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

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
@@ skipping 10 matching lines @@
  * 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 RenderMultiColumnFlowThread_h
 #define RenderMultiColumnFlowThread_h
 
 #include "core/rendering/RenderFlowThread.h"
-#include "wtf/HashMap.h"
 
 namespace blink {
 
 class RenderMultiColumnSet;
-class RenderMultiColumnSpannerSet;
+class RenderMultiColumnSpannerPlaceholder;
 
 // 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.
 //
 // If there is any column content inside the multicol container, we create a
 // RenderMultiColumnSet. We only need to create multiple sets if there are spanners
 // (column-span:all) in the multicol container. When a spanner is inserted, content preceding it
 // gets its own set, and content succeeding it will get another set. The spanner itself will also
-// get its own set (RenderMultiColumnSpannerSet).
+// get its own placeholder between the sets (RenderMultiColumnSpannerPlaceholder), so that it gets
+// positioned and sized correctly. The column-span:all element is inside the flow thread, but its
+// containing block is the multicol container.
 //
 // The width of the flow thread is the same as the column width. The width of a column set is the
 // same as the content box width of the multicol container; in other words exactly enough to hold
 // the number of columns to be used, stacked horizontally, plus column gaps between them.
 //
 // Since it's the first child of the multicol container, the flow thread is laid out first, albeit
 // in a slightly special way, since it's not to take up any space in its ancestors. Afterwards, the
 // column sets are laid out. Column sets get their height from the columns that they hold. In single
 // column-row constrained height non-balancing cases without spanners this will simply be the same
 // as the content height of the multicol container itself. In most other cases we'll have to
@@ skipping 28 matching lines @@
 
     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;
 
-    // Return the spanner set (if any) that contains the specified renderer. This includes the
-    // renderer for the element that actually establishes the spanner too.
-    RenderMultiColumnSpannerSet* containingColumnSpannerSet(const RenderObject* descendant) const;
+    // Return the first column set or spanner placeholder.
+    RenderBox* firstMultiColumnBox() const
+    {
+        return nextSiblingBox();
+    }
+    // Return the last column set or spanner placeholder.
+    RenderBox* lastMultiColumnBox() const
+    {
+        RenderBox* lastSiblingBox = multiColumnBlockFlow()->lastChildBox();
+        return lastSiblingBox != this ? lastSiblingBox : 0;

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

This comparison warrants some explanations as it doesn't match
firstMultiColumnBox.

Also why don't we try the previous child box if that doesn't work?

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

Done.
The flow thread needs to be the first child. If the last child is the flow
thread, it means that we have no column boxes (spanner placeholders or column
sets).

+    }
+    // Return the previous sibling column set or spanner placeholder.
+    static RenderBox* previousSiblingMultiColumnBoxOf(RenderBox* renderer)

[Julien - ping for review, 2014/12/11 19:09:38]

Those are plain weird being static instead of on RenderBox (maybe with an ASSERT
that we are in a flow thread).

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

Indeed. I was afraid to bloat RenderBox too much, but if you like it, fine. :)

Done.

+    {
+        RenderBox* previousBox = renderer->previousSiblingBox();
+        if (previousBox->isRenderFlowThread())
+            return 0;
+        return previousBox;
+    }
+    // Return the next sibling column set or spanner placeholder.
+    static RenderBox* nextSiblingMultiColumnBoxOf(RenderBox* renderer)
+    {
+        return renderer->nextSiblingBox();
+    }
+
+    // Return the spanner placeholder that belongs to the spanner in the containing block chain, if
+    // any. This includes the renderer for the element that actually establishes the spanner too.
+    RenderMultiColumnSpannerPlaceholder* containingColumnSpannerPlaceholder(const RenderObject* descendant) const;
 
     // 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();
 
@@ skipping 14 matching lines @@
 
 protected:
     RenderMultiColumnFlowThread();
     void setProgressionIsInline(bool isInline) { m_progressionIsInline = isInline; }
 
     virtual void layout() override;
 
 private:
     void calculateColumnCountAndWidth(LayoutUnit& width, unsigned& count) const;
     void createAndInsertMultiColumnSet();
-    void createAndInsertSpannerSet(RenderBox* spanner);
+    void createAndInsertSpannerPlaceholder(RenderBox* spanner);
     virtual bool descendantIsValidColumnSpanner(RenderObject* descendant) const;
 
     virtual const char* renderName() const override;
     virtual void addRegionToThread(RenderMultiColumnSet*) override;
     virtual void willBeRemovedFromTree() override;
     virtual void flowThreadDescendantWasInserted(RenderObject*) override;
+    virtual void flowThreadDescendantWillBeRemoved(RenderObject*) override;
     virtual void computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues&) const override;
     virtual void updateLogicalWidth() override;
     virtual void setPageBreak(LayoutUnit offset, LayoutUnit spaceShortage) override;
     virtual void updateMinimumPageHeight(LayoutUnit offset, LayoutUnit minHeight) override;
     virtual RenderMultiColumnSet* columnSetAtBlockOffset(LayoutUnit) const override;
     virtual bool addForcedRegionBreak(LayoutUnit, RenderObject* breakChild, bool isBefore, LayoutUnit* offsetBreakAdjustment = 0) override;
     virtual bool isPageLogicalHeightKnown() const override;
 
-    typedef HashMap<const RenderObject*, RenderMultiColumnSpannerSet*> SpannerMap;
-    SpannerMap m_spannerMap;
-
     unsigned m_columnCount; // The used value of column-count
     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.
     bool m_progressionIsInline; // Always true for regular multicol. False for paged-y overflow.
+    bool m_isBeingEvacuated;
 };
 
 } // namespace blink
 
 #endif // RenderMultiColumnFlowThread_h
-