aframe-particle-system-component.js

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/* 0 */
/***/ (function(module, exports, __webpack_require__) {

	/**
	 * Particles component for A-Frame.
	 *
	 * ShaderParticleEngine by Squarefeet (https://github.com/squarefeet).
	 */

	var SPE = __webpack_require__(1);

	if (typeof AFRAME === 'undefined') {
	  throw new Error('Component attempted to register before AFRAME was available.');
	}

	AFRAME.registerComponent('particle-system', {

	    schema: {
	        preset: {
	            type: 'string',
	            default: '',
	            oneOf: ['default', 'dust', 'snow', 'rain']
	        },
	        maxAge: {
	            type: 'number',
	            default: 6
	        },
	        positionSpread: {
	            type: 'vec3',
	            default: { x: 0, y: 0, z: 0 }
	        },
	        type: {
	            type: 'number',
	            default: SPE.distributions.BOX
	        },
	        rotationAxis: {
	            type: 'string',
	            default: 'x'
	        },
	        rotationAngle: {
	            type: 'number',
	            default: 0
	        },
	        rotationAngleSpread: {
	            type: 'number',
	            default: 0
	        },
	        accelerationValue: {
	            type: 'vec3',
	            default: { x: 0, y: -10, z: 0 }
	        },
	        accelerationSpread: {
	            type: 'vec3',
	            default: { x: 10, y: 0, z: 10 }
	        },
	        velocityValue: {
	            type: 'vec3',
	            default: { x: 0, y: 25, z: 0 }
	        },
	        velocitySpread: {
	            type: 'vec3',
	            default: { x: 10, y: 7.5, z: 10 }
	        },
	        dragValue: {
	            type: 'number',
	            default: 0
	        },
	        dragSpread: {
	            type: 'number',
	            default: 0
	        },
	        dragRandomise: {
	            type: 'boolean',
	            default: false
	        },
	        color: {
	            type: 'array',
	            default: [ '#0000FF', '#FF0000' ]
	        },
	        size: {
	            type: 'array',
	            default: [ '1' ]
	        },
	        sizeSpread: {
	            type: 'array',
	            default: [ '0' ]
	        },
	        direction: {
	            type: 'number',
	            default: 1
	        },
	        duration: {
	            type: 'number',
	            default: Infinity
	        },
	        particleCount: {
	            type: 'number',
	            default: 1000
	        },
	        texture: {
	            type: 'asset',
	            default: 'https://cdn.rawgit.com/IdeaSpaceVR/aframe-particle-system-component/master/dist/images/star2.png'
	        },
	        randomise: {
	            type: 'boolean',
	            default: false
	        },
	        opacity: {
	          type: 'array',
	          default: [ '1' ]
	        },
	        opacitySpread: {
	            type: 'array',
	            default: [ '0' ]
	          },
	        maxParticleCount: {
	            type: 'number',
	            default: 250000
	        },
	        blending: {
	            type: 'number',
	            default: THREE.AdditiveBlending,
	            oneOf: [THREE.NoBlending,THREE.NormalBlending,THREE.AdditiveBlending,THREE.SubtractiveBlending,THREE.MultiplyBlending]
	        },
	        enabled: {
	            type:'boolean',
	            default:true
	        }
	    },


	    init: function() {

	        this.presets = {};

	        /* preset settings can be overwritten */

	        this.presets['dust'] = {
	            maxAge: 20,
	            positionSpread: {x:100,y:100,z:100},
	            rotationAngle: 3.14,
	            accelerationValue: {x: 0, y: 0, z: 0},
	            accelerationSpread: {x: 0, y: 0, z: 0},
	            velocityValue: {x: 1, y: 0.3, z: 1},
	            velocitySpread: {x: 0.5, y: 1, z: 0.5},
	            color: ['#FFFFFF'],
	            particleCount: 100,
	            texture: 'https://cdn.rawgit.com/IdeaSpaceVR/aframe-particle-system-component/master/dist/images/smokeparticle.png'
	        };


	        this.presets['snow'] = {
	            maxAge: 20,
	            positionSpread: {x:100,y:100,z:100},
	            rotationAngle: 3.14,
	            accelerationValue: {x: 0, y: 0, z: 0},
	            accelerationSpread: {x: 0.2, y: 0, z: 0.2},
	            velocityValue: {x: 0, y: 8, z: 0},
	            velocitySpread: {x: 2, y: 0, z: 2},
	            color: ['#FFFFFF'],
	            particleCount: 200,
	            texture: 'https://cdn.rawgit.com/IdeaSpaceVR/aframe-particle-system-component/master/dist/images/smokeparticle.png'
	        };


	        this.presets['rain'] = {
	            maxAge: 1,
	            positionSpread: {x:100,y:100,z:100},
	            rotationAngle: 3.14,
	            accelerationValue: {x: 0, y: 3, z: 0},
	            accelerationSpread: {x: 2, y: 1, z: 2},
	            velocityValue: {x: 0, y: 75, z: 0},
	            velocitySpread: {x: 10, y: 50, z: 10},
	            color: ['#FFFFFF'],
	            size: 0.4,
	            texture: 'https://cdn.rawgit.com/IdeaSpaceVR/aframe-particle-system-component/master/dist/images/raindrop.png'
	        };


	    },


	    update: function (oldData) {

	        // Remove old particle group.
	        if (this.particleGroup) {
	            this.el.removeObject3D('particle-system');
	        }

