p2s/src/constraints/GearConstraint.js

A JavaScript 2D physics engine.

var Constraint = require('./Constraint')
,   AngleLockEquation = require('../equations/AngleLockEquation')
,   Utils = require('../utils/Utils');

module.exports = GearConstraint;

/**
 * Constrains the angle of two bodies to each other to be equal. If a gear ratio is not one, the angle of bodyA must be a multiple of the angle of bodyB.
 * @class GearConstraint
 * @constructor
 * @author schteppe
 * @param {Body}            bodyA
 * @param {Body}            bodyB
 * @param {Object}          [options]
 * @param {Number}          [options.angle=0] Relative angle between the bodies. Will be set to the current angle between the bodies (the gear ratio is accounted for).
 * @param {Number}          [options.ratio=1] Gear ratio.
 * @param {Number}          [options.maxTorque] Maximum torque to apply.
 * @extends Constraint
 *
 * @example
 *     var constraint = new GearConstraint(bodyA, bodyB);
 *     world.addConstraint(constraint);
 *
 * @example
 *     var constraint = new GearConstraint(bodyA, bodyB, {
 *         ratio: 2,
 *         maxTorque: 1000
 *     });
 *     world.addConstraint(constraint);
 */
function GearConstraint(bodyA, bodyB, options){
    options = options || {};

    Constraint.call(this, bodyA, bodyB, Constraint.GEAR, options);

    /**
     * The gear ratio.
     * @property ratio
     * @type {Number}
     */
    this.ratio = options.ratio !== undefined ? options.ratio : 1;

    /**
     * The relative angle
     * @property angle
     * @type {Number}
     */
    this.angle = options.angle !== undefined ? options.angle : bodyB.angle - this.ratio * bodyA.angle;

    // Send same parameters to the equation
    var angleLockOptions = Utils.shallowClone(options);
    angleLockOptions.angle = this.angle;
    angleLockOptions.ratio = this.ratio;

    this.equations = [
        new AngleLockEquation(bodyA,bodyB,angleLockOptions),
    ];

    // Set max torque
    if(options.maxTorque !== undefined){
        this.setMaxTorque(options.maxTorque);
    }
}
GearConstraint.prototype = new Constraint();
GearConstraint.prototype.constructor = GearConstraint;

GearConstraint.prototype.update = function(){
    var eq = this.equations[0];
    var ratio = this.ratio;
    if(eq.ratio !== ratio){
        eq.setRatio(ratio);
    }
    eq.angle = this.angle;
};

/**
 * Set the max torque for the constraint.
 * @method setMaxTorque
 * @param {Number} torque
 */
GearConstraint.prototype.setMaxTorque = function(torque){
    this.equations[0].setMaxTorque(torque);
};

/**
 * Get the max torque for the constraint.
 * @method getMaxTorque
 * @return {Number}
 */
GearConstraint.prototype.getMaxTorque = function(){
    return this.equations[0].maxForce;
};