Add shade and highlight to clouds

[depressed-pho]

Possibly with ray marching? But of course nobody will be happy about single digit FPS so we can't do anything expensive.

[depressed-pho]

An interesting blog post: http://www.iquilezles.org/www/articles/dynclouds/dynclouds.htm

And of course this one: https://www.slideshare.net/guerrillagames/the-realtime-volumetric-cloudscapes-of-horizon-zero-dawn

[depressed-pho]

And this: http://www.oceanopticsbook.info/view/scattering/the_henyeygreenstein_phase_function

But the biggest problem we have is that the game doesn't tell us the position of the sun and the moon. The best we can do is to assume the sun is always located at the origin of the world coordinates, and only do it during the daytime (i.e. when the skylight level is high enough).