Marc Jacquier wrote:

> concentrical semi-transparent spheres?
> And is it faster than a scattering media?
> C U
> Marc

I'm impressed. Progressively transparent is more like it, as the loop
increses the filter value and the rgb value, and decreases the roughness and
diffuse value as the spheres get bigger. Not really faster, or better than
media yet, just different.

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Glad to see you're still posting here, Dave :) Have you tried this trick 
using cylinders, cones and torii in csg operations yet? Those objects 
should take well to linear transformations, as opposed to blobs and 
isosurfaces which may give strange results using this technique.

Dave Dunn wrote:

> Here is an image that came out of a discussion in our Thrursday night
> POV-Ray chat on AOL. The idea was to obtain a subsurface scattering
> effect without using media, just to see if it could be done. While far
> from perfect, this method shows promise, but is very slow.
> 
> 
> 
> 
> 
> 
> ------------------------------------------------------------------------
> 


-- 
Samuel Benge

sbe### [at] caltelcom

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Samuel Benge wrote:

> Glad to see you're still posting here, Dave :) Have you tried this trick
> using cylinders, cones and torii in csg operations yet? Those objects
> should take well to linear transformations, as opposed to blobs and
> isosurfaces which may give strange results using this technique.

As a matter of fact, I am currently working on a couple of crayons using this
technique, involving CSG of a cylinder and a cone, scaled in two directions.
If it works out, I will post.

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I tried doing this myself a few weeks ago and the results using concentric
spheres were significantly slower then media.  I thought this was a similar
technique to the stacked-planes-clouds which are remarkably faster then
scattering media clouds.  I must be mistaken somewhere.

Skip

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BTW if you want hi Q stacked clouds , you need a lot of planes and it
becomes slower and slower
Marc

3d2c9a21$1@news.povray.org...
> I tried doing this myself a few weeks ago and the results using concentric
> spheres were significantly slower then media.  I thought this was a
similar
> technique to the stacked-planes-clouds which are remarkably faster then
> scattering media clouds.  I must be mistaken somewhere.
>
> Skip
>
>

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Skip Talbot wrote:

> I tried doing this myself a few weeks ago and the results using concentric
> spheres were significantly slower then media.  I thought this was a similar
> technique to the stacked-planes-clouds which are remarkably faster then
> scattering media clouds.  I must be mistaken somewhere.

Well, as I said, I just started playing with this method. The thing I like
about it is that it gives you a lot of control over things that happen
incrementally "inside" your composite object. By incrementing and decrementing
features (such as roughness), you can get some interesting effects. I don't
think it's any better than media, overall, just an interesting thought
exercise. The slowness factor, in my case, was a max_trace_level of 100, for
100 nested spheres. I believe the falloff is much sooner than that, and I
probably could have gotten by with a lower trace level. More on this method
when the crayons are finished.

Dave

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> > I tried doing this myself a few weeks ago and the results using concentric
> > spheres were significantly slower then media.  I thought this was a similar
> > technique to the stacked-planes-clouds which are remarkably faster then
> > scattering media clouds.  I must be mistaken somewhere.
> 
> Well, as I said, I just started playing with this method. The thing I like
> about it is that it gives you a lot of control over things that happen
> incrementally "inside" your composite object. By incrementing and decrementing
> features (such as roughness), you can get some interesting effects. I don't
> think it's any better than media, overall, just an interesting thought
> exercise. The slowness factor, in my case, was a max_trace_level of 100, for
> 100 nested spheres. I believe the falloff is much sooner than that, and I
> probably could have gotten by with a lower trace level. More on this method
> when the crayons are finished.

Hmm...  To really slow things down, would there be any way to use the 
trick to simulate variable internal IOR, however crudely?

It would probably require an obscenely high max_trace_level though.

And i can't remember if you can apply a pattern to the surface iro or 
not, as I't sbeen a while since I played with POV.

Jamie.

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In article <MPG.1797f33af91f8e37989b84@news.povray.org>,
 Jamie Davison <jam### [at] ntlworldcom> wrote:

> Hmm...  To really slow things down, would there be any way to use the 
> trick to simulate variable internal IOR, however crudely?
> 
> It would probably require an obscenely high max_trace_level though.

You can, and it does. It can get very slow.


> And i can't remember if you can apply a pattern to the surface iro or 
> not, as I't sbeen a while since I played with POV.

You can't any more, that was removed in 3.1 because it didn't really 
make any sense. Earlier versions had ior in the finish block, so you 
could use a texture_map, 3.1 and 3.5 have it in the interior block.

However, you could apply a normal to the refracting layers if all you 
want is to introduce some irregularities.

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

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Jamie Davison wrote:

> Hmm...  To really slow things down, would there be any way to use the
> trick to simulate variable internal IOR, however crudely?

The problem I had when using ior of any kind on nested objects is that POV goes on
vacation and says see you next month. I couln't even get it to the point where it
would render a single line.

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> > Hmm...  To really slow things down, would there be any way to use the 
> > trick to simulate variable internal IOR, however crudely?
> > 
> > It would probably require an obscenely high max_trace_level though.
> 
> You can, and it does. It can get very slow.

I thought it might :)

> > And i can't remember if you can apply a pattern to the surface iro or 
> > not, as I't sbeen a while since I played with POV.

translation:

And I can't remember if you can apply a pattern to the surface ior or 
not, as it's been a while since I played with POV.
 
> You can't any more, that was removed in 3.1 because it didn't really 
> make any sense. Earlier versions had ior in the finish block, so you 
> could use a texture_map, 3.1 and 3.5 have it in the interior block.

Oh, I knew it was in the interior block, I just couldn't remember if 
there was any way to vary the ior over the surface of an object.

> However, you could apply a normal to the refracting layers if all you 
> want is to introduce some irregularities.

As well as increasing the render time further still, and requiring even 
higher max_trace etc. etc.

Yeesh.  Please ignore the typo's, my brain has gone on holiday for the 
evening :)

Jamie.

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