Source/WebCore/rendering/RenderGrid.cpp - WebKit - Git at Google

 /*
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2013-2017 Igalia S.L.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */

 #include "config.h"
 #include "RenderGrid.h"

 #include "GridArea.h"
 #include "GridPositionsResolver.h"
 #include "GridTrackSizingAlgorithm.h"
 #include "LayoutRepainter.h"
 #include "RenderLayer.h"
 #include "RenderView.h"
 #include <cstdlib>

 namespace WebCore {

 enum TrackSizeRestriction {
     AllowInfinity,
     ForbidInfinity,
 };

 struct ContentAlignmentData {
     WTF_MAKE_FAST_ALLOCATED;
 public:
     bool isValid() { return positionOffset >= 0 && distributionOffset >= 0; }
     static ContentAlignmentData defaultOffsets() { return {-1, -1}; }

     LayoutUnit positionOffset;
     LayoutUnit distributionOffset;
 };

 RenderGrid::RenderGrid(Element& element, RenderStyle&& style)
     : RenderBlock(element, WTFMove(style), 0)
     , m_grid(*this)
     , m_trackSizingAlgorithm(this, m_grid)
 {
     // All of our children must be block level.
     setChildrenInline(false);
 }

 RenderGrid::~RenderGrid()
 {
 }

 static inline bool defaultAlignmentIsStretch(ItemPosition position)
 {
     return position == ItemPositionStretch || position == ItemPositionAuto;
 }

 static inline bool defaultAlignmentChangedToStretchInRowAxis(const RenderStyle& oldStyle, const RenderStyle& newStyle)
 {
     return !defaultAlignmentIsStretch(oldStyle.justifyItems().position()) && defaultAlignmentIsStretch(newStyle.justifyItems().position());
 }

 static inline bool defaultAlignmentChangedFromStretchInRowAxis(const RenderStyle& oldStyle, const RenderStyle& newStyle)
 {
     return defaultAlignmentIsStretch(oldStyle.justifyItems().position()) && !defaultAlignmentIsStretch(newStyle.justifyItems().position());
 }

 static inline bool defaultAlignmentChangedFromStretchInColumnAxis(const RenderStyle& oldStyle, const RenderStyle& newStyle)
 {
     return defaultAlignmentIsStretch(oldStyle.alignItems().position()) && !defaultAlignmentIsStretch(newStyle.alignItems().position());
 }

 static inline bool selfAlignmentChangedToStretchInRowAxis(const RenderStyle& oldStyle, const RenderStyle& newStyle, const RenderStyle& childStyle, ItemPosition selfAlignNormalBehavior)
 {
     return childStyle.resolvedJustifySelf(&oldStyle, selfAlignNormalBehavior).position() != ItemPositionStretch && childStyle.resolvedJustifySelf(&newStyle, selfAlignNormalBehavior).position() == ItemPositionStretch;
 }

 static inline bool selfAlignmentChangedFromStretchInRowAxis(const RenderStyle& oldStyle, const RenderStyle& newStyle, const RenderStyle& childStyle, ItemPosition selfAlignNormalBehavior)
 {
     return childStyle.resolvedJustifySelf(&oldStyle, selfAlignNormalBehavior).position() == ItemPositionStretch && childStyle.resolvedJustifySelf(&newStyle, selfAlignNormalBehavior).position() != ItemPositionStretch;
 }

 static inline bool selfAlignmentChangedFromStretchInColumnAxis(const RenderStyle& oldStyle, const RenderStyle& newStyle, const RenderStyle& childStyle, ItemPosition selfAlignNormalBehavior)
 {
     return childStyle.resolvedAlignSelf(&oldStyle, selfAlignNormalBehavior).position() == ItemPositionStretch && childStyle.resolvedAlignSelf(&newStyle, selfAlignNormalBehavior).position() != ItemPositionStretch;
 }

 void RenderGrid::addChild(RenderObject* newChild, RenderObject* beforeChild)
 {
     RenderBlock::addChild(newChild, beforeChild);

     // The grid needs to be recomputed as it might contain auto-placed items that
     // will change their position.
     dirtyGrid();
 }

 void RenderGrid::removeChild(RenderObject& child)
 {
     RenderBlock::removeChild(child);

     // The grid needs to be recomputed as it might contain auto-placed items that
     // will change their position.
     dirtyGrid();
 }

 void RenderGrid::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle)
 {
     RenderBlock::styleDidChange(diff, oldStyle);
     if (!oldStyle || diff != StyleDifferenceLayout)
         return;

     const RenderStyle& newStyle = style();
     if (defaultAlignmentChangedToStretchInRowAxis(*oldStyle, newStyle) || defaultAlignmentChangedFromStretchInRowAxis(*oldStyle, newStyle)
         || defaultAlignmentChangedFromStretchInColumnAxis(*oldStyle, newStyle)) {
         // Grid items that were not previously stretched in row-axis need to be relayed out so we can compute new available space.
         // Grid items that were previously stretching in column-axis need to be relayed out so we can compute new available space.
         // This is only necessary for stretching since other alignment values don't change the size of the box.
         for (RenderBox* child = firstChildBox(); child; child = child->nextSiblingBox()) {
             if (child->isOutOfFlowPositioned())
                 continue;
             if (selfAlignmentChangedToStretchInRowAxis(*oldStyle, newStyle, child->style(), selfAlignmentNormalBehavior()) || selfAlignmentChangedFromStretchInRowAxis(*oldStyle, newStyle, child->style(), selfAlignmentNormalBehavior())
                 || selfAlignmentChangedFromStretchInColumnAxis(*oldStyle, newStyle, child->style(), selfAlignmentNormalBehavior())) {
                 child->setChildNeedsLayout(MarkOnlyThis);
             }
         }
     }

     if (explicitGridDidResize(*oldStyle) || namedGridLinesDefinitionDidChange(*oldStyle) || oldStyle->gridAutoFlow() != style().gridAutoFlow()
         || (style().gridAutoRepeatColumns().size() || style().gridAutoRepeatRows().size()))
         dirtyGrid();
 }

 bool RenderGrid::explicitGridDidResize(const RenderStyle& oldStyle) const
 {
     return oldStyle.gridColumns().size() != style().gridColumns().size()
         || oldStyle.gridRows().size() != style().gridRows().size()
         || oldStyle.namedGridAreaColumnCount() != style().namedGridAreaColumnCount()
         || oldStyle.namedGridAreaRowCount() != style().namedGridAreaRowCount()
         || oldStyle.gridAutoRepeatColumns().size() != style().gridAutoRepeatColumns().size()
         || oldStyle.gridAutoRepeatRows().size() != style().gridAutoRepeatRows().size();
 }

 bool RenderGrid::namedGridLinesDefinitionDidChange(const RenderStyle& oldStyle) const
 {
     return oldStyle.namedGridRowLines() != style().namedGridRowLines()
         || oldStyle.namedGridColumnLines() != style().namedGridColumnLines();
 }

 LayoutUnit RenderGrid::computeTrackBasedLogicalHeight() const
 {
     LayoutUnit logicalHeight;

     auto& allRows = m_trackSizingAlgorithm.tracks(ForRows);
     for (const auto& row : allRows)
         logicalHeight += row.baseSize();

     logicalHeight += guttersSize(m_grid, ForRows, 0, allRows.size(), m_trackSizingAlgorithm.sizingOperation());

     return logicalHeight;
 }

 void RenderGrid::computeTrackSizesForDefiniteSize(GridTrackSizingDirection direction, LayoutUnit availableSpace)
 {
     LayoutUnit totalGuttersSize = guttersSize(m_grid, direction, 0, m_grid.numTracks(direction), m_trackSizingAlgorithm.sizingOperation());
     LayoutUnit freeSpace = availableSpace - totalGuttersSize;

     m_trackSizingAlgorithm.setup(direction, numTracks(direction, m_grid), TrackSizing, availableSpace, freeSpace);
     m_trackSizingAlgorithm.run();

     ASSERT(m_trackSizingAlgorithm.tracksAreWiderThanMinTrackBreadth());
 }

 void RenderGrid::repeatTracksSizingIfNeeded(LayoutUnit availableSpaceForColumns, LayoutUnit availableSpaceForRows)
 {
     // In orthogonal flow cases column track's size is determined by using the computed
     // row track's size, which it was estimated during the first cycle of the sizing
     // algorithm. Hence we need to repeat computeUsedBreadthOfGridTracks for both,
     // columns and rows, to determine the final values.
     // TODO (lajava): orthogonal flows is just one of the cases which may require
     // a new cycle of the sizing algorithm; there may be more. In addition, not all the
     // cases with orthogonal flows require this extra cycle; we need a more specific
     // condition to detect whether child's min-content contribution has changed or not.
     if (m_grid.hasAnyOrthogonalGridItem()) {
         computeTrackSizesForDefiniteSize(ForColumns, availableSpaceForColumns);
         computeTrackSizesForDefiniteSize(ForRows, availableSpaceForRows);
     }
 }

 bool RenderGrid::canPerformSimplifiedLayout() const
 {
     // We cannot perform a simplified layout if we need to position the items and we have some
     // positioned items to be laid out.
     if (m_grid.needsItemsPlacement() && posChildNeedsLayout())
         return false;

     return RenderBlock::canPerformSimplifiedLayout();
 }

 void RenderGrid::layoutBlock(bool relayoutChildren, LayoutUnit)
 {
     ASSERT(needsLayout());

     if (!relayoutChildren && simplifiedLayout())
         return;

     LayoutRepainter repainter(*this, checkForRepaintDuringLayout());
     LayoutStateMaintainer statePusher(view(), *this, locationOffset(), hasTransform() || hasReflection() || style().isFlippedBlocksWritingMode());

     preparePaginationBeforeBlockLayout(relayoutChildren);

     LayoutSize previousSize = size();

     // We need to clear both own and containingBlock override sizes of orthogonal items to ensure we get the
     // same result when grid's intrinsic size is computed again in the updateLogicalWidth call bellow.
     if (sizesLogicalWidthToFitContent(MaxSize) || style().logicalWidth().isIntrinsicOrAuto()) {
         for (auto* child = firstChildBox(); child; child = child->nextSiblingBox()) {
             if (child->isOutOfFlowPositioned() || !isOrthogonalChild(*child))
                 continue;
             child->clearOverrideSize();
             child->clearContainingBlockOverrideSize();
             child->setNeedsLayout();
             child->layoutIfNeeded();
         }
     }

     setLogicalHeight(0);
     updateLogicalWidth();

     placeItemsOnGrid(m_grid, TrackSizing);

     // At this point the logical width is always definite as the above call to updateLogicalWidth()
     // properly resolves intrinsic sizes. We cannot do the same for heights though because many code
     // paths inside updateLogicalHeight() require a previous call to setLogicalHeight() to resolve
     // heights properly (like for positioned items for example).
     LayoutUnit availableSpaceForColumns = availableLogicalWidth();
     computeTrackSizesForDefiniteSize(ForColumns, availableSpaceForColumns);