	        // Set the selected preset, if any, or use an empty object to keep schema defaults
	        this.preset = this.presets[this.data.preset] || {};

	        // Get custom, preset, or default data for each property defined in the schema
	        for (var key in this.data) {
	            this.data[key] = this.applyPreset(key);
	        }

	        this.initParticleSystem(this.data);

	        if(this.data.enabled === true) {
	            this.startParticles()
	        } else {
	            this.stopParticles()
	        }
	    },


	    applyPreset: function (key) {
	        // !this.attrValue[key] = the user did not set a custom value
	        // this.preset[key] = there exists a value for this key in the selected preset
	        if (!this.attrValue[key] && this.preset[key]) {
	            return this.preset[key];
	        } else {
	            // Otherwise stick to the user or schema default value
	            return this.data[key];
	        }
	    },


	    tick: function(time, dt) {

	        this.particleGroup.tick(dt / 1000);
	    },


	    remove: function() {

	        // Remove particle system.
	        if (!this.particleGroup) { return; }
	        this.el.removeObject3D('particle-system');
	    },

	    startParticles: function() {
	        this.particleGroup.emitters.forEach(function(em) { em.enable() });
	    },

	    stopParticles: function() {
	        this.particleGroup.emitters.forEach(function(em) { em.disable() });
	    },


	    initParticleSystem: function(settings) {

	        var loader = new THREE.TextureLoader();
	        var particle_texture = loader.load(
	            settings.texture,
	            function (texture) {
	                return texture;
	            },
	            function (xhr) {
	              console.log((xhr.loaded / xhr.total * 100) + '% loaded');
	            },
	            function (xhr) {
	              console.log('An error occurred');
	            }
	        );

	        this.particleGroup = new SPE.Group({
	            texture: {
	                value: particle_texture
	            },
	            maxParticleCount: settings.maxParticleCount,
	            blending: settings.blending
	        });

	        var emitter = new SPE.Emitter({
	            maxAge: {
	                value: settings.maxAge
	            },
	            type: {
	                value: settings.type
	            },
	            position: {                
	                spread: new THREE.Vector3(settings.positionSpread.x, settings.positionSpread.y, settings.positionSpread.z),
	                randomise: settings.randomise
	                //spreadClamp: new THREE.Vector3( 2, 2, 2 ),
	                //radius: 4
	            },
	            rotation: {
	                axis: (settings.rotationAxis=='x'?new THREE.Vector3(1, 0, 0):(settings.rotationAxis=='y'?new THREE.Vector3(0, 1, 0):(settings.rotationAxis=='z'?new THREE.Vector3(0, 0, 1):new THREE.Vector3(0, 1, 0)))),
	                angle: settings.rotationAngle,
	                angleSpread: settings.rotationAngleSpread,
	                static: true
	            },
	            acceleration: {
	                value: new THREE.Vector3(settings.accelerationValue.x, settings.accelerationValue.y, settings.accelerationValue.z),
	                spread: new THREE.Vector3(settings.accelerationSpread.x, settings.accelerationSpread.y, settings.accelerationSpread.z)
	            },
	            velocity: {
	                value: new THREE.Vector3(settings.velocityValue.x, settings.velocityValue.y, settings.velocityValue.z),
	                spread: new THREE.Vector3(settings.velocitySpread.x, settings.velocitySpread.y, settings.velocitySpread.z)
	            },
	            drag: {
	                value: new THREE.Vector3(settings.dragValue.x, settings.dragValue.y, settings.dragValue.z),
	                spread: new THREE.Vector3(settings.dragSpread.x, settings.dragSpread.y, settings.dragSpread.z),
	                randomise: settings.dragRandomise
	            },
	            color: {
	                value: settings.color.map(function(c) { return new THREE.Color(c); })            
	            },
	            size: { value: settings.size.map(function (s) { return parseFloat(s); }),
	                    spread: settings.sizeSpread.map(function (s) { return parseFloat(s); }) },
	            
	            /*wiggle: { value: 4, spread: 2 }, //settings.wiggle,*/
	            /*drag: {
	                value: settings.drag
	            },*/
	            direction: {
	                value: settings.direction
	            },
	            duration: settings.duration,
	            opacity: { value: settings.opacity.map(function (o) { return parseFloat(o); }),
	                       spread: settings.opacitySpread.map(function (o) { return parseFloat(o); }) },            
	            particleCount: settings.particleCount
	        });

	        this.particleGroup.addEmitter(emitter);
	        this.particleGroup.mesh.frustumCulled = false;
	        this.el.setObject3D('particle-system', this.particleGroup.mesh);
	    }
	});


/***/ }),
/* 1 */
/***/ (function(module, exports, __webpack_require__) {

	var __WEBPACK_AMD_DEFINE_FACTORY__, __WEBPACK_AMD_DEFINE_RESULT__;/* shader-particle-engine 1.0.6
	 * 
	 * (c) 2015 Luke Moody (http://www.github.com/squarefeet)
	 *     Originally based on Lee Stemkoski's original work (https://github.com/stemkoski/stemkoski.github.com/blob/master/Three.js/js/ParticleEngine.js).
	 *
	 * shader-particle-engine may be freely distributed under the MIT license (See LICENSE at root of this repository.)
	 */
	/**
	 * @typedef {Number} distribution
	 * @property {Number} SPE.distributions.BOX Values will be distributed within a box.
	 * @property {Number} SPE.distributions.SPHERE Values will be distributed within a sphere.
	 * @property {Number} SPE.distributions.DISC Values will be distributed within a 2D disc.
	 */

