Skip PaintLayer empty paint phases if it previously painted nothing

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 1464 matching lines @@
     LayoutRect rect = visualOverflowRect();
     LayoutView* layoutView = view();
     while (layoutView->frame()->ownerLayoutObject())
         layoutView = layoutView->frame()->ownerLayoutObject()->view();
     mapToVisibleRectInAncestorSpace(layoutView, rect, nullptr);
     return rect.intersects(LayoutRect(layoutView->frameView()->scrollableArea()->visibleContentRectDouble()));
 }
 
 PaintInvalidationReason LayoutBox::invalidatePaintIfNeeded(PaintInvalidationState& paintInvalidationState, const LayoutBoxModelObject& paintInvalidationContainer)
 {
-    if (isFloating())
-        paintInvalidationState.enclosingSelfPaintingLayer(*this).setNeedsPaintPhaseFloat();
+    PaintLayer& enclosingSelfPaintingLayer = paintInvalidationState.enclosingSelfPaintingLayer(*this);
+    if (enclosingSelfPaintingLayer.layoutObject() != this) {
+        if (isFloating())
+            enclosingSelfPaintingLayer.setNeedsPaintPhaseFloat();

[Xianzhu, 2016/03/08 22:08:42]

This change is because a self-painting floating layer just paints its contents
normally, not needing PaintPhaseFloat by itself.

 
-    if (hasBoxDecorationBackground()
-        // We also paint overflow controls in background phase.
-        || (hasOverflowClip() && scrollableArea()->hasOverflowControls())) {
-        PaintLayer& layer = paintInvalidationState.enclosingSelfPaintingLayer(*this);
-        if (layer.layoutObject() != this)
-            layer.setNeedsPaintPhaseDescendantBlockBackgrounds();
+        if (hasBoxDecorationBackground()
+            // We also paint overflow controls in background phase.
+            || (hasOverflowClip() && scrollableArea()->hasOverflowControls()))
+            enclosingSelfPaintingLayer.setNeedsPaintPhaseDescendantBlockBackgrounds();

[chrishtr, 2016/03/09 03:40:47]

A self-painting layer also doesn't need PaintPhaseDescendantBlockBackgrounds?

[Xianzhu, 2016/03/09 21:39:52]

Right. The layer paints its own background in PaintPhaseSelfBlockBackgroundOnly.

     }
 
     PaintInvalidationReason fullInvalidationReason = fullPaintInvalidationReason();
     // If the current paint invalidation reason is PaintInvalidationDelayedFull, then this paint invalidation can delayed if the
     // LayoutBox in question is not on-screen. The logic to decide whether this is appropriate exists at the site of the original
     // paint invalidation that chose PaintInvalidationDelayedFull.
     if (fullInvalidationReason == PaintInvalidationDelayedFull) {
         if (!intersectsVisibleViewport())
             return PaintInvalidationDelayedFull;
 
@@ skipping 3174 matching lines @@
 }
 
 void LayoutBox::IntrinsicSizingInfo::transpose()
 {
     size = size.transposedSize();
     aspectRatio = aspectRatio.transposedSize();
     std::swap(hasWidth, hasHeight);
 }
 
 } // namespace blink