     // FIXME: We should use RenderBlock::hasDefiniteLogicalHeight() but it does not work for positioned stuff.
     // FIXME: Consider caching the hasDefiniteLogicalHeight value throughout the layout.
     bool hasDefiniteLogicalHeight = hasOverrideLogicalContentHeight() || computeContentLogicalHeight(MainOrPreferredSize, style().logicalHeight(), std::nullopt);
     if (!hasDefiniteLogicalHeight) {
         m_minContentHeight = LayoutUnit();
         m_maxContentHeight = LayoutUnit();
         computeTrackSizesForIndefiniteSize(m_trackSizingAlgorithm, ForRows, m_grid, *m_minContentHeight, *m_maxContentHeight);
         // FIXME: This should be really added to the intrinsic height in RenderBox::computeContentAndScrollbarLogicalHeightUsing().
         // Remove this when that is fixed.
         ASSERT(m_minContentHeight);
         ASSERT(m_maxContentHeight);
         LayoutUnit scrollbarHeight = scrollbarLogicalHeight();
         *m_minContentHeight += scrollbarHeight;
         *m_maxContentHeight += scrollbarHeight;
     } else
         computeTrackSizesForDefiniteSize(ForRows, availableLogicalHeight(ExcludeMarginBorderPadding));
     LayoutUnit trackBasedLogicalHeight = computeTrackBasedLogicalHeight() + borderAndPaddingLogicalHeight() + scrollbarLogicalHeight();
     setLogicalHeight(trackBasedLogicalHeight);

     LayoutUnit oldClientAfterEdge = clientLogicalBottom();
     updateLogicalHeight();

     // Once grid's indefinite height is resolved, we can compute the
     // available free space for Content Alignment.
     if (!hasDefiniteLogicalHeight)
         m_trackSizingAlgorithm.setFreeSpace(ForRows, logicalHeight() - trackBasedLogicalHeight);

     // 3- If the min-content contribution of any grid items have changed based on the row
     // sizes calculated in step 2, steps 1 and 2 are repeated with the new min-content
     // contribution (once only).
     repeatTracksSizingIfNeeded(availableSpaceForColumns, contentLogicalHeight());

     // Grid container should have the minimum height of a line if it's editable. That does not affect track sizing though.
     if (hasLineIfEmpty()) {
         LayoutUnit minHeightForEmptyLine = borderAndPaddingLogicalHeight()
             + lineHeight(true, isHorizontalWritingMode() ? HorizontalLine : VerticalLine, PositionOfInteriorLineBoxes)
             + scrollbarLogicalHeight();
         setLogicalHeight(std::max(logicalHeight(), minHeightForEmptyLine));
     }

     applyStretchAlignmentToTracksIfNeeded(ForColumns);
     applyStretchAlignmentToTracksIfNeeded(ForRows);

     layoutGridItems();
     m_trackSizingAlgorithm.reset();

     if (size() != previousSize)
         relayoutChildren = true;

     layoutPositionedObjects(relayoutChildren || isDocumentElementRenderer());

     computeOverflow(oldClientAfterEdge);
     statePusher.pop();

     updateLayerTransform();

     // Update our scroll information if we're overflow:auto/scroll/hidden now that we know if
     // we overflow or not.
     updateScrollInfoAfterLayout();

     repainter.repaintAfterLayout();

     clearNeedsLayout();
 }

 LayoutUnit RenderGrid::gridGapForDirection(GridTrackSizingDirection direction, SizingOperation sizingOperation) const
 {
     LayoutUnit availableSize;
     const Length& gap = direction == ForColumns ? style().gridColumnGap() : style().gridRowGap();

     // FIXME: Figure out what to do when availableLogicalHeightForPercentageComputation has
     // no value.
     if (sizingOperation == TrackSizing && gap.isPercent())
         availableSize = direction == ForColumns ? availableLogicalWidth() : availableLogicalHeightForPercentageComputation().value_or(LayoutUnit());

     // FIXME: Maybe we could cache the computed percentage as a performance
     // improvement.
     return valueForLength(gap, availableSize);
 }

 LayoutUnit RenderGrid::guttersSize(const Grid& grid, GridTrackSizingDirection direction, unsigned startLine, unsigned span, SizingOperation sizingOperation) const
 {
     if (span <= 1)
         return { };

     LayoutUnit gap = gridGapForDirection(direction, sizingOperation);

     // Fast path, no collapsing tracks.
     if (!grid.hasAutoRepeatEmptyTracks(direction))
         return gap * (span - 1);

     // If there are collapsing tracks we need to be sure that gutters are properly collapsed. Apart
     // from that, if we have a collapsed track in the edges of the span we're considering, we need
     // to move forward (or backwards) in order to know whether the collapsed tracks reach the end of
     // the grid (so the gap becomes 0) or there is a non empty track before that.

     LayoutUnit gapAccumulator;
     unsigned endLine = startLine + span;

     for (unsigned line = startLine; line < endLine - 1; ++line) {
         if (!grid.isEmptyAutoRepeatTrack(direction, line))
             gapAccumulator += gap;
     }

     // The above loop adds one extra gap for trailing collapsed tracks.
     if (gapAccumulator && grid.isEmptyAutoRepeatTrack(direction, endLine - 1)) {
         ASSERT(gapAccumulator >= gap);
         gapAccumulator -= gap;
     }

     // If the startLine is the start line of a collapsed track we need to go backwards till we reach
     // a non collapsed track. If we find a non collapsed track we need to add that gap.
     if (startLine && grid.isEmptyAutoRepeatTrack(direction, startLine)) {
         unsigned nonEmptyTracksBeforeStartLine = startLine;
         auto begin = grid.autoRepeatEmptyTracks(direction)->begin();
         for (auto it = begin; *it != startLine; ++it) {
             ASSERT(nonEmptyTracksBeforeStartLine);
             --nonEmptyTracksBeforeStartLine;
         }
         if (nonEmptyTracksBeforeStartLine)
             gapAccumulator += gap;
     }

     // If the endLine is the end line of a collapsed track we need to go forward till we reach a non
     // collapsed track. If we find a non collapsed track we need to add that gap.
     if (grid.isEmptyAutoRepeatTrack(direction, endLine - 1)) {
         unsigned nonEmptyTracksAfterEndLine = grid.numTracks(direction) - endLine;
         auto currentEmptyTrack = grid.autoRepeatEmptyTracks(direction)->find(endLine - 1);
         auto endEmptyTrack = grid.autoRepeatEmptyTracks(direction)->end();
         // HashSet iterators do not implement operator- so we have to manually iterate to know the number of remaining empty tracks.
         for (auto it = ++currentEmptyTrack; it != endEmptyTrack; ++it) {
             ASSERT(nonEmptyTracksAfterEndLine >= 1);
             --nonEmptyTracksAfterEndLine;
         }
         if (nonEmptyTracksAfterEndLine)
             gapAccumulator += gap;
     }

     return gapAccumulator;
 }

 void RenderGrid::computeIntrinsicLogicalWidths(LayoutUnit& minLogicalWidth, LayoutUnit& maxLogicalWidth) const
 {
     Grid grid(const_cast<RenderGrid&>(*this));
     placeItemsOnGrid(grid, IntrinsicSizeComputation);

     GridTrackSizingAlgorithm algorithm(this, grid);
     computeTrackSizesForIndefiniteSize(algorithm, ForColumns, grid, minLogicalWidth, maxLogicalWidth);

     LayoutUnit scrollbarWidth = intrinsicScrollbarLogicalWidth();
     minLogicalWidth += scrollbarWidth;
     maxLogicalWidth += scrollbarWidth;
 }

 void RenderGrid::computeTrackSizesForIndefiniteSize(GridTrackSizingAlgorithm& algorithm, GridTrackSizingDirection direction, Grid& grid, LayoutUnit& minIntrinsicSize, LayoutUnit& maxIntrinsicSize) const
 {
     algorithm.setup(direction, numTracks(direction, grid), IntrinsicSizeComputation, std::nullopt, std::nullopt);
     algorithm.run();

     size_t numberOfTracks = algorithm.tracks(direction).size();
     LayoutUnit totalGuttersSize = guttersSize(grid, direction, 0, numberOfTracks, algorithm.sizingOperation());

     minIntrinsicSize = algorithm.minContentSize() + totalGuttersSize;
     maxIntrinsicSize = algorithm.maxContentSize() + totalGuttersSize;

     ASSERT(algorithm.tracksAreWiderThanMinTrackBreadth());
 }

 std::optional<LayoutUnit> RenderGrid::computeIntrinsicLogicalContentHeightUsing(Length logicalHeightLength, std::optional<LayoutUnit> intrinsicLogicalHeight, LayoutUnit borderAndPadding) const
 {
     if (!intrinsicLogicalHeight)
         return std::nullopt;

     if (logicalHeightLength.isMinContent())
         return m_minContentHeight;

     if (logicalHeightLength.isMaxContent())
         return m_maxContentHeight;

     if (logicalHeightLength.isFitContent()) {
         LayoutUnit fillAvailableExtent = containingBlock()->availableLogicalHeight(ExcludeMarginBorderPadding);
         return std::min(m_maxContentHeight.value_or(0), std::max(m_minContentHeight.value_or(0), fillAvailableExtent));
     }

     if (logicalHeightLength.isFillAvailable())
         return containingBlock()->availableLogicalHeight(ExcludeMarginBorderPadding) - borderAndPadding;
     ASSERT_NOT_REACHED();
     return std::nullopt;
 }

 static std::optional<LayoutUnit> overrideContainingBlockContentSizeForChild(const RenderBox& child, GridTrackSizingDirection direction)
 {
     return direction == ForColumns ? child.overrideContainingBlockContentLogicalWidth() : child.overrideContainingBlockContentLogicalHeight();
 }

 bool RenderGrid::isOrthogonalChild(const RenderBox& child) const
 {
     return child.isHorizontalWritingMode() != isHorizontalWritingMode();
 }

