Re: Flimmering

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Angus Dorbie (dorbie++at++bitch.reading.sgi.com)
Wed, 14 Aug 1996 22:56:30 +0100

If you add my suggestion for writing and testing a new incremented value to
the stencil planes for each base - decal set then that would solve of the
problems you've listed below, and probably most others.

The trouble is you need more than a single bit of stencil and you could
only stack up #stencil_planes^2-1 decal layers before you roll over and risk
the same problems, probably not a problem

Rgds,
Angus..

On Aug 14, 4:35pm, Steve Baker wrote:
> Subject: Re: Flimmering
>
> Sharon Clay said (of Stencil plane coplanarity):-
>
> > The only case where you get into trouble is if a decal overflows
> > its base because then the base cannot set all of the proper stencil
> > bits and the base may hit junk set by previous bases. So, decals
> > must lie completely within their base poygons.
>
> ...or the base polygon is translucent and using multisample transparency...
> in which case there is no guarantee that the base polygon hits all those
> teeny-tiny subpixels...
>
> ...or the case where the daughter polygon lines up exactly along the edge
> of the host - but teeny-tiny roundoff errors cause the decal polygon to hit
> a couple of sub-pixels off the edge of the base....
>
> Technically, Sharon is correct in that in both of the cases that I list
> above are properly cases where the decal overflowed the base. But in a
> practical world of automatically generated or converted databases, I
> can't guarantee that these kinds of conditions won't sometimes crop up.
>
> The problem with this trick is that it looks great on paper but fails in
> so many practical examples. When it fails, it does not do so gracefully
> but peppers your display with thin slivers of screwed up mess. What's worse
> is that a surface very close to your eye can get corrupted by some other
> polygons twenty miles away behind it.
>
>
>
> Steve Baker 817-323-1361 (Vox-Lab)
> Hughes Training Inc. 817-695-8776 (Vox-Office/vMail)
> 2200 Arlington Downs Road 817-695-4028 (Fax)
> Arlington, Texas. TX 76005-6171 steve++at++mred.bgm.link.com (eMail)
>
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>-- End of excerpt from Steve Baker

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