Source/core/rendering/RenderMultiColumnFlowThread.cpp

/*
 * Copyright (C) 2012 Apple Inc.  All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
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 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
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#include "config.h"
#include "core/rendering/RenderMultiColumnFlowThread.h"

#include "core/rendering/RenderMultiColumnBlock.h"
#include "core/rendering/RenderMultiColumnSet.h"

namespace WebCore {

RenderMultiColumnFlowThread::RenderMultiColumnFlowThread()
{
    setFlowThreadState(InsideInFlowThread);
}

RenderMultiColumnFlowThread::~RenderMultiColumnFlowThread()
{
}

RenderMultiColumnFlowThread* RenderMultiColumnFlowThread::createAnonymous(Document* document)
{
    RenderMultiColumnFlowThread* renderer = new (document->renderArena()) RenderMultiColumnFlowThread();
    renderer->setDocumentForAnonymous(document);
    return renderer;
}

const char* RenderMultiColumnFlowThread::renderName() const
{
    return "RenderMultiColumnFlowThread";
}

void RenderMultiColumnFlowThread::computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues& computedValues) const
{
    // We simply remain at our intrinsic height.
    computedValues.m_extent = logicalHeight;
    computedValues.m_position = logicalTop;
}

LayoutUnit RenderMultiColumnFlowThread::initialLogicalWidth() const
{
    RenderMultiColumnBlock* parentBlock = toRenderMultiColumnBlock(parent());
    return parentBlock->columnWidth();
}

void RenderMultiColumnFlowThread::autoGenerateRegionsToBlockOffset(LayoutUnit /*offset*/)
{
    // This function ensures we have the correct column set information at all times.
    // For a simple multi-column layout in continuous media, only one column set child is required.
    // Once a column is nested inside an enclosing pagination context, the number of column sets
    // required becomes 2n-1, where n is the total number of nested pagination contexts. For example:
    //
    // Column layout with no enclosing pagination model = 2 * 1 - 1 = 1 column set.
    // Columns inside pages = 2 * 2 - 1 = 3 column sets (bottom of first page, all the subsequent pages, then the last page).
    // Columns inside columns inside pages = 2 * 3 - 1 = 5 column sets.
    //
    // In addition, column spans will force a column set to "split" into before/after sets around the spanning element.
    //
    // Finally, we will need to deal with columns inside regions. If regions have variable widths, then there will need
    // to be unique column sets created inside any region whose width is different from its surrounding regions. This is
    // actually pretty similar to the spanning case, in that we break up the column sets whenever the width varies.
    //
    // FIXME: For now just make one column set. This matches the old multi-column code.
    // Right now our goal is just feature parity with the old multi-column code so that we can switch over to the
    // new code as soon as possible.
    RenderMultiColumnSet* firstSet = toRenderMultiColumnSet(firstRegion());
    if (firstSet)
        return;

    invalidateRegions();

    RenderMultiColumnBlock* parentBlock = toRenderMultiColumnBlock(parent());
    firstSet = RenderMultiColumnSet::createAnonymous(this);
    firstSet->setStyle(RenderStyle::createAnonymousStyleWithDisplay(parentBlock->style(), BLOCK));
    parentBlock->RenderBlock::addChild(firstSet);

    // Even though we aren't placed yet, we can go ahead and set up our size. At this point we're
    // typically in the middle of laying out the thread, attempting to paginate, and we need to do
    // some rudimentary "layout" of the set now, so that pagination will work.
    firstSet->prepareForLayout();

    validateRegions();
}

void RenderMultiColumnFlowThread::setPageBreak(LayoutUnit offset, LayoutUnit spaceShortage)
{
    if (RenderMultiColumnSet* multicolSet = toRenderMultiColumnSet(regionAtBlockOffset(offset)))
        multicolSet->recordSpaceShortage(spaceShortage);
}

void RenderMultiColumnFlowThread::updateMinimumPageHeight(LayoutUnit offset, LayoutUnit minHeight)
{
    if (RenderMultiColumnSet* multicolSet = toRenderMultiColumnSet(regionAtBlockOffset(offset)))
        multicolSet->updateMinimumColumnHeight(minHeight);
}

}