An animated model of the provided skeleton and one common way of filling its gaps. Messages travel along channels; click any box or channel to inspect it. It is a teaching model, not your solution, and your own design may differ.
main() and follows the program: start-up, loading the image, evolving turns, the 2 s ticker, key presses, saving, and shutting down.Click a goroutine or a channel in the diagram.
The window only changes when a frame is drawn: on a 60 FPS tick, and only if a TurnComplete event has set dirty. Flips alone change a hidden pixel buffer.
ioFilename, ioOutput and ioInput are nil: tick “skeleton exactly as provided” and start the model to see what that does.ioCommand, ioIdle (and the three nil ones once you create them) are unbuffered: a send completes only when the other goroutine receives. The IO goroutine and the distributor must agree on the order of messages.CellFlipped or CellsFlipped for a turn before TurnComplete, which is what makes SDL draw a frame. Never send both kinds for the same cell, or it flips twice.ioCheckIdle), so a PGM write is not cut short.close(events) is how SDL learns to stop. Removing it may deadlock the program, as the skeleton comment says.events has a buffer of 1000. If the reader stops, the buffer fills and the sender blocks, which is more likely if you send one event per flipped cell.keyPresses (buffer 10); your distributor must keep receiving from it, including while paused.