Prevent players from setting invalid lane arrows

Description

Players should not be able to set lane arrows that do not point to an outgoing segment. For example, in issue #361 the player mistakenly used straight lane arrows where the angle between the 4-lane highway and 8-lane road with median requires a right pointing arrow.

Technical Info

• Lane arrow logic is one of the features that is still handled by the legacy Flags class. We could use this opportunity to move the code to LaneArrowManager.
• LaneArrowManager:
  • Implement logic to check which kind of lane arrows may be set for a given segment end
  • Implement logic to correct invalid lane arrows
  • Make ToggleLaneArrows() call SetLaneArrows()
  • SetLaneArrows(): Check if the intended lane arrow is valid
  • HandleValidSegment(): (gets called when a segment is updated) Make sure that old lane arrows are valid. If not, call correction code.
• LaneArrowTool: Disable/Remove invalid lane arrow toggle buttons

[VictorPhilipp]

Lane arrows and lane connections have different semantics. Lane arrows are thought to be less restrictive. Lane connections on the other hand cannot be ignored by vehicles. Thus, as of now you cannot represent lane arrows as lane connections.

Some use cases for “soft” lane arrows which cannot be covered by lane connections currently:

• the player can set that busses may ignore lane arrows if necessary
• Vehicles must be able to ignore lane arrows when they set off (think of a cemetery which is placed next to a junction)

I also think that showing so many lane connections would clutter the UI.

[originalfoo]

On complex junctions, where there are say 6 segments connected to a node, some at strange angles, it is often difficult to discern exactly where traffic will go based on lane arrows alone. For precisely this reason I no longer use lane arrows feature and instead always use lane connectors feature.

In terms of cluttering UI, this would not be an issue if only the ‘active lane’ gets the connector line display. For example, user hovers the lane arrow panel for lane X, only the lane connectors for lane X are shown.

Lane arrows then become just a quick alternate way of setting lane connectors.

Instead of ignoring lane arrows, the relevant mod options would ignore lane routing (ie. lane connectors).

And, with everything now using lane connections the pathfinder & vehicle AIs have a single source of truth for routing through nodes.