	/**
	 * Namespace for Shader Particle Engine.
	 *
	 * All SPE-related code sits under this namespace.
	 *
	 * @type {Object}
	 * @namespace
	 */
	var SPE = {

	    /**
	     * A map of supported distribution types used
	     * by SPE.Emitter instances.
	     *
	     * These distribution types can be applied to
	     * an emitter globally, which will affect the
	     * `position`, `velocity`, and `acceleration`
	     * value calculations for an emitter, or they
	     * can be applied on a per-property basis.
	     *
	     * @enum {Number}
	     */
	    distributions: {
	        /**
	         * Values will be distributed within a box.
	         * @type {Number}
	         */
	        BOX: 1,

	        /**
	         * Values will be distributed on a sphere.
	         * @type {Number}
	         */
	        SPHERE: 2,

	        /**
	         * Values will be distributed on a 2d-disc shape.
	         * @type {Number}
	         */
	        DISC: 3,

	        /**
	         * Values will be distributed along a line.
	         * @type {Number}
	         */
	        LINE: 4
	    },


	    /**
	     * Set this value to however many 'steps' you
	     * want value-over-lifetime properties to have.
	     *
	     * It's adjustable to fix an interpolation problem:
	     *
	     * Assuming you specify an opacity value as [0, 1, 0]
	     *      and the `valueOverLifetimeLength` is 4, then the
	     *      opacity value array will be reinterpolated to
	     *      be [0, 0.66, 0.66, 0].
	     *   This isn't ideal, as particles would never reach
	     *   full opacity.
	     *
	     * NOTE:
	     *     This property affects the length of ALL
	     *       value-over-lifetime properties for ALL
	     *       emitters and ALL groups.
	     *
	     *     Only values >= 3 && <= 4 are allowed.
	     *
	     * @type {Number}
	     */
	    valueOverLifetimeLength: 4
	};

	// Module loader support:
	if ( true ) {
	    !(__WEBPACK_AMD_DEFINE_FACTORY__ = (SPE), __WEBPACK_AMD_DEFINE_RESULT__ = (typeof __WEBPACK_AMD_DEFINE_FACTORY__ === 'function' ? (__WEBPACK_AMD_DEFINE_FACTORY__.call(exports, __webpack_require__, exports, module)) : __WEBPACK_AMD_DEFINE_FACTORY__), __WEBPACK_AMD_DEFINE_RESULT__ !== undefined && (module.exports = __WEBPACK_AMD_DEFINE_RESULT__));
	}
	else if ( typeof exports !== 'undefined' && typeof module !== 'undefined' ) {
	    module.exports = SPE;
	}


	/**
	 * A helper class for TypedArrays.
	 *
	 * Allows for easy resizing, assignment of various component-based
	 * types (Vector2s, Vector3s, Vector4s, Mat3s, Mat4s),
	 * as well as Colors (where components are `r`, `g`, `b`),
	 * Numbers, and setting from other TypedArrays.
	 *
	 * @author Luke Moody
	 * @constructor
	 * @param {Function} TypedArrayConstructor The constructor to use (Float32Array, Uint8Array, etc.)
	 * @param {Number} size                 The size of the array to create
	 * @param {Number} componentSize        The number of components per-value (ie. 3 for a vec3, 9 for a Mat3, etc.)
	 * @param {Number} indexOffset          The index in the array from which to start assigning values. Default `0` if none provided
	 */
	SPE.TypedArrayHelper = function( TypedArrayConstructor, size, componentSize, indexOffset ) {
	    'use strict';

	    this.componentSize = componentSize || 1;
	    this.size = ( size || 1 );
	    this.TypedArrayConstructor = TypedArrayConstructor || Float32Array;
	    this.array = new TypedArrayConstructor( size * this.componentSize );
	    this.indexOffset = indexOffset || 0;
	};

	SPE.TypedArrayHelper.constructor = SPE.TypedArrayHelper;

	/**
	 * Sets the size of the internal array.
	 *
	 * Delegates to `this.shrink` or `this.grow` depending on size
	 * argument's relation to the current size of the internal array.
	 *
	 * Note that if the array is to be shrunk, data will be lost.
	 *
	 * @param {Number} size The new size of the array.
	 */
	SPE.TypedArrayHelper.prototype.setSize = function( size, noComponentMultiply ) {
	    'use strict';

	    var currentArraySize = this.array.length;

	    if ( !noComponentMultiply ) {
	        size = size * this.componentSize;
	    }

	    if ( size < currentArraySize ) {
	        return this.shrink( size );
	    }
	    else if ( size > currentArraySize ) {
	        return this.grow( size );
	    }
	    else {
	        console.info( 'TypedArray is already of size:', size + '.', 'Will not resize.' );
	    }
	};

	/**
	 * Shrinks the internal array.
	 *
	 * @param  {Number} size The new size of the typed array. Must be smaller than `this.array.length`.
	 * @return {SPE.TypedArrayHelper}      Instance of this class.
	 */
	SPE.TypedArrayHelper.prototype.shrink = function( size ) {
	    'use strict';

	    this.array = this.array.subarray( 0, size );
	    this.size = size;
	    return this;
	};

