Support for mapping from outer/visual to flowthread coord space in nested multicol.

third_party/WebKit/Source/core/layout/LayoutMultiColumnSet.cpp

 /*
  * 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 46 matching lines @@
         return 0;
     // TODO(mstensho): Introduce an interval tree or similar to speed up this.
     for (unsigned index = 0; index < m_fragmentainerGroups.size(); index++) {
         const auto& row = m_fragmentainerGroups[index];
         if (row.logicalTopInFlowThread() <= flowThreadOffset && row.logicalBottomInFlowThread() > flowThreadOffset)
             return index;
     }
     return m_fragmentainerGroups.size() - 1;
 }
 
-const MultiColumnFragmentainerGroup& LayoutMultiColumnSet::fragmentainerGroupAtVisualPoint(const LayoutPoint&) const
+const MultiColumnFragmentainerGroup& LayoutMultiColumnSet::fragmentainerGroupAtVisualPoint(const LayoutPoint& visualPoint) const
 {
-    // FIXME: implement this, once we have support for multiple rows.
-    return m_fragmentainerGroups.first();
+    LayoutUnit blockOffset = isHorizontalWritingMode() ? visualPoint.y() : visualPoint.x();
+    for (unsigned index = 0; index < m_fragmentainerGroups.size(); index++) {
+        const auto& row = m_fragmentainerGroups[index];
+        if (row.logicalTop() + row.logicalHeight() > blockOffset)
+            return row;
+    }
+    return m_fragmentainerGroups.last();

[eae, 2016/04/22 19:35:39]

Do we need to assert that there is at least one entry in m_fragmentainerGroups?

[mstensho (USE GERRIT), 2016/04/22 19:46:00]

I was thinking that it really shouldn't be necessary, but I see now that
fragmentainerGroupIndexAtFlowThreadOffset() (the method above) does it, so I
think it makes sense to add it here too, for the sake of consistency and lurking
dragons.

Done.

 }
 
 LayoutUnit LayoutMultiColumnSet::pageLogicalHeightForOffset(LayoutUnit offsetInFlowThread) const
 {
     const MultiColumnFragmentainerGroup &lastRow = lastFragmentainerGroup();
     if (!lastRow.logicalHeight()) {
         // In the first layout pass of an auto-height multicol container, height isn't set. No need
         // to perform the series of complicated dance steps below to figure out that we should
         // simply return 0. Bail now.
         ASSERT(m_fragmentainerGroups.size() == 1);
@@ skipping 386 matching lines @@
 
 LayoutRect LayoutMultiColumnSet::flowThreadPortionRect() const
 {
     LayoutRect portionRect(LayoutUnit(), logicalTopInFlowThread(), pageLogicalWidth(), logicalHeightInFlowThread());
     if (!isHorizontalWritingMode())
         return portionRect.transposedRect();
     return portionRect;
 }
 
 } // namespace blink