void RenderMultiColumnBlock::ensureColumnSets()
{
// This function ensures we have the correct column set information before we get into layout.
// 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 region.
//
// 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.
if (!flowThread())
return;
RenderMultiColumnSet* columnSet = firstChild()->isRenderMultiColumnSet() ? toRenderMultiColumnSet(firstChild()) : 0;
if (!columnSet) {
columnSet = RenderMultiColumnSet::createAnonymous(flowThread());
columnSet->setStyle(RenderStyle::createAnonymousStyleWithDisplay(style(), BLOCK));
RenderBlock::addChild(columnSet, firstChild());
}
columnSet->setRequiresBalancing(requiresBalancing());
}
bool RenderMultiColumnBlock::relayoutForPagination(bool, LayoutUnit, LayoutStateMaintainer& statePusher)
{
if (m_inBalancingPass || !requiresBalancing())
return false;
m_inBalancingPass = true; // Prevent re-entering this method (and recursion into layout).
bool needsRelayout;
bool neededRelayout = false;
bool firstPass = true;
do {
// Column heights may change here because of balancing. We may have to do multiple layout
// passes, depending on how the contents is fitted to the changed column heights. In most
// cases, laying out again twice or even just once will suffice. Sometimes we need more
// passes than that, though, but the number of retries should not exceed the number of
// columns, unless we have a bug.
needsRelayout = false;
for (RenderBox* childBox = firstChildBox(); childBox; childBox = childBox->nextSiblingBox())
if (childBox != m_flowThread && childBox->isRenderMultiColumnSet()) {
RenderMultiColumnSet* multicolSet = toRenderMultiColumnSet(childBox);
if (multicolSet->calculateBalancedHeight(firstPass)) {
multicolSet->setChildNeedsLayout(MarkOnlyThis);
needsRelayout = true;
}
}
if (needsRelayout) {
// Layout again. Column balancing resulted in a new height.
neededRelayout = true;
m_flowThread->setChildNeedsLayout(MarkOnlyThis);
setChildNeedsLayout(MarkOnlyThis);
if (firstPass)
statePusher.pop();
layoutBlock(false);
}
firstPass = false;
} while (needsRelayout);
m_inBalancingPass = false;
return neededRelayout;
}