Actually I was commenting on how to fade reflections, not the funniness with
media you pointed out, I had just mentioned your post in regards to the
using of media for this.

-tgq

"Ron Parker" <ron### [at] povrayorg> wrote in message
news:slr### [at] fwicom...
> On Mon, 22 Oct 2001 14:35:57 -0400, Trevor Quayle wrote:
> > work that way). As Ron shows, one way to simulate this is with absorbing
> > media.  As a quicker method, you could use constant fog with a black
> > pigment, as the features of media aren't really required here. Adding
this
>
> You have greatly misunderstood the point of my demonstration.
>
> That absorbing media is funny.  Notice how it doesn't do anything to the
> first five green cylinders, but the other five (the reflections of the
> first five in the surface of the sphere) fade out?  There's something
special
> going on there that you can't do with fog.
>
> For more fun, try adding another reflective sphere to the scene somewhere
and
> notice how it doesn't behave the same as the one that's there now.  So
> there's something about that absorbing media that's not only strange from
> the camera's point of view, but also from that one sphere's point of view.
>
> The answer, of course, lies in the two spheres that are differenced out of
> the media, and in the no_image keyword.  It's hard to state the exact
rules
> that dictate when the media appears and when it doesn't, but I'll give it
> a shot:
>
> - a camera ray that originates inside the media container is affected.
This
>   might very well be a bug, depending on whether you believe that the
no_image
>   keyword should affect the media in the interior of the object.  Luckily,
>   even if this bug is fixed it won't matter for this technique.
>
> - a camera ray that originates outside the media container is not
affected,
>   because its intersections with the media container are ignored due to
the
>   no_image.
>
> - When the camera is outside the media container, a reflected ray that
>   originates inside the media container is not affected.  This is because
>   we only add the media to the list of things to consider when the ray
>   enters the media container, which doesn't happen in this case unless
>   the ray happens to intersect a "bubble" in the container.  This fact
>   is probably also a bug.  If it's fixed, it will limit the technique
>   considerably (requiring all reflective objects in your scene to fade,
>   and requiring them all to fade to the same color.)  It probably should
>   be fixed, but fixing it seems like it would cause a performance hit,
>   and it's not as though it's really a real-world feature anyway.  The
>   part about the "bubbles" has some effect on what sort of objects and
>   scene geometry you can use, but not too much.
>
> - When a reflected ray originates outside the media container, it is
>   always affected by the media.  This is the only part that really makes
>   sense about the whole thing. :)
>
> --
> #macro R(L P)sphere{L __}cylinder{L P __}#end#macro P(_1)union{R(z+_
z)R(-z _-z)
> R(_-z*3_+z)torus{1__ clipped_by{plane{_ 0}}}translate z+_1}#end#macro
S(_)9-(_1-
> _)*(_1-_)#end#macro Z(_1 _
__)union{P(_)P(-_)R(y-z-1_)translate.1*_1-y*8pigment{
> rgb<S(7)S(5)S(3)>}}#if(_1)Z(_1-__,_,__)#end#end Z(10x*-2,.2)camera{rotate
x*90}

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