Consider subpixel accumulation when invalidating paint

Source/core/rendering/compositing/CompositedLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 1901 matching lines @@
             IntRect layerDirtyRect = r;
             layerDirtyRect.move(-layer->offsetFromRenderer());
             layer->setNeedsDisplayInRect(layerDirtyRect);
         }
     }
 
     IntRect r;
 };
 
 // r is in the coordinate space of the layer's render object
-void CompositedLayerMapping::setContentsNeedDisplayInRect(const IntRect& r)
+void CompositedLayerMapping::setContentsNeedDisplayInRect(const LayoutRect& r)
 {
     // FIXME: need to split out repaints for the background.
     ASSERT(!paintsIntoCompositedAncestor());
-    SetContentsNeedsDisplayInRectFunctor functor = { r };
+
+    SetContentsNeedsDisplayInRectFunctor functor = {
+        pixelSnappedIntRect(r.location() + m_owningLayer.subpixelAccumulation(), r.size())

[chrishtr, 2014/07/02 16:59:24]

It's not quite what I had in mind. Instead of using
m_owningLayer.subpixelAccumulation() here,
you can use m_renderer.layer()->subpixelAccumulation() for both the squashing
and non-squashing
case in RenderLayerRepainter.

For non-squashed laeyrs, m_renderer.layer() will be the same as m_owningLayer

[Xianzhu, 2014/07/02 17:17:54]

I think we should keep 'adjusting of rects with subpixel accumulation' only
above the GraphicsLayer interface, otherwise it's difficult to know which
LayoutRect contains subpixel accumulation which doesn't.

There is a FIXME in RenderLayerRepainter::setBackingNeedsRepaintInRect saying
that we should combine the squashing and non-squashing path. When it is fixed,
the subpixel accumulation adjustment code will be also combined.

+    };
     ApplyToGraphicsLayers(this, functor, ApplyToContentLayers);
 }
 
 const GraphicsLayerPaintInfo* CompositedLayerMapping::containingSquashedLayer(const RenderObject* renderObject, const Vector<GraphicsLayerPaintInfo>& layers)
 {
     for (size_t i = 0; i < layers.size(); ++i) {
         if (renderObject->isDescendantOf(layers[i].renderLayer->renderer())) {
             return &layers[i];
             break;
         }
@@ skipping 299 matching lines @@
     } else if (graphicsLayer == m_scrollingBlockSelectionLayer.get()) {
         name = "Scrolling Block Selection Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore