Improve Grid handling, prevent overlapping items

- Move snapping logic to Grid class
- Add Grid.CanPlaceAt to check for item overlap
  (no test for collision with physics-enabled items)
- Change outline color depending on if can place

assets/shaders/outline_material.tres

@@ -0,0 +1,8 @@
+[gd_resource type="ShaderMaterial" load_steps=2 format=3 uid="uid://c0q35rri3vb07"]
+
+[ext_resource type="Shader" path="res://assets/shaders/outline.gdshader" id="1_yi6vm"]
+
+[resource]
+shader = ExtResource("1_yi6vm")
+shader_parameter/line_color = Color(1, 1, 1, 0.75)
+shader_parameter/line_thickness = 3.0

game.tscn

@@ -1,20 +1,15 @@
-[gd_scene load_steps=11 format=3 uid="uid://puuk72ficqhu"]
+[gd_scene load_steps=10 format=3 uid="uid://puuk72ficqhu"]
 
 [ext_resource type="Script" path="res://scripts/MultiplayerManager.cs" id="1_7shyh"]
 [ext_resource type="Script" path="res://Game.cs" id="1_uywdd"]
 [ext_resource type="PackedScene" uid="uid://dmd7w2r8s0x6y" path="res://player/player.tscn" id="2_iv2f7"]
 [ext_resource type="PackedScene" uid="uid://bwfuet1irfi17" path="res://scenes/workshop.tscn" id="3_4u5ql"]
-[ext_resource type="Shader" path="res://assets/shaders/outline.gdshader" id="4_gacvj"]
+[ext_resource type="Material" uid="uid://c0q35rri3vb07" path="res://assets/shaders/outline_material.tres" id="5_a3fxj"]
 [ext_resource type="Script" path="res://scripts/OutlineCamera.cs" id="5_qpc14"]
 [ext_resource type="PackedScene" uid="uid://c5ooi36ibspfo" path="res://ui/menu.tscn" id="6_ol0j5"]
 [ext_resource type="Texture2D" uid="uid://lxxfestfg2dt" path="res://assets/crosshair.png" id="7_0l5tv"]
 [ext_resource type="Script" path="res://scripts/Crosshair.cs" id="8_mfhgr"]
 
-[sub_resource type="ShaderMaterial" id="ShaderMaterial_ke1l3"]
-shader = ExtResource("4_gacvj")
-shader_parameter/line_color = Color(1, 1, 1, 0.75)
-shader_parameter/line_thickness = 2.0
-
 [node name="Game" type="Node" node_paths=PackedStringArray("LocalPlayer")]
 script = ExtResource("1_uywdd")
 LocalPlayer = NodePath("Players/Local")
@@ -33,7 +28,7 @@ PlayerScene = ExtResource("2_iv2f7")
 IsLocal = true
 
 [node name="OutlineViewportContainer" type="SubViewportContainer" parent="."]
-material = SubResource("ShaderMaterial_ke1l3")
+material = ExtResource("5_a3fxj")
 anchors_preset = 15
 anchor_right = 1.0
 anchor_bottom = 1.0

objects/Grid.cs

@@ -10,13 +10,22 @@ public partial class Grid : Area3D
 	static readonly Color ThickLineColor = new(0.25f, 0.25f, 0.25f);
 	static readonly Color ThinLineColor = new(0.35f, 0.35f, 0.35f);
 
+	// TODO: Make GridSize be three-dimensional?
 	Vector2I _gridSize = new(16, 16);
+	Vector3 _halfGridActualSize = new(8.0f, 0.0f, 8.0f);
 	[Export] public Vector2I GridSize {
 		get => _gridSize;
-		set { _gridSize = value; Update(); }
+		set {
+			_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();
+		}
 	}
 
-	public override void _Ready() => Update();
+
+	public override void _Ready()
+		=> Update();
 
 	void Update()
 	{
@@ -24,6 +33,69 @@ public partial class Grid : Area3D
 		UpdateImmediateMesh();
 	}
 
