cannon/src/objects/RigidVehicle.js

A lightweight 3D physics engine written in JavaScript.

var Body = require('./Body');
var Sphere = require('../shapes/Sphere');
var Box = require('../shapes/Box');
var Vec3 = require('../math/Vec3');
var HingeConstraint = require('../constraints/HingeConstraint');

module.exports = RigidVehicle;

/**
 * Simple vehicle helper class with spherical rigid body wheels.
 * @class RigidVehicle
 * @constructor
 * @param {Body} [options.chassisBody]
 */
function RigidVehicle(options){
    this.wheelBodies = [];

    /**
     * @property coordinateSystem
     * @type {Vec3}
     */
    this.coordinateSystem = typeof(options.coordinateSystem)==='undefined' ? new Vec3(1, 2, 3) : options.coordinateSystem.clone();

    /**
     * @property {Body} chassisBody
     */
    this.chassisBody = options.chassisBody;

    if(!this.chassisBody){
        // No chassis body given. Create it!
        var chassisShape = new Box(new Vec3(5, 2, 0.5));
        this.chassisBody = new Body(1, chassisShape);
    }

    /**
     * @property constraints
     * @type {Array}
     */
    this.constraints = [];

    this.wheelAxes = [];
    this.wheelForces = [];
}

/**
 * Add a wheel
 * @method addWheel
 * @param {object} options
 * @param {boolean} [options.isFrontWheel]
 * @param {Vec3} [options.position] Position of the wheel, locally in the chassis body.
 * @param {Vec3} [options.direction] Slide direction of the wheel along the suspension.
 * @param {Vec3} [options.axis] Axis of rotation of the wheel, locally defined in the chassis.
 * @param {Body} [options.body] The wheel body.
 */
RigidVehicle.prototype.addWheel = function(options){
    options = options || {};
    var wheelBody = options.body;
    if(!wheelBody){
        wheelBody =  new Body(1, new Sphere(1.2));
    }
    this.wheelBodies.push(wheelBody);
    this.wheelForces.push(0);

    // Position constrain wheels
    var zero = new Vec3();
    var position = typeof(options.position) !== 'undefined' ? options.position.clone() : new Vec3();

    // Set position locally to the chassis
    var worldPosition = new Vec3();
    this.chassisBody.pointToWorldFrame(position, worldPosition);
    wheelBody.position.set(worldPosition.x, worldPosition.y, worldPosition.z);

    // Constrain wheel
    var axis = typeof(options.axis) !== 'undefined' ? options.axis.clone() : new Vec3(0, 1, 0);
    this.wheelAxes.push(axis);

    var hingeConstraint = new HingeConstraint(this.chassisBody, wheelBody, {
        pivotA: position,
        axisA: axis,
        pivotB: Vec3.ZERO,
        axisB: axis,
        collideConnected: false
    });
    this.constraints.push(hingeConstraint);

    return this.wheelBodies.length - 1;
};

/**
 * Set the steering value of a wheel.
 * @method setSteeringValue
 * @param {number} value
 * @param {integer} wheelIndex
 * @todo check coordinateSystem
 */
RigidVehicle.prototype.setSteeringValue = function(value, wheelIndex){
    // Set angle of the hinge axis
    var axis = this.wheelAxes[wheelIndex];

    var c = Math.cos(value),
        s = Math.sin(value),
        x = axis.x,
        y = axis.y;
    this.constraints[wheelIndex].axisA.set(
        c*x -s*y,
        s*x +c*y,
        0
    );
};

/**
 * Set the target rotational speed of the hinge constraint.
 * @method setMotorSpeed
 * @param {number} value
 * @param {integer} wheelIndex
 */
RigidVehicle.prototype.setMotorSpeed = function(value, wheelIndex){
    var hingeConstraint = this.constraints[wheelIndex];
    hingeConstraint.enableMotor();
    hingeConstraint.motorTargetVelocity = value;
};

/**
 * Set the target rotational speed of the hinge constraint.
 * @method disableMotor
 * @param {number} value
 * @param {integer} wheelIndex
 */
RigidVehicle.prototype.disableMotor = function(wheelIndex){
    var hingeConstraint = this.constraints[wheelIndex];
    hingeConstraint.disableMotor();
};

var torque = new Vec3();

/**
 * Set the wheel force to apply on one of the wheels each time step
 * @method setWheelForce
 * @param  {number} value
 * @param  {integer} wheelIndex
 */
RigidVehicle.prototype.setWheelForce = function(value, wheelIndex){
    this.wheelForces[wheelIndex] = value;
};

/**
 * Apply a torque on one of the wheels.
 * @method applyWheelForce
 * @param  {number} value
 * @param  {integer} wheelIndex
 */
RigidVehicle.prototype.applyWheelForce = function(value, wheelIndex){
    var axis = this.wheelAxes[wheelIndex];
    var wheelBody = this.wheelBodies[wheelIndex];
    var bodyTorque = wheelBody.torque;

    axis.scale(value, torque);
    wheelBody.vectorToWorldFrame(torque, torque);
    bodyTorque.vadd(torque, bodyTorque);
};

/**
 * Add the vehicle including its constraints to the world.
 * @method addToWorld
 * @param {World} world
 */
RigidVehicle.prototype.addToWorld = function(world){
    var constraints = this.constraints;
    var bodies = this.wheelBodies.concat([this.chassisBody]);

    for (var i = 0; i < bodies.length; i++) {
        world.add(bodies[i]);
    }

    for (var i = 0; i < constraints.length; i++) {
        world.addConstraint(constraints[i]);
    }

    world.addEventListener('preStep', this._update.bind(this));
};

RigidVehicle.prototype._update = function(){
    var wheelForces = this.wheelForces;
    for (var i = 0; i < wheelForces.length; i++) {
        this.applyWheelForce(wheelForces[i], i);
    }
};

/**
 * Remove the vehicle including its constraints from the world.
 * @method removeFromWorld
 * @param {World} world
 */
RigidVehicle.prototype.removeFromWorld = function(world){
    var constraints = this.constraints;
    var bodies = this.wheelBodies.concat([this.chassisBody]);

    for (var i = 0; i < bodies.length; i++) {
        world.remove(bodies[i]);
    }

    for (var i = 0; i < constraints.length; i++) {
        world.removeConstraint(constraints[i]);
    }
};

var worldAxis = new Vec3();

/**
 * Get current rotational velocity of a wheel
 * @method getWheelSpeed
 * @param {integer} wheelIndex
 */
RigidVehicle.prototype.getWheelSpeed = function(wheelIndex){
    var axis = this.wheelAxes[wheelIndex];
    var wheelBody = this.wheelBodies[wheelIndex];
    var w = wheelBody.angularVelocity;
    this.chassisBody.vectorToWorldFrame(axis, worldAxis);
    return w.dot(worldAxis);
};