The Universe

A flat Vec of cells, neighbour counting, and a tick function.

#[wasm_bindgen]
pub struct Universe {
    width: u32,
    height: u32,
    cells: Vec<Cell>,
}

Store the grid as one flat Vec, indexed row * width + column. A Vec<Vec<Cell>> costs you an extra pointer chase per row and scatters the data across the heap.

#[repr(u8)] on the Cell enum lets you count live neighbours by adding the cells directly — Dead = 0, Alive = 1. Small representation choices like this are most of the performance difference in a tight loop.

Use modular arithmetic for wrapping edges so there is no special case at the borders.