Rules and algorithms in general (and in the US) are not covered by copyright. The expression of those rules as a creative work is, but the rules themselves are

Rules and algorithms in general (and in the US) are not covered by copyright. The expression of those rules as a creative work is, but the rules themselves are not. To that end, anyone could take your procedures and duplicate the effects of them to release their own game. The combination of those procedures in the specific form of your game is protected, but only to the extent that what is protected isn’t essential to running the procedure. So in its simplest (and most general because law is complex) form, if you release a “game” that uses a deterministic procedure to change individual pixel colors on the screen in response to user input, almost nothing of that is covered under copyright. If your procedure instead places tiles of artwork created by you, those tiles and a game using your procedure to place those tiles in that way is protected, but someone else could replace all your tiles and release their own game with the same procedures.