I believe it was originally displaying extended ASCII in a nCurses console, and switched to bitmaps with SDL. The majority of the world is still visualized by those character codes and two colors, but entities can be assigned arbitrary sprites <a href="http:&#x2F;&#x2F;i.imgur.com&#x2F;zuMdqbv.jpg" rel="nofollow">http:&#x2F;&#x2F;i.imgur.com&#x2F;zuMdqbv.jpg</a>