C++ LayoutMultiColumnFlowThread::columnHeightAvailable方法代码示例

LayoutUnit MultiColumnFragmentainerGroup::calculateMaxColumnHeight() const
{
    LayoutBlockFlow* multicolBlock = m_columnSet.multiColumnBlockFlow();
    const ComputedStyle& multicolStyle = multicolBlock->styleRef();
    LayoutMultiColumnFlowThread* flowThread = m_columnSet.multiColumnFlowThread();
    LayoutUnit availableHeight = flowThread->columnHeightAvailable();
    LayoutUnit maxColumnHeight = availableHeight ? availableHeight : LayoutUnit::max();
    if (!multicolStyle.logicalMaxHeight().isMaxSizeNone()) {
        LayoutUnit logicalMaxHeight = multicolBlock->computeContentLogicalHeight(MaxSize, multicolStyle.logicalMaxHeight(), -1);
        if (logicalMaxHeight != -1 && maxColumnHeight > logicalMaxHeight)
            maxColumnHeight = logicalMaxHeight;
    }
    LayoutUnit maxHeight = heightAdjustedForRowOffset(maxColumnHeight);
    if (LayoutMultiColumnFlowThread* enclosingFlowThread = flowThread->enclosingFlowThread()) {
        if (enclosingFlowThread->isPageLogicalHeightKnown()) {
            // We're nested inside another fragmentation context whose fragmentainer heights are
            // known. This constrains the max height.
            LayoutUnit remainingOuterLogicalHeight = enclosingFlowThread->pageRemainingLogicalHeightForOffset(blockOffsetInEnclosingFlowThread(), LayoutBlock::AssociateWithLatterPage);
            ASSERT(remainingOuterLogicalHeight > 0);
            if (maxHeight > remainingOuterLogicalHeight)
                maxHeight = remainingOuterLogicalHeight;
        }
    }
    return maxHeight;
}

void MultiColumnFragmentainerGroup::resetColumnHeight()
{
    m_maxColumnHeight = calculateMaxColumnHeight();

    LayoutMultiColumnFlowThread* flowThread = m_columnSet.multiColumnFlowThread();
    if (m_columnSet.heightIsAuto()) {
        FragmentationContext* enclosingFragmentationContext = flowThread->enclosingFragmentationContext();
        if (enclosingFragmentationContext && enclosingFragmentationContext->isFragmentainerLogicalHeightKnown()) {
            // Even if height is auto, we set an initial height, in order to tell how much content
            // this MultiColumnFragmentainerGroup can hold, and when we need to append a new one.
            m_columnHeight = m_maxColumnHeight;
        } else {
            m_columnHeight = LayoutUnit();
        }
    } else {
        setAndConstrainColumnHeight(heightAdjustedForRowOffset(flowThread->columnHeightAvailable()));
    }
}

void MultiColumnFragmentainerGroup::resetColumnHeight()
{
    // Nuke previously stored minimum column height. Contents may have changed for all we know.
    m_minimumColumnHeight = 0;

    m_maxColumnHeight = calculateMaxColumnHeight();

    LayoutMultiColumnFlowThread* flowThread = m_columnSet.multiColumnFlowThread();
    LayoutMultiColumnFlowThread* enclosingFlowThread = flowThread->enclosingFlowThread();
    if (enclosingFlowThread && enclosingFlowThread->isPageLogicalHeightKnown()) {
        // TODO(mstensho): Do this better. If height is auto here, we shouldn't set a
        // height, or forced breaks and pagination struts might mess up column balancing.
        LayoutUnit columnHeight = heightIsAuto() ? m_maxColumnHeight : heightAdjustedForRowOffset(flowThread->columnHeightAvailable());
        setAndConstrainColumnHeight(columnHeight);
    } else if (heightIsAuto()) {
        m_columnHeight = LayoutUnit();
    } else {
        setAndConstrainColumnHeight(heightAdjustedForRowOffset(flowThread->columnHeightAvailable()));
    }
}

bool LayoutMultiColumnSet::heightIsAuto() const
{
    LayoutMultiColumnFlowThread* flowThread = multiColumnFlowThread();
    if (!flowThread->isLayoutPagedFlowThread()) {
        // If support for the column-fill property isn't enabled, we want to behave as if
        // column-fill were auto, so that multicol containers with specified height don't get their
        // columns balanced (auto-height multicol containers will still get their columns balanced,
        // even if column-fill isn't 'balance' - in accordance with the spec). Pretending that
        // column-fill is auto also matches the old multicol implementation, which has no support
        // for this property.
        if (multiColumnBlockFlow()->style()->getColumnFill() == ColumnFillBalance)
            return true;
        if (LayoutBox* next = nextSiblingBox()) {
            if (next->isLayoutMultiColumnSpannerPlaceholder()) {
                // If we're followed by a spanner, we need to balance.
                return true;
            }
        }
    }
    return !flowThread->columnHeightAvailable();
}