[csilva at sbcs.sunysb.edu: Re: Holes and seams in GeomView]

[mbp]

With respect to your message below, I think the 3Dkit on the NeXT
*does* let you choose whether you want to skip hidden lines (I think
it implements a software Z-buffer), when you open up the 3D Camera
object, but it is very slow ... if that's what you mean by a corresponding
switch. One way to do this is to create an action on the interface for
rendering and let the user choose the Z-buffer option for a given 
view.

I really have not tried this yet (but will do so tonight), but I've
seen some NeXT applications that must be using it for rendering.

BTW, you guys did a great job on geomview. Congratulations !!!

See you,

Claudio.

> From mbp at geom.umn.edu Thu Dec  9 17:56:41 1993
> Date: Thu, 9 Dec 93 16:35:30 -0600
> From: mbp at geom.umn.edu
> To: wjabi at libra.arch.umich.edu
> Cc: geomview-users at geom.umn.edu
> Subject: Holes and seams in GeomView
> Content-Length: 1198
> 
> Geomview on the NeXT does not correctly handle nonconvex polygons (in
> an OFF object or in any other object).  To draw nonconvex polygons you
> need to first decompose them into convex pieces.  One way to do this
> with your example is to chop the bottom and top faces into four parts;
> I've done this and have appended the modified OFF file below.
> 
> The SGI version does correctly handle nonconvex polygons; the file you
> sent looks fine on an SGI.  The reason has to do with the underlying
> graphics software.  SGI's GL has a switch that we use to turn on
> correct handling of nonconvex polygons.  We'll check into whether
> NeXT's Quick Renderman has a corresponding switch.
> 
> Congradulations on your "crude picture", by the way!  It's the best
> 3D ascii diagram I've ever seen!
> 
> --Mark
> 
> 
> OFF
> 16 16 0
> 0.0  0.0  0.0
> 1.0  0.0  0.0
> 1.0  0.0  1.0
> 0.0  0.0  1.0
> 0.0  1.0  1.0
> 1.0  1.0  1.0
> 1.0  1.0  0.0
> 0.0  1.0  0.0
> 0.8  0.8  1.0
> 0.8  0.2  1.0
> 0.2  0.2  1.0
> 0.2  0.8  1.0
> 0.8  0.8  0.0
> 0.8  0.2  0.0
> 0.2  0.2  0.0
> 0.2  0.8  0.0
> 4 0 1 2 3
> 4 1 6 5 2
> 4 6 7 4 5
> 4 0 3 4 7
> 4 8 9 13 12
> 4 11 8 12 15
> 4 11 15 14 10
> 4 9 10 14 13
> 4 6 12 13 1
> 4 14 0 1 13
> 4 15 7 0 14
> 4 12 6 7 15
> 4 5 8 9 2
> 4 10 3 2 9
> 4 11 4 3 10
> 4 8 5 4 11
>