Tek wrote:
> No, it doesn't work. The media tag in radiosity is just to tell the 
> radiosity on the non-media objects to sample from the media. i.e. if you 
> have a glowing red media next to a white wall you'll get red radiosity on 
> the wall, but if you have a white scattering media next to a glowing red 
> wall the media won't pick up any of the red.
> 
> It's a matter of the complexity of the problem. With light only coming from 
> light sources the media needs to trace a shadow ray for every sample point 
> inside the media, then numerically integrate the samples to work out how 
> much self-shadowing the media is doing, which in turn requires multiple 
> samples along the shadow ray, effectively an n^2 complex algorithm (though I 
> suspect the pov implementation's a little more optimal than that). Anyway, 
> if you wanted to do that with radiosity you'd need to do these shadow rays 
> in random directions at every point, and to get a smooth effect you'd need 
> far more samples than for an opaque object, and I'd guess that the tricks 
> for smoothing out radiosity on opaque objects don't work nearly as well on 
> media, so you could be talking about several orders of magnitude more 
> complexity than just switching radiosity off and using a few extra light 
> sources.
> 
> At least, that's how I think it works.
> 
> Still, I'm puzzled that there's no option to do it in POV. Pov's happy to 
> let me do any of the hundreds of other things that give me infeasibly long 
> render times :)
> 
Thanks for that.  Your explanation does awaken some dim and nearly 
extinguished memories.

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