	/**
	 * Grows the internal array.
	 * @param  {Number} size The new size of the typed array. Must be larger than `this.array.length`.
	 * @return {SPE.TypedArrayHelper}      Instance of this class.
	 */
	SPE.TypedArrayHelper.prototype.grow = function( size ) {
	    'use strict';

	    var existingArray = this.array,
	        newArray = new this.TypedArrayConstructor( size );

	    newArray.set( existingArray );
	    this.array = newArray;
	    this.size = size;

	    return this;
	};


	/**
	 * Perform a splice operation on this array's buffer.
	 * @param  {Number} start The start index of the splice. Will be multiplied by the number of components for this attribute.
	 * @param  {Number} end The end index of the splice. Will be multiplied by the number of components for this attribute.
	 * @returns {Object} The SPE.TypedArrayHelper instance.
	 */
	SPE.TypedArrayHelper.prototype.splice = function( start, end ) {
	    'use strict';
	    start *= this.componentSize;
	    end *= this.componentSize;

	    var data = [],
	        array = this.array,
	        size = array.length;

	    for ( var i = 0; i < size; ++i ) {
	        if ( i < start || i >= end ) {
	            data.push( array[ i ] );
	        }
	        // array[ i ] = 0;
	    }

	    this.setFromArray( 0, data );

	    return this;
	};


	/**
	 * Copies from the given TypedArray into this one, using the index argument
	 * as the start position. Alias for `TypedArray.set`. Will automatically resize
	 * if the given source array is of a larger size than the internal array.
	 *
	 * @param {Number} index      The start position from which to copy into this array.
	 * @param {TypedArray} array The array from which to copy; the source array.
	 * @return {SPE.TypedArrayHelper} Instance of this class.
	 */
	SPE.TypedArrayHelper.prototype.setFromArray = function( index, array ) {
	    'use strict';

	    var sourceArraySize = array.length,
	        newSize = index + sourceArraySize;

	    if ( newSize > this.array.length ) {
	        this.grow( newSize );
	    }
	    else if ( newSize < this.array.length ) {
	        this.shrink( newSize );
	    }

	    this.array.set( array, this.indexOffset + index );

	    return this;
	};

	/**
	 * Set a Vector2 value at `index`.
	 *
	 * @param {Number} index The index at which to set the vec2 values from.
	 * @param {Vector2} vec2  Any object that has `x` and `y` properties.
	 * @return {SPE.TypedArrayHelper} Instance of this class.
	 */
	SPE.TypedArrayHelper.prototype.setVec2 = function( index, vec2 ) {
	    'use strict';

	    return this.setVec2Components( index, vec2.x, vec2.y );
	};

	/**
	 * Set a Vector2 value using raw components.
	 *
	 * @param {Number} index The index at which to set the vec2 values from.
	 * @param {Number} x     The Vec2's `x` component.
	 * @param {Number} y     The Vec2's `y` component.
	 * @return {SPE.TypedArrayHelper} Instance of this class.
	 */
	SPE.TypedArrayHelper.prototype.setVec2Components = function( index, x, y ) {
	    'use strict';

	    var array = this.array,
	        i = this.indexOffset + ( index * this.componentSize );

	    array[ i ] = x;
	    array[ i + 1 ] = y;
	    return this;
	};

	/**
	 * Set a Vector3 value at `index`.
	 *
	 * @param {Number} index The index at which to set the vec3 values from.
	 * @param {Vector3} vec2  Any object that has `x`, `y`, and `z` properties.
	 * @return {SPE.TypedArrayHelper} Instance of this class.
	 */
	SPE.TypedArrayHelper.prototype.setVec3 = function( index, vec3 ) {
	    'use strict';

	    return this.setVec3Components( index, vec3.x, vec3.y, vec3.z );
	};

	/**
	 * Set a Vector3 value using raw components.
	 *
	 * @param {Number} index The index at which to set the vec3 values from.
	 * @param {Number} x     The Vec3's `x` component.
	 * @param {Number} y     The Vec3's `y` component.
	 * @param {Number} z     The Vec3's `z` component.
	 * @return {SPE.TypedArrayHelper} Instance of this class.
	 */
	SPE.TypedArrayHelper.prototype.setVec3Components = function( index, x, y, z ) {
	    'use strict';

	    var array = this.array,
	        i = this.indexOffset + ( index * this.componentSize );

	    array[ i ] = x;
	    array[ i + 1 ] = y;
	    array[ i + 2 ] = z;
	    return this;
	};

	/**
	 * Set a Vector4 value at `index`.
	 *
	 * @param {Number} index The index at which to set the vec4 values from.
	 * @param {Vector4} vec2  Any object that has `x`, `y`, `z`, and `w` properties.
	 * @return {SPE.TypedArrayHelper} Instance of this class.
	 */
	SPE.TypedArrayHelper.prototype.setVec4 = function( index, vec4 ) {
	    'use strict';

	    return this.setVec4Components( index, vec4.x, vec4.y, vec4.z, vec4.w );
	};

	/**
	 * Set a Vector4 value using raw components.
	 *
	 * @param {Number} index The index at which to set the vec4 values from.
	 * @param {Number} x     The Vec4's `x` component.
	 * @param {Number} y     The Vec4's `y` component.
	 * @param {Number} z     The Vec4's `z` component.
	 * @param {Number} w     The Vec4's `w` component.
	 * @return {SPE.TypedArrayHelper} Instance of this class.
	 */
	SPE.TypedArrayHelper.prototype.setVec4Components = function( index, x, y, z, w ) {
	    'use strict';

	    var array = this.array,
	        i = this.indexOffset + ( index * this.componentSize );

	    array[ i ] = x;
	    array[ i + 1 ] = y;
	    array[ i + 2 ] = z;
	    array[ i + 3 ] = w;
	    return this;
	};

