[SPInvalidation] Handle pixel-snapping of paint invalidation rects

third_party/WebKit/Source/core/paint/BoxPaintInvalidator.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/paint/BoxPaintInvalidator.h"
 
 #include "core/frame/Settings.h"
 #include "core/layout/LayoutView.h"
 #include "core/paint/ObjectPaintInvalidator.h"
 #include "core/paint/PaintInvalidator.h"
@@ skipping 139 matching lines @@
     // invalidated for box changes, because the background always covers the
     // whole document rect and clipping is done by
     // compositor()->m_containerLayer. Also the scrollbars are always
     // composited. There are no other box decoration on the LayoutView thus we
     // can safely exit here.
     if (layoutView.usesCompositing() &&
         !RuntimeEnabledFeatures::rootLayerScrollingEnabled())
       return reason;
   }
 
-  // If the transform is not identity or translation, incremental invalidation
-  // is not applicable because the difference between oldBounds and newBounds
-  // doesn't cover all area needing invalidation.
-  // FIXME: Should also consider ancestor transforms since
-  // paintInvalidationContainer. crbug.com/426111.
   if (reason == PaintInvalidationIncremental &&
-      m_context.oldBounds != m_context.newBounds &&
-      m_context.paintInvalidationContainer != m_box && m_box.hasLayer() &&
-      m_box.layer()->transform() &&
-      !m_box.layer()->transform()->isIdentityOrTranslation())
-    return PaintInvalidationBoundsChange;
+      m_context.oldBounds != m_context.newBounds) {
+    if (m_context.newBoundsCoversExtraPixels ||
+        m_context.oldBoundsCoversExtraPixels) {
+      // Incremental invalidation is not applicable because the difference
+      // between oldBounds and newBounds may not cover all changed pixels along
+      // the edges.
+      return PaintInvalidationBoundsChange;
+    }
+
+    // If the transform is not identity or translation, incremental invalidation
+    // is not applicable because the difference between oldBounds and newBounds
+    // doesn't cover all area needing invalidation.
+    // TODO(crbug.com/426111): Should also consider ancestor transforms
+    // since paintInvalidationContainer. Combine this logic into the above
+    // boundsCoversExtraPixels logic.
+    if (m_context.paintInvalidationContainer != m_box && m_box.hasLayer() &&
+        m_box.layer()->transform() &&
+        !m_box.layer()->transform()->isIdentityOrTranslation())
+      return PaintInvalidationBoundsChange;
+  }
 
   const ComputedStyle& style = m_box.styleRef();
   if (style.backgroundLayers().thisOrNextLayersUseContentBox() ||
       style.maskLayers().thisOrNextLayersUseContentBox() ||
       style.boxSizing() == BoxSizingBorderBox) {
     if (previousBoxSizesMap().get(&m_box).contentBoxRect !=
         m_box.contentBoxRect())
       return PaintInvalidationContentBoxChange;
   }
 
@@ skipping 126 matching lines @@
   auto it = previousBoxSizesMap().find(&m_box);
   if (it != previousBoxSizesMap().end())
     return it->value.borderBoxSize;
 
   // We didn't save the old border box size because it was the same as the size
   // of oldBounds.
   return previousBoundsSize;
 }
 
 }  // namespace blink