Hello, I wrote a program that generates random planets using perlin noise. Right now the planet is just a textured sphere. I would like to create a cloud texture and layer it on top of the terrain texture. Simple multitexturing - I''ve never done it before, but that part should be easy. The trick is, I want to animate that cloud texture procedurally in realtime. I want them to swirl around, move across the sky at different rates, interact with each other, and generally make my the sky of my random planet look like earth does from space. I was thinking that my best bet would either be some kind of particle system (where the particles would be chunks of cloud mass that could clump together, but also be dynamic - think some kind of flocking demo) or cellular automaton (one that would mainly be active around the perimeter of the clouds). Has this kind of thing been done before? I''m not interested in doing volumetric rendering or anything like that. I just want an animated sky that looks good from space. It doesn''t even have to update too fast, since the real sky doesn''t move too fast when viewed from space.

Celluar Automation has been used been for clouds before, but I don''t think thats your best bet performance wise. Same with particles, esp if you aren''t going for volume rendering. What you want is a 4D fBm fractal based off some type of noise(maybe value or Perlin). Use the fourth deminsion to animate the clouds(you can do 3d noise, but then there will be artifacts at the poles of your cloud sphere.) If you want a book that has this check out Texturing and Modeling or Game Programming Gems. Otherwise do a web search. Btw, you can get a good pseudo-volumetric effect by rendering several cloud layers on top of each other. Looks very good from a distance.
Jesse
www.laeuchli.com/jesse/