RE concave polys

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2 total messages Started by Alan Dorin Tue, 26 Jan 1993 00:14

#132

Author: Alan Dorin
Date: Tue, 26 Jan 1993 00:14

15 lines
938 bytes

When drawing polys on the Reality Engine using concave(TRUE)
I get a few polys that appear to be missed out. (Ie. some
convex polys become invisible) The polys _are_ visible on
PI's and Indigo's though so the problem appears to be with
the RE.

If I turn concave polys off, obviously the RE (and other machines)
screws up the truly concave polys. Anyone know of a bug that
would cause this and how to overcome it? (apart from removing the
concave polys)


					Thanks,
					Alan Dorin
					(alan@godzilla.cgl.citri.edu.au)

Re: RE concave polys

#136

Author: Erik Lindholm
Date: Tue, 26 Jan 1993 03:57

33 lines
1733 bytes

In article <alan.728007287@godzilla.cgl.citri.edu.au> alan@cgl.citri.edu.au (Alan Dorin) writes:
>When drawing polys on the Reality Engine using concave(TRUE)
>I get a few polys that appear to be missed out. (Ie. some
>convex polys become invisible) The polys _are_ visible on
>PI's and Indigo's though so the problem appears to be with
>the RE.
>
>If I turn concave polys off, obviously the RE (and other machines)
>screws up the truly concave polys. Anyone know of a bug that
>would cause this and how to overcome it? (apart from removing the
>concave polys)
>
>
>					Thanks,
>					Alan Dorin
>					(alan@godzilla.cgl.citri.edu.au)

Does your concave polygons have any shared vertices? The concave decomposition
code is very sensitive about illegal polygons and will abort early if any are 
detected. From the man page:

      Polygons whose edges intersect each other are never guaranteed to be
     drawn correctly.

this includes repeating vertices. Each architecture tends to implement slightly
different algorithms for concave polygons, and illegal polygons are good for
detecting these differences.

Erik
-- 
Of course I'm lying,  .....but I think I love you.       (Yello)

                      .|\!/|.  erikl@shogun.asd.sgi.com  .|\!/|.

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