Make compositingState explicit

Source/core/rendering/RenderLayer.h

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 456 matching lines @@
 
     void filterNeedsRepaint();
     bool hasFilter() const { return renderer()->hasFilter(); }
 
     bool hasBlendMode() const;
 
     void* operator new(size_t);
     // Only safe to call from RenderLayerModelObject::destroyLayer()
     void operator delete(void*);
 
-    bool isComposited() const { return m_backing != 0; }
+    CompositingState compositingState() const;
+
+    RenderLayerBacking* backing() const
+    {
+        // NOTE: Checking whether backing exists is equivalent to asking if you are in one of these two compositing states.
+        //       If this is why you are using backing(), please try to use compositingState() instead.
+        ASSERT(compositingState() == HasOwnBackingButPaintsIntoAncestor || compositingState() == PaintsIntoOwnBacking);
+        return m_backing.get();
+    }
+
+    RenderLayerBacking* ensureBacking();
+    void clearBacking(bool layerBeingDestroyed = false);
+
     bool hasCompositedMask() const;
     bool hasCompositedClippingMask() const;
-    RenderLayerBacking* backing() const { return m_backing.get(); }
-    RenderLayerBacking* ensureBacking();
-    void clearBacking(bool layerBeingDestroyed = false);
     bool needsCompositedScrolling() const;
     bool needsToBeStackingContainer() const;
 
     RenderLayer* scrollParent() const;
     RenderLayer* clipParent() const;
 
     bool needsCompositingLayersRebuiltForClip(const RenderStyle* oldStyle, const RenderStyle* newStyle) const;
     bool needsCompositingLayersRebuiltForOverflow(const RenderStyle* oldStyle, const RenderStyle* newStyle) const;
     bool needsCompositingLayersRebuiltForFilters(const RenderStyle* oldStyle, const RenderStyle* newStyle, bool didPaintWithFilters) const;
 
     bool paintsWithTransparency(PaintBehavior paintBehavior) const
     {
-        return isTransparent() && ((paintBehavior & PaintBehaviorFlattenCompositingLayers) || !isComposited());
+        // FIXME: shouldn't we return true if this layer has a backing but paints into its ancestor?

[Ian Vollick, 2013/10/01 19:46:22]

This should return true everywhere opacity won't be handled by the render
surface. I think you're right; if we're painting into our ancestor's backing and
we're transparent, the painting code has to handle the blending.

[shawnsingh, 2013/10/03 03:04:04]

done.

+        return isTransparent() && ((paintBehavior & PaintBehaviorFlattenCompositingLayers) || !backing());
     }
 
     bool paintsWithTransform(PaintBehavior) const;
 
     // Returns true if background phase is painted opaque in the given rect.
     // The query rect is given in local coordinates.
     bool backgroundIsKnownToBeOpaqueInRect(const LayoutRect&) const;
 
     bool containsDirtyOverlayScrollbars() const { return m_containsDirtyOverlayScrollbars; }
     void setContainsDirtyOverlayScrollbars(bool dirtyScrollbars) { m_containsDirtyOverlayScrollbars = dirtyScrollbars; }
@@ skipping 545 matching lines @@
 
 } // namespace WebCore
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showLayerTree(const WebCore::RenderLayer*);
 void showLayerTree(const WebCore::RenderObject*);
 #endif
 
 #endif // RenderLayer_h