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27 #ifndef RenderMultiColumnSet_h
28 #define RenderMultiColumnSet_h
30 #include "core/rendering/RenderRegionSet.h"
31 #include "wtf/Vector.h"
35 // RenderMultiColumnSet represents a set of columns that all have the same width and height. By combining runs of same-size columns into a single
36 // object, we significantly reduce the number of unique RenderObjects required to represent columns.
38 // A simple multi-column block will have exactly one RenderMultiColumnSet child. A simple paginated multi-column block will have three
39 // RenderMultiColumnSet children: one for the content at the bottom of the first page (whose columns will have a shorter height), one
40 // 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
43 // 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
44 // come before and after the span.
45 class RenderMultiColumnSet FINAL : public RenderRegionSet {
47 static RenderMultiColumnSet* createAnonymous(RenderFlowThread*);
49 virtual bool isRenderMultiColumnSet() const OVERRIDE { return true; }
51 unsigned computedColumnCount() const { return m_computedColumnCount; }
52 LayoutUnit computedColumnWidth() const { return m_computedColumnWidth; }
53 LayoutUnit computedColumnHeight() const { return m_computedColumnHeight; }
55 void setComputedColumnWidthAndCount(LayoutUnit width, unsigned count)
57 m_computedColumnWidth = width;
58 m_computedColumnCount = count;
61 LayoutUnit heightAdjustedForSetOffset(LayoutUnit height) const;
63 void updateMinimumColumnHeight(LayoutUnit height) { m_minimumColumnHeight = std::max(height, m_minimumColumnHeight); }
64 LayoutUnit minimumColumnHeight() const { return m_minimumColumnHeight; }
66 unsigned forcedBreaksCount() const { return m_contentRuns.size(); }
67 void clearForcedBreaks();
68 void addForcedBreak(LayoutUnit offsetFromFirstPage);
70 // (Re-)calculate the column height when contents are supposed to be balanced. If 'initial' is
71 // set, guess an initial column height; otherwise, stretch the column height a tad. Return true
72 // if column height changed and another layout pass is required.
73 bool recalculateBalancedHeight(bool initial);
75 // Record space shortage (the amount of space that would have been enough to prevent some
76 // element from being moved to the next column) at a column break. The smallest amount of space
77 // shortage we find is the amount with which we will stretch the column height, if it turns out
78 // after layout that the columns weren't tall enough.
79 void recordSpaceShortage(LayoutUnit spaceShortage);
81 virtual void updateLogicalWidth() OVERRIDE;
83 void prepareForLayout();
86 RenderMultiColumnSet(RenderFlowThread*);
88 virtual void computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues&) const OVERRIDE;
90 virtual void paintObject(PaintInfo&, const LayoutPoint& paintOffset) OVERRIDE;
92 virtual LayoutUnit pageLogicalWidth() const OVERRIDE { return m_computedColumnWidth; }
93 virtual LayoutUnit pageLogicalHeight() const OVERRIDE { return m_computedColumnHeight; }
95 virtual LayoutUnit pageLogicalTopForOffset(LayoutUnit offset) const OVERRIDE;
97 // FIXME: This will change once we have column sets constrained by enclosing pages, etc.
98 virtual LayoutUnit logicalHeightOfAllFlowThreadContent() const OVERRIDE { return m_computedColumnHeight; }
100 virtual void repaintFlowThreadContent(const LayoutRect& repaintRect) const OVERRIDE;
102 virtual void collectLayerFragments(LayerFragments&, const LayoutRect& layerBoundingBox, const LayoutRect& dirtyRect) OVERRIDE;
104 virtual const char* renderName() const OVERRIDE;
106 void paintColumnRules(PaintInfo&, const LayoutPoint& paintOffset);
108 LayoutUnit columnGap() const;
109 LayoutRect columnRectAt(unsigned index) const;
110 unsigned columnCount() const;
112 LayoutRect flowThreadPortionRectAt(unsigned index) const;
113 LayoutRect flowThreadPortionOverflowRect(const LayoutRect& flowThreadPortion, unsigned index, unsigned colCount, LayoutUnit colGap) const;
115 enum ColumnIndexCalculationMode {
116 ClampToExistingColumns, // Stay within the range of already existing columns.
117 AssumeNewColumns // Allow column indices outside the range of already existing columns.
119 unsigned columnIndexAtOffset(LayoutUnit, ColumnIndexCalculationMode = ClampToExistingColumns) const;
121 void setAndConstrainColumnHeight(LayoutUnit);
123 // Return the index of the content run with the currently tallest columns, taking all implicit
124 // breaks assumed so far into account.
125 unsigned findRunWithTallestColumns() const;
127 // Given the current list of content runs, make assumptions about where we need to insert
128 // implicit breaks (if there's room for any at all; depending on the number of explicit breaks),
129 // and store the results. This is needed in order to balance the columns.
130 void distributeImplicitBreaks();
132 LayoutUnit calculateBalancedHeight(bool initial) const;
134 unsigned m_computedColumnCount; // Used column count (the resulting 'N' from the pseudo-algorithm in the multicol spec)
135 LayoutUnit m_computedColumnWidth; // Used column width (the resulting 'W' from the pseudo-algorithm in the multicol spec)
136 LayoutUnit m_computedColumnHeight;
138 // The following variables are used when balancing the column set.
139 LayoutUnit m_maxColumnHeight; // Maximum column height allowed.
140 LayoutUnit m_minSpaceShortage; // The smallest amout of space shortage that caused a column break.
141 LayoutUnit m_minimumColumnHeight;
143 // A run of content without explicit (forced) breaks; i.e. a flow thread portion between two
144 // explicit breaks, between flow thread start and an explicit break, between an explicit break
145 // and flow thread end, or, in cases when there are no explicit breaks at all: between flow flow
146 // thread start and flow thread end. We need to know where the explicit breaks are, in order to
147 // figure out where the implicit breaks will end up, so that we get the columns properly
148 // balanced. A content run starts out as representing one single column, and will represent one
149 // additional column for each implicit break "inserted" there.
152 ContentRun(LayoutUnit breakOffset)
153 : m_breakOffset(breakOffset)
154 , m_assumedImplicitBreaks(0) { }
156 unsigned assumedImplicitBreaks() const { return m_assumedImplicitBreaks; }
157 void assumeAnotherImplicitBreak() { m_assumedImplicitBreaks++; }
158 LayoutUnit breakOffset() const { return m_breakOffset; }
160 // Return the column height that this content run would require, considering the implicit
161 // breaks assumed so far.
162 LayoutUnit columnLogicalHeight(LayoutUnit startOffset) const { return ceilf(float(m_breakOffset - startOffset) / float(m_assumedImplicitBreaks + 1)); }
165 LayoutUnit m_breakOffset; // Flow thread offset where this run ends.
166 unsigned m_assumedImplicitBreaks; // Number of implicit breaks in this run assumed so far.
168 Vector<ContentRun, 1> m_contentRuns;
171 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderMultiColumnSet, isRenderMultiColumnSet());
173 } // namespace WebCore
175 #endif // RenderMultiColumnSet_h