Added setThreadSafeRefUnref, resizeGLObjectBuffers and releaseGLObjects to OverlayNode

include/osgSim/OverlayNode

@@ -87,6 +87,17 @@ class OSGSIM_EXPORT OverlayNode : public osg::Group
         /** Get the const camera used to implement the render to texture of the overlay subgraph.*/
         const osg::Camera* getCamera() const { return _camera.get(); }
         
+        /** Set whether to use a mutex to ensure ref() and unref() are thread safe.*/
+        virtual void setThreadSafeRefUnref(bool threadSafe);
+
+        /** Resize any per context GLObject buffers to specified size. */
+        virtual void resizeGLObjectBuffers(unsigned int /*maxSize*/);
+
+        /** If State is non-zero, this function releases any associated OpenGL objects for
+           * the specified graphics context. Otherwise, releases OpenGL objexts
+           * for all graphics contexts. */
+        virtual void releaseGLObjects(osg::State* = 0) const;
+
     protected :
 
         virtual ~OverlayNode() {}