From Farshid Lashkari, "As discussed, I've added the ability to handle Drawable objects within the NodeVisitor class. Here is an overview of the changes:

- Added apply(Drawable) and apply(Geometry) to NodeVisitor

- Added accept(NodeVisitor) method to Drawable/Geometry

- Added traverse(NodeVisitor) to Geode which calls accept(NodeVisitor) on all Drawables

- Updated CullVisitor to use new apply(Drawable) to handle drawables. The apply(Billboard) method still manually handles the drawables since it is depends on the billboard settings. I needed to disable the traverse within billboard to prevent duplicate traversal of drawables.

- Update other osgUtil node visitors (GLObjectsVisitor, IncrementalCompileOperation, ..) to use new apply(Drawable) method.
"

include/osg/Drawable

@@ -115,6 +115,8 @@ class OSG_EXPORT Drawable : public Object
           * Equivalent to dynamic_cast<const Geometry*>(this).*/
         virtual const Geometry* asGeometry() const { return 0; }
 
+        /** Visitor Pattern : calls the apply method of a NodeVisitor with this drawable's type.*/
+        virtual void accept(NodeVisitor& nv);
 
         /** Compute the DataVariance based on an assessment of callback etc.*/
         virtual void computeDataVariance();