This is pretty similar to Peter Shirley's "Ray Tracing in a Weekend" series, which gives some more detail and discusses the ideas more, and which recently was put online as "pay what you want": https://twitter.com/peter_shirley/status/984947257035243520?...

The bible for raytracing techniques is PBRT, which, funny enough, is also now available online: http://www.pbr-book.org/

It is a pretty fantastic time for easily available, high quality resources on rendering in general and ray tracing in particular.