Column balancing support in the region based multicol implementation.

Source/core/rendering/RenderMultiColumnBlock.h

 /*
  * 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 19 matching lines @@
 #include "core/rendering/RenderBlock.h"
 
 namespace WebCore {
 
 class RenderMultiColumnFlowThread;
 
 class RenderMultiColumnBlock FINAL : public RenderBlock {
 public:
     RenderMultiColumnBlock(Element*);
 
-    LayoutUnit columnHeight() const { return m_columnHeight; }
-    void setColumnHeight(LayoutUnit columnHeight) { m_columnHeight = columnHeight; }
+    LayoutUnit columnHeightAvailable() const { return m_columnHeightAvailable; }
 
     LayoutUnit columnWidth() const { return m_columnWidth; }
     unsigned columnCount() const { return m_columnCount; }
 
     RenderMultiColumnFlowThread* flowThread() const { return m_flowThread; }
 
-    bool requiresBalancing() const { return m_requiresBalancing; }
+    bool requiresBalancing() const { return !m_columnHeightAvailable; }
 
 private:
     virtual bool isRenderMultiColumnBlock() const { return true; }
     
     virtual const char* renderName() const;
 
     virtual RenderObject* layoutSpecialExcludedChild(bool relayoutChildren) OVERRIDE;
 
     virtual void styleDidChange(StyleDifference, const RenderStyle*) OVERRIDE;
     
     virtual bool updateLogicalWidthAndColumnWidth() OVERRIDE;
     virtual void checkForPaginationLogicalHeightChange(LayoutUnit& pageLogicalHeight, bool& pageLogicalHeightChanged, bool& hasSpecifiedPageLogicalHeight) OVERRIDE;
     virtual bool relayoutForPagination(bool hasSpecifiedPageLogicalHeight, LayoutUnit pageLogicalHeight, LayoutStateMaintainer&) OVERRIDE;
 
     virtual void addChild(RenderObject* newChild, RenderObject* beforeChild = 0) OVERRIDE;
 
     void computeColumnCountAndWidth();
 
     void ensureColumnSets();
 
     RenderMultiColumnFlowThread* m_flowThread;
     unsigned m_columnCount;   // The default column count/width that are based off our containing block width. These values represent only the default,
     LayoutUnit m_columnWidth; // since a multi-column block that is split across variable width pages or regions will have different column counts and widths in each.
                               // These values will be cached (eventually) for multi-column blocks.
-    LayoutUnit m_columnHeight; // The current column height.
-    bool m_requiresBalancing; // Whether or not the block specified any kind of logical height. We have to balance by default if it didn't.
+    LayoutUnit m_columnHeightAvailable; // Total height available to columns, or 0 if auto.
+    bool m_inBalancingPass; // Set when relayouting for column balancing.
 };
 
 inline RenderMultiColumnBlock* toRenderMultiColumnBlock(RenderObject* object)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isRenderMultiColumnBlock());
     return static_cast<RenderMultiColumnBlock*>(object);
 }
 
 inline const RenderMultiColumnBlock* toRenderMultiColumnBlock(const RenderObject* object)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isRenderMultiColumnBlock());
     return static_cast<const RenderMultiColumnBlock*>(object);
 }
 
 // This will catch anyone doing an unnecessary cast.
 void toRenderMultiColumnBlock(const RenderMultiColumnBlock*);
 
 } // namespace WebCore
 
 #endif // RenderMultiColumnBlock_h