Deep water
After day 2 i have a bit better underwater environment and terrain, and the start of basic collision and placement of samples that are sought. I think the challenges will mostly be making this thing not devour poor player's cpus, as I am definitely layering many things on top of each other using blit. Perhaps I might need to do an emergency port to pyglet at some point.. we will see. Anyway, here is where my underwater world stands:
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I can see CPU munching being a problem as you said though. It looks fairly munchy with that dynamic lighting.