Hi.

I think I have found a bug in POVRay. I'm trying to make several
concentric spheres which are all completely transparent, but which have a
reflection. If I make three or more transparent objects inside one
another, the inmost ones will be rendered totally black.

For example the following code:
---snip---
#include "colors.inc"
camera { location <0, 0, -2>  look_at 0 }
light_source { <1,1,-2> White*8 }
plane { -z, -2   pigment { Green } }

#declare COUNT=0.1;
#while (COUNT<0.31)
sphere {
        <0,0,0>,COUNT
        pigment { transmit 1.0 }
}
#declare COUNT=COUNT+0.1;
#end
---snip---

If the number 0.31 is changed to 0.21 (so there are only two concentric
spheres), the image renders, as expected, to a totally green image. But
with 0.31 or larger, there is a black sphere in the middle of the image.
(It gets bigger with larger values, so that the third outmost object is
always black.)

I originally noticed it in the Debian version "3.02.Linux.cc", but trying
the official Linux version "3.1g.Linux.gcc" didn't help. I've also tried
changing want of the options (eg. bounding box on/off), but nothing has
helped.

I'm sorry if this is a known bug/feature, but I couldn't find any info
about it. If there's a way around this, I'd be grateful if you could tell
me how to do it. (It's for a project of mine which is in a bit of a
hurry.)


(I sent this originally to tea### [at] povrayorg, they suggested I post it
here.)

-- 
  __________________________________________________
 /____\   Sampo Niskanen <=> sam### [at] ikifi  \
       \       http://www.iki.fi/sampo.niskanen/     \
        \     ________________________________________\___
         \___/___________________________________________/

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Sampo Niskanen wrote:
> 
> Hi.
> 
> I think I have found a bug in POVRay. I'm trying to make several
> concentric spheres which are all completely transparent, but which have a
> reflection. If I make three or more transparent objects inside one
> another, the inmost ones will be rendered totally black.

> I'm sorry if this is a known bug/feature, but I couldn't find any info
> about it. If there's a way around this, I'd be grateful if you could tell
> me how to do it. (It's for a project of mine which is in a bit of a
> hurry.)

See the following for an explaination and an easy fix -
http://www.students.tut.fi/~warp/povVFAQ/languageVFAQ.html#maxtracelevel

-- 
Ken Tyler

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Increase max_trace_level in your global_settings block to about 5 or so.

"Sampo Niskanen" <sam### [at] ikifi> wrote in message
news:3c1b6cc5@news.povray.org...
>
> Hi.
>
> I think I have found a bug in POVRay. I'm trying to make several
> concentric spheres which are all completely transparent, but which have a
> reflection. If I make three or more transparent objects inside one
> another, the inmost ones will be rendered totally black.
>
> For example the following code:
> ---snip---
> #include "colors.inc"
> camera { location <0, 0, -2>  look_at 0 }
> light_source { <1,1,-2> White*8 }
> plane { -z, -2   pigment { Green } }
>
> #declare COUNT=0.1;
> #while (COUNT<0.31)
> sphere {
>         <0,0,0>,COUNT
>         pigment { transmit 1.0 }
> }
> #declare COUNT=COUNT+0.1;
> #end
> ---snip---
>
> If the number 0.31 is changed to 0.21 (so there are only two concentric
> spheres), the image renders, as expected, to a totally green image. But
> with 0.31 or larger, there is a black sphere in the middle of the image.
> (It gets bigger with larger values, so that the third outmost object is
> always black.)
>
> I originally noticed it in the Debian version "3.02.Linux.cc", but trying
> the official Linux version "3.1g.Linux.gcc" didn't help. I've also tried
> changing want of the options (eg. bounding box on/off), but nothing has
> helped.
>
> I'm sorry if this is a known bug/feature, but I couldn't find any info
> about it. If there's a way around this, I'd be grateful if you could tell
> me how to do it. (It's for a project of mine which is in a bit of a
> hurry.)
>
>
> (I sent this originally to tea### [at] povrayorg, they suggested I post it
> here.)
>
> --
>   __________________________________________________
>  /____\   Sampo Niskanen <=> sam### [at] ikifi  \
>        \       http://www.iki.fi/sampo.niskanen/     \
>         \     ________________________________________\___
>          \___/___________________________________________/
>

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"Mahalis" <don### [at] fakeycom> wrote in message
news:3c1c8847@news.povray.org...
> Increase max_trace_level in your global_settings block to about 5 or so.

Sorry but I have to correct you on that, 5 is the default.  Three
semitransparent spheres have 6 surfaces for the ray to pass through and so
max_trace_level must be more than the number of instances of surfaces.
I knew what you meant though  :-)

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