BoxEmitter.js

define([
        '../Core/Cartesian3',
        '../Core/Check',
        '../Core/defaultValue',
        '../Core/defineProperties',
        '../Core/Math'
    ], function(
        Cartesian3,
        Check,
        defaultValue,
        defineProperties,
        CesiumMath) {
    'use strict';

    var defaultDimensions = new Cartesian3(1.0, 1.0, 1.0);

    /**
     * A ParticleEmitter that emits particles within a box.
     * Particles will be positioned randomly within the box and have initial velocities emanating from the center of the box.
     *
     * @alias BoxEmitter
     * @constructor
     *
     * @param {Cartesian3} dimensions The width, height and depth dimensions of the box.
     */
    function BoxEmitter(dimensions) {
        dimensions = defaultValue(dimensions, defaultDimensions);

        //>>includeStart('debug', pragmas.debug);
        Check.defined('dimensions', dimensions);
        Check.typeOf.number.greaterThanOrEquals('dimensions.x', dimensions.x, 0.0);
        Check.typeOf.number.greaterThanOrEquals('dimensions.y', dimensions.y, 0.0);
        Check.typeOf.number.greaterThanOrEquals('dimensions.z', dimensions.z, 0.0);
        //>>includeEnd('debug');

        this._dimensions = Cartesian3.clone(dimensions);
    }

    defineProperties(BoxEmitter.prototype, {
        /**
         * The width, height and depth dimensions of the box in meters.
         * @memberof BoxEmitter.prototype
         * @type {Cartesian3}
         * @default new Cartesian3(1.0, 1.0, 1.0)
         */
        dimensions : {
            get : function() {
                return this._dimensions;
            },
            set : function(value) {
                //>>includeStart('debug', pragmas.debug);
                Check.defined('value', value);
                Check.typeOf.number.greaterThanOrEquals('value.x', value.x, 0.0);
                Check.typeOf.number.greaterThanOrEquals('value.y', value.y, 0.0);
                Check.typeOf.number.greaterThanOrEquals('value.z', value.z, 0.0);
                //>>includeEnd('debug');
                Cartesian3.clone(value, this._dimensions);
            }
        }

    });

    var scratchHalfDim = new Cartesian3();

    /**
     * Initializes the given {Particle} by setting it's position and velocity.
     *
     * @private
     * @param {Particle} particle The particle to initialize.
     */
    BoxEmitter.prototype.emit = function(particle) {
        var dim = this._dimensions;
        var halfDim = Cartesian3.multiplyByScalar(dim, 0.5, scratchHalfDim);

        var x = CesiumMath.randomBetween(-halfDim.x, halfDim.x);
        var y = CesiumMath.randomBetween(-halfDim.y, halfDim.y);
        var z = CesiumMath.randomBetween(-halfDim.z, halfDim.z);

        particle.position = Cartesian3.fromElements(x, y, z, particle.position);
        particle.velocity = Cartesian3.normalize(particle.position, particle.velocity);
    };

    return BoxEmitter;
});