LayoutMultiColumnFlowThread* LayoutMultiColumnFlowThread::enclosingFlowThread() const
{
if (isLayoutPagedFlowThread()) {
// Paged overflow containers should never be fragmented by enclosing fragmentation
// contexts. They are to be treated as unbreakable content.
return nullptr;
}
if (multiColumnBlockFlow()->isInsideFlowThread())
return toLayoutMultiColumnFlowThread(locateFlowThreadContainingBlockOf(*multiColumnBlockFlow()));
return nullptr;
}
LayoutUnit LayoutMultiColumnSet::columnGap() const
{
LayoutBlockFlow* parentBlock = multiColumnBlockFlow();
if (parentBlock->style()->hasNormalColumnGap())
return parentBlock->style()->fontDescription().computedPixelSize(); // "1em" is recommended as the normal gap setting. Matches <p> margins.
return parentBlock->style()->columnGap();
}
void RenderMultiColumnFlowThread::evacuateAndDestroy()
{
RenderBlockFlow* multicolContainer = multiColumnBlockFlow();
m_beingEvacuated = true;
// Delete the line box tree.
deleteLines();
LayoutStateDisabler layoutStateDisabler(&view());
// First promote all children of the flow thread. Before we move them to the flow thread's
// container, we need to unregister the flow thread, so that they aren't just re-added again to
// the flow thread that we're trying to empty.
multicolContainer->setMultiColumnFlowThread(nullptr);
moveAllChildrenTo(multicolContainer, true);
// Move spanners back to their original DOM position in the tree, and destroy the placeholders.
SpannerMap::iterator it;
while ((it = m_spannerMap.begin()) != m_spannerMap.end()) {
RenderBox* spanner = it->key;
RenderMultiColumnSpannerPlaceholder* placeholder = it->value;
RenderBlockFlow* originalContainer = toRenderBlockFlow(placeholder->parent());
multicolContainer->removeChild(*spanner);
originalContainer->addChild(spanner, placeholder);
placeholder->destroy();
m_spannerMap.remove(it);
}
// Remove all sets.
while (RenderMultiColumnSet* columnSet = firstMultiColumnSet())
columnSet->destroy();
destroy();
}
void LayoutMultiColumnFlowThread::layoutColumns(SubtreeLayoutScope& layoutScope)
{
// Since we ended up here, it means that the multicol container (our parent) needed
// layout. Since contents of the multicol container are diverted to the flow thread, the flow
// thread needs layout as well.
layoutScope.setChildNeedsLayout(this);
m_blockOffsetInEnclosingFragmentationContext = enclosingFragmentationContext() ? multiColumnBlockFlow()->offsetFromLogicalTopOfFirstPage() : LayoutUnit();
for (LayoutBox* columnBox = firstMultiColumnBox(); columnBox; columnBox = columnBox->nextSiblingMultiColumnBox()) {
if (!columnBox->isLayoutMultiColumnSet()) {
ASSERT(columnBox->isLayoutMultiColumnSpannerPlaceholder()); // no other type is expected.
continue;
}
LayoutMultiColumnSet* columnSet = toLayoutMultiColumnSet(columnBox);
layoutScope.setChildNeedsLayout(columnSet);
if (!m_columnHeightsChanged) {
// This is the initial layout pass. We need to reset the column height, because contents
// typically have changed.
columnSet->resetColumnHeight();
}
// Since column sets are regular block flow objects, and their position is changed in
// regular block layout code (with no means for the multicol code to notice unless we add
// hooks there), store the previous position now. If it changes in the imminent layout
// pass, we may have to rebalance its columns.
columnSet->storeOldPosition();
}
m_columnHeightsChanged = false;
invalidateColumnSets();
layout();
validateColumnSets();
}
void LayoutMultiColumnFlowThread::computePreferredLogicalWidths()
{
LayoutFlowThread::computePreferredLogicalWidths();
// The min/max intrinsic widths calculated really tell how much space elements need when
// laid out inside the columns. In order to eventually end up with the desired column width,
// we need to convert them to values pertaining to the multicol container.
