Chris Huff wrote:
> 
> A sor should be pretty easy, a lathe shouldn't be extremely difficult. A
> mesh may not be a huge problem either. Simple convex prisms also
> wouldn't be hard, but concave or self-intersecting prisms could be a
> bigger problem.

With linear splines this should be easy too, but the others would involve
some more complicated math that would probably be quite slow when not hard
coded.

> Basically the distance of the nearest point on the surface, with a
> negative sign if inside the object and a positive sign if outside.
> This is what my proximity pattern will eventually do.

proximity pattern is quite slow right now, but for linear spline
prisms/lathe/sor, i could think of a different algorithm dividing space
into segments where proximity only depends on a single plane, that would
use quite a lot of memory, but it would be fast.  Of course this would
also have some problems with concave shapes, but since the isosurface use
only needs good results near the actual surface, this is not that
problematic.

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
Homepage: http://www.schunter.etc.tu-bs.de/~chris/

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Christoph Hormann wrote in message
<3A1F8692.ECF21C45@schunter.etc.tu-bs.de>...
> > Basically the distance of the nearest point on the surface, with a
> > negative sign if inside the object and a positive sign if outside.
> > This is what my proximity pattern will eventually do.
>
> proximity pattern is quite slow right now...

but don't need so much small accuracy and perhaps so big max_gradient
therefore this could be faster than pigment{object{}}
I'll tell you after (ray)tracing

ABX
VooVoo is not VooDoo -> http://www.voovoo.art.pl/

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In article <3a1f8d4b@news.povray.org>, "Wlodzimierz ABX Skiba" 
<abx### [at] abxartpl> wrote:

> but don't need so much small accuracy and perhaps so big max_gradient
> therefore this could be faster than pigment{object{}}

In order to get a smooth enough pattern that the isosurface algorithm 
can use it, you need to use a huge number of samples. It has been tried 
before, but was too slow to be of practical use.
However, I am working on an updated version that has specialized 
proximity functions for each object as well as the existing sampling 
function...this will be much faster for many objects.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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Chris Huff wrote in message ...
> However, I am working on an updated version that has specialized
> proximity functions for each object as well as the existing sampling
> function...this will be much faster for many objects.


sounds great

ABX

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Chris Huff <chr### [at] maccom> wrote:
: but 
: his color_map is [0 rgb 1][0 rgb 0][1 rgb 0], which looks like a mistake 
: to me...it is completely black, with no variation at all

  Did you actually try to render an object with that pigment?
  It's not completely black :)

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):_;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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Chris Huff <chr### [at] maccom> wrote:
: What are you expecting this color_map to result in? It starts out as 
: white, but goes to black in 0 distance and ends in black, basically a 
: black pigment...

  Try rendering a plane with that pigment.

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):_;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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In article <3a221a8d@news.povray.org>, Warp <war### [at] tagpovrayorg> 
wrote:

>   Did you actually try to render an object with that pigment?

I rendered a unit-radius sphere... :-(


>   It's not completely black :)

Right...it's a black cube surrounded with white, something that could 
just as easily been done using the object pattern with a box. It still 
won't work very well for isosurfaces, which dislike instantaneous 
changes in value.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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Well, my original idea was precisely trying to recreate any object with
an isosurface using an object pigment. Seems that I'm not the first to
get the idea.
  And I understand now why it doesn't work.

  So still no easy non-uniform transformations. Sorry :)

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):_;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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Warp wrote:
> 
>   Well, my original idea was precisely trying to recreate any object with
> an isosurface using an object pigment. Seems that I'm not the first to
> get the idea.

Someone tried it a while ago.  Using "object" pattern doesn't work,
because of the "abrupt changes".  Using "proximity" pattern works
better, but is, as expected, awfully slow...

Fabien.

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Fabien Mosen wrote in message <3A227FD2.280D7793@skynet.be>...
> Someone tried it a while ago.  Using "object" pattern doesn't work,
> because of the "abrupt changes".  Using "proximity" pattern works
> better, but is, as expected, awfully slow...


currently I'm trying with specialized patch

ABX

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