Offset repeating theads correctly when two tables adjoin at a page border

third_party/WebKit/Source/core/paint/TableSectionPainter.cpp

 // Copyright 2014 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/paint/TableSectionPainter.h"
 
 #include "core/layout/LayoutTableCell.h"
 #include "core/layout/LayoutTableCol.h"
 #include "core/layout/LayoutTableRow.h"
 #include "core/paint/BoxClipper.h"
@@ skipping 24 matching lines @@
     return cell;
 }
 
 void TableSectionPainter::paintRepeatingHeaderGroup(const PaintInfo& paintInfo, const LayoutPoint& paintOffset, const CollapsedBorderValue& currentBorderValue, ItemToPaint itemToPaint)
 {
     if (!m_layoutTableSection.hasRepeatingHeaderGroup())
         return;
 
     LayoutTable* table = m_layoutTableSection.table();
     LayoutPoint paginationOffset = paintOffset;
     LayoutUnit pageHeight = table->pageLogicalHeightForOffset(LayoutUnit());

[mstensho (USE GERRIT), 2016/08/10 09:42:47]

(not for this CL) Page height isn't necessarily uniform throughout the entire
fragmentation context, so this is potentially wrong.

     // Move paginationOffset to the top of the second page.
-    paginationOffset.move(0, pageHeight - table->pageLogicalOffset());
+    LayoutUnit headerGroupOffset = table->pageLogicalOffset() + m_layoutTableSection.paginationStrutForRow(m_layoutTableSection.firstRow(), table->pageLogicalOffset());

[rhogan, 2016/08/09 20:34:39]

We need to account for any pagination strut on the header group because it, plus
the table's offset within the page, represents the position at which the header
group actually starts.

[mstensho (USE GERRIT), 2016/08/10 09:42:47]

Just an observation (probably not something to do as part of this CL): I wonder
if everything would be easier if we propagated the strut to the LayoutTable, so
that we wouldn't have to deal with it here. That might require some work, but it
would be the correct thing to do. Spec-wise, there are no break opportunities
between the top border edge of the table and the bottom edge of the first piece
of actual content (inside a cell in the first row in the first section,
typically).

+    LayoutUnit offsetToNextPage = pageHeight - intMod(headerGroupOffset, pageHeight);
+    paginationOffset.move(0, offsetToNextPage);
     // Now move paginationOffset to the top of the page the cull rect starts on.
     if (paintInfo.cullRect().m_rect.y() > paginationOffset.y())
         paginationOffset.move(0, pageHeight * static_cast<int>((paintInfo.cullRect().m_rect.y() - paginationOffset.y()) / pageHeight));
     LayoutUnit bottomBound = std::min(LayoutUnit(paintInfo.cullRect().m_rect.maxY()), paintOffset.y() + table->logicalHeight());
     while (paginationOffset.y() < bottomBound) {
         LayoutPoint nestedOffset = paginationOffset + LayoutPoint(0, m_layoutTableSection.offsetForRepeatingHeader());
         if (itemToPaint == PaintCollapsedBorders)
             paintCollapsedSectionBorders(paintInfo, nestedOffset, currentBorderValue);
         else
             paintSection(paintInfo, nestedOffset);
@@ skipping 236 matching lines @@
     DisplayItem::Type type = shadowStyle == Normal ? DisplayItem::TableSectionBoxShadowNormal : DisplayItem::TableSectionBoxShadowInset;
     if (LayoutObjectDrawingRecorder::useCachedDrawingIfPossible(paintInfo.context, m_layoutTableSection, type))
         return;
 
     LayoutRect bounds = BoxPainter(m_layoutTableSection).boundsForDrawingRecorder(paintOffset);
     LayoutObjectDrawingRecorder recorder(paintInfo.context, m_layoutTableSection, type, bounds);
     BoxPainter::paintBoxShadow(paintInfo, LayoutRect(paintOffset, m_layoutTableSection.size()), m_layoutTableSection.styleRef(), shadowStyle);
 }
 
 } // namespace blink