Support for multiple block fragments in getClientRects().

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/layout/MultiColumnFragmentainerGroup.h"
 
 #include "core/layout/ColumnBalancer.h"
 #include "core/layout/FragmentationContext.h"
 #include "core/layout/LayoutMultiColumnSet.h"
 
@@ skipping 419 matching lines @@
         return 0;
     return std::min(unsigned(index), actualColumnCount() - 1);
 }
 
 void MultiColumnFragmentainerGroup::columnIntervalForBlockRangeInFlowThread(LayoutUnit logicalTopInFlowThread, LayoutUnit logicalBottomInFlowThread, unsigned& firstColumn, unsigned& lastColumn) const
 {
     logicalTopInFlowThread = std::max(logicalTopInFlowThread, this->logicalTopInFlowThread());
     logicalBottomInFlowThread = std::min(logicalBottomInFlowThread, this->logicalBottomInFlowThread());
     ASSERT(logicalTopInFlowThread <= logicalBottomInFlowThread);
     firstColumn = columnIndexAtOffset(logicalTopInFlowThread, LayoutBox::AssociateWithLatterPage);
-    lastColumn = columnIndexAtOffset(logicalBottomInFlowThread, LayoutBox::AssociateWithFormerPage);
+    if (logicalBottomInFlowThread == logicalTopInFlowThread) {
+        // Zero-height block range. There'll be one column in the interval. Set it right away. This
+        // is important if we're at a column boundary, since calling columnIndexAtOffset() with the
+        // end-exclusive bottom offset would actually give us the *previous* column.
+        lastColumn = firstColumn;

[mstensho (USE GERRIT), 2016/09/28 19:58:55]

There's something fishy about this whole PageBoundaryRule business. I don't like
to do what I'm doing here.

[eae, 2016/09/28 20:55:17]

Yeah, this smells bad. Would you mind filing a bug about it and adding a link
here?

[mstensho (USE GERRIT), 2016/09/28 21:20:23]

Good idea! crbug.com/651213

+    } else {
+        lastColumn = columnIndexAtOffset(logicalBottomInFlowThread, LayoutBox::AssociateWithFormerPage);
+    }
 }
 
 void MultiColumnFragmentainerGroup::columnIntervalForVisualRect(const LayoutRect& rect, unsigned& firstColumn, unsigned& lastColumn) const
 {
     bool isColumnProgressionInline = m_columnSet.multiColumnFlowThread()->progressionIsInline();
     bool isFlippedColumnProgression = !m_columnSet.style()->isLeftToRightDirection() && isColumnProgressionInline;
     if (m_columnSet.isHorizontalWritingMode() == isColumnProgressionInline) {
         if (isFlippedColumnProgression) {
             firstColumn = columnIndexAtVisualPoint(rect.maxXMinYCorner());
             lastColumn = columnIndexAtVisualPoint(rect.minXMinYCorner());
@@ skipping 33 matching lines @@
     append(MultiColumnFragmentainerGroup(m_columnSet));
     return last();
 }
 
 void MultiColumnFragmentainerGroupList::deleteExtraGroups()
 {
     shrink(1);
 }
 
 } // namespace blink