After reading some interesting stuff on how the Flight Simulator people did their cloud rendering, I decided to try my hand at it as well.
They’re not much more than a quick hack at the moment, but the results aren’t too bad. The biggest problem is the shading - it isn’t smooth, so you can make out the individual particles. That’s a result of the particles rotating to face the camera. I should update the particles in real time with their proper colours, which would fix that. I’m not sure if I’ll bother though 
The next step is to implement a render-to-texture based imposter system that will let me scale this planet-wide. This isn’t quite as simple as the Flight Simulator people made it out to be though, as I have to deal with three dimensions of imposters (due to the whole space flight thing). I’ll probably end up having two levels of imposters - one on a sphere that encompasses the whole planet which is faded out when you get below a certain altitude, and one on a cylinder that is used when you’re near the surface.
