Source/core/rendering/RenderMultiColumnFlowThread.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,
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#ifndef RenderMultiColumnFlowThread_h
#define RenderMultiColumnFlowThread_h

#include "core/rendering/RenderFlowThread.h"

namespace WebCore {

class RenderMultiColumnSet;

// Flow thread implementation for CSS multicol. This will be inserted as an anonymous child block of
// the actual multicol container (i.e. the RenderBlockFlow whose style computes to non-auto
// column-count and/or column-width). RenderMultiColumnFlowThread is the heart of the multicol
// implementation, and there is only one instance per multicol container. Child content of the
// multicol container is parented into the flow thread at the time of renderer insertion.
//
// Apart from this flow thread child, the multicol container will also have RenderMultiColumnSet
// "region" children, which are used to position the columns visually. The flow thread is in charge
// of layout, and, after having calculated the column width, it lays out content as if everything
// were in one tall single column, except that there will typically be some amount of blank space
// (also known as pagination struts) at the offsets where the actual column boundaries are. This
// way, content that needs to be preceded by a break will appear at the top of the next
// column. Content needs to be preceded by a break when there's a forced break or when the content
// is unbreakable and cannot fully fit in the same column as the preceding piece of
// content. Although a RenderMultiColumnFlowThread is laid out, it does not take up any space in its
// container. It's the RenderMultiColumnSet objects that take up the necessary amount of space, and
// make sure that the columns are painted and hit-tested correctly.
class RenderMultiColumnFlowThread FINAL : public RenderFlowThread {
public:
    virtual ~RenderMultiColumnFlowThread();

    static RenderMultiColumnFlowThread* createAnonymous(Document&, RenderStyle* parentStyle);

    virtual bool isRenderMultiColumnFlowThread() const OVERRIDE FINAL { return true; }

    RenderBlockFlow* multiColumnBlockFlow() const { return toRenderBlockFlow(parent()); }

    RenderMultiColumnSet* firstMultiColumnSet() const;
    RenderMultiColumnSet* lastMultiColumnSet() const;

    virtual void addChild(RenderObject* newChild, RenderObject* beforeChild = 0) OVERRIDE;

    // Populate the flow thread with what's currently its siblings. Called when a regular block
    // becomes a multicol container.
    void populate();

    // Empty the flow thread by moving everything to the parent. Remove all multicol specific
    // renderers. Then destroy the flow thread. Called when a multicol container becomes a regular
    // block.
    void evacuateAndDestroy();

    unsigned columnCount() const { return m_columnCount; }
    LayoutUnit columnWidth() const { return m_columnWidth; }
    LayoutUnit columnHeightAvailable() const { return m_columnHeightAvailable; }
    void setColumnHeightAvailable(LayoutUnit available) { m_columnHeightAvailable = available; }
    bool requiresBalancing() const { return !columnHeightAvailable() || multiColumnBlockFlow()->style()->columnFill() == ColumnFillBalance; }

    virtual LayoutSize columnOffset(const LayoutPoint&) const OVERRIDE FINAL;

    void layoutColumns(bool relayoutChildren, SubtreeLayoutScope&);
    bool computeColumnCountAndWidth();
    bool recalculateColumnHeights();

private:
    RenderMultiColumnFlowThread();

    virtual const char* renderName() const OVERRIDE;
    virtual void addRegionToThread(RenderRegion*) OVERRIDE;
    virtual void willBeRemovedFromTree() OVERRIDE;
    virtual void computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues&) const OVERRIDE;
    virtual void updateLogicalWidth() OVERRIDE FINAL;
    virtual void layout() OVERRIDE FINAL;
    virtual void setPageBreak(LayoutUnit offset, LayoutUnit spaceShortage) OVERRIDE;
    virtual void updateMinimumPageHeight(LayoutUnit offset, LayoutUnit minHeight) OVERRIDE;
    virtual RenderRegion* regionAtBlockOffset(LayoutUnit) const OVERRIDE;
    virtual bool addForcedRegionBreak(LayoutUnit, RenderObject* breakChild, bool isBefore, LayoutUnit* offsetBreakAdjustment = 0) OVERRIDE;
    virtual bool isPageLogicalHeightKnown() const OVERRIDE;

    unsigned m_columnCount; // The used value of column-count
    LayoutUnit m_columnWidth; // The used value of column-width
    LayoutUnit m_columnHeightAvailable; // Total height available to columns, or 0 if auto.
    bool m_inBalancingPass; // Set when relayouting for column balancing.
    bool m_needsColumnHeightsRecalculation; // Set when we need to recalculate the column set heights after layout.
};

} // namespace WebCore

#endif // RenderMultiColumnFlowThread_h