Column balancing refactoring. Don't propagate data during layout.

third_party/WebKit/Source/core/layout/LayoutMultiColumnFlowThread.cpp

 /*
  * Copyright (C) 2012 Apple Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 429 matching lines @@
         return toLayoutMultiColumnFlowThread(locateFlowThreadContainingBlockOf(*multiColumnBlockFlow()));
     return nullptr;
 }
 
 bool LayoutMultiColumnFlowThread::hasFragmentainerGroupForColumnAt(LayoutUnit offsetInFlowThread) const
 {
     // If there's no enclosing flow thread, there'll always be only one fragmentainer group, and it
     // can hold as many columns as we like. We shouldn't even be here in that case.
     ASSERT(enclosingFlowThread());
 
+    if (!isPageLogicalHeightKnown()) {
+        // If we have no clue about the height of the multicol container, bail. This situation
+        // occurs initially when an auto-height multicol container is nested inside another
+        // auto-height multicol container. We need at least an estimated height of the outer
+        // multicol container before we can check what an inner fragmentainer group has room for.
+        // Its height height is indefinite for now.
+        return true;
+    }
+
     LayoutMultiColumnSet* lastColumnSet = lastMultiColumnSet();
     if (!lastColumnSet) {
         ASSERT_NOT_REACHED();
         return true;
     }
     if (lastColumnSet->logicalTopInFlowThread() > offsetInFlowThread)
         return true;
     const MultiColumnFragmentainerGroup& lastRow = lastColumnSet->lastFragmentainerGroup();
     if (lastRow.logicalTopInFlowThread() > offsetInFlowThread)
         return true;
@@ skipping 458 matching lines @@
             // remaining in the currently last row.
             LayoutRect layoutRect = layoutOverflowRect();
             LayoutUnit logicalBottomInFlowThread = isHorizontalWritingMode() ? layoutRect.maxY() : layoutRect.maxX();
             ASSERT(logicalBottomInFlowThread >= logicalHeight());
             lastSet->endFlow(logicalBottomInFlowThread);
         }
     }
     m_lastSetWorkedOn = nullptr;
 }
 
-void LayoutMultiColumnFlowThread::setPageBreak(LayoutUnit offset, LayoutUnit spaceShortage)
+void LayoutMultiColumnFlowThread::contentWasLaidOut(LayoutUnit logicalTopInFlowThreadAfterPagination)
 {
-    // Only positive values are interesting (and allowed) here. Zero space shortage may be reported
-    // when we're at the top of a column and the element has zero height. Ignore this, and also
-    // ignore any negative values, which may occur when we set an early break in order to honor
-    // widows in the next column.
-    if (spaceShortage <= 0)
+    // Check if we need another fragmentainer group. If we've run out of columns in the last
+    // fragmentainer group (column row), we need to insert another fragmentainer group to hold more
+    // columns.
+    if (!multiColumnBlockFlow()->isInsideFlowThread())
+        return; // Early bail. We're not nested, so waste no more time on this.
+    if (!isInInitialLayoutPass()) {
+        // We only insert additional fragmentainer groups in the initial layout pass. We only want
+        // to balance columns in the last fragmentainer group (if we need to balance at all), so we
+        // want that last fragmentainer group to be the same one in all layout passes that follow.
         return;
-
-    if (LayoutMultiColumnSet* multicolSet = columnSetAtBlockOffset(offset))
-        multicolSet->recordSpaceShortage(offset, spaceShortage);
+    }
+    LayoutMultiColumnSet* columnSet = columnSetAtBlockOffset(logicalTopInFlowThreadAfterPagination);
+    if (!columnSet)
+        return;
+    MultiColumnFragmentainerGroup& row = columnSet->fragmentainerGroupAtFlowThreadOffset(logicalTopInFlowThreadAfterPagination);
+    if (!row.isLastGroup())
+        return;
+    appendNewFragmentainerGroupIfNeeded(logicalTopInFlowThreadAfterPagination);
 }
 
 void LayoutMultiColumnFlowThread::updateMinimumPageHeight(LayoutUnit offset, LayoutUnit minHeight)
 {
     if (LayoutMultiColumnSet* multicolSet = columnSetAtBlockOffset(offset))
         multicolSet->updateMinimumColumnHeight(offset, minHeight);
 }
 
-bool LayoutMultiColumnFlowThread::addForcedColumnBreak(LayoutUnit offset, LayoutObject* /*breakChild*/, bool /*isBefore*/, LayoutUnit* offsetBreakAdjustment)
-{
-    if (LayoutMultiColumnSet* multicolSet = columnSetAtBlockOffset(offset)) {
-        multicolSet->addContentRun(offset);
-        if (offsetBreakAdjustment)
-            *offsetBreakAdjustment = pageLogicalHeightForOffset(offset) ? pageRemainingLogicalHeightForOffset(offset, AssociateWithFormerPage) : LayoutUnit();
-        return true;
-    }
-    return false;
 }
-
-}