core/rendering/RenderFlexibleBox.cpp

/*
 * Copyright (C) 2011 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
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 * in the documentation and/or other materials provided with the
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 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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#include "config.h"
#include "core/rendering/RenderFlexibleBox.h"

#include <limits>
#include "core/rendering/LayoutRepainter.h"
#include "core/rendering/RenderLayer.h"
#include "core/rendering/RenderView.h"
#include "wtf/MathExtras.h"

namespace WebCore {

struct RenderFlexibleBox::LineContext {
    LineContext(LayoutUnit crossAxisOffset, LayoutUnit crossAxisExtent, size_t numberOfChildren, LayoutUnit maxAscent)
        : crossAxisOffset(crossAxisOffset)
        , crossAxisExtent(crossAxisExtent)
        , numberOfChildren(numberOfChildren)
        , maxAscent(maxAscent)
    {
    }

    LayoutUnit crossAxisOffset;
    LayoutUnit crossAxisExtent;
    size_t numberOfChildren;
    LayoutUnit maxAscent;
};

struct RenderFlexibleBox::Violation {
    Violation(RenderBox* child, LayoutUnit childSize)
        : child(child)
        , childSize(childSize)
    {
    }

    RenderBox* child;
    LayoutUnit childSize;
};


RenderFlexibleBox::RenderFlexibleBox(Element* element)
    : RenderBlock(element)
    , m_orderIterator(this)
    , m_numberOfInFlowChildrenOnFirstLine(-1)
{
    setChildrenInline(false); // All of our children must be block-level.
}

RenderFlexibleBox::~RenderFlexibleBox()
{
}

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

const char* RenderFlexibleBox::renderName() const
{
    return "RenderFlexibleBox";
}

static LayoutUnit marginLogicalWidthForChild(RenderBox* child, RenderStyle* parentStyle)
{
    // A margin has three types: fixed, percentage, and auto (variable).
    // Auto and percentage margins become 0 when computing min/max width.
    // Fixed margins can be added in as is.
    Length marginLeft = child->style()->marginStartUsing(parentStyle);
    Length marginRight = child->style()->marginEndUsing(parentStyle);
    LayoutUnit margin = 0;
    if (marginLeft.isFixed())
        margin += marginLeft.value();
    if (marginRight.isFixed())
        margin += marginRight.value();
    return margin;
}

void RenderFlexibleBox::computeIntrinsicLogicalWidths(LayoutUnit& minLogicalWidth, LayoutUnit& maxLogicalWidth) const
{
    // FIXME: We're ignoring flex-basis here and we shouldn't. We can't start honoring it though until
    // the flex shorthand stops setting it to 0.
    // See https://bugs.webkit.org/show_bug.cgi?id=116117 and http://crbug.com/240765.
    for (RenderBox* child = firstChildBox(); child; child = child->nextSiblingBox()) {
        if (child->isOutOfFlowPositioned())
            continue;

        LayoutUnit margin = marginLogicalWidthForChild(child, style());
        bool hasOrthogonalWritingMode = child->isHorizontalWritingMode() != isHorizontalWritingMode();
        LayoutUnit minPreferredLogicalWidth = hasOrthogonalWritingMode ? child->logicalHeight() : child->minPreferredLogicalWidth();
        LayoutUnit maxPreferredLogicalWidth = hasOrthogonalWritingMode ? child->logicalHeight() : child->maxPreferredLogicalWidth();
        minPreferredLogicalWidth += margin;
        maxPreferredLogicalWidth += margin;
        if (!isColumnFlow()) {
            maxLogicalWidth += maxPreferredLogicalWidth;
            if (isMultiline()) {
                // For multiline, the min preferred width is if you put a break between each item.
                minLogicalWidth = std::max(minLogicalWidth, minPreferredLogicalWidth);
            } else
                minLogicalWidth += minPreferredLogicalWidth;
        } else {
            minLogicalWidth = std::max(minPreferredLogicalWidth, minLogicalWidth);
            if (isMultiline()) {
                // For multiline, the max preferred width is if you never break between items.
                maxLogicalWidth += maxPreferredLogicalWidth;
            } else
                maxLogicalWidth = std::max(maxPreferredLogicalWidth, maxLogicalWidth);
        }
    }

    maxLogicalWidth = std::max(minLogicalWidth, maxLogicalWidth);

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

static int synthesizedBaselineFromContentBox(const RenderBox* box, LineDirectionMode direction)
{
    return direction == HorizontalLine ? box->borderTop() + box->paddingTop() + box->contentHeight() : box->borderRight() + box->paddingRight() + box->contentWidth();
}

int RenderFlexibleBox::baselinePosition(FontBaseline, bool, LineDirectionMode direction, LinePositionMode mode) const
{
    ASSERT(mode == PositionOnContainingLine);
    int baseline = firstLineBoxBaseline();
    if (baseline == -1)
        baseline = synthesizedBaselineFromContentBox(this, direction);

    int marginAscent = direction == HorizontalLine ? marginTop() : marginRight();
    return baseline + marginAscent;
}

int RenderFlexibleBox::firstLineBoxBaseline() const
{
    if (isWritingModeRoot() || m_numberOfInFlowChildrenOnFirstLine <= 0)
        return -1;
    RenderBox* baselineChild = 0;
    int childNumber = 0;
    for (RenderBox* child = m_orderIterator.first(); child; child = m_orderIterator.next()) {
        if (child->isOutOfFlowPositioned())
            continue;
        if (alignmentForChild(child) == AlignBaseline && !hasAutoMarginsInCrossAxis(child)) {
            baselineChild = child;
            break;
        }
        if (!baselineChild)
            baselineChild = child;

        ++childNumber;
        if (childNumber == m_numberOfInFlowChildrenOnFirstLine)
            break;
    }

    if (!baselineChild)
        return -1;

    if (!isColumnFlow() && hasOrthogonalFlow(baselineChild))
        return crossAxisExtentForChild(baselineChild) + baselineChild->logicalTop();
    if (isColumnFlow() && !hasOrthogonalFlow(baselineChild))
        return mainAxisExtentForChild(baselineChild) + baselineChild->logicalTop();

    int baseline = baselineChild->firstLineBoxBaseline();
    if (baseline == -1) {
        // FIXME: We should pass |direction| into firstLineBoxBaseline and stop bailing out if we're a writing mode root.
        // This would also fix some cases where the flexbox is orthogonal to its container.
        LineDirectionMode direction = isHorizontalWritingMode() ? HorizontalLine : VerticalLine;
        return synthesizedBaselineFromContentBox(baselineChild, direction) + baselineChild->logicalTop();
    }

    return baseline + baselineChild->logicalTop();
}

int RenderFlexibleBox::inlineBlockBaseline(LineDirectionMode direction) const
{
    int baseline = firstLineBoxBaseline();
    if (baseline != -1)
        return baseline;

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

static EAlignItems resolveAlignment(const RenderStyle* parentStyle, const RenderStyle* childStyle)
{
    EAlignItems align = childStyle->alignSelf();
    if (align == AlignAuto)
        align = parentStyle->alignItems();
    return align;
}

void RenderFlexibleBox::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle)
{
    RenderBlock::styleDidChange(diff, oldStyle);

    if (oldStyle && oldStyle->alignItems() == AlignStretch && diff == StyleDifferenceLayout) {
        // Flex items that were previously stretching need to be relayed out so we can compute new available cross axis 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()) {
            EAlignItems previousAlignment = resolveAlignment(oldStyle, child->style());
            if (previousAlignment == AlignStretch && previousAlignment != resolveAlignment(style(), child->style()))
                child->setChildNeedsLayout(MarkOnlyThis);
        }
    }
}

