Physics · interface

JointDesc

Explained in Your first game, Rigid bodies.

interface JointDesc

import type { JointDesc } from '@driftengine/physics';

Properties

Name	Type	Description
`type`readonly	`JointType`
`bodyA`readonly	`number`
`bodyB`readonly	`number`
`anchorAX`readonlyoptional	`number`	Anchor in each body's local frame.
`anchorAY`readonlyoptional	`number`
`anchorAZ`readonlyoptional	`number`
`anchorBX`readonlyoptional	`number`
`anchorBY`readonlyoptional	`number`
`anchorBZ`readonlyoptional	`number`
`axisX`readonlyoptional	`number`	The free axis, in A's local frame: a hinge turns about it, a slider travels along it.
`axisY`readonlyoptional	`number`
`axisZ`readonlyoptional	`number`
`length`readonlyoptional	`number`	Distance joints: the length held. Others: unused.
`lower`readonlyoptional	`number`	Limits, as a cosine for a cone and as metres or a sine of a half-angle otherwise.
`upper`readonlyoptional	`number`
`swingCos`readonlyoptional	`number`	A cone half-angle's cosine, and a twist half-angle's sine. Cone-twist only.
`twistSin`readonlyoptional	`number`
`motorSpeed`readonlyoptional	`number`
`motorMaxForce`readonlyoptional	`number`
`breakImpulse`readonlyoptional	`number`	Accumulated impulse above which the joint gives way. `Infinity` never breaks.
`dof`readonlyoptional	`readonly DofMode[]`	Six-DOF only: what each degree of freedom does. More The order is linear x, y, z then angular x, y, z, all in body A's local frame — not in a frame of the joint's own. Cost: a caller wanting axes that are not A's own has to orient A, or place the anchors so that A's frame is the one it means. What would reverse it: a consumer whose parent body cannot be oriented, and the answer then is four more floats per joint holding a frame quaternion. Shorter than six, or absent, and the rest are locked.
`dofLower`readonlyoptional	`readonly number[]`	Lower bounds, one per degree, read only where the mode is `DOF_LIMITED`. More Linear bounds are metres of offset from the anchor; angular bounds are sines of half angles. The second is this package's own convention rather than a shortcut — a swing limit compares a dot product against a stored cosine and a twist limit a quaternion component against a half-angle's sine, because `Math.acos` and `Math.atan2` are both on the banned list and the comparison is what the solver wanted anyway. A quarter turn is `Math.sin(Math.PI / 4)`.
`dofUpper`readonlyoptional	`readonly number[]`	Upper bounds, in the same units and the same order.