	/**
	 * Set a Matrix3 value at `index`.
	 *
	 * @param {Number} index The index at which to set the matrix values from.
	 * @param {Matrix3} mat3 The 3x3 matrix to set from. Must have a TypedArray property named `elements` to copy from.
	 * @return {SPE.TypedArrayHelper} Instance of this class.
	 */
	SPE.TypedArrayHelper.prototype.setMat3 = function( index, mat3 ) {
	    'use strict';

	    return this.setFromArray( this.indexOffset + ( index * this.componentSize ), mat3.elements );
	};

	/**
	 * Set a Matrix4 value at `index`.
	 *
	 * @param {Number} index The index at which to set the matrix values from.
	 * @param {Matrix4} mat3 The 4x4 matrix to set from. Must have a TypedArray property named `elements` to copy from.
	 * @return {SPE.TypedArrayHelper} Instance of this class.
	 */
	SPE.TypedArrayHelper.prototype.setMat4 = function( index, mat4 ) {
	    'use strict';

	    return this.setFromArray( this.indexOffset + ( index * this.componentSize ), mat4.elements );
	};

	/**
	 * Set a Color value at `index`.
	 *
	 * @param {Number} index The index at which to set the vec3 values from.
	 * @param {Color} color  Any object that has `r`, `g`, and `b` properties.
	 * @return {SPE.TypedArrayHelper} Instance of this class.
	 */
	SPE.TypedArrayHelper.prototype.setColor = function( index, color ) {
	    'use strict';

	    return this.setVec3Components( index, color.r, color.g, color.b );
	};

	/**
	 * Set a Number value at `index`.
	 *
	 * @param {Number} index The index at which to set the vec3 values from.
	 * @param {Number} numericValue  The number to assign to this index in the array.
	 * @return {SPE.TypedArrayHelper} Instance of this class.
	 */
	SPE.TypedArrayHelper.prototype.setNumber = function( index, numericValue ) {
	    'use strict';

	    this.array[ this.indexOffset + ( index * this.componentSize ) ] = numericValue;
	    return this;
	};

	/**
	 * Returns the value of the array at the given index, taking into account
	 * the `indexOffset` property of this class.
	 *
	 * Note that this function ignores the component size and will just return a
	 * single value.
	 *
	 * @param  {Number} index The index in the array to fetch.
	 * @return {Number}       The value at the given index.
	 */
	SPE.TypedArrayHelper.prototype.getValueAtIndex = function( index ) {
	    'use strict';

	    return this.array[ this.indexOffset + index ];
	};

	/**
	 * Returns the component value of the array at the given index, taking into account
	 * the `indexOffset` property of this class.
	 *
	 * If the componentSize is set to 3, then it will return a new TypedArray
	 * of length 3.
	 *
	 * @param  {Number} index The index in the array to fetch.
	 * @return {TypedArray}       The component value at the given index.
	 */
	SPE.TypedArrayHelper.prototype.getComponentValueAtIndex = function( index ) {
	    'use strict';

	    return this.array.subarray( this.indexOffset + ( index * this.componentSize ) );
	};

	/**
	 * A helper to handle creating and updating a THREE.BufferAttribute instance.
	 *
	 * @author  Luke Moody
	 * @constructor
	 * @param {String} type          The buffer attribute type. See SPE.ShaderAttribute.typeSizeMap for valid values.
	 * @param {Boolean=} dynamicBuffer Whether this buffer attribute should be marked as dynamic or not.
	 * @param {Function=} arrayType     A reference to a TypedArray constructor. Defaults to Float32Array if none provided.
	 */
	SPE.ShaderAttribute = function( type, dynamicBuffer, arrayType ) {
		'use strict';

		var typeMap = SPE.ShaderAttribute.typeSizeMap;

		this.type = typeof type === 'string' && typeMap.hasOwnProperty( type ) ? type : 'f';
		this.componentSize = typeMap[ this.type ];
		this.arrayType = arrayType || Float32Array;
		this.typedArray = null;
		this.bufferAttribute = null;
		this.dynamicBuffer = !!dynamicBuffer;

		this.updateMin = 0;
		this.updateMax = 0;
	};

	SPE.ShaderAttribute.constructor = SPE.ShaderAttribute;

	/**
	 * A map of uniform types to their component size.
	 * @enum {Number}
	 */
	SPE.ShaderAttribute.typeSizeMap = {
		/**
		 * Float
		 * @type {Number}
		 */
		f: 1,

		/**
		 * Vec2
		 * @type {Number}
		 */
		v2: 2,

		/**
		 * Vec3
		 * @type {Number}
		 */
		v3: 3,

		/**
		 * Vec4
		 * @type {Number}
		 */
		v4: 4,

		/**
		 * Color
		 * @type {Number}
		 */
		c: 3,

		/**
		 * Mat3
		 * @type {Number}
		 */
		m3: 9,

		/**
		 * Mat4
		 * @type {Number}
		 */
		m4: 16
	};

