cannon/src/constraints/PointToPointConstraint.js

A lightweight 3D physics engine written in JavaScript.

module.exports = PointToPointConstraint;

var Constraint = require('./Constraint');
var ContactEquation = require('../equations/ContactEquation');
var Vec3 = require('../math/Vec3');

/**
 * Connects two bodies at given offset points.
 * @class PointToPointConstraint
 * @extends Constraint
 * @constructor
 * @param {Body} bodyA
 * @param {Vec3} pivotA The point relative to the center of mass of bodyA which bodyA is constrained to.
 * @param {Body} bodyB Body that will be constrained in a similar way to the same point as bodyA. We will therefore get a link between bodyA and bodyB. If not specified, bodyA will be constrained to a static point.
 * @param {Vec3} pivotB See pivotA.
 * @param {Number} maxForce The maximum force that should be applied to constrain the bodies.
 *
 * @example
 *     var bodyA = new Body({ mass: 1 });
 *     var bodyB = new Body({ mass: 1 });
 *     bodyA.position.set(-1, 0, 0);
 *     bodyB.position.set(1, 0, 0);
 *     bodyA.addShape(shapeA);
 *     bodyB.addShape(shapeB);
 *     world.addBody(bodyA);
 *     world.addBody(bodyB);
 *     var localPivotA = new Vec3(1, 0, 0);
 *     var localPivotB = new Vec3(-1, 0, 0);
 *     var constraint = new PointToPointConstraint(bodyA, localPivotA, bodyB, localPivotB);
 *     world.addConstraint(constraint);
 */
function PointToPointConstraint(bodyA,pivotA,bodyB,pivotB,maxForce){
    Constraint.call(this,bodyA,bodyB);

    maxForce = typeof(maxForce) !== 'undefined' ? maxForce : 1e6;

    /**
     * Pivot, defined locally in bodyA.
     * @property {Vec3} pivotA
     */
    this.pivotA = pivotA ? pivotA.clone() : new Vec3();

    /**
     * Pivot, defined locally in bodyB.
     * @property {Vec3} pivotB
     */
    this.pivotB = pivotB ? pivotB.clone() : new Vec3();

    /**
     * @property {ContactEquation} equationX
     */
    var x = this.equationX = new ContactEquation(bodyA,bodyB);

    /**
     * @property {ContactEquation} equationY
     */
    var y = this.equationY = new ContactEquation(bodyA,bodyB);

    /**
     * @property {ContactEquation} equationZ
     */
    var z = this.equationZ = new ContactEquation(bodyA,bodyB);

    // Equations to be fed to the solver
    this.equations.push(x, y, z);

    // Make the equations bidirectional
    x.minForce = y.minForce = z.minForce = -maxForce;
    x.maxForce = y.maxForce = z.maxForce =  maxForce;

    x.ni.set(1, 0, 0);
    y.ni.set(0, 1, 0);
    z.ni.set(0, 0, 1);
}
PointToPointConstraint.prototype = new Constraint();

PointToPointConstraint.prototype.update = function(){
    var bodyA = this.bodyA;
    var bodyB = this.bodyB;
    var x = this.equationX;
    var y = this.equationY;
    var z = this.equationZ;

    // Rotate the pivots to world space
    bodyA.quaternion.vmult(this.pivotA,x.ri);
    bodyB.quaternion.vmult(this.pivotB,x.rj);

    y.ri.copy(x.ri);
    y.rj.copy(x.rj);
    z.ri.copy(x.ri);
    z.rj.copy(x.rj);
};