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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 RenderBlockFlow* multiColumnBlockFlow() const { return toRenderBlockFlow(parent()); }
52 RenderMultiColumnFlowThread* multiColumnFlowThread() const { return multiColumnBlockFlow()->multiColumnFlowThread(); }
53 unsigned computedColumnCount() const { return m_computedColumnCount; }
54 LayoutUnit computedColumnWidth() const { return m_computedColumnWidth; }
55 LayoutUnit computedColumnHeight() const { return m_computedColumnHeight; }
57 void setComputedColumnWidthAndCount(LayoutUnit width, unsigned count)
59 m_computedColumnWidth = width;
60 m_computedColumnCount = count;
63 LayoutUnit heightAdjustedForSetOffset(LayoutUnit height) const;
65 void updateMinimumColumnHeight(LayoutUnit height) { m_minimumColumnHeight = std::max(height, m_minimumColumnHeight); }
66 LayoutUnit minimumColumnHeight() const { return m_minimumColumnHeight; }
68 unsigned forcedBreaksCount() const { return m_contentRuns.size(); }
69 void clearForcedBreaks();
70 void addForcedBreak(LayoutUnit offsetFromFirstPage);
72 // (Re-)calculate the column height when contents are supposed to be balanced. If 'initial' is
73 // set, guess an initial column height; otherwise, stretch the column height a tad. Return true
74 // if column height changed and another layout pass is required.
75 bool recalculateBalancedHeight(bool initial);
77 // Record space shortage (the amount of space that would have been enough to prevent some
78 // element from being moved to the next column) at a column break. The smallest amount of space
79 // shortage we find is the amount with which we will stretch the column height, if it turns out
80 // after layout that the columns weren't tall enough.
81 void recordSpaceShortage(LayoutUnit spaceShortage);
83 virtual void updateLogicalWidth() OVERRIDE;
85 void prepareForLayout();
88 RenderMultiColumnSet(RenderFlowThread*);
90 virtual void computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues&) const OVERRIDE;
92 virtual void paintObject(PaintInfo&, const LayoutPoint& paintOffset) OVERRIDE;
94 virtual LayoutUnit pageLogicalWidth() const OVERRIDE { return m_computedColumnWidth; }
95 virtual LayoutUnit pageLogicalHeight() const OVERRIDE { return m_computedColumnHeight; }
97 virtual LayoutUnit pageLogicalTopForOffset(LayoutUnit offset) const OVERRIDE;
99 // FIXME: This will change once we have column sets constrained by enclosing pages, etc.
100 virtual LayoutUnit logicalHeightOfAllFlowThreadContent() const OVERRIDE { return m_computedColumnHeight; }
102 virtual void repaintFlowThreadContent(const LayoutRect& repaintRect) const OVERRIDE;
104 virtual void collectLayerFragments(LayerFragments&, const LayoutRect& layerBoundingBox, const LayoutRect& dirtyRect) OVERRIDE;
106 virtual const char* renderName() const OVERRIDE;
108 void paintColumnRules(PaintInfo&, const LayoutPoint& paintOffset);
110 LayoutUnit columnGap() const;
111 LayoutRect columnRectAt(unsigned index) const;
112 unsigned columnCount() const;
114 LayoutRect flowThreadPortionRectAt(unsigned index) const;
115 LayoutRect flowThreadPortionOverflowRect(const LayoutRect& flowThreadPortion, unsigned index, unsigned colCount, LayoutUnit colGap) const;
117 enum ColumnIndexCalculationMode {
118 ClampToExistingColumns, // Stay within the range of already existing columns.
119 AssumeNewColumns // Allow column indices outside the range of already existing columns.
121 unsigned columnIndexAtOffset(LayoutUnit, ColumnIndexCalculationMode = ClampToExistingColumns) const;
123 void setAndConstrainColumnHeight(LayoutUnit);
125 // Return the index of the content run with the currently tallest columns, taking all implicit
126 // breaks assumed so far into account.
127 unsigned findRunWithTallestColumns() const;
129 // Given the current list of content runs, make assumptions about where we need to insert
130 // implicit breaks (if there's room for any at all; depending on the number of explicit breaks),
131 // and store the results. This is needed in order to balance the columns.
132 void distributeImplicitBreaks();
134 LayoutUnit calculateBalancedHeight(bool initial) const;
136 unsigned m_computedColumnCount; // Used column count (the resulting 'N' from the pseudo-algorithm in the multicol spec)
137 LayoutUnit m_computedColumnWidth; // Used column width (the resulting 'W' from the pseudo-algorithm in the multicol spec)
138 LayoutUnit m_computedColumnHeight;
140 // The following variables are used when balancing the column set.
141 LayoutUnit m_maxColumnHeight; // Maximum column height allowed.
142 LayoutUnit m_minSpaceShortage; // The smallest amout of space shortage that caused a column break.
143 LayoutUnit m_minimumColumnHeight;
145 // A run of content without explicit (forced) breaks; i.e. a flow thread portion between two
146 // explicit breaks, between flow thread start and an explicit break, between an explicit break
147 // and flow thread end, or, in cases when there are no explicit breaks at all: between flow flow
148 // thread start and flow thread end. We need to know where the explicit breaks are, in order to
149 // figure out where the implicit breaks will end up, so that we get the columns properly
150 // balanced. A content run starts out as representing one single column, and will represent one
151 // additional column for each implicit break "inserted" there.
154 ContentRun(LayoutUnit breakOffset)
155 : m_breakOffset(breakOffset)
156 , m_assumedImplicitBreaks(0) { }
158 unsigned assumedImplicitBreaks() const { return m_assumedImplicitBreaks; }
159 void assumeAnotherImplicitBreak() { m_assumedImplicitBreaks++; }
160 LayoutUnit breakOffset() const { return m_breakOffset; }
162 // Return the column height that this content run would require, considering the implicit
163 // breaks assumed so far.
164 LayoutUnit columnLogicalHeight(LayoutUnit startOffset) const { return ceilf((m_breakOffset - startOffset).toFloat() / float(m_assumedImplicitBreaks + 1)); }
167 LayoutUnit m_breakOffset; // Flow thread offset where this run ends.
168 unsigned m_assumedImplicitBreaks; // Number of implicit breaks in this run assumed so far.
170 Vector<ContentRun, 1> m_contentRuns;
173 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderMultiColumnSet, isRenderMultiColumnSet());
175 } // namespace WebCore
177 #endif // RenderMultiColumnSet_h