Paint collapsed borders of a table as one display item

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

Index: third_party/WebKit/Source/core/paint/TablePainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/TablePainter.cpp b/third_party/WebKit/Source/core/paint/TablePainter.cpp
index 16f910484ae6263f1cb44bbaf6332af82bd83f8f..acd6d7572faefbc79922dc93fab14043c4ee5a15 100644
--- a/third_party/WebKit/Source/core/paint/TablePainter.cpp
+++ b/third_party/WebKit/Source/core/paint/TablePainter.cpp
@@ -44,31 +44,60 @@ void TablePainter::paintObject(const PaintInfo& paintInfo,
       }
     }
 
-    if (m_layoutTable.collapseBorders() &&
-        shouldPaintDescendantBlockBackgrounds(paintPhase) &&
-        m_layoutTable.style()->visibility() == EVisibility::Visible) {
-      // Using our cached sorted styles, we then do individual passes,
-      // painting each style of border from lowest precedence to highest
-      // precedence.
-      LayoutTable::CollapsedBorderValues collapsedBorders =
-          m_layoutTable.collapsedBorders();
-      size_t count = collapsedBorders.size();
-      for (size_t i = 0; i < count; ++i) {
-        for (LayoutTableSection* section = m_layoutTable.bottomSection();
-             section; section = m_layoutTable.sectionAbove(section)) {
-          LayoutPoint childPoint =
-              m_layoutTable.flipForWritingModeForChild(section, paintOffset);
-          TableSectionPainter(*section).paintCollapsedBorders(
-              paintInfoForDescendants, childPoint, collapsedBorders[i]);
-        }
-      }
-    }
+    if (shouldPaintDescendantBlockBackgrounds(paintPhase))
+      paintCollapsedBorders(paintInfoForDescendants, paintOffset);
   }
 
   if (shouldPaintSelfOutline(paintPhase))
     ObjectPainter(m_layoutTable).paintOutline(paintInfo, paintOffset);
 }
 
+void TablePainter::paintCollapsedBorders(const PaintInfo& paintInfo,
+                                         const LayoutPoint& paintOffset) {
+  if (!m_layoutTable.hasCollapsedBorders() ||
+      m_layoutTable.style()->visibility() != EVisibility::Visible)
+    return;
+
+  LayoutTable::CollapsedBordersInfo& collapsedBorders =
+      m_layoutTable.getCollapsedBordersInfo();
+
+  // Normally we don't clip individual display items by paint dirty rect

[chrishtr, 2016/11/03 21:16:29]

Is such an optimization already implemented in the old code?

[Xianzhu, 2016/11/03 21:26:55]

Yes, in TableSectionPainter, to skip painting collapsed borders for cells out of
the interest rect. Actually the new code here is to adapt to the old
optimization, because the display item may change when interest rect changes.

+  // (aka interest rect), to keep display items independent with paint dirty
+  // rect so we can just depend on paint invalidation status to repaint them.
+  // However, the collapsed border display item may be too big to contain all
+  // collapsed borders in a huge table, so we clip it to paint dirty rect.
+  // We need to invalidate the display item if the previous paint is clipped
+  // and the paint dirty rect changed.
+  if (collapsedBorders.lastPaintResult != FullyPainted &&
+      collapsedBorders.lastPaintRect != paintInfo.cullRect())
+    m_layoutTable.setDisplayItemsUncached();
+
+  if (!DrawingRecorder::useCachedDrawingIfPossible(

[chrishtr, 2016/11/03 21:16:29]

if (DrawingRecorder::useCachedDrawingIfPossible(...))
  return;

[Xianzhu, 2016/11/03 21:26:55]

Done.

+          paintInfo.context, m_layoutTable,
+          DisplayItem::kTableCollapsedBorders)) {
+    DrawingRecorder recorder(
+        paintInfo.context, m_layoutTable, DisplayItem::kTableCollapsedBorders,
+        FloatRect(LayoutRect(paintOffset, m_layoutTable.size())));
+
+    // Using our cached sorted styles, we then do individual passes, painting
+    // each style of border from lowest precedence to highest precedence.
+    PaintResult paintResult = FullyPainted;
+    for (const auto& borderValue : collapsedBorders.values) {
+      for (LayoutTableSection* section = m_layoutTable.bottomSection(); section;
+           section = m_layoutTable.sectionAbove(section)) {
+        LayoutPoint childPoint =
+            m_layoutTable.flipForWritingModeForChild(section, paintOffset);
+        if (TableSectionPainter(*section).paintCollapsedBorders(
+                paintInfo, childPoint, borderValue) ==
+            MayBeClippedByPaintDirtyRect)
+          paintResult = MayBeClippedByPaintDirtyRect;
+      }
+    }
+    collapsedBorders.lastPaintResult = paintResult;
+    collapsedBorders.lastPaintRect = paintInfo.cullRect();
+  }
+}
+
 void TablePainter::paintBoxDecorationBackground(
     const PaintInfo& paintInfo,
     const LayoutPoint& paintOffset) {