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 27 matching lines @@
 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());
 
     // Move paginationOffset to the top of the next page.
-    LayoutUnit offsetToNextPage = pageHeight - intMod(table->pageLogicalOffset(), pageHeight);
+    // The header may have a pagination strut before it so we need to account for that when establishing its position.
+    LayoutUnit headerGroupOffset = table->pageLogicalOffset() + m_layoutTableSection.paginationStrutForRow(m_layoutTableSection.firstRow(), table->pageLogicalOffset());

[mstensho (USE GERRIT), 2016/08/10 09:42:48]

m_layoutTableSection.firstRow() may be nullptr.

What's the difference between calculating the pagination strut for the first
row, and simply using its logicalTop(), BTW?

[rhogan, 2016/08/10 18:05:14]

We don't propagate the strut to the logical top of the row or the section, we
just add it to the logicalHeight() of the row. We don't even store it like we do
for LayoutBox. I'm thinking it might be cleaner to just store it on the
paginationStrut() on the LayoutTableRow rather than calculate it like this. We
only need to call on it when the section is a header group but I guess it would
be less confusing to store it in all cases.

+    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
@@ skipping 237 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