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      1 /*
      2  * Copyright (C) 2012 Apple Inc.  All rights reserved.
      3  *
      4  * Redistribution and use in source and binary forms, with or without
      5  * modification, are permitted provided that the following conditions
      6  * are met:
      7  * 1. Redistributions of source code must retain the above copyright
      8  *    notice, this list of conditions and the following disclaimer.
      9  * 2. Redistributions in binary form must reproduce the above copyright
     10  *    notice, this list of conditions and the following disclaimer in the
     11  *    documentation and/or other materials provided with the distribution.
     12  *
     13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
     14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
     17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
     18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
     19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
     20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
     21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
     23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     24  */
     25 
     26 
     27 #ifndef RenderMultiColumnSet_h
     28 #define RenderMultiColumnSet_h
     29 
     30 #include "core/rendering/RenderRegionSet.h"
     31 
     32 namespace WebCore {
     33 
     34 // RenderMultiColumnSet represents a set of columns that all have the same width and height. By combining runs of same-size columns into a single
     35 // object, we significantly reduce the number of unique RenderObjects required to represent columns.
     36 //
     37 // A simple multi-column block will have exactly one RenderMultiColumnSet child. A simple paginated multi-column block will have three
     38 // RenderMultiColumnSet children: one for the content at the bottom of the first page (whose columns will have a shorter height), one
     39 // for the 2nd to n-1 pages, and then one last column set that will hold the shorter columns on the final page (that may have to be balanced
     40 // as well).
     41 //
     42 // Column spans result in the creation of new column sets as well, since a spanning region has to be placed in between the column sets that
     43 // come before and after the span.
     44 class RenderMultiColumnSet FINAL : public RenderRegionSet {
     45 public:
     46     static RenderMultiColumnSet* createAnonymous(RenderFlowThread*);
     47 
     48     virtual bool isRenderMultiColumnSet() const OVERRIDE { return true; }
     49 
     50     unsigned computedColumnCount() const { return m_computedColumnCount; }
     51     LayoutUnit computedColumnWidth() const { return m_computedColumnWidth; }
     52     LayoutUnit computedColumnHeight() const { return m_computedColumnHeight; }
     53 
     54     void setComputedColumnWidthAndCount(LayoutUnit width, unsigned count)
     55     {
     56         m_computedColumnWidth = width;
     57         m_computedColumnCount = count;
     58     }
     59 
     60     LayoutUnit heightAdjustedForSetOffset(LayoutUnit height) const;
     61 
     62     void updateMinimumColumnHeight(LayoutUnit height) { m_minimumColumnHeight = std::max(height, m_minimumColumnHeight); }
     63     LayoutUnit minimumColumnHeight() const { return m_minimumColumnHeight; }
     64 
     65     unsigned forcedBreaksCount() const { return m_forcedBreaksCount; }
     66     LayoutUnit forcedBreakOffset() const { return m_forcedBreakOffset; }
     67     LayoutUnit maximumDistanceBetweenForcedBreaks() const { return m_maximumDistanceBetweenForcedBreaks; }
     68     void clearForcedBreaks()
     69     {
     70         m_forcedBreaksCount = 0;
     71         m_maximumDistanceBetweenForcedBreaks = 0;
     72         m_forcedBreakOffset = 0;
     73     }
     74     void addForcedBreak(LayoutUnit offsetFromFirstPage)
     75     {
     76         ASSERT(!computedColumnHeight());
     77         LayoutUnit distanceFromLastBreak = offsetFromFirstPage - m_forcedBreakOffset;
     78         if (!distanceFromLastBreak)
     79             return;
     80         m_forcedBreaksCount++;
     81         m_maximumDistanceBetweenForcedBreaks = std::max(m_maximumDistanceBetweenForcedBreaks, distanceFromLastBreak);
     82         m_forcedBreakOffset = offsetFromFirstPage;
     83     }
     84 
     85     // Calculate the column height when contents are supposed to be balanced. If 'initial' is set,
     86     // guess an initial column height; otherwise, stretch the column height a tad. Return true if
     87     // column height changed and another layout pass is required.
