Gas Giant Shadows

More shaders: gas giant shadows. You can see in the screenshot below the shadow of the rings on the planet surface, and the shadow of the planet on the rings (to the right).

It is done by ray-tracing from the pixel position to the light direction. Since there are only spheres and a plane to intersect, it is feasible to do it in the GPU and it is fast.

In case you were thinking about gas giants flatteness: yes, in Antares all the planets are perfect spheres. Flateness won't add much to the gameplay (and if I don't mention it, almost nobody will notice)