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

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

Index: third_party/WebKit/Source/core/paint/TableSectionPainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/TableSectionPainter.cpp b/third_party/WebKit/Source/core/paint/TableSectionPainter.cpp
index e1534bc61efca9ee9b6c9a575602ebd4994c4754..8dc5abdd43a1dce4ca7dddfad55f1bd607f18b96 100644
--- a/third_party/WebKit/Source/core/paint/TableSectionPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/TableSectionPainter.cpp
@@ -44,7 +44,9 @@ void TableSectionPainter::paintRepeatingHeaderGroup(const PaintInfo& paintInfo,
     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));