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

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

 // Copyright 2016 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/layout/LayoutTableBoxComponent.h"
 
 #include "core/layout/LayoutTable.h"
+#include "core/paint/ObjectPaintInvalidator.h"
 #include "core/style/ComputedStyle.h"
 
 namespace blink {
 
 bool LayoutTableBoxComponent::doCellsHaveDirtyWidth(
     const LayoutObject& tablePart,
     const LayoutTable& table,
     const StyleDifference& diff,
     const ComputedStyle& oldStyle) {
   // ComputedStyle::diffNeedsFullLayoutAndPaintInvalidation sets needsFullLayout
   // when border sizes change: checking diff.needsFullLayout() is an
   // optimization, not required for correctness.
   // TODO(dgrogan): Remove tablePart.needsLayout()? Perhaps it was an old
   // optimization but now it seems that diff.needsFullLayout() implies
   // tablePart.needsLayout().
   return diff.needsFullLayout() && tablePart.needsLayout() &&
          table.collapseBorders() &&
          !oldStyle.border().sizeEquals(tablePart.style()->border());
 }
 
+void LayoutTableBoxComponent::MutableForPainting::updatePaintResult(

[chrishtr, 2017/04/03 17:10:51]

This method is new in this CL, right? I'm not sure why it is needed now
but not before.

[Xianzhu, 2017/04/03 17:23:05]

Previously for any display item, we either paint it if it intersects paint rect
or skip painting of it. This ensures that we only need to invalidate a display
item client if required by changes of style, layout or compositing update.

This CL introduces table section and table row display items that can be bigger
than paint rect (interest rect) and clipped. As change of paint rect may affect
the display items, we also need to invalidate the display items when the
previous paint didn't paint the whole display item and paint rect changes. This
is like we invalidate a subsequence when paint rect changes.

+    PaintResult paintResult,
+    const CullRect& paintRect) {
+  // A table row or section may paint large background display item which
+  // contains paint operations of the background in each contained cell.
+  // The display item can be clipped by the paint rect to avoid painting
+  // on areas not interested. If we didn't fully paint and paint rect changes,
+  // we need to invalidate the display item.
+  auto& box = static_cast<LayoutTableBoxComponent&>(m_layoutObject);

[chrishtr, 2017/04/03 17:53:25]

I think you need a setNeedsRepaint also on the paintingLayer.

+  if (box.m_lastPaintResult != FullyPainted &&
+      box.m_lastPaintRect != paintRect) {
+    ObjectPaintInvalidator(m_layoutObject)
+        .invalidateDisplayItemClient(m_layoutObject, PaintInvalidationFull);
+  }
+
+  box.m_lastPaintResult = paintResult;
+  box.m_lastPaintRect = paintRect;
+}
+
 }  // namespace blink