+
+	public Vector3I LocalToGrid(Vector3 pos)
+		=> (Vector3I)((pos + _halfGridActualSize) / StepSize);
+	public Vector3 GridToLocal(Vector3I pos)
+		=> (pos + Vector3.One * 0.5f) * StepSize - _halfGridActualSize;
+
+	public Vector3I GlobalToGrid(Vector3 pos)
+		=> LocalToGrid(ToLocal(pos));
+	public Vector3 GridToGlobal(Vector3I pos)
+		=> ToGlobal(GridToLocal(pos));
+
+	public static Aabb LocalItemTransformToLocalAabb(Transform3D transform, Item item)
+	{
+		var bounds = (transform.Basis * ((Vector3)item.Size * StepSize)).Abs();
+		return new(transform.Origin - bounds / 2, bounds);
+	}
+
+
+	/// <summary>
+	/// Returns whether the item can be placed at the specified global transform.
+	/// The transform needs to be grid-aligned, such as by calling <see cref="Snap"/>.
+	/// </summary>
+	public bool CanPlaceAt(Item item, Transform3D transform)
+	{
+		transform = GlobalTransform.AffineInverse() * transform;
+		var region = LocalItemTransformToLocalAabb(transform, item).Grow(-0.01f);
+		foreach (var other in GetChildren().OfType<Item>())
+			if (region.Intersects(LocalItemTransformToLocalAabb(other.Transform, other)))
+				return false;
+		return true;
+	}
+
+	/// <summary>
+	/// Snaps a global transform to line up with the grid.
+	/// The transform will be "pushed out" into the normal vector's
+	/// direction according to the current rotation and item's size.
+	/// </summary>
+	public Transform3D Snap(Transform3D transform, Vector3 normal, Item item)
+	{
+		var inverseTransform = GlobalTransform.AffineInverse();
+		var inverseBasis     = GlobalBasis.Inverse();
+		var halfSize         = (Vector3)item.Size * StepSize / 2;
+
+		// Get grid-local values of the global transform and normal.
+		var pos    = inverseTransform * transform.Origin;
+		var basis  = inverseBasis     * transform.Basis;
+		    normal = inverseBasis     * normal;
+
+		// Snap rotation to nearest axis.
+		basis = Basis.FromEuler(basis.GetEuler().Snapped(Tau / 4));
+
+		// Offset / "push out" by half of the item's size.
+		var offsetAxis = (int)(normal * basis).Abs().MaxAxisIndex();
+		pos += halfSize[offsetAxis] * normal;
+
+		// Snap the position to the grid.
+		var halfOff = basis * halfSize.PosMod(1.0f);
+		pos = halfOff + (pos - halfOff).Snapped(StepSize);
+
+		return new(GlobalBasis * basis, GlobalTransform * pos);
+	}
+
+
 	static StandardMaterial3D _material;
 	static StandardMaterial3D GetOrCreateMaterial()
 	{

player/PickupController.cs

@@ -1,18 +1,25 @@
 public partial class PickupController : Node3D
 {
+	static readonly Color OutlinePickup   = Colors.White with { A = 0.75f };
+	static readonly Color OutlineYesPlace = Colors.Green with { A = 0.75f };
+	static readonly Color OutlineNoPlace  = Colors.Red   with { A = 0.75f };
+
+	Node3D _preview; // Placement preview of the item - a duplicate of its model.
+	Grid   _grid;    // Grid currently being hovered over.
+
 	public Item CurrentItem { get; private set; }
 	public bool HasItemsHeld => GetChildCount() > 0;
-	Node3D _placementPreview;
 
 	[Export] public float PickupDistance { get; set; } = 2.0f;
 
 	Player _player;
 	Node3D _world;
+	ShaderMaterial _outlineShaderMaterial;
 	public override void _Ready()
 	{
 		_player = GetParent<Player>();
-		// TODO: Find a better way to find the world.
+		_world  = GetNode<Node3D>("/root/Game/Workshop"); // TODO: Find a better way to get the world.
-		_world = GetNode<Node3D>("/root/Game/Workshop");
+		_outlineShaderMaterial = Load<ShaderMaterial>("res://assets/shaders/outline_material.tres");
 	}
 
 	public override void _UnhandledInput(InputEvent @event)
@@ -24,12 +31,12 @@ public partial class PickupController : Node3D
 		if (@event.IsActionPressed("interact_pickup")) {
 			if (!HasItemsHeld) {
 				// Create clone of the item's model, use it as placement preview.
-				_placementPreview = (Node3D)CurrentItem.Model.Duplicate(0);
+				_preview = (Node3D)CurrentItem.Model.Duplicate(0);
-				_placementPreview.Name = "PlacementPreview";
+				_preview.Name = "PlacementPreview";
-				_placementPreview.TopLevel = true;
+				_preview.TopLevel = true;
-				_placementPreview.Visible = false;
+				_preview.Visible = false;
-				SetMeshLayerOutline(_placementPreview, OutlineMode.Exclusive);
+				SetMeshLayerOutline(_preview, OutlineMode.Exclusive);
-				AddChild(_placementPreview);
+				AddChild(_preview);
 
