Pick a related topic that makes use of what you want to learn, and learn what you want to learn as side effect from practice in the related topic. Another poste

Pick a related topic that makes use of what you want to learn, and learn what you want to learn as side effect from practice in the related topic. Another poster already mentioned linear algebra for simple computer graphics. From there you could branch out into more dynamic stuff, like realtime 3D rendering or particle simulations, where you'd need calculus.