Suppress layer creation for descendants of GPU-rasterized layers

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 486 matching lines @@
 
     CompositingReasons compositingReasons() const { return m_compositingProperties.compositingReasons; }
     void setCompositingReasons(CompositingReasons, CompositingReasons mask = CompositingReasonAll);
 
     bool hasCompositingDescendant() const { return m_compositingProperties.hasCompositingDescendant; }
     void setHasCompositingDescendant(bool b)  { m_compositingProperties.hasCompositingDescendant = b; }
 
     bool shouldIsolateCompositedDescendants() const { return m_compositingProperties.shouldIsolateCompositedDescendants; }
     void setShouldIsolateCompositedDescendants(bool b)  { m_compositingProperties.shouldIsolateCompositedDescendants = b; }
 
+    bool suppressingCompositedLayerCreation() const { return m_compositingProperties.suppressingCompositedLayerCreation; }
+    void setSuppressingCompositedLayerCreation(bool b) { m_compositingProperties.suppressingCompositedLayerCreation = b; }

[abarth-chromium, 2014/04/14 20:25:53]

Please add an ASSERT that we're allowed to query compositing properties.

Ideally, the way we'd do this is to access the m_compositingProperties through a
getter and have that getter contain the assert.  If that triggers asserts from
the other places m_compositingProperties is used, please add a FIXME comment to
those places.

[ajuma, 2014/04/15 19:11:34]

Added a getter for m_compositingProperties with an assert, and added FIXMEs in
places where this assert is getting tripped.

+
     void updateDescendantDependentFlags();
 
     void updateOrRemoveFilterEffectRenderer();
 
     void updateSelfPaintingLayer();
 
     void paintLayerContents(GraphicsContext*, const LayerPaintingInfo&, PaintLayerFlags);
 
     RenderLayer* enclosingTransformedAncestor() const;
 
@@ skipping 204 matching lines @@
     // Properties that are computed while updating compositing layers. These values may be dirty/invalid if
     // compositing status is not up-to-date before using them.
     struct CompositingProperties {
         CompositingProperties()
             : hasCompositingDescendant(false)
             , hasNonCompositedChild(false)
             , shouldIsolateCompositedDescendants(false)
             , lostGroupedMapping(false)
             , viewportConstrainedNotCompositedReason(NoNotCompositedReason)
             , compositingReasons(CompositingReasonNone)
+            , suppressingCompositedLayerCreation(false)
         { }
 
         // Used only while determining what layers should be composited. Applies to the tree of z-order lists.
         bool hasCompositingDescendant : 1;
 
         // Applies to the real render layer tree (i.e., the tree determined by the layer's parent and children and
         // as opposed to the tree formed by the z-order and normal flow lists).
         bool hasNonCompositedChild : 1;
 
         // Should be for stacking contexts having unisolated blending descendants.
         bool shouldIsolateCompositedDescendants : 1;
 
         // True if this render layer just lost its grouped mapping due to the CompositedLayerMapping being destroyed,
         // and we don't yet know to what graphics layer this RenderLayer will be assigned.
         bool lostGroupedMapping : 1;
 
         // The reason, if any exists, that a fixed-position layer is chosen not to be composited.
         unsigned viewportConstrainedNotCompositedReason : ViewportConstrainedNotCompositedReasonBits;
 
         // Once computed, indicates all that a layer needs to become composited using the CompositingReasons enum bitfield.
         CompositingReasons compositingReasons;
 
         // Used for invalidating this layer's contents on the squashing GraphicsLayer.
         IntSize offsetFromSquashingLayerOrigin;
+
+        // Whether this render layer is trying to avoid becoming composited, if possible.
+        bool suppressingCompositedLayerCreation : 1;

[abarth-chromium, 2014/04/14 20:25:53]

Please move this earlier in the struct so that it packs correctly with the other
bools.

[ajuma, 2014/04/15 19:11:34]

Done.

     };
 
     AncestorDependentProperties m_ancestorDependentProperties;
 
     CompositingProperties m_compositingProperties;
 
     IntRect m_blockSelectionGapsBounds;
 
     OwnPtr<CompositedLayerMapping> m_compositedLayerMapping;
     OwnPtr<RenderLayerScrollableArea> m_scrollableArea;
@@ skipping 11 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