It is relatively straightforward (at least conceptually) - you're just projecting 3D vectors down onto a 2D plane (your screen)[1]. Conceptually, this is just the bread and butter of vector algebra (first year physics undergrad).

[1] Of course, it gets more complicated if you want to be more realistic, like including a field of view (cone) rather than a screen-sized chunk (prism) of 3D objects, and so on, but these are just details.