Added releaseGLObjects to NodeCallbacks, Drawable::DrawCallbacks and wired up

osgProducer to use it when doing cleanup_frame.

include/osgProducer/Viewer

@@ -305,6 +305,12 @@ class OSGPRODUCER_EXPORT Viewer : public OsgCameraGroup, public osgGA::GUIAction
         /** Update internal structures w.r.t updated scene data.*/
         virtual void updatedSceneData();
 
+        /** Dispatch a clean up frame that should be called before closing a OsgCameraGroup, i.e. on exit from an app.
+          * The clean up frame first release all GL objects associated with all the graphics context associated with
+          * the camera group, then runs a special frame that does the actual OpenGL deletion of GL objects for each
+          * graphics context. */
+        virtual void cleanup_frame();
+
     protected :
 
 

include/osgProducer/ViewerEventHandler

@@ -61,6 +61,11 @@ class OSGPRODUCER_EXPORT ViewerEventHandler : public osgGA::GUIEventHandler
         void setWriteImageFileName(const std::string& filename);
         const std::string& getWriteImageFileName() const { return _writeImageFileName; }
 
+        /** release OpenGL objects in specified graphics context if State
+            object is passed, otherwise release OpenGL objexts for all graphics context if
+            State object pointer NULL.*/
+        virtual void releaseGLObjects(osg::State* =0) const;
+
     protected:
         
         osgProducer::OsgCameraGroup* _cg;