I'm into computer graphics, so for me it's raytracing. The principle is simple, so one can quickly code some "shiny spheres" example, but then there's a lot of

I'm into computer graphics, so for me it's raytracing. The principle is simple, so one can quickly code some "shiny spheres" example, but then there's a lot of interesting connected stuff to learn: linear algebra, spatial data structures, Monte Carlo extensions, ...