Improve grid and placement code

- Grid is no longer a collision object,
  instead we just ray-cast against its parent
- Refactored some placement code into
  its own method 'GetValidPlacement'

objects/Grid.cs

@@ -1,5 +1,6 @@
+
 [Tool]
-public partial class Grid : Area3D
+public partial class Grid : Node3D
 {
 	public const float StepSize = 0.05f; // 5cm
 
@@ -19,19 +20,13 @@ public partial class Grid : Area3D
 			_gridSize = value;
 			// Helper value for converting grid pos to local pos and back.
 			_halfGridActualSize = new Vector3(GridSize.X, 0, GridSize.Y) * (StepSize / 2.0f);
-			Update();
+			UpdateImmediateMesh();
 		}
 	}
 
 
 	public override void _Ready()
-		=> Update();
+		=> UpdateImmediateMesh();
-
-	void Update()
-	{
-		UpdateCollisionShape();
-		UpdateImmediateMesh();
-	}
 
 
 	/// <summary> Returns whether the specified item is contained in this or any nested grids. </summary>
@@ -44,6 +39,21 @@ public partial class Grid : Area3D
 		return false;
 	}
 
+	/// <summary>
+	/// Recursively adds all items included in this grid to the specified
+	/// collection. The collection must be of a valid super-type of Item.
+	/// </summary>
+	public void AddItemsRecursively<T>(ICollection<T> collection)
+	{
+		if (!typeof(T).IsAssignableFrom(typeof(Item)))
+			throw new ArgumentException($"Type '{typeof(T)}' is not a super-type of Item", nameof(T));
+
+		foreach (var child in GetChildren().OfType<Item>()) {
+			collection.Add((T)(object)child);
+			child.GetNodeOrNull<Grid>(nameof(Grid))?.AddItemsRecursively(collection);
+		}
+	}
+
 
 	public Vector3I LocalToGrid(Vector3 pos)
 		=> (Vector3I)((pos + _halfGridActualSize) / StepSize);
@@ -108,28 +118,6 @@ public partial class Grid : Area3D
 	static StandardMaterial3D GetOrCreateMaterial()
 		=> _material ??= new() { VertexColorUseAsAlbedo = true };
 
-	ConvexPolygonShape3D _shape;
-	void UpdateCollisionShape()
-	{
-		if (Engine.IsEditorHint()) return;
-
-		if (_shape == null) {
-			_shape = new ConvexPolygonShape3D();
-			AddChild(new CollisionShape3D { Shape = _shape }, true);
-		}
-
-		const float Offset = 0.001f;
-		var x = GridSize.X * StepSize / 2;
-		var y = GridSize.Y * StepSize / 2;
-
-		_shape.Points = [
-			new(-x, Offset, -y),
-			new( x, Offset, -y),
-			new( x, Offset,  y),
-			new(-x, Offset,  y),
-		];
-	}
-
 	ImmediateMesh _mesh;
 	void UpdateImmediateMesh()
 	{

objects/grid.tscn

@@ -2,8 +2,5 @@
 
 [ext_resource type="Script" path="res://objects/Grid.cs" id="1_7yhbt"]
 
-[node name="Grid" type="Area3D"]
+[node name="Grid" type="Node3D"]
-collision_layer = 512
-collision_mask = 0
-monitoring = false
 script = ExtResource("1_7yhbt")

player/PickupController.cs

@@ -61,39 +61,17 @@ public partial class PickupController : Node3D
 		if (!_player.IsLocal) return;
 
 		if (HasItemsHeld) {
-			// This ray will be blocked by static and dynamic objects.
+			if (GetValidPlacement(HeldItem) is var (grid, transform, isFree)) {
-			const PhysicsLayer Mask = PhysicsLayer.Place | PhysicsLayer.Static | PhysicsLayer.Dynamic;
+				var outlineColor = isFree ? OutlineYesPlace : OutlineNoPlace;
-
-			if ((RayToMouseCursor(Mask) is RayResult ray) && (ray.Collider is Grid grid)
-				// Not pointing at item's own grid, or one of its nested grids.
-				&& (grid.GetParent() != HeldItem) && !grid.ContainsItem(HeldItem))
-			{
-				var inverseTransform = grid.GlobalTransform.AffineInverse();
-				var inverseBasis     = grid.GlobalBasis.Inverse();
-
-				var pos     = inverseTransform * ray.Position;
-				var normal  = inverseBasis     * ray.Normal;
-
-				if (grid.CanPlaceAgainst(HeldItem, pos, normal)) {
-					var transform = new Transform3D(inverseBasis * HeldItem.GlobalBasis, pos);
-					    transform = grid.Snap(transform, normal, HeldItem);
-					var canPlace  = grid.CanPlaceAt(HeldItem, transform);
-
-					var outlineColor = canPlace ? OutlineYesPlace : OutlineNoPlace;
 				_outlineMaterial.SetShaderParameter("line_color", outlineColor);
 
 				_preview.GlobalTransform = grid.GlobalTransform * transform;
 				_preview.Visible = true;
-					_targetedGrid = canPlace ? grid : null;
+				_targetedGrid = isFree ? grid : null;
-				} else {
-					_preview.Visible = false;
-					_targetedGrid = null;
-				}
 			} else {
 				_preview.Visible = false;
 				_targetedGrid = null;
 			}
-
 		} else {
 			var interactable = RayToMouseCursor(PhysicsLayer.Pickup)?.Collider;
 
