[New Multicolumn] Let a spanner's containing block be the multicol container.

Source/core/rendering/RenderMultiColumnFlowThread.cpp

 /*
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 #include "config.h"
 #include "core/rendering/RenderMultiColumnFlowThread.h"
 
 #include "core/rendering/RenderMultiColumnSet.h"
-#include "core/rendering/RenderMultiColumnSpannerSet.h"
+#include "core/rendering/RenderMultiColumnSpannerPlaceholder.h"
 
 namespace blink {
 
 RenderMultiColumnFlowThread::RenderMultiColumnFlowThread()
     : m_columnCount(1)
     , m_columnHeightAvailable(0)
     , m_inBalancingPass(false)
     , m_needsColumnHeightsRecalculation(false)
     , m_progressionIsInline(true)
+    , m_isBeingEvacuated(false)
 {
     setFlowThreadState(InsideInFlowThread);
 }
 
 RenderMultiColumnFlowThread::~RenderMultiColumnFlowThread()
 {
 }
 
 RenderMultiColumnFlowThread* RenderMultiColumnFlowThread::createAnonymous(Document& document, RenderStyle* parentStyle)
 {
@@ skipping 14 matching lines @@
 
 RenderMultiColumnSet* RenderMultiColumnFlowThread::lastMultiColumnSet() const
 {
     for (RenderObject* sibling = multiColumnBlockFlow()->lastChild(); sibling; sibling = sibling->previousSibling()) {
         if (sibling->isRenderMultiColumnSet())
             return toRenderMultiColumnSet(sibling);
     }
     return 0;
 }
 
-RenderMultiColumnSpannerSet* RenderMultiColumnFlowThread::containingColumnSpannerSet(const RenderObject* descendant) const
+RenderMultiColumnSpannerPlaceholder* RenderMultiColumnFlowThread::containingColumnSpannerPlaceholder(const RenderObject* descendant) const
 {
     ASSERT(descendant->isDescendantOf(this));
 
     // Before we spend time on searching the ancestry, see if there's a quick way to determine
     // whether there might be any spanners at all.
-    RenderMultiColumnSet* firstSet = firstMultiColumnSet();
-    if (!firstSet || (firstSet == lastMultiColumnSet() && !firstSet->isRenderMultiColumnSpannerSet()))
+    RenderBox* firstBox = firstMultiColumnBox();
+    if (!firstBox || (firstBox == lastMultiColumnBox() && firstBox->isRenderMultiColumnSet()))
         return 0;
 
     // We have spanners. See if the renderer in question is one or inside of one then.
     for (const RenderObject* ancestor = descendant; ancestor && ancestor != this; ancestor = ancestor->parent()) {
-        if (RenderMultiColumnSpannerSet* spanner = m_spannerMap.get(ancestor))
-            return spanner;
+        if (RenderMultiColumnSpannerPlaceholder* placeholder = ancestor->spannerPlaceholder())
+            return placeholder;
     }
     return 0;
 }
 
 void RenderMultiColumnFlowThread::populate()
 {
     RenderBlockFlow* multicolContainer = multiColumnBlockFlow();
     ASSERT(!nextSibling());
     // Reparent children preceding the flow thread into the flow thread. It's multicol content
     // now. At this point there's obviously nothing after the flow thread, but renderers (column
     // sets and spanners) will be inserted there as we insert elements into the flow thread.
     multicolContainer->moveChildrenTo(this, multicolContainer->firstChild(), this, true);
 }
 
 void RenderMultiColumnFlowThread::evacuateAndDestroy()
 {
     RenderBlockFlow* multicolContainer = multiColumnBlockFlow();
+    m_isBeingEvacuated = true;
 
-    // Remove all sets.
-    while (RenderMultiColumnSet* columnSet = firstMultiColumnSet())
-        columnSet->destroy();
+    // Remove all sets and spanners.
+    while (RenderBox* columnBox = firstMultiColumnBox()) {
+        ASSERT(columnBox->isAnonymous());
+        columnBox->destroy();
+    }
 
