BTABLE));
        if (!result.exists())
            return result;
    }

    return result;
}

CollapsedBorderValue RenderTableCell::collapsedAfterBorder(IncludeBorderColorOrNot includeColor) const
{
    CollapsedBorderValue result = computeCollapsedAfterBorder(includeColor);
    if (includeColor)
        section()->setCachedCollapsedBorder(this, CBSAfter, result);
    return result;
}

CollapsedBorderValue RenderTableCell::computeCollapsedAfterBorder(IncludeBorderColorOrNot includeColor) const
{
    RenderTable* table = this->table();

    // For after border, we need to check, in order of precedence:
    // (1) Our after border.
    int beforeColorProperty = includeColor ? CSSProperty::resolveDirectionAwareProperty(CSSPropertyWebkitBorderBeforeColor, styleForCellFlow()->direction(), styleForCellFlow()->writingMode()) : 0;
    int afterColorProperty = includeColor ? CSSProperty::resolveDirectionAwareProperty(CSSPropertyWebkitBorderAfterColor, styleForCellFlow()->direction(), styleForCellFlow()->writingMode()) : 0;
    CollapsedBorderValue result = CollapsedBorderValue(style()->borderAfter(), includeColor ? resolveColor(afterColorProperty) : Color(), BCELL);

    RenderTableCell* nextCell = table->cellBelow(this);
    if (nextCell) {
        // (2) An after cell's before border.
        result = chooseBorder(result, CollapsedBorderValue(nextCell->style()->borderBefore(), includeColor ? nextCell->resolveColor(beforeColorProperty) : Color(), BCELL));
        if (!result.exists())
            return result;
    }

    // (3) Our row's after border. (FIXME: Deal with rowspan!)
    result = chooseBorder(result, CollapsedBorderValue(parent()->style()->borderAfter(), includeColor ? parent()->resolveColor(afterColorProperty) : Color(), BROW));
    if (!result.exists())
        return result;

    // (4) The next row's before border.
    if (nextCell) {
        result = chooseBorder(result, CollapsedBorderValue(nextCell->parent()->style()->borderBefore(), includeColor ? nextCell->parent()->resolveColor(beforeColorProperty) : Color(), BROW));
        if (!result.exists())
            return result;
    }

    // Now check row groups.
    RenderTableSection* currSection = section();
    if (rowIndex() + rowSpan() >= currSection->numRows()) {
        // (5) Our row group's after border.
        result = chooseBorder(result, CollapsedBorderValue(currSection->style()->borderAfter(), includeColor ? currSection->resolveColor(afterColorProperty) : Color(), BROWGROUP));
        if (!result.exists())
            return result;

        // (6) Following row group's before border.
        currSection = table->sectionBelow(currSection, SkipEmptySections);
        if (currSection) {
            result = chooseBorder(result, CollapsedBorderValue(currSection->style()->borderBefore(), includeColor ? currSection->resolveColor(beforeColorProperty) : Color(), BROWGROUP));
            if (!result.exists())
                return result;
        }
    }

    if (!currSection) {
        // (8) Our column and column group's after borders.
        RenderTableCol* colElt = table->colElement(col());
        if (colElt) {
            result = chooseBorder(result, CollapsedBorderValue(colElt->style()->borderAfter(), includeColor ? colElt->resolveColor(afterColorProperty) : Color(), BCOL));
            if (!result.exists()) return result;
            if (RenderTableCol* enclosingColumnGroup = colElt->enclosingColumnGroup()) {
                result = chooseBorder(result, CollapsedBorderValue(enclosingColumnGroup->style()->borderAfter(), includeColor ? enclosingColumnGroup->resolveColor(afterColorProperty) : Color(), BCOLGROUP));
                if (!result.exists())
                    return result;
            }
        }

