MANTA While traditional z-buffer based graphics accelerators operate by “pushing” all of the geometry in a scene “through” the screen, ray-tracing works by “casting” a ray through each pixel of the screen and finding the scene geometry intersected by that ray. Though the final images produced by these two approaches are often identical (though not always: ray-tracers can often produce images with much greater visual richness), the computational complexities are quite different. The traditional graphics pipeline scales linearly with the number of polygons in the scene, and sub-linearly with the number of pixels on the screen. That is, for twice as many polygons, a typical graphics card will take twice as long to render the scene. In contrast, ray-tracing scales sub-linearly with the number of polygons. So for twice as many polygons, ray-tracing will typically require far less than twice as long to produce a complete final rendering. With the increasing power of modern computer architectures, geometric models continue to grow larger every year. In the case of medical datasets, model sizes are typically doubling every two years. In contrast to dataset sizes, our monitor resolutions (the number of pixels on our screens) are doubling at a much slower rate. As shown in the graph above, this discrepancy ultimately translates into a “cross-over point” – for large models and complex scenes, ray-tracing becomes a far more efficient rendering approach than traditional graphics rasterization. In addition to the long-term algorithmic complexity advantages of ray-tracing, there are three primary technical advantages of ray-traced rendering: scalability, flexibility, and interactivity. SCALABILITY The MANTA system has been demonstrated to scale near-linearly on a 1024-processor SGI Origin system. The fast shared-memory architectures of the SGI Origins have provided an ideal architecture for MANTA’s image-space parallel algorithm. Pioneered by Dr. Steve Parker, MANTA has been intricately designed and implemented to target linear scalability, with elegant load-balancing and ultra-efficient ray-object intersection algorithms at its core. FLEXIBILITY Designed as a flexible platform for prototyping and evaluating new ray-tracing research, MANTA provides an intuitive interface for adding new lighting and shading models, as well as new objects into the system. Because of this flexibility, the software was easily extended to handle the myriad new models that were incorporated for the SIGGRAPH demo. INTERACTIVITY While the photo-realistic benefits of MANTA are impressive, the system would not be nearly so compelling if it were not for its interactivity. The system supports adaptive jittered sampling and frameless rendering in order to provide maximal interactivity without sacrificing image quality.