In article <1992Aug10.153515.14594@husc3.harvard.edu>, basu@scws4.harvard.edu (Archan Basu) writes:
|> Hi!
|>
|> I'm working on a Vision application on the SGI Iris Indigo.
|> The current problem is to render a human face (from lazer rangefinder data)
|> including cast shadows, say across the left eye due to occlusion by the
|> nose, of incident light from the right. The face is an 86x31 rectangle
|> represented as a polygonal mesh (~5000 triangles) or perhaps as a NURB
|> with ~2600 control points.
|>
|> The shadows, ofcourse, are the stumbling block. One idea I had was
|> (assuming access to SGI's internal data representations, including
|> transform's, zbuffer's, etc): Place eye at light source. Perform hidden
|> surface elimination, and save zbuffer. Now transform to actual eye frame.
|> Determine, for each viewport pixel, whether its corresponding scene point
|> was visible to light source. Hence, shade bright or dark.
|>
|> Have others tried this? Are there other approaches? Where can I get
|> the info I need to access SGI memory, etc? I need your help BADLY. Please
|> respond with any relevant thoughts to basu@zeus.harvard.edu
Try checking back issues of the IRIS Universe magazine. There was an article two or three issues back on using Stencil planes for shadow generation. The article was written for a VGX class graphics machine, but it might work in software on an Indigo - try it out.
