train on bogie on track

scenes/Main.tscn

@@ -7,6 +7,7 @@
 [node name="Main" type="Node2D"]
 
 [node name="Train" parent="." instance=ExtResource( 1 )]
+_speed = 5.0
 _railwayPath = NodePath("../Railway")
 
 [node name="DirectionalLight" type="DirectionalLight" parent="."]

scenes/Train.tscn

@@ -5,5 +5,6 @@
 
 [node name="Train" type="Spatial"]
 script = ExtResource( 1 )
+_carPath = NodePath("Train Car")
 
 [node name="Train Car" parent="." instance=ExtResource( 2 )]

scenes/TrainCar.tscn

@@ -5,6 +5,7 @@
 
 [node name="Train Car" type="Spatial"]
 script = ExtResource( 1 )
+Wheelbase = 5.0
 _boxNode = NodePath("CSGBox")
 _bogiePaths = [ NodePath("Bogie"), NodePath("Bogie2") ]
 
@@ -15,7 +16,7 @@ height = 1.0
 depth = 8.0
 
 [node name="Bogie" parent="." instance=ExtResource( 2 )]
-transform = Transform( 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, -2 )
+transform = Transform( 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, -2.5 )
 
 [node name="Bogie2" parent="." instance=ExtResource( 2 )]
-transform = Transform( 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 2 )
+transform = Transform( 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 2.5 )

scripts/Train.cs

@@ -1,5 +1,6 @@
 using Godot;
 using System;
+using System.Collections.Generic;
 
 public class Train : Spatial
 {
@@ -10,17 +11,48 @@ public class Train : Spatial
     private NodePath _railwayPath;
 
     private Railway _railway;
-    private readonly PathFollow _pathFollow = new PathFollow
-    {
-        RotationMode = PathFollow.RotationModeEnum.Oriented
-    };
     private float _distance = 0;
 
+    [Export]
+    private NodePath _carPath;
+    private TrainCar _car;
+
+    private Spatial[] _bogies;
+    private readonly Dictionary<Spatial, PathFollow> _bogiePathFollows = new Dictionary<Spatial, PathFollow>();
+
+    private ImmediateGeometry _imgui;
+
     // Called when the node enters the scene tree for the first time.
     public override void _Ready()
     {
-        _railway = GetNode<Railway>(_railwayPath) as Railway;
+        _imgui = new ImmediateGeometry();
-        _railway.AddPathFollower(_pathFollow);
+        var m = new SpatialMaterial();
+        m.VertexColorUseAsAlbedo = true;
+        m.FlagsUnshaded = true;
+        _imgui.MaterialOverride = m;
+        AddChild(_imgui);
+
+        _railway = GetNode<Railway>(_railwayPath);
+        _car = GetNode<TrainCar>(_carPath);
+
+        _bogies = new Spatial[_car.Bogies.Length];
+        for (int i = 0; i < _bogies.Length; i++)
+        {
+            var b = _car.Bogies[i];
+            _bogies[i] = b;
+            _bogiePathFollows[b] = new PathFollow
+            {
+                RotationMode = PathFollow.RotationModeEnum.Oriented
+            };
+            _railway.AddPathFollower(_bogiePathFollows[b]);
+
+            // detach the bogies from the car as we need to set the bogie
+            // positions in order to calculate the car position and it will
+            // get confusing if they're in a parent/child relationship,
+            // so make them all siblings
+            _car.RemoveChild(b);
+            this.AddChild(b);
+        }
     }
 
     // Called every frame. 'delta' is the elapsed time since the previous frame.
@@ -28,6 +60,12 @@ public class Train : Spatial
     {
         var length = _railway.Curve.GetBakedLength();
 
+        // first determine which is the front bogie. this is dependent
+        // on the direction of travel.
+        int travelDir = (int)(_distance / length) == 0 ? -1 : 1;
+
+        DrawTravelDirectionIndicator(travelDir);
+
         // keep track of total distance
         _distance += delta * _speed;
         // wrap at 2x total distance
@@ -35,9 +73,40 @@ public class Train : Spatial
 
         var distance = PingPong(_distance, length);
 
-        _pathFollow.Offset = distance;
+        // get the position of the first bogie on the track
-        Translation = _pathFollow.Translation;
+        var b = _bogies[0];
-        Rotation = _pathFollow.Rotation;
+        var pathFollow = _bogiePathFollows[b];
+
+        pathFollow.Offset = distance;
+        b.Translation = pathFollow.Translation;
+        b.Rotation = pathFollow.Rotation;
+
+        // now we want to position the car over the first bogie
+        GD.Print(_car.Wheelbase);
+        _car.Translation = b.Translation;
+        _car.Rotation = b.Rotation;
+
+        // TODO: this rotation quat needs to position the other 
+        // bogie over the curve
+        _car.Translation += _car.Transform.basis
+            .RotationQuat()
+            .Xform(Vector3.Back) * _car.Wheelbase * 0.5f;
+    }
+
+    private void DrawTravelDirectionIndicator(int travelDir)
+    {
+        _imgui.Clear();
+        _imgui.Begin(Mesh.PrimitiveType.LineStrip);
+        _imgui.SetColor(new Color(1, 0, 0));
+        var c = _car.Translation + Vector3.Up * 2;
+        _imgui.AddVertex(c);
+        var d = travelDir;
+        var l = 5;
+        var e = c + _car.Transform.basis
+            .RotationQuat()
+            .Xform(Vector3.Forward) * d * l;
+        _imgui.AddVertex(e);
+        _imgui.End();
     }
 
     // poor mans branching ping pong

scripts/TrainCar.cs

@@ -13,21 +13,37 @@ public class TrainCar : Spatial
     private NodePath[] _bogiePaths;
 
     [Export]
-    private float Wheelbase
+    public float Wheelbase
     {
         get => _wheelbase;
         set
         {
             _wheelbase = value;
-            if (Engine.EditorHint)
+
-            {
+            // don't set the wheelbase except from the editor
+            if (!Engine.EditorHint) return;
+
             SetBogeyPositions();
         }
     }
-    }
     private float _wheelbase;
 
-    private readonly Spatial[] _bogies = new Spatial[2];
+    public Spatial[] Bogies
+    {
+        get
+        {
+            if (_bogies == null)
+            {
+                _bogies = new Spatial[2];
+                for (int i = 0; i < _bogiePaths.Length; i++)
+                {
+                    _bogies[i] = GetNode<Spatial>(_bogiePaths[i]);
+                }
+            }
+            return _bogies;
+        }
+    }
+    private Spatial[] _bogies = null;
 
     private CSGBox _box;
     private CSGBox Box
@@ -42,6 +58,8 @@ public class TrainCar : Spatial
         }
     }
 
+    public Railway Railway { get; set; }
+
     public override void _Ready()
     {