Select a number (not too big) of tiles to add to the center of the screen. Tiles stacked together will get pushed apart, so they spread out into a pattern. (Not really pushed, more like popped apart, since the tiles always have to have whole numbers as their coordinates and snap to a grid) Use turbo mode to draw the screen faster. Shift-click the green flag to activate turbo mode. The field size refers to about half of the length the field, since only a forth of the screen is calculated, and the drawing is mirrored twice as it is being drawn. You can click the button to change it, but there's no point in making it too big since big numbers break the program anyway. If you write "k" as your answer, it will enter "keep on adding that many tiles" mode until you press "s" for "stop."
Tried editing an older program. I wanted to make it more efficient, but too lazy to go implement a complicated algorithm, so it's pretty much the same thing. Big numbers still push things off the screen and cause ridiculous lag. Larger numbers may take exponentially longer to compute, maybe even indefinitely once you reach a certain size. My computer is decently fast so it works fine for me.. Of course, none of my stuff are 100% original. Look up sandpile model on Google. I did the programming, of course, but these ideas were there for some time.