This is great and so concise, but I'm surprised that the author didn't implement OpenGL's interface (obviously not all of it), if the goal is to show how OpenGL works.

Another good example of this is Trenki's software renderer for the GPX2[1], which implements a shader architecture if memory serves. I haven't looked at it for many years, but I remember it being a useful resource when learning this stuff.

Other useful resources are, of course, Michael Abrash's Graphics Programming Black Book[2] (despite it's age, is still a great read filled with useful information), and for a really deep dive into the graphic's pipeline, ryg's (of Farbrausch fame) A Trip Through the Graphics Pipeline[3].

[1] http://www.trenki.net/content/view/18/38/

[2] https://github.com/jagregory/abrash-black-book

[3] https://fgiesen.wordpress.com/2011/07/09/a-trip-through-the-...