Fix #11528: Don't auto-build past tunnelbridge ends

[LordAro]

Motivation / Problem

#11528 - autodragging over existing rail/road would start under a bridge, which is not expected behaviour

Description

Keep track of whether we're under a tunnel or bridge when dragging and toggle as appropriate.

Limitations

Feels very "just increase complexity" and there's probably additional edge cases that aren't covered, or are created, by this change.

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR touches english.txt or translations? Check the guidelines
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, game_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker

[PeterN]

Is it possible to make it continue on the other side of a bridge if you drag over it?

[LordAro]

That's what it does :)

Causes a certain amount of weirdness if you drag over different/multiple bridges though...

[PeterN]

Hmm, I dragged over a bridge and it did not continue on the other side.

[Kuhnovic]

This is similar to my PR (draft) from quite a while ago: #9616

One thing to keep in mind is that the "drag and hold ctrl to delete"-behavior will behave different from the "drag to build"-behavior. There are already differences, this will add more differences. Not bad or good per se, but something to consider.

[LordAro]

The differences as far as the code is concerned is just a toggle of whether the road/rail is built or deconstructed, so i'm not quite sure what the overall problem with the complexity is there.

Though I do agree that as a whole this function is starting to get a bit on the unreadable side

[LordAro]

On the other hand, your PR is much more "complete" in terms of what it achieves. What would you say still needs doing to it to bring it "up to spec" ?

[Kuhnovic]

@LordAro The main thing I struggled with was the visualisation of it. I messed around quite a bit to get the highlighting to look somewhat good, but it always felt like a giant hack.

For sure it needs a rebase and a fresh look, the PR is quite old and there's a good change some of the construction logic has changed by now. Unfortunately I have quite limited time available for development ATM...

[TrueBrain]

Might not be perfect, but it is another step in the right direction.

And yeah, all the scoping, it is a bit annoying. I guess we could take a look at "why", as having the if-condition and if-increment not in the if is a bit weird. But, not for this PR!