2D Physics

Expert guidance for collision detection, triggers, and raycasting in Godot 2D.

NEVER Do

• NEVER scale CollisionShape2D nodes — Use the shape handles in the editor, NOT the Node2D scale property. Scaling causes unpredictable physics behavior and incorrect collision normals [12].
• NEVER confuse collision_layer with collision_mask — Layer = "What AM I?", Mask = "What do I DETECT?". Setting both to the same value is usually wrong [13].
• NEVER multiply velocity by delta when using move_and_slide() — move_and_slide() automatically includes timestep. Only multiply gravity/acceleration by delta [14].
• NEVER forget force_raycast_update() for manual mid-frame raycasts — Raycasts update once per physics frame. If you change target_position, you MUST force an update [15].
• NEVER use get_overlapping_bodies() every frame — It is expensive. Cache results with body_entered/body_exited signals instead [16].
• NEVER modify RigidBody2D state directly in _process — Use _integrate_forces() for safe, synchronized access to PhysicsDirectBodyState2D [17, 411].
• NEVER move PhysicsBody2D nodes in _process() — Use _physics_process(). Moving bodies outside the physics step causes stutter and unreliable collision detection.
• NEVER use RigidBody2D for 1000+ simple entities — Use PhysicsServer2D to bypass node overhead for massive performance gains (Swarms/Bullets) [18, 397].
• NEVER use Area2D for high-frequency blocking (Bullets) — Area signals can be delayed. Use move_and_collide() or ShapeCast2D for frame-perfect results [19].
• NEVER ignore 'Physics Jitter' on high-refresh monitors — Enable Physics Interpolation to prevent micro-stutter in motion [21, 400].
• NEVER scale collision shapes directly at runtime — It causes major instability. Resize the shape resource (size/radius) instead.
• NEVER use set_deferred for immediate physics transform logic — It happens at the end of the frame. Use force_raycast_update() or PhysicsServer2D instead.
• NEVER leave Continuous CD (CCD) enabled for slow objects — It adds significant CPU overhead. Reserve it for high-speed projectiles to prevent tunneling.
• NEVER use a single collision layer for all tiles/entities — Separate layers (Ground, Walls, Enemies) to allow selective filtering via masks.
• NEVER forget to free PhysicsServer2D RIDs manually — They are not garbage collected and will leak memory permanently.

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Available Scripts

MANDATORY: Read the script matching your workflow branch before coding. Query/Area cookbook samples live in scripts — not in this body.

Workflow router (MANDATORY / Do NOT Load)

Canonical vs overlap (dedupe guide)

• ShapeCast AOE: load shapecast_aoe.gd for combat AOE; shapecast_aoe_detection.gd only for grounded/volume checks — never both for one feature.
• Space queries: start with physics_queries.gd; add physics_direct_query.gd / physics_direct_space_query.gd only if that specialist matches.
• Custom physics: CharacterBody → custom_physics_2d.gd; RigidBody integrate → custom_physics.gd.
• Interpolation: jitter_interpolation_fix.gd wins over physics_interpolation_smoothing.gd.

Script index

• collision_setup.gd / collision_bitmask_helper.gd / collision_layer_matrix_manager.gd
• physics_queries.gd / physics_direct_query.gd / physics_direct_space_query.gd / physics_query_cache.gd
• raycast_vision_stack.gd / raycast_hit_prediction.gd
• shapecast_aoe.gd / shapecast_aoe_detection.gd
• physics_server_swarm.gd / physics_server_direct_body.gd
• continuous_collision_detection.gd / substepping_logic.gd
• safe_rigidbody_state.gd / custom_physics.gd / custom_physics_2d.gd
• custom_gravity_area.gd / custom_gravity_override.gd
• collision_debouncer.gd / jitter_interpolation_fix.gd
• compound_body_sync.gd / collision_visual_debugger.gd
• move_and_collide_precision.gd / performance_batch_mover.gd
• physics_interpolation_smoothing.gd — legacy; prefer jitter fix script

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Decision Tree: Collision Detection Methods

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Mental model (keep short)

• Layer = who I am; Mask = who I detect. Bitmask cookbook → collision-layers-masks.md.
• Area2D with multiple shapes fires body_entered once per shape — dedupe with a Set/dict or collision_debouncer.gd.
• Mid-frame ray/shape changes require force_raycast_update() / force_shapecast_update().
• _ready physics queries are false until after a physics frame (await get_tree().physics_frame).
• CharacterBody2D ships with collision_layer = 0 — Areas won't see it until you set a layer.
• Free PhysicsServer RIDs yourself — they are not GC'd.

