Ask HN: Toy app that takes a function and renders a grid of red and white dots?

I am trying to remember the name of a toy app that I saw on here. It takes a user-supplied function and, based on the return value, renders a grid of red and white dots of varying sizes and pulse animations.

I believe that it is part of a personal portfolio of mini apps and games.

I believe that its name is comprised of the single-letter arguments of the function.

I am going mad searching for this thing. Any leads would be appreciated. Thanks!