void LayoutMultiColumnFlowThread::skipColumnSpanner(LayoutBox* layoutObject, LayoutUnit logicalTopInFlowThread)
{
ASSERT(layoutObject->isColumnSpanAll());
LayoutMultiColumnSpannerPlaceholder* placeholder = layoutObject->spannerPlaceholder();
LayoutBox* previousColumnBox = placeholder->previousSiblingMultiColumnBox();
if (previousColumnBox && previousColumnBox->isLayoutMultiColumnSet()) {
LayoutMultiColumnSet* columnSet = toLayoutMultiColumnSet(previousColumnBox);
if (logicalTopInFlowThread < columnSet->logicalTopInFlowThread())
logicalTopInFlowThread = columnSet->logicalTopInFlowThread(); // Negative margins may cause this.
columnSet->endFlow(logicalTopInFlowThread);
}
LayoutBox* nextColumnBox = placeholder->nextSiblingMultiColumnBox();
if (nextColumnBox && nextColumnBox->isLayoutMultiColumnSet()) {
LayoutMultiColumnSet* nextSet = toLayoutMultiColumnSet(nextColumnBox);
m_lastSetWorkedOn = nextSet;
nextSet->beginFlow(logicalTopInFlowThread);
}
// We'll lay out of spanners after flow thread layout has finished (during layout of the spanner
// placeholders). There may be containing blocks for out-of-flow positioned descendants of the
// spanner in the flow thread, so that out-of-flow objects inside the spanner will be laid out
// as part of flow thread layout (even if the spanner itself won't). We need to add such
// out-of-flow positioned objects to their containing blocks now, or they'll never get laid
// out. Since it's non-trivial to determine if we need this, and where such out-of-flow objects
// might be, just go through the whole subtree.
for (LayoutObject* descendant = layoutObject->slowFirstChild(); descendant; descendant = descendant->nextInPreOrder()) {
if (descendant->isBox() && descendant->isOutOfFlowPositioned())
descendant->containingBlock()->insertPositionedObject(toLayoutBox(descendant));
}
}
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();
}
LayoutMultiColumnSet* LayoutMultiColumnSet::nextSiblingMultiColumnSet() const
{
for (LayoutObject* sibling = nextSibling(); sibling; sibling = sibling->nextSibling()) {
if (sibling->isLayoutMultiColumnSet())
return toLayoutMultiColumnSet(sibling);
}
return nullptr;
}
LayoutMultiColumnSet* LayoutMultiColumnFlowThread::lastMultiColumnSet() const
{
for (LayoutObject* sibling = multiColumnBlockFlow()->lastChild(); sibling; sibling = sibling->previousSibling()) {
if (sibling->isLayoutMultiColumnSet())
return toLayoutMultiColumnSet(sibling);
}
return nullptr;
}
void LayoutMultiColumnFlowThread::flowThreadDescendantWillBeRemoved(LayoutObject* descendant)
{
// This method ensures that the list of column sets and spanner placeholders reflects the
// multicol content that we'll be left with after removal of a descendant (or descendant
// subtree). See the header file for more information. Removing content may mean that we need to
// remove column sets and/or spanner placeholders.
if (m_isBeingEvacuated)
return;
if (shouldSkipInsertedOrRemovedChild(this, *descendant))
return;
bool hadContainingPlaceholder = containingColumnSpannerPlaceholder(descendant);
bool processedSomething = false;
LayoutObject* next;
// Remove spanner placeholders that are no longer needed, and merge column sets around them.
for (LayoutObject* layoutObject = descendant; layoutObject; layoutObject = next) {
if (layoutObject != descendant && shouldSkipInsertedOrRemovedChild(this, *layoutObject)) {
next = layoutObject->nextInPreOrderAfterChildren(descendant);
continue;
}
processedSomething = true;
LayoutMultiColumnSpannerPlaceholder* placeholder = layoutObject->spannerPlaceholder();
if (!placeholder) {
next = layoutObject->nextInPreOrder(descendant);
continue;
}
next = layoutObject->nextInPreOrderAfterChildren(descendant); // It's a spanner. Its children are of no interest to us.
destroySpannerPlaceholder(placeholder);
}
if (hadContainingPlaceholder || !processedSomething)
return; // No column content will be removed, so we can stop here.
// Column content will be removed. Does this mean that we should destroy a column set?
LayoutMultiColumnSpannerPlaceholder* adjacentPreviousSpannerPlaceholder = nullptr;
LayoutObject* previousLayoutObject = previousInPreOrderSkippingOutOfFlow(this, descendant);
if (previousLayoutObject && previousLayoutObject != this) {
adjacentPreviousSpannerPlaceholder = containingColumnSpannerPlaceholder(previousLayoutObject);
if (!adjacentPreviousSpannerPlaceholder)
return; // Preceded by column content. Set still needed.
}
LayoutMultiColumnSpannerPlaceholder* adjacentNextSpannerPlaceholder = nullptr;
LayoutObject* nextLayoutObject = nextInPreOrderAfterChildrenSkippingOutOfFlow(this, descendant);
if (nextLayoutObject) {
adjacentNextSpannerPlaceholder = containingColumnSpannerPlaceholder(nextLayoutObject);
if (!adjacentNextSpannerPlaceholder)
return; // Followed by column content. Set still needed.
}
// We have now determined that, with the removal of |descendant|, we should remove a column
// set. Locate it and remove it. Do it without involving mapDescendantToColumnSet(), as that
// might be very slow. Deduce the right set from the spanner placeholders that we've already
// found.
LayoutMultiColumnSet* columnSetToRemove;
if (adjacentNextSpannerPlaceholder) {
columnSetToRemove = toLayoutMultiColumnSet(adjacentNextSpannerPlaceholder->previousSiblingMultiColumnBox());
ASSERT(!adjacentPreviousSpannerPlaceholder || columnSetToRemove == adjacentPreviousSpannerPlaceholder->nextSiblingMultiColumnBox());
} else if (adjacentPreviousSpannerPlaceholder) {
columnSetToRemove = toLayoutMultiColumnSet(adjacentPreviousSpannerPlaceholder->nextSiblingMultiColumnBox());
} else {
// If there were no adjacent spanners, it has to mean that there's only one column set,
// since it's only spanners that may cause creation of multiple sets.
columnSetToRemove = firstMultiColumnSet();
ASSERT(columnSetToRemove);
ASSERT(!columnSetToRemove->nextSiblingMultiColumnSet());
}
ASSERT(columnSetToRemove);
columnSetToRemove->destroy();
}