Source/WebCore/rendering/BaselineAlignment.cpp

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#include "config.h"
#include "BaselineAlignment.h"

#include "BaselineAlignmentInlines.h"
#include "RenderBox.h"
#include "RenderBoxModelObjectInlines.h"
#include "StyleComputedStyle+GettersInlines.h"
#include <wtf/TZoneMallocInlines.h>

namespace WebCore {

WTF_MAKE_TZONE_ALLOCATED_IMPL(BaselineGroup);
WTF_MAKE_TZONE_ALLOCATED_IMPL(BaselineAlignmentState);

BaselineGroup::BaselineGroup(FlowDirection blockFlow, ItemPosition preference)
    : m_blockFlow(blockFlow)
    , m_preference(preference)
{
}

bool BaselineGroup::isOppositeBlockFlow(FlowDirection blockFlow) const
{
    switch (blockFlow) {
    case FlowDirection::TopToBottom:
        return false;
    case FlowDirection::LeftToRight:
        return m_blockFlow == FlowDirection::RightToLeft;
    case FlowDirection::RightToLeft:
        return m_blockFlow == FlowDirection::LeftToRight;
    default:
        ASSERT_NOT_REACHED();
        return false;
    }
}

bool BaselineGroup::isOrthogonalBlockFlow(FlowDirection blockFlow) const
{
    switch (blockFlow) {
    case FlowDirection::TopToBottom:
        return m_blockFlow != FlowDirection::TopToBottom;
    case FlowDirection::LeftToRight:
    case FlowDirection::RightToLeft:
        return m_blockFlow == FlowDirection::TopToBottom;
    default:
        ASSERT_NOT_REACHED();
        return false;
    }
}

bool BaselineGroup::isCompatible(FlowDirection alignmentSubjectBlockFlow, ItemPosition alignmentSubjectPreference) const
{
    ASSERT(isBaselinePosition(alignmentSubjectPreference));
    return ((m_blockFlow == alignmentSubjectBlockFlow || isOrthogonalBlockFlow(alignmentSubjectBlockFlow)) && m_preference == alignmentSubjectPreference)
        || (isOppositeBlockFlow(alignmentSubjectBlockFlow) && m_preference != alignmentSubjectPreference);
}

BaselineAlignmentState::BaselineAlignmentState(LogicalBoxAxis alignmentContextAxis, WritingMode alignmentContainerWritingMode)
    : m_alignmentContainerWritingMode(alignmentContainerWritingMode)
    , m_alignmentContextAxis(alignmentContextAxis)
{
}

size_t BaselineAlignmentState::sharedGroupIndex(WritingMode alignmentSubjectWritingMode, ItemPosition preference) const
{
    ASSERT(isBaselinePosition(preference));
    return const_cast<BaselineAlignmentState*>(this)->findCompatibleSharedGroup(alignmentSubjectWritingMode, preference);
}

FontBaseline BaselineAlignment::dominantBaseline(WritingMode writingMode)
{
    // https://drafts.csswg.org/css-inline-3/#alignment-baseline-property
    // https://drafts.csswg.org/css-inline-3/#dominant-baseline-property
    return writingMode.prefersCentralBaseline() ? FontBaseline::Central : FontBaseline::Alphabetic;
}

LayoutUnit BaselineAlignment::synthesizedBaseline(const RenderBox& box, FontBaseline baselineType, WritingMode writingModeForSynthesis, LineDirection lineDirection, BaselineSynthesisEdge edge)
{
    auto boxSize = lineDirection == LineDirection::Horizontal ? box.borderBoxHeight() : box.borderBoxWidth();
    if (edge == BaselineSynthesisEdge::ContentBox)
        boxSize -= lineDirection == LineDirection::Horizontal ? box.verticalBorderAndPaddingExtent() : box.horizontalBorderAndPaddingExtent();
    else if (edge == BaselineSynthesisEdge::MarginBox)
        boxSize += lineDirection == LineDirection::Horizontal ? box.verticalMarginExtent() : box.horizontalMarginExtent();

    if (baselineType == FontBaseline::Alphabetic) {
        // When synthesizing the alphabetic baseline for a box we are determining the distance
        // to the line-under edge. For a box with vertical-lr writing mode the location
        // of the line-under edge should be the same as the box's block-start edge. For
        // vertical-rl writing mode we need the box's size since they are on opposiate sides.
        auto shouldTreatAsHorizontal = lineDirection == LineDirection::Horizontal || writingModeForSynthesis.computedWritingMode() == StyleWritingMode::VerticalRl;
        return shouldTreatAsHorizontal ? boxSize : LayoutUnit();
    }
    return boxSize / 2;
}

WritingMode BaselineAlignment::usedWritingModeForBaselineAlignment(LogicalBoxAxis alignmentContextAxis,
    WritingMode alignmentContainerWritingMode, WritingMode aligmentSubjectWritingMode)
{

    auto isAlignmentSubjectBlockFlowParallelToAlignmentContextAxis = [&] {
        if (alignmentContextAxis == LogicalBoxAxis::Block)
            return !alignmentContainerWritingMode.isOrthogonal(aligmentSubjectWritingMode);
        return alignmentContainerWritingMode.isOrthogonal(aligmentSubjectWritingMode);
    };

    // css-align-3: 9.1. Determining the Baselines of a Box
    // In general, the writing mode of the box, shape, or other object being aligned is used to determine
    // the line-under and line-over edges for synthesis...
    if (!isAlignmentSubjectBlockFlowParallelToAlignmentContextAxis())
        return aligmentSubjectWritingMode;

    // ... However, when that writing mode’s block flow direction
    // is parallel to the axis of the alignment context, an axis-compatible writing mode must be assumed:
    //

    // If the box establishing the alignment context has a block flow direction that is orthogonal to the
    // axis of the alignment context, use its writing mode.
    if (alignmentContextAxis == LogicalBoxAxis::Inline)
        return alignmentContainerWritingMode;

    // Otherwise:
    // If the box’s own writing mode is vertical, assume horizontal-tb.
    // If the box’s own writing mode is horizontal, assume vertical-lr if
    // direction is ltr and vertical-rl if direction is rtl.
    if (!aligmentSubjectWritingMode.isHorizontal())
        return { };
    auto styleWritingMode = alignmentContainerWritingMode.isBidiLTR() ? StyleWritingMode::VerticalLr : StyleWritingMode::VerticalRl;
    return { styleWritingMode, TextDirection::LTR, TextOrientation::Mixed };
}

size_t BaselineAlignmentState::findCompatibleSharedGroup(WritingMode alignmentSubjectWritingMode, ItemPosition preference)
{
    auto usedWritingModeForBaselineAlignment = BaselineAlignment::usedWritingModeForBaselineAlignment(m_alignmentContextAxis, m_alignmentContainerWritingMode, alignmentSubjectWritingMode);
    auto blockFlowDirection = usedWritingModeForBaselineAlignment.blockDirection();
    for (size_t index = 0; index < m_sharedGroups.size(); ++index) {
        if (m_sharedGroups[index].isCompatible(blockFlowDirection, preference))
            return index;
    }
    m_sharedGroups.append(BaselineGroup(blockFlowDirection, preference));
    return m_sharedGroups.size() - 1;
}

} // namespace WebCore