POV-Ray : Newsgroups : povray.beta-test : absorption media/media attenuation-bug? Server Time
29 Jul 2024 18:30:51 EDT (-0400)
  absorption media/media attenuation-bug? (Message 1 to 4 of 4)  
From: Abe
Subject: absorption media/media attenuation-bug?
Date: 7 Mar 2002 19:10:14
Message: <3C880122.9C9C0CE4@taconic.net>
I got no reply on my previous post, so I'll try again.

The following code should in my understanding produce a redish sphere
(attenuation of colors appearing behind the sphere) but no shadow with
media_attenuation off on the light source. 
////////////////////
camera {location  -z*4.0}
background{color rgb .7}

light_source {<-30, 60, 30> color rgb 1  
  media_interaction off
  media_attenuation off
}

box {<-2,-1.2,-2><2,-1,2>  pigment { color rgb 1 } finish{diffuse .9}}

sphere {  0.0, 1 hollow
  pigment {rgbt 1}
  interior{
   media{absorption rgb <0,1,1>}
   //media{scattering{1 rgb <1,0,0>*5 extinction 0 }}
  }
}
////////////

POV 3.1 seems to respond appropriately, but both MegaPOV and POV 3.5 do
not respond to media_attenuation (or media_interaction for that matter)
with absorption media. Sample pics posted in povray.beta-test.binaries.

Can someone substantiate this?

Abe


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From: ingo
Subject: Re: absorption media/media attenuation-bug?
Date: 8 Mar 2002 02:09:59
Message: <Xns91CB536B5DDE2seed7@povray.org>
in news:3C880122.9C9C0CE4@taconic.net Abe wrote:

> sphere {  0.0, 1 hollow
>   pigment {rgbt 1}

If you change it to :

sphere {  0.0, 1 hollow
   pigment {rgbf 1}

You also get the shadow in 3.1g.
To get no shadow in 3.5 you have to use no_shadow in the object. The 
difference in behaviour between rgbf an rgbt that was there in 3.1 was a 
bug that is fixed in 3.5. See:
"2.6.14  Changed features that may 'break' old scenes"
and "6.8  Media" near the end.

Also the documentation gives me the impression that  media_interaction 
and media_attenuation are for use with atmospheric media only.
"6.5.7.10  Atmospheric Media Interaction" and "6.5.7.11  Atmospheric 
Attenuation".
My impression, or the docs, may be wrong here.

Ingo



Ingo


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From: Abe
Subject: Re: absorption media/media attenuation-bug?
Date: 8 Mar 2002 20:08:31
Message: <3C89604E.36473A82@taconic.net>
Hmm. I have used the no_shadow flag you suggested also, but that will
turn off any shadows cast by surface textures. I guess it does come down
to the filter v. transmit behavior in 3.1. Phooy! 

Anyway, thanks much for your reply!
Abe

ingo wrote:
> 
> in news:3C880122.9C9C0CE4@taconic.net Abe wrote:
> 
> > sphere {  0.0, 1 hollow
> >   pigment {rgbt 1}
> 
> If you change it to :
> 
> sphere {  0.0, 1 hollow
>    pigment {rgbf 1}
> 
> You also get the shadow in 3.1g.
> To get no shadow in 3.5 you have to use no_shadow in the object. The
> difference in behaviour between rgbf an rgbt that was there in 3.1 was a
> bug that is fixed in 3.5. See:
> "2.6.14  Changed features that may 'break' old scenes"
> and "6.8  Media" near the end.
> 
> Also the documentation gives me the impression that  media_interaction
> and media_attenuation are for use with atmospheric media only.
> "6.5.7.10  Atmospheric Media Interaction" and "6.5.7.11  Atmospheric
> Attenuation".
> My impression, or the docs, may be wrong here.
> 
> Ingo
> 
> Ingo


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From: bob h
Subject: Re: absorption media/media attenuation-bug?
Date: 10 Mar 2002 17:07:43
Message: <3c8bd92f@news.povray.org>
"Abe" <bul### [at] taconicnet> wrote in message
news:3C89604E.36473A82@taconic.net...
> Hmm. I have used the no_shadow flag you suggested also, but that will
> turn off any shadows cast by surface textures. I guess it does come down
> to the filter v. transmit behavior in 3.1. Phooy!

Ha, well, I believe the real problem (which actually is not one) is due to
the fact absorbing and emitting media both do not react according to light
sources in the way scattering does.  Those are different things.  absorption
and emission do not rely on light.

bob h


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