Smooth moves: your belts run at 60 fps now

Here's a confession about how The Last Factory works under the hood: the simulation ticks ten times a second. Every belt, smelter, turret, and enemy updates on a fixed 100 ms heartbeat. That's a deliberate choice — it keeps big factories cheap to simulate and your phone battery alive.

It also meant items on belts moved ten frames a second. Your screen draws sixty. So every item hopped six pixels, ten times a second, forever. You stop noticing it — until you see the fixed version.

The trick: draw where the item is going to be

We didn't speed up the simulation (that heartbeat is sacred; multiplying it by six would eat batteries for breakfast). Instead, the renderer now does a tiny bit of prediction: belt motion is perfectly deterministic, so at any moment between two ticks the renderer knows exactly where the next tick will put each item — and draws it there, fractionally, every frame.

It's not an approximation. The extrapolation uses the same formula as the simulation itself, clamped where the simulation clamps, frozen when a belt is unpowered, damaged, paused, or lost in the fog. If the sim wouldn't move the item, neither does your screen. The cost is a couple of multiplications per visible item — effectively free, on desktop and on phones.

That corner bug — you were right

Several of you noticed items misbehaving on bent belts: an item would sail past the bend in its old direction, then snap back and carry on the right way. That was a real bug in the corner math — the inbound leg covered a full tile of travel in half the time, sending the item straight through the turn before the exit leg yanked it back.

While fixing it we went one better. Items now sweep a smooth quarter-circle arc through corners — entry edge, around the bend, out the other side — and the new path math is covered by a test that proves an item can never leave its tile mid-turn. The overshoot isn't just fixed; it's impossible.

Splitters stopped teleporting

A splitter used to draw its item moving in the arrow direction no matter what — an item that entered from the side, or left through the side output, just teleported at the moment of transfer. Splitters now remember which side each item physically entered from and draw the real journey: in from the actual entry side, out toward the side it will actually leave. Side entries curve through the splitter on the same arc as belt corners.

Easing in and out of machines

The last hard edge was the handoff. Items used to blink out of existence the instant a belt fed a smelter, and machine outputs popped onto belts fully formed. Now items visibly slide off the belt into the machine, shrinking as they're absorbed, and fresh outputs grow onto the belt as they leave the fabricator. Small thing; your eyes will thank you.

For the curious

All of this is render-side only. The simulation is byte-for-byte unchanged — same tick, same transfer timing, same save format, and your existing saves are untouched. If you compare a factory before and after this update, every item arrives everywhere at exactly the same moment. It just looks like a factory now, instead of a slideshow of one.

More polish where that came from — that's what this DEV LOG is for.