Yar is an independent study project I wrote on as part of my doctoral studies at Arizona State University. It implements raytracing for the OFF file format, which I have used extensively in other programs (RoffView, MeshMan, and numerous OFF tools).
Version 1.0 - First public release. Implements raycasting, raytracing, Monte Carlo raytracing, photon mapping, soft shadows and jittering. Supports two object types: triangle mesh OFF files and spheres. (5/9/04)
Realistic Image Synthesis Using Photon Mapping by Henrik Wann Jensen
ISBN: 1568811470
A very detailed book, but it feels like the compilation of papers and dissertation
that it is. Be sure to check the errata page,
there are a number of important typos in both the formulas and the source code.