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/NodeVisitor.cpp

@@ -33,6 +33,7 @@
 #include <osg/Transform>
 #include <osg/Camera>
 #include <osg/CameraView>
+#include <osg/Geometry>
 
 #include <stdlib.h>
 
@@ -75,6 +76,16 @@ NodeVisitor::~NodeVisitor()
     // if (_traversalVisitor) detach from _traversalVisitor;
 }
 
+void NodeVisitor::apply(Drawable& drawable)
+{
+    // It all ends here...
+}
+
+void NodeVisitor::apply(Geometry& drawable)
+{
+    apply(static_cast<Drawable&>(drawable));
+}
+
 void NodeVisitor::apply(Node& node)
 {
     traverse(node);