Though as part of this effort, I did finally get various issues relating to window size sorted out. I can now spawn the game window at any size I want and the 2D elements are appropriately scaled. This includes fullscreen, and WIDESCREEEEEEEN. And I must say, the planet rendering engine looks good in 1920x1080 fullscreen.
I'm especially pleased with how smooth and curvy the land-water boundary on the planet is, even when we're quite close to it. The texture defining if something is land or water is a simple two-color mask (black = land, white = water, or maybe the other way around, whatever) but in order to decide if a pixel is over the ocean I check if the color value is greater than 0.5, not if the color value is 1.0 as you might first think. Why? Because when the texture is filtered (that is, resized up or down by the graphics card) the land-water boundary gets blurred out. If you follow the 0.5 contour line on such a blurred image, it ends up being nice and curvy, not straight and blocky. So yeah, that's pretty good.
That said, I'm at a bit of a stopping point for the planet renderer since I don't have a good solid design for the game I want to make with it -- I do have some clever ideas for a space combat engine, but don't quite have a game said engine would slot into. So I'm thinking maybe it's time to swap back over to Neon Galaxy for a bit. Even though I'm not sure what to do next there, either... maybe it's time to work on the general game flow a bit, something I've been putting off for a while. It would be nice to be able to theoretically play through an entire level from start to finish, even if the level is minimally populated.