void RenderMultiColumnFlowThread::autoGenerateRegionsToBlockOffset(LayoutUnit /*offset*/)
{
// This function ensures we have the correct column set information at all times.
// For a simple multi-column layout in continuous media, only one column set child is required.
// Once a column is nested inside an enclosing pagination context, the number of column sets
// required becomes 2n-1, where n is the total number of nested pagination contexts. For example:
//
// Column layout with no enclosing pagination model = 2 * 1 - 1 = 1 column set.
// Columns inside pages = 2 * 2 - 1 = 3 column sets (bottom of first page, all the subsequent pages, then the last page).
// Columns inside columns inside pages = 2 * 3 - 1 = 5 column sets.
//
// In addition, column spans will force a column set to "split" into before/after sets around the spanning element.
//
// Finally, we will need to deal with columns inside regions. If regions have variable widths, then there will need
// to be unique column sets created inside any region whose width is different from its surrounding regions. This is
// actually pretty similar to the spanning case, in that we break up the column sets whenever the width varies.
//
// FIXME: For now just make one column set. This matches the old multi-column code.
// Right now our goal is just feature parity with the old multi-column code so that we can switch over to the
// new code as soon as possible.
RenderMultiColumnSet* firstSet = toRenderMultiColumnSet(firstRegion());
if (firstSet)
return;
invalidateRegions();
RenderBlockFlow* parentBlock = toRenderBlockFlow(parent());
firstSet = new RenderMultiColumnSet(*this, RenderStyle::createAnonymousStyleWithDisplay(&parentBlock->style(), BLOCK));
firstSet->initializeStyle();
parentBlock->RenderBlock::addChild(firstSet);
// Even though we aren't placed yet, we can go ahead and set up our size. At this point we're
// typically in the middle of laying out the thread, attempting to paginate, and we need to do
// some rudimentary "layout" of the set now, so that pagination will work.
firstSet->prepareForLayout();
validateRegions();
}
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());
}
}