[New Multicolumn] flowThreadTranslationAtOffset() needs to be relative to the flow thread.

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/LayoutMultiColumnSet.h"
 
@@ skipping 117 matching lines @@
     LayoutMultiColumnFlowThread* flowThread = m_columnSet.multiColumnFlowThread();
     LayoutRect layoutRect = flowThread->layoutOverflowRect();
     m_logicalBottomInFlowThread = flowThread->isHorizontalWritingMode() ? layoutRect.maxY() : layoutRect.maxX();
 }
 
 LayoutSize MultiColumnFragmentainerGroup::flowThreadTranslationAtOffset(LayoutUnit offsetInFlowThread) const
 {
     unsigned columnIndex = columnIndexAtOffset(offsetInFlowThread);
     LayoutRect portionRect(flowThreadPortionRectAt(columnIndex));
     m_columnSet.flipForWritingMode(portionRect);
-    LayoutRect columnRect(columnRectAt(columnIndex));
-    m_columnSet.flipForWritingMode(columnRect);
-    return columnRect.location() - portionRect.location();
+    LayoutSize translation(translationAtColumn(columnIndex));
+    // TODO(mstensho): need a rectangle (not a point) to flip for writing mode here, once we get support for multiple rows.
+    return toLayoutPoint(translation) - portionRect.location();
 }
 
 LayoutUnit MultiColumnFragmentainerGroup::columnLogicalTopForOffset(LayoutUnit offsetInFlowThread) const
 {
     unsigned columnIndex = columnIndexAtOffset(offsetInFlowThread, AssumeNewColumns);
     return logicalTopInFlowThreadAt(columnIndex);
 }
 
 LayoutPoint MultiColumnFragmentainerGroup::visualPointToFlowThreadPoint(const LayoutPoint& visualPoint) const
 {
@@ skipping 280 matching lines @@
     // amount of space shortage found during layout.
 
     ASSERT(m_minSpaceShortage > 0); // We should never _shrink_ the height!
     ASSERT(m_minSpaceShortage != LayoutFlowThread::maxLogicalHeight()); // If this happens, we probably have a bug.
     if (m_minSpaceShortage == LayoutFlowThread::maxLogicalHeight())
         return m_columnHeight; // So bail out rather than looping infinitely.
 
     return m_columnHeight + m_minSpaceShortage;
 }
 
+LayoutSize MultiColumnFragmentainerGroup::translationAtColumn(unsigned columnIndex) const
+{
+    LayoutUnit logicalTopOffset;
+    LayoutUnit logicalLeftOffset;
+    LayoutUnit columnGap = m_columnSet.columnGap();
+    if (m_columnSet.multiColumnFlowThread()->progressionIsInline()) {
+        logicalLeftOffset = columnIndex * (m_columnSet.pageLogicalWidth() + columnGap);
+        if (!m_columnSet.style()->isLeftToRightDirection())
+            logicalLeftOffset = -logicalLeftOffset;
+    } else {
+        logicalTopOffset = columnIndex * (m_columnHeight + columnGap);
+    }
+
+    LayoutSize offset(logicalLeftOffset, logicalTopOffset);
+    return m_columnSet.isHorizontalWritingMode() ? offset : offset.transposedSize();
+}
+
 LayoutRect MultiColumnFragmentainerGroup::columnRectAt(unsigned columnIndex) const
 {
     LayoutUnit columnLogicalWidth = m_columnSet.pageLogicalWidth();
     LayoutUnit columnLogicalHeight = m_columnHeight;
     LayoutUnit columnLogicalTop;
     LayoutUnit columnLogicalLeft;
     LayoutUnit columnGap = m_columnSet.columnGap();
 
     if (m_columnSet.multiColumnFlowThread()->progressionIsInline()) {
         if (m_columnSet.style()->isLeftToRightDirection())
@@ skipping 102 matching lines @@
     append(MultiColumnFragmentainerGroup(m_columnSet));
     return last();
 }
 
 void MultiColumnFragmentainerGroupList::deleteExtraGroups()
 {
     shrink(1);
 }
 
 } // namespace blink