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

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

    LayoutRepainter repainter(*this, checkForRepaintDuringLayout());

    if (updateLogicalWidthAndColumnWidth())
        relayoutChildren = true;

    LayoutUnit previousHeight = logicalHeight();
    setLogicalHeight(borderAndPaddingLogicalHeight() + scrollbarLogicalHeight());

    LayoutStateMaintainer statePusher(view(), this, locationOffset(), hasTransform() || hasReflection() || style()->isFlippedBlocksWritingMode());

    // Regions changing widths can force us to relayout our children.
    RenderFlowThread* flowThread = flowThreadContainingBlock();
    if (logicalWidthChangedInRegions(flowThread))
        relayoutChildren = true;
    if (updateRegionsAndShapesLogicalSize(flowThread))
        relayoutChildren = true;

    m_numberOfInFlowChildrenOnFirstLine = -1;

    RenderBlock::startDelayUpdateScrollInfo();

    prepareOrderIteratorAndMargins();

    ChildFrameRects oldChildRects;
    appendChildFrameRects(oldChildRects);

    Vector<LineContext> lineContexts;
    layoutFlexItems(relayoutChildren, lineContexts);

    updateLogicalHeight();
    repositionLogicalHeightDependentFlexItems(lineContexts);

    RenderBlock::finishDelayUpdateScrollInfo();

    if (logicalHeight() != previousHeight)
        relayoutChildren = true;

    layoutPositionedObjects(relayoutChildren || isRoot());

    computeRegionRangeForBlock(flowThread);

    repaintChildrenDuringLayoutIfMoved(oldChildRects);
    // FIXME: css3/flexbox/repaint-rtl-column.html seems to repaint more overflow than it needs to.
    computeOverflow(clientLogicalBottomAfterRepositioning());
    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();
}

void RenderFlexibleBox::appendChildFrameRects(ChildFrameRects& childFrameRects)
{
    for (RenderBox* child = m_orderIterator.first(); child; child = m_orderIterator.next()) {
        if (!child->isOutOfFlowPositioned())
            childFrameRects.append(child->frameRect());
    }
}

void RenderFlexibleBox::repaintChildrenDuringLayoutIfMoved(const ChildFrameRects& oldChildRects)
{
    size_t childIndex = 0;
    for (RenderBox* child = m_orderIterator.first(); child; child = m_orderIterator.next()) {
        if (child->isOutOfFlowPositioned())
            continue;

        // 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(oldChildRects[childIndex]);
        ++childIndex;
    }
    ASSERT(childIndex == oldChildRects.size());
}

void RenderFlexibleBox::paintChildren(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
{
    for (RenderBox* child = m_orderIterator.first(); child; child = m_orderIterator.next())
        paintChild(child, paintInfo, paintOffset);
}

void RenderFlexibleBox::repositionLogicalHeightDependentFlexItems(Vector<LineContext>& lineContexts)
{
    LayoutUnit crossAxisStartEdge = lineContexts.isEmpty() ? LayoutUnit() : lineContexts[0].crossAxisOffset;
    alignFlexLines(lineContexts);

    // If we have a single line flexbox, the line height is all the available space.
    // For flex-direction: row, this means we need to use the height, so we do this after calling updateLogicalHeight.
    if (!isMultiline() && lineContexts.size() == 1)
        lineContexts[0].crossAxisExtent = crossAxisContentExtent();
    alignChildren(lineContexts);

    if (style()->flexWrap() == FlexWrapReverse)
        flipForWrapReverse(lineContexts, crossAxisStartEdge);

    // direction:rtl + flex-direction:column means the cross-axis direction is flipped.
    flipForRightToLeftColumn();
}

LayoutUnit RenderFlexibleBox::clientLogicalBottomAfterRepositioning()
{
    LayoutUnit maxChildLogicalBottom = 0;
    for (RenderBox* child = firstChildBox(); child; child = child->nextSiblingBox()) {
        if (child->isOutOfFlowPositioned())
            continue;
        LayoutUnit childLogicalBottom = logicalTopForChild(child) + logicalHeightForChild(child) + marginAfterForChild(child);
        maxChildLogicalBottom = std::max(maxChildLogicalBottom, childLogicalBottom);
    }
    return std::max(clientLogicalBottom(), maxChildLogicalBottom);
}

bool RenderFlexibleBox::hasOrthogonalFlow(RenderBox* child) const
{
    // FIXME: If the child is a flexbox, then we need to check isHorizontalFlow.
    return isHorizontalFlow() != child->isHorizontalWritingMode();
}

bool RenderFlexibleBox::isColumnFlow() const
{
    return style()->isColumnFlexDirection();
}

bool RenderFlexibleBox::isHorizontalFlow() const
{
    if (isHorizontalWritingMode())
        return !isColumnFlow();
    return isColumnFlow();
}

bool RenderFlexibleBox::isLeftToRightFlow() const
{
    if (isColumnFlow())
        return style()->writingMode() == TopToBottomWritingMode || style()->writingMode() == LeftToRightWritingMode;
    return style()->isLeftToRightDirection() ^ (style()->flexDirection() == FlowRowReverse);
}

bool RenderFlexibleBox::isMultiline() const
{
    return style()->flexWrap() != FlexNoWrap;
}

Length RenderFlexibleBox::flexBasisForChild(RenderBox* child) const
{
    Length flexLength = child->style()->flexBasis();
    if (flexLength.isAuto())
        flexLength = isHorizontalFlow() ? child->style()->width() : child->style()->height();
    return flexLength;
}

void RenderFlexibleBox::setCrossAxisExtent(LayoutUnit extent)
{
    if (isHorizontalFlow())
        setHeight(extent);
    else
        setWidth(extent);
}

LayoutUnit RenderFlexibleBox::crossAxisExtentForChild(RenderBox* child) const
{
    return isHorizontalFlow() ? child->height() : child->width();
}

LayoutUnit RenderFlexibleBox::mainAxisExtentForChild(RenderBox* child) const
{
    return isHorizontalFlow() ? child->width() : child->height();
}

LayoutUnit RenderFlexibleBox::crossAxisExtent() const
{
    return isHorizontalFlow() ? height() : width();
}

LayoutUnit RenderFlexibleBox::mainAxisExtent() const
{
    return isHorizontalFlow() ? width() : height();
}

LayoutUnit RenderFlexibleBox::crossAxisContentExtent() const
{
    return isHorizontalFlow() ? contentHeight() : contentWidth();
}

LayoutUnit RenderFlexibleBox::mainAxisContentExtent(LayoutUnit contentLogicalHeight)
{
    if (isColumnFlow()) {
        LogicalExtentComputedValues computedValues;
        LayoutUnit borderPaddingAndScrollbar = borderAndPaddingLogicalHeight() + scrollbarLogicalHeight();
        // FIXME: Remove this std:max once we enable saturated layout arithmetic. It's just here to handle overflow.
        LayoutUnit borderBoxLogicalHeight = std::max(contentLogicalHeight, contentLogicalHeight + borderPaddingAndScrollbar);
        computeLogicalHeight(borderBoxLogicalHeight, logicalTop(), computedValues);
        if (computedValues.m_extent == LayoutUnit::max())
            return computedValues.m_extent;
        return std::max(LayoutUnit(0), computedValues.m_extent - borderPaddingAndScrollbar);
    }
    return contentLogicalWidth();
}

