POV-Ray : Newsgroups : povray.beta-test : media & fog bug? Server Time
30 Jun 2022 11:47:24 EDT (-0400)
  media & fog bug? (Message 1 to 6 of 6)  
From: Kevin Ellis
Subject: media & fog bug?
Date: 9 Dec 2001 09:49:04
Message: <3c1379e0$1@news.povray.org>
Hi,

Is this a bug with media containers and fog, surely the following scene
should render the same for all possible combinations of FogSw, MediaSw=1or
0, due to media being totally transparent, adding fog seems to be the
culprit



//Begin buggy scene

#declare FogSw=1; // 1=on, 0=off
#declare MediaSw=1; //1=on, 0=off

camera {
  location <0,2,-14>
  right <16/9,0,0>
  look_at <-1,2,0>
}

light_source {
  <0,200000000,0>
  color rgb <1,0.8,0.65>*1.8
  rotate <0,0,50>
  rotate <0,20,0>
}

sky_sphere {
  pigment {
    bozo
    color_map {
      [0 rgb <0.4,0.6,0.8>*0.87]
      [1 rgb <0.4,0.65,0.9>*1]
    }
    scale 0.1
    turbulence 0.8
    octaves 4
    lambda 2
    omega 0.4
  }
}

#if(FogSw)
fog {
  fog_type 2
  distance 200
  fog_offset 0
  fog_alt 80
  color rgb <0.8,0.8,0.75>*1
}
#end

#if(MediaSw)
box {
  <-30000,700,-60000>
  <30000,900,60000>
  material {
    texture {
      pigment {rgbt 1}

    }
    interior {
      media {
        scattering {5, 0.00 extinction 1 eccentricity 0.005}
        method 3
        intervals 1
        aa_level 4
        jitter 0.1
        density {
          rgb 1
        }
      }
    }
  }
  hollow
}
#end

plane {y,0 texture {pigment {rgb 1}


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From: Kevin Ellis
Subject: Re: media & fog bug?
Date: 9 Dec 2001 09:59:57
Message: <3c137c6d@news.povray.org>
oops Pov 3.5 b8, Intel compile, Win98, 1.33Ghz Athlon, 512MB ram
.................and a partridge in a pear tree :)

Kev


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From: Ken
Subject: Re: media & fog bug?
Date: 9 Dec 2001 18:50:30
Message: <3C13F95B.E4E09D82@pacbell.net>
Kevin Ellis wrote:
> 
> Hi,
> 
> Is this a bug with media containers and fog, surely the following scene
> should render the same for all possible combinations of FogSw, MediaSw=1or
> 0, due to media being totally transparent, adding fog seems to be the
> culprit

I am pretty sure that this falls into the "not a bug" category. I know
this problem was present in v3.1g and have seen someone suggest a work
around for it. I just can't seem to find the article in question at the
moment.

-- 
Ken Tyler - POV-Ray Technical Assistance Group


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From: bob h
Subject: Re: media & fog bug?
Date: 9 Dec 2001 21:30:25
Message: <3c141e41@news.povray.org>
"Ken" <tyl### [at] pacbellnet> wrote in message
news:3C13F95B.E4E09D82@pacbell.net...
>
> Kevin Ellis wrote:
> >
> > Is this a bug with media containers and fog, surely the following scene
> > should render the same for all possible combinations of FogSw,
MediaSw=1or
> > 0, due to media being totally transparent, adding fog seems to be the
> > culprit
>
> I am pretty sure that this falls into the "not a bug" category. I know
> this problem was present in v3.1g and have seen someone suggest a work
> around for it. I just can't seem to find the article in question at the
> moment.

