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Implementation Notes

These effects were implemented using Open GL and Open Inventor  [8] on both an SGI Reality Engine and an Ultra SPARC with a Creator 3D graphics accelerator. The effects are constructed as new Open Inventor node types  [9] using Open GL directly to render the effects. This lets these effects be used in a wide variety of applications, while providing extremely good performance. We tested the nodes in an Inventor-based application called vrapp. This application supports wide-area distribution of immersive environments, including text, audio, and video communication, manipulation of shared objects, avatars, and support of specialized immersive hardware.

All of the transparency or blur-based effects that we describe could be implemented in a straightforward way using multiple copies of the object and varying levels of transparency. Naively, this can be done by using Inventor's support of multiple instantiation of a scene graph, with varying transparency and transformation nodes interspersed between the instantiations. However, most of the visual techniques are amenable to more clever implementations that provide an improved appearance and performance, as detailed in the papers that first described them.

Loring Holden
Tue Dec 17 17:11:50 EST 1996