Godot Physics skill

Godot Physics (4.x, 2D + 3D)

Pick the right physics body, wire up collision layers/masks, detect overlaps, and cast rays. Concepts apply to both 2D and 3D (swap the 2D/3D suffix). Targets Godot 4.7. In 3D, projects created with Godot 4.6 or later run Jolt Physics by default; older projects keep GodotPhysics3D unless someone switched them. 2D always uses Godot's own 2D engine.

When to use

• Use when choosing between body types, setting collision layers/masks so the right things collide, detecting overlaps (triggers, hurtboxes) with Area, applying forces/impulses to a RigidBody, or casting rays for line-of-sight/ground checks.

When not to use: kinematic character controllers (move_and_slide) → godot-2d-movement; tile collision setup → godot-tilemap; tuning the feel of physics (timestep, mass, jitter) → physics-tuning.

Core workflow

1. For 3D, check which engine runs before debugging behavior: Project Settings > Physics > 3D > Physics Engine ([physics] 3d/physics_engine="Jolt Physics" in project.godot). Projects created in 4.6+ get Jolt written there by default; with no such line (DEFAULT) the engine is GodotPhysics3D. The API is the same, but joints, ray-cast face indices, kinematic contacts, and collision margins behave differently (see Pitfalls).
2. Choose the body type:
   • StaticBody — never moves (floors, walls). Collides, no simulation.
   • RigidBody — fully simulated (gravity, forces, bouncing). Don't set its position directly; apply forces/impulses or set linear_velocity.
   • CharacterBody — script-driven kinematic (see godot-2d-movement).
   • Area — detects overlaps and can apply gravity/damping; no solid collision. Every body needs a CollisionShape (or CollisionPolygon) child.
3. Configure layers and masks. A body is on its layers and scans for its masks. Two bodies interact only if one's layer is in the other's mask. Name layers in Project Settings > Layer Names for clarity.
4. Detect overlaps with Area signals (body_entered, area_entered).
5. Drive RigidBodies with forces/impulses, or override _integrate_forces for full control.
6. Cast rays with a RayCast2D/3D node (polled each frame) or a one-shot space-state query from code.

Patterns

1. Collision layers vs masks (set from code)

# Player is on layer 1, scans layers 2 (walls) and 3 (enemies).
func _ready() -> void:
    set_collision_layer_value(1, true)    # I am on layer 1
    set_collision_mask_value(2, true)     # I collide with things on layer 2
    set_collision_mask_value(3, true)     # ...and layer 3
    # Bit-field forms also exist: collision_layer = 1; collision_mask = 0b110

2. Area2D as a trigger / hurtbox

extends Area2D                            # e.g. a damage zone

func _ready() -> void:
    body_entered.connect(_on_body_entered)
    area_entered.connect(_on_area_entered)

func _on_body_entered(body: Node2D) -> void:
    if body.has_method("take_damage"):
        body.take_damage(10)

func _on_area_entered(area: Area2D) -> void:
    print("Overlapped area: ", area.name)

3. Applying force and impulse to a RigidBody3D

extends RigidBody3D

func push(direction: Vector3) -> void:
    apply_central_impulse(direction * 8.0)     # instantaneous velocity change

func _physics_process(_delta: float) -> void:
    apply_central_force(Vector3.FORWARD * 4.0) # continuous force (per tick)
    # Never set `position` on a RigidBody to move it; use forces/impulses or
    # set linear_velocity. Use freeze=true if you must hold it in place.

