I don't know if you guys are taking requests in this forum or not. This 
is something I would like to have appear in POV-Ray in the near future.

It would be nice if media could shadow the object it resides inside, and 
for there to be a force_shadow keyword for media. Let's say I had a mesh 
and I gave it a white pigment with zero brilliance, double_illuminate, 
and a no_shadow keyword. I would add absorbing media with a force_shadow 
keyword, and the result would be a reasonably fast subsurface scattering 
effect.

Right now I'm having to make a copy of the mesh which is slightly fatter 
than the original, and I'm getting strange artifacts resulting from 
ior+media. I would simply use scattering and absorbing media for this 
project, but it's impossible to reduce certain artifacts in thin 
portions, short of adding a surface normal which would increase the 
render time to new highs.

So, could this be done? To have an object with media shadow itself 
(affecting the double_illuminate diffuse), and for there to be a 
force_shadow keyword for media so that a shadowless object's media can 
still cast a shadow?

Sam

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stbenge <THI### [at] hotmailcom> wrote:
> I don't know if you guys are taking requests in this forum or not. This
> is something I would like to have appear in POV-Ray in the near future.
>
> It would be nice if media could shadow the object it resides inside, and
> for there to be a force_shadow keyword for media. Let's say I had a mesh
> and I gave it a white pigment with zero brilliance, double_illuminate,
> and a no_shadow keyword. I would add absorbing media with a force_shadow
> keyword, and the result would be a reasonably fast subsurface scattering
> effect.
>
> Right now I'm having to make a copy of the mesh which is slightly fatter
> than the original, and I'm getting strange artifacts resulting from
> ior+media. I would simply use scattering and absorbing media for this
> project, but it's impossible to reduce certain artifacts in thin
> portions, short of adding a surface normal which would increase the
> render time to new highs.
>
> So, could this be done? To have an object with media shadow itself
> (affecting the double_illuminate diffuse), and for there to be a
> force_shadow keyword for media so that a shadowless object's media can
> still cast a shadow?
>
> Sam

I've read this a few times, and I am not sure I fully understand.  What it
sounds like you are describing is scattering media.  What is the difference
between what you are describing and scattering media?

I have used scattering and absorbing medias for SSS before.  What types of
artifacts are you getting?  Can you post the related code?

FYI, there is a forum for discussion of POV-ray 4, which is where most feature
requests are.


-Reactor

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Reactor wrote:
>> So, could this be done? To have an object with media shadow itself
>> (affecting the double_illuminate diffuse), and for there to be a
>> force_shadow keyword for media so that a shadowless object's media can
>> still cast a shadow?
>>
>> Sam
> 
> I've read this a few times, and I am not sure I fully understand.  What it
> sounds like you are describing is scattering media.  What is the difference
> between what you are describing and scattering media?

Using what I am proposing, the surfaces would not be transparent. Say 
you had a plastic butter knife model. Using scattering media the usual 
way, the blade edge would be transparent. This is good for some things, 
but not others. In real life, objects have imperfections within and 
without which help to (truly) scatter passing light, thus blurring an 
image viewed through such a substance. In POV we can only blur the light 
by using a surface normal on the object. It would be impractical to 
actually blur light passing through an object, as this would render very 
slowly. Therefore, it would be nice to simply keep the object opaque 
while still achieving a SSS effect. (the effect would be much like my 
recently-posted SSS code)

The features I propose would render faster than scattering media. I can 
post examples and code if somebody is actually interested in 
implementing it, and wants to understand how it should work.

> I have used scattering and absorbing medias for SSS before.  What types of
> artifacts are you getting?  Can you post the related code?

Right near the side of the head near the eyelid, you can see straight 
through to the eye! I could use really high scattering and absorption 
settings, but new problems then arise. I could add a surface normal to 
the head, which would be somewhat more realistic, but the render times 
would skyrocket.

The code is too large to post, as it contains a mesh.

> FYI, there is a forum for discussion of POV-ray 4, which is where most feature
> requests are.

Why is the 3.x version still being updated, if not for improvement :)

Sam

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> Reactor wrote:
> What is the difference between what you are describing and scattering media?

In other words, the object gets lighter and darker not because of 
visible scattering media, but because its surface color is occluded by 
absorbing media contained within it. The effect works very well in 
conjunction with area_lights.

Sam

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