     ASSERT(!previousSibling());
     ASSERT(!nextSibling());
 
     // Finally we can promote all flow thread's children. Before we move them to the flow thread's
     // container, we need to unregister the flow thread, so that they aren't just re-added again to
     // the flow thread that we're trying to empty.
     multicolContainer->resetMultiColumnFlowThread();
     moveAllChildrenTo(multicolContainer, true);
 
@@ skipping 36 matching lines @@
         // Just before the multicol container (our parent RenderBlockFlow) finishes laying out, it
         // will call recalculateColumnHeights() on us unconditionally, but we only want that method
         // to do any work if we actually laid out the flow thread. Otherwise, the balancing
         // machinery would kick in needlessly, and trigger additional layout passes. Furthermore, we
         // actually depend on a proper flowthread layout pass in order to do balancing, since it's
         // flowthread layout that sets up content runs.
         m_needsColumnHeightsRecalculation = false;
         return;
     }
 
-    for (RenderMultiColumnSet* columnSet = firstMultiColumnSet(); columnSet; columnSet = columnSet->nextSiblingMultiColumnSet()) {
-        if (!m_inBalancingPass) {
-            // This is the initial layout pass. We need to reset the column height, because contents
-            // typically have changed.
-            columnSet->resetColumnHeight();
+    for (RenderBox* columnBox = firstMultiColumnBox(); columnBox; columnBox = columnBox->nextSiblingBox()) {
+        if (columnBox->isRenderMultiColumnSet()) {

[Julien - ping for review, 2014/12/11 19:09:37]

Should we early continue by flipping the condition? (I prefer avoiding too much
indentation but could live with the current structure).

[mstensho (USE GERRIT), 2014/12/11 21:01:14]

Done.

+            RenderMultiColumnSet* columnSet = toRenderMultiColumnSet(columnBox);
+            if (!m_inBalancingPass) {
+                // This is the initial layout pass. We need to reset the column height, because contents
+                // typically have changed.
+                columnSet->resetColumnHeight();
+            }
+        } else {
+            ASSERT(columnBox->isRenderMultiColumnSpannerPlaceholder()); // no other type is expected.
         }
     }
 
     invalidateRegions();
     m_needsColumnHeightsRecalculation = heightIsAuto();
     layout();
 }
 
 bool RenderMultiColumnFlowThread::recalculateColumnHeights()
 {
@@ skipping 51 matching lines @@
 
 void RenderMultiColumnFlowThread::createAndInsertMultiColumnSet()
 {
     RenderBlockFlow* multicolContainer = multiColumnBlockFlow();
     RenderMultiColumnSet* newSet = RenderMultiColumnSet::createAnonymous(this, multicolContainer->style());
     multicolContainer->RenderBlock::addChild(newSet);
     invalidateRegions();
 
     // We cannot handle immediate column set siblings (and there's no need for it, either).
     // There has to be at least one spanner separating them.
-    ASSERT(!newSet->previousSiblingMultiColumnSet() || newSet->previousSiblingMultiColumnSet()->isRenderMultiColumnSpannerSet());
-    ASSERT(!newSet->nextSiblingMultiColumnSet() || newSet->nextSiblingMultiColumnSet()->isRenderMultiColumnSpannerSet());
+    ASSERT(!previousSiblingMultiColumnBoxOf(newSet) || !previousSiblingMultiColumnBoxOf(newSet)->isRenderMultiColumnSet());
+    ASSERT(!nextSiblingMultiColumnBoxOf(newSet) || !nextSiblingMultiColumnBoxOf(newSet)->isRenderMultiColumnSet());
 }
 
