Steve Baker (sbaker++at++link.com)
Fri, 15 May 1998 14:12:32 -0500 (CDT)
> Kenneth Sewell wrote:
> >
> > I have been working on a flight sim that loads in several
> > rectangular patches of terrain. The problem is that the z-buffer
> > works correctly for the elements of each patch individually but
> > not between the elements of two different patches. I apologize
> > if I'm not being very clear, I'll give an example. If I have two
> > patches A and B (each of them made up of a few thousand
> > polygons) with A being closer to the viewer than B. All of
> > the polygons in A have been rendered properly with respect
> > to each other, all of the polygons of B have been rendered
> > properly with respect to each other. However parts of B
> > that should be hidden behind A, are drawn as though they
> > are nearer. This only happens to part of B, the rest of it is
> > behind A, like it should be. I am loading all of the patches
> > at the same time and they are all children of one DCS node.
> > I would appreciate any help you can offer. Thanks.
> >
>
> This is very strange.
It certainly is.
> Are you sure that you have a zbuffer, could you be getting lucky
> with the order of the polygons and just seeing a painters effect
> but the tiles are in the wrong order and betray what's really happening?
I think he must have a Z buffer of some kind because he says:
> > However parts of B
> > that should be hidden behind A, are drawn as though they
> > are nearer. This only happens to part of B, the rest of it is
> > behind A, like it should be.
If *some* of B comes out in front and some behind then we probably
have to assume that some kind of pixel occultation is going on.
Although it's possible that Performer is sorting polygons by
GeoState - which might explain this behaviour in the absence
of a Z buffer.
Another possibility is that the terrain is being rendered
in some manner that makes Performer see some of the polygons
as translucent - so they are sorted into a different bucket
and rendered at the end.
I would suggest that perhaps the most likely reason for this
strange behaviour is that the Z buffer *is* present but it's
precision is really, really, terrible. As all who read this
list regularly will know, it's very easy for beginners to
get this wrong.
Kenneth: What near and far clip planes are you using?
Does your terrain use a variety of pfGeoState's
or does it all share a single pfGeoState?
Steve Baker (817)619-8776 (Vox/Vox-Mail)
Raytheon Systems Inc. (817)619-4028 (Fax)
Work: SBaker++at++link.com http://www.hti.com
Home: SJBaker1++at++airmail.net http://web2.airmail.net/sjbaker1
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