*** DO NOT LAND *** Attempt to understand Regions complexity

Source/core/rendering/RenderMultiColumnBlock.cpp

Index: Source/core/rendering/RenderMultiColumnBlock.cpp
diff --git a/Source/core/rendering/RenderMultiColumnBlock.cpp b/Source/core/rendering/RenderMultiColumnBlock.cpp
deleted file mode 100644
index 53c1fe86a66c5df918107f3922f3ffc85aac4933..0000000000000000000000000000000000000000
--- a/Source/core/rendering/RenderMultiColumnBlock.cpp
+++ /dev/null
@@ -1,200 +0,0 @@
-/*
- * 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.
- */
-
-#include "config.h"
-#include "core/rendering/RenderMultiColumnBlock.h"
-
-#include "core/rendering/RenderMultiColumnFlowThread.h"
-#include "core/rendering/RenderMultiColumnSet.h"
-#include "core/rendering/RenderView.h"
-
-using namespace std;
-
-namespace WebCore {
-
-RenderMultiColumnBlock::RenderMultiColumnBlock(Element* element)
-    : RenderBlockFlow(element)
-    , m_flowThread(0)
-    , m_columnCount(1)
-    , m_columnWidth(0)
-    , m_columnHeightAvailable(0)
-    , m_inBalancingPass(false)
-{
-}
-
-void RenderMultiColumnBlock::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle)
-{
-    RenderBlock::styleDidChange(diff, oldStyle);
-    for (RenderBox* child = firstChildBox(); child; child = child->nextSiblingBox())
-        child->setStyle(RenderStyle::createAnonymousStyleWithDisplay(style(), BLOCK));
-}
-
-void RenderMultiColumnBlock::computeColumnCountAndWidth()
-{
-    // Calculate our column width and column count.
-    // FIXME: Can overflow on fast/block/float/float-not-removed-from-next-sibling4.html, see https://bugs.webkit.org/show_bug.cgi?id=68744
-    m_columnCount = 1;
-    m_columnWidth = contentLogicalWidth();
-
-    ASSERT(!style()->hasAutoColumnCount() || !style()->hasAutoColumnWidth());
-
-    LayoutUnit availWidth = m_columnWidth;
-    LayoutUnit colGap = columnGap();
-    LayoutUnit colWidth = max<LayoutUnit>(1, LayoutUnit(style()->columnWidth()));
-    int colCount = max<int>(1, style()->columnCount());
-
-    if (style()->hasAutoColumnWidth() && !style()->hasAutoColumnCount()) {
-        m_columnCount = colCount;
-        m_columnWidth = max<LayoutUnit>(0, (availWidth - ((m_columnCount - 1) * colGap)) / m_columnCount);
-    } else if (!style()->hasAutoColumnWidth() && style()->hasAutoColumnCount()) {
-        m_columnCount = max<LayoutUnit>(1, (availWidth + colGap) / (colWidth + colGap));
-        m_columnWidth = ((availWidth + colGap) / m_columnCount) - colGap;
-    } else {
-        m_columnCount = max<LayoutUnit>(min<LayoutUnit>(colCount, (availWidth + colGap) / (colWidth + colGap)), 1);
-        m_columnWidth = ((availWidth + colGap) / m_columnCount) - colGap;
-    }
-}
-
-bool RenderMultiColumnBlock::updateLogicalWidthAndColumnWidth()
-{
-    bool relayoutChildren = RenderBlock::updateLogicalWidthAndColumnWidth();
-    LayoutUnit oldColumnWidth = m_columnWidth;
-    computeColumnCountAndWidth();
-    if (m_columnWidth != oldColumnWidth)
-        relayoutChildren = true;
-    return relayoutChildren;
-}
-
-void RenderMultiColumnBlock::checkForPaginationLogicalHeightChange(LayoutUnit& /*pageLogicalHeight*/, bool& /*pageLogicalHeightChanged*/, bool& /*hasSpecifiedPageLogicalHeight*/)
-{
-    // We don't actually update any of the variables. We just subclassed to adjust our column height.
-    updateLogicalHeight();
-    m_columnHeightAvailable = max<LayoutUnit>(contentLogicalHeight(), 0);
-    setLogicalHeight(0);
-}
-
-bool RenderMultiColumnBlock::relayoutForPagination(bool, LayoutUnit, LayoutStateMaintainer& statePusher)
-{
-    if (m_inBalancingPass || !requiresBalancing())
-        return false;
-    m_inBalancingPass = true; // Prevent re-entering this method (and recursion into layout).
