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27 #ifndef RenderMultiColumnSet_h
28 #define RenderMultiColumnSet_h
30 #include "core/rendering/RenderRegionSet.h"
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.
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
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 {
46 static RenderMultiColumnSet* createAnonymous(RenderFlowThread*);
48 virtual bool isRenderMultiColumnSet() const OVERRIDE { return true; }
50 unsigned computedColumnCount() const { return m_computedColumnCount; }
51 LayoutUnit computedColumnWidth() const { return m_computedColumnWidth; }
52 LayoutUnit computedColumnHeight() const { return m_computedColumnHeight; }
54 void setComputedColumnWidthAndCount(LayoutUnit width, unsigned count)
56 m_computedColumnWidth = width;
57 m_computedColumnCount = count;
60 LayoutUnit heightAdjustedForSetOffset(LayoutUnit height) const;
62 void updateMinimumColumnHeight(LayoutUnit height) { m_minimumColumnHeight = std::max(height, m_minimumColumnHeight); }
63 LayoutUnit minimumColumnHeight() const { return m_minimumColumnHeight; }
65 unsigned forcedBreaksCount() const { return m_forcedBreaksCount; }
66 LayoutUnit forcedBreakOffset() const { return m_forcedBreakOffset; }
67 LayoutUnit maximumDistanceBetweenForcedBreaks() const { return m_maximumDistanceBetweenForcedBreaks; }
68 void clearForcedBreaks()
70 m_forcedBreaksCount = 0;
71 m_maximumDistanceBetweenForcedBreaks = 0;
72 m_forcedBreakOffset = 0;
74 void addForcedBreak(LayoutUnit offsetFromFirstPage)
76 ASSERT(!computedColumnHeight());
77 LayoutUnit distanceFromLastBreak = offsetFromFirstPage - m_forcedBreakOffset;
78 if (!distanceFromLastBreak)
80 m_forcedBreaksCount++;
81 m_maximumDistanceBetweenForcedBreaks = std::max(m_maximumDistanceBetweenForcedBreaks, distanceFromLastBreak);
82 m_forcedBreakOffset = offsetFromFirstPage;
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);
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);
96 virtual void updateLogicalWidth() OVERRIDE;
98 void prepareForLayout();
101 RenderMultiColumnSet(RenderFlowThread*);
103 virtual void computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues&) const OVERRIDE;
105 virtual void paintObject(PaintInfo&, const LayoutPoint& paintOffset) OVERRIDE;
107 virtual LayoutUnit pageLogicalWidth() const OVERRIDE { return m_computedColumnWidth; }
108 virtual LayoutUnit pageLogicalHeight() const OVERRIDE { return m_computedColumnHeight; }
110 virtual LayoutUnit pageLogicalTopForOffset(LayoutUnit offset) const OVERRIDE;
112 // FIXME: This will change once we have column sets constrained by enclosing pages, etc.
113 virtual LayoutUnit logicalHeightOfAllFlowThreadContent() const OVERRIDE { return m_computedColumnHeight; }
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; }
119 virtual void repaintFlowThreadContent(const LayoutRect& repaintRect) const OVERRIDE;
121 virtual void collectLayerFragments(LayerFragments&, const LayoutRect& layerBoundingBox, const LayoutRect& dirtyRect) OVERRIDE;
123 virtual const char* renderName() const OVERRIDE;
125 void paintColumnRules(PaintInfo&, const LayoutPoint& paintOffset);
127 LayoutUnit columnGap() const;
128 LayoutRect columnRectAt(unsigned index) const;
129 unsigned columnCount() const;
131 LayoutRect flowThreadPortionRectAt(unsigned index) const;
132 LayoutRect flowThreadPortionOverflowRect(const LayoutRect& flowThreadPortion, unsigned index, unsigned colCount, LayoutUnit colGap) const;
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.
138 unsigned columnIndexAtOffset(LayoutUnit, ColumnIndexCalculationMode = ClampToExistingColumns) const;
140 void setAndConstrainColumnHeight(LayoutUnit);
142 unsigned m_computedColumnCount;
143 LayoutUnit m_computedColumnWidth;
144 LayoutUnit m_computedColumnHeight;
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;
155 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderMultiColumnSet, isRenderMultiColumnSet());
157 } // namespace WebCore
159 #endif // RenderMultiColumnSet_h