The CAVE™

Technological Innovation

NEM-Avatar Implementation

Software/Hardware

The technical implementation of the MMB calls for the design and development of "XPn", an authoring system for immersive art exhibitions and framework for creating large-scale, interactive virtual-reality applications.

"XPn,” an Authoring System for Immersive Art Exhibitions, presently known as the Ygdrasil system, was created by Dave Pape (PhD, EVL, The University of Illinois at Chicago), was the software utilized for developing the MMB project.

The XP system grew from software developed for the Multi Mega Book in the CAVE. Thw application and was further refined during the development of "Mythologies.” Both applications are large-scale environments. Most of the artists involved were experienced with tools such as Softimage, Photoshop, and basic Unix, but were not professional computer graphics programmers. The goal was to create a framework which included many of the features common to virtual art environments, one that would allow experienced VR programmers to build tools needed for the features unique to a specific application, and allow artists to create the final environment by assembling the appropriate pieces.

The XP system provides a framework for creating large scale, interactive virtual-reality applications. By dividing the development of applications into two distinct components—the coding of nodes that encapsulate specific behaviors, and the assembling of these nodes into a scene—XP allows teams comprising both artists and programmers to work on projects efficiently. It has been used to develop several successful artistic virtual worlds. Although originally developed for art applications, the general system should be useful in building a wide range of virtual worlds.

XP is based on Performer, the CAVE (TM) libraries, a sound library, and C++. The system is divided into two major aspects: the text file(s) defining an application as a collection of nodes and their connections via events and messages, and the lower-level C++ classes which implement the nodes. With this division, it is possible to split the work of world-creation between experienced programmers and non-programmers. The programmers create any new node classes which are needed for application-specific behaviors, such as graphical effects or elements of a character’s intelligence. The other team members build the full application by plugging together object and behavior nodes in the text files. In practice, there is likely to be an overlap between these groups; because XP handles many of the trickier details of Performer and the CAVE™ libraries, artists have been able to start doing some of the C++ programming of new nodes using a prototype class template. The XP framework also makes it easier to re-use code between applications, because the code is in completely modular nodes with standardized interfaces. Application authors create a virtual environment in XP by editing a scene file.

The basic XP system is designed for single-user applications. However, further extension of the system to support networked, multi-user worlds has begun. Using the CAVE soft networking architecture, a scene graph is replicated among multiple CAVEs; changes made by one user are automatically shared with all others. This approach was used in building the V-Mail (virtual mail) system for collaborative design. New node classes were created which can record user actions and spoken comments, and then send them to remote collaborators, who may be in the shared environment at different times. Future plans include such networking of the scene graph at the core of the system.

Virtual-reality applications can use a wide variety of methods for animating. The MMB makes use of flipbooks, key framing, motion capture, and procedural (computer-programmed) animation for various purposes throughout the application.

Figure 2. MMB: