Re: Q: pfLayerModes

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Angus Dorbie (dorbie++at++multipass.asd.sgi.com)
Fri, 20 Jun 1997 11:19:42 -0700

On Jun 20, 7:44am, Steve Baker wrote:
> Subject: Re: Q: pfLayerModes
>
> On Jun 11, 12:43pm, Mark Baranowski wrote:
>
> >> PFDECAL_BASE_HIGH_QUALITY solves the Z fighting problem, but *some* of
> >> the subfaces tend to "poke through" when they should be hidden by
> >> other parts of the model/scene. Is this is the problem that occurs if
> >> the subfaces are not coplanar with, or bounded by, the parent face?
>
> Marcus Barnes <marcus++at++multigen.com> replied:
>
> > Coplanarity tolerance can be a problem for STENCIL. Performer 2.x requires
a
> > much tighter (truer) tolerance than 1.x did.
>
> ...I find this hard to believe. Isn't Z buffer testing disabled
> when the layer polygon is rendered in STENCIL mode? I thought that was
> the entire point of using STENCIL.
>
> That being the case, surely the tolerance is unimportant. So long as the
> layered polygons appear to be entirely inside the base polys, there should
> be no problem.

I concur.

>
> [Of course if the layer polygons are a very large distance in front or behind
> the base then parallax effects can push the layer outside the base - but
> that's an extreme case]
>
> I think Mark Baranowski's problem with STENCIL is more likely to be to
> do with the layer polygons not lying entirely inside the base. That causes
> some strange behaviour - especially when the layer+base are viewed in front
> or behind other STENCIL mode pfLayers.

Very insightfull, this would be an explanation for "punch through" on
other stencil base geometry but it wouldn't explain any z fighting
problems.

Cheers,Angus.

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