Restricting to straight lines would be the most straightforward, I think. It follows the convention of only changing squares that you touch.
Drawing rectangles introduces a new paradigm where you can fill in squares you don’t actually touch, so it might be less intuitive. At the least, you would probably want to highlight the affected squares in a different color before finalizing the action.
Drawing rectangles introduces a new paradigm where you can fill in squares you don’t actually touch, so it might be less intuitive. At the least, you would probably want to highlight the affected squares in a different color before finalizing the action.