     88     bool calculateBalancedHeight(bool initial);
     89 
     90     // Record space shortage (the amount of space that would have been enough to prevent some
     91     // element from being moved to the next column) at a column break. The smallest amount of space
     92     // shortage we find is the amount with which we will stretch the column height, if it turns out
     93     // after layout that the columns weren't tall enough.
     94     void recordSpaceShortage(LayoutUnit spaceShortage);
     95 
     96     virtual void updateLogicalWidth() OVERRIDE;
     97 
     98     void prepareForLayout();
     99 
    100 private:
    101     RenderMultiColumnSet(RenderFlowThread*);
    102 
    103     virtual void computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues&) const OVERRIDE;
    104 
    105     virtual void paintObject(PaintInfo&, const LayoutPoint& paintOffset) OVERRIDE;
    106 
    107     virtual LayoutUnit pageLogicalWidth() const OVERRIDE { return m_computedColumnWidth; }
    108     virtual LayoutUnit pageLogicalHeight() const OVERRIDE { return m_computedColumnHeight; }
    109 
    110     virtual LayoutUnit pageLogicalTopForOffset(LayoutUnit offset) const OVERRIDE;
    111 
    112     // FIXME: This will change once we have column sets constrained by enclosing pages, etc.
    113     virtual LayoutUnit logicalHeightOfAllFlowThreadContent() const OVERRIDE { return m_computedColumnHeight; }
    114 
    115     // FIXME: For now we return false, but it's likely we will leverage the auto height region code to do column
    116     // balancing. That's why we have an override of this function that is distinct from RenderRegionSet's override.
    117     virtual bool shouldHaveAutoLogicalHeight() const OVERRIDE { return false; }
    118 
    119     virtual void repaintFlowThreadContent(const LayoutRect& repaintRect) const OVERRIDE;
    120 
    121     virtual void collectLayerFragments(LayerFragments&, const LayoutRect& layerBoundingBox, const LayoutRect& dirtyRect) OVERRIDE;
    122 
    123     virtual const char* renderName() const;
    124 
    125     void paintColumnRules(PaintInfo&, const LayoutPoint& paintOffset);
    126 
    127     LayoutUnit columnGap() const;
    128     LayoutRect columnRectAt(unsigned index) const;
    129     unsigned columnCount() const;
    130 
    131     LayoutRect flowThreadPortionRectAt(unsigned index) const;
    132     LayoutRect flowThreadPortionOverflowRect(const LayoutRect& flowThreadPortion, unsigned index, unsigned colCount, LayoutUnit colGap) const;
    133 
    134     enum ColumnIndexCalculationMode {
    135         ClampToExistingColumns, // Stay within the range of already existing columns.
    136         AssumeNewColumns // Allow column indices outside the range of already existing columns.
    137     };
    138     unsigned columnIndexAtOffset(LayoutUnit, ColumnIndexCalculationMode = ClampToExistingColumns) const;
    139 
    140     void setAndConstrainColumnHeight(LayoutUnit);
    141 
    142     unsigned m_computedColumnCount;
    143     LayoutUnit m_computedColumnWidth;
    144     LayoutUnit m_computedColumnHeight;
    145 
    146     // The following variables are used when balancing the column set.
    147     LayoutUnit m_maxColumnHeight; // Maximum column height allowed.
    148     LayoutUnit m_minSpaceShortage; // The smallest amout of space shortage that caused a column break.
    149     LayoutUnit m_minimumColumnHeight;
    150     unsigned m_forcedBreaksCount; // FIXME: We will ultimately need to cache more information to balance around forced breaks properly.
    151     LayoutUnit m_maximumDistanceBetweenForcedBreaks;
    152     LayoutUnit m_forcedBreakOffset;
    153 };
    154 
    155 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderMultiColumnSet, isRenderMultiColumnSet());
    156 
    157 } // namespace WebCore
    158 
    159 #endif // RenderMultiColumnSet_h
    160 
    161