 GridTrackSizingDirection RenderGrid::flowAwareDirectionForChild(const RenderBox& child, GridTrackSizingDirection direction) const
 {
     return !isOrthogonalChild(child) ? direction : (direction == ForColumns ? ForRows : ForColumns);
 }

 unsigned RenderGrid::computeAutoRepeatTracksCount(GridTrackSizingDirection direction, SizingOperation sizingOperation) const
 {
     bool isRowAxis = direction == ForColumns;
     const auto& autoRepeatTracks = isRowAxis ? style().gridAutoRepeatColumns() : style().gridAutoRepeatRows();
     unsigned autoRepeatTrackListLength = autoRepeatTracks.size();

     if (!autoRepeatTrackListLength)
         return 0;

     std::optional<LayoutUnit> availableSize;
     if (isRowAxis) {
         if (sizingOperation != IntrinsicSizeComputation)
             availableSize = availableLogicalWidth();
     } else {
         availableSize = computeContentLogicalHeight(MainOrPreferredSize, style().logicalHeight(), std::nullopt);
         if (!availableSize) {
             const Length& maxLength = style().logicalMaxHeight();
             if (!maxLength.isUndefined())
                 availableSize = computeContentLogicalHeight(MaxSize, maxLength, std::nullopt);
         }
         if (availableSize)
             availableSize = constrainContentBoxLogicalHeightByMinMax(availableSize.value(), std::nullopt);
     }

     bool needsToFulfillMinimumSize = false;
     if (!availableSize) {
         const Length& minSize = isRowAxis ? style().logicalMinWidth() : style().logicalMinHeight();
         if (!minSize.isSpecified())
             return autoRepeatTrackListLength;

         LayoutUnit containingBlockAvailableSize = isRowAxis ? containingBlockLogicalWidthForContent() : containingBlockLogicalHeightForContent(ExcludeMarginBorderPadding);
         availableSize = valueForLength(minSize, containingBlockAvailableSize);
         needsToFulfillMinimumSize = true;
     }

     LayoutUnit autoRepeatTracksSize;
     for (auto& autoTrackSize : autoRepeatTracks) {
         ASSERT(autoTrackSize.minTrackBreadth().isLength());
         ASSERT(!autoTrackSize.minTrackBreadth().isFlex());
         bool hasDefiniteMaxTrackSizingFunction = autoTrackSize.maxTrackBreadth().isLength() && !autoTrackSize.maxTrackBreadth().isContentSized();
         auto trackLength = hasDefiniteMaxTrackSizingFunction ? autoTrackSize.maxTrackBreadth().length() : autoTrackSize.minTrackBreadth().length();
         autoRepeatTracksSize += valueForLength(trackLength, availableSize.value());
     }
     // For the purpose of finding the number of auto-repeated tracks, the UA must floor the track size to a UA-specified
     // value to avoid division by zero. It is suggested that this floor be 1px.
     autoRepeatTracksSize = std::max<LayoutUnit>(LayoutUnit(1), autoRepeatTracksSize);

     // There will be always at least 1 auto-repeat track, so take it already into account when computing the total track size.
     LayoutUnit tracksSize = autoRepeatTracksSize;
     auto& trackSizes = isRowAxis ? style().gridColumns() : style().gridRows();

     for (const auto& track : trackSizes) {
         bool hasDefiniteMaxTrackBreadth = track.maxTrackBreadth().isLength() && !track.maxTrackBreadth().isContentSized();
         ASSERT(hasDefiniteMaxTrackBreadth || (track.minTrackBreadth().isLength() && !track.minTrackBreadth().isContentSized()));
         tracksSize += valueForLength(hasDefiniteMaxTrackBreadth ? track.maxTrackBreadth().length() : track.minTrackBreadth().length(), availableSize.value());
     }

     // Add gutters as if there where only 1 auto repeat track. Gaps between auto repeat tracks will be added later when
     // computing the repetitions.
     LayoutUnit gapSize = gridGapForDirection(direction, sizingOperation);
     tracksSize += gapSize * trackSizes.size();

     LayoutUnit freeSpace = availableSize.value() - tracksSize;
     if (freeSpace <= 0)
         return autoRepeatTrackListLength;

     unsigned repetitions = 1 + (freeSpace / (autoRepeatTracksSize + gapSize)).toInt();

     // Provided the grid container does not have a definite size or max-size in the relevant axis,
     // if the min size is definite then the number of repetitions is the largest possible positive
     // integer that fulfills that minimum requirement.
     if (needsToFulfillMinimumSize)
         ++repetitions;

     return repetitions * autoRepeatTrackListLength;
 }


 std::unique_ptr<OrderedTrackIndexSet> RenderGrid::computeEmptyTracksForAutoRepeat(Grid& grid, GridTrackSizingDirection direction) const
 {
     bool isRowAxis = direction == ForColumns;
     if ((isRowAxis && style().gridAutoRepeatColumnsType() != AutoFit)
         || (!isRowAxis && style().gridAutoRepeatRowsType() != AutoFit))
         return nullptr;

     std::unique_ptr<OrderedTrackIndexSet> emptyTrackIndexes;
     unsigned insertionPoint = isRowAxis ? style().gridAutoRepeatColumnsInsertionPoint() : style().gridAutoRepeatRowsInsertionPoint();
     unsigned firstAutoRepeatTrack = insertionPoint + std::abs(grid.smallestTrackStart(direction));
     unsigned lastAutoRepeatTrack = firstAutoRepeatTrack + grid.autoRepeatTracks(direction);

     if (!grid.hasGridItems()) {
         emptyTrackIndexes = std::make_unique<OrderedTrackIndexSet>();
         for (unsigned trackIndex = firstAutoRepeatTrack; trackIndex < lastAutoRepeatTrack; ++trackIndex)
             emptyTrackIndexes->add(trackIndex);
     } else {
         for (unsigned trackIndex = firstAutoRepeatTrack; trackIndex < lastAutoRepeatTrack; ++trackIndex) {
             GridIterator iterator(grid, direction, trackIndex);
             if (!iterator.nextGridItem()) {
                 if (!emptyTrackIndexes)
                     emptyTrackIndexes = std::make_unique<OrderedTrackIndexSet>();
                 emptyTrackIndexes->add(trackIndex);
             }
         }
     }
     return emptyTrackIndexes;
 }

 void RenderGrid::placeItemsOnGrid(Grid& grid, SizingOperation sizingOperation) const
 {
     unsigned autoRepeatColumns = computeAutoRepeatTracksCount(ForColumns, sizingOperation);
     unsigned autoRepeatRows = computeAutoRepeatTracksCount(ForRows, sizingOperation);
     if (autoRepeatColumns != grid.autoRepeatTracks(ForColumns) || autoRepeatRows != grid.autoRepeatTracks(ForRows)) {
         grid.setNeedsItemsPlacement(true);
         grid.setAutoRepeatTracks(autoRepeatRows, autoRepeatColumns);
     }

     if (!grid.needsItemsPlacement())
         return;

     ASSERT(!grid.hasGridItems());
     populateExplicitGridAndOrderIterator(grid);

     Vector<RenderBox*> autoMajorAxisAutoGridItems;
     Vector<RenderBox*> specifiedMajorAxisAutoGridItems;
     bool hasAnyOrthogonalGridItem = false;
     for (auto* child = grid.orderIterator().first(); child; child = grid.orderIterator().next()) {
         if (child->isOutOfFlowPositioned())
             continue;

         hasAnyOrthogonalGridItem = hasAnyOrthogonalGridItem || isOrthogonalChild(*child);

         GridArea area = grid.gridItemArea(*child);
         if (!area.rows.isIndefinite())
             area.rows.translate(std::abs(grid.smallestTrackStart(ForRows)));
         if (!area.columns.isIndefinite())
             area.columns.translate(std::abs(grid.smallestTrackStart(ForColumns)));

         if (area.rows.isIndefinite() || area.columns.isIndefinite()) {
             grid.setGridItemArea(*child, area);
             bool majorAxisDirectionIsForColumns = autoPlacementMajorAxisDirection() == ForColumns;
             if ((majorAxisDirectionIsForColumns && area.columns.isIndefinite())
                 || (!majorAxisDirectionIsForColumns && area.rows.isIndefinite()))
                 autoMajorAxisAutoGridItems.append(child);
             else
                 specifiedMajorAxisAutoGridItems.append(child);
             continue;
         }
         grid.insert(*child, { area.rows, area.columns });
     }
     grid.setHasAnyOrthogonalGridItem(hasAnyOrthogonalGridItem);

 #if ENABLE(ASSERT)
     if (grid.hasGridItems()) {
         ASSERT(grid.numTracks(ForRows) >= GridPositionsResolver::explicitGridRowCount(style(), grid.autoRepeatTracks(ForRows)));
         ASSERT(grid.numTracks(ForColumns) >= GridPositionsResolver::explicitGridColumnCount(style(), grid.autoRepeatTracks(ForColumns)));
     }
 #endif

     placeSpecifiedMajorAxisItemsOnGrid(grid, specifiedMajorAxisAutoGridItems);
     placeAutoMajorAxisItemsOnGrid(grid, autoMajorAxisAutoGridItems);

     // Compute collapsible tracks for auto-fit.
     grid.setAutoRepeatEmptyColumns(computeEmptyTracksForAutoRepeat(grid, ForColumns));
     grid.setAutoRepeatEmptyRows(computeEmptyTracksForAutoRepeat(grid, ForRows));

     grid.setNeedsItemsPlacement(false);

 #if ENABLE(ASSERT)
     for (auto* child = grid.orderIterator().first(); child; child = grid.orderIterator().next()) {
         if (child->isOutOfFlowPositioned())
             continue;

         GridArea area = grid.gridItemArea(*child);
         ASSERT(area.rows.isTranslatedDefinite() && area.columns.isTranslatedDefinite());
     }
 #endif
 }

 void RenderGrid::populateExplicitGridAndOrderIterator(Grid& grid) const
 {
     OrderIteratorPopulator populator(grid.orderIterator());
     int smallestRowStart = 0;
     int smallestColumnStart = 0;
     unsigned autoRepeatRows = grid.autoRepeatTracks(ForRows);
     unsigned autoRepeatColumns = grid.autoRepeatTracks(ForColumns);
     unsigned maximumRowIndex = GridPositionsResolver::explicitGridRowCount(style(), autoRepeatRows);
     unsigned maximumColumnIndex = GridPositionsResolver::explicitGridColumnCount(style(), autoRepeatColumns);

     for (RenderBox* child = firstChildBox(); child; child = child->nextSiblingBox()) {
         if (child->isOutOfFlowPositioned())
             continue;

         populator.collectChild(*child);

         GridSpan rowPositions = GridPositionsResolver::resolveGridPositionsFromStyle(style(), *child, ForRows, autoRepeatRows);
         if (!rowPositions.isIndefinite()) {
             smallestRowStart = std::min(smallestRowStart, rowPositions.untranslatedStartLine());
             maximumRowIndex = std::max<int>(maximumRowIndex, rowPositions.untranslatedEndLine());
         } else {
             // Grow the grid for items with a definite row span, getting the largest such span.
             unsigned spanSize = GridPositionsResolver::spanSizeForAutoPlacedItem(style(), *child, ForRows);
             maximumRowIndex = std::max(maximumRowIndex, spanSize);
         }