const LayoutBlockFlow* multicolContainer = multiColumnBlockFlow();
const ComputedStyle* multicolStyle = multicolContainer->style();
int columnCount = multicolStyle->hasAutoColumnCount() ? 1 : multicolStyle->columnCount();
LayoutUnit columnWidth;
LayoutUnit gapExtra = (columnCount - 1) * multicolContainer->columnGap();
if (multicolStyle->hasAutoColumnWidth()) {
m_minPreferredLogicalWidth = m_minPreferredLogicalWidth * columnCount + gapExtra;
} else {
columnWidth = multicolStyle->columnWidth();
m_minPreferredLogicalWidth = std::min(m_minPreferredLogicalWidth, columnWidth);
}
// Note that if column-count is auto here, we should resolve it to calculate the maximum
// intrinsic width, instead of pretending that it's 1. The only way to do that is by performing
// a layout pass, but this is not an appropriate time or place for layout. The good news is that
// if height is unconstrained and there are no explicit breaks, the resolved column-count really
// should be 1.
m_maxPreferredLogicalWidth = std::max(m_maxPreferredLogicalWidth, columnWidth) * columnCount + gapExtra;
}
void LayoutMultiColumnFlowThread::evacuateAndDestroy()
{
LayoutBlockFlow* multicolContainer = multiColumnBlockFlow();
m_isBeingEvacuated = true;
// Remove all sets and spanners.
while (LayoutBox* columnBox = firstMultiColumnBox()) {
ASSERT(columnBox->isAnonymous());
columnBox->destroy();
}
ASSERT(!previousSibling());
ASSERT(!nextSibling());
// Finally we can promote all flow thread's children. Before we move them to the flow thread's
// container, we need to unregister the flow thread, so that they aren't just re-added again to
// the flow thread that we're trying to empty.
multicolContainer->resetMultiColumnFlowThread();
moveAllChildrenTo(multicolContainer, true);
// We used to manually nuke the line box tree here, but that should happen automatically when
// moving children around (the code above).
ASSERT(!firstLineBox());
destroy();
}
LayoutUnit RenderMultiColumnSet::heightAdjustedForSetOffset(LayoutUnit height) const
{
RenderBlockFlow* multicolBlock = multiColumnBlockFlow();
LayoutUnit contentLogicalTop = logicalTop() - multicolBlock->borderBefore() - multicolBlock->paddingBefore();
height -= contentLogicalTop;
return max(height, LayoutUnit(1)); // Let's avoid zero height, as that would probably cause an infinite amount of columns to be created.
}
LayoutMultiColumnSet* LayoutMultiColumnFlowThread::lastMultiColumnSet() const
{
for (LayoutObject* sibling = multiColumnBlockFlow()->lastChild(); sibling; sibling = sibling->previousSibling()) {
if (sibling->isLayoutMultiColumnSet())
return toLayoutMultiColumnSet(sibling);
}
return nullptr;
}
void LayoutMultiColumnFlowThread::populate()
{
LayoutBlockFlow* multicolContainer = multiColumnBlockFlow();
ASSERT(!nextSibling());
// Reparent children preceding the flow thread into the flow thread. It's multicol content
// now. At this point there's obviously nothing after the flow thread, but layoutObjects (column
// sets and spanners) will be inserted there as we insert elements into the flow thread.
multicolContainer->moveChildrenTo(this, multicolContainer->firstChild(), this, true);
}
void LayoutMultiColumnFlowThread::willBeRemovedFromTree()
{
// Detach all column sets from the flow thread. Cannot destroy them at this point, since they
// are siblings of this object, and there may be pointers to this object's sibling somewhere
// further up on the call stack.
for (LayoutMultiColumnSet* columnSet = firstMultiColumnSet(); columnSet; columnSet = columnSet->nextSiblingMultiColumnSet())
columnSet->detachFromFlowThread();
multiColumnBlockFlow()->resetMultiColumnFlowThread();
LayoutFlowThread::willBeRemovedFromTree();
}
void LayoutMultiColumnFlowThread::createAndInsertMultiColumnSet(LayoutBox* insertBefore)
{
LayoutBlockFlow* multicolContainer = multiColumnBlockFlow();
LayoutMultiColumnSet* newSet = LayoutMultiColumnSet::createAnonymous(*this, multicolContainer->styleRef());
multicolContainer->LayoutBlock::addChild(newSet, insertBefore);
invalidateColumnSets();
// We cannot handle immediate column set siblings (and there's no need for it, either).