 				// Parent item to the `PickupController`.
 				var prevRot = CurrentItem.GlobalRotation;
@@ -47,11 +54,12 @@ public partial class PickupController : Node3D
 				// Parent item back to the world.
 				var prevTransform = CurrentItem.GlobalTransform;
 				RemoveChild(CurrentItem);
-				_world.AddChild(CurrentItem);
 
-				if (_placementPreview.Visible) {
+				if (_preview.Visible && _grid != null) {
-					CurrentItem.GlobalTransform = _placementPreview.GlobalTransform;
+					_grid.AddChild(CurrentItem);
+					CurrentItem.GlobalTransform = _preview.GlobalTransform;
 				} else {
+					_world.AddChild(CurrentItem);
 					CurrentItem.GlobalTransform = prevTransform;
 					CurrentItem.Freeze = false;
 
@@ -61,9 +69,13 @@ public partial class PickupController : Node3D
 					CurrentItem.ApplyImpulse(direction * 2);
 				}
 
-				RemoveChild(_placementPreview);
+				// Reset the color of the outline shader material.
-				_placementPreview.QueueFree();
+				_outlineShaderMaterial.SetShaderParameter("line_color", OutlinePickup);
-				_placementPreview = null;
+
+				RemoveChild(_preview);
+				_preview.QueueFree();
+				_preview = null;
+				_grid = null;
 
 				GetViewport().SetInputAsHandled();
 			}
@@ -77,25 +89,19 @@ public partial class PickupController : Node3D
 
 		if (HasItemsHeld) {
 			if ((RayToMouseCursor() is RayResult ray) && (ray.Collider is Grid grid)) {
-				// Snao rotation to nearest axis.
+				var transform = CurrentItem.GlobalTransform with { Origin = ray.Position };
-				var localBasis = grid.GlobalBasis.Inverse() * CurrentItem.GlobalBasis;
+				transform = grid.Snap(transform, ray.Normal, CurrentItem);
-				localBasis = Basis.FromEuler(localBasis.GetEuler().Snapped(Tau / 4));
+				_preview.GlobalTransform = transform;
-				_placementPreview.GlobalBasis = grid.GlobalBasis * localBasis;
+
-
+				var canPlace = grid.CanPlaceAt(CurrentItem, transform);
-				// Snap the position to the grid.
+				var outlineColor = canPlace ? OutlineYesPlace : OutlineNoPlace;
-				var halfSize = (Vector3)CurrentItem.Size * Grid.StepSize / 2;
+				_outlineShaderMaterial.SetShaderParameter("line_color", outlineColor);
-				var localPos    = ray.Position * grid.GlobalTransform;      // Get grid-local ray position.
+
-				var localNormal = ray.Normal   * grid.GlobalBasis;          // Get grid-local ray normal. (Pointing away from surface hit.)
+				_preview.Visible = true;
-				var off = localBasis * halfSize.PosMod(1.0f);               // Calculate an offset for grid snapping.
+				_grid = canPlace ? grid : null;
-				off[(int)localNormal.Abs().MaxAxisIndex()] = 0;             // Do not include offset in the normal direction.
-				localPos = off + (localPos - off).Snapped(Grid.StepSize);   // Snap `localPos` to nearest grid value.
-				var axis = (localNormal * localBasis).Abs().MaxAxisIndex(); // Find object-local axis that the normal is pointing towards.
-				localPos += halfSize[(int)axis] * localNormal;              // Offset (push out) object by half its size.
-				_placementPreview.GlobalPosition = grid.GlobalTransform * localPos;
-
-				_placementPreview.Visible = true;
 			} else {
-				_placementPreview.Visible = false;
+				_preview.Visible = false;
+				_grid = null;
 			}
 		} else {
 			var interactable = RayToMouseCursor()?.Collider;
@@ -114,10 +120,10 @@ public partial class PickupController : Node3D
 		if (CurrentItem == null) return;
 		if (!IsInstanceValid(CurrentItem)) {
 			CurrentItem = null;
-			if (_placementPreview != null) {
+			if (_preview != null) {
-				RemoveChild(_placementPreview);
+				RemoveChild(_preview);
-				_placementPreview.QueueFree();
+				_preview.QueueFree();
-				_placementPreview = null;
+				_preview = null;
 			}
 		}
 	}