	/**
	 * Calculate the minimum and maximum update range for this buffer attribute using
	 * component size independant min and max values.
	 *
	 * @param {Number} min The start of the range to mark as needing an update.
	 * @param {Number} max The end of the range to mark as needing an update.
	 */
	SPE.ShaderAttribute.prototype.setUpdateRange = function( min, max ) {
		'use strict';

		this.updateMin = Math.min( min * this.componentSize, this.updateMin * this.componentSize );
		this.updateMax = Math.max( max * this.componentSize, this.updateMax * this.componentSize );
	};

	/**
	 * Calculate the number of indices that this attribute should mark as needing
	 * updating. Also marks the attribute as needing an update.
	 */
	SPE.ShaderAttribute.prototype.flagUpdate = function() {
		'use strict';

		var attr = this.bufferAttribute,
			range = attr.updateRange;

		range.offset = this.updateMin;
		range.count = Math.min( ( this.updateMax - this.updateMin ) + this.componentSize, this.typedArray.array.length );
		// console.log( range.offset, range.count, this.typedArray.array.length );
		// console.log( 'flagUpdate:', range.offset, range.count );
		attr.needsUpdate = true;
	};



	/**
	 * Reset the index update counts for this attribute
	 */
	SPE.ShaderAttribute.prototype.resetUpdateRange = function() {
		'use strict';

		this.updateMin = 0;
		this.updateMax = 0;
	};

	SPE.ShaderAttribute.prototype.resetDynamic = function() {
		'use strict';
		this.bufferAttribute.usage = this.dynamicBuffer ?
			THREE.DynamicDrawUsage :
			THREE.StaticDrawUsage;
	};

	/**
	 * Perform a splice operation on this attribute's buffer.
	 * @param  {Number} start The start index of the splice. Will be multiplied by the number of components for this attribute.
	 * @param  {Number} end The end index of the splice. Will be multiplied by the number of components for this attribute.
	 */
	SPE.ShaderAttribute.prototype.splice = function( start, end ) {
		'use strict';

		this.typedArray.splice( start, end );

		// Reset the reference to the attribute's typed array
		// since it has probably changed.
		this.forceUpdateAll();
	};

	SPE.ShaderAttribute.prototype.forceUpdateAll = function() {
		'use strict';

		this.bufferAttribute.array = this.typedArray.array;
		this.bufferAttribute.updateRange.offset = 0;
		this.bufferAttribute.updateRange.count = -1;
		// this.bufferAttribute.dynamic = false;
		// this.bufferAttribute.usage = this.dynamicBuffer ?
		// 	THREE.DynamicDrawUsage :
		// 	THREE.StaticDrawUsage;

		this.bufferAttribute.usage = THREE.StaticDrawUsage;
		this.bufferAttribute.needsUpdate = true;
	};

	/**
	 * Make sure this attribute has a typed array associated with it.
	 *
	 * If it does, then it will ensure the typed array is of the correct size.
	 *
	 * If not, a new SPE.TypedArrayHelper instance will be created.
	 *
	 * @param  {Number} size The size of the typed array to create or update to.
	 */
	SPE.ShaderAttribute.prototype._ensureTypedArray = function( size ) {
		'use strict';

		// Condition that's most likely to be true at the top: no change.
		if ( this.typedArray !== null && this.typedArray.size === size * this.componentSize ) {
			return;
		}

		// Resize the array if we need to, telling the TypedArrayHelper to
		// ignore it's component size when evaluating size.
		else if ( this.typedArray !== null && this.typedArray.size !== size ) {
			this.typedArray.setSize( size );
		}

		// This condition should only occur once in an attribute's lifecycle.
		else if ( this.typedArray === null ) {
			this.typedArray = new SPE.TypedArrayHelper( this.arrayType, size, this.componentSize );
		}
	};


	/**
	 * Creates a THREE.BufferAttribute instance if one doesn't exist already.
	 *
	 * Ensures a typed array is present by calling _ensureTypedArray() first.
	 *
	 * If a buffer attribute exists already, then it will be marked as needing an update.
	 *
	 * @param  {Number} size The size of the typed array to create if one doesn't exist, or resize existing array to.
	 */
	SPE.ShaderAttribute.prototype._createBufferAttribute = function( size ) {
		'use strict';

		// Make sure the typedArray is present and correct.
		this._ensureTypedArray( size );

		// Don't create it if it already exists, but do
		// flag that it needs updating on the next render
		// cycle.
		if ( this.bufferAttribute !== null ) {
			this.bufferAttribute.array = this.typedArray.array;

			// Since THREE.js version 81, dynamic count calculation was removed
			// so I need to do it manually here.
			//
			// In the next minor release, I may well remove this check and force
			// dependency on THREE r81+.
			if ( parseFloat( THREE.REVISION ) >= 81 ) {
				this.bufferAttribute.count = this.bufferAttribute.array.length / this.bufferAttribute.itemSize;
			}

			this.bufferAttribute.needsUpdate = true;
			return;
		}

		this.bufferAttribute = new THREE.BufferAttribute( this.typedArray.array, this.componentSize );
		// this.bufferAttribute.dynamic = this.dynamicBuffer;
		this.bufferAttribute.usage = this.dynamicBuffer ?
			THREE.DynamicDrawUsage :
			THREE.StaticDrawUsage;
	};

	/**
	 * Returns the length of the typed array associated with this attribute.
	 * @return {Number} The length of the typed array. Will be 0 if no typed array has been created yet.
	 */
	SPE.ShaderAttribute.prototype.getLength = function() {
		'use strict';

		if ( this.typedArray === null ) {
			return 0;
		}

		return this.typedArray.array.length;
	};


