[2.0.20] Train moves slightly when connecting locomotive or wagon in a bend

[TiemDuJardin]

I'm making a big artillery train and I noticed that my first parts were off by a tile. Adding locomotives in a bend shows the train snapping but I thought this would cancel out with future locomotives, instead it seems to add up and after a while move the train a bit back. Intuitively, when adding a locomotive at the end, the locomotive should snap to the train while the train stays in the same place.
This problem is pretty niche and I'm not sure if it's easily fixable (the snapping points seem fixed on the tracks and thats why the whole train snaps to the closest point).

Anyways here's a video of the problem:

And here is a picture of the front of the train (originally placed at the stop):

11-21-2024, 16-58-02.png (3.49 MiB) Viewed 428 times

[robot256]

This is not a bug, train alignment on curves is always a little wonky and they do realign themselves when connecting wagons (whether newly placed or not). There is also no guarantee that wagons will line up with inserters if they are stopped with any part of the train on a curved rail.

Once the train starts moving, the gaps between wagons equalize. The next time it drives to the train stop under automatic control, everything will be aligned in a consistent manner.

[boskid]

Under the hood that is a property of how "vertical selection shift" was implemented: it shifts graphics of a rolling stock by an amount that is dependant on orientation difference between train's front rolling stock and rolling stock that is to be rendered. By adding rolling stocks the train changes which rolling stock is considered to be "front" and as such all rolling stocks in the "back" tail that got attached are visually changing the position. That is effectively a duplicate of 109804 which given the current decisions of graphics team is a wont fix.