-
-    bool needsRelayout;
-    bool neededRelayout = false;
-    bool firstPass = true;
-    do {
-        // Column heights may change here because of balancing. We may have to do multiple layout
-        // passes, depending on how the contents is fitted to the changed column heights. In most
-        // cases, laying out again twice or even just once will suffice. Sometimes we need more
-        // passes than that, though, but the number of retries should not exceed the number of
-        // columns, unless we have a bug.
-        needsRelayout = false;
-        for (RenderBox* childBox = firstChildBox(); childBox; childBox = childBox->nextSiblingBox()) {
-            if (childBox != m_flowThread && childBox->isRenderMultiColumnSet()) {
-                RenderMultiColumnSet* multicolSet = toRenderMultiColumnSet(childBox);
-                if (multicolSet->calculateBalancedHeight(firstPass)) {
-                    multicolSet->setChildNeedsLayout(MarkOnlyThis);
-                    needsRelayout = true;
-                }
-            }
-        }
-
-        if (needsRelayout) {
-            // Layout again. Column balancing resulted in a new height.
-            neededRelayout = true;
-            m_flowThread->setChildNeedsLayout(MarkOnlyThis);
-            setChildNeedsLayout(MarkOnlyThis);
-            if (firstPass)
-                statePusher.pop();
-            layoutBlock(false);
-        }
-        firstPass = false;
-    } while (needsRelayout);
-    m_inBalancingPass = false;
-    return neededRelayout;
-}
-
-void RenderMultiColumnBlock::addChild(RenderObject* newChild, RenderObject* beforeChild)
-{
-    if (!m_flowThread) {
-        m_flowThread = RenderMultiColumnFlowThread::createAnonymous(&document());
-        m_flowThread->setStyle(RenderStyle::createAnonymousStyleWithDisplay(style(), BLOCK));
-        RenderBlock::addChild(m_flowThread);
-    }
-    m_flowThread->addChild(newChild, beforeChild);
-}
-
-RenderObject* RenderMultiColumnBlock::layoutSpecialExcludedChild(bool relayoutChildren, SubtreeLayoutScope& layoutScope)
-{
-    if (!m_flowThread)
-        return 0;
-
-    // Update the dimensions of our regions before we lay out the flow thread.
-    // FIXME: Eventually this is going to get way more complicated, and we will be destroying regions
-    // instead of trying to keep them around.
-    bool shouldInvalidateRegions = false;
-    for (RenderBox* childBox = firstChildBox(); childBox; childBox = childBox->nextSiblingBox()) {
-        if (childBox == m_flowThread)
-            continue;
-
-        if (relayoutChildren || childBox->needsLayout()) {
-            if (!m_inBalancingPass && childBox->isRenderMultiColumnSet())
-                toRenderMultiColumnSet(childBox)->prepareForLayout();
-            shouldInvalidateRegions = true;
-        }
-    }
-
-    if (shouldInvalidateRegions)
-        m_flowThread->invalidateRegions();
-
-    if (relayoutChildren)
-        layoutScope.setChildNeedsLayout(m_flowThread);
-
-    setLogicalTopForChild(m_flowThread, borderBefore() + paddingBefore());
-    m_flowThread->layoutIfNeeded();
-    determineLogicalLeftPositionForChild(m_flowThread);
-
-    return m_flowThread;
-}
-
-const char* RenderMultiColumnBlock::renderName() const
-{
-    if (isFloating())
-        return "RenderMultiColumnBlock (floating)";
-    if (isOutOfFlowPositioned())
-        return "RenderMultiColumnBlock (positioned)";
-    if (isAnonymousBlock())
-        return "RenderMultiColumnBlock (anonymous)";
-    // FIXME: Temporary hack while the new generated content system is being implemented.
-    if (isPseudoElement())
-        return "RenderMultiColumnBlock (generated)";
-    if (isAnonymous())
-        return "RenderMultiColumnBlock (generated)";
-    if (isRelPositioned())
-        return "RenderMultiColumnBlock (relative positioned)";
-    return "RenderMultiColumnBlock";
-}
-
-}