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tutorial_raycasting.md

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+# Physics Ray Casting and Queries (2D and 3D)
+
+### Introduction
+
+One of the most common tasks in game development is casting a ray (or custom shaped object) and see what it hits. This enables complex behaviors, AI, etc. to take place.
+This tutorial will explain how to do this 2D, but it's pretty much the same for 3D.
+
+Godot stores all the low level game information in servers, while the scene is just a frontend. As such, ray casting is generally a lower-level task. For simple raycasts, node such as [RayCast](class_raycast) and [RayCast2D](class_raycast2d) will work, as they will 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 calling [CanvasItem.get_world_2d().get_space()](class_canvasitem#get_world_2d). For 3D, it's [Spatial.get_world().get_space()](class_spatial#get_world).
+
+The resulting space [RID](class_rid) can be used in [PhysicsServer](class_physicsserver) and [Physics2DServer](class_physics2dserver) respectively for 3D and 2D.
+
+### Acessing 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._fixed_process(delta)](class_node#_fixed_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 [Physics2DDirectSpaceState](class_physics2ddirectspacestate) and [PhysicsDirectSpaceState](class_physicsdirectspacestate) must be used. 
+
+In code, for 2D spacestate, this code must be used:
+
+```python
+func _fixed_process(delta):
+    var space_rid = get_world_2d().get_space()
+    var space_state = Physics2DServer.space_get_direct_state(space_rid)
+```
+
+Of course, there is a simpler shortcut:
+
+```python
+func _fixed_process(delta):
+    var space_state = get_world_2d().get_direct_space_state()
+```
+
+For 3D:
+
+```python
+func _fixed_process(delta):
+    var space_state = get_world().get_direct_space_state()
+```
+
+### Raycast Query