/*
* 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
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE COMPUTER, INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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*/
#ifndef RenderMultiColumnSet_h
#define RenderMultiColumnSet_h
#include "core/rendering/RenderRegionSet.h"
#include "wtf/Vector.h"
namespace WebCore {
// RenderMultiColumnSet represents a set of columns that all have the same width and height. By combining runs of same-size columns into a single
// object, we significantly reduce the number of unique RenderObjects required to represent columns.
//
// A simple multi-column block will have exactly one RenderMultiColumnSet child. A simple paginated multi-column block will have three
// RenderMultiColumnSet children: one for the content at the bottom of the first page (whose columns will have a shorter height), one
// 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
// as well).
//
// 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
// come before and after the span.
class RenderMultiColumnSet FINAL : public RenderRegionSet {
public:
static RenderMultiColumnSet* createAnonymous(RenderFlowThread*);
virtual bool isRenderMultiColumnSet() const OVERRIDE { return true; }
RenderBlockFlow* multiColumnBlockFlow() const { return toRenderBlockFlow(parent()); }
RenderMultiColumnFlowThread* multiColumnFlowThread() const { return multiColumnBlockFlow()->multiColumnFlowThread(); }
unsigned computedColumnCount() const { return m_computedColumnCount; }
LayoutUnit computedColumnWidth() const { return m_computedColumnWidth; }
LayoutUnit computedColumnHeight() const { return m_computedColumnHeight; }
void setComputedColumnWidthAndCount(LayoutUnit width, unsigned count)
{
m_computedColumnWidth = width;
m_computedColumnCount = count;
}
LayoutUnit heightAdjustedForSetOffset(LayoutUnit height) const;
void updateMinimumColumnHeight(LayoutUnit height) { m_minimumColumnHeight = std::max(height, m_minimumColumnHeight); }
LayoutUnit minimumColumnHeight() const { return m_minimumColumnHeight; }
unsigned forcedBreaksCount() const { return m_contentRuns.size(); }
void clearForcedBreaks();
void addForcedBreak(LayoutUnit offsetFromFirstPage);
// (Re-)calculate the column height when contents are supposed to be balanced. 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 recalculateBalancedHeight(bool initial);
// 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();
private:
RenderMultiColumnSet(RenderFlowThread*);
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;
// FIXME: This will change once we have column sets constrained by enclosing pages, etc.
virtual LayoutUnit logicalHeightOfAllFlowThreadContent() const OVERRIDE { return m_computedColumnHeight; }
virtual void repaintFlowThreadContent(const LayoutRect& repaintRect) const OVERRIDE;
virtual void collectLayerFragments(LayerFragments&, const LayoutRect& layerBoundingBox, const LayoutRect& dirtyRect) OVERRIDE;
virtual const char* renderName() const OVERRIDE;
void paintColumnRules(PaintInfo&, const LayoutPoint& paintOffset);
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 calculateBalancedHeight(bool initial) 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;
// A run of content without explicit (forced) breaks; i.e. a flow thread portion between two
// explicit breaks, between flow thread start and an explicit break, between an explicit break
// and flow thread end, or, in cases when there are no explicit breaks at all: between flow flow
// thread start and flow thread end. We need to know where the explicit breaks are, in order to
// figure out where the implicit breaks will end up, so that we get the columns properly
// balanced. A content run starts out as representing one single column, and will represent one
// additional column for each implicit break "inserted" there.
class ContentRun {
public:
ContentRun(LayoutUnit breakOffset)
: m_breakOffset(breakOffset)
, m_assumedImplicitBreaks(0) { }
unsigned assumedImplicitBreaks() const { return m_assumedImplicitBreaks; }
void assumeAnotherImplicitBreak() { m_assumedImplicitBreaks++; }
LayoutUnit breakOffset() const { return m_breakOffset; }
// Return the column height that this content run would require, considering the implicit
// breaks assumed so far.
LayoutUnit columnLogicalHeight(LayoutUnit startOffset) const { return ceilf((m_breakOffset - startOffset).toFloat() / float(m_assumedImplicitBreaks + 1)); }
private:
LayoutUnit m_breakOffset; // Flow thread offset where this run ends.
unsigned m_assumedImplicitBreaks; // Number of implicit breaks in this run assumed so far.
};
Vector<ContentRun, 1> m_contentRuns;
};
DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderMultiColumnSet, isRenderMultiColumnSet());
} // namespace WebCore
#endif // RenderMultiColumnSet_h