.. _doc_ray-casting: Ray-casting =========== Introduction ------------ One of the most common tasks in game development is casting a ray (or custom shaped object) and checking what it hits. This enables complex behaviors, AI, etc. to take place. This tutorial will explain how to do this in 2D and 3D. Godot stores all the low level game information in servers, while the scene is only a frontend. As such, ray casting is generally a lower-level task. For simple raycasts, nodes like :ref:`RayCast3D ` and :ref:`RayCast2D ` will work, as they return every frame what the result of a raycast is. Many times, though, ray-casting needs to be a more interactive process so a way to do this by code must exist. Space ----- In the physics world, Godot stores all the low level collision and physics information in a *space*. The current 2d space (for 2D Physics) can be obtained by accessing :ref:`CanvasItem.get_world_2d().space `. For 3D, it's :ref:`Node3D.get_world_3d().space `. The resulting space :ref:`RID ` can be used in :ref:`PhysicsServer3D ` and :ref:`PhysicsServer2D ` respectively for 3D and 2D. Accessing space --------------- Godot physics runs by default in the same thread as game logic, but may be set to run on a separate thread to work more efficiently. Due to this, the only time accessing space is safe is during the :ref:`Node._physics_process() ` callback. Accessing it from outside this function may result in an error due to space being *locked*. To perform queries into physics space, the :ref:`PhysicsDirectSpaceState2D ` and :ref:`PhysicsDirectSpaceState3D ` must be used. Use the following code in 2D: .. tabs:: .. code-tab:: gdscript GDScript func _physics_process(delta): var space_rid = get_world_2d().space var space_state = PhysicsServer2D.space_get_direct_state(space_rid) .. code-tab:: csharp public override void _PhysicsProcess(double delta) { var spaceRid = GetWorld2D().Space; var spaceState = Physics2DServer.SpaceGetDirectState(spaceRid); } Or more directly: .. tabs:: .. code-tab:: gdscript GDScript func _physics_process(delta): var space_state = get_world_2d().direct_space_state .. code-tab:: csharp public override void _PhysicsProcess(double delta) { var spaceState = GetWorld2D().DirectSpaceState; } And in 3D: .. tabs:: .. code-tab:: gdscript GDScript func _physics_process(delta): var space_state = get_world_3d().direct_space_state .. code-tab:: csharp public override void _PhysicsProcess(double delta) { var spaceState = GetWorld3D().DirectSpaceState; } Raycast query ------------- For performing a 2D raycast query, the method :ref:`PhysicsDirectSpaceState2D.intersect_ray() ` may be used. For example: .. tabs:: .. code-tab:: gdscript GDScript func _physics_process(delta): var space_state = get_world_2d().direct_space_state # use global coordinates, not local to node var query = PhysicsRayQueryParameters2D.create(Vector2(0, 0), Vector2(50, 100)) var result = space_state.intersect_ray(query) .. code-tab:: csharp public override void _PhysicsProcess(double delta) { var spaceState = GetWorld2D().DirectSpaceState; // use global coordinates, not local to node var query = PhysicsRayQueryParameters2D.Create(Vector2.Zero, new Vector2(50, 100)); var result = spaceState.IntersectRay(query); } The result is a dictionary. If the ray didn't hit anything, the dictionary will be empty. If it did hit something, it will contain collision information: .. tabs:: .. code-tab:: gdscript GDScript if result: print("Hit at point: ", result.position) .. code-tab:: csharp if (result.Count > 0) GD.Print("Hit at point: ", result["position"]); The ``result`` dictionary when a collision occurs contains the following data: :: { position: Vector2 # point in world space for collision normal: Vector2 # normal in world space for collision collider: Object # Object collided or null (if unassociated) collider_id: ObjectID # Object it collided against rid: RID # RID it collided against shape: int # shape index of collider metadata: Variant() # metadata of collider } The data is similar in 3D space, using Vector3 coordinates. Note that to enable collisions with Area3D, the boolean parameter ``collide_with_areas`` must be set to ``true``. .. tabs:: .. code-tab:: gdscript GDScript const RAY_LENGTH = 1000 func _physics_process(delta): var space_state = get_world_3d().direct_space_state var cam = $Camera3D var mousepos = get_viewport().get_mouse_position() var origin = cam.project_ray_origin(mousepos) var