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.
"

src/osg/Drawable.cpp

@@ -272,6 +272,11 @@ Drawable::~Drawable()
     dirtyDisplayList();
 }
 
+void Drawable::accept(NodeVisitor& nv)
+{
+    nv.apply(*this);
+}
+
 osg::MatrixList Drawable::getWorldMatrices(const osg::Node* haltTraversalAtNode) const
 {
     osg::MatrixList matrices;