        // (9) The table's after border.
        result = chooseBorder(result, CollapsedBorderValue(table->style()->borderAfter(), includeColor ? table->resolveColor(afterColorProperty) : Color(), BTABLE));
        if (!result.exists())
            return result;
    }

    return result;
}

inline CollapsedBorderValue RenderTableCell::cachedCollapsedLeftBorder(const RenderStyle* styleForCellFlow) const
{
    if (styleForCellFlow->isHorizontalWritingMode())
        return styleForCellFlow->isLeftToRightDirection() ? section()->cachedCollapsedBorder(this, CBSStart) : section()->cachedCollapsedBorder(this, CBSEnd);
    return styleForCellFlow->isFlippedBlocksWritingMode() ? section()->cachedCollapsedBorder(this, CBSAfter) : section()->cachedCollapsedBorder(this, CBSBefore);
}

inline CollapsedBorderValue RenderTableCell::cachedCollapsedRightBorder(const RenderStyle* styleForCellFlow) const
{
    if (styleForCellFlow->isHorizontalWritingMode())
        return styleForCellFlow->isLeftToRightDirection() ? section()->cachedCollapsedBorder(this, CBSEnd) : section()->cachedCollapsedBorder(this, CBSStart);
    return styleForCellFlow->isFlippedBlocksWritingMode() ? section()->cachedCollapsedBorder(this, CBSBefore) : section()->cachedCollapsedBorder(this, CBSAfter);
}

inline CollapsedBorderValue RenderTableCell::cachedCollapsedTopBorder(const RenderStyle* styleForCellFlow) const
{
    if (styleForCellFlow->isHorizontalWritingMode())
        return styleForCellFlow->isFlippedBlocksWritingMode() ? section()->cachedCollapsedBorder(this, CBSAfter) : section()->cachedCollapsedBorder(this, CBSBefore);
    return styleForCellFlow->isLeftToRightDirection() ? section()->cachedCollapsedBorder(this, CBSStart) : section()->cachedCollapsedBorder(this, CBSEnd);
}

inline CollapsedBorderValue RenderTableCell::cachedCollapsedBottomBorder(const RenderStyle* styleForCellFlow) const
{
    if (styleForCellFlow->isHorizontalWritingMode())
        return styleForCellFlow->isFlippedBlocksWritingMode() ? section()->cachedCollapsedBorder(this, CBSBefore) : section()->cachedCollapsedBorder(this, CBSAfter);
    return styleForCellFlow->isLeftToRightDirection() ? section()->cachedCollapsedBorder(this, CBSEnd) : section()->cachedCollapsedBorder(this, CBSStart);
}

int RenderTableCell::borderLeft() const
{
    return table()->collapseBorders() ? borderHalfLeft(false) : RenderBlockFlow::borderLeft();
}

int RenderTableCell::borderRight() const
{
    return table()->collapseBorders() ? borderHalfRight(false) : RenderBlockFlow::borderRight();
}

int RenderTableCell::borderTop() const
{
    return table()->collapseBorders() ? borderHalfTop(false) : RenderBlockFlow::borderTop();
}

int RenderTableCell::borderBottom() const
{
    return table()->collapseBorders() ? borderHalfBottom(false) : RenderBlockFlow::borderBottom();
}

// FIXME: https://bugs.webkit.org/show_bug.cgi?id=46191, make the collapsed border drawing
// work with different block flow values instead of being hard-coded to top-to-bottom.
int RenderTableCell::borderStart() const
{
    return table()->collapseBorders() ? borderHalfStart(false) : RenderBlockFlow::borderStart();
}

int RenderTableCell::borderEnd() const
{
    return table()->collapseBorders() ? borderHalfEnd(false) : RenderBlockFlow::borderEnd();
}

int RenderTableCell::borderBefore() const
{
    return table()->collapseBorders() ? borderHalfBefore(false) : RenderBlockFlow::borderBefore();
}

int RenderTableCell::borderAfter() const
{
    return table()->collapseBorders() ? borderHalfAfter(false) : RenderBlockFlow::borderAfter();
}

