Paint collapsed borders of a table as one display item

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

Index: third_party/WebKit/Source/core/layout/LayoutTable.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutTable.cpp b/third_party/WebKit/Source/core/layout/LayoutTable.cpp
index 6f0b62e686cc00807ab2b155b451a7adfd20c415..7b0bc6f24a44849a4dca2d8243bb3f867fb421da 100644
--- a/third_party/WebKit/Source/core/layout/LayoutTable.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutTable.cpp
@@ -752,7 +752,7 @@ void LayoutTable::layout() {
 }
 
 void LayoutTable::invalidateCollapsedBorders() {
-  m_collapsedBorders.clear();
+  m_collapsedBordersInfo = nullptr;
   if (!collapseBorders())
     return;
 
@@ -765,24 +765,64 @@ void LayoutTable::invalidateCollapsedBorders() {
 // cache of its containing section, and invalidates itself if any border
 // changes. This method doesn't affect layout.
 void LayoutTable::recalcCollapsedBordersIfNeeded() {
-  if (m_collapsedBordersValid || !collapseBorders())
+  if (m_collapsedBordersValid)
     return;
   m_collapsedBordersValid = true;
-  m_collapsedBorders.clear();
+  m_collapsedBordersInfo = nullptr;
+  if (!collapseBorders())
+    return;
+
+  // This records if any cell changed collapsed border and the cell is on a
+  // composited layer of the cell itself, the row or the section.
+  bool changedWithChildCompositedLayers = false;
+
+  Vector<CollapsedBorderValue> values;
   for (LayoutObject* section = firstChild(); section;
        section = section->nextSibling()) {
     if (!section->isTableSection())
       continue;
+    bool sectionChanged = false;
     for (LayoutTableRow* row = toLayoutTableSection(section)->firstRow(); row;
          row = row->nextRow()) {
+      bool rowChanged = false;
       for (LayoutTableCell* cell = row->firstCell(); cell;
            cell = cell->nextCell()) {
         ASSERT(cell->table() == this);
-        cell->collectBorderValues(m_collapsedBorders);
+        bool cellChanged = cell->collectBorderValues(values);
+        rowChanged |= cellChanged;
+        sectionChanged |= cellChanged;
+        changedWithChildCompositedLayers |=
+            cellChanged && cell->isPaintInvalidationContainer();
       }
+      changedWithChildCompositedLayers |=
+          rowChanged && row->isPaintInvalidationContainer();
     }
+    changedWithChildCompositedLayers |=
+        sectionChanged && section->isPaintInvalidationContainer();
+  }
+  if (!values.isEmpty()) {
+    LayoutTableCell::sortBorderValues(values);
+    m_collapsedBordersInfo =
+        wrapUnique(new CollapsedBordersInfo(std::move(values)));
+  }
+
+  if (shouldDoFullPaintInvalidation())
+    return;
+
+  // All collapsed borders are painted on the table's composited layer.
+  // If there is no changed collapsed borders on child composited layer, the
+  // changed cells should have already set paint invalidation flags because of
+  // layout or style change that affected collapsed borders, and their paint
+  // invalidation will invalidate the rects of the cells on the table's layer.
+  // Otherwise we conservatively mark the whole table as needing paint
+  // invalidation to cover any changed cells on the table's composited layer.
+  if (changedWithChildCompositedLayers) {

[chrishtr, 2016/11/11 19:18:01]

How about using invalidatePaintRectangle of the union of the affected cells? We
will
need to make paint rectangle invalidation work for SPv2, for at least the use
case of
HTMLCanvas.

[Xianzhu, 2016/11/11 20:09:30]

Done.

The new patch issues redundant rectangle paint invalidations for the table and
cells (existing, caused by style change) when there is no composited layers
within the table. The extra cost should be trivial, and this seems the best for
code clarity and SPv2.

+    setShouldDoFullPaintInvalidation();
+  } else if (!shouldDoFullPaintInvalidation()) {
+    ObjectPaintInvalidator(*this)
+        .slowSetPaintingLayerNeedsRepaintAndInvalidateDisplayItemClient(
+            *this, PaintInvalidationStyleChange);
   }
-  LayoutTableCell::sortBorderValues(m_collapsedBorders);
 }
 
 void LayoutTable::addOverflowFromChildren() {
@@ -1662,10 +1702,10 @@ void LayoutTable::ensureIsReadyForPaintInvalidation() {
 
 PaintInvalidationReason LayoutTable::invalidatePaintIfNeeded(
     const PaintInvalidationState& paintInvalidationState) {
-  if (collapseBorders() && !m_collapsedBorders.isEmpty())
+  if (hasCollapsedBorders()) {
     paintInvalidationState.paintingLayer()
         .setNeedsPaintPhaseDescendantBlockBackgrounds();
-
+  }
   return LayoutBlock::invalidatePaintIfNeeded(paintInvalidationState);
 }