Paint backgrounds of a table section/row in one display item

third_party/WebKit/Source/core/layout/LayoutTableSection.cpp

Index: third_party/WebKit/Source/core/layout/LayoutTableSection.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutTableSection.cpp b/third_party/WebKit/Source/core/layout/LayoutTableSection.cpp
index 2bde0f0ab436ca7d0be1c675afd42fcd2e7431d8..c7bef6819474dc71ccaa57ad055425335ec8efed 100644
--- a/third_party/WebKit/Source/core/layout/LayoutTableSection.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutTableSection.cpp
@@ -1280,11 +1280,8 @@ void LayoutTableSection::computeOverflowFromCells(unsigned totalRows,
   for (unsigned r = 0; r < totalRows; r++) {
     unsigned nCols = numCols(r);
     for (unsigned c = 0; c < nCols; c++) {
-      CellStruct& cs = cellAt(r, c);
-      LayoutTableCell* cell = cs.primaryCell();
-      if (!cell || cs.inColSpan)
-        continue;
-      if (r < totalRows - 1 && cell == primaryCellAt(r + 1, c))
+      const auto* cell = originatingCellAt(r, c);

[chrishtr, 2017/03/31 22:59:06]

Why the changes here?

[Xianzhu, 2017/03/31 23:26:30]

I added originatingCellAt() in a previous CL. The old code is just to find
originatingCellAt().

+      if (!cell)
         continue;
       addOverflowFromChild(cell);
 #if DCHECK_IS_ON()
@@ -1530,7 +1527,7 @@ LayoutRect LayoutTableSection::logicalRectForWritingModeAndDirection(
 
 CellSpan LayoutTableSection::dirtiedRows(const LayoutRect& damageRect) const {
   if (m_forceSlowPaintPathWithOverflowingCell)
-    return fullTableRowSpan();
+    return fullSectionRowSpan();
 
   if (!m_grid.size())
     return CellSpan(0, 0);
@@ -2138,4 +2135,13 @@ bool LayoutTableSection::mapToVisualRectInAncestorSpaceInternal(
       ancestor, transformState, flags);
 }
 
+bool LayoutTableSection::paintedOutputOfObjectHasNoEffectRegardlessOfSize()
+    const {
+  // LayoutTableSection paints background from columns.
+  if (table()->hasColElements())

[wkorman, 2017/03/31 22:15:41]

Sometimes I expect table might have col elements but no need to paint anything
due to style, is that worth considering now or in future?

[Xianzhu, 2017/03/31 23:26:30]

paintedOutputOfObjectHasNoEffectRegardlessOfSize() should be super fast
otherwise the purpose would be defeated. Table cols are rare, and I think in
many cases cols are defined to add col backgrounds, so I prefer not checking col
backgrounds.

+    return false;
+  return LayoutTableBoxComponent::
+      paintedOutputOfObjectHasNoEffectRegardlessOfSize();
+}
+
 }  // namespace blink