Wind III: Swirls

I needed to redo the wind algorithm, but I want to avoid solving the Reynolds equation over the surface, because that's dangerously close to my real-world research.

So instead of pushing it along hex vector directions, I propagate each wind cell to every neighbor, and then add the vectors in inelastic collisions.

This puts me on the right track, but there's still something missing. For one, the code is ignorant of the hexmap layout, and so it's unaware that there are 60 degree turns at the folds, and the equator is also a problem (notice the big black splotch below). However, I'm getting much more simulated flow this time, and so I think I'm close.

I'm also using a box blur here on the values to make them smoother. If you do this a few times, it approximates a Gaussian blur, so that's easy to do. I'm not sure if I'll stick with this for the final iteration or just use it for display.

Another interesting effect is that the wind dies out going up a mountain slope, but increases to gale-like proportions on the other side. Hm. Some experimentation will be necessary but I can tweak that after I fix the actual propagation.