Well, after another week's work on it, I'm happy to say I think I've got this pretty well nailed.

It took a rather large amount of work with algebra, trigonometry, and calculus. I don't often find much need for calculus in shader work. But to get the correct behavior of the attenuation and scattering of light caused by tiny particles, I needed it. I had to do line integrals in a 3D field.

78 nodes later, this is the result. Click for full size.

Now the question is - does anybody want to see how I did it, or do you just want the shader?

Note: I really should sell this shader as it is truly a masterpiece, even for me, but what the heck. I'll give it away. There's probably not a very big market for this effect.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)