why would top-down remove the vent ducts?
you could make them transparent bricks floating, and then when a person goes into the vents they're teleported into a vent system
Um... I might just have to do that. It'd require a bit more coding, though, to make it so that the camera always stays pointing the same direction and the WASD keys determine direction. Also, it'd need to make it so your cursor is always on, and clicking something with your cursor will call onActivate if you're close enough to it.
The third issue is that you won't be able to see what's down below you (like in the real game) which might be quite a setback, because you wouldn't see if a guard heads toward your cell.
I'll post a request for a playertype like that, and see what happens.