// There has to be at least one spanner separating them.
ASSERT(!newSet->previousSiblingMultiColumnBox() || !newSet->previousSiblingMultiColumnBox()->isLayoutMultiColumnSet());
ASSERT(!newSet->nextSiblingMultiColumnBox() || !newSet->nextSiblingMultiColumnBox()->isLayoutMultiColumnSet());
}
void RenderMultiColumnSet::paintColumnRules(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
{
if (paintInfo.context->paintingDisabled())
return;
RenderStyle* blockStyle = multiColumnBlockFlow()->style();
const Color& ruleColor = resolveColor(blockStyle, CSSPropertyWebkitColumnRuleColor);
bool ruleTransparent = blockStyle->columnRuleIsTransparent();
EBorderStyle ruleStyle = blockStyle->columnRuleStyle();
LayoutUnit ruleThickness = blockStyle->columnRuleWidth();
LayoutUnit colGap = columnGap();
bool renderRule = ruleStyle > BHIDDEN && !ruleTransparent;
if (!renderRule)
return;
unsigned colCount = columnCount();
if (colCount <= 1)
return;
bool antialias = shouldAntialiasLines(paintInfo.context);
bool leftToRight = style()->isLeftToRightDirection();
LayoutUnit currLogicalLeftOffset = leftToRight ? LayoutUnit() : contentLogicalWidth();
LayoutUnit ruleAdd = borderAndPaddingLogicalLeft();
LayoutUnit ruleLogicalLeft = leftToRight ? LayoutUnit() : contentLogicalWidth();
LayoutUnit inlineDirectionSize = computedColumnWidth();
BoxSide boxSide = isHorizontalWritingMode()
? leftToRight ? BSLeft : BSRight
: leftToRight ? BSTop : BSBottom;
for (unsigned i = 0; i < colCount; i++) {
// Move to the next position.
if (leftToRight) {
ruleLogicalLeft += inlineDirectionSize + colGap / 2;
currLogicalLeftOffset += inlineDirectionSize + colGap;
} else {
ruleLogicalLeft -= (inlineDirectionSize + colGap / 2);
currLogicalLeftOffset -= (inlineDirectionSize + colGap);
}
// Now paint the column rule.
if (i < colCount - 1) {
LayoutUnit ruleLeft = isHorizontalWritingMode() ? paintOffset.x() + ruleLogicalLeft - ruleThickness / 2 + ruleAdd : paintOffset.x() + borderLeft() + paddingLeft();
LayoutUnit ruleRight = isHorizontalWritingMode() ? ruleLeft + ruleThickness : ruleLeft + contentWidth();
LayoutUnit ruleTop = isHorizontalWritingMode() ? paintOffset.y() + borderTop() + paddingTop() : paintOffset.y() + ruleLogicalLeft - ruleThickness / 2 + ruleAdd;
LayoutUnit ruleBottom = isHorizontalWritingMode() ? ruleTop + contentHeight() : ruleTop + ruleThickness;
IntRect pixelSnappedRuleRect = pixelSnappedIntRectFromEdges(ruleLeft, ruleTop, ruleRight, ruleBottom);
drawLineForBoxSide(paintInfo.context, pixelSnappedRuleRect.x(), pixelSnappedRuleRect.y(), pixelSnappedRuleRect.maxX(), pixelSnappedRuleRect.maxY(), boxSide, ruleColor, ruleStyle, 0, 0, antialias);
}
ruleLogicalLeft = currLogicalLeftOffset;
}
}
LayoutUnit RenderMultiColumnSet::calculateMaxColumnHeight() const
{
RenderBlockFlow* multicolBlock = multiColumnBlockFlow();
RenderStyle* multicolStyle = multicolBlock->style();
LayoutUnit availableHeight = multiColumnFlowThread()->columnHeightAvailable();
LayoutUnit maxColumnHeight = availableHeight ? availableHeight : RenderFlowThread::maxLogicalHeight();
if (!multicolStyle->logicalMaxHeight().isUndefined()) {
LayoutUnit logicalMaxHeight = multicolBlock->computeContentLogicalHeight(multicolStyle->logicalMaxHeight(), -1);
if (logicalMaxHeight != -1 && maxColumnHeight > logicalMaxHeight)
maxColumnHeight = logicalMaxHeight;
}
return heightAdjustedForSetOffset(maxColumnHeight);
}
LayoutUnit LayoutMultiColumnSet::logicalTopFromMulticolContentEdge() const
{
// We subtract the position of the first column set or spanner placeholder, rather than the
// "before" border+padding of the multicol container. This distinction doesn't matter after
// layout, but during layout it does: The flow thread (i.e. the multicol contents) is laid out
// before the column sets and spanner placeholders, which means that compesating for a top
// border+padding that hasn't yet been baked into the offset will produce the wrong results in
// the first layout pass, and we'd end up performing a wasted layout pass in many cases.
