POV-Ray : Newsgroups : povray.beta-test : Revisiting SSLT with 3.7.1 beta 9 Server Time
28 Mar 2024 19:38:09 EDT (-0400)
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From: clipka
Subject: Re: Revisiting SSLT with 3.7.1 beta 9
Date: 9 Aug 2017 18:51:33
Message: <598b91f5$1@news.povray.org>
Am 09.08.2017 um 22:25 schrieb Kenneth:

> I take the "true geometric surface normal" to mean the unalterted,
> un-interpolated *single* normal on the face of the flat triangle. Is that
> correct?

Yes.

> Also: It is becoming clearer to me as to why SSLT works better on an object with
> finer-and-finer triangle subdivisions (and perhaps not so well with large flat
> 'mathematical' slabs like a box object?)

The results are actually quite accurate for "large flat 'mathematical'
slabs", if that's the shape you intend to model. The problem isn't the
presence of edges /per se/ -- the problem is the presence of edges in
places where you want to pretend that there are none.

> The smaller triangles-- curving away at
> slightly different angles-- cause the (many) incoming rays (and subsequent
> subsurface 'volume gathering') to be averaged together in a smoother way, with
> the artifacts contributing less to the 'larger' average, or being swamped by it.
> This is my layman's understanding, anyway ;-)  Please correct me if I'm mistaken
> or hopelessly wrong. If I'm at least somewhat correct, then POV-Ray's in-built
> documentation doesn't actually mention the need for finer triangle-mesh
> subdivisions, to get a smoother look. Perhaps it should, in light of Flyer X's
> results.

The SSLT feature is still considered highly experimental, and so are its
docs.


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From: Kenneth
Subject: Re: Revisiting SSLT with 3.7.1 beta 9
Date: 9 Aug 2017 23:00:00
Message: <web.598bcb995151470f883fb31c0@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:

>
> The results are actually quite accurate for "large flat 'mathematical'
> slabs", if that's the shape you intend to model. The problem isn't the
> presence of edges /per se/ -- the problem is the presence of edges in
> places where you want to pretend that there are none.
>

Ah yes, I see now. Thanks.

From reading lots of newgroup comments over the years, I had come to the
(mistaken) impression that SSLT actually *worked* better on complex, CURVED
objects-- meaning, an object with LOTS of small triangles and their attendent
interpolated normals. (Such objects do show a nicer, more complex 'look' from
the SSLT effect-- like the ears on the Stanford Bunny.) And conversely, that
more-or-less 'flat-surfaced' featureless objects were to be avoided. But I
understand more clearly now that SSLT *works* equally well on simpler shapes--
like a superellipsoid 'bar of soap', for example. It's just that the final
effect isn't as visually complex (leading me to the mistaken conclusion that it
didn't work well on such shapes.)


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From: Mr
Subject: Re: Revisiting SSLT with 3.7.1 beta 9
Date: 10 Aug 2017 05:05:01
Message: <web.598c21275151470fe10e80840@news.povray.org>
"Kenneth" <kdw### [at] gmailcom> wrote:
> clipka <ano### [at] anonymousorg> wrote:
>
> >
> > The results are actually quite accurate for "large flat 'mathematical'
> > slabs", if that's the shape you intend to model. The problem isn't the
> > presence of edges /per se/ -- the problem is the presence of edges in
> > places where you want to pretend that there are none.
> >
>
> Ah yes, I see now. Thanks.
>
> From reading lots of newgroup comments over the years, I had come to the
> (mistaken) impression that SSLT actually *worked* better on complex, CURVED
> objects-- meaning, an object with LOTS of small triangles and their attendent
> interpolated normals. (Such objects do show a nicer, more complex 'look' from
> the SSLT effect-- like the ears on the Stanford Bunny.) And conversely, that
> more-or-less 'flat-surfaced' featureless objects were to be avoided. But I
> understand more clearly now that SSLT *works* equally well on simpler shapes--
> like a superellipsoid 'bar of soap', for example. It's just that the final
> effect isn't as visually complex (leading me to the mistaken conclusion that it
> didn't work well on such shapes.)


Indeed, what we are all saying about SSLT, is that it's actually *too* accurate
and looks (too?) great !... :-) We are not used to that behaviour from other
renderers especially with the smoothed average normal cheat  enabled.
I am hoping a normal overhaul will also bring many other goodies to POV (such as
tangeant space (/parallax) normal mapping if we don't forget :-P )
meanwhile, I would love to have a fast biased cheated sstl simulated effect
shipped along under the subsurface/translucency command with a keyword similar
to the (fake photonless) caustics. A result similar to ST Benge fastprox macro
would be enough.


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