Source/core/rendering/RenderMultiColumnSet.h - chromium/blink - Git at Google

 /*
  * 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,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */


 #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
	/*
	* 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,
	* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
	* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
	* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/


	#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