Thanks! That's correct, I built the ray tracing "GPU" from scratch. It's highly optimized because it needs to trace 256 * 128 * 30 = 0.98 million rays per second on very under powered hardware. It's specifically tailored to fast traversal of voxel grids. There's too many details to go into here, but as I wrote in another comment, I'm considering writing a few blog posts to explain how everything works in more detail!