My focus area in college was Computer Graphics. There is not enough focus about the math in this article, it just kind of passively mentions it. "Well you can get by with just a little bit of this and that" -- Linear Algebra is huge! So is an Engineering style Calculus course -- not your business calc. Those two require a year of their own to gain mastery. IMO, pick up:

Linear Alegbra Done Right Calculus Better Explained Concrete Mathmetics.

Then you can move on to the low level APIs.