Editing the turns allowed for individual lanes

[kerbylane]

I'm trying to add a turn-only lane to an intersection. Adding a lane is easy enough. But I can't figure out how to make it turn only, instead of turn + straight. I've looked at existing turn-only lanes. But I don't see anything different about them, when compared to my new lane.

More generally, is there a detailed description of the map editing functionality. The videos available are very helpful. But I expect there are things, like turn-only lanes, that aren't covered.

[dabreegster]

Hi! Unfortunately turn lanes and turn restrictions (#70) aren't supported. If you'd be interested in working on that feature, I can help guide.

More generally, is there a detailed description of the map editing functionality.

Also not yet. A comprehensive user guide would be really awesome, since there's so many features spread out among different tools. There are pieces of things written at https://a-b-street.github.io/docs/user/asu.html, a-b-street/docs#2, and a few other scattered Google docs. Help also welcome here.

[dabreegster]

A very rough outline of what a new feature to designate turn lanes would need:

1. Change the UI to mark what turns are allowed. Maybe just icons indicating left/straight/right and letting the user enable/disable them? https://github.com/a-b-street/abstreet/blob/master/apps/game/src/edit/roads.rs is the lane editor UI code; it's some of the more complex because you can interact with lanes on the map or using the draggable cards, and keeping things in sync is ad-hoc.
   

2. Plumbing through a way to represent the turn lanes through the edit system. Probably just adding explicit turn lanes to LaneSpec would work. https://github.com/a-b-street/abstreet/tree/master/map_model/src/edits has lots of logic for saving edits in a semi-permanent format, but I think you could just piggyback on the existing EditRoad

3. When anything near an intersection is edited, all the turns are regenerated there using the same logic used when importing from OSM. So you'd just need to make sure https://github.com/a-b-street/abstreet/blob/master/map_model/src/make/turns.rs pays attention to lane-level turn restrictions. It should call get_lane_level_turn_restrictions now. This parses OSM tags right now, but we could probably consider storing the allowed turn types on the Lane object directly. Parse from OSM once and fill those out, then let that set be edited.