4. Raycast two ways

# A) RayCast2D node: enable it, then poll after physics has updated.
@onready var ray: RayCast2D = $RayCast2D    # set target_position in the editor

func _physics_process(_delta: float) -> void:
    if ray.is_colliding():
        var hit := ray.get_collider()
        var point := ray.get_collision_point()

# B) One-shot query from code (no node needed).
func ground_under(global_from: Vector2) -> Dictionary:
    var space := get_world_2d().direct_space_state
    var query := PhysicsRayQueryParameters2D.create(global_from, global_from + Vector2(0, 64))
    query.collision_mask = 1                 # only layer 1
    return space.intersect_ray(query)        # {} if nothing hit, else collider/position/normal

Pitfalls

• Layer vs mask confusion is the #1 bug. Layer = "what I am"; mask = "what I look for". For A to detect B, B's layer must be in A's mask. Detection can be one-directional.
• Moving a RigidBody by position fights the solver and causes tunneling/jitter. Use impulses/forces, set linear_velocity, or freeze it. To teleport, set position and zero the velocities inside _integrate_forces.
• Area doesn't fire when neither monitoring nor monitorable is set, or layers/masks don't overlap. monitoring must be on for the Area to detect; monitorable lets others detect it.
• RayCast2D/3D read stale or no data if enabled is false, or if you read it before physics updated — read in _physics_process, and call force_raycast_update() after moving it within the same tick.
• Forgetting a CollisionShape (or leaving it empty) means the body never collides.
• Fast objects tunnel through thin walls; enable continuous CD on the RigidBody (continuous_cd) or use a raycast-based check.
• intersect_ray excludes its own body? Pass query.exclude = [self.get_rid()] (an Array[RID], not an array of nodes) to skip self-hits.

Jolt Physics (3D) differences

• face_index is always -1 in intersect_ray() / RayCast3D results under Jolt. Turn on Project Settings > Physics > Jolt Physics 3D > Queries > Enable Ray Cast Face Index if you need it (it costs roughly 25% more memory for ConcavePolygonShape3D).
• A joint with only one body gets inverted limits after switching engines. Jolt treats the lone body as node_b with node_a as the world; GodotPhysics3D always treats it as node_a. Assign the body to the slot Jolt expects, or use Physics > Jolt Physics 3D > Joints > World Node for compatibility with an older project.
• Joint soft-limit properties do nothing under Jolt: bias/damping/impulse_clamp on PinJoint3D; bias/softness/relaxation on HingeJoint3D and ConeTwistJoint3D; angular_* and limit softness/restitution/damping on SliderJoint3D; limit softness/restitution/damping/erp on Generic6DOFJoint3D. Godot warns when they are set to non-default values.
• A frozen kinematic RigidBody3D reports no contacts with static or kinematic bodies, even with max_contacts_reported > 0. Enable Physics > Jolt Physics 3D > Simulation > Generate All Kinematic Contacts if gameplay depends on those contacts.
• Shape margin shrinks the shape instead of padding it under Jolt, so sizes stay true but shape queries can return odd normals on small shapes; the effective margin comes from Physics > Jolt Physics 3D > Collisions > Collision Margin Fraction.
• Area3D now fires body_entered for SoftBody3D under Jolt (GodotPhysics3D never did). Filter soft bodies out with layers/masks if the old behavior is expected.
• A WorldBoundaryShape3D floor sits at the wrong height after upgrading to 4.7 → under Jolt, 4.7 reads plane.d with Godot's sign convention, the opposite of 4.6; flip the sign of d in projects tuned on 4.6. Jolt also caps the plane's effective size (Physics > Jolt Physics 3D > Limits > World Boundary Shape Size), so bodies far from the origin can fall off an "infinite" floor.

References

• For _integrate_forces, joints, one-way collision, PhysicsServer direct access, shape queries (intersect_shape), and 3D move_and_collide, read references/bodies-and-queries.md.
• Jolt specifics: Godot docs "Using Jolt Physics" (https://docs.godotengine.org/en/stable/tutorials/physics/using_jolt_physics.html).

Related skills

• godot-2d-movement — kinematic CharacterBody2D controllers.
• godot-tilemap — tile collision shapes and their layers.
• physics-tuning — engine-agnostic feel: timestep, mass, drag, CCD.
• godot-3d-essentials — 3D scene setup these bodies live in.