https://bugs.webkit.org/show_bug.cgi?id=109866
--- Comment #5 from Tien-Ren Chen <trchen at chromium.org> 2013-02-14 15:44:34 PST ---
By the way, there is a comment in the code I don't really understand though:
The comment says "The root layer always has a compositing layer, but it may not have backing." but code reads the opposite.
@ bool RenderLayerCompositor::requiresCompositingLayer(const RenderLayer* layer, RenderLayer::ViewportConstrainedNotCompositedReason* viewportConstrainedNotCompositedReason) const
// The root layer always has a compositing layer, but it may not have backing.
return requiresCompositingForTransform(renderer)
|| requiresCompositingForVideo(renderer)
|| requiresCompositingForCanvas(renderer)
|| requiresCompositingForPlugin(renderer)
|| requiresCompositingForFrame(renderer)
|| (canRender3DTransforms() && renderer->style()->backfaceVisibility() == BackfaceVisibilityHidden)
|| clipsCompositingDescendants(layer)
|| requiresCompositingForAnimation(renderer)
|| requiresCompositingForFilters(renderer)
|| requiresCompositingForPosition(renderer, layer, viewportConstrainedNotCompositedReason)
|| requiresCompositingForOverflowScrolling(layer)
|| requiresCompositingForBlending(renderer);
@ bool RenderLayerCompositor::requiresOwnBackingStore(const RenderLayer* layer, const RenderLayer* compositingAncestorLayer) const
if (layer->isRootLayer()
|| layer->transform() // note: excludes perspective and transformStyle3D.
|| requiresCompositingForVideo(renderer)
|| requiresCompositingForCanvas(renderer)
|| requiresCompositingForPlugin(renderer)
|| (canRender3DTransforms() && renderer->style()->backfaceVisibility() == BackfaceVisibilityHidden)
|| requiresCompositingForAnimation(renderer)
|| requiresCompositingForFilters(renderer)
|| requiresCompositingForBlending(renderer)
|| requiresCompositingForPosition(renderer, layer)
|| requiresCompositingForOverflowScrolling(layer)
|| renderer->isTransparent()
|| renderer->hasMask()
|| renderer->hasReflection()
|| renderer->hasFilter())
return true;
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