LayoutUnit RenderFlexibleBox::computeMainAxisExtentForChild(RenderBox* child, SizeType sizeType, const Length& size)
{
    // FIXME: This is wrong for orthogonal flows. It should use the flexbox's writing-mode, not the child's in order
    // to figure out the logical height/width.
    if (isColumnFlow()) {
        // We don't have to check for "auto" here - computeContentLogicalHeight will just return -1 for that case anyway.
        if (size.isIntrinsic())
            child->layoutIfNeeded();
        return child->computeContentLogicalHeight(size, child->logicalHeight() - child->borderAndPaddingLogicalHeight());
    }
    // FIXME: Figure out how this should work for regions and pass in the appropriate values.
    LayoutUnit offsetFromLogicalTopOfFirstPage = 0;
    RenderRegion* region = 0;
    return child->computeLogicalWidthInRegionUsing(sizeType, size, contentLogicalWidth(), this, region, offsetFromLogicalTopOfFirstPage) - child->borderAndPaddingLogicalWidth();
}

WritingMode RenderFlexibleBox::transformedWritingMode() const
{
    WritingMode mode = style()->writingMode();
    if (!isColumnFlow())
        return mode;

    switch (mode) {
    case TopToBottomWritingMode:
    case BottomToTopWritingMode:
        return style()->isLeftToRightDirection() ? LeftToRightWritingMode : RightToLeftWritingMode;
    case LeftToRightWritingMode:
    case RightToLeftWritingMode:
        return style()->isLeftToRightDirection() ? TopToBottomWritingMode : BottomToTopWritingMode;
    }
    ASSERT_NOT_REACHED();
    return TopToBottomWritingMode;
}

LayoutUnit RenderFlexibleBox::flowAwareBorderStart() const
{
    if (isHorizontalFlow())
        return isLeftToRightFlow() ? borderLeft() : borderRight();
    return isLeftToRightFlow() ? borderTop() : borderBottom();
}

LayoutUnit RenderFlexibleBox::flowAwareBorderEnd() const
{
    if (isHorizontalFlow())
        return isLeftToRightFlow() ? borderRight() : borderLeft();
    return isLeftToRightFlow() ? borderBottom() : borderTop();
}

LayoutUnit RenderFlexibleBox::flowAwareBorderBefore() const
{
    switch (transformedWritingMode()) {
    case TopToBottomWritingMode:
        return borderTop();
    case BottomToTopWritingMode:
        return borderBottom();
    case LeftToRightWritingMode:
        return borderLeft();
    case RightToLeftWritingMode:
        return borderRight();
    }
    ASSERT_NOT_REACHED();
    return borderTop();
}

LayoutUnit RenderFlexibleBox::flowAwareBorderAfter() const
{
    switch (transformedWritingMode()) {
    case TopToBottomWritingMode:
        return borderBottom();
    case BottomToTopWritingMode:
        return borderTop();
    case LeftToRightWritingMode:
        return borderRight();
    case RightToLeftWritingMode:
        return borderLeft();
    }
    ASSERT_NOT_REACHED();
    return borderTop();
}

LayoutUnit RenderFlexibleBox::flowAwarePaddingStart() const
{
    if (isHorizontalFlow())
        return isLeftToRightFlow() ? paddingLeft() : paddingRight();
    return isLeftToRightFlow() ? paddingTop() : paddingBottom();
}

LayoutUnit RenderFlexibleBox::flowAwarePaddingEnd() const
{
    if (isHorizontalFlow())
        return isLeftToRightFlow() ? paddingRight() : paddingLeft();
    return isLeftToRightFlow() ? paddingBottom() : paddingTop();
}

LayoutUnit RenderFlexibleBox::flowAwarePaddingBefore() const
{
    switch (transformedWritingMode()) {
    case TopToBottomWritingMode:
        return paddingTop();
    case BottomToTopWritingMode:
        return paddingBottom();
    case LeftToRightWritingMode:
        return paddingLeft();
    case RightToLeftWritingMode:
        return paddingRight();
    }
    ASSERT_NOT_REACHED();
    return paddingTop();
}

LayoutUnit RenderFlexibleBox::flowAwarePaddingAfter() const
{
    switch (transformedWritingMode()) {
    case TopToBottomWritingMode:
        return paddingBottom();
    case BottomToTopWritingMode:
        return paddingTop();
    case LeftToRightWritingMode:
        return paddingRight();
    case RightToLeftWritingMode:
        return paddingLeft();
    }
    ASSERT_NOT_REACHED();
    return paddingTop();
}

LayoutUnit RenderFlexibleBox::flowAwareMarginStartForChild(RenderBox* child) const
{
    if (isHorizontalFlow())
        return isLeftToRightFlow() ? child->marginLeft() : child->marginRight();
    return isLeftToRightFlow() ? child->marginTop() : child->marginBottom();
}

LayoutUnit RenderFlexibleBox::flowAwareMarginEndForChild(RenderBox* child) const
{
    if (isHorizontalFlow())
        return isLeftToRightFlow() ? child->marginRight() : child->marginLeft();
    return isLeftToRightFlow() ? child->marginBottom() : child->marginTop();
}

LayoutUnit RenderFlexibleBox::flowAwareMarginBeforeForChild(RenderBox* child) const
{
    switch (transformedWritingMode()) {
    case TopToBottomWritingMode:
        return child->marginTop();
    case BottomToTopWritingMode:
        return child->marginBottom();
    case LeftToRightWritingMode:
        return child->marginLeft();
    case RightToLeftWritingMode:
        return child->marginRight();
    }
    ASSERT_NOT_REACHED();
    return marginTop();
}

LayoutUnit RenderFlexibleBox::flowAwareMarginAfterForChild(RenderBox* child) const
{
    switch (transformedWritingMode()) {
    case TopToBottomWritingMode:
        return child->marginBottom();
    case BottomToTopWritingMode:
        return child->marginTop();
    case LeftToRightWritingMode:
        return child->marginRight();
    case RightToLeftWritingMode:
        return child->marginLeft();
    }
    ASSERT_NOT_REACHED();
    return marginBottom();
}

LayoutUnit RenderFlexibleBox::crossAxisMarginExtentForChild(RenderBox* child) const
{
    return isHorizontalFlow() ? child->marginHeight() : child->marginWidth();
}

LayoutUnit RenderFlexibleBox::crossAxisScrollbarExtent() const
{
    return isHorizontalFlow() ? horizontalScrollbarHeight() : verticalScrollbarWidth();
}

LayoutPoint RenderFlexibleBox::flowAwareLocationForChild(RenderBox* child) const
{
    return isHorizontalFlow() ? child->location() : child->location().transposedPoint();
}

void RenderFlexibleBox::setFlowAwareLocationForChild(RenderBox* child, const LayoutPoint& location)
{
    if (isHorizontalFlow())
        child->setLocation(location);
    else
        child->setLocation(location.transposedPoint());
}

LayoutUnit RenderFlexibleBox::mainAxisBorderAndPaddingExtentForChild(RenderBox* child) const
{
    return isHorizontalFlow() ? child->borderAndPaddingWidth() : child->borderAndPaddingHeight();
}

LayoutUnit RenderFlexibleBox::mainAxisScrollbarExtentForChild(RenderBox* child) const
{
    return isHorizontalFlow() ? child->verticalScrollbarWidth() : child->horizontalScrollbarHeight();
}

LayoutUnit RenderFlexibleBox::preferredMainAxisContentExtentForChild(RenderBox* child, bool hasInfiniteLineLength)
{
    bool hasOverrideSize = child->hasOverrideWidth() || child->hasOverrideHeight();
    if (hasOverrideSize)
        child->clearOverrideSize();

    Length flexBasis = flexBasisForChild(child);
    if (flexBasis.isAuto() || (flexBasis.isFixed() && !flexBasis.value() && hasInfiniteLineLength)) {
        if (hasOrthogonalFlow(child)) {
            if (hasOverrideSize)
                child->setChildNeedsLayout(MarkOnlyThis);
            child->layoutIfNeeded();
        }
        LayoutUnit mainAxisExtent = hasOrthogonalFlow(child) ? child->logicalHeight() : child->maxPreferredLogicalWidth();
        ASSERT(mainAxisExtent - mainAxisBorderAndPaddingExtentForChild(child) >= 0);
        return mainAxisExtent - mainAxisBorderAndPaddingExtentForChild(child);
    }
    return std::max(LayoutUnit(0), computeMainAxisExtentForChild(child, MainOrPreferredSize, flexBasis));
}

void RenderFlexibleBox::layoutFlexItems(bool relayoutChildren, Vector<LineContext>& lineContexts)
{
    OrderedFlexItemList orderedChildren;
    LayoutUnit sumFlexBaseSize;
    double totalFlexGrow;
    double totalWeightedFlexShrink;
    LayoutUnit sumHypotheticalMainSize;

    m_orderIterator.first();
    LayoutUnit crossAxisOffset = flowAwareBorderBefore() + flowAwarePaddingBefore();
    bool hasInfiniteLineLength = false;
    while (computeNextFlexLine(orderedChildren, sumFlexBaseSize, totalFlexGrow, totalWeightedFlexShrink, sumHypotheticalMainSize, hasInfiniteLineLength)) {
        LayoutUnit containerMainInnerSize = mainAxisContentExtent(sumHypotheticalMainSize);
        LayoutUnit availableFreeSpace = containerMainInnerSize - sumFlexBaseSize;
        FlexSign flexSign = (sumHypotheticalMainSize < containerMainInnerSize) ? PositiveFlexibility : NegativeFlexibility;
        InflexibleFlexItemSize inflexibleItems;
        Vector<LayoutUnit> childSizes;
        while (!resolveFlexibleLengths(flexSign, orderedChildren, availableFreeSpace, totalFlexGrow, totalWeightedFlexShrink, inflexibleItems, childSizes, hasInfiniteLineLength)) {
            ASSERT(totalFlexGrow >= 0 && totalWeightedFlexShrink >= 0);
            ASSERT(inflexibleItems.size() > 0);
        }

        layoutAndPlaceChildren(crossAxisOffset, orderedChildren, childSizes, availableFreeSpace, relayoutChildren, lineContexts);
    }
    if (hasLineIfEmpty()) {
        // Even if computeNextFlexLine returns true, the flexbox might not have
        // a line because all our children might be out of flow positioned.
        // Instead of just checking if we have a line, make sure the flexbox
        // has at least a line's worth of height to cover this case.
        LayoutUnit minHeight = borderAndPaddingLogicalHeight()
            + lineHeight(true, isHorizontalWritingMode() ? HorizontalLine : VerticalLine, PositionOfInteriorLineBoxes)
            + scrollbarLogicalHeight();
        if (height() < minHeight)
            setLogicalHeight(minHeight);
    }
}

LayoutUnit RenderFlexibleBox::autoMarginOffsetInMainAxis(const OrderedFlexItemList& children, LayoutUnit& availableFreeSpace)
{
    if (availableFreeSpace <= 0)
        return 0;

    int numberOfAutoMargins = 0;
    bool isHorizontal = isHorizontalFlow();
    for (size_t i = 0; i < children.size(); ++i) {
        RenderBox* child = children[i];
        if (child->isOutOfFlowPositioned())
            continue;
        if (isHorizontal) {
            if (child->style()->marginLeft().isAuto())
                ++numberOfAutoMargins;
            if (child->style()->marginRight().isAuto())
                ++numberOfAutoMargins;
        } else {
            if (child->style()->marginTop().isAuto())
                ++numberOfAutoMargins;
            if (child->style()->marginBottom().isAuto())
                ++numberOfAutoMargins;
        }
    }
    if (!numberOfAutoMargins)
        return 0;

    LayoutUnit sizeOfAutoMargin = availableFreeSpace / numberOfAutoMargins;
    availableFreeSpace = 0;
    return sizeOfAutoMargin;
}

void RenderFlexibleBox::updateAutoMarginsInMainAxis(RenderBox* child, LayoutUnit autoMarginOffset)
{
    ASSERT(autoMarginOffset >= 0);

    if (isHorizontalFlow()) {
        if (child->style()->marginLeft().isAuto())
            child->setMarginLeft(autoMarginOffset);
        if (child->style()->marginRight().isAuto())
            child->setMarginRight(autoMarginOffset);
    } else {
        if (child->style()->marginTop().isAuto())
            child->setMarginTop(autoMarginOffset);
        if (child->style()->marginBottom().isAuto())
            child->setMarginBottom(autoMarginOffset);
    }
}

bool RenderFlexibleBox::hasAutoMarginsInCrossAxis(RenderBox* child) const
{
    if (isHorizontalFlow())
        return child->style()->marginTop().isAuto() || child->style()->marginBottom().isAuto();
    return child->style()->marginLeft().isAuto() || child->style()->marginRight().isAuto();
}

LayoutUnit RenderFlexibleBox::availableAlignmentSpaceForChild(LayoutUnit lineCrossAxisExtent, RenderBox* child)
{
    ASSERT(!child->isOutOfFlowPositioned());
    LayoutUnit childCrossExtent = crossAxisMarginExtentForChild(child) + crossAxisExtentForChild(child);
    return lineCrossAxisExtent - childCrossExtent;
}

bool RenderFlexibleBox::updateAutoMarginsInCrossAxis(RenderBox* child, LayoutUnit availableAlignmentSpace)
{
    ASSERT(!child->isOutOfFlowPositioned());
    ASSERT(availableAlignmentSpace >= 0);

    bool isHorizontal = isHorizontalFlow();
    Length topOrLeft = isHorizontal ? child->style()->marginTop() : child->style()->marginLeft();
    Length bottomOrRight = isHorizontal ? child->style()->marginBottom() : child->style()->marginRight();
    if (topOrLeft.isAuto() && bottomOrRight.isAuto()) {
        adjustAlignmentForChild(child, availableAlignmentSpace / 2);
        if (isHorizontal) {
            child->setMarginTop(availableAlignmentSpace / 2);
            child->setMarginBottom(availableAlignmentSpace / 2);
        } else {
            child->setMarginLeft(availableAlignmentSpace / 2);
            child->setMarginRight(availableAlignmentSpace / 2);
        }
        return true;
    }
    bool shouldAdjustTopOrLeft = true;
    if (isColumnFlow() && !child->style()->isLeftToRightDirection()) {
        // For column flows, only make this adjustment if topOrLeft corresponds to the "before" margin,
        // so that flipForRightToLeftColumn will do the right thing.
        shouldAdjustTopOrLeft = false;
    }
    if (!isColumnFlow() && child->style()->isFlippedBlocksWritingMode()) {
        // If we are a flipped writing mode, we need to adjust the opposite side. This is only needed
        // for row flows because this only affects the block-direction axis.
        shouldAdjustTopOrLeft = false;
    }

    if (topOrLeft.isAuto()) {
        if (shouldAdjustTopOrLeft)
            adjustAlignmentForChild(child, availableAlignmentSpace);

        if (isHorizontal)
            child->setMarginTop(availableAlignmentSpace);
        else
            child->setMarginLeft(availableAlignmentSpace);
        return true;
    }
    if (bottomOrRight.isAuto()) {
        if (!shouldAdjustTopOrLeft)
            adjustAlignmentForChild(child, availableAlignmentSpace);

        if (isHorizontal)
            child->setMarginBottom(availableAlignmentSpace);
        else
            child->setMarginRight(availableAlignmentSpace);
        return true;
    }
    return false;
}

