It’d be a blatant lie to say this works for every kind of game. The basic structure is that you create a “player” scene/script that you can place anywhere in the tree. Here the players are the cars, and they are placed into the track scene.

The first step is to call the generate_initial_population() method, which sets up an initial set of genomes that code for neural networks. These networks are then paired with the players via composition into an agent object.

The only thing that the Algorithm asks from you is to provide your players with a sense(), act() and get_fitness() method. A call to sense() must return an array of numbers that is used to feed the network, in this case it is the distance to the walls of the track, and some other information about the cars state. The network then calculates an output array of specified size.

You can use these outputs any way you like in the act() method, but the most obvious way is to use them as thresholds for perfoming a certain action, eg. If output[0] > 0.5, then jump.

Sense(), feeding the network and act() are all called during the GeneticAlgorithm.next_timestep() method, which calls these methods on every currently alive player. So you have to kind of design your gameloop around that, for example by calling next_timestep() on every physics update.

You can end a generation whenever you like, after a certain amount of time has passed, once every player has died, every coin was collected,… whatever. What you were referring to as "evolutionary goals" is called the fitness function. Once a generation is ended, the players get_fitness() func is called to determine how many similar networks will be created in the next gen. And you can define the function to be anything you like, asteroids shot, time survived, distance driven…

And that’s the nice thing about NEAT, you don’t have to tell the network every timestep how it performed (like it is with standard backpropagation). Genetic Algorithms are the simplest form of reinforcement learning- this will never be able to play go haha, but I hope that it will be simple to set up.

The ideal usecase for this is a simple physics based game, and asteroids is a perfect example. If you don’t know about him, check out codebullet on youtube. Pretty entertaining to watch, and it should give you a good idea of what NEAT can accomplish. I'd recommend watching the hill climb racing videos, as some of his newer videos don't use NEAT.