Island Generator

I had read the wave function collapse write-ups and could have described the idea accurately at a whiteboard. Then I tried to implement it and found I understood the idea and none of the engineering, which is a gap that only appears when you build the thing.

The collapse step is easy. Propagation is not: when a cell settles, every neighbour's option set narrows, and theirs after that. Getting that to terminate, stay correct, and run fast enough to watch is the actual problem, and no description had made that clear.

The solver takes no map. Its entire input is a set of tiles and, for each, what is allowed on each of its edges. Everything the output looks like is emergent from those constraints.

That is what makes it worth building rather than reading about. The design surface is not the picture, it is the ruleset, and the relationship between the two is not obvious in either direction. Tightening one edge rule changes the character of the whole island, and wanting a particular look means reasoning backwards to the constraints that would produce it.

The thing I did not expect is how often this shape turns up once you have built it once. A design system's token layers are a constraint propagation problem wearing different clothes: change a primitive, and the change has to reach every component that depends on it, exactly once, without cycling.

I recognised that faster at work for having written a solver first.