From: leathm AT solwarra DOT gbrmpa DOT gov DOT au (Leath Muller)
Message-Id: <199704020131.LAA01488@solwarra.gbrmpa.gov.au>
Subject: Re: Allegro 3d question/bug?
To: sigma AT ctv DOT es
Date: Wed, 2 Apr 1997 11:31:53 +1000 (EST)
Cc: djgpp AT delorie DOT com
In-Reply-To: <3341758B.38C9@ctv.es> from "Jose Manuel Lopez-Cepero" at Apr 1, 97 10:52:27 pm
Content-Type: text

> > what you mean by very large coords... are you talking world or view space?
> > and if your talking view, do you mean the z value is very large? If you have
> > clipped the polygons correctly to your view volume, you shouldn't have  this
> > problem...
 
> The problem is that once projected the coordinates fly up to a value
> that overflows the poly routine. I think the clipping is being good done
> (I placed it and it seemed to work), but the trouble is now when I get
> very (*very*) close to a polygon with relatively large world
> coordinates; the projection routine would map correctly the vertex that
> falls into the screen, but the other ones would get to the edge.
> Example: a vertex on 0,0 and others on 30,0 and 30,30, getting closer to
> the first one, when z gets small then dividing by it (what project does)
> is really a multiply. I have to display it because 0,0 maps on the
> screen, but meanwhile the 30's on the coordinates project to larger
> values, larger, larger... crash :-)

Ok, if your having trouble with the z coord below 1, why not make the front
clipping plane at z = 1.0? That way, the coords will never 'grow'... :)
If your perspective dividing, your coords will always be either the same
size or smaller... I don't use Allegro, so I don't know how Shawn does his
routines... Shawn?
 
Leathal.