Pygame Snake, Pt. 2

In part 1, we just got pygame going. We have a 1000x1000 pixel canvas, with a 50x50 square moving more-or-less continuously. Snake is played on a fixed grid. Instead of 50x50 pixels, we'll shrink the snake parts/tiles to 20x20, and we'll shrink the canvas to 600x600 pixels, treated as a 30x30 grid. (30 tiles x 20 pixels = 600 pixels.) We'll add three variables to represent these values: W = 30 # width H = 30 # height S = 20 # tile size Now we should replace all other numbers in the code with ref