[2.1.12] Inscrutable inserter perpendicular lane grabbing preference

Woggle · Post by **Woggle** » Tue Jul 21, 2026 1:15 pm

What did you do?

Tried to build a copy of a design that contains an inserter grabbing chunks from a perpendicular belt fed from both left and right, and the lane grabbing preference is critical to the crusher design not reaching deadlock.

What happened?

The inserters sometimes have a different preference of which lane they grab from, breaking the design. However, I just discovered that a ctrl-c or blueprinted flipped copy does work for reasons unknown. I vaguely remember trying this in 2.0 and manual building always worked but the design broke when the blueprint was flipped. Now, flipping works but manual building sometimes doesn't.

What did you expect to happen instead? It might be obvious to you, but do it anyway!

I expected building the same design would always have the same behavior, but now evidently there is some object state on the inserters that is not exposed in the UI anywhere I can see.

Does it happen always, once, or sometimes?

Copying seems to always work (now?), but manual placing only sometimes works.

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robot256 · Post by **robot256** » Tue Jul 21, 2026 1:29 pm

The 2.1 changelog includes the line "Inserters can be flipped to make blueprint flipping reliable.". The stated intent of this change was so the drop-position onto the end of a belt (carrying items directly away from the inserter) would flip when the blueprint is flipped. Previously it would be biased toward one cardinal direction no matter the rotation/flip of the blueprint, which messed up the most common train unloading blueprint when rotated or flipped.

It is likely that the effect documented here is a side effect of this change. The new behavior is some mix of floating point rounding errors and the new flipping logic.

The "mirrored" state of the inserter is visible when tooltip debug information is enabled. I assume from your comment it is hidden when debug tooltips are disabled. I agree it shoud be visible somehow, either in the tooltips or in the alt-icon arrow positions.

Post by **boskid** » Tue Jul 21, 2026 2:17 pm

I am not seeing anything here that is broken. What you are asking for is for inserters to magically know which side you wanted them to pickup from. You can build inserter in a normal configuration and in flipped configuration. Blueprint flip will switch between the two to preserve pickup priority side relative to other entities from a placed blueprint.

Woggle · Post by **Woggle** » Tue Jul 21, 2026 2:54 pm

now evidently there is some object state on the inserters that is not exposed in the UI anywhere I can see

^This is the part that is broken in my view.

The UI does not provide any information about the flipped status when outputting to anything not a perpendicular belt, nor an indication that the input side is also flipped when the flipped-ness is revealed via belts. This was the source of my confusion.

The FFF and patch notes only mention the output case, and it seems the input flipping was implemented but the UI not updated to show it.

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(Just made this in 2.0.77 to verify I wasn't crazy and I did remember how it used to work.)

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