"Dennis Clarke" <dcl### [at] blastwaveorg> wrote:
>   Oh?  I guess in my mind I think of a fog bank as being "everywhere" and
> smoke would be the same.  I guess in any computer based representation I
> would need to contain the mathematical model of smoke in some bounded
> manifold.  Makes perfect sense although not intuitive.

Well, you can use media as a scene-wide effect. Simply declare the media
statement without attaching it to any object, eg:

camera { ... }

light_source { ... }

object { ... } // scene objects, no media

media { ... } // media declaration as before, but is now everywhere.

I don't normally do this, because it's very slow (every pixel in the image
will involve media samples).

If you are using scattering media with absorbing media (quite common when
extra control is desired), you may want to turn the scattering media's own
absorption off by setting

scattering { 1, 1 /* <-- or whatever */ extinction 0 }

Then the amount and colour of absorption is entirely up to you.

> Then I have been doing "quick" renders at full +Q9 with 800x600 images and
> then my test images are at 4096x3072.  Needless to say the final images are
> taking an hour or so with a lot of reflection and refraction on some glass
> objects.  I am happy with the result thus far and want to now add in the
> smoke effect with search beams.

Yes, the quality switch is normally a great help. But I find scattering
media defeats it because it's a high-quality feature (+Q9 at least, IIRC),
and you need a full quality view anyway to debug it. So, when I have to
deal with scattering media I hide objects that aren't relevant by switching
them in and out;

#declare FinalImage = false;

#if(FinalImage)
  object { ... }  // incidental object that doesn't depend much on media
effects
#end

media { ... }

This can help. Sometimes. Also tweaking the samples used can help, although
the quality difference between samples 3,3 and samples 30,30 can be
enormous (like, no cast volumetric shadows vs. very obvious shadows).
Again, makes debugging slow.

> OKay .. that is odd.  I keep thinking of smoke as particles but in reality
> its not the case.  I think to actually model smoke one would need several
> trillion tiny spheroids with a supercomputer ( BlueGene ) to perform the
> render.

Sure, but that's not necessary. If you want dust motes or larger particles
to be visible in your media you could just add another density or a
separate media. As for shadowless lights, they're just odd. Normal lights
work as you would probably expect with all media types.

Tom

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