LayoutUnit RenderFlexibleBox::marginBoxAscentForChild(RenderBox* child)
{
    LayoutUnit ascent = child->firstLineBoxBaseline();
    if (ascent == -1)
        ascent = crossAxisExtentForChild(child);
    return ascent + flowAwareMarginBeforeForChild(child);
}

LayoutUnit RenderFlexibleBox::computeChildMarginValue(Length margin, RenderView* view)
{
    // When resolving the margins, we use the content size for resolving percent and calc (for percents in calc expressions) margins.
    // Fortunately, percent margins are always computed with respect to the block's width, even for margin-top and margin-bottom.
    LayoutUnit availableSize = contentLogicalWidth();
    return minimumValueForLength(margin, availableSize, view);
}

void RenderFlexibleBox::prepareOrderIteratorAndMargins()
{
    RenderView* renderView = view();
    OrderIteratorPopulator populator(m_orderIterator);

    for (RenderBox* child = firstChildBox(); child; child = child->nextSiblingBox()) {
        populator.collectChild(child);

        if (child->isOutOfFlowPositioned())
            continue;

        // Before running the flex algorithm, 'auto' has a margin of 0.
        // Also, if we're not auto sizing, we don't do a layout that computes the start/end margins.
        if (isHorizontalFlow()) {
            child->setMarginLeft(computeChildMarginValue(child->style()->marginLeft(), renderView));
            child->setMarginRight(computeChildMarginValue(child->style()->marginRight(), renderView));
        } else {
            child->setMarginTop(computeChildMarginValue(child->style()->marginTop(), renderView));
            child->setMarginBottom(computeChildMarginValue(child->style()->marginBottom(), renderView));
        }
    }
}

LayoutUnit RenderFlexibleBox::adjustChildSizeForMinAndMax(RenderBox* child, LayoutUnit childSize)
{
    Length max = isHorizontalFlow() ? child->style()->maxWidth() : child->style()->maxHeight();
    if (max.isSpecifiedOrIntrinsic()) {
        LayoutUnit maxExtent = computeMainAxisExtentForChild(child, MaxSize, max);
        if (maxExtent != -1 && childSize > maxExtent)
            childSize = maxExtent;
    }

    Length min = isHorizontalFlow() ? child->style()->minWidth() : child->style()->minHeight();
    LayoutUnit minExtent = 0;
    if (min.isSpecifiedOrIntrinsic())
        minExtent = computeMainAxisExtentForChild(child, MinSize, min);
    return std::max(childSize, minExtent);
}

bool RenderFlexibleBox::computeNextFlexLine(OrderedFlexItemList& orderedChildren, LayoutUnit& sumFlexBaseSize, double& totalFlexGrow, double& totalWeightedFlexShrink, LayoutUnit& sumHypotheticalMainSize, bool& hasInfiniteLineLength)
{
    orderedChildren.clear();
    sumFlexBaseSize = 0;
    totalFlexGrow = totalWeightedFlexShrink = 0;
    sumHypotheticalMainSize = 0;

    if (!m_orderIterator.currentChild())
        return false;

    LayoutUnit lineBreakLength = mainAxisContentExtent(LayoutUnit::max());
    hasInfiniteLineLength = lineBreakLength == LayoutUnit::max();

    bool lineHasInFlowItem = false;

    for (RenderBox* child = m_orderIterator.currentChild(); child; child = m_orderIterator.next()) {
        if (child->isOutOfFlowPositioned()) {
            orderedChildren.append(child);
            continue;
        }

        LayoutUnit childMainAxisExtent = preferredMainAxisContentExtentForChild(child, hasInfiniteLineLength);
        LayoutUnit childMainAxisMarginBorderPadding = mainAxisBorderAndPaddingExtentForChild(child)
            + (isHorizontalFlow() ? child->marginWidth() : child->marginHeight());
        LayoutUnit childMainAxisMarginBoxExtent = childMainAxisExtent + childMainAxisMarginBorderPadding;

        if (isMultiline() && sumFlexBaseSize + childMainAxisMarginBoxExtent > lineBreakLength && lineHasInFlowItem)
            break;
        orderedChildren.append(child);
        lineHasInFlowItem  = true;
        sumFlexBaseSize += childMainAxisMarginBoxExtent;
        totalFlexGrow += child->style()->flexGrow();
        totalWeightedFlexShrink += child->style()->flexShrink() * childMainAxisExtent;

        LayoutUnit childMinMaxAppliedMainAxisExtent = adjustChildSizeForMinAndMax(child, childMainAxisExtent);
        sumHypotheticalMainSize += childMinMaxAppliedMainAxisExtent + childMainAxisMarginBorderPadding;
    }
    return true;
}

void RenderFlexibleBox::freezeViolations(const Vector<Violation>& violations, LayoutUnit& availableFreeSpace, double& totalFlexGrow, double& totalWeightedFlexShrink, InflexibleFlexItemSize& inflexibleItems, bool hasInfiniteLineLength)
{
    for (size_t i = 0; i < violations.size(); ++i) {
        RenderBox* child = violations[i].child;
        LayoutUnit childSize = violations[i].childSize;
        LayoutUnit preferredChildSize = preferredMainAxisContentExtentForChild(child, hasInfiniteLineLength);
        availableFreeSpace -= childSize - preferredChildSize;
        totalFlexGrow -= child->style()->flexGrow();
        totalWeightedFlexShrink -= child->style()->flexShrink() * preferredChildSize;
        inflexibleItems.set(child, childSize);
    }
}

// Returns true if we successfully ran the algorithm and sized the flex items.
bool RenderFlexibleBox::resolveFlexibleLengths(FlexSign flexSign, const OrderedFlexItemList& children, LayoutUnit& availableFreeSpace, double& totalFlexGrow, double& totalWeightedFlexShrink, InflexibleFlexItemSize& inflexibleItems, Vector<LayoutUnit>& childSizes, bool hasInfiniteLineLength)
{
    childSizes.clear();
    LayoutUnit totalViolation = 0;
    LayoutUnit usedFreeSpace = 0;
    Vector<Violation> minViolations;
    Vector<Violation> maxViolations;
    for (size_t i = 0; i < children.size(); ++i) {
        RenderBox* child = children[i];
        if (child->isOutOfFlowPositioned()) {
            childSizes.append(0);
            continue;
        }

        if (inflexibleItems.contains(child))
            childSizes.append(inflexibleItems.get(child));
        else {
            LayoutUnit preferredChildSize = preferredMainAxisContentExtentForChild(child, hasInfiniteLineLength);
            LayoutUnit childSize = preferredChildSize;
            double extraSpace = 0;
            if (availableFreeSpace > 0 && totalFlexGrow > 0 && flexSign == PositiveFlexibility && std::isfinite(totalFlexGrow))
                extraSpace = availableFreeSpace * child->style()->flexGrow() / totalFlexGrow;
            else if (availableFreeSpace < 0 && totalWeightedFlexShrink > 0 && flexSign == NegativeFlexibility && std::isfinite(totalWeightedFlexShrink))
                extraSpace = availableFreeSpace * child->style()->flexShrink() * preferredChildSize / totalWeightedFlexShrink;
            if (std::isfinite(extraSpace))
                childSize += LayoutUnit::fromFloatRound(extraSpace);

