As game starts on the planet with null atmosphere I wanted a way to simulate 'air' filling up the closed space of player's buildings connected to oxygen source/network. That would also allow to quickly decompress them when wall or door is breached (suffocating unprepared crew members inside ;) and enforce use of airlocks, introducing more 'spacely' mood. I started with water simulation as it appeared more obvious to implement, despite the fact that in the game beginnings there will be no water sources as such, only ice. After making water time had come to implement the 'oxygen' behavior which turned out to be tricky subject. I ended up with thin air trying to escape the presence of vacuum, dividing itself when in larger mass and teleporting here and there for fast dispersion. Here's how it looks in action:
