A weekend of raytracing

I decided to give some nice, simple raytracing a go, inspired by Raytracing in one weekend. Currently, my whole raytracing 'engine' is one C program, and is very rudimentary, but I hope to add to it in time. Raytracing is fun to puzzle out without 'spoilers': I hadn't looked at the maths/explanations for years, so I was drawing diagrams with pencil and paper and figuring out the algebra for shere-ray collision tests.
It's clean and elegant, diametrically opposed to getting graphics going with a modern raster pipeline.
Fun stuff!