| This dissertation describes the design of a framework, Ygdrasil, for creating networked virtual environments. The intent of the framework is to address the problem of composability in virtual reality applications. Composability refers to being able to dynamically construct a new virtual environment by bringing in existing objects and code associated with them without special modifications for the new environment. In particular, Ygdrasil concentrates on applications such as art and education, where the focus is on worlds planned out by an author, with objects or characters that have their own autonomous behaviors and that can interact with users.; Ygdrasil is built on two primary elements, a shared scene graph structure, with automatic data sharing and discovery, and a script-like method to define a virtual world. As part of this, a standardized structure for world components is defined. The scripting is a simple, textual description of the layout of a scene graph and event/message connections between elements. The networked scene graph uses a distributed database to share data members for every node in the graph.; Ygdrasil was evaluated through its use in two testbed applications and in some more basic performance tests. The tests demonstrate that Ygdrasil works well for constructing significant networked worlds. However, they also showed that although the distributed database model simplifies programming, it requires significant network bandwidth; future work should focus on improving this performance while maintaining Ygdrasil's flexibility and ease of use. |
