Game Engine LLD: The Fixed-Timestep Loop and Entity-Component-System

Every game engine — Unreal, Unity, Godot, the one in your favourite indie roguelike — is built on two ideas you can design in an interview. The first is a loop that advances the world in equal, deterministic steps no matter how fast or slow the machine renders. The second is a way to compose game objects that doesn't collapse into a tangled inheritance tree the moment you add a flying, exploding, healing enemy. Get the fixed-timestep loop and the Entity-Component-System right and the rest of the engine hangs off them. This is an LLD problem: the win is in the object model and the loop's arithm…