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 RayCast3D and 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 CanvasItem.get_world_2d().space. For 3D, it's Node3D.get_world_3d().space.

The resulting space RID can be used in PhysicsServer3D and 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 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 PhysicsDirectSpaceState2D and PhysicsDirectSpaceState3D must be used.

Use the following code in 2D:

func _physics_process(delta):
    var space_rid = get_world_2d().space
    var space_state = PhysicsServer2D.space_get_direct_state(space_rid)

Or more directly:

func _physics_process(delta):
    var space_state = get_world_2d().direct_space_state

And in 3D:

func _physics_process(delta):
    var space_state = get_world_3d().direct_space_state

Raycast query

For performing a 2D raycast query, the method PhysicsDirectSpaceState2D.intersect_ray() may be used. For example:

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)

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:

if result:
    print("Hit at point: ", result.position)