Deduct pagination struts when calculating initial column height.

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 "config.h"
 
 #include "core/layout/MultiColumnFragmentainerGroup.h"
 
 #include "core/layout/ColumnBalancer.h"
 #include "core/layout/LayoutMultiColumnSet.h"
@@ skipping 37 matching lines @@
 }
 
 void MultiColumnFragmentainerGroup::resetColumnHeight()
 {
     // Nuke previously stored minimum column height. Contents may have changed for all we know.
     m_minimumColumnHeight = 0;
 
     m_maxColumnHeight = calculateMaxColumnHeight();
 
     LayoutMultiColumnFlowThread* flowThread = m_columnSet.multiColumnFlowThread();
-    LayoutMultiColumnFlowThread* enclosingFlowThread = flowThread->enclosingFlowThread();
-    if (enclosingFlowThread && enclosingFlowThread->isPageLogicalHeightKnown()) {
-        // TODO(mstensho): Do this better. If height is auto here, we shouldn't set a
-        // height, or forced breaks and pagination struts might mess up column balancing.
-        LayoutUnit columnHeight = heightIsAuto() ? m_maxColumnHeight : heightAdjustedForRowOffset(flowThread->columnHeightAvailable());
-        setAndConstrainColumnHeight(columnHeight);
-    } else if (heightIsAuto()) {
-        m_columnHeight = LayoutUnit();
+    if (heightIsAuto()) {
+        LayoutMultiColumnFlowThread* enclosingFlowThread = flowThread->enclosingFlowThread();
+        if (enclosingFlowThread && enclosingFlowThread->isPageLogicalHeightKnown()) {
+            // Even if height is auto, we set an initial height, in order to tell how much content
+            // this MultiColumnFragmentainerGroup can hold, and when we need to append a new one.
+            m_columnHeight = m_maxColumnHeight;
+        } else {
+            m_columnHeight = LayoutUnit();
+        }
     } else {
         setAndConstrainColumnHeight(heightAdjustedForRowOffset(flowThread->columnHeightAvailable()));
     }
 }
 
 bool MultiColumnFragmentainerGroup::recalculateColumnHeight(BalancedColumnHeightCalculation calculationMode)
 {
     LayoutUnit oldColumnHeight = m_columnHeight;
 
     m_maxColumnHeight = calculateMaxColumnHeight();
@@ skipping 480 matching lines @@
     append(MultiColumnFragmentainerGroup(m_columnSet));
     return last();
 }
 
 void MultiColumnFragmentainerGroupList::deleteExtraGroups()
 {
     shrink(1);
 }
 
 } // namespace blink