int RenderTableCell::borderHalfLeft(bool outer) const
{
    const RenderStyle* styleForCellFlow = this->styleForCellFlow();
    if (styleForCellFlow->isHorizontalWritingMode())
        return styleForCellFlow->isLeftToRightDirection() ? borderHalfStart(outer) : borderHalfEnd(outer);
    return styleForCellFlow->isFlippedBlocksWritingMode() ? borderHalfAfter(outer) : borderHalfBefore(outer);
}

int RenderTableCell::borderHalfRight(bool outer) const
{
    const RenderStyle* styleForCellFlow = this->styleForCellFlow();
    if (styleForCellFlow->isHorizontalWritingMode())
        return styleForCellFlow->isLeftToRightDirection() ? borderHalfEnd(outer) : borderHalfStart(outer);
    return styleForCellFlow->isFlippedBlocksWritingMode() ? borderHalfBefore(outer) : borderHalfAfter(outer);
}

int RenderTableCell::borderHalfTop(bool outer) const
{
    const RenderStyle* styleForCellFlow = this->styleForCellFlow();
    if (styleForCellFlow->isHorizontalWritingMode())
        return styleForCellFlow->isFlippedBlocksWritingMode() ? borderHalfAfter(outer) : borderHalfBefore(outer);
    return styleForCellFlow->isLeftToRightDirection() ? borderHalfStart(outer) : borderHalfEnd(outer);
}

int RenderTableCell::borderHalfBottom(bool outer) const
{
    const RenderStyle* styleForCellFlow = this->styleForCellFlow();
    if (styleForCellFlow->isHorizontalWritingMode())
        return styleForCellFlow->isFlippedBlocksWritingMode() ? borderHalfBefore(outer) : borderHalfAfter(outer);
    return styleForCellFlow->isLeftToRightDirection() ? borderHalfEnd(outer) : borderHalfStart(outer);
}

int RenderTableCell::borderHalfStart(bool outer) const
{
    CollapsedBorderValue border = collapsedStartBorder(DoNotIncludeBorderColor);
    if (border.exists())
        return (border.width() + ((styleForCellFlow()->isLeftToRightDirection() ^ outer) ? 1 : 0)) / 2; // Give the extra pixel to top and left.
    return 0;
}

int RenderTableCell::borderHalfEnd(bool outer) const
{
    CollapsedBorderValue border = collapsedEndBorder(DoNotIncludeBorderColor);
    if (border.exists())
        return (border.width() + ((styleForCellFlow()->isLeftToRightDirection() ^ outer) ? 0 : 1)) / 2;
    return 0;
}

int RenderTableCell::borderHalfBefore(bool outer) const
{
    CollapsedBorderValue border = collapsedBeforeBorder(DoNotIncludeBorderColor);
    if (border.exists())
        return (border.width() + ((styleForCellFlow()->isFlippedBlocksWritingMode() ^ outer) ? 0 : 1)) / 2; // Give the extra pixel to top and left.
    return 0;
}

int RenderTableCell::borderHalfAfter(bool outer) const
{
    CollapsedBorderValue border = collapsedAfterBorder(DoNotIncludeBorderColor);
    if (border.exists())
        return (border.width() + ((styleForCellFlow()->isFlippedBlocksWritingMode() ^ outer) ? 1 : 0)) / 2;
    return 0;
}

void RenderTableCell::paint(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
{
    ASSERT(paintInfo.phase != PaintPhaseCollapsedTableBorders);
    RenderBlockFlow::paint(paintInfo, paintOffset);
}

static EBorderStyle collapsedBorderStyle(EBorderStyle style)
{
    if (style == OUTSET)
        return GROOVE;
    if (style == INSET)
        return RIDGE;
    return style;
}

