|12||10||Users can interact with a scene graph using callbacks. Callbacks can be thought of as user-defined functions that are automatically executed depending on the type of traversal (update, cull, draw) being performed. Callbacks can be associated with individual nodes or they can be associated with selected types (or subtypes) of nodes. During each traversal of a scene graph if a node is encountered that has a user-defined callback associated with it, that callback is executed. For more information on traversals and callbacks see chapter four of David Eberly's '3D Game Engine Design' and SGI's Chapter Four of the 'Performer Programmer's Guide'. For a more complete example see osgExampleCallback.