On the way out (as dirty rects) those calls are in RenderLayerBacking (RenderLayerBacking::setContentsNeedDisplay()), while on the way in (as clip rects) offsetFromRenderer() is in GraphicsLayer (GraphicsLayer::paintGraphicsLayerContents) while devicePixelFractionFromRenderer() is in RenderLayerBacking (RenderLayerBacking::paintContents) They both should either be in GraphicsLayer or in RenderLayerBacking.