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();
}
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();
}
LayoutMultiColumnSpannerPlaceholder* LayoutMultiColumnFlowThread::containingColumnSpannerPlaceholder(const LayoutObject* descendant) const
{
ASSERT(descendant->isDescendantOf(this));
// Before we spend time on searching the ancestry, see if there's a quick way to determine
// whether there might be any spanners at all.
LayoutBox* firstBox = firstMultiColumnBox();
if (!firstBox || (firstBox == lastMultiColumnBox() && firstBox->isLayoutMultiColumnSet()))
return nullptr;
// We have spanners. See if the layoutObject in question is one or inside of one then.
for (const LayoutObject* ancestor = descendant; ancestor && ancestor != this; ancestor = ancestor->parent()) {
if (LayoutMultiColumnSpannerPlaceholder* placeholder = ancestor->spannerPlaceholder())
return placeholder;
}
return nullptr;
}
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);
}
