I've not had much of a chance to post any updates for a while. This is partly because I've been very preoccupied with real-life distractions (finishing the first draft of a book 😱) and partly because the process of translating everything into spherical form is pretty time-consuming.
Much of the difficulty comes from having to deal with multiple coordinate systems at once. The cube-sphere, as described in my last post, is really good for creating terrain that looks reasonably good from all angles, without the distortions you get from just wrapping a rectangle directly onto a sphere. From any given point on the cube-sphere you can easily move to the neighbouring points in a grid fashion, just like on a 2D plane (except at the corners of the faces, where it gets tricky). However, if you want to move due east or west, or north or south, it's much more complicated, because the grid doesn't line up with those directions unless you're right on the equator. To work those out you need to know the longitude and latitude of the points, and converting from cube-sphere coordinates to longitude and latitude (and back) is both fiddly and resource-intensive. And being able to specify directions of this kind is essential for the climate simulation.
Still, I've made some progress. I've converted most of the standard continental terrain generation to the spherical form, and made a good start on the climate model. Temperature and basic rainfall are in place, as well as wind directions and sea ice. Here are some pictures - they are all of the same world, which hopefully gives a sense of how the globe looks from different angles:
Here's the south pole, so you can see it's possible to have polar continents without distortion:
And here are the wind bands (red: westerly; cyan: easterly), which aren't very realistic, but I'm not going to try to change them:
There's a still a lot to do. I've been having a lot of difficulty getting the mountain generation methods to work well with the globe - in fact I've had to create an entirely new way of doing the mountains along continental edges, which is based on the functions I originally created to import user-generated mountain maps. But there's more work to be done with them (the world shown here is one of the most mountainous I've been able to generate, and it still looks very flat). Then I need to add the monsoon routines, before getting to grips with rivers and lakes, which is never much fun. But I think I've reached the point where it looks like converting this whole thing to spherical worlds can actually work, so I'm hoping the final results will be worth the effort...
