erich@eye.com (Eric Haines) (02/13/91)
In article <1991Feb12.075204.12542@world.std.com> katefans@world.std.com (Chris'n'Vickie of Chicago) writes: > If Wavefront were made available from an FTP site, someone would have a >large lawsuit on their hands, as it is one of the most famous commercial >3d animation systems around. (So much so that it has become a synonym for >"3d animation system" to video producers.) A watered-down version is >supplied as a "teaser" on SGI machines. Wavefront is also offering a watered down version of their software on HP workstations. I believe you get it bundled in with the high-end workstations; it's called the Personal Visualizer. One nice feature is that it does radiosity renderings by calling our software (something not currently available in the SGI version). Contact your HP rep for info - hey, I just write software. >"Dante" is a program that uses >custom hardware in HP workstations to do fast radiosity rendering. I believe >it is only available on HP, Once upon a time this was true. Now it doesn't require special hardware. (By the way, the bundled HP version is known as the "Starbase Radiosity and Ray Tracing" package. Dante is the internal name - I called it this because HP was using Renaissance related names internally, and we thought this project would be hellish to implement.) If you're seriously interested in learning more, call Ron Firooz (303-229-4542) at HP for info. Enough on this - it's starting to smack of advertising. >It isn't the only ray-tracer to render patch objects; "Explore" from >Thomson Digital Image (France) traces Bspline patches. It doesn't work with >the patches directly (what does?), instead it sub-divides the patches >adaptively based on z-distance from the camera. This works very well, and >avoids Phong shading edges on the objects by creating micro-polygons one >pixel in size. This is one of the methods HP uses when they use their scan-line hardware to display spline surfaces. One potential problem with it for ray tracing is that the object gets split up enough for the eye rays, but the shadows cast by the object may be noticeably polygonalized. For example, a teapot which is far away & tiny in the scene casts a shadow into the foreground. Since it's far away, the renderer decides to polygonalize just a little, but when it casts its shadow the minimal polygonalization can be seen in the shadow edge. Luckily this particular situation is pretty rare, though it points out that implicit polygonalization (as above) & explicit tessellation control both have their uses. For example, at what resolution do you polygonalize a spline surface that is off the screen, but casts shadows into the scene? Implicit, view-based polygonalization can mess up big time in this case. Eric Haines