ecs.PhysicsJoint

Component spec for ecs.PhysicsJoint, which maps to the native PhysicsJoint, a constraint binding this entity's body to another. connectedEntityId names the other body; the anchors and axis are single Vec3 fields. Each end is the nearest body at or above its entity: an entity under a body (a marker at a beam's end) joins that body at the marker's position and orientation, with its anchor and axis measured in the marker's frame, so a body takes any number of joints, each on an entity of its own. The constructor ecs.PhysicsJoint{...} builds a value the generic ecs verbs apply, and the component is behavior-bearing: ecs.get exposes a motor drive.

Fields

• jointType: string? — "Fixed" | "Hinge" | "Ball" | "Prismatic" | "Spring".
• connectedEntityId: string? — the other body to bind to.
• anchorSelf: { number }? — {x, y, z}.
• anchorOther: { number }? — {x, y, z}.
• axis: { number }? — {x, y, z}.
• breakForce: number?
• stiffness: number?: a "Spring" joint's spring constant, in newtons per metre; on a "Hinge", "Ball", "Prismatic" or "Generic" joint with no motorMode, a spring pulling each of its axes back to where its frames align. Negative (the default) takes the kind's own: 100 on a spring joint, no spring on every other kind.
• damping: number?: how strongly that spring resists the speed it moves at. Negative (the default) takes the kind's own: 10 on a spring joint, none on every other kind.
• restLength: number?: the distance in metres between the anchors a "Spring" joint settles at. Negative (the default) takes their distance when the joint is built; written negative on the live joint, the spring keeps the length it rests at.
• regionSelf: { [string]: any }?: when this entity is a soft body, the particles the joint is anchored on: { kind, min, max, point, world }, kind "Whole" (the body's frame, the default), "Box" (the particles between min and max) or "Nearest" (the particle nearest point), in the entity's local space or, with world = true, in world space.
• regionOther: { [string]: any }?: the same for the connected entity, when it is a soft body.
• built: boolean?: set by the simulation while the solver holds the joint.
• problem: string?: set by the simulation when it cannot build the joint (an end with no body at or above it, a connected id no entity carries, two ends on one body), naming the entity; empty otherwise.

Handle methods

ecs.get(id, ecs.PhysicsJoint) returns the generic data handle plus this method, bound to the entity's id.

• setMotor(targetVelocity, maxForce) — drive the joint motor.

Usage

ecs.insert(id, ecs.PhysicsJoint{ jointType = "Hinge", connectedEntityId = otherId, axis = { 0, 1, 0 } })
local joint = ecs.get(id, ecs.PhysicsJoint)
joint:setMotor(2, 50)