const LayoutBox& firstColumnBox = *multiColumnFlowThread()->firstMultiColumnBox();
// The top margin edge of the first column set or spanner placeholder is flush with the top
// content edge of the multicol container. The margin here never collapses with other margins,
// so we can just subtract it. Column sets never have margins, but spanner placeholders may.
LayoutUnit firstColumnBoxMarginEdge = firstColumnBox.logicalTop() - multiColumnBlockFlow()->marginBeforeForChild(firstColumnBox);
return logicalTop() - firstColumnBoxMarginEdge;
}
LayoutUnit RenderMultiColumnSet::heightAdjustedForSetOffset(LayoutUnit height) const
{
// Adjust for the top offset within the content box of the multicol container (containing
// block), unless this is the first set. We know that the top offset for the first set will be
// zero, but if the multicol container has non-zero top border or padding, the set's top offset
// (initially being 0 and relative to the border box) will be negative until it has been laid
// out. Had we used this bogus offset, we would calculate the wrong height, and risk performing
// a wasted layout iteration. Of course all other sets (if any) have this problem in the first
// layout pass too, but there's really nothing we can do there until the flow thread has been
// laid out anyway.
if (previousSiblingMultiColumnSet()) {
RenderBlockFlow* multicolBlock = multiColumnBlockFlow();
LayoutUnit contentLogicalTop = logicalTop() - multicolBlock->borderAndPaddingBefore();
height -= contentLogicalTop;
}
return max(height, LayoutUnit(1)); // Let's avoid zero height, as that would probably cause an infinite amount of columns to be created.
}
void LayoutMultiColumnFlowThread::contentWasLaidOut(LayoutUnit logicalTopInFlowThreadAfterPagination)
{
// Check if we need another fragmentainer group. If we've run out of columns in the last
// fragmentainer group (column row), we need to insert another fragmentainer group to hold more
// columns.
// First figure out if there's any chance that we're nested at all. If we can be sure that
// we're not, bail early. This code is run very often, and since locating a containing flow
// thread has some cost (depending on tree depth), avoid calling
// enclosingFragmentationContext() right away. This test may give some false positives (hence
// the "mayBe"), if we're in an out-of-flow subtree and have an outer multicol container that
// doesn't affect us, but that's okay. We'll discover that further down the road when trying to
// locate our enclosing flow thread for real.
bool mayBeNested = multiColumnBlockFlow()->isInsideFlowThread() || view()->fragmentationContext();
if (!mayBeNested)
return;
appendNewFragmentainerGroupIfNeeded(logicalTopInFlowThreadAfterPagination);
}
void LayoutMultiColumnFlowThread::createAndInsertSpannerPlaceholder(LayoutBox* spannerObjectInFlowThread, LayoutObject* insertedBeforeInFlowThread)
{
LayoutBox* insertBeforeColumnBox = nullptr;
LayoutMultiColumnSet* setToSplit = nullptr;
if (insertedBeforeInFlowThread) {
// The spanner is inserted before something. Figure out what this entails. If the
// next object is a spanner too, it means that we can simply insert a new spanner
// placeholder in front of its placeholder.
insertBeforeColumnBox = insertedBeforeInFlowThread->spannerPlaceholder();
if (!insertBeforeColumnBox) {
// The next object isn't a spanner; it's regular column content. Examine what
// comes right before us in the flow thread, then.
LayoutObject* previousLayoutObject = previousInPreOrderSkippingOutOfFlow(this, spannerObjectInFlowThread);
if (!previousLayoutObject || previousLayoutObject == this) {
// The spanner is inserted as the first child of the multicol container,
// which means that we simply insert a new spanner placeholder at the
// beginning.
insertBeforeColumnBox = firstMultiColumnBox();
} else if (LayoutMultiColumnSpannerPlaceholder* previousPlaceholder = containingColumnSpannerPlaceholder(previousLayoutObject)) {
// Before us is another spanner. We belong right after it then.
insertBeforeColumnBox = previousPlaceholder->nextSiblingMultiColumnBox();
} else {
// We're inside regular column content with both feet. Find out which column
// set this is. It needs to be split it into two sets, so that we can insert
// a new spanner placeholder between them.
setToSplit = mapDescendantToColumnSet(previousLayoutObject);
ASSERT(setToSplit == mapDescendantToColumnSet(insertedBeforeInFlowThread));
insertBeforeColumnBox = setToSplit->nextSiblingMultiColumnBox();
// We've found out which set that needs to be split. Now proceed to
// inserting the spanner placeholder, and then insert a second column set.
}
}
ASSERT(setToSplit || insertBeforeColumnBox);
}
LayoutBlockFlow* multicolContainer = multiColumnBlockFlow();
LayoutMultiColumnSpannerPlaceholder* newPlaceholder = LayoutMultiColumnSpannerPlaceholder::createAnonymous(multicolContainer->styleRef(), *spannerObjectInFlowThread);
ASSERT(!insertBeforeColumnBox || insertBeforeColumnBox->parent() == multicolContainer);
multicolContainer->LayoutBlock::addChild(newPlaceholder, insertBeforeColumnBox);
spannerObjectInFlowThread->setSpannerPlaceholder(*newPlaceholder);
if (setToSplit)
createAndInsertMultiColumnSet(insertBeforeColumnBox);
}
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();
}
void LayoutMultiColumnFlowThread::calculateColumnCountAndWidth(LayoutUnit& width, unsigned& count) const
{
LayoutBlock* columnBlock = multiColumnBlockFlow();
const ComputedStyle* columnStyle = columnBlock->style();
LayoutUnit availableWidth = columnBlock->contentLogicalWidth();
LayoutUnit columnGap = columnBlock->columnGap();
LayoutUnit computedColumnWidth = max<LayoutUnit>(1, LayoutUnit(columnStyle->columnWidth()));
unsigned computedColumnCount = max<int>(1, columnStyle->columnCount());
ASSERT(!columnStyle->hasAutoColumnCount() || !columnStyle->hasAutoColumnWidth());
if (columnStyle->hasAutoColumnWidth() && !columnStyle->hasAutoColumnCount()) {
count = computedColumnCount;
width = std::max<LayoutUnit>(0, (availableWidth - ((count - 1) * columnGap)) / count);
} else if (!columnStyle->hasAutoColumnWidth() && columnStyle->hasAutoColumnCount()) {
count = std::max<LayoutUnit>(1, (availableWidth + columnGap) / (computedColumnWidth + columnGap));
width = ((availableWidth + columnGap) / count) - columnGap;
} else {
count = std::max<LayoutUnit>(std::min<LayoutUnit>(computedColumnCount, (availableWidth + columnGap) / (computedColumnWidth + columnGap)), 1);
width = ((availableWidth + columnGap) / count) - columnGap;
}
}
void RenderMultiColumnSet::prepareForLayout()
{
RenderBlockFlow* multicolBlock = multiColumnBlockFlow();
RenderStyle* multicolStyle = multicolBlock->style();
// Set box logical top.
ASSERT(!previousSiblingBox() || !previousSiblingBox()->isRenderMultiColumnSet()); // FIXME: multiple set not implemented; need to examine previous set to calculate the correct logical top.
setLogicalTop(multicolBlock->borderBefore() + multicolBlock->paddingBefore());
// Set box width.
updateLogicalWidth();
if (multicolBlock->multiColumnFlowThread()->requiresBalancing()) {
// Set maximum column height. We will not stretch beyond this.
m_maxColumnHeight = RenderFlowThread::maxLogicalHeight();
if (!multicolStyle->logicalHeight().isAuto()) {
m_maxColumnHeight = multicolBlock->computeContentLogicalHeight(multicolStyle->logicalHeight(), -1);
if (m_maxColumnHeight == -1)
m_maxColumnHeight = RenderFlowThread::maxLogicalHeight();
}
if (!multicolStyle->logicalMaxHeight().isUndefined()) {
LayoutUnit logicalMaxHeight = multicolBlock->computeContentLogicalHeight(multicolStyle->logicalMaxHeight(), -1);
if (logicalMaxHeight != -1 && m_maxColumnHeight > logicalMaxHeight)
m_maxColumnHeight = logicalMaxHeight;
}
m_maxColumnHeight = heightAdjustedForSetOffset(m_maxColumnHeight);
m_computedColumnHeight = 0; // Restart balancing.
} else {
setAndConstrainColumnHeight(heightAdjustedForSetOffset(multicolBlock->multiColumnFlowThread()->columnHeightAvailable()));
}
clearForcedBreaks();
// Nuke previously stored minimum column height. Contents may have changed for all we know.
m_minimumColumnHeight = 0;
}
void RenderMultiColumnFlowThread::flowThreadDescendantInserted(RenderObject* descendant)
{
if (gShiftingSpanner || m_beingEvacuated || descendant->isInFlowRenderFlowThread())
return;
RenderObject* subtreeRoot = descendant;
for (; descendant; descendant = (descendant ? descendant->nextInPreOrder(subtreeRoot) : nullptr)) {
if (descendant->isRenderMultiColumnSpannerPlaceholder()) {
// A spanner's placeholder has been inserted. The actual spanner renderer is moved from
// where it would otherwise occur (if it weren't a spanner) to becoming a sibling of the
// column sets.
RenderMultiColumnSpannerPlaceholder* placeholder = toRenderMultiColumnSpannerPlaceholder(descendant);
if (placeholder->flowThread() != this) {
// This isn't our spanner! It shifted here from an ancestor multicolumn block. It's going to end up
// becoming our spanner instead, but for it to do that we first have to nuke the original spanner,
// and get the spanner content back into this flow thread.
RenderBox* spanner = placeholder->spanner();
// Get info for the move of the original content back into our flow thread.
RenderBoxModelObject* placeholderParent = toRenderBoxModelObject(placeholder->parent());
// We have to nuke the placeholder, since the ancestor already lost the mapping to it when
// we shifted the placeholder down into this flow thread.
RenderObject* placeholderNextSibling = placeholderParent->removeChild(*placeholder);
// Get the ancestor multicolumn flow thread to clean up its mess.
RenderBlockFlow* ancestorBlock = toRenderBlockFlow(spanner->parent());
ancestorBlock->multiColumnFlowThread()->flowThreadRelativeWillBeRemoved(spanner);
// Now move the original content into our flow thread. It will end up calling flowThreadDescendantInserted
// on the new content only, and everything will get set up properly.
ancestorBlock->moveChildTo(placeholderParent, spanner, placeholderNextSibling, true);
// Advance descendant.
descendant = placeholderNextSibling;
// If the spanner was the subtree root, then we're done, since there is nothing else left to insert.
if (!descendant)
return;
// Now that we have done this, we can continue past the spanning content, since we advanced
// descendant already.
if (descendant)
descendant = descendant->previousInPreOrder(subtreeRoot);
continue;
}
ASSERT(!m_spannerMap.get(placeholder->spanner()));
m_spannerMap.add(placeholder->spanner(), placeholder);
ASSERT(!placeholder->firstChild()); // There should be no children here, but if there are, we ought to skip them.
continue;
}
RenderBlockFlow* multicolContainer = multiColumnBlockFlow();
RenderObject* nextRendererInFlowThread = descendant->nextInPreOrderAfterChildren(this);
RenderObject* insertBeforeMulticolChild = nullptr;
if (isValidColumnSpanner(this, descendant)) {
// This is a spanner (column-span:all). Such renderers are moved from where they would
// otherwise occur in the render tree to becoming a direct child of the multicol container,
// so that they live among the column sets. This simplifies the layout implementation, and
// basically just relies on regular block layout done by the RenderBlockFlow that
// establishes the multicol container.
