[New Multicolumn] Rebalance properly when child content changes.

Source/core/rendering/RenderMultiColumnSet.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 34 matching lines @@
 // coordinates to visual ones. It is in charge of both positioning columns correctly relatively to
 // the parent multicol container, and to calculate the correct translation for each column's
 // contents, and to paint any rules between them. RenderMultiColumnSet objects are used for
 // painting, hit testing, and any other type of operation that requires mapping from flow thread
 // coordinates to visual coordinates.
 //
 // Column spans result in the creation of new column sets, since a spanning renderer has to be
 // placed in between the column sets that come before and after the span.
 class RenderMultiColumnSet FINAL : public RenderRegion {
 public:
+    enum BalancedHeightCalculation { GuessFromFlowThreadPortion, StretchBySpaceShortage };
+
     static RenderMultiColumnSet* createAnonymous(RenderFlowThread*, RenderStyle* parentStyle);
 
     virtual bool isRenderMultiColumnSet() const OVERRIDE { return true; }
 
     RenderBlockFlow* multiColumnBlockFlow() const { return toRenderBlockFlow(parent()); }
     RenderMultiColumnFlowThread* multiColumnFlowThread() const
     {
         ASSERT_WITH_SECURITY_IMPLICATION(!flowThread() || flowThread()->isRenderMultiColumnFlowThread());
         return static_cast<RenderMultiColumnFlowThread*>(flowThread());
     }
 
     RenderMultiColumnSet* nextSiblingMultiColumnSet() const;
+    RenderMultiColumnSet* previousSiblingMultiColumnSet() const;
 
     LayoutUnit logicalTopInFlowThread() const { return isHorizontalWritingMode() ? flowThreadPortionRect().y() : flowThreadPortionRect().x(); }
     LayoutUnit logicalBottomInFlowThread() const { return isHorizontalWritingMode() ? flowThreadPortionRect().maxY() : flowThreadPortionRect().maxX(); }
 
     LayoutUnit logicalHeightInFlowThread() const { return isHorizontalWritingMode() ? flowThreadPortionRect().height() : flowThreadPortionRect().width(); }
 
     unsigned computedColumnCount() const { return m_computedColumnCount; }
     LayoutUnit computedColumnWidth() const { return m_computedColumnWidth; }
     LayoutUnit computedColumnHeight() const { return m_computedColumnHeight; }
 
@@ skipping 11 matching lines @@
 
     void updateMinimumColumnHeight(LayoutUnit height) { m_minimumColumnHeight = std::max(height, m_minimumColumnHeight); }
     LayoutUnit minimumColumnHeight() const { return m_minimumColumnHeight; }
 
     // Add a content run, specified by its end position. A content run is appended at every
     // forced/explicit break and at the end of the column set. The content runs are used to
     // determine where implicit/soft breaks will occur, in order to calculate an initial column
     // height.
     void addContentRun(LayoutUnit endOffsetFromFirstPage);
 
-    // (Re-)calculate the column height if it's auto. If 'initial' is set, guess an initial column
-    // height; otherwise, stretch the column height a tad. Return true if column height changed and
-    // another layout pass is required.
-    bool recalculateColumnHeight(bool initial);
+    // (Re-)calculate the column height if it's auto.
+    bool recalculateColumnHeight(BalancedHeightCalculation);
 
     // Record space shortage (the amount of space that would have been enough to prevent some
     // element from being moved to the next column) at a column break. The smallest amount of space
     // shortage we find is the amount with which we will stretch the column height, if it turns out
     // after layout that the columns weren't tall enough.
     void recordSpaceShortage(LayoutUnit spaceShortage);
 
-    virtual void updateLogicalWidth() OVERRIDE;
-
-    void prepareForLayout();
+    // Reset previously calculated column height. Will mark for layout if needed.
+    void resetColumnHeight();
 
     // Expand this set's flow thread portion rectangle to contain all trailing flow thread
     // overflow. Only to be called on the last set.
     void expandToEncompassFlowThreadContentsIfNeeded();
 
 private:
     RenderMultiColumnSet(RenderFlowThread*);
 
-    virtual void layout() OVERRIDE;
     virtual void computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues&) const OVERRIDE;
 
     virtual void paintObject(PaintInfo&, const LayoutPoint& paintOffset) OVERRIDE;
 
     virtual LayoutUnit pageLogicalWidth() const OVERRIDE { return m_computedColumnWidth; }
     virtual LayoutUnit pageLogicalHeight() const OVERRIDE { return m_computedColumnHeight; }
 
     virtual LayoutUnit pageLogicalTopForOffset(LayoutUnit offset) const OVERRIDE;
 
     virtual LayoutUnit logicalHeightOfAllFlowThreadContent() const OVERRIDE { return logicalHeightInFlowThread(); }
 
     virtual void repaintFlowThreadContent(const LayoutRect& repaintRect) const OVERRIDE;
 
     virtual void collectLayerFragments(LayerFragments&, const LayoutRect& layerBoundingBox, const LayoutRect& dirtyRect) OVERRIDE;
 
+    virtual void addOverflowFromChildren() OVERRIDE;
+
     virtual const char* renderName() const OVERRIDE;
 
     void paintColumnRules(PaintInfo&, const LayoutPoint& paintOffset);
 
+    LayoutUnit calculateMaxColumnHeight() const;
     LayoutUnit columnGap() const;
     LayoutRect columnRectAt(unsigned index) const;
     unsigned columnCount() const;
 
     LayoutRect flowThreadPortionRectAt(unsigned index) const;
     LayoutRect flowThreadPortionOverflowRect(const LayoutRect& flowThreadPortion, unsigned index, unsigned colCount, LayoutUnit colGap) const;
 
     enum ColumnIndexCalculationMode {
         ClampToExistingColumns, // Stay within the range of already existing columns.
         AssumeNewColumns // Allow column indices outside the range of already existing columns.
     };
     unsigned columnIndexAtOffset(LayoutUnit, ColumnIndexCalculationMode = ClampToExistingColumns) const;
 
     void setAndConstrainColumnHeight(LayoutUnit);
 
     // Return the index of the content run with the currently tallest columns, taking all implicit
     // breaks assumed so far into account.
     unsigned findRunWithTallestColumns() const;
 
     // Given the current list of content runs, make assumptions about where we need to insert
     // implicit breaks (if there's room for any at all; depending on the number of explicit breaks),
     // and store the results. This is needed in order to balance the columns.
     void distributeImplicitBreaks();
 
-    LayoutUnit calculateColumnHeight(bool initial) const;
+    LayoutUnit calculateColumnHeight(BalancedHeightCalculation) const;
 
     unsigned m_computedColumnCount; // Used column count (the resulting 'N' from the pseudo-algorithm in the multicol spec)
     LayoutUnit m_computedColumnWidth; // Used column width (the resulting 'W' from the pseudo-algorithm in the multicol spec)
     LayoutUnit m_computedColumnHeight;
 
     // The following variables are used when balancing the column set.
     LayoutUnit m_maxColumnHeight; // Maximum column height allowed.
     LayoutUnit m_minSpaceShortage; // The smallest amout of space shortage that caused a column break.
     LayoutUnit m_minimumColumnHeight;
 
@@ skipping 24 matching lines @@
     };
     Vector<ContentRun, 1> m_contentRuns;
 };
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderMultiColumnSet, isRenderMultiColumnSet());
 
 } // namespace WebCore
 
 #endif // RenderMultiColumnSet_h