struct CollapsedBorder {
    CollapsedBorderValue borderValue;
    BoxSide side;
    bool shouldPaint;
    int x1;
    int y1;
    int x2;
    int y2;
    EBorderStyle style;
};

class CollapsedBorders {
public:
    CollapsedBorders()
        : m_count(0)
    {
    }

    void addBorder(const CollapsedBorderValue& borderValue, BoxSide borderSide, bool shouldPaint,
                   int x1, int y1, int x2, int y2, EBorderStyle borderStyle)
    {
        if (borderValue.exists() && shouldPaint) {
            m_borders[m_count].borderValue = borderValue;
            m_borders[m_count].side = borderSide;
            m_borders[m_count].shouldPaint = shouldPaint;
            m_borders[m_count].x1 = x1;
            m_borders[m_count].x2 = x2;
            m_borders[m_count].y1 = y1;
            m_borders[m_count].y2 = y2;
            m_borders[m_count].style = borderStyle;
            m_count++;
        }
    }

    CollapsedBorder* nextBorder()
    {
        for (unsigned i = 0; i < m_count; i++) {
            if (m_borders[i].borderValue.exists() && m_borders[i].shouldPaint) {
                m_borders[i].shouldPaint = false;
                return &m_borders[i];
            }
        }

        return 0;
    }

    CollapsedBorder m_borders[4];
    unsigned m_count;
};

static void addBorderStyle(RenderTable::CollapsedBorderValues& borderValues,
                           CollapsedBorderValue borderValue)
{
    if (!borderValue.exists())
        return;
    size_t count = borderValues.size();
    for (size_t i = 0; i < count; ++i)
        if (borderValues[i].isSameIgnoringColor(borderValue))
            return;
    borderValues.append(borderValue);
}

void RenderTableCell::collectBorderValues(RenderTable::CollapsedBorderValues& borderValues) const
{
    addBorderStyle(borderValues, collapsedStartBorder());
    addBorderStyle(borderValues, collapsedEndBorder());
    addBorderStyle(borderValues, collapsedBeforeBorder());
    addBorderStyle(borderValues, collapsedAfterBorder());
}

static int compareBorderValuesForQSort(const void* pa, const void* pb)
{
    const CollapsedBorderValue* a = static_cast<const CollapsedBorderValue*>(pa);
    const CollapsedBorderValue* b = static_cast<const CollapsedBorderValue*>(pb);
    if (a->isSameIgnoringColor(*b))
        return 0;
    return compareBorders(*a, *b);
}

void RenderTableCell::sortBorderValues(RenderTable::CollapsedBorderValues& borderValues)
{
    qsort(borderValues.data(), borderValues.size(), sizeof(CollapsedBorderValue),
        compareBorderValuesForQSort);
}

void RenderTableCell::paintCollapsedBorders(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
{
    ASSERT(paintInfo.phase == PaintPhaseCollapsedTableBorders);

    if (!paintInfo.shouldPaintWithinRoot(this) || style()->visibility() != VISIBLE)
        return;

    LayoutRect paintRect = LayoutRect(paintOffset + location(), pixelSnappedSize());
    if (paintRect.y() - table()->outerBorderTop() >= paintInfo.rect.maxY())
        return;

    if (paintRect.maxY() + table()->outerBorderBottom() <= paintInfo.rect.y())
        return;

    GraphicsContext* graphicsContext = paintInfo.context;
    if (!table()->currentBorderValue() || graphicsContext->paintingDisabled())
        return;

    const RenderStyle* styleForCellFlow = this->styleForCellFlow();
    CollapsedBorderValue leftVal = cachedCollapsedLeftBorder(styleForCellFlow);
    CollapsedBorderValue rightVal = cachedCollapsedRightBorder(styleForCellFlow);
    CollapsedBorderValue topVal = cachedCollapsedTopBorder(styleForCellFlow);
    CollapsedBorderValue bottomVal = cachedCollapsedBottomBorder(styleForCellFlow);