         GridSpan columnPositions = GridPositionsResolver::resolveGridPositionsFromStyle(style(), *child, ForColumns, autoRepeatColumns);
         if (!columnPositions.isIndefinite()) {
             smallestColumnStart = std::min(smallestColumnStart, columnPositions.untranslatedStartLine());
             maximumColumnIndex = std::max<int>(maximumColumnIndex, columnPositions.untranslatedEndLine());
         } else {
             // Grow the grid for items with a definite column span, getting the largest such span.
             unsigned spanSize = GridPositionsResolver::spanSizeForAutoPlacedItem(style(), *child, ForColumns);
             maximumColumnIndex = std::max(maximumColumnIndex, spanSize);
         }

         grid.setGridItemArea(*child, { rowPositions, columnPositions });
     }

     grid.setSmallestTracksStart(smallestRowStart, smallestColumnStart);
     grid.ensureGridSize(maximumRowIndex + std::abs(smallestRowStart), maximumColumnIndex + std::abs(smallestColumnStart));
 }

 std::unique_ptr<GridArea> RenderGrid::createEmptyGridAreaAtSpecifiedPositionsOutsideGrid(Grid& grid, const RenderBox& gridItem, GridTrackSizingDirection specifiedDirection, const GridSpan& specifiedPositions) const
 {
     GridTrackSizingDirection crossDirection = specifiedDirection == ForColumns ? ForRows : ForColumns;
     const unsigned endOfCrossDirection = grid.numTracks(crossDirection);
     unsigned crossDirectionSpanSize = GridPositionsResolver::spanSizeForAutoPlacedItem(style(), gridItem, crossDirection);
     GridSpan crossDirectionPositions = GridSpan::translatedDefiniteGridSpan(endOfCrossDirection, endOfCrossDirection + crossDirectionSpanSize);
     return std::make_unique<GridArea>(specifiedDirection == ForColumns ? crossDirectionPositions : specifiedPositions, specifiedDirection == ForColumns ? specifiedPositions : crossDirectionPositions);
 }

 void RenderGrid::placeSpecifiedMajorAxisItemsOnGrid(Grid& grid, const Vector<RenderBox*>& autoGridItems) const
 {
     bool isForColumns = autoPlacementMajorAxisDirection() == ForColumns;
     bool isGridAutoFlowDense = style().isGridAutoFlowAlgorithmDense();

     // Mapping between the major axis tracks (rows or columns) and the last auto-placed item's position inserted on
     // that track. This is needed to implement "sparse" packing for items locked to a given track.
     // See http://dev.w3.org/csswg/css-grid/#auto-placement-algorithm
     HashMap<unsigned, unsigned, DefaultHash<unsigned>::Hash, WTF::UnsignedWithZeroKeyHashTraits<unsigned>> minorAxisCursors;

     for (auto& autoGridItem : autoGridItems) {
         GridSpan majorAxisPositions = grid.gridItemSpan(*autoGridItem, autoPlacementMajorAxisDirection());
         ASSERT(majorAxisPositions.isTranslatedDefinite());
         ASSERT(grid.gridItemSpan(*autoGridItem, autoPlacementMinorAxisDirection()).isIndefinite());
         unsigned minorAxisSpanSize = GridPositionsResolver::spanSizeForAutoPlacedItem(style(), *autoGridItem, autoPlacementMinorAxisDirection());
         unsigned majorAxisInitialPosition = majorAxisPositions.startLine();

         GridIterator iterator(grid, autoPlacementMajorAxisDirection(), majorAxisPositions.startLine(), isGridAutoFlowDense ? 0 : minorAxisCursors.get(majorAxisInitialPosition));
         std::unique_ptr<GridArea> emptyGridArea = iterator.nextEmptyGridArea(majorAxisPositions.integerSpan(), minorAxisSpanSize);
         if (!emptyGridArea)
             emptyGridArea = createEmptyGridAreaAtSpecifiedPositionsOutsideGrid(grid, *autoGridItem, autoPlacementMajorAxisDirection(), majorAxisPositions);

         grid.insert(*autoGridItem, *emptyGridArea);

         if (!isGridAutoFlowDense)
             minorAxisCursors.set(majorAxisInitialPosition, isForColumns ? emptyGridArea->rows.startLine() : emptyGridArea->columns.startLine());
     }
 }

 void RenderGrid::placeAutoMajorAxisItemsOnGrid(Grid& grid, const Vector<RenderBox*>& autoGridItems) const
 {
     AutoPlacementCursor autoPlacementCursor = {0, 0};
     bool isGridAutoFlowDense = style().isGridAutoFlowAlgorithmDense();

     for (auto& autoGridItem : autoGridItems) {
         placeAutoMajorAxisItemOnGrid(grid, *autoGridItem, autoPlacementCursor);

         if (isGridAutoFlowDense) {
             autoPlacementCursor.first = 0;
             autoPlacementCursor.second = 0;
         }
     }
 }

 void RenderGrid::placeAutoMajorAxisItemOnGrid(Grid& grid, RenderBox& gridItem, AutoPlacementCursor& autoPlacementCursor) const
 {
     ASSERT(grid.gridItemSpan(gridItem, autoPlacementMajorAxisDirection()).isIndefinite());
     unsigned majorAxisSpanSize = GridPositionsResolver::spanSizeForAutoPlacedItem(style(), gridItem, autoPlacementMajorAxisDirection());

     const unsigned endOfMajorAxis = grid.numTracks(autoPlacementMajorAxisDirection());
     unsigned majorAxisAutoPlacementCursor = autoPlacementMajorAxisDirection() == ForColumns ? autoPlacementCursor.second : autoPlacementCursor.first;
     unsigned minorAxisAutoPlacementCursor = autoPlacementMajorAxisDirection() == ForColumns ? autoPlacementCursor.first : autoPlacementCursor.second;

     std::unique_ptr<GridArea> emptyGridArea;
     GridSpan minorAxisPositions = grid.gridItemSpan(gridItem, autoPlacementMinorAxisDirection());
     if (minorAxisPositions.isTranslatedDefinite()) {
         // Move to the next track in major axis if initial position in minor axis is before auto-placement cursor.
         if (minorAxisPositions.startLine() < minorAxisAutoPlacementCursor)
             majorAxisAutoPlacementCursor++;

         if (majorAxisAutoPlacementCursor < endOfMajorAxis) {
             GridIterator iterator(grid, autoPlacementMinorAxisDirection(), minorAxisPositions.startLine(), majorAxisAutoPlacementCursor);
             emptyGridArea = iterator.nextEmptyGridArea(minorAxisPositions.integerSpan(), majorAxisSpanSize);
         }

         if (!emptyGridArea)
             emptyGridArea = createEmptyGridAreaAtSpecifiedPositionsOutsideGrid(grid, gridItem, autoPlacementMinorAxisDirection(), minorAxisPositions);
     } else {
         unsigned minorAxisSpanSize = GridPositionsResolver::spanSizeForAutoPlacedItem(style(), gridItem, autoPlacementMinorAxisDirection());

         for (unsigned majorAxisIndex = majorAxisAutoPlacementCursor; majorAxisIndex < endOfMajorAxis; ++majorAxisIndex) {
             GridIterator iterator(grid, autoPlacementMajorAxisDirection(), majorAxisIndex, minorAxisAutoPlacementCursor);
             emptyGridArea = iterator.nextEmptyGridArea(majorAxisSpanSize, minorAxisSpanSize);

             if (emptyGridArea) {
                 // Check that it fits in the minor axis direction, as we shouldn't grow in that direction here (it was already managed in populateExplicitGridAndOrderIterator()).
                 unsigned minorAxisFinalPositionIndex = autoPlacementMinorAxisDirection() == ForColumns ? emptyGridArea->columns.endLine() : emptyGridArea->rows.endLine();
                 const unsigned endOfMinorAxis = grid.numTracks(autoPlacementMinorAxisDirection());
                 if (minorAxisFinalPositionIndex <= endOfMinorAxis)
                     break;

                 // Discard empty grid area as it does not fit in the minor axis direction.
                 // We don't need to create a new empty grid area yet as we might find a valid one in the next iteration.
                 emptyGridArea = nullptr;
             }

             // As we're moving to the next track in the major axis we should reset the auto-placement cursor in the minor axis.
             minorAxisAutoPlacementCursor = 0;
         }

         if (!emptyGridArea)
             emptyGridArea = createEmptyGridAreaAtSpecifiedPositionsOutsideGrid(grid, gridItem, autoPlacementMinorAxisDirection(), GridSpan::translatedDefiniteGridSpan(0, minorAxisSpanSize));
     }

     grid.insert(gridItem, *emptyGridArea);
     autoPlacementCursor.first = emptyGridArea->rows.startLine();
     autoPlacementCursor.second = emptyGridArea->columns.startLine();
 }

 GridTrackSizingDirection RenderGrid::autoPlacementMajorAxisDirection() const
 {
     return style().isGridAutoFlowDirectionColumn() ? ForColumns : ForRows;
 }

 GridTrackSizingDirection RenderGrid::autoPlacementMinorAxisDirection() const
 {
     return style().isGridAutoFlowDirectionColumn() ? ForRows : ForColumns;
 }

 void RenderGrid::dirtyGrid()
 {
     if (m_grid.needsItemsPlacement())
         return;

     m_grid.setNeedsItemsPlacement(true);
 }

 Vector<LayoutUnit> RenderGrid::trackSizesForComputedStyle(GridTrackSizingDirection direction) const
 {
     bool isRowAxis = direction == ForColumns;
     auto& positions = isRowAxis ? m_columnPositions : m_rowPositions;
     size_t numPositions = positions.size();
     LayoutUnit offsetBetweenTracks = isRowAxis ? m_offsetBetweenColumns : m_offsetBetweenRows;

     Vector<LayoutUnit> tracks;
     if (numPositions < 2)
         return tracks;

     ASSERT(!m_grid.needsItemsPlacement());
     bool hasCollapsedTracks = m_grid.hasAutoRepeatEmptyTracks(direction);
     LayoutUnit gap = !hasCollapsedTracks ? gridGapForDirection(direction, TrackSizing) : LayoutUnit();
     tracks.reserveCapacity(numPositions - 1);
     for (size_t i = 0; i < numPositions - 2; ++i)
         tracks.append(positions[i + 1] - positions[i] - offsetBetweenTracks - gap);
     tracks.append(positions[numPositions - 1] - positions[numPositions - 2]);

     if (!hasCollapsedTracks)
         return tracks;

     size_t remainingEmptyTracks = m_grid.autoRepeatEmptyTracks(direction)->size();
     size_t lastLine = tracks.size();
     gap = gridGapForDirection(direction, TrackSizing);
     for (size_t i = 1; i < lastLine; ++i) {
         if (m_grid.isEmptyAutoRepeatTrack(direction, i - 1))
             --remainingEmptyTracks;
         else {
             // Remove the gap between consecutive non empty tracks. Remove it also just once for an
             // arbitrary number of empty tracks between two non empty ones.
             bool allRemainingTracksAreEmpty = remainingEmptyTracks == (lastLine - i);
             if (!allRemainingTracksAreEmpty || !m_grid.isEmptyAutoRepeatTrack(direction, i))
                 tracks[i - 1] -= gap;
         }
     }

     return tracks;
 }

 static const StyleContentAlignmentData& contentAlignmentNormalBehaviorGrid()
 {
     static const StyleContentAlignmentData normalBehavior = {ContentPositionNormal, ContentDistributionStretch};
     return normalBehavior;
 }

 void RenderGrid::applyStretchAlignmentToTracksIfNeeded(GridTrackSizingDirection direction)
 {
     std::optional<LayoutUnit> freeSpace = m_trackSizingAlgorithm.freeSpace(direction);
     if (!freeSpace
         || freeSpace.value() <= 0
         || (direction == ForColumns && style().resolvedJustifyContentDistribution(contentAlignmentNormalBehaviorGrid()) != ContentDistributionStretch)
         || (direction == ForRows && style().resolvedAlignContentDistribution(contentAlignmentNormalBehaviorGrid()) != ContentDistributionStretch))
         return;

