Space runs or pauses, S takes one step, R starts again with a new seed, E switches to the entropy map, P toggles drawing pins.
Paint a small sample. Every small square window in it becomes a tile, and a larger picture is woven so that each of its windows is one of those tiles. Every cell starts undecided; the most constrained cell is settled first, and the choice ripples out to rule out whatever no longer fits beside it.
Space runs or pauses, S takes one step, R starts again with a new seed, E switches to the entropy map, P toggles drawing pins.