[Celestia-developers] Cloud shadows

[Chris L. <cl...@gm...>]

I checked in the code to enable cloud shadows in the OpenGL 2.0 path.
Currently, there's no option to disable cloud shadows. It's easy to add a
new render flag, but I'm not sure how to expose it in the UI. I might just
make it a scripting only toggle for now.

Calculating cloud shadows is rather computationally expensive, because it
involves a ray-sphere intersection calculation and a rectangular to
spherical coordinate conversion per vertex. The coordinate conversion is the
more serious problem, because it needs inverse trigonometric operations that
aren't natively supported by the graphics hardware. There's also an
unfortunate bug caused by the range discontinuity in arctangent; it's
visible as a striped band near the 90W meridian. I'll be working on a fix
soon.

--Chris