Perhaps I'm suffering from an intellectual low here... I'll let you decide.

Excerpt from the docs:

Normally light coming from light sources is not influenced by fog or
atmospheric media. This can be changed by turning the media_attenuation on
for a given light source on. All light coming from this light source will
now be diminished as it travels through the fog or media.

The way I understand this, media should not cast shadows unless I turn
media_attenuation on. Much to my surprise, I discovered this to be
incorrect - absorbing media always casts shadows (unless the container
object uses transmit). I'm suddenly puzzled as to the meaning and use of
media_attenuation.

Please enlighten me...

Margus

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interaction should mean media shows up, shadows and all. attenuation
must mean then distance fading. If I'm right do I win anything?


Margus Ramst wrote:
> 
> The way I understand this, media should not cast shadows unless I turn
> media_attenuation on. Much to my surprise, I discovered this to be
> incorrect - absorbing media always casts shadows (unless the container
> object uses transmit). I'm suddenly puzzled as to the meaning and use of
> media_attenuation.
> 
> Please enlighten me...
> 
> Margus

-- 
 omniVERSE: beyond the universe
  http://members.aol.com/inversez/homepage.htm
 mailto:inv### [at] aolcom?Subject=PoV-News

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No winners. Turning media_interaction off doesn't get rid of the shadow. The
media simply isn't lit by the light source. And IMO, distance fading _is_
what causes the media to cast shadows. The thicker the media, the darker the
shadow.

Margus

Bob Hughes wrote in message <371### [at] aolcom>...
>interaction should mean media shows up, shadows and all. attenuation
>must mean then distance fading. If I'm right do I win anything?
>
>--
> omniVERSE: beyond the universe
>  http://members.aol.com/inversez/homepage.htm
> mailto:inv### [at] aolcom?Subject=PoV-News

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The Point for the media_interaction parameter is that
you can exclude some of your light sources from the media computing
process, let's say you have a scene with one primary light ( The Sun )
and you have an media object ( some clouds ) and then you have many other
lights, with fade_power and distance assigned, which never reach the clouds,
then you can turn the media_interaction for those lightsources off to get
faster rendering times.

i think thats the only reason this feature exists.

by the way does anybody know how to turn off recieving shadows
with scattering media ?

greetings Lars

Margus Ramst schrieb in Nachricht <3710d9fd.0@news.povray.org>...
>Perhaps I'm suffering from an intellectual low here... I'll let you decide.
>
>Excerpt from the docs:
>
>Normally light coming from light sources is not influenced by fog or
>atmospheric media. This can be changed by turning the media_attenuation on
>for a given light source on. All light coming from this light source will
>now be diminished as it travels through the fog or media.
>
>The way I understand this, media should not cast shadows unless I turn
>media_attenuation on. Much to my surprise, I discovered this to be
>incorrect - absorbing media always casts shadows (unless the container
>object uses transmit). I'm suddenly puzzled as to the meaning and use of
>media_attenuation.
>
>Please enlighten me...
>
>Margus
>
>
>
>

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I understand what media_interaction does. The problem is, even when light is
not scattered by media, the media still casts shadows!

IMO, the correct behaviour would be the following:
1) interaction on & attenuation on - light is scattered and attenuated (the
media casts shadows, unto itself and other objects/medias);
2) interaction off & attenuation on - light is not scattered but the media
still casts shadows from this light source;
3) interaction on & attenuation off - light is scattered, but _not_
attenuated, i.e. the media casts _no shadows_ from this light source, not
unto itself, not anywhere else;
4) interaction off & attenuation off - the media is not affected by this
light source in any way.

Because of a pseudo-bug in transmit, conditions 3) and 4) behave in the
described way when the container objects uses transmitted transparency
(regardless of media_attenuation setting). But with filtered transparency,
media casts shadows under all of these conditions.
All in all, I cannot see any difference in the rendered image, whether
media_attenuation is on or off.

Margus

Lars W. wrote in message <3711dff8.0@news.povray.org>...
>The Point for the media_interaction parameter is that
>you can exclude some of your light sources from the media computing
>process, let's say you have a scene with one primary light ( The Sun )
>and you have an media object ( some clouds ) and then you have many other
>lights, with fade_power and distance assigned, which never reach the
clouds,
>then you can turn the media_interaction for those lightsources off to get
>faster rendering times.
>
>i think thats the only reason this feature exists.
>
>by the way does anybody know how to turn off recieving shadows
>with scattering media ?
>
>greetings Lars
>

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Not that I understand all this any but the interactive part sounds like
it was intended to do just that, interact with the media in a normal
way. The little I've done in this regard doesn't allow me much insight.
But I understand your predicament there. Obviously the workings of media
allow for absorption to create a shadow by simple interaction with a
light and attenuation is only to fade.
But I'm not going to try and remember what the behaviours all are, Id
rather do some checking of this myself before committing to a judgement.
Keep in mind though what you say makes sense though could easily be a
observation of what was intended. No doubt since the transmit lacking a
shadow and all that as many of us know, there's possibility of
incorrectness in the thing elsewhere.