            LayoutUnit adjustedChildSize = adjustChildSizeForMinAndMax(child, childSize);
            childSizes.append(adjustedChildSize);
            usedFreeSpace += adjustedChildSize - preferredChildSize;

            LayoutUnit violation = adjustedChildSize - childSize;
            if (violation > 0)
                minViolations.append(Violation(child, adjustedChildSize));
            else if (violation < 0)
                maxViolations.append(Violation(child, adjustedChildSize));
            totalViolation += violation;
        }
    }

    if (totalViolation)
        freezeViolations(totalViolation < 0 ? maxViolations : minViolations, availableFreeSpace, totalFlexGrow, totalWeightedFlexShrink, inflexibleItems, hasInfiniteLineLength);
    else
        availableFreeSpace -= usedFreeSpace;

    return !totalViolation;
}

static LayoutUnit initialJustifyContentOffset(LayoutUnit availableFreeSpace, EJustifyContent justifyContent, unsigned numberOfChildren)
{
    if (justifyContent == JustifyFlexEnd)
        return availableFreeSpace;
    if (justifyContent == JustifyCenter)
        return availableFreeSpace / 2;
    if (justifyContent == JustifySpaceAround) {
        if (availableFreeSpace > 0 && numberOfChildren)
            return availableFreeSpace / (2 * numberOfChildren);
        else
            return availableFreeSpace / 2;
    }
    return 0;
}

static LayoutUnit justifyContentSpaceBetweenChildren(LayoutUnit availableFreeSpace, EJustifyContent justifyContent, unsigned numberOfChildren)
{
    if (availableFreeSpace > 0 && numberOfChildren > 1) {
        if (justifyContent == JustifySpaceBetween)
            return availableFreeSpace / (numberOfChildren - 1);
        if (justifyContent == JustifySpaceAround)
            return availableFreeSpace / numberOfChildren;
    }
    return 0;
}

void RenderFlexibleBox::setLogicalOverrideSize(RenderBox* child, LayoutUnit childPreferredSize)
{
    if (hasOrthogonalFlow(child))
        child->setOverrideLogicalContentHeight(childPreferredSize - child->borderAndPaddingLogicalHeight());
    else
        child->setOverrideLogicalContentWidth(childPreferredSize - child->borderAndPaddingLogicalWidth());
}

void RenderFlexibleBox::prepareChildForPositionedLayout(RenderBox* child, LayoutUnit mainAxisOffset, LayoutUnit crossAxisOffset, PositionedLayoutMode layoutMode)
{
    ASSERT(child->isOutOfFlowPositioned());
    child->containingBlock()->insertPositionedObject(child);
    RenderLayer* childLayer = child->layer();
    LayoutUnit inlinePosition = isColumnFlow() ? crossAxisOffset : mainAxisOffset;
    if (layoutMode == FlipForRowReverse && style()->flexDirection() == FlowRowReverse)
        inlinePosition = mainAxisExtent() - mainAxisOffset;
    childLayer->setStaticInlinePosition(inlinePosition); // FIXME: Not right for regions.

    LayoutUnit staticBlockPosition = isColumnFlow() ? mainAxisOffset : crossAxisOffset;
    if (childLayer->staticBlockPosition() != staticBlockPosition) {
        childLayer->setStaticBlockPosition(staticBlockPosition);
        if (child->style()->hasStaticBlockPosition(style()->isHorizontalWritingMode()))
            child->setChildNeedsLayout(MarkOnlyThis);
    }
}

EAlignItems RenderFlexibleBox::alignmentForChild(RenderBox* child) const
{
    EAlignItems align = resolveAlignment(style(), child->style());

    if (align == AlignBaseline && hasOrthogonalFlow(child))
        align = AlignFlexStart;

    if (style()->flexWrap() == FlexWrapReverse) {
        if (align == AlignFlexStart)
            align = AlignFlexEnd;
        else if (align == AlignFlexEnd)
            align = AlignFlexStart;
    }

    return align;
}

size_t RenderFlexibleBox::numberOfInFlowPositionedChildren(const OrderedFlexItemList& children) const
{
    size_t count = 0;
    for (size_t i = 0; i < children.size(); ++i) {
        RenderBox* child = children[i];
        if (!child->isOutOfFlowPositioned())
            ++count;
    }
    return count;
}

bool RenderFlexibleBox::needToStretchChild(RenderBox* child)
{
    if (alignmentForChild(child) != AlignStretch)
        return false;

    Length crossAxisLength = isHorizontalFlow() ? child->style()->height() : child->style()->width();
    return crossAxisLength.isAuto();
}

void RenderFlexibleBox::resetAutoMarginsAndLogicalTopInCrossAxis(RenderBox* child)
{
    if (hasAutoMarginsInCrossAxis(child))
        child->updateLogicalHeight();
}

void RenderFlexibleBox::layoutAndPlaceChildren(LayoutUnit& crossAxisOffset, const OrderedFlexItemList& children, const Vector<LayoutUnit>& childSizes, LayoutUnit availableFreeSpace, bool relayoutChildren, Vector<LineContext>& lineContexts)
{
    ASSERT(childSizes.size() == children.size());

    size_t numberOfChildrenForJustifyContent = numberOfInFlowPositionedChildren(children);
    LayoutUnit autoMarginOffset = autoMarginOffsetInMainAxis(children, availableFreeSpace);
    LayoutUnit mainAxisOffset = flowAwareBorderStart() + flowAwarePaddingStart();
    mainAxisOffset += initialJustifyContentOffset(availableFreeSpace, style()->justifyContent(), numberOfChildrenForJustifyContent);
    if (style()->flexDirection() == FlowRowReverse)
        mainAxisOffset += isHorizontalFlow() ? verticalScrollbarWidth() : horizontalScrollbarHeight();

    LayoutUnit totalMainExtent = mainAxisExtent();
    LayoutUnit maxAscent = 0, maxDescent = 0; // Used when align-items: baseline.
    LayoutUnit maxChildCrossAxisExtent = 0;
    size_t seenInFlowPositionedChildren = 0;
    bool shouldFlipMainAxis = !isColumnFlow() && !isLeftToRightFlow();
    for (size_t i = 0; i < children.size(); ++i) {
        RenderBox* child = children[i];
        if (child->isOutOfFlowPositioned()) {
            prepareChildForPositionedLayout(child, mainAxisOffset, crossAxisOffset, FlipForRowReverse);
            continue;
        }

        LayoutUnit childPreferredSize = childSizes[i] + mainAxisBorderAndPaddingExtentForChild(child);
        setLogicalOverrideSize(child, childPreferredSize);
        // FIXME: Can avoid laying out here in some cases. See https://webkit.org/b/87905.
        if (needToStretchChild(child) || childPreferredSize != mainAxisExtentForChild(child))
            child->setChildNeedsLayout(MarkOnlyThis);
        else {
            // To avoid double applying margin changes in updateAutoMarginsInCrossAxis, we reset the margins here.
            resetAutoMarginsAndLogicalTopInCrossAxis(child);
        }
        updateBlockChildDirtyBitsBeforeLayout(relayoutChildren, child);
        child->layoutIfNeeded();

        updateAutoMarginsInMainAxis(child, autoMarginOffset);

