[0.15.12][kovarex] Player can't build signals where bots can

[aaargha]

The way this bug was solved has resulted in there being situations where the player needs to keep signals blueprinted and build them with bots to be able to place them in all correct locations. The suggestions shown to the player does not show all valid locations for signal placement. In the attached picture the top part shows where the player wants to build the signals but can't, the bottom shows that they attach properly when built by robots. Also attached is a save with the setup.

My guess is that the tile in question is not properly recognized as a two way track (the fact that the bots can build it prove that it still is though). Removing the chain signals or making the east part explicitly two way with signals further to the east makes the suggestion code detect the valid locations.

[Valeskas]

There are two rails near this signals, curved and straight. I dont expect this case to work as it is looking, this signals are probably not attached to curved rail.

[aaargha]

There are two rails near this signals, curved and straight. I dont expect this case to work as it is looking, this signals are probably not attached to curved rail.

They do attach, that was what was fixed in the linked report. You can also verify this for yourself in the reproduction save attached in the OP.

[Aeternus]

It does appear a little glitchy. The game -will- allow placement of signals at the hazard concrete spots by the player, if you add signals on both sides of the track further to the right (4 or so spots right of where the hazard concrete is).
It also doesn't seem to matter if you use chain or normal signals on the monodirectional rails past the branch.

[Valeskas]

My bad. The game allows to place signals manually if you do it 1,2,3,4, but does not allow if you do it 4,3,2,1

test.png (717.05 KiB) Viewed 2234 times

[kovarex]

It actually isn't bug, but corner case of the gameplay decision and it worked like that all the time since the signal helper markers were introduced.

The reason why the signal Can't be placed on A3 is the same as why it can't be placed on A1 and A2, the same with B3 versus B1 and B2.
As the point is after the junction the logic that searches the endings of the block and direction in which it ends sees only one side, so it is decided that making signal with the other direction there wouldn't be consistent with the rail direction. After the junction it is possible to place the signal, as the direction searching algorithm sees both branches so it sees that both directions are possible.

Robots can build there, as they can now ignore the rail direction limitation (including A1, A2, B1, B2).

The solution is not perfect, but it is internally consistent and I don't think that the issue is big enough to change it.

Edit: I would like to add, that also allowing Making signal on A1 for example, makes the whole top branch wrong, until other signal is added.

[aaargha]

Thanks for the explanation, a very interesting read!

If I understand correctly, it's that both rails affect where the signals can be placed for that tile but, for that tile they're also unaware of each other when removing possible placements.

As you say it's a minor issue and there are plenty of workarounds available. I'll just have to keep it in mind when designing.

Thanks again for the explanation and have a great day!