Margus Ramst wrote:
> 
> I understand what media_interaction does. The problem is, even when light is
> not scattered by media, the media still casts shadows!
> 
> IMO, the correct behaviour would be the following:
> 1) interaction on & attenuation on - light is scattered and attenuated (the
> media casts shadows, unto itself and other objects/medias);
> 2) interaction off & attenuation on - light is not scattered but the media
> still casts shadows from this light source;
> 3) interaction on & attenuation off - light is scattered, but _not_
> attenuated, i.e. the media casts _no shadows_ from this light source, not
> unto itself, not anywhere else;
> 4) interaction off & attenuation off - the media is not affected by this
> light source in any way.
> 
> Because of a pseudo-bug in transmit, conditions 3) and 4) behave in the
> described way when the container objects uses transmitted transparency
> (regardless of media_attenuation setting). But with filtered transparency,
> media casts shadows under all of these conditions.
> All in all, I cannot see any difference in the rendered image, whether
> media_attenuation is on or off.
> 
> Margus
> 
> Lars W. wrote in message <3711dff8.0@news.povray.org>...
> >The Point for the media_interaction parameter is that
> >you can exclude some of your light sources from the media computing
> >process, let's say you have a scene with one primary light ( The Sun )
> >and you have an media object ( some clouds ) and then you have many other
> >lights, with fade_power and distance assigned, which never reach the
> clouds,
> >then you can turn the media_interaction for those lightsources off to get
> >faster rendering times.
> >
> >i think thats the only reason this feature exists.
> >
> >by the way does anybody know how to turn off recieving shadows
> >with scattering media ?
> >
> >greetings Lars
> >

-- 
 omniVERSE: beyond the universe
  http://members.aol.com/inversez/homepage.htm
 mailto:inv### [at] aolcom?Subject=PoV-News

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Well, I'll simply say this:
Somebody, ANYBODY, please show me a scene where turning media_attenuation on
or off makes any difference at all.
I'm beginning to feel this keyword is completely useless, because of a bug.
Prove me wrong, if you can. Otherwise, a bug report is imminent.

Margus

Bob Hughes wrote in message <3712BC15.1EAC0421@aol.com>...
>Not that I understand all this any but the interactive part sounds like
>it was intended to do just that, interact with the media in a normal
>way. The little I've done in this regard doesn't allow me much insight.
>But I understand your predicament there. Obviously the workings of media
>allow for absorption to create a shadow by simple interaction with a
>light and attenuation is only to fade.
>But I'm not going to try and remember what the behaviours all are, Id
>rather do some checking of this myself before committing to a judgement.
>Keep in mind though what you say makes sense though could easily be a
>observation of what was intended. No doubt since the transmit lacking a
>shadow and all that as many of us know, there's possibility of
>incorrectness in the thing elsewhere.
>

Post a reply to this message

After testing that out i can say too that this thing seems to be useless,
a tried all types of media, with filter and transmit and other
things.
By the Way i found an other thing which seems to be incorrect :
i understand it that way, when you use mediainteraction off on a
light_source
the light should interact in no way with the media, but it interacts with
the
absorption value, i mean the light gets dismished, when travelling thru
the media even if media interaction s off. should that be in that way ?

Margus Ramst <mar### [at] peakeduee> schrieb in im Newsbeitrag:
37137a2e.0@news.povray.org...
> Well, I'll simply say this:
> Somebody, ANYBODY, please show me a scene where turning media_attenuation
on
> or off makes any difference at all.
> I'm beginning to feel this keyword is completely useless, because of a
bug.
> Prove me wrong, if you can. Otherwise, a bug report is imminent.
>
> Margus
>
> Bob Hughes wrote in message <3712BC15.1EAC0421@aol.com>...
> >Not that I understand all this any but the interactive part sounds like
> >it was intended to do just that, interact with the media in a normal
> >way. The little I've done in this regard doesn't allow me much insight.
> >But I understand your predicament there. Obviously the workings of media
> >allow for absorption to create a shadow by simple interaction with a
> >light and attenuation is only to fade.
> >But I'm not going to try and remember what the behaviours all are, Id
> >rather do some checking of this myself before committing to a judgement.
> >Keep in mind though what you say makes sense though could easily be a
> >observation of what was intended. No doubt since the transmit lacking a
> >shadow and all that as many of us know, there's possibility of
> >incorrectness in the thing elsewhere.
> >
>
>
>

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Lars W. wrote in message <3713b2cd.0@news.povray.org>...
>After testing that out i can say too that this thing seems to be useless,
>a tried all types of media, with filter and transmit and other
>things.
>By the Way i found an other thing which seems to be incorrect :
>i understand it that way, when you use mediainteraction off on a
>light_source
>the light should interact in no way with the media, but it interacts with
>the
>absorption value, i mean the light gets dismished, when travelling thru
>the media even if media interaction s off. should that be in that way ?
>


Yes, this is correct behaviour. The only type affected by media_interaction
is scattering media, because AFAIK media_interaction simply toggles
scattering. The other types do not get lit by the light source. But
absorbing (and scattering) media can attenuate, i.e. dim light, in effect
casting a shadow. This should be controlled by the media_attenuation
keyword, but apparently isn't.

Margus

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Oh, BTW, I've posted a bugreport about this.

Margus

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