Godot Physics 3d Agent Skill

3D Physics (Jolt/Native)

High-performance 3D simulation: body choice, CCD, stairs, vehicles, ragdolls, SoftBody — routed through scripts.

NEVER Do

• NEVER move PhysicsBody3D nodes in _process() — Use _physics_process(). Moving bodies outside the physics step causes visual jitter and unreliable collision detection [12, 13].
• NEVER scale collision shapes directly — Scaling physics shapes causes instability, inaccurate normals, and jitter. Use the shape properties (height, radius, size) instead.
• NEVER modify RigidBody3D transforms directly — This ignores the physics solver. Use apply_impulse(), apply_torque(), or the _integrate_forces() callback for safe manipulation [17].
• NEVER use RigidBody3D for platformer player controllers — RigidBody is for objects driven by physics. For refined movement, use CharacterBody3D with move_and_slide() [move_and_slide].
• NEVER leave Continuous CD (CCD) enabled for static meshes — It adds heavy CPU cost. Reserve it for high-speed small objects (bullets) to prevent them from passing through walls.
• NEVER use PhysicsServer3D RIDs without manual cleanup — RIDs are not garbage collected. If you create bodies via the server, you MUST call free_rid() when done to avoid memory leaks.
• NEVER use RayCast3D for precise ground detection on stairs — A single ray is too thin. Use ShapeCast3D with a cylinder or sphere shape to detect walkable steps reliably [Stair Logic].
• NEVER rely on VehicleBody3D for non-racing arcade vehicles — It's a complex sim. For arcade hovercraft or simple cars, a custom CharacterBody3D with Raycasts is often easier to tune.
• NEVER forget to set collision_layer and collision_mask properly — If everything is on layer 1, performance will tank from redundant checks. Categorize your world.
• NEVER use Area3D for high-frequency blocking — Areas are for detection. For walls/barriers, use StaticBody3D to ensure immediate, robust containment.

Godot 4.7: Jolt Physics Behavior

• WorldBoundaryShape3D (Jolt): plane.d sign convention flipped vs 4.6 — flip sign to match prior behavior.
• SoftBody3D (Jolt): mass defaults to 1 kg total (not per-point); retune linear_stiffness and damping_coefficient.
• Area3D now reports overlaps with SoftBody3D — adjust layers/masks to avoid unwanted overlap signals.

Body / Symptom Decision Tree

> MANDATORY — load the script for the chosen row before writing movement or sim code.

>

> Do NOT Load every physics script for one controller.

| Need / symptom | Body / API | Script |

|----------------|------------|--------|

| Player locomotion, stairs, slopes | CharacterBody3D | MANDATORY kinematic_3d_stairs_logic.gd + shapecast_3d_ground_check.gd |

| Debris, props, impulse-driven objects | RigidBody3D | NEVER + impulses; layers via physics_layers_3d_config.gd |

| Racing / wheeled sim | VehicleBody3D | MANDATORY vehicle_simulation_tuning.gd |

| Arcade hover / simple cars | Custom CharacterBody3D + rays | Prefer stairs/ray scripts; avoid full VehicleBody |

| Death / blend to physics pose | PhysicalBone3D / Skeleton | MANDATORY ragdoll_manager.gd |

| Cloaks, soft cloth, foliage soft | SoftBody3D | MANDATORY soft_body_3d_interaction.gd |

| Tunneling bullets | CCD / server bullets | MANDATORY physics_ccd_3d_projectile.gd or physics_server_3d_bullets.gd |

| Joint snap / destructibles | Joint3D stress | joint_3d_breakage_logic.gd |

| Gravity wells / zero-G | Area priority | custom_gravity_well_3d.gd |

| LOS / AI vision | Direct space state | ray_query_3d_vision.gd |

| Debug hit normals | visualizer | raycast_visualizer.gd |

3D Layer Pitfalls (not a 2D primer)

• Layer = what the object *is*; mask = what it *hits*. Name bits in physics_layers_3d_config.gd.
• SoftBody overlaps Area3D in 4.7 — retune masks or you get surprise signals.
• WorldBoundaryShape3D plane.d sign flipped under Jolt vs 4.6 — flip when migrating.
• Do not dump a same-as-2D layers tutorial here; Official Docs cover the shared mental model.

