I used and extended this tutorial to write the rayvertex [1][2] package, which is a deferred parallel software rasterizer in R. Explicitly building the rendering pipeline really helped me understand the underlying data flow and rasterization techniques, which in turn made me understand GLSL much better. And extending the rasterizer with order-independent transparency, multicore rendering, antialiasing, and other niceties made me appreciate the work that goes into modern renderers.

Highly recommend.

[1] https://www.rayvertex.com/ [2] https://github.com/tylermorganwall/rayvertex