This page contains a few examples of rendering volumetric textures with Imagine. Don't get TOO excited.. the technique has a few major problems aside from probably having been thought up before, and being a really ugly hack. :-) I did manage to do some nice 3D Fire Objects that came out pretty well. (I need to clean up the object I did this test render with to get rid of some artifacting on the wall.)
The method is pretty simple. And no, I am not joking. :-)
(I tried using 45 concentic spheres, but it looked terrible except for head on, which looked really neat.)
You are now ready to choose a texture. You need one that can modify the transparency settings back to 0,0,0. Otherwise, you will get an invisible object. After selecting a texture, like Worms, render. Make sure to set Resolve Depth to max or your object will have a dark, chewy center.
This is pretty close to a true volumetric render. It casts shadows, can be viewed from any angle and even self-shades! The many problems with this hack method are...
Here are some Texture Samples I have rendered. They are rather interesting to look at.. you can see how some of the textures are built. As a rendering tool, it works ok for a few small applications.. but it works great for learning how some of the textures work. You can also view a 1MB Electric Texture AVI.
Well, thats about it. Hopefully this will inspire some truly interesting ideas. Using textures that turn color into filter settings could produce more interesting results. Or maybe fog? Let me know if anyone comes up with anything really neat and I'll add a link.