-void RenderMultiColumnFlowThread::createAndInsertSpannerSet(RenderBox* spanner)
+void RenderMultiColumnFlowThread::createAndInsertSpannerPlaceholder(RenderBox* spanner)
 {
     RenderBlockFlow* multicolContainer = multiColumnBlockFlow();
-    RenderMultiColumnSpannerSet* newSpannerSet = RenderMultiColumnSpannerSet::createAnonymous(this, multicolContainer->style(), spanner);
-    multicolContainer->RenderBlock::addChild(newSpannerSet);
-    m_spannerMap.add(spanner, newSpannerSet);
-    invalidateRegions();
+    RenderMultiColumnSpannerPlaceholder* newPlaceholder = RenderMultiColumnSpannerPlaceholder::createAnonymous(multicolContainer->style(), spanner);
+    multicolContainer->RenderBlock::addChild(newPlaceholder);
+    spanner->setSpannerPlaceholder(newPlaceholder);
 }
 
 bool RenderMultiColumnFlowThread::descendantIsValidColumnSpanner(RenderObject* descendant) const
 {
     // We assume that we're inside the flow thread. This function is not to be called otherwise.
     ASSERT(descendant->isDescendantOf(this));
 
+    // We're evaluating if the descendant should be turned into a proper spanner. It shouldn't
+    // already be one.
+    ASSERT(!descendant->spannerPlaceholder());
+
     // The spec says that column-span only applies to in-flow block-level elements.
     if (descendant->style()->columnSpan() != ColumnSpanAll || !descendant->isBox() || descendant->isInline() || descendant->isFloatingOrOutOfFlowPositioned())
         return false;
 
     if (!descendant->containingBlock()->isRenderBlockFlow()) {
         // Needs to be in a block-flow container, and not e.g. a table.
         return false;
     }
 
     // This looks like a spanner, but if we're inside something unbreakable, it's not to be treated as one.
-    for (RenderBlock* ancestor = descendant->containingBlock(); ancestor && ancestor->flowThreadContainingBlock() == this; ancestor = ancestor->containingBlock()) {
+    for (RenderBlock* ancestor = descendant->containingBlock(); ancestor; ancestor = ancestor->containingBlock()) {
         if (ancestor->isRenderFlowThread()) {
             ASSERT(ancestor == this);
             return true;
         }
-        if (m_spannerMap.get(ancestor)) {
+        if (ancestor->spannerPlaceholder()) {
             // FIXME: do we want to support nested spanners in a different way? The outer spanner
             // has already broken out from the columns to become sized by the multicol container,
             // which may be good enough for the inner spanner. But margins, borders, padding and
             // explicit widths on the outer spanner, or on any children between the outer and inner
             // spanner, will affect the width of the inner spanner this way, which might be
             // undesirable. The spec has nothing to say on the matter.
             return false; // Ignore nested spanners.
         }
         if (ancestor->isUnsplittableForPagination())
             return false;
@@ skipping 14 matching lines @@
         ASSERT(it != m_multiColumnSetList.end());
         m_multiColumnSetList.insertBefore(it, columnSet);
     } else {
         m_multiColumnSetList.add(columnSet);
     }
     columnSet->setIsValid(true);
 }
 
 void RenderMultiColumnFlowThread::willBeRemovedFromTree()
 {
-    m_spannerMap.clear();
     // Detach all column sets from the flow thread. Cannot destroy them at this point, since they
     // are siblings of this object, and there may be pointers to this object's sibling somewhere
     // further up on the call stack.
     for (RenderMultiColumnSet* columnSet = firstMultiColumnSet(); columnSet; columnSet = columnSet->nextSiblingMultiColumnSet())
         columnSet->detachRegion();
     multiColumnBlockFlow()->resetMultiColumnFlowThread();
     RenderFlowThread::willBeRemovedFromTree();
 }
 