        LayoutUnit childCrossAxisMarginBoxExtent;
        if (alignmentForChild(child) == AlignBaseline && !hasAutoMarginsInCrossAxis(child)) {
            LayoutUnit ascent = marginBoxAscentForChild(child);
            LayoutUnit descent = (crossAxisMarginExtentForChild(child) + crossAxisExtentForChild(child)) - ascent;

            maxAscent = std::max(maxAscent, ascent);
            maxDescent = std::max(maxDescent, descent);

            childCrossAxisMarginBoxExtent = maxAscent + maxDescent;
        } else
            childCrossAxisMarginBoxExtent = crossAxisExtentForChild(child) + crossAxisMarginExtentForChild(child);
        if (!isColumnFlow())
            setLogicalHeight(std::max(logicalHeight(), crossAxisOffset + flowAwareBorderAfter() + flowAwarePaddingAfter() + childCrossAxisMarginBoxExtent + crossAxisScrollbarExtent()));
        maxChildCrossAxisExtent = std::max(maxChildCrossAxisExtent, childCrossAxisMarginBoxExtent);

        mainAxisOffset += flowAwareMarginStartForChild(child);

        LayoutUnit childMainExtent = mainAxisExtentForChild(child);
        // In an RTL column situation, this will apply the margin-right/margin-end on the left.
        // This will be fixed later in flipForRightToLeftColumn.
        LayoutPoint childLocation(shouldFlipMainAxis ? totalMainExtent - mainAxisOffset - childMainExtent : mainAxisOffset,
            crossAxisOffset + flowAwareMarginBeforeForChild(child));

        // FIXME: Supporting layout deltas.
        setFlowAwareLocationForChild(child, childLocation);
        mainAxisOffset += childMainExtent + flowAwareMarginEndForChild(child);

        ++seenInFlowPositionedChildren;
        if (seenInFlowPositionedChildren < numberOfChildrenForJustifyContent)
            mainAxisOffset += justifyContentSpaceBetweenChildren(availableFreeSpace, style()->justifyContent(), numberOfChildrenForJustifyContent);
    }

    if (isColumnFlow())
        setLogicalHeight(mainAxisOffset + flowAwareBorderEnd() + flowAwarePaddingEnd() + scrollbarLogicalHeight());

    if (style()->flexDirection() == FlowColumnReverse) {
        // We have to do an extra pass for column-reverse to reposition the flex items since the start depends
        // on the height of the flexbox, which we only know after we've positioned all the flex items.
        updateLogicalHeight();
        layoutColumnReverse(children, crossAxisOffset, availableFreeSpace);
    }

    if (m_numberOfInFlowChildrenOnFirstLine == -1)
        m_numberOfInFlowChildrenOnFirstLine = seenInFlowPositionedChildren;
    lineContexts.append(LineContext(crossAxisOffset, maxChildCrossAxisExtent, children.size(), maxAscent));
    crossAxisOffset += maxChildCrossAxisExtent;
}

void RenderFlexibleBox::layoutColumnReverse(const OrderedFlexItemList& children, LayoutUnit crossAxisOffset, LayoutUnit availableFreeSpace)
{
    // This is similar to the logic in layoutAndPlaceChildren, except we place the children
    // starting from the end of the flexbox. We also don't need to layout anything since we're
    // just moving the children to a new position.
    size_t numberOfChildrenForJustifyContent = numberOfInFlowPositionedChildren(children);
    LayoutUnit mainAxisOffset = logicalHeight() - flowAwareBorderEnd() - flowAwarePaddingEnd();
    mainAxisOffset -= initialJustifyContentOffset(availableFreeSpace, style()->justifyContent(), numberOfChildrenForJustifyContent);
    mainAxisOffset -= isHorizontalFlow() ? verticalScrollbarWidth() : horizontalScrollbarHeight();

    size_t seenInFlowPositionedChildren = 0;
    for (size_t i = 0; i < children.size(); ++i) {
        RenderBox* child = children[i];
        if (child->isOutOfFlowPositioned()) {
            child->layer()->setStaticBlockPosition(mainAxisOffset);
            continue;
        }
        mainAxisOffset -= mainAxisExtentForChild(child) + flowAwareMarginEndForChild(child);

        setFlowAwareLocationForChild(child, LayoutPoint(mainAxisOffset, crossAxisOffset + flowAwareMarginBeforeForChild(child)));

        mainAxisOffset -= flowAwareMarginStartForChild(child);

        ++seenInFlowPositionedChildren;
        if (seenInFlowPositionedChildren < numberOfChildrenForJustifyContent)
            mainAxisOffset -= justifyContentSpaceBetweenChildren(availableFreeSpace, style()->justifyContent(), numberOfChildrenForJustifyContent);
    }
}

static LayoutUnit initialAlignContentOffset(LayoutUnit availableFreeSpace, EAlignContent alignContent, unsigned numberOfLines)
{
    if (alignContent == AlignContentFlexEnd)
        return availableFreeSpace;
    if (alignContent == AlignContentCenter)
        return availableFreeSpace / 2;
    if (alignContent == AlignContentSpaceAround) {
        if (availableFreeSpace > 0 && numberOfLines)
            return availableFreeSpace / (2 * numberOfLines);
        if (availableFreeSpace < 0)
            return availableFreeSpace / 2;
    }
    return 0;
}

static LayoutUnit alignContentSpaceBetweenChildren(LayoutUnit availableFreeSpace, EAlignContent alignContent, unsigned numberOfLines)
{
    if (availableFreeSpace > 0 && numberOfLines > 1) {
        if (alignContent == AlignContentSpaceBetween)
            return availableFreeSpace / (numberOfLines - 1);
        if (alignContent == AlignContentSpaceAround || alignContent == AlignContentStretch)
            return availableFreeSpace / numberOfLines;
    }
    return 0;
}

void RenderFlexibleBox::alignFlexLines(Vector<LineContext>& lineContexts)
{
    if (!isMultiline() || style()->alignContent() == AlignContentFlexStart)
        return;

    LayoutUnit availableCrossAxisSpace = crossAxisContentExtent();
    for (size_t i = 0; i < lineContexts.size(); ++i)
        availableCrossAxisSpace -= lineContexts[i].crossAxisExtent;

    RenderBox* child = m_orderIterator.first();
    LayoutUnit lineOffset = initialAlignContentOffset(availableCrossAxisSpace, style()->alignContent(), lineContexts.size());
    for (unsigned lineNumber = 0; lineNumber < lineContexts.size(); ++lineNumber) {
        lineContexts[lineNumber].crossAxisOffset += lineOffset;
        for (size_t childNumber = 0; childNumber < lineContexts[lineNumber].numberOfChildren; ++childNumber, child = m_orderIterator.next())
            adjustAlignmentForChild(child, lineOffset);

        if (style()->alignContent() == AlignContentStretch && availableCrossAxisSpace > 0)
            lineContexts[lineNumber].crossAxisExtent += availableCrossAxisSpace / static_cast<unsigned>(lineContexts.size());

        lineOffset += alignContentSpaceBetweenChildren(availableCrossAxisSpace, style()->alignContent(), lineContexts.size());
    }
}

void RenderFlexibleBox::adjustAlignmentForChild(RenderBox* child, LayoutUnit delta)
{
    if (child->isOutOfFlowPositioned()) {
        LayoutUnit staticInlinePosition = child->layer()->staticInlinePosition();
        LayoutUnit staticBlockPosition = child->layer()->staticBlockPosition();
        LayoutUnit mainAxis = isColumnFlow() ? staticBlockPosition : staticInlinePosition;
        LayoutUnit crossAxis = isColumnFlow() ? staticInlinePosition : staticBlockPosition;
        crossAxis += delta;
        prepareChildForPositionedLayout(child, mainAxis, crossAxis, NoFlipForRowReverse);
        return;
    }

    setFlowAwareLocationForChild(child, flowAwareLocationForChild(child) + LayoutSize(0, delta));
}

void RenderFlexibleBox::alignChildren(const Vector<LineContext>& lineContexts)
{
    // Keep track of the space between the baseline edge and the after edge of the box for each line.
    Vector<LayoutUnit> minMarginAfterBaselines;