	SPE.shaderChunks = {
	    // Register color-packing define statements.
	    defines: [
	        '#define PACKED_COLOR_SIZE 256.0',
	        '#define PACKED_COLOR_DIVISOR 255.0'
	    ].join( '\n' ),

	    // All uniforms used by vertex / fragment shaders
	    uniforms: [
	        'uniform float deltaTime;',
	        'uniform float runTime;',
	        'uniform sampler2D tex;',
	        'uniform vec4 textureAnimation;',
	        'uniform float scale;',
	    ].join( '\n' ),

	    // All attributes used by the vertex shader.
	    //
	    // Note that some attributes are squashed into other ones:
	    //
	    // * Drag is acceleration.w
	    attributes: [
	        'attribute vec4 acceleration;',
	        'attribute vec3 velocity;',
	        'attribute vec4 rotation;',
	        'attribute vec3 rotationCenter;',
	        'attribute vec4 params;',
	        'attribute vec4 size;',
	        'attribute vec4 angle;',
	        'attribute vec4 color;',
	        'attribute vec4 opacity;'
	    ].join( '\n' ),

	    //
	    varyings: [
	        'varying vec4 vColor;',
	        '#ifdef SHOULD_ROTATE_TEXTURE',
	        '    varying float vAngle;',
	        '#endif',

	        '#ifdef SHOULD_CALCULATE_SPRITE',
	        '    varying vec4 vSpriteSheet;',
	        '#endif'
	    ].join( '\n' ),


	    // Branch-avoiding comparison fns
	    // - http://theorangeduck.com/page/avoiding-shader-conditionals
	    branchAvoidanceFunctions: [
	        'float when_gt(float x, float y) {',
	        '    return max(sign(x - y), 0.0);',
	        '}',

	        'float when_lt(float x, float y) {',
	        '    return min( max(1.0 - sign(x - y), 0.0), 1.0 );',
	        '}',

	        'float when_eq( float x, float y ) {',
	        '    return 1.0 - abs( sign( x - y ) );',
	        '}',

	        'float when_ge(float x, float y) {',
	        '  return 1.0 - when_lt(x, y);',
	        '}',

	        'float when_le(float x, float y) {',
	        '  return 1.0 - when_gt(x, y);',
	        '}',

	        // Branch-avoiding logical operators
	        // (to be used with above comparison fns)
	        'float and(float a, float b) {',
	        '    return a * b;',
	        '}',

	        'float or(float a, float b) {',
	        '    return min(a + b, 1.0);',
	        '}',
	    ].join( '\n' ),


	    // From:
	    // - http://stackoverflow.com/a/12553149
	    // - https://stackoverflow.com/questions/22895237/hexadecimal-to-rgb-values-in-webgl-shader
	    unpackColor: [
	        'vec3 unpackColor( in float hex ) {',
	        '   vec3 c = vec3( 0.0 );',

	        '   float r = mod( (hex / PACKED_COLOR_SIZE / PACKED_COLOR_SIZE), PACKED_COLOR_SIZE );',
	        '   float g = mod( (hex / PACKED_COLOR_SIZE), PACKED_COLOR_SIZE );',
	        '   float b = mod( hex, PACKED_COLOR_SIZE );',

	        '   c.r = r / PACKED_COLOR_DIVISOR;',
	        '   c.g = g / PACKED_COLOR_DIVISOR;',
	        '   c.b = b / PACKED_COLOR_DIVISOR;',

	        '   return c;',
	        '}',
	    ].join( '\n' ),

	    unpackRotationAxis: [
	        'vec3 unpackRotationAxis( in float hex ) {',
	        '   vec3 c = vec3( 0.0 );',

	        '   float r = mod( (hex / PACKED_COLOR_SIZE / PACKED_COLOR_SIZE), PACKED_COLOR_SIZE );',
	        '   float g = mod( (hex / PACKED_COLOR_SIZE), PACKED_COLOR_SIZE );',
	        '   float b = mod( hex, PACKED_COLOR_SIZE );',

	        '   c.r = r / PACKED_COLOR_DIVISOR;',
	        '   c.g = g / PACKED_COLOR_DIVISOR;',
	        '   c.b = b / PACKED_COLOR_DIVISOR;',

	        '   c *= vec3( 2.0 );',
	        '   c -= vec3( 1.0 );',

	        '   return c;',
	        '}',
	    ].join( '\n' ),

	    floatOverLifetime: [
	        'float getFloatOverLifetime( in float positionInTime, in vec4 attr ) {',
	        '    highp float value = 0.0;',
	        '    float deltaAge = positionInTime * float( VALUE_OVER_LIFETIME_LENGTH - 1 );',
	        '    float fIndex = 0.0;',
	        '    float shouldApplyValue = 0.0;',

	        // This might look a little odd, but it's faster in the testing I've done than using branches.
	        // Uses basic maths to avoid branching.
	        //
	        // Take a look at the branch-avoidance functions defined above,
	        // and be sure to check out The Orange Duck site where I got this
	        // from (link above).

