Continuing with the idea of shading a 2D texture to appear 3D.

The trick seems to be to pick a point and march along a ray on the sky 
plane toward the sun, sampling the 2D cloud texture along the way. Based 
  on the samples collected, the point is assigned a degree of 
"illumination" or brightness.

I have a lot of fun with the idea, but so far my implementation is no 
where near as elegant as I think it could be. Come to think of it, 
writing it as a shader for POVman might be smoother.

What's here is a set of layered textures which have the following tasks 
(in order): sky color, sun and sun glow, base cloud color, cloud 
illumination, haze, flare.

What's not here is any attempt at implementing pronounced forward 
scattering or multiple scattering effects. There is also no 
comprehensive model which steers the different colors - they are all set 
individually through trial and error (and will probably still be off 
when I get a chance to look at them on a CRT!).

Abe

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