Consider subpixel accumulation when invalidating paint

Source/core/rendering/compositing/CompositedLayerMapping.cpp

Index: Source/core/rendering/compositing/CompositedLayerMapping.cpp
diff --git a/Source/core/rendering/compositing/CompositedLayerMapping.cpp b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
index d5637522c90fb7713d9fcaebb75fd8f0977c2077..5f209729e89ae19650bdf898a8e1a81c381c6bc2 100644
--- a/Source/core/rendering/compositing/CompositedLayerMapping.cpp
+++ b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
@@ -1919,11 +1919,14 @@ struct SetContentsNeedsDisplayInRectFunctor {
 };
 
 // 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);
 }