Available Scripts

kinematic_3d_stairs_logic.gd

Procedural stair-step + snap for CharacterBody3D.

shapecast_3d_ground_check.gd

Volume ground/stair detection (rays tunnel).

ragdoll_manager.gd

Animation → PhysicalBone simulation transition, impulses, cleanup.

vehicle_simulation_tuning.gd

VehicleBody3D / VehicleWheel3D arcade vs sim knobs.

soft_body_3d_interaction.gd

SoftBody3D flags and attachments after 4.7 mass defaults.

physics_ccd_3d_projectile.gd

CCD / sub-step anti-tunneling for small fast bodies.

physics_server_3d_bullets.gd

RID bullets at scale with mandatory free_rid().

physics_layers_3d_config.gd

Named 3D collision matrix architecture.

custom_gravity_well_3d.gd

Planet / zero-G Area3D gravity priority.

joint_3d_breakage_logic.gd

Joint stress monitoring and procedural snaps.

ray_query_3d_vision.gd

Low-level LOS / AI vision queries.

raycast_visualizer.gd

In-game ray hit/normal debug draw.

Expert Pointers (Jolt 4.7)

• Prefer Generic6DOFJoint3D over stacking specialized joints unless you need a specific node UX.
• SoftBody total mass default is 1 kg under Jolt — retune stiffness/damping after upgrade.
• Ragdoll/vehicle/soft samples live in scripts above — do not expand Create Physical Skeleton editor tutorials in this body.

Deep dives (on demand)

• Hover ray constraints, Jolt suspension tuning, ragdoll influence blend → expert-3d-constraints.md
• Scripts: hover_constraint_3d.gd, ragdoll_blender.gd

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 — Layers vs masks, body types, and the shared 2D/3D collision mental model every 3D setup depends on.
• Collision shapes (3D) — Primitive vs convex/concave shapes and why scaling CollisionShape3D breaks normals and contacts.
• Using Jolt Physics — Engine switch, joint-property gaps vs Godot Physics, and project-setting caveats for stable 3D sims.
• Using RigidBody — Safe control via forces, impulses, and _integrate_forces instead of fighting the solver with per-frame transforms.
• Ragdoll system — PhysicalBoneSimulator3D / PhysicalBone3D setup for death sims and animation↔physics handoff.
• Using SoftBody3D — Cloth/flag deformation, pinning, and why Jolt is preferred for soft-body robustness.
• Ray-casting — RayCast3D vs PhysicsDirectSpaceState3D queries, exclusions, and space access during the physics tick.
• Troubleshooting physics issues — Tunneling, jitter, CCD misuse, and common layer/mask misconfigurations.
• Physics interpolation introduction — Why fixed physics ticks stutter on high-refresh displays and when interpolation smooths 3D motion.
• PhysicsServer3D — RID-based body/shape APIs for swarm-scale projectiles with mandatory free_rid cleanup.
• PhysicsDirectSpaceState3D — Ray/shape/point queries for LOS, hover constraints, and custom suspensions without permanent query nodes.
• ShapeCast3D — Volume casts for stair/ground detection when a thin RayCast3D misses ledges or uneven floors.

Related Skills

Prerequisites

• godot-project-foundations — 3D physics engine choice, tick rate, gravity, and named layer bits must be set before matrices and Jolt tuning stay sane.
• godot-gdscript-mastery — Typed RIDs, bitmask enums, and _physics_process discipline underpin server-side and CharacterBody3D patterns here.
• godot-signal-architecture — body_entered / contact-monitor wiring needs clean ownership so Area3D gravity wells and CCD hits do not spam.

Complements

• godot-2d-physics — Parallel layer/mask and body-type contracts when sharing policy across dimensions or porting mechanics.
• godot-raycasting-queries — Deeper query-parameter recipes (masks, exclusions, shape casts) when vision/hitscan systems outgrow the basics.
• godot-3d-world-building — Static collision from GridMap/CSG/meshes must match the same 3D layer matrix used by characters and projectiles.
• godot-animation-tree-mastery — AnimationTree poses and state machines feed ragdoll start/stop and influence blending on PhysicalBoneSimulator3D.
• godot-performance-optimization — Profiling and pooling guidance when PhysicsServer3D swarms, soft bodies, or CCD counts become bottlenecks.
• godot-debugging-profiling — Visible collision shapes, contact normals, and profiler traps when diagnosing jitter, tunneling, or missed stairs.

Downstream / consumers

• godot-combat-system — 3D hitboxes/hurtboxes and projectile CCD inherit layer/mask and space-query choices from this domain.
• godot-genre-racing — VehicleBody3D suspension/friction tuning and drift feel consume the vehicle and Jolt guidance here.
• godot-genre-shooter-fps — Hitscan rays, CharacterBody3D movement, and high-speed projectile CCD are direct consumers of these contracts.
• godot-navigation-pathfinding — Agents still need physics layers for blockers and LOS; keep nav meshes and the collision world consistent.
• godot-monte-carlo-balancer — Gravity, CCD, joint break thresholds, and hitbox size change win-rates; simulate those physics knobs instead of guessing.

Master

• godot-master — Library router and mirrored entry point for discovering 3D physics alongside sibling domains.