Re: bad polygons, BAD!

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Marcus Barnes (marcus++at++multigen.com)
Tue, 11 Jun 1996 16:45:49 -0700

On Jun 11, 3:29pm, Ken Lindsay wrote:
> Subject: bad polygons, BAD!
> hey, i have a model that was working fine on an IMPACT a couple
> weeks ago, but now i am running on EXTREME. there is an ugly
> bug culling polygons in a semi-random way (typ looks like every
> other one is being culled as backfacing).
>
> i suspect that when performer tesselated the geometry, it did
> it differently than was happening on the IMPACT.

No. Performer tesselation is ignorant of the machine in use.

> i can get around it by turning culling off, but as you might
> suspect, the frame rate gets cut in half.
>
> any suggestions??

Sounds like you are using geosets with prim type PFGS_POLYS . They draw in the
order specified with OpenGL (Impact) but in tri-strip order with IRISGL
(Extreme).

from the man page:

"
pfGeoSet(3pf) IRIS Performer 2.0 libpr C Reference Pages pfGeoSet(3pf)

BUGS
     In IRIS GL, PFGS_POLYS are rendered as triangle strips for best perfor-
     mance so that in wireframe the edges internal to the polygon are visible.
     In OpenGL the internal edges will not be visible.
"

Regards.

--
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