@@ -142,8 +120,48 @@ public partial class PickupController : Node3D
 		return preview;
 	}
 
+	(Grid Grid, Transform3D Target, bool IsFree)? GetValidPlacement(Item itemToPlace)
+	{
+		// This ray will be blocked by static and dynamic objects.
+		const PhysicsLayer Mask = PhysicsLayer.Static | PhysicsLayer.Dynamic | PhysicsLayer.Item;
+		// FIXME: Remove .Place and .Pickup physics layers?
+		// TODO: We need a separate physics layers for:
+		//       - The physical item collider used for physics calculations (simplified).
+		//       - The placement collider which should match the item's appearance.
+		//       - The general space / size an item takes up, as a cuboid.
+		// TODO: Probably just overhaul the physics layers altogether.
+		//       It would be better to have a "collides with player" and "player collides with it" layer, etc.
+
+		var excludeSet = new HashSet<CollisionObject3D> { HeldItem };
+		var heldItemGrid = HeldItem.GetNodeOrNull<Grid>(nameof(Grid));
+		heldItemGrid?.AddItemsRecursively(excludeSet);
+
+		// Cast a ray and make sure it hit something.
+		if (RayToMouseCursor(Mask, excludeSet) is not RayResult ray) return null;
+
+		// Find a grid to place against, which will be either the grid belonging
+		// to the item the ray intersected, or the grid said item is placed upon.
+		var grid = ray.Collider.GetNodeOrNull<Grid>(nameof(Grid))
+				?? ray.Collider.GetParentOrNull<Grid>();
+		if (grid == null) return null; // No suitable grid found.
+
+		var inverseTransform = grid.GlobalTransform.AffineInverse();
+		var inverseBasis     = grid.GlobalBasis.Inverse();
+
+		var pos     = inverseTransform * ray.Position;
+		var normal  = inverseBasis     * ray.Normal;
+
+		if (!grid.CanPlaceAgainst(itemToPlace, pos, normal)) return null;
+
+		var transform = new Transform3D(inverseBasis * itemToPlace.GlobalBasis, pos);
+			transform = grid.Snap(transform, normal, itemToPlace);
+		var isFree    = grid.CanPlaceAt(itemToPlace, transform);
+
+		return (grid, transform, isFree);
+	}
+
 	record class RayResult(CollisionObject3D Collider, Vector3 Position, Vector3 Normal);
-	RayResult RayToMouseCursor(PhysicsLayer collisionMask)
+	RayResult RayToMouseCursor(PhysicsLayer collisionMask, IEnumerable<CollisionObject3D> excluded = null)
 	{
 		var camera = _player.Camera.Camera;
 		var mouse  = GetViewport().GetMousePosition();
@@ -153,12 +171,10 @@ public partial class PickupController : Node3D
 		var query = PhysicsRayQueryParameters3D.Create(from, to);
 		query.CollisionMask = (uint)collisionMask;
 		query.CollideWithAreas = true;
-		// Exclude the `CurrentItem` from collision checking if it's being held.
+		query.Exclude = new((excluded ?? []).Select(obj => obj.GetRid()));
-		query.Exclude = HasItemsHeld ? [ HeldItem.GetRid() ] : [];
 
 		var result = GetWorld3D().DirectSpaceState.IntersectRay(query);
 		return (result.Count > 0) ? new(
-				// FIXME: Unable to cast object of type 'ReplacePalette' to type 'Godot.CollisionObject3D'.
 				result["collider"].As<CollisionObject3D>(),
 				(Vector3)result["position"],
 				(Vector3)result["normal"]

scenes/workshop.tscn

@@ -109,13 +109,13 @@ transform = Transform3D(-4.37114e-08, 0, -1, 0, 1, 0, 1, 0, -4.37114e-08, 0.775,
 [node name="Cutting Board" parent="Objects/Table/Grid" instance=ExtResource("5_hj6pf")]
 transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0.025, 0.2)
 
-[node name="Bolt" parent="Objects/Table/Grid/Cutting Board/Grid" index="1" instance=ExtResource("5_r6ljd")]
+[node name="Bolt" parent="Objects/Table/Grid/Cutting Board/Grid" index="0" instance=ExtResource("5_r6ljd")]
 transform = Transform3D(1, 0, 0, 0, -4.37114e-08, 1, 0, -1, -4.37114e-08, 0.1, 0.025, -0.0250001)
 
-[node name="Bolt2" parent="Objects/Table/Grid/Cutting Board/Grid" index="2" instance=ExtResource("5_r6ljd")]
+[node name="Bolt2" parent="Objects/Table/Grid/Cutting Board/Grid" index="1" instance=ExtResource("5_r6ljd")]
 transform = Transform3D(-1, 8.74228e-08, 3.82137e-15, 0, -4.37114e-08, 1, 8.74228e-08, 1, 4.37114e-08, 0.15, 0.025, -0.0250001)
 
-[node name="Bolt3" parent="Objects/Table/Grid/Cutting Board/Grid" index="3" instance=ExtResource("5_r6ljd")]
+[node name="Bolt3" parent="Objects/Table/Grid/Cutting Board/Grid" index="2" instance=ExtResource("5_r6ljd")]
 transform = Transform3D(1, 0, 0, 0, -4.37114e-08, 1, 0, -1, -4.37114e-08, 0.2, 0.025, -0.0250001)
 
 [node name="Small Box" parent="Objects/Table/Grid" instance=ExtResource("10_kgm3d")]