Ray Tracing in One Weekend
in1weekend.blogspot.com
in1weekend.blogspot.com
http://www.amazon.com/Realistic-Tracing-Second-Peter-Shirley...
He has also written one of my favorite general introductions to computer graphics if your looking for a usable survey text that has most of the basic formulas.
http://www.amazon.com/Fundamentals-Computer-Graphics-Fourth-...
http://psgraphics.blogspot.com/2016/01/process-for-speed-wri...
What makes Swift so good for writing ray tracers?
Will definitely be buying the book.
Both the computing tech and raytracing/graphics theory and algorithms have changed significantly over that time, with better algorithms and much more powerful computing resources allowing more brute-force/accurate stuff to be more practically done.
Writing a raytracer/renderer is also rather addictive, and it's quite cool writing something which produces something else (as is writing compilers).
Currently I'm doing a C++ one that describes the model, colour handling and animation etc. using the type system directly rather than a traditional class hierarchy. https://github.com/KayEss/AnimRay
I think I know what I'm doing this weekend...