Conveyor Belts!
Ok, so there are conveyor belts in the game now. They don't actually convey things, but you can pick them up and put them down with your alien. Spent a long time trying to tweak the UI to make it intuitive, but I'm still not 100% happy with it. Never mind, onwards, onwards - I'm sure it'll change a bit as the game goes on anyway.
There's also multiplayer, so if you have multiple joysticks, the aliens can each have a conveyor of their own.
And if anyone's testing this (I doubt it), at the moment there's a hack in the PygameZero joystick handlers to get around the numbering due to my Gamecube adapter. Let me know if you have trouble fixing it and I can help out :)
Update: Just fixed a few weird bugs and reworked how the conveyor belt moves. Now instead of having three positions, it maintains a linear distance and updates it constantly, so that the items move smoothly. A couple of bug fixes later and it seems to work pretty well. The annoying one was forgetting to return True when a conveyor accepts an item, so it was pushing (and duplicating) the same item along the belt.
Anyway, next up is making conveyors move things up, down and right to left, which I might leave for tomorrow. I've done the images, not sure they're up to Kenney's high standards though.