My first attempt at writing a Ray-Marching shader did not work correctly but gave me this interresting result anyway. I used a modified version (with build in glow) for the opening animation to my thesis piece if(!NULL){ See it rotate: QuickTime movie (228kB) You can also take a look at the shader code.

I finally ended up with this solid cloud ---> See it change from fluffy/cloudy to solid: QuickTime movie (450kB) Getting it to self-shadow was a pain in the something