If a node detects that an event has occurred, any messages associated with this event are placed in a queue. All nodes include a method to reset them to their initial state. This feature is important for running applications in public shows. Applications which have a specific narrative or flow need to be re-initialized whenever a new user, or group of users, enters the environment. Because of the scale of the applications we have been working on, we cannot simply exit the program and reload everything from scratch long delays are not acceptable at showtime.
Many nodes also have a debugging state, which is used during development and testing.
When debugging is enabled, additional elements are drawn, showing normally invisible aspects of the scene. Events and significant messages are printed to the terminal, so that the flow of the application can be monitored. Figure 2 shows a view of the Multi-MegaBook environment in debugging mode. In addition to the scene graph defining the virtual world, other major elements of the XP framework include the navigator and world nodes, which are automatically created parts of the scene. The navigator aids the user s movement through the world.