I started working on a rotating animation of a sandbox. This was my first time working with C++ or NeoPixels, so it took a bit of getting used to, but I was able to slowly work into my intended animations. Eventually I realized I could learn more and get more out of my project if I started with simpler ideas and built up to a more detailed idea. Thats how I came to this. The code is extremely simple, but it's able to get a couple shapes and animations.
Looks pretty neat - is it for square grids only?
Also, see: https://github.com/DedeHai/NeoPixelPainter