White spots appear at the edges of the cutted torus. I use POVray
3.6.1.icl8.win32 and Win2k (1GB RAM, 1GHz Pentium). I also tried to install
3.6.1a, but it crashes on startup.

This is my scene file:

// Commandline options:
// +W1024 +H768


camera {
 location <0, 1, -5.5>
 look_at <0, 1, 0>
}


light_source {<-10, 20, -45> color rgb 1}


object {
 intersection {
  torus { 2 , 0.25 }
  plane { -x, 0 }
 }

 pigment { rgbf 1 }

 interior {
  media {
   absorption 0
   emission .75

   density {
    color rgb <1, .8, .8>
   }
  }
 }

 hollow

 rotate <60, -60, 0>
}


object {
 difference
 {
  sphere { <0, -9750, 0>, 10000 }
  sphere { <0, -9750, 0>, 9990 }
 }
 pigment { color rgb 1 }
}

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AnaMark nous apporta ses lumieres en ce 2005-08-19 04:11:
> White spots appear at the edges of the cutted torus. I use POVray
> 3.6.1.icl8.win32 and Win2k (1GB RAM, 1GHz Pentium). I also tried to install
> 3.6.1a, but it crashes on startup.
> 
> This is my scene file:
> 
> // Commandline options:
> // +W1024 +H768
> 
> 
> camera {
>  location <0, 1, -5.5>
>  look_at <0, 1, 0>
> }
> 
> 
> light_source {<-10, 20, -45> color rgb 1}
> 
> 
> object {
>  intersection {
>   torus { 2 , 0.25 }
>   plane { -x, 0 }
Using 0.01 get rid of the white pixels.
>  }
> 
>  pigment { rgbf 1 }
> 
>  interior {
>   media {
>    absorption 0
>    emission .75
> 
>    density {
>     color rgb <1, .8, .8>
>    }
>   }
>  }
> 
>  hollow
> 
>  rotate <60, -60, 0>
> }
> 
> 
> object {
>  difference
>  {
>   sphere { <0, -9750, 0>, 10000 }
>   sphere { <0, -9750, 0>, 9990 }
>  }
>  pigment { color rgb 1 }
> }
> 
> 
Also, rendering at another size elliminated those white pixels. I think that those are
related to 
presision and rounding errors.

Alain

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Alain <ele### [at] netscapenet> wrote:
> > White spots appear at the edges of the cutted torus. [...]
> >
> > This is my scene file:
> > [...]
> >  intersection {
> >   torus { 2 , 0.25 }
> >   plane { -x, 0 }
> Using 0.01 get rid of the white pixels.

I know; I already tried this (and many, many other variations).
Unfortunately, this is an animation. And although the white spots do no
longer appear in this image, they will appear in another image at another
place. So nothing is won.

> Also, rendering at another size elliminated those white pixels.

Again, it's the same: The spots may disappear in this image. Therefore, in
another image, new spots will appear. Nothing is won.

BTW: It's a video animation, and so resolution is fixed.
BTW^2: The final rendering has to be done with anti-aliasing. But using AA
(doesn't matter, which of the both algorithms will be used) makes the
problem even worse.

> I think that those are related to
> presision and rounding errors.

Sorry, but - imo - a raytracer should be capable to properly render such
simple things as a cut torus, shouldn't it?

Post a reply to this message

"AnaMark" <mh### [at] homologde> wrote:
> Alain <ele### [at] netscapenet> wrote:
> > > White spots appear at the edges of the cutted torus. [...]
> > >
> > > This is my scene file:
> > > [...]
> > >  intersection {
> > >   torus { 2 , 0.25 }
> > >   plane { -x, 0 }
> > Using 0.01 get rid of the white pixels.
>
> I know; I already tried this (and many, many other variations).
> Unfortunately, this is an animation. And although the white spots do no
> longer appear in this image, they will appear in another image at another
> place. So nothing is won.
>
> > Also, rendering at another size elliminated those white pixels.
>
> Again, it's the same: The spots may disappear in this image. Therefore, in
> another image, new spots will appear. Nothing is won.
>
> BTW: It's a video animation, and so resolution is fixed.
> BTW^2: The final rendering has to be done with anti-aliasing. But using AA
> (doesn't matter, which of the both algorithms will be used) makes the
> problem even worse.
>
> > I think that those are related to
> > presision and rounding errors.
>
> Sorry, but - imo - a raytracer should be capable to properly render such
> simple things as a cut torus, shouldn't it?

The bug is more likely cause by the ray entering and leaving the media at
the same moment, but the tracer only registering the fact that it entered
(thereby finding an infinite amount of white space).  Does adding a crushed
sphere on to each end mess your file up any?  That fixes it.  Values of
..001 or less are probably enough, and only noticible in things like
reflections.

Post a reply to this message

davvblack nous apporta ses lumieres en ce 2005-08-31 18:08:

> 
> The bug is more likely cause by the ray entering and leaving the media at
> the same moment, but the tracer only registering the fact that it entered
> (thereby finding an infinite amount of white space).  Does adding a crushed
> sphere on to each end mess your file up any?  That fixes it.  Values of
> ..001 or less are probably enough, and only noticible in things like
> reflections.
> 
> 
As this is an animation, and that the cuting plane does change, placing those sphere
can become very 
difficult or impossible. That's because the edges are not circles nor ellipses: the
top and bottom 
dadiuses are not the same and the shape will change from frame to frame.


Alain

Post a reply to this message

AnaMark <mh### [at] homologde> wrote:

> White spots appear at the edges of the cutted torus. I use POVray
> 3.6.1.icl8.win32 and Win2k (1GB RAM, 1GHz Pentium).

The white spots are a result of the changed clipping of colors in
POV-Ray 3.6 . Using anti-aliasing will accentuate the problem.

Either go back to POV-Ray 3.5 for the old behaviour, or use MegaPOV 1.21
and the tone mapping feature.

With MegaPOV 1.21, add the following to the source to get the POV-Ray
3.5 clipping:

#version unofficial MegaPov 1.21;
global_settings {
  tone_mapping { function { min(1,x) } }
}

or use the macro from the tone_mapping.inc file:

#include "tone_mapping.inc"
#version unofficial MegaPov 1.21;
global_settings {
  Clip_Colors()
}


-- 
e-mail:sme### [at] skynetbe

http://users.skynet.be/smellenbergh

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