If you're talking about using larger than 1 for transparency then it isn't
really possible to get a correct result, esp. not in every situation.  I
tried the script and with rgbt 1.6 for the box media container the plane is
approx. the same color as without media.  The fog becomes enhanced too
though.  If a filter value which matches that of the box is used in the fog
color then the original coloration appears.
--
text{ttf"arial","bob h",.1,0pigment{rgb 9}translate<-1,-.2,3>}


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From: Kevin Ellis
Subject: Re: media & fog bug?
Date: 10 Dec 2001 03:06:50
Message: <3c146d1a@news.povray.org>
"Ken" <tyl### [at] pacbellnet> wrote in message
news:3C13F95B.E4E09D82@pacbell.net...
> I am pretty sure that this falls into the "not a bug" category. I know
> this problem was present in v3.1g and have seen someone suggest a work
> around for it. I just can't seem to find the article in question at the
> moment.

Sorry Ken, but I'll have to disagree with you on this one as in my opinion
it is definitely a bug. The work around that I have found is to use
radiosity with the media on switch, but this is incredibly slow when the
ground is an isosurface, but this is still not a complete solution.

The media container in the example should contain clouds so I should get
some shadow from just the clouds, at the moment the whole box casts a shadow
with the above radiosity solution I still get no shadows from the clouds. I
have been experimenting with media clouds since MegaPOV and have never
experienced this problem before. I realise that POV v3.5 is not MegaPOV it's
just that MegaPOV seemed to have the correct behaviour, or maybe I was just
plain lucky and never ran into the problem, could someone please check
MegaPOV for me as I no longer have it or v3.1 installed?

Kev


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From: bob h
Subject: Re: media & fog bug?
Date: 10 Dec 2001 03:58:29
Message: <3c147935@news.povray.org>
"Kevin Ellis" <kev### [at] tiscalicouk> wrote in message
news:3c146d1a@news.povray.org...
>
> "Ken" <tyl### [at] pacbellnet> wrote in message
> news:3C13F95B.E4E09D82@pacbell.net...
> > I am pretty sure that this falls into the "not a bug" category. I know
> > this problem was present in v3.1g and have seen someone suggest a work
> > around for it. I just can't seem to find the article in question at the
> > moment.
>
> Sorry Ken, but I'll have to disagree with you on this one as in my opinion
> it is definitely a bug. The work around that I have found is to use
> radiosity with the media on switch, but this is incredibly slow when the
> ground is an isosurface, but this is still not a complete solution.
>
> The media container in the example should contain clouds so I should get
> some shadow from just the clouds, at the moment the whole box casts a
shadow
> with the above radiosity solution I still get no shadows from the clouds.
I
> have been experimenting with media clouds since MegaPOV and have never
> experienced this problem before. I realise that POV v3.5 is not MegaPOV
it's
> just that MegaPOV seemed to have the correct behaviour, or maybe I was
just
> plain lucky and never ran into the problem, could someone please check
> MegaPOV for me as I no longer have it or v3.1 installed?

Admittedly the box container object itself does seem to cast a shadow when
it should not be.  I'm just uncertain of the fact myself.
For media transmit can cast shadows too now, although at transmit 1 there
shouldn't be anything to cast a shadow from the box alone.  Before, in
earlier MegaPOV versions media couldn't cast shadows unless filter was used
instead (correct me if I'm wrong on that, anyone) but it didn't hamper
regular objects.

I can get shadows from clouds to show up simply by using:

box {
  <-30000,700,-60000>/10
  <30000,900,60000>/10
  material {
    texture {
      pigment {rgbt 1}

    }

    interior {
      media {
        scattering {5, .01 extinction 1 eccentricity 0.005}
        method 2 // speedier
        intervals 1
        aa_level 4
        jitter 0.1
        density {
                marble
                density_map {
                        [0 rgb 10] [.25 rgb 0]
                        } frequency 2 turbulence 1 scale 500
        }
      }
    }

  }
  hollow
}

instead of the box object you have there now, plus I put keyword parallel
into the light source.
Anyway, it does look as if there might be a problem since the shadow is not
seen when looking from above the lowest part of the box.  It manifests
itself when viewed from under the box.  At least I think it does.


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