[LarsDu88]

First of all ray tracing was invented well before real-time rendering.

Second of all, all these difficult things are difficult things that game ENGINE developers are responsible for tackling nowadays.

In the 90s and early 2000s, most of the people building engines were laying down games at the same time, which is very much akin to building a railroad while running the train. For most folks (like me; I'm developing an indie VR game on the side) this is all handled by Unreal, Unity, or Godot.

I've tried to build a simple game engine in the past... you wind up reinventing the wheel a lot...