     // Spec defines auto-sized tracks as the ones with an 'auto' max-sizing function.
     Vector<GridTrack>& allTracks = m_trackSizingAlgorithm.tracks(direction);
     Vector<unsigned> autoSizedTracksIndex;
     for (unsigned i = 0; i < allTracks.size(); ++i) {
         const GridTrackSize& trackSize = m_trackSizingAlgorithm.gridTrackSize(direction, i, TrackSizing);
         if (trackSize.hasAutoMaxTrackBreadth())
             autoSizedTracksIndex.append(i);
     }

     unsigned numberOfAutoSizedTracks = autoSizedTracksIndex.size();
     if (numberOfAutoSizedTracks < 1)
         return;

     LayoutUnit sizeToIncrease = freeSpace.value() / numberOfAutoSizedTracks;
     for (const auto& trackIndex : autoSizedTracksIndex) {
         auto& track = allTracks[trackIndex];
         track.setBaseSize(track.baseSize() + sizeToIncrease);
     }
     m_trackSizingAlgorithm.setFreeSpace(direction, LayoutUnit());
 }

 void RenderGrid::layoutGridItems()
 {
     populateGridPositionsForDirection(ForColumns);
     populateGridPositionsForDirection(ForRows);

     for (RenderBox* child = firstChildBox(); child; child = child->nextSiblingBox()) {
         if (child->isOutOfFlowPositioned()) {
             prepareChildForPositionedLayout(*child);
             continue;
         }

         // Because the grid area cannot be styled, we don't need to adjust
         // the grid breadth to account for 'box-sizing'.
         std::optional<LayoutUnit> oldOverrideContainingBlockContentLogicalWidth = child->hasOverrideContainingBlockLogicalWidth() ? child->overrideContainingBlockContentLogicalWidth() : LayoutUnit();
         std::optional<LayoutUnit> oldOverrideContainingBlockContentLogicalHeight = child->hasOverrideContainingBlockLogicalHeight() ? child->overrideContainingBlockContentLogicalHeight() : LayoutUnit();

         LayoutUnit overrideContainingBlockContentLogicalWidth = gridAreaBreadthForChildIncludingAlignmentOffsets(*child, ForColumns);
         LayoutUnit overrideContainingBlockContentLogicalHeight = gridAreaBreadthForChildIncludingAlignmentOffsets(*child, ForRows);
         if (!oldOverrideContainingBlockContentLogicalWidth || oldOverrideContainingBlockContentLogicalWidth.value() != overrideContainingBlockContentLogicalWidth
             || ((!oldOverrideContainingBlockContentLogicalHeight || oldOverrideContainingBlockContentLogicalHeight.value() != overrideContainingBlockContentLogicalHeight)
                 && child->hasRelativeLogicalHeight()))
             child->setNeedsLayout(MarkOnlyThis);

         child->setOverrideContainingBlockContentLogicalWidth(overrideContainingBlockContentLogicalWidth);
         child->setOverrideContainingBlockContentLogicalHeight(overrideContainingBlockContentLogicalHeight);

         LayoutRect oldChildRect = child->frameRect();

         // Stretching logic might force a child layout, so we need to run it before the layoutIfNeeded
         // call to avoid unnecessary relayouts. This might imply that child margins, needed to correctly
         // determine the available space before stretching, are not set yet.
         applyStretchAlignmentToChildIfNeeded(*child);

         child->layoutIfNeeded();

         // We need pending layouts to be done in order to compute auto-margins properly.
         updateAutoMarginsInColumnAxisIfNeeded(*child);
         updateAutoMarginsInRowAxisIfNeeded(*child);

         child->setLogicalLocation(findChildLogicalPosition(*child));

         // If the child moved, we have to repaint it as well as any floating/positioned
         // descendants. An exception is if we need a layout. In this case, we know we're going to
         // repaint ourselves (and the child) anyway.
         if (!selfNeedsLayout() && child->checkForRepaintDuringLayout())
             child->repaintDuringLayoutIfMoved(oldChildRect);
     }
 }

 void RenderGrid::prepareChildForPositionedLayout(RenderBox& child)
 {
     ASSERT(child.isOutOfFlowPositioned());
     child.containingBlock()->insertPositionedObject(child);

     RenderLayer* childLayer = child.layer();
     childLayer->setStaticInlinePosition(borderAndPaddingStart());
     childLayer->setStaticBlockPosition(borderAndPaddingBefore());
 }

 void RenderGrid::layoutPositionedObject(RenderBox& child, bool relayoutChildren, bool fixedPositionObjectsOnly)
 {
     // FIXME: Properly support orthogonal writing mode.
     if (!isOrthogonalChild(child)) {
         LayoutUnit columnOffset = LayoutUnit();
         LayoutUnit columnBreadth = LayoutUnit();
         offsetAndBreadthForPositionedChild(child, ForColumns, columnOffset, columnBreadth);
         LayoutUnit rowOffset = LayoutUnit();
         LayoutUnit rowBreadth = LayoutUnit();
         offsetAndBreadthForPositionedChild(child, ForRows, rowOffset, rowBreadth);

         child.setOverrideContainingBlockContentLogicalWidth(columnBreadth);
         child.setOverrideContainingBlockContentLogicalHeight(rowBreadth);
         child.setExtraInlineOffset(columnOffset);
         child.setExtraBlockOffset(rowOffset);

         if (child.parent() == this) {
             auto& childLayer = *child.layer();
             childLayer.setStaticInlinePosition(borderStart() + columnOffset);
             childLayer.setStaticBlockPosition(borderBefore() + rowOffset);
         }
     }

     RenderBlock::layoutPositionedObject(child, relayoutChildren, fixedPositionObjectsOnly);
 }

 void RenderGrid::offsetAndBreadthForPositionedChild(const RenderBox& child, GridTrackSizingDirection direction, LayoutUnit& offset, LayoutUnit& breadth)
 {
     ASSERT(!isOrthogonalChild(child));
     bool isRowAxis = direction == ForColumns;

     unsigned autoRepeatCount = m_grid.autoRepeatTracks(direction);
     GridSpan positions = GridPositionsResolver::resolveGridPositionsFromStyle(style(), child, direction, autoRepeatCount);
     if (positions.isIndefinite()) {
         offset = LayoutUnit();
         breadth = isRowAxis ? clientLogicalWidth() : clientLogicalHeight();
         return;
     }

     // For positioned items we cannot use GridSpan::translate() because we could end up with negative values, as the positioned items do not create implicit tracks per spec.
     int smallestStart = std::abs(m_grid.smallestTrackStart(direction));
     int startLine = positions.untranslatedStartLine() + smallestStart;
     int endLine = positions.untranslatedEndLine() + smallestStart;

     GridPosition startPosition = isRowAxis ? child.style().gridItemColumnStart() : child.style().gridItemRowStart();
     GridPosition endPosition = isRowAxis ? child.style().gridItemColumnEnd() : child.style().gridItemRowEnd();
     int lastLine = numTracks(direction, m_grid);

     bool startIsAuto = startPosition.isAuto()
         || (startPosition.isNamedGridArea() && !NamedLineCollection::isValidNamedLineOrArea(startPosition.namedGridLine(), style(), (direction == ForColumns) ? ColumnStartSide : RowStartSide))
         || (startLine < 0)
         || (startLine > lastLine);
     bool endIsAuto = endPosition.isAuto()
         || (endPosition.isNamedGridArea() && !NamedLineCollection::isValidNamedLineOrArea(endPosition.namedGridLine(), style(), (direction == ForColumns) ? ColumnEndSide : RowEndSide))
         || (endLine < 0)
         || (endLine > lastLine);

     // We're normalizing the positions to avoid issues with RTL (as they're stored in the same order than LTR but adding an offset).
     LayoutUnit start;
     if (!startIsAuto) {
         if (isRowAxis) {
             if (style().isLeftToRightDirection())
                 start = m_columnPositions[startLine] - borderLogicalLeft();
             else
                 start = logicalWidth() - translateRTLCoordinate(m_columnPositions[startLine]) - borderLogicalRight();
         } else
             start = m_rowPositions[startLine] - borderBefore();
     }

     LayoutUnit end = isRowAxis ? clientLogicalWidth() : clientLogicalHeight();
     if (!endIsAuto) {
         if (isRowAxis) {
             if (style().isLeftToRightDirection())
                 end = m_columnPositions[endLine] - borderLogicalLeft();
             else
                 end = logicalWidth() - translateRTLCoordinate(m_columnPositions[endLine]) - borderLogicalRight();
         } else
             end = m_rowPositions[endLine] - borderBefore();

         // These vectors store line positions including gaps, but we shouldn't consider them for the edges of the grid.
         if (endLine > 0 && endLine < lastLine) {
             ASSERT(!m_grid.needsItemsPlacement());
             end -= guttersSize(m_grid, direction, endLine - 1, 2, TrackSizing);
             end -= isRowAxis ? m_offsetBetweenColumns : m_offsetBetweenRows;
         }
     }

     breadth = end - start;
     offset = start;

     if (isRowAxis && !style().isLeftToRightDirection() && !child.style().hasStaticInlinePosition(child.isHorizontalWritingMode())) {
         // If the child doesn't have a static inline position (i.e. "left" and/or "right" aren't "auto",
         // we need to calculate the offset from the left (even if we're in RTL).
         if (endIsAuto)
             offset = LayoutUnit();
         else {
             offset = translateRTLCoordinate(m_columnPositions[endLine]) - borderLogicalLeft();

             if (endLine > 0 && endLine < lastLine) {
                 ASSERT(!m_grid.needsItemsPlacement());
                 offset += guttersSize(m_grid, direction, endLine - 1, 2, TrackSizing);
                 offset += isRowAxis ? m_offsetBetweenColumns : m_offsetBetweenRows;
             }
         }
     }
 }

 LayoutUnit RenderGrid::gridAreaBreadthForChildIncludingAlignmentOffsets(const RenderBox& child, GridTrackSizingDirection direction) const
 {
     // We need the cached value when available because Content Distribution alignment properties
     // may have some influence in the final grid area breadth.
     const auto& tracks = m_trackSizingAlgorithm.tracks(direction);
     const auto& span = m_grid.gridItemSpan(child, direction);
     const auto& linePositions = (direction == ForColumns) ? m_columnPositions : m_rowPositions;

     LayoutUnit initialTrackPosition = linePositions[span.startLine()];
     LayoutUnit finalTrackPosition = linePositions[span.endLine() - 1];

     // Track Positions vector stores the 'start' grid line of each track, so we have to add last track's baseSize.
     return finalTrackPosition - initialTrackPosition + tracks[span.endLine() - 1].baseSize();
 }

 void RenderGrid::populateGridPositionsForDirection(GridTrackSizingDirection direction)
 {
     // Since we add alignment offsets and track gutters, grid lines are not always adjacent. Hence we will have to
     // assume from now on that we just store positions of the initial grid lines of each track,
     // except the last one, which is the only one considered as a final grid line of a track.