    // Adjust our x/y/width/height so that we paint the collapsed borders at the correct location.
    int topWidth = topVal.width();
    int bottomWidth = bottomVal.width();
    int leftWidth = leftVal.width();
    int rightWidth = rightVal.width();

    IntRect borderRect = pixelSnappedIntRect(paintRect.x() - leftWidth / 2,
            paintRect.y() - topWidth / 2,
            paintRect.width() + leftWidth / 2 + (rightWidth + 1) / 2,
            paintRect.height() + topWidth / 2 + (bottomWidth + 1) / 2);

    EBorderStyle topStyle = collapsedBorderStyle(topVal.style());
    EBorderStyle bottomStyle = collapsedBorderStyle(bottomVal.style());
    EBorderStyle leftStyle = collapsedBorderStyle(leftVal.style());
    EBorderStyle rightStyle = collapsedBorderStyle(rightVal.style());

    bool renderTop = topStyle > BHIDDEN && !topVal.isTransparent();
    bool renderBottom = bottomStyle > BHIDDEN && !bottomVal.isTransparent();
    bool renderLeft = leftStyle > BHIDDEN && !leftVal.isTransparent();
    bool renderRight = rightStyle > BHIDDEN && !rightVal.isTransparent();

    // We never paint diagonals at the joins.  We simply let the border with the highest
    // precedence paint on top of borders with lower precedence.
    CollapsedBorders borders;
    borders.addBorder(topVal, BSTop, renderTop, borderRect.x(), borderRect.y(), borderRect.maxX(), borderRect.y() + topWidth, topStyle);
    borders.addBorder(bottomVal, BSBottom, renderBottom, borderRect.x(), borderRect.maxY() - bottomWidth, borderRect.maxX(), borderRect.maxY(), bottomStyle);
    borders.addBorder(leftVal, BSLeft, renderLeft, borderRect.x(), borderRect.y(), borderRect.x() + leftWidth, borderRect.maxY(), leftStyle);
    borders.addBorder(rightVal, BSRight, renderRight, borderRect.maxX() - rightWidth, borderRect.y(), borderRect.maxX(), borderRect.maxY(), rightStyle);

    bool antialias = shouldAntialiasLines(graphicsContext);

    for (CollapsedBorder* border = borders.nextBorder(); border; border = borders.nextBorder()) {
        if (border->borderValue.isSameIgnoringColor(*table()->currentBorderValue())) {
            drawLineForBoxSide(graphicsContext, border->x1, border->y1, border->x2, border->y2, border->side,
                border->borderValue.color().resolve(style()->visitedDependentColor(CSSPropertyColor)), border->style, 0, 0, antialias);
        }
    }
}

void RenderTableCell::paintBackgroundsBehindCell(PaintInfo& paintInfo, const LayoutPoint& paintOffset, RenderObject* backgroundObject)
{
    if (!paintInfo.shouldPaintWithinRoot(this))
        return;

    if (!backgroundObject)
        return;

    if (style()->visibility() != VISIBLE)
        return;

    RenderTable* tableElt = table();
    if (!tableElt->collapseBorders() && style()->emptyCells() == HIDE && !firstChild())
        return;

    LayoutPoint adjustedPaintOffset = paintOffset;
    if (backgroundObject != this)
        adjustedPaintOffset.moveBy(location());

    Color c = backgroundObject->resolveColor(CSSPropertyBackgroundColor);
    const FillLayer* bgLayer = backgroundObject->style()->backgroundLayers();

