Shader and OpenGL programming. It was many foreign jagons, concepts, and computation models. Took me a while and couple tries to get a hang of it.
Also UC Davis professor Key Joy's Computer Graphics course [1] is the best intro course on 3D graphics programming, covering many key concepts and math. I found it better than any other courses from MIT/Berkeley/CMU/etc. It doesn't have some of the newer techniques in recent years but is still very much relevant and forms the foundational knowledge to level up.
[1] https://www.youtube.com/watch?v=01YSK5gIEYQ&list=PL_w_qWAQZt...