Green flag. (You can use turbo mode (shift-click green flag) to speed it up if you want.) How complicated do you think this is to code? Take a look inside. For better quality graphics, try it at https://turbowarp.org/961001769/fullscreen?hqpen (thanks to @papipupepappa for the link/suggestion). Thanks to @heldlaw for noticing that the original version of this was actually stamping each cube 20 times!
