cannon/src/equations/RotationalEquation.js

A lightweight 3D physics engine written in JavaScript.

module.exports = RotationalEquation;

var Vec3 = require('../math/Vec3');
var Mat3 = require('../math/Mat3');
var Equation = require('./Equation');

/**
 * Rotational constraint. Works to keep the local vectors orthogonal to each other in world space.
 * @class RotationalEquation
 * @constructor
 * @author schteppe
 * @param {Body} bodyA
 * @param {Body} bodyB
 * @param {Vec3} [options.axisA]
 * @param {Vec3} [options.axisB]
 * @param {number} [options.maxForce]
 * @extends Equation
 */
function RotationalEquation(bodyA, bodyB, options){
    options = options || {};
    var maxForce = typeof(options.maxForce) !== 'undefined' ? options.maxForce : 1e6;

    Equation.call(this,bodyA,bodyB,-maxForce, maxForce);

    this.axisA = options.axisA ? options.axisA.clone() : new Vec3(1, 0, 0);
    this.axisB = options.axisB ? options.axisB.clone() : new Vec3(0, 1, 0);

    this.maxAngle = Math.PI / 2;
}

RotationalEquation.prototype = new Equation();
RotationalEquation.prototype.constructor = RotationalEquation;

var tmpVec1 = new Vec3();
var tmpVec2 = new Vec3();

RotationalEquation.prototype.computeB = function(h){
    var a = this.a,
        b = this.b,

        ni = this.axisA,
        nj = this.axisB,

        nixnj = tmpVec1,
        njxni = tmpVec2,

        GA = this.jacobianElementA,
        GB = this.jacobianElementB;

    // Caluclate cross products
    ni.cross(nj, nixnj);
    nj.cross(ni, njxni);

    // g = ni * nj
    // gdot = (nj x ni) * wi + (ni x nj) * wj
    // G = [0 njxni 0 nixnj]
    // W = [vi wi vj wj]
    GA.rotational.copy(njxni);
    GB.rotational.copy(nixnj);

    var g = Math.cos(this.maxAngle) - ni.dot(nj),
        GW = this.computeGW(),
        GiMf = this.computeGiMf();

    var B = - g * a - GW * b - h * GiMf;

    return B;
};