    if (bgLayer->hasImage() || c.alpha()) {
        // We have to clip here because the background would paint
        // on top of the borders otherwise.  This only matters for cells and rows.
        bool shouldClip = backgroundObject->hasLayer() && (backgroundObject == this || backgroundObject == parent()) && tableElt->collapseBorders();
        GraphicsContextStateSaver stateSaver(*paintInfo.context, shouldClip);
        if (shouldClip) {
            LayoutRect clipRect(adjustedPaintOffset.x() + borderLeft(), adjustedPaintOffset.y() + borderTop(),
                width() - borderLeft() - borderRight(), height() - borderTop() - borderBottom());
            paintInfo.context->clip(clipRect);
        }
        paintFillLayers(paintInfo, c, bgLayer, LayoutRect(adjustedPaintOffset, pixelSnappedSize()), BackgroundBleedNone, CompositeSourceOver, backgroundObject);
    }
}

void RenderTableCell::paintBoxDecorations(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
{
    if (!paintInfo.shouldPaintWithinRoot(this))
        return;

    RenderTable* tableElt = table();
    if (!tableElt->collapseBorders() && style()->emptyCells() == HIDE && !firstChild())
        return;

    LayoutRect paintRect = LayoutRect(paintOffset, pixelSnappedSize());
    paintBoxShadow(paintInfo, paintRect, style(), Normal);

    // Paint our cell background.
    paintBackgroundsBehindCell(paintInfo, paintOffset, this);

    paintBoxShadow(paintInfo, paintRect, style(), Inset);

    if (!style()->hasBorder() || tableElt->collapseBorders())
        return;

    paintBorder(paintInfo, paintRect, style());
}

void RenderTableCell::paintMask(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
{
    if (style()->visibility() != VISIBLE || paintInfo.phase != PaintPhaseMask)
        return;

    RenderTable* tableElt = table();
    if (!tableElt->collapseBorders() && style()->emptyCells() == HIDE && !firstChild())
        return;

    paintMaskImages(paintInfo, LayoutRect(paintOffset, pixelSnappedSize()));
}

bool RenderTableCell::boxShadowShouldBeAppliedToBackground(BackgroundBleedAvoidance, InlineFlowBox*) const
{
    return false;
}

void RenderTableCell::scrollbarsChanged(bool horizontalScrollbarChanged, bool verticalScrollbarChanged)
{
    LayoutUnit scrollbarHeight = scrollbarLogicalHeight();
    if (!scrollbarHeight)
        return; // Not sure if we should be doing something when a scrollbar goes away or not.

    // We only care if the scrollbar that affects our intrinsic padding has been added.
    if ((isHorizontalWritingMode() && !horizontalScrollbarChanged) ||
        (!isHorizontalWritingMode() && !verticalScrollbarChanged))
        return;

    // Shrink our intrinsic padding as much as possible to accommodate the scrollbar.
    if (style()->verticalAlign() == MIDDLE) {
        LayoutUnit totalHeight = logicalHeight();
        LayoutUnit heightWithoutIntrinsicPadding = totalHeight - intrinsicPaddingBefore() - intrinsicPaddingAfter();
        totalHeight -= scrollbarHeight;
        LayoutUnit newBeforePadding = (totalHeight - heightWithoutIntrinsicPadding) / 2;
        LayoutUnit newAfterPadding = totalHeight - heightWithoutIntrinsicPadding - newBeforePadding;
        setIntrinsicPaddingBefore(newBeforePadding);
        setIntrinsicPaddingAfter(newAfterPadding);
    } else
        setIntrinsicPaddingAfter(intrinsicPaddingAfter() - scrollbarHeight);
}

RenderTableCell* RenderTableCell::createAnonymous(Document* document)
{
    RenderTableCell* renderer = new RenderTableCell(0);
    renderer->setDocumentForAnonymous(document);
    return renderer;
}

RenderTableCell* RenderTableCell::createAnonymousWithParentRenderer(const RenderObject* parent)
{
    RenderTableCell* newCell = RenderTableCell::createAnonymous(&parent->document());
    RefPtr<RenderStyle> newStyle = RenderStyle::createAnonymousStyleWithDisplay(parent->style(), TABLE_CELL);
    newCell->setStyle(newStyle.release());
    return newCell;
}

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

DEFINITIONS