end = origin + cam.project_ray_normal(mousepos) * RAY_LENGTH var query = PhysicsRayQueryParameters3D.create(origin, end) query.collide_with_areas = true var result = space_state.intersect_ray(query) Collision exceptions -------------------- A common use case for ray casting is to enable a character to gather data about the world around it. One problem with this is that the same character has a collider, so the ray will only detect its parent's collider, as shown in the following image: .. image:: img/raycast_falsepositive.webp To avoid self-intersection, the ``intersect_ray()`` parameters object can take an array of exceptions via its ``exclude`` property. This is an example of how to use it from a CharacterBody2D or any other collision object node: .. tabs:: .. code-tab:: gdscript GDScript extends CharacterBody2D func _physics_process(delta): var space_state = get_world_2d().direct_space_state var query = PhysicsRayQueryParameters2D.create(global_position, player_position) query.exclude = [self] var result = space_state.intersect_ray(query) .. code-tab:: csharp using Godot; public partial class MyCharacterBody2D : CharacterBody2D { public override void _PhysicsProcess(double delta) { var spaceState = GetWorld2D().DirectSpaceState; var query = PhysicsRayQueryParameters2D.Create(globalPosition, playerPosition); query.Exclude = new Godot.Collections.Array { GetRid() }; var result = spaceState.IntersectRay(query); } } The exceptions array can contain objects or RIDs. Collision Mask -------------- While the exceptions method works fine for excluding the parent body, it becomes very inconvenient if you need a large and/or dynamic list of exceptions. In this case, it is much more efficient to use the collision layer/mask system. The ``intersect_ray()`` parameters object can also be supplied a collision mask. For example, to use the same mask as the parent body, use the ``collision_mask`` member variable. The array of exceptions can be supplied as the last argument as well: .. tabs:: .. code-tab:: gdscript GDScript extends CharacterBody2D func _physics_process(delta): var space_state = get_world_2d().direct_space_state var query = PhysicsRayQueryParameters2D.create(global_position, target_position, collision_mask, [self]) var result = space_state.intersect_ray(query) .. code-tab:: csharp using Godot; public partial class MyCharacterBody2D : CharacterBody2D { public override void _PhysicsProcess(double delta) { var spaceState = GetWorld2D().DirectSpaceState; var query = PhysicsRayQueryParameters2D.Create(globalPosition, targetPosition, CollisionMask, new Godot.Collections.Array { GetRid() }); var result = spaceState.IntersectRay(query); } } See :ref:`doc_physics_introduction_collision_layer_code_example` for details on how to set the collision mask. 3D ray casting from screen -------------------------- Casting a ray from screen to 3D physics space is useful for object picking. There is not much need to do this because :ref:`CollisionObject3D ` has an "input_event" signal that will let you know when it was clicked, but in case there is any desire to do it manually, here's how. To cast a ray from the screen, you need a :ref:`Camera3D ` node. A ``Camera3D`` can be in two projection modes: perspective and orthogonal. Because of this, both the ray origin and direction must be obtained. This is because ``origin`` changes in orthogonal mode, while ``normal`` changes in perspective mode: .. image:: img/raycast_projection.png To obtain it using a camera, the following code can be used: .. tabs:: .. code-tab:: gdscript GDScript const RAY_LENGTH = 1000.0 func _input(event): if event is InputEventMouseButton and event.pressed and event.button_index == 1: var camera3d = $Camera3D var from = camera3d.project_ray_origin(event.position) var to = from + camera3d.project_ray_normal(event.position) * RAY_LENGTH .. code-tab:: csharp private const float RayLength = 1000.0f; public override void _Input(InputEvent @event) { if (@event is InputEventMouseButton eventMouseButton && eventMouseButton.Pressed && eventMouseButton.ButtonIndex == MouseButton.Left) { var camera3D = GetNode("Camera3D"); var from = camera3D.ProjectRayOrigin(eventMouseButton.Position); var to = from + camera3D.ProjectRayNormal(eventMouseButton.Position) * RayLength; } } Remember that during ``_input()``, the space may be locked, so in practice this query should be run in ``_physics_process()``.