[tomvbussel]

The CG by UC Berkeley on EdX is a great starting point. One of the exercises involves building a simple ray tracer. A slightly more advanced source on ray tracing is http://www.scratchapixel.com/. Of course the best way to learn about ray tracing is by reading Physically Based Rendering: From Theory to Implementation by Pharr and Humphreys.

Pixar has ditched RSL in favor of BSDFs written in C++, so there is no real reason for learning RSL anymore. Open Shading Language (OSL) is a new shading language which is getting more and more use in the industry, but it's completely different by design.

[Keyframe]

Yes, you're right about RSL. What I've meant is that it is (was) a good learning tool. Maybe something like shadertoy today with an appropriate course would be apt?

PBRT is a great resource too. I don't know if they opted out of literate programming? I can't stand that for some reason. I've leafed through PBRT though. I've learned (back in the day, hah) from Shirley's Ray Tracing book and bibles that Andrew Glassner wrote (Principles of Digital Image Synthesis) which I still consider awesome resource.

[tomvbussel]

Yeah it was a great learning tool. pbrt is a good learning tool, but sadly it already implements most of the basics. Courses at Cornell and ETH Zürich used a small rendering framework called Nori [1], which is a pretty good learning tool. Shadertoy is nice, but perhaps a bit annoying to work in (as it involves a lot of tricks). I guess the best way to learn is to write your own ray tracer, but that takes a lot of time.

The current edition of Physically Based Rendering still uses literate programming, but most of the maths are separated from the code, so you can skip over most of the code. Even if you can't stand I can really recommend reading it, as it's a great book. Shirley's Realistic Ray Tracing is still very useful these days, but obviously it's lacking the state of the art. If you really want to avoid any code you should read Veach's PhD thesis [2] and then some papers on BSDFs [3], shapes [4] and ray tracing acceleration [5].

[1] http://wjakob.github.io/nori/

[2] http://graphics.stanford.edu/papers/veach_thesis/

[3] http://www.cs.cornell.edu/~srm/publications/EGSR07-btdf.html

[4] http://www.graphics.cornell.edu/pubs/1997/MT97.html

[5] http://www.nvidia.com/object/nvidia_research_pub_012.html