Until a week or so ago, buildings in Voxel City levelled up by popping. One moment a cottage, the next a terrace. It worked, but it felt like a spreadsheet updating.
Now a level up is a small event you can watch, and it's tied to the materials side of the game, which needed a reason to exist.
The materials have to turn up
Homes and shops need materials to go up a level. Planks come first, then bricks, concrete and so on as the eras move along. That rule switches on when the thing that makes the material is unlocked (planks at 150 people), not when you build one. I had it the other way round at first, and building a sawmill made your town grow slower, which is not the lesson anyone should take from a sawmill.
When a building is ready for its next level it orders what it needs. The nearest works or store sends it out on the builders' flatbed, a marigold cab with an open deck and the crates standing on the back. My first go at this used the ordinary delivery van with crates stuck to its roof. It looked like someone moving house in a hurry, so the flatbed got built.
There are never more than eight on the road at once. If one gets properly lost it's delivered anyway after three minutes, because nobody's town should stall on a lorry that took a wrong turn.
On the default materials setting, which is called Gentle, you're never stuck. If the city hasn't got the stock, the building still levels, just half as often, and the city buys the shortfall in at one and a half times the cost. Build the works and you grow faster and save money. On Full, a building that's short waits for the delivery.
Then it goes up
When the materials arrive the plot wraps itself in scaffolding, with grey poles round the edge and wooden boards at each floor. For about four seconds the new building rises inside it a floor at a time. Then the scaffolding comes down and a little white pill floats off the roof saying how many Voxies have moved in, or for a shop or works how many jobs it added. The pill is gone in under two seconds. If you're zoomed right out it doesn't draw at all, so a busy city doesn't fill the screen with them.
The bug
The scaffolding was attached to the building it surrounds. That sounds sensible. The trouble is that a building on its way up isn't a fixed size. The game stretches it upwards floor by floor while it rises, and anything attached to it gets stretched along with it.
So the scaffolding grew. By the last floor of a tall building it was about five times taller than it should have been, a lattice of poles sticking up into the sky long after the building had stopped.
I didn't catch it in play, because it only lasts four seconds and you're usually looking at something else. I caught it in the store art, which holds a few building sites half built on purpose so there's something going on in the picture. A still holds them for as long as you like, and there it was.
The fix was a few lines. The scaffolding now keeps its own size whatever the building is doing. There's a test that raises a building floor by floor and checks the scaffolding stays the height it started. It's the kind of bug that comes back if nothing's watching for it.