Reduce invalidation on children-needs-layout containers

Source/core/rendering/LayoutRepainter.cpp

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  *
  */
 
 #include "config.h"
 #include "core/rendering/LayoutRepainter.h"
 
+#include "core/rendering/RenderBlock.h"
 #include "core/rendering/RenderLayer.h"
 #include "core/rendering/RenderObject.h"
 
 namespace WebCore {
 
 LayoutRepainter::LayoutRepainter(RenderObject& object, bool checkForRepaint)
     : m_object(object)
     , m_repaintContainer(0)
     , m_checkForRepaint(checkForRepaint)
 {
     if (RuntimeEnabledFeatures::repaintAfterLayoutEnabled())
         return;
 
     if (m_checkForRepaint) {
         m_repaintContainer = m_object.containerForRepaint();
         {
             // Hits in compositing/video/video-controls-layer-creation.html
             DisableCompositingQueryAsserts disabler;
             m_oldBounds = m_object.clippedOverflowRectForRepaint(m_repaintContainer);
         }
         m_oldOutlineBox = m_object.outlineBoundsForRepaint(m_repaintContainer);
     }
 }
 
+bool LayoutRepainter::skipInvalidationWhenLayingOutChildren() const

[eseidel, 2014/03/21 00:37:09]

I would have pushed this check onto the RenderObject itself.

I'm also surprised that this is only useful in the children-changed case. A
similar "is self painting" check could be used to avoid repaints for empty divs
changing size, etc.

[Julien - ping for review, 2014/03/24 18:00:01]

That wouldn't work currently as changing size triggers a full layout
(selfNeedsLayout() == true) so we have to be conservative. This is one of the
reasons I am advocating for more granular layout phases.

If we had a way of detecting this case, then yes this code should be reused as
you mentioned. I will add a FIXME about that.

+{
+    if (!m_object.needsLayoutBecauseOfChildren())
+        return false;
+
+    // FIXME: We don't skip invalidations for SVG renderers for now.

[pdr., 2014/03/21 00:25:06]

This is fine, we'll never need this.

[Julien - ping for review, 2014/03/24 18:00:01]

Done.

+    // RenderBlock with line boxes are responsible to invalidate them so we can't ignore them.
+    if (m_object.isSVG() || (m_object.isRenderBlock() && toRenderBlock(&m_object)->firstLineBox()))
+        return false;
+
+    return !m_object.style()->hasVisualOverflowingEffect() && !m_object.style()->hasBorder() && !m_object.style()->hasBackground();
+}
+
 bool LayoutRepainter::repaintAfterLayout()
 {
     if (RuntimeEnabledFeatures::repaintAfterLayoutEnabled())
         return false;
 
+    if (skipInvalidationWhenLayingOutChildren())
+        return false;
+
     // Hits in compositing/video/video-controls-layer-creation.html
     DisableCompositingQueryAsserts disabler;
 
     return m_checkForRepaint ? m_object.repaintAfterLayoutIfNeeded(m_repaintContainer, m_object.selfNeedsLayout(), m_oldBounds, m_oldOutlineBox) : false;
 }
 
 } // namespace WebCore