cannon/src/constraints/HingeConstraint.js

A lightweight 3D physics engine written in JavaScript.

module.exports = HingeConstraint;

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

/**
 * Hinge constraint. Think of it as a door hinge. It tries to keep the door in the correct place and with the correct orientation.
 * @class HingeConstraint
 * @constructor
 * @author schteppe
 * @param {Body} bodyA
 * @param {Body} bodyB
 * @param {object} [options]
 * @param {Vec3} [options.pivotA] A point defined locally in bodyA. This defines the offset of axisA.
 * @param {Vec3} [options.axisA] An axis that bodyA can rotate around, defined locally in bodyA.
 * @param {Vec3} [options.pivotB]
 * @param {Vec3} [options.axisB]
 * @param {Number} [options.maxForce=1e6]
 * @extends PointToPointConstraint
 */
function HingeConstraint(bodyA, bodyB, options){
    options = options || {};
    var maxForce = typeof(options.maxForce) !== 'undefined' ? options.maxForce : 1e6;
    var pivotA = options.pivotA ? options.pivotA.clone() : new Vec3();
    var pivotB = options.pivotB ? options.pivotB.clone() : new Vec3();

    PointToPointConstraint.call(this, bodyA, pivotA, bodyB, pivotB, maxForce);

    /**
     * Rotation axis, defined locally in bodyA.
     * @property {Vec3} axisA
     */
    var axisA = this.axisA = options.axisA ? options.axisA.clone() : new Vec3(1,0,0);
    axisA.normalize();

    /**
     * Rotation axis, defined locally in bodyB.
     * @property {Vec3} axisB
     */
    var axisB = this.axisB = options.axisB ? options.axisB.clone() : new Vec3(1,0,0);
    axisB.normalize();

    /**
     * @property {RotationalEquation} rotationalEquation1
     */
    var r1 = this.rotationalEquation1 = new RotationalEquation(bodyA,bodyB,options);

    /**
     * @property {RotationalEquation} rotationalEquation2
     */
    var r2 = this.rotationalEquation2 = new RotationalEquation(bodyA,bodyB,options);

    /**
     * @property {RotationalMotorEquation} motorEquation
     */
    var motor = this.motorEquation = new RotationalMotorEquation(bodyA,bodyB,maxForce);
    motor.enabled = false; // Not enabled by default

    // Equations to be fed to the solver
    this.equations.push(
        r1, // rotational1
        r2, // rotational2
        motor
    );
}
HingeConstraint.prototype = new PointToPointConstraint();
HingeConstraint.constructor = HingeConstraint;

/**
 * @method enableMotor
 */
HingeConstraint.prototype.enableMotor = function(){
    this.motorEquation.enabled = true;
};

/**
 * @method disableMotor
 */
HingeConstraint.prototype.disableMotor = function(){
    this.motorEquation.enabled = false;
};

/**
 * @method setMotorSpeed
 * @param {number} speed
 */
HingeConstraint.prototype.setMotorSpeed = function(speed){
    this.motorEquation.targetVelocity = speed;
};

/**
 * @method setMotorMaxForce
 * @param {number} maxForce
 */
HingeConstraint.prototype.setMotorMaxForce = function(maxForce){
    this.motorEquation.maxForce = maxForce;
    this.motorEquation.minForce = -maxForce;
};

var HingeConstraint_update_tmpVec1 = new Vec3();
var HingeConstraint_update_tmpVec2 = new Vec3();

HingeConstraint.prototype.update = function(){
    var bodyA = this.bodyA,
        bodyB = this.bodyB,
        motor = this.motorEquation,
        r1 = this.rotationalEquation1,
        r2 = this.rotationalEquation2,
        worldAxisA = HingeConstraint_update_tmpVec1,
        worldAxisB = HingeConstraint_update_tmpVec2;

    var axisA = this.axisA;
    var axisB = this.axisB;

    PointToPointConstraint.prototype.update.call(this);

    // Get world axes
    bodyA.quaternion.vmult(axisA, worldAxisA);
    bodyB.quaternion.vmult(axisB, worldAxisB);

    worldAxisA.tangents(r1.axisA, r2.axisA);
    r1.axisB.copy(worldAxisB);
    r2.axisB.copy(worldAxisB);

    if(this.motorEquation.enabled){
        bodyA.quaternion.vmult(this.axisA, motor.axisA);
        bodyB.quaternion.vmult(this.axisB, motor.axisB);
    }
};