	        // Fix for static emitters (age is always zero).
	        '    value += attr[ 0 ] * when_eq( deltaAge, 0.0 );',
	        '',
	        '    for( int i = 0; i < VALUE_OVER_LIFETIME_LENGTH - 1; ++i ) {',
	        '       fIndex = float( i );',
	        '       shouldApplyValue = and( when_gt( deltaAge, fIndex ), when_le( deltaAge, fIndex + 1.0 ) );',
	        '       value += shouldApplyValue * mix( attr[ i ], attr[ i + 1 ], deltaAge - fIndex );',
	        '    }',
	        '',
	        '    return value;',
	        '}',
	    ].join( '\n' ),

	    colorOverLifetime: [
	        'vec3 getColorOverLifetime( in float positionInTime, in vec3 color1, in vec3 color2, in vec3 color3, in vec3 color4 ) {',
	        '    vec3 value = vec3( 0.0 );',
	        '    value.x = getFloatOverLifetime( positionInTime, vec4( color1.x, color2.x, color3.x, color4.x ) );',
	        '    value.y = getFloatOverLifetime( positionInTime, vec4( color1.y, color2.y, color3.y, color4.y ) );',
	        '    value.z = getFloatOverLifetime( positionInTime, vec4( color1.z, color2.z, color3.z, color4.z ) );',
	        '    return value;',
	        '}',
	    ].join( '\n' ),

	    paramFetchingFunctions: [
	        'float getAlive() {',
	        '   return params.x;',
	        '}',

	        'float getAge() {',
	        '   return params.y;',
	        '}',

	        'float getMaxAge() {',
	        '   return params.z;',
	        '}',

	        'float getWiggle() {',
	        '   return params.w;',
	        '}',
	    ].join( '\n' ),

	    forceFetchingFunctions: [
	        'vec4 getPosition( in float age ) {',
	        '   return modelViewMatrix * vec4( position, 1.0 );',
	        '}',

	        'vec3 getVelocity( in float age ) {',
	        '   return velocity * age;',
	        '}',

	        'vec3 getAcceleration( in float age ) {',
	        '   return acceleration.xyz * age;',
	        '}',
	    ].join( '\n' ),


	    rotationFunctions: [
	        // Huge thanks to:
	        // - http://www.neilmendoza.com/glsl-rotation-about-an-arbitrary-axis/
	        '#ifdef SHOULD_ROTATE_PARTICLES',
	        '   mat4 getRotationMatrix( in vec3 axis, in float angle) {',
	        '       axis = normalize(axis);',
	        '       float s = sin(angle);',
	        '       float c = cos(angle);',
	        '       float oc = 1.0 - c;',
	        '',
	        '       return mat4(oc * axis.x * axis.x + c,           oc * axis.x * axis.y - axis.z * s,  oc * axis.z * axis.x + axis.y * s,  0.0,',
	        '                   oc * axis.x * axis.y + axis.z * s,  oc * axis.y * axis.y + c,           oc * axis.y * axis.z - axis.x * s,  0.0,',
	        '                   oc * axis.z * axis.x - axis.y * s,  oc * axis.y * axis.z + axis.x * s,  oc * axis.z * axis.z + c,           0.0,',
	        '                   0.0,                                0.0,                                0.0,                                1.0);',
	        '   }',
	        '',
	        '   vec3 getRotation( in vec3 pos, in float positionInTime ) {',
	        '      if( rotation.y == 0.0 ) {',
	        '           return pos;',
	        '      }',
	        '',
	        '      vec3 axis = unpackRotationAxis( rotation.x );',
	        '      vec3 center = rotationCenter;',
	        '      vec3 translated;',
	        '      mat4 rotationMatrix;',

	        '      float angle = 0.0;',
	        '      angle += when_eq( rotation.z, 0.0 ) * rotation.y;',
	        '      angle += when_gt( rotation.z, 0.0 ) * mix( 0.0, rotation.y, positionInTime );',
	        '      translated = rotationCenter - pos;',
	        '      rotationMatrix = getRotationMatrix( axis, angle );',
	        '      return center - vec3( rotationMatrix * vec4( translated, 0.0 ) );',
	        '   }',
	        '#endif'
	    ].join( '\n' ),


	    // Fragment chunks
	    rotateTexture: [
	        '    vec2 vUv = vec2( gl_PointCoord.x, 1.0 - gl_PointCoord.y );',
	        '',
	        '    #ifdef SHOULD_ROTATE_TEXTURE',
	        '       float x = gl_PointCoord.x - 0.5;',
	        '       float y = 1.0 - gl_PointCoord.y - 0.5;',
	        '       float c = cos( -vAngle );',
	        '       float s = sin( -vAngle );',

	        '       vUv = vec2( c * x + s * y + 0.5, c * y - s * x + 0.5 );',
	        '    #endif',
	        '',

	        // Spritesheets overwrite angle calculations.
	        '    #ifdef SHOULD_CALCULATE_SPRITE',
	        '        float framesX = vSpriteSheet.x;',
	        '        float framesY = vSpriteSheet.y;',
	        '        float columnNorm = vSpriteSheet.z;',
	        '        float rowNorm = vSpriteSheet.w;',

	        '        vUv.x = gl_PointCoord.x * framesX + columnNorm;',
	        '        vUv.y = 1.0 - (gl_PointCoord.y * framesY + rowNorm);',
	        '    #endif',

	        '',
	        '    vec4 rotatedTexture = texture2D( tex, vUv );',
	    ].join( '\n' )
	};

	SPE.shaders = {
		vertex: [
			SPE.shaderChunks.defines,
			SPE.shaderChunks.uniforms,
			SPE.shaderChunks.attributes,
			SPE.shaderChunks.varyings,

			THREE.ShaderChunk.common,
			THREE.ShaderChunk.logdepthbuf_pars_vertex,
			THREE.ShaderChunk.fog_