 void RenderMultiColumnFlowThread::flowThreadDescendantWasInserted(RenderObject* descendant)
 {
+    ASSERT(!m_isBeingEvacuated);
     // Go through the subtree that was just inserted and create column sets (needed by regular
-    // column content) and spanner sets (one needed by each spanner).
+    // column content) and spanner placeholders (one needed by each spanner).
     for (RenderObject* renderer = descendant; renderer; renderer = renderer->nextInPreOrder(descendant)) {
-        if (containingColumnSpannerSet(renderer))
-            continue; // Inside a column spanner set. Nothing to do, then.
+        if (containingColumnSpannerPlaceholder(renderer))
+            continue; // Inside a column spanner. Nothing to do, then.
         if (descendantIsValidColumnSpanner(renderer)) {
-            // This renderer is a spanner, so it needs to establish a spanner set.
-            createAndInsertSpannerSet(toRenderBox(renderer));
+            // This renderer is a spanner, so it needs to establish a spanner placeholder.
+            createAndInsertSpannerPlaceholder(toRenderBox(renderer));
             continue;
         }
         // This renderer is regular column content (i.e. not a spanner). Create a set if necessary.
-        RenderMultiColumnSet* lastSet = lastMultiColumnSet();
-        if (!lastSet || lastSet->isRenderMultiColumnSpannerSet())
+        RenderBox* lastColumnBox = lastMultiColumnBox();
+        if (!lastColumnBox || !lastColumnBox->isRenderMultiColumnSet())
             createAndInsertMultiColumnSet();
     }
 }
 
+void RenderMultiColumnFlowThread::flowThreadDescendantWillBeRemoved(RenderObject* descendant)
+{
+    if (m_isBeingEvacuated)
+        return;
+    RenderObject* next;
+    // Remove spanner placeholders that are no longer needed, and merge column sets around them.
+    for (RenderObject* renderer = descendant; renderer; renderer = next) {
+        RenderMultiColumnSpannerPlaceholder* placeholder = renderer->spannerPlaceholder();
+        if (!placeholder) {
+            next = renderer->nextInPreOrder(descendant);
+            continue;
+        }
+        next = renderer->nextInPreOrderAfterChildren(descendant); // It's a spanner. Its children are of no interest to us.
+        if (RenderBox* nextColumnBox = nextSiblingMultiColumnBoxOf(placeholder)) {
+            RenderBox* previousColumnBox = previousSiblingMultiColumnBoxOf(placeholder);
+            if (nextColumnBox && nextColumnBox->isRenderMultiColumnSet()
+                && previousColumnBox && previousColumnBox->isRenderMultiColumnSet()) {
+                // Need to merge two column sets.
+                nextColumnBox->destroy();
+                previousColumnBox->setNeedsLayout();
+                invalidateRegions();
+            }
+        }
+        placeholder->destroy();
+    }
+}
+
 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;
 }
 
 void RenderMultiColumnFlowThread::updateLogicalWidth()
 {
     LayoutUnit columnWidth;
     calculateColumnCountAndWidth(columnWidth, m_columnCount);
     setLogicalWidth(columnWidth);
 }
 
 void RenderMultiColumnFlowThread::layout()
 {
     RenderFlowThread::layout();
-    if (RenderMultiColumnSet* lastSet = lastMultiColumnSet())
-        lastSet->expandToEncompassFlowThreadContentsIfNeeded();
+    if (RenderMultiColumnSet* lastSet = lastMultiColumnSet()) {
+        if (!nextSiblingMultiColumnBoxOf(lastSet))
+            lastSet->expandToEncompassFlowThreadContentsIfNeeded();
+    }
 }
 
 void RenderMultiColumnFlowThread::setPageBreak(LayoutUnit offset, LayoutUnit spaceShortage)
 {
     // Only positive values are interesting (and allowed) here. Zero space shortage may be reported
     // when we're at the top of a column and the element has zero height. Ignore this, and also
     // ignore any negative values, which may occur when we set an early break in order to honor
     // widows in the next column.
     if (spaceShortage <= 0)
         return;
@@ skipping 26 matching lines @@
 }
 
 bool RenderMultiColumnFlowThread::isPageLogicalHeightKnown() const
 {
     if (RenderMultiColumnSet* columnSet = lastMultiColumnSet())
         return columnSet->pageLogicalHeight();
     return false;
 }
 
 }