Joints

A joint constrains two rigid bodies relative to each other. Joints are declared by the joint schema (packages/engine/src/scene/schema/joint.ts) on an entity and link it to a target entity by id. They are created in the loader’s second pass, after all bodies exist (see the three-pass loader).

The five joint types.

Types

type	Constraint
fixed	Welds two bodies rigidly together.
revolute	A hinge — rotation about a single axis (doors, wheels).
prismatic	A slider — translation along a single axis (pistons, lifts).
spherical	A ball-and-socket — free rotation about a point (ragdoll joints).
spring	A soft constraint with stiffness, damping, and restLength.

Fields

• target — entity id of the body this joint connects to.
• anchor / targetAnchor — local anchor points on this body and the target.
• axis — rotation/slide axis for revolute and prismatic.
• limits — { min, max } angle (degrees) or distance for revolute / prismatic.
• stiffness, damping, restLength — spring parameters.

Need a motor or custom behavior?

The schema covers the common constraints. For motors, custom limits, or runtime reconfiguration, reach ctx.rapierWorld directly and use Rapier’s joint API — vgai adds no wrapper around it.

See also

• Rigid bodies — the bodies a joint connects.
• Scene Schema reference — every joint field.
• Capstone: Vehicle — joints in a working build.