RenderBlockFlow* container = toRenderBlockFlow(descendant->parent());
RenderMultiColumnSet* setToSplit = nullptr;
if (nextRendererInFlowThread) {
setToSplit = findSetRendering(descendant);
if (setToSplit) {
setToSplit->setNeedsLayout();
insertBeforeMulticolChild = setToSplit->nextSibling();
}
}
// Moving a spanner's renderer so that it becomes a sibling of the column sets requires us
// to insert an anonymous placeholder in the tree where the spanner's renderer otherwise
// would have been. This is needed for a two reasons: We need a way of separating inline
// content before and after the spanner, so that it becomes separate line boxes. Secondly,
// this placeholder serves as a break point for column sets, so that, when encountered, we
// end flowing one column set and move to the next one.
RenderMultiColumnSpannerPlaceholder* placeholder = RenderMultiColumnSpannerPlaceholder::createAnonymous(this, toRenderBox(descendant), &container->style());
container->addChild(placeholder, descendant->nextSibling());
container->removeChild(*descendant);
// This is a guard to stop an ancestor flow thread from processing the spanner.
gShiftingSpanner = true;
multicolContainer->RenderBlock::addChild(descendant, insertBeforeMulticolChild);
gShiftingSpanner = false;
// The spanner has now been moved out from the flow thread, but we don't want to
// examine its children anyway. They are all part of the spanner and shouldn't trigger
// creation of column sets or anything like that. Continue at its original position in
// the tree, i.e. where the placeholder was just put.
if (subtreeRoot == descendant)
subtreeRoot = placeholder;
descendant = placeholder;
} else {
// This is regular multicol content, i.e. not part of a spanner.
if (nextRendererInFlowThread && nextRendererInFlowThread->isRenderMultiColumnSpannerPlaceholder()) {
// Inserted right before a spanner. Is there a set for us there?
RenderMultiColumnSpannerPlaceholder* placeholder = toRenderMultiColumnSpannerPlaceholder(nextRendererInFlowThread);
if (RenderObject* previous = placeholder->spanner()->previousSibling()) {
if (previous->isRenderMultiColumnSet())
continue; // There's already a set there. Nothing to do.
}
insertBeforeMulticolChild = placeholder->spanner();
} else if (RenderMultiColumnSet* lastSet = lastMultiColumnSet()) {
// This child is not an immediate predecessor of a spanner, which means that if this
// child precedes a spanner at all, there has to be a column set created for us there
// already. If it doesn't precede any spanner at all, on the other hand, we need a
// column set at the end of the multicol container. We don't really check here if the
// child inserted precedes any spanner or not (as that's an expensive operation). Just
// make sure we have a column set at the end. It's no big deal if it remains unused.
if (!lastSet->nextSibling())
continue;
}
}
// Need to create a new column set when there's no set already created. We also always insert
// another column set after a spanner. Even if it turns out that there are no renderers
// following the spanner, there may be bottom margins there, which take up space.
RenderMultiColumnSet* newSet = new RenderMultiColumnSet(*this, RenderStyle::createAnonymousStyleWithDisplay(&multicolContainer->style(), BLOCK));
newSet->initializeStyle();
multicolContainer->RenderBlock::addChild(newSet, insertBeforeMulticolChild);
invalidateRegions();
// We cannot handle immediate column set siblings at the moment (and there's no need for
// it, either). There has to be at least one spanner separating them.
ASSERT(!previousColumnSetOrSpannerSiblingOf(newSet) || !previousColumnSetOrSpannerSiblingOf(newSet)->isRenderMultiColumnSet());
ASSERT(!nextColumnSetOrSpannerSiblingOf(newSet) || !nextColumnSetOrSpannerSiblingOf(newSet)->isRenderMultiColumnSet());
}
}