Hi everyone,

Now that we have backside illumination in 3.7, I thought I would try to 
combine subsurface scattering and radiosity with it.

I used two objects to get the SSS effect. One object is inside the 
other, scaled along the normals so that it fits neatly inside. The 
outside object uses unrealistic diffuse n,n values. The inside object is 
just a container for media.

The backside illumination takes media (and also the 
fade_power/fade_distance/fade_color interior attributes, not used here) 
into account, so what we have is an opaque, paper-like shell filled with 
a light-attenuating medium to keep the rays from going too far.

If POV could have an object look at its own interior media (and 
fade_power stuff), two objects would not be needed for this effect.

Here is a quick look at the objects and materials:

union{
  object{dodecaWire_p1_
   pigment{rgb 1 transmit 0}
   finish{diffuse .25,.75}
  }
  object{dodecaWire_p2_
   pigment{rgbt 1}
   interior{
    media{absorption<.25,.5,1>*15}
   }
  }
  hollow
}

Notice in the image how shadows cast from the POV logo do not make much 
of a difference in the SSS effect. The is the main reason I consider 
this only a partial success.

Perhaps this technique could shed some light on how radiosity and 
subsurface scattering may someday be joined happily? Perhaps also 
somebody can trick POV into allowing an object to recognize its own 
interior media and fade_stuff as far as backside illumination goes? That 
would be cool :D

Sam

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stbenge schrieb:
 > Perhaps also
> somebody can trick POV into allowing an object to recognize its own 
> interior media and fade_stuff as far as backside illumination goes? That 
> would be cool :D

I must confess I have no idea whatsoever what you mean by that.

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clipka wrote:
> stbenge schrieb:
>  > Perhaps also
>> somebody can trick POV into allowing an object to recognize its own 
>> interior media and fade_stuff as far as backside illumination goes? 
>> That would be cool :D
> 
> I must confess I have no idea whatsoever what you mean by that.

Okay, take this object for instance:

object{dodecaWire_p1_
  pigment{rgb 1}
  finish{diffuse .25,.75}
  interior{
   media{absorption<.25,.5,1>*15}
  }
  hollow
}

Render that and you have no SSS effect, you only get backside 
illumination effects. You might as well have not even given that object 
media.

An object's media (or interior fading) will not cast shadows onto the 
object itself.

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stbenge schrieb:
> Render that and you have no SSS effect, you only get backside 
> illumination effects. You might as well have not even given that object 
> media.
> 
> An object's media (or interior fading) will not cast shadows onto the 
> object itself.

That's not how it should be of course.

Now that you mention it, I didn't add any code to explicitly inform 
POV-Ray that during the backside shadow testing we're /inside/ the 
object of course (if it is solid and not just a patch). Symptoms to be 
expected: Failure of POV-Ray to compute media for the object...

Ouch.

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clipka wrote:
> stbenge schrieb:
>> Render that and you have no SSS effect, you only get backside 
>> illumination effects. You might as well have not even given that 
>> object media.
>>
>> An object's media (or interior fading) will not cast shadows onto the 
>> object itself.
> 
> That's not how it should be of course.

I thought so too, but figured there was a good reason why the developers 
left out support for it.

> Now that you mention it, I didn't add any code to explicitly inform 
> POV-Ray that during the backside shadow testing we're /inside/ the 
> object of course (if it is solid and not just a patch). Symptoms to be 
> expected: Failure of POV-Ray to compute media for the object...
> 
> Ouch.

Unless I'm mistaken, such a thing would have gone unnoticed for a long 
time...

BTW, thank you for all the effort you've been putting into POV lately :)

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