Deep recipes (on demand)

Reference

Progressive disclosure: open Official Documentation links only when researching a specific API; load Related Skills when routing work to a peer domain — do not preload the whole lattice.

Official Documentation

• Physics introduction — Collision layers vs masks, body types, and the mental model every 2D setup depends on.
• Collision shapes (2D) — Correct shape sizing and why scaling CollisionShape2D nodes breaks normals and contacts.
• Using CharacterBody2D — move_and_slide / move_and_collide, floor detection, and kinematic movement contracts.
• Using Area2D — Trigger monitoring, overlap signals, and space/gravity overrides for zones.
• Ray-casting — RayCast2D vs PhysicsDirectSpaceState2D rays, exclusions, and mid-frame force_raycast_update.
• RigidBody — Safe rigid-body control via _integrate_forces / PhysicsDirectBodyState2D instead of fighting the solver in _process.
• Troubleshooting physics issues — Tunneling, jitter, one-way platforms, and common layer/mask misconfigurations.
• Physics interpolation introduction — Why fixed physics ticks stutter on high-refresh displays and when interpolation fixes it.
• PhysicsServer2D — RID-based body/shape APIs for swarm-scale 2D physics without SceneTree overhead.
• PhysicsDirectSpaceState2D — Point, ray, and shape queries for LOS, AOE, and click-picking without permanent query nodes.
• ShapeCast2D — Volume casts for frame-perfect melee/AOE detection when Area2D signal lag is unacceptable.

Related Skills

Prerequisites

• godot-project-foundations — Project Settings layer names, physics ticks, and default gravity must be set before layer/mask matrices stay sane.
• godot-gdscript-mastery — Bitmask enums, typed dictionaries for overlap sets, and _physics_process discipline underpin every pattern here.
• godot-signal-architecture — body_entered / body_exited wiring and debounce patterns need clean signal ownership to avoid spam.

Complements

• godot-characterbody-2d — Coyote time, jump buffers, and one-way platforms sit on top of the collision contracts this skill defines.
• godot-raycasting-queries — Deeper query parameter recipes (exclusions, masks, shape casts) when vision/hitscan systems grow beyond basics.
• godot-tilemap-mastery — Tile physics layers and one-way tile collisions must match the same layer matrix used by bodies and areas.
• godot-input-handling — Physics-step input sampling and vsync/latency choices couple tightly with move_and_slide feel.
• godot-physics-3d — Parallel 3D body/query concepts when porting or sharing layer policy across dimensions.
• godot-performance-optimization — Profiling and batching guidance when PhysicsServer2D swarms or query caches become bottlenecks.
• godot-debugging-profiling — Visible collision shapes, contact normals, and frame-time traps when diagnosing jitter or missed hits.

Downstream / consumers

• godot-combat-system — Hitboxes/hurtboxes are Area2D + layer/mask products; damage timing inherits overlap and CCD choices.
• godot-genre-platformer — Platformer feel (floors, ledges, one-ways) consumes CharacterBody2D + collision setup from this domain.
• godot-navigation-pathfinding — Agents still need physics layers for blockers and LOS; keep nav meshes and collision worlds consistent.
• godot-monte-carlo-balancer — Jump windows, projectile speed/CCD, gravity, and hitbox size directly change win-rate and difficulty curves; simulate those physics knobs instead of guessing.

Master

• godot-master — Library router and mirrored entry point for discovering 2D physics alongside sibling domains.