    RenderBox* child = m_orderIterator.first();
    for (size_t lineNumber = 0; lineNumber < lineContexts.size(); ++lineNumber) {
        LayoutUnit minMarginAfterBaseline = LayoutUnit::max();
        LayoutUnit lineCrossAxisExtent = lineContexts[lineNumber].crossAxisExtent;
        LayoutUnit maxAscent = lineContexts[lineNumber].maxAscent;

        for (size_t childNumber = 0; childNumber < lineContexts[lineNumber].numberOfChildren; ++childNumber, child = m_orderIterator.next()) {
            ASSERT(child);
            if (child->isOutOfFlowPositioned()) {
                if (style()->flexWrap() == FlexWrapReverse)
                    adjustAlignmentForChild(child, lineCrossAxisExtent);
                continue;
            }

            if (updateAutoMarginsInCrossAxis(child, std::max(LayoutUnit(0), availableAlignmentSpaceForChild(lineCrossAxisExtent, child))))
                continue;

            switch (alignmentForChild(child)) {
            case AlignAuto:
                ASSERT_NOT_REACHED();
                break;
            case AlignStretch: {
                applyStretchAlignmentToChild(child, lineCrossAxisExtent);
                // Since wrap-reverse flips cross start and cross end, strech children should be aligned with the cross end.
                if (style()->flexWrap() == FlexWrapReverse)
                    adjustAlignmentForChild(child, availableAlignmentSpaceForChild(lineCrossAxisExtent, child));
                break;
            }
            case AlignFlexStart:
                break;
            case AlignFlexEnd:
                adjustAlignmentForChild(child, availableAlignmentSpaceForChild(lineCrossAxisExtent, child));
                break;
            case AlignCenter:
                adjustAlignmentForChild(child, availableAlignmentSpaceForChild(lineCrossAxisExtent, child) / 2);
                break;
            case AlignBaseline: {
                // FIXME: If we get here in columns, we want the use the descent, except we currently can't get the ascent/descent of orthogonal children.
                // https://bugs.webkit.org/show_bug.cgi?id=98076
                LayoutUnit ascent = marginBoxAscentForChild(child);
                LayoutUnit startOffset = maxAscent - ascent;
                adjustAlignmentForChild(child, startOffset);

                if (style()->flexWrap() == FlexWrapReverse)
                    minMarginAfterBaseline = std::min(minMarginAfterBaseline, availableAlignmentSpaceForChild(lineCrossAxisExtent, child) - startOffset);
                break;
            }
            }
        }
        minMarginAfterBaselines.append(minMarginAfterBaseline);
    }

    if (style()->flexWrap() != FlexWrapReverse)
        return;

    // wrap-reverse flips the cross axis start and end. For baseline alignment, this means we
    // need to align the after edge of baseline elements with the after edge of the flex line.
    child = m_orderIterator.first();
    for (size_t lineNumber = 0; lineNumber < lineContexts.size(); ++lineNumber) {
        LayoutUnit minMarginAfterBaseline = minMarginAfterBaselines[lineNumber];
        for (size_t childNumber = 0; childNumber < lineContexts[lineNumber].numberOfChildren; ++childNumber, child = m_orderIterator.next()) {
            ASSERT(child);
            if (alignmentForChild(child) == AlignBaseline && !hasAutoMarginsInCrossAxis(child) && minMarginAfterBaseline)
                adjustAlignmentForChild(child, minMarginAfterBaseline);
        }
    }
}

void RenderFlexibleBox::applyStretchAlignmentToChild(RenderBox* child, LayoutUnit lineCrossAxisExtent)
{
    if (!isColumnFlow() && child->style()->logicalHeight().isAuto()) {
        // FIXME: If the child has orthogonal flow, then it already has an override height set, so use it.
        if (!hasOrthogonalFlow(child)) {
            LayoutUnit stretchedLogicalHeight = child->logicalHeight() + availableAlignmentSpaceForChild(lineCrossAxisExtent, child);
            ASSERT(!child->needsLayout());
            LayoutUnit desiredLogicalHeight = child->constrainLogicalHeightByMinMax(stretchedLogicalHeight, child->logicalHeight() - child->borderAndPaddingLogicalHeight());

            // FIXME: Can avoid laying out here in some cases. See https://webkit.org/b/87905.
            if (desiredLogicalHeight != child->logicalHeight()) {
                child->setOverrideLogicalContentHeight(desiredLogicalHeight - child->borderAndPaddingLogicalHeight());
                child->setLogicalHeight(0);
                child->forceChildLayout();
            }
        }
    } else if (isColumnFlow() && child->style()->logicalWidth().isAuto()) {
        // FIXME: If the child doesn't have orthogonal flow, then it already has an override width set, so use it.
        if (hasOrthogonalFlow(child)) {
            LayoutUnit childWidth = std::max<LayoutUnit>(0, lineCrossAxisExtent - crossAxisMarginExtentForChild(child));
            childWidth = child->constrainLogicalWidthInRegionByMinMax(childWidth, childWidth, this);

            if (childWidth != child->logicalWidth()) {
                child->setOverrideLogicalContentWidth(childWidth - child->borderAndPaddingLogicalWidth());
                child->forceChildLayout();
            }
        }
    }
}

void RenderFlexibleBox::flipForRightToLeftColumn()
{
    if (style()->isLeftToRightDirection() || !isColumnFlow())
        return;

    LayoutUnit crossExtent = crossAxisExtent();
    for (RenderBox* child = m_orderIterator.first(); child; child = m_orderIterator.next()) {
        if (child->isOutOfFlowPositioned())
            continue;
        LayoutPoint location = flowAwareLocationForChild(child);
        // For vertical flows, setFlowAwareLocationForChild will transpose x and y,
        // so using the y axis for a column cross axis extent is correct.
        location.setY(crossExtent - crossAxisExtentForChild(child) - location.y());
        setFlowAwareLocationForChild(child, location);
    }
}

void RenderFlexibleBox::flipForWrapReverse(const Vector<LineContext>& lineContexts, LayoutUnit crossAxisStartEdge)
{
    LayoutUnit contentExtent = crossAxisContentExtent();
    RenderBox* child = m_orderIterator.first();
    for (size_t lineNumber = 0; lineNumber < lineContexts.size(); ++lineNumber) {
        for (size_t childNumber = 0; childNumber < lineContexts[lineNumber].numberOfChildren; ++childNumber, child = m_orderIterator.next()) {
            ASSERT(child);
            LayoutUnit lineCrossAxisExtent = lineContexts[lineNumber].crossAxisExtent;
            LayoutUnit originalOffset = lineContexts[lineNumber].crossAxisOffset - crossAxisStartEdge;
            LayoutUnit newOffset = contentExtent - originalOffset - lineCrossAxisExtent;
            adjustAlignmentForChild(child, newOffset - originalOffset);
        }
    }
}

}