bool MultiColumnFragmentainerGroup::heightIsAuto() const
{
// Only the last row may have auto height, and thus be balanced. There are no good reasons to
// balance the preceding rows, and that could potentially lead to an insane number of layout
// passes as well.
return isLastGroup() && m_columnSet.heightIsAuto();
}
void MultiColumnFragmentainerGroup::expandToEncompassFlowThreadOverflow()
{
ASSERT(isLastGroup());
// Get the offset within the flow thread in its block progression direction. Then get the
// flow thread's remaining logical height including its overflow and expand our rect
// to encompass that remaining height and overflow. The idea is that we will generate
// additional columns and pages to hold that overflow, since people do write bad
// content like <body style="height:0px"> in multi-column layouts.
LayoutMultiColumnFlowThread* flowThread = m_columnSet.multiColumnFlowThread();
LayoutRect layoutRect = flowThread->layoutOverflowRect();
m_logicalBottomInFlowThread = flowThread->isHorizontalWritingMode() ? layoutRect.maxY() : layoutRect.maxX();
}
bool MultiColumnFragmentainerGroup::recalculateColumnHeight(
LayoutMultiColumnSet& columnSet) {
LayoutUnit oldColumnHeight = m_columnHeight;
m_maxColumnHeight = calculateMaxColumnHeight();
// Only the last row may have auto height, and thus be balanced. There are no
// good reasons to balance the preceding rows, and that could potentially lead
// to an insane number of layout passes as well.
if (isLastGroup() && columnSet.heightIsAuto()) {
LayoutUnit newColumnHeight;
if (!columnSet.isInitialHeightCalculated()) {
// Initial balancing: Start with the lowest imaginable column height. Also
// calculate the height of the tallest piece of unbreakable content.
// Columns should never get any shorter than that (unless constrained by
// max-height). Propagate this to our containing column set, in case there
// is an outer multicol container that also needs to balance. After having
// calculated the initial column height, the multicol container needs
// another layout pass with the column height that we just calculated.
InitialColumnHeightFinder initialHeightFinder(
columnSet, logicalTopInFlowThread(), logicalBottomInFlowThread());
LayoutUnit tallestUnbreakableLogicalHeight =
initialHeightFinder.tallestUnbreakableLogicalHeight();
columnSet.propagateTallestUnbreakableLogicalHeight(
tallestUnbreakableLogicalHeight);
newColumnHeight =
std::max(initialHeightFinder.initialMinimalBalancedHeight(),
tallestUnbreakableLogicalHeight);
} else {
// Rebalancing: After having laid out again, we'll need to rebalance if
// the height wasn't enough and we're allowed to stretch it, and then
// re-lay out. There are further details on the column balancing
// machinery in ColumnBalancer and its derivates.
newColumnHeight = rebalanceColumnHeightIfNeeded();
}
setAndConstrainColumnHeight(newColumnHeight);
} else {
// The position of the column set may have changed, in which case height
// available for columns may have changed as well.
setAndConstrainColumnHeight(m_columnHeight);
}
if (m_columnHeight == oldColumnHeight)
return false; // No change. We're done.
return true; // Need another pass.
}