     // The grid container's frame elements (border, padding and <content-position> offset) are sensible to the
     // inline-axis flow direction. However, column lines positions are 'direction' unaware. This simplification
     // allows us to use the same indexes to identify the columns independently on the inline-axis direction.
     bool isRowAxis = direction == ForColumns;
     auto& tracks = m_trackSizingAlgorithm.tracks(direction);
     unsigned numberOfTracks = tracks.size();
     unsigned numberOfLines = numberOfTracks + 1;
     unsigned lastLine = numberOfLines - 1;

     ContentAlignmentData offset = computeContentPositionAndDistributionOffset(direction, m_trackSizingAlgorithm.freeSpace(direction).value(), numberOfTracks);
     auto& positions = isRowAxis ? m_columnPositions : m_rowPositions;
     positions.resize(numberOfLines);
     auto borderAndPadding = isRowAxis ? borderAndPaddingLogicalLeft() : borderAndPaddingBefore();
     positions[0] = borderAndPadding + offset.positionOffset;
     if (numberOfLines > 1) {
         // If we have collapsed tracks we just ignore gaps here and add them later as we might not
         // compute the gap between two consecutive tracks without examining the surrounding ones.
         bool hasCollapsedTracks = m_grid.hasAutoRepeatEmptyTracks(direction);
         LayoutUnit gap = !hasCollapsedTracks ? gridGapForDirection(direction, m_trackSizingAlgorithm.sizingOperation()) : LayoutUnit();
         unsigned nextToLastLine = numberOfLines - 2;
         for (unsigned i = 0; i < nextToLastLine; ++i)
             positions[i + 1] = positions[i] + offset.distributionOffset + tracks[i].baseSize() + gap;
         positions[lastLine] = positions[nextToLastLine] + tracks[nextToLastLine].baseSize();

         // Adjust collapsed gaps. Collapsed tracks cause the surrounding gutters to collapse (they
         // coincide exactly) except on the edges of the grid where they become 0.
         if (hasCollapsedTracks) {
             gap = gridGapForDirection(direction, m_trackSizingAlgorithm.sizingOperation());
             unsigned remainingEmptyTracks = m_grid.autoRepeatEmptyTracks(direction)->size();
             LayoutUnit gapAccumulator;
             for (unsigned i = 1; i < lastLine; ++i) {
                 if (m_grid.isEmptyAutoRepeatTrack(direction, i - 1))
                     --remainingEmptyTracks;
                 else {
                     // Add gap between consecutive non empty tracks. Add it also just once for an
                     // arbitrary number of empty tracks between two non empty ones.
                     bool allRemainingTracksAreEmpty = remainingEmptyTracks == (lastLine - i);
                     if (!allRemainingTracksAreEmpty || !m_grid.isEmptyAutoRepeatTrack(direction, i))
                         gapAccumulator += gap;
                 }
                 positions[i] += gapAccumulator;
             }
             positions[lastLine] += gapAccumulator;
         }
     }
     auto& offsetBetweenTracks = isRowAxis ? m_offsetBetweenColumns : m_offsetBetweenRows;
     offsetBetweenTracks = offset.distributionOffset;
 }

 static LayoutUnit computeOverflowAlignmentOffset(OverflowAlignment overflow, LayoutUnit trackSize, LayoutUnit childSize)
 {
     LayoutUnit offset = trackSize - childSize;
     switch (overflow) {
     case OverflowAlignmentSafe:
         // If overflow is 'safe', we have to make sure we don't overflow the 'start'
         // edge (potentially cause some data loss as the overflow is unreachable).
         return std::max<LayoutUnit>(0, offset);
     case OverflowAlignmentUnsafe:
     case OverflowAlignmentDefault:
         // If we overflow our alignment container and overflow is 'true' (default), we
         // ignore the overflow and just return the value regardless (which may cause data
         // loss as we overflow the 'start' edge).
         return offset;
     }

     ASSERT_NOT_REACHED();
     return 0;
 }

 // FIXME: This logic is shared by RenderFlexibleBox, so it should be moved to RenderBox.
 LayoutUnit RenderGrid::marginLogicalHeightForChild(const RenderBox& child) const
 {
     return isHorizontalWritingMode() ? child.verticalMarginExtent() : child.horizontalMarginExtent();
 }

 LayoutUnit RenderGrid::computeMarginLogicalSizeForChild(GridTrackSizingDirection direction, const RenderBox& child) const
 {
     if (!child.style().hasMargin())
         return 0;

     LayoutUnit marginStart;
     LayoutUnit marginEnd;
     if (direction == ForColumns)
         child.computeInlineDirectionMargins(*this, child.containingBlockLogicalWidthForContentInRegion(nullptr), child.logicalWidth(), marginStart, marginEnd);
     else
         child.computeBlockDirectionMargins(*this, marginStart, marginEnd);

     return marginStart + marginEnd;
 }

 LayoutUnit RenderGrid::availableAlignmentSpaceForChildBeforeStretching(LayoutUnit gridAreaBreadthForChild, const RenderBox& child) const
 {
     // Because we want to avoid multiple layouts, stretching logic might be performed before
     // children are laid out, so we can't use the child cached values. Hence, we need to
     // compute margins in order to determine the available height before stretching.
     return gridAreaBreadthForChild - (child.needsLayout() ? computeMarginLogicalSizeForChild(ForRows, child) : marginLogicalHeightForChild(child));
 }

 StyleSelfAlignmentData RenderGrid::alignSelfForChild(const RenderBox& child) const
 {
     return child.style().resolvedAlignSelf(&style(), selfAlignmentNormalBehavior());
 }

 StyleSelfAlignmentData RenderGrid::justifySelfForChild(const RenderBox& child) const
 {
     return child.style().resolvedJustifySelf(&style(), selfAlignmentNormalBehavior());
 }

 // FIXME: This logic is shared by RenderFlexibleBox, so it should be moved to RenderBox.
 void RenderGrid::applyStretchAlignmentToChildIfNeeded(RenderBox& child)
 {
     ASSERT(child.overrideContainingBlockContentLogicalHeight());

     // We clear height override values because we will decide now whether it's allowed or
     // not, evaluating the conditions which might have changed since the old values were set.
     child.clearOverrideLogicalContentHeight();

     GridTrackSizingDirection childBlockDirection = flowAwareDirectionForChild(child, ForRows);
     bool blockFlowIsColumnAxis = childBlockDirection == ForRows;
     bool allowedToStretchChildBlockSize = blockFlowIsColumnAxis ? allowedToStretchChildAlongColumnAxis(child) : allowedToStretchChildAlongRowAxis(child);
     if (allowedToStretchChildBlockSize) {
         LayoutUnit stretchedLogicalHeight = availableAlignmentSpaceForChildBeforeStretching(overrideContainingBlockContentSizeForChild(child, childBlockDirection).value(), child);
         LayoutUnit desiredLogicalHeight = child.constrainLogicalHeightByMinMax(stretchedLogicalHeight, LayoutUnit(-1));
         child.setOverrideLogicalContentHeight(desiredLogicalHeight - child.borderAndPaddingLogicalHeight());
         if (desiredLogicalHeight != child.logicalHeight()) {
             // FIXME: Can avoid laying out here in some cases. See https://webkit.org/b/87905.
             child.setLogicalHeight(LayoutUnit());
             child.setNeedsLayout();
         }
     }
 }

 // FIXME: This logic is shared by RenderFlexibleBox, so it should be moved to RenderBox.
 bool RenderGrid::hasAutoMarginsInColumnAxis(const RenderBox& child) const
 {
     if (isHorizontalWritingMode())
         return child.style().marginTop().isAuto() || child.style().marginBottom().isAuto();
     return child.style().marginLeft().isAuto() || child.style().marginRight().isAuto();
 }

 // FIXME: This logic is shared by RenderFlexibleBox, so it should be moved to RenderBox.
 bool RenderGrid::hasAutoMarginsInRowAxis(const RenderBox& child) const
 {
     if (isHorizontalWritingMode())
         return child.style().marginLeft().isAuto() || child.style().marginRight().isAuto();
     return child.style().marginTop().isAuto() || child.style().marginBottom().isAuto();
 }

 // FIXME: This logic is shared by RenderFlexibleBox, so it should be moved to RenderBox.
 void RenderGrid::updateAutoMarginsInRowAxisIfNeeded(RenderBox& child)
 {
     ASSERT(!child.isOutOfFlowPositioned());

     LayoutUnit availableAlignmentSpace = child.overrideContainingBlockContentLogicalWidth().value() - child.logicalWidth() - child.marginLogicalWidth();
     if (availableAlignmentSpace <= 0)
         return;

     const RenderStyle& parentStyle = style();
     Length marginStart = child.style().marginStartUsing(&parentStyle);
     Length marginEnd = child.style().marginEndUsing(&parentStyle);
     if (marginStart.isAuto() && marginEnd.isAuto()) {
         child.setMarginStart(availableAlignmentSpace / 2, &parentStyle);
         child.setMarginEnd(availableAlignmentSpace / 2, &parentStyle);
     } else if (marginStart.isAuto()) {
         child.setMarginStart(availableAlignmentSpace, &parentStyle);
     } else if (marginEnd.isAuto()) {
         child.setMarginEnd(availableAlignmentSpace, &parentStyle);
     }
 }

 // FIXME: This logic is shared by RenderFlexibleBox, so it should be moved to RenderBox.
 void RenderGrid::updateAutoMarginsInColumnAxisIfNeeded(RenderBox& child)
 {
     ASSERT(!child.isOutOfFlowPositioned());

     LayoutUnit availableAlignmentSpace = child.overrideContainingBlockContentLogicalHeight().value() - child.logicalHeight() - child.marginLogicalHeight();
     if (availableAlignmentSpace <= 0)
         return;

     const RenderStyle& parentStyle = style();
     Length marginBefore = child.style().marginBeforeUsing(&parentStyle);
     Length marginAfter = child.style().marginAfterUsing(&parentStyle);
     if (marginBefore.isAuto() && marginAfter.isAuto()) {
         child.setMarginBefore(availableAlignmentSpace / 2, &parentStyle);
         child.setMarginAfter(availableAlignmentSpace / 2, &parentStyle);
     } else if (marginBefore.isAuto()) {
         child.setMarginBefore(availableAlignmentSpace, &parentStyle);
     } else if (marginAfter.isAuto()) {
         child.setMarginAfter(availableAlignmentSpace, &parentStyle);
     }
 }

 // FIXME: This logic could be refactored somehow and defined in RenderBox.
 static int synthesizedBaselineFromBorderBox(const RenderBox& box, LineDirectionMode direction)
 {
     return (direction == HorizontalLine ? box.size().height() : box.size().width()).toInt();
 }

 bool RenderGrid::isInlineBaselineAlignedChild(const RenderBox& child) const
 {
     return alignSelfForChild(child).position() == ItemPositionBaseline && !isOrthogonalChild(child) && !hasAutoMarginsInColumnAxis(child);
 }

 // FIXME: This logic is shared by RenderFlexibleBox, so it might be refactored somehow.
 int RenderGrid::baselinePosition(FontBaseline, bool, LineDirectionMode direction, LinePositionMode mode) const
 {
 #if ENABLE(ASSERT)
     ASSERT(mode == PositionOnContainingLine);
 #else
     UNUSED_PARAM(mode);
 #endif
     int baseline = firstLineBaseline().value_or(synthesizedBaselineFromBorderBox(*this, direction));

     int marginSize = direction == HorizontalLine ? verticalMarginExtent() : horizontalMarginExtent();
     return baseline + marginSize;
 }

 std::optional<int> RenderGrid::firstLineBaseline() const
 {
     if (isWritingModeRoot() || !m_grid.hasGridItems())
         return std::nullopt;

     const RenderBox* baselineChild = nullptr;
     // Finding the first grid item in grid order.
     unsigned numColumns = m_grid.numTracks(ForColumns);
     for (size_t column = 0; column < numColumns; column++) {
         for (const auto* child : m_grid.cell(0, column)) {
             // If an item participates in baseline alignment, we select such item.
             if (isInlineBaselineAlignedChild(*child)) {
                 // FIXME: self-baseline and content-baseline alignment not implemented yet.
                 baselineChild = child;
                 break;
             }
             if (!baselineChild)
                 baselineChild = child;
         }
     }

     if (!baselineChild)
         return std::nullopt;

     auto baseline = isOrthogonalChild(*baselineChild) ? std::nullopt : baselineChild->firstLineBaseline();
     // We take border-box's bottom if no valid baseline.
     if (!baseline) {
         // FIXME: We should pass |direction| into firstLineBaseline and stop bailing out if we're a writing
         // mode root. This would also fix some cases where the grid is orthogonal to its container.
         LineDirectionMode direction = isHorizontalWritingMode() ? HorizontalLine : VerticalLine;
         return synthesizedBaselineFromBorderBox(*baselineChild, direction) + baselineChild->logicalTop().toInt();
     }
     return baseline.value() + baselineChild->logicalTop().toInt();
 }

 std::optional<int> RenderGrid::inlineBlockBaseline(LineDirectionMode direction) const
 {
     if (std::optional<int> baseline = firstLineBaseline())
         return baseline;

     int marginAscent = direction == HorizontalLine ? marginTop() : marginRight();
     return synthesizedBaselineFromBorderBox(*this, direction) + marginAscent;
 }

 GridAxisPosition RenderGrid::columnAxisPositionForChild(const RenderBox& child) const
 {
     bool hasSameWritingMode = child.style().writingMode() == style().writingMode();
     bool childIsLTR = child.style().isLeftToRightDirection();

     switch (child.style().resolvedAlignSelf(&style(), selfAlignmentNormalBehavior()).position()) {
     case ItemPositionSelfStart:
         // FIXME: Should we implement this logic in a generic utility function ?
         // Aligns the alignment subject to be flush with the edge of the alignment container
         // corresponding to the alignment subject's 'start' side in the column axis.
         if (isOrthogonalChild(child)) {
             // If orthogonal writing-modes, self-start will be based on the child's inline-axis
             // direction (inline-start), because it's the one parallel to the column axis.
             if (style().isFlippedBlocksWritingMode())
                 return childIsLTR ? GridAxisEnd : GridAxisStart;
             return childIsLTR ? GridAxisStart : GridAxisEnd;
         }
         // self-start is based on the child's block-flow direction. That's why we need to check against the grid container's block-flow direction.
         return hasSameWritingMode ? GridAxisStart : GridAxisEnd;
     case ItemPositionSelfEnd:
         // FIXME: Should we implement this logic in a generic utility function ?
         // Aligns the alignment subject to be flush with the edge of the alignment container
         // corresponding to the alignment subject's 'end' side in the column axis.
         if (isOrthogonalChild(child)) {
             // If orthogonal writing-modes, self-end will be based on the child's inline-axis
             // direction, (inline-end) because it's the one parallel to the column axis.
             if (style().isFlippedBlocksWritingMode())
                 return childIsLTR ? GridAxisStart : GridAxisEnd;
             return childIsLTR ? GridAxisEnd : GridAxisStart;
         }
         // self-end is based on the child's block-flow direction. That's why we need to check against the grid container's block-flow direction.
         return hasSameWritingMode ? GridAxisEnd : GridAxisStart;
     case ItemPositionLeft:
         // Aligns the alignment subject to be flush with the alignment container's 'line-left' edge.
         // The alignment axis (column axis) is always orthogonal to the inline axis, hence this value behaves as 'start'.
         return GridAxisStart;
     case ItemPositionRight:
         // Aligns the alignment subject to be flush with the alignment container's 'line-right' edge.
         // The alignment axis (column axis) is always orthogonal to the inline axis, hence this value behaves as 'start'.
         return GridAxisStart;
     case ItemPositionCenter:
         return GridAxisCenter;
     case ItemPositionFlexStart: // Only used in flex layout, otherwise equivalent to 'start'.
         // Aligns the alignment subject to be flush with the alignment container's 'start' edge (block-start) in the column axis.
     case ItemPositionStart:
         return GridAxisStart;
     case ItemPositionFlexEnd: // Only used in flex layout, otherwise equivalent to 'end'.
         // Aligns the alignment subject to be flush with the alignment container's 'end' edge (block-end) in the column axis.
     case ItemPositionEnd:
         return GridAxisEnd;
     case ItemPositionStretch:
         return GridAxisStart;
     case ItemPositionBaseline:
     case ItemPositionLastBaseline:
         // FIXME: Implement the previous values. For now, we always 'start' align the child.
         return GridAxisStart;
     case ItemPositionAuto:
     case ItemPositionNormal:
         break;
     }

     ASSERT_NOT_REACHED();
     return GridAxisStart;
 }

 GridAxisPosition RenderGrid::rowAxisPositionForChild(const RenderBox& child) const
 {
     bool hasSameDirection = child.style().direction() == style().direction();
     bool gridIsLTR = style().isLeftToRightDirection();

     switch (child.style().resolvedJustifySelf(&style(), selfAlignmentNormalBehavior()).position()) {
     case ItemPositionSelfStart:
         // FIXME: Should we implement this logic in a generic utility function ?
         // Aligns the alignment subject to be flush with the edge of the alignment container
         // corresponding to the alignment subject's 'start' side in the row axis.
         if (isOrthogonalChild(child)) {
             // If orthogonal writing-modes, self-start will be based on the child's block-axis
             // direction, because it's the one parallel to the row axis.
             if (child.style().isFlippedBlocksWritingMode())
                 return gridIsLTR ? GridAxisEnd : GridAxisStart;
             return gridIsLTR ? GridAxisStart : GridAxisEnd;
         }
         // self-start is based on the child's inline-flow direction. That's why we need to check against the grid container's direction.
         return hasSameDirection ? GridAxisStart : GridAxisEnd;
     case ItemPositionSelfEnd:
         // FIXME: Should we implement this logic in a generic utility function ?
         // Aligns the alignment subject to be flush with the edge of the alignment container
         // corresponding to the alignment subject's 'end' side in the row axis.
         if (isOrthogonalChild(child)) {
             // If orthogonal writing-modes, self-end will be based on the child's block-axis
             // direction, because it's the one parallel to the row axis.
             if (child.style().isFlippedBlocksWritingMode())
                 return gridIsLTR ? GridAxisStart : GridAxisEnd;
             return gridIsLTR ? GridAxisEnd : GridAxisStart;
         }
         // self-end is based on the child's inline-flow direction. That's why we need to check against the grid container's direction.
         return hasSameDirection ? GridAxisEnd : GridAxisStart;
     case ItemPositionLeft:
         // Aligns the alignment subject to be flush with the alignment container's 'line-left' edge.
         // We want the physical 'left' side, so we have to take account, container's inline-flow direction.
         return gridIsLTR ? GridAxisStart : GridAxisEnd;
     case ItemPositionRight:
         // Aligns the alignment subject to be flush with the alignment container's 'line-right' edge.
         // We want the physical 'right' side, so we have to take account, container's inline-flow direction.
         return gridIsLTR ? GridAxisEnd : GridAxisStart;
     case ItemPositionCenter:
         return GridAxisCenter;
     case ItemPositionFlexStart: // Only used in flex layout, otherwise equivalent to 'start'.
         // Aligns the alignment subject to be flush with the alignment container's 'start' edge (inline-start) in the row axis.
     case ItemPositionStart:
         return GridAxisStart;
     case ItemPositionFlexEnd: // Only used in flex layout, otherwise equivalent to 'end'.
         // Aligns the alignment subject to be flush with the alignment container's 'end' edge (inline-end) in the row axis.
     case ItemPositionEnd:
         return GridAxisEnd;
     case ItemPositionStretch:
         return GridAxisStart;
     case ItemPositionBaseline:
     case ItemPositionLastBaseline:
         // FIXME: Implement the previous values. For now, we always 'start' align the child.
         return GridAxisStart;
     case ItemPositionAuto:
     case ItemPositionNormal:
         break;
     }

     ASSERT_NOT_REACHED();
     return GridAxisStart;
 }

 LayoutUnit RenderGrid::columnAxisOffsetForChild(const RenderBox& child) const
 {
     const GridSpan& rowsSpan = m_grid.gridItemSpan(child, ForRows);
     unsigned childStartLine = rowsSpan.startLine();
     LayoutUnit startOfRow = m_rowPositions[childStartLine];
     LayoutUnit startPosition = startOfRow + marginBeforeForChild(child);
     if (hasAutoMarginsInColumnAxis(child))
         return startPosition;
     GridAxisPosition axisPosition = columnAxisPositionForChild(child);
     switch (axisPosition) {
     case GridAxisStart:
         return startPosition;
     case GridAxisEnd:
     case GridAxisCenter: {
         unsigned childEndLine = rowsSpan.endLine();
         LayoutUnit endOfRow = m_rowPositions[childEndLine];
         // m_rowPositions include distribution offset (because of content alignment) and gutters
         // so we need to subtract them to get the actual end position for a given row
         // (this does not have to be done for the last track as there are no more m_rowPositions after it).
         if (childEndLine < m_rowPositions.size() - 1)
             endOfRow -= gridGapForDirection(ForRows, TrackSizing) + m_offsetBetweenRows;
         LayoutUnit columnAxisChildSize = isOrthogonalChild(child) ? child.logicalWidth() + child.marginLogicalWidth() : child.logicalHeight() + child.marginLogicalHeight();
         auto overflow = child.style().resolvedAlignSelf(&style(), selfAlignmentNormalBehavior()).overflow();
         LayoutUnit offsetFromStartPosition = computeOverflowAlignmentOffset(overflow, endOfRow - startOfRow, columnAxisChildSize);
         return startPosition + (axisPosition == GridAxisEnd ? offsetFromStartPosition : offsetFromStartPosition / 2);
     }
     }

     ASSERT_NOT_REACHED();
     return 0;
 }

 LayoutUnit RenderGrid::rowAxisOffsetForChild(const RenderBox& child) const
 {
     const GridSpan& columnsSpan = m_grid.gridItemSpan(child, ForColumns);
     unsigned childStartLine = columnsSpan.startLine();
     LayoutUnit startOfColumn = m_columnPositions[childStartLine];
     LayoutUnit startPosition = startOfColumn + marginStartForChild(child);
     if (hasAutoMarginsInRowAxis(child))
         return startPosition;
     GridAxisPosition axisPosition = rowAxisPositionForChild(child);
     switch (axisPosition) {
     case GridAxisStart:
         return startPosition;
     case GridAxisEnd:
     case GridAxisCenter: {
         unsigned childEndLine = columnsSpan.endLine();
         LayoutUnit endOfColumn = m_columnPositions[childEndLine];
         // m_columnPositions include distribution offset (because of content alignment) and gutters
         // so we need to subtract them to get the actual end position for a given column
         // (this does not have to be done for the last track as there are no more m_columnPositions after it).
         if (childEndLine < m_columnPositions.size() - 1)
             endOfColumn -= gridGapForDirection(ForColumns, TrackSizing) + m_offsetBetweenColumns;
         LayoutUnit rowAxisChildSize = isOrthogonalChild(child) ? child.logicalHeight() + child.marginLogicalHeight() : child.logicalWidth() + child.marginLogicalWidth();
         auto overflow = child.style().resolvedJustifySelf(&style(), selfAlignmentNormalBehavior()).overflow();
         LayoutUnit offsetFromStartPosition = computeOverflowAlignmentOffset(overflow, endOfColumn - startOfColumn, rowAxisChildSize);
         return startPosition + (axisPosition == GridAxisEnd ? offsetFromStartPosition : offsetFromStartPosition / 2);
     }
     }

     ASSERT_NOT_REACHED();
     return 0;
 }

 ContentPosition static resolveContentDistributionFallback(ContentDistributionType distribution)
 {
     switch (distribution) {
     case ContentDistributionSpaceBetween:
         return ContentPositionStart;
     case ContentDistributionSpaceAround:
         return ContentPositionCenter;
     case ContentDistributionSpaceEvenly:
         return ContentPositionCenter;
     case ContentDistributionStretch:
         return ContentPositionStart;
     case ContentDistributionDefault:
         return ContentPositionNormal;
     }

     ASSERT_NOT_REACHED();
     return ContentPositionNormal;
 }

 static ContentAlignmentData contentDistributionOffset(const LayoutUnit& availableFreeSpace, ContentPosition& fallbackPosition, ContentDistributionType distribution, unsigned numberOfGridTracks)
 {
     if (distribution != ContentDistributionDefault && fallbackPosition == ContentPositionNormal)
         fallbackPosition = resolveContentDistributionFallback(distribution);

     if (availableFreeSpace <= 0)
         return ContentAlignmentData::defaultOffsets();

     LayoutUnit distributionOffset;
     switch (distribution) {
     case ContentDistributionSpaceBetween:
         if (numberOfGridTracks < 2)
             return ContentAlignmentData::defaultOffsets();
         return {0, availableFreeSpace / (numberOfGridTracks - 1)};
     case ContentDistributionSpaceAround:
         if (numberOfGridTracks < 1)
             return ContentAlignmentData::defaultOffsets();
         distributionOffset = availableFreeSpace / numberOfGridTracks;
         return {distributionOffset / 2, distributionOffset};
     case ContentDistributionSpaceEvenly:
         distributionOffset = availableFreeSpace / (numberOfGridTracks + 1);
         return {distributionOffset, distributionOffset};
     case ContentDistributionStretch:
     case ContentDistributionDefault:
         return ContentAlignmentData::defaultOffsets();
     }

     ASSERT_NOT_REACHED();
     return ContentAlignmentData::defaultOffsets();
 }

 ContentAlignmentData RenderGrid::computeContentPositionAndDistributionOffset(GridTrackSizingDirection direction, const LayoutUnit& availableFreeSpace, unsigned numberOfGridTracks) const
 {
     bool isRowAxis = direction == ForColumns;
     auto position = isRowAxis ? style().resolvedJustifyContentPosition(contentAlignmentNormalBehaviorGrid()) : style().resolvedAlignContentPosition(contentAlignmentNormalBehaviorGrid());
     auto distribution = isRowAxis ? style().resolvedJustifyContentDistribution(contentAlignmentNormalBehaviorGrid()) : style().resolvedAlignContentDistribution(contentAlignmentNormalBehaviorGrid());
     // If <content-distribution> value can't be applied, 'position' will become the associated
     // <content-position> fallback value.
     auto contentAlignment = contentDistributionOffset(availableFreeSpace, position, distribution, numberOfGridTracks);
     if (contentAlignment.isValid())
         return contentAlignment;

     auto overflow = (isRowAxis ? style().justifyContent() : style().alignContent()).overflow();
     if (availableFreeSpace <= 0 && overflow == OverflowAlignmentSafe)
         return {0, 0};

     switch (position) {
     case ContentPositionLeft:
         // The align-content's axis is always orthogonal to the inline-axis.
         return {0, 0};
     case ContentPositionRight:
         if (isRowAxis)
             return {availableFreeSpace, 0};
         // The align-content's axis is always orthogonal to the inline-axis.
         return {0, 0};
     case ContentPositionCenter:
         return {availableFreeSpace / 2, 0};
     case ContentPositionFlexEnd: // Only used in flex layout, for other layout, it's equivalent to 'end'.
     case ContentPositionEnd:
         if (isRowAxis)
             return {style().isLeftToRightDirection() ? availableFreeSpace : LayoutUnit(), LayoutUnit()};
         return {availableFreeSpace, 0};
     case ContentPositionFlexStart: // Only used in flex layout, for other layout, it's equivalent to 'start'.
     case ContentPositionStart:
         if (isRowAxis)
             return {style().isLeftToRightDirection() ? LayoutUnit() : availableFreeSpace, LayoutUnit()};
         return {0, 0};
     case ContentPositionBaseline:
     case ContentPositionLastBaseline:
         // FIXME: Implement the previous values. For now, we always 'start' align.
         // http://webkit.org/b/145566
         if (isRowAxis)
             return {style().isLeftToRightDirection() ? LayoutUnit() : availableFreeSpace, LayoutUnit()};
         return {0, 0};
     case ContentPositionNormal:
         break;
     }

     ASSERT_NOT_REACHED();
     return {0, 0};
 }

 LayoutUnit RenderGrid::translateRTLCoordinate(LayoutUnit coordinate) const
 {
     ASSERT(!style().isLeftToRightDirection());

     LayoutUnit alignmentOffset = m_columnPositions[0];
     LayoutUnit rightGridEdgePosition = m_columnPositions[m_columnPositions.size() - 1];
     return rightGridEdgePosition + alignmentOffset - coordinate;
 }

 LayoutPoint RenderGrid::findChildLogicalPosition(const RenderBox& child) const
 {
     LayoutUnit columnAxisOffset = columnAxisOffsetForChild(child);
     LayoutUnit rowAxisOffset = rowAxisOffsetForChild(child);

     // We stored m_columnPositions's data ignoring the direction, hence we might need now
     // to translate positions from RTL to LTR, as it's more convenient for painting.
     if (!style().isLeftToRightDirection())
         rowAxisOffset = translateRTLCoordinate(rowAxisOffset) - (isOrthogonalChild(child) ? child.logicalHeight()  : child.logicalWidth());

     // "In the positioning phase [...] calculations are performed according to the writing mode
     // of the containing block of the box establishing the orthogonal flow." However, the
     // resulting LayoutPoint will be used in 'setLogicalPosition' in order to set the child's
     // logical position, which will only take into account the child's writing-mode.
     LayoutPoint childLocation(rowAxisOffset, columnAxisOffset);
     return isOrthogonalChild(child) ? childLocation.transposedPoint() : childLocation;
 }

 unsigned RenderGrid::numTracks(GridTrackSizingDirection direction, const Grid& grid) const
 {
     // Due to limitations in our internal representation, we cannot know the number of columns from
     // m_grid *if* there is no row (because m_grid would be empty). That's why in that case we need
     // to get it from the style. Note that we know for sure that there are't any implicit tracks,
     // because not having rows implies that there are no "normal" children (out-of-flow children are
     // not stored in m_grid).
     ASSERT(!grid.needsItemsPlacement());
     if (direction == ForRows)
         return grid.numTracks(ForRows);

     // FIXME: This still requires knowledge about m_grid internals.
     return grid.numTracks(ForRows) ? grid.numTracks(ForColumns) : GridPositionsResolver::explicitGridColumnCount(style(), grid.autoRepeatTracks(ForColumns));
 }

 void RenderGrid::paintChildren(PaintInfo& paintInfo, const LayoutPoint& paintOffset, PaintInfo& forChild, bool usePrintRect)
 {
     ASSERT(!m_grid.needsItemsPlacement());
     for (RenderBox* child = m_grid.orderIterator().first(); child; child = m_grid.orderIterator().next())
         paintChild(*child, paintInfo, paintOffset, forChild, usePrintRect, PaintAsInlineBlock);
 }

 const char* RenderGrid::renderName() const
 {
     if (isFloating())
         return "RenderGrid (floating)";
     if (isOutOfFlowPositioned())
         return "RenderGrid (positioned)";
     if (isAnonymous())
         return "RenderGrid (generated)";
     if (isRelPositioned())
         return "RenderGrid (relative positioned)";
     return "RenderGrid";
 }

 } // namespace WebCore