shmodot/scripts/Railway.cs

using Godot;
using System;

[Tool]
public class Railway : Node
{
    [Export]
    private NodePath[] _railPaths;


    [Export]
    private NodePath _centreLine;

    [Export]
    private float _railWidth;
    [Export]
    private float _railHeight;
    [Export]
    private float _railGauge = 1.0f;

    private Path _path = null;
    private Path Path
    {
        get
        {
            if (_path == null)
            {
                _path = GetNode<Path>(_centreLine);
            }
            return _path;
        }
    }

    public Curve3D Curve => Path.Curve;

    // the centre line should not have geometry directly associated with it.
    // instead, two additional path/csgpolygon combinations should be managed
    // in reference to the centre line for the left and right rails.

    // Called when the node enters the scene tree for the first time.
    public override void _Ready()
    {
    }

    private void SetRailCrossSection()
    {
        // error checkin
        if (_railPaths.Length != 2)
            throw new Exception("need 2 rails");

        // set rail geometry
        for (int i = 0; i < 2; i++)
        {
            var rail = GetNode<CSGPolygon>(_railPaths[i]);

            float w = _railWidth;
            float h = _railHeight;
            // horizontal offset of rail from centreline
            float c = (-.5f + i) * _railGauge;

            var polygon = new Vector2[4];
            polygon[0] = new Vector2(c - w, 0);
            polygon[1] = new Vector2(c - w, h);
            polygon[2] = new Vector2(c + w, h);
            polygon[3] = new Vector2(c + w, 0);
            rail.Polygon = polygon;
        }
    }

    public override void _Process(float delta)
    {
        if (Engine.EditorHint)
        {
            SetRailCrossSection();
        }
    }

    public void AddPathFollower(PathFollow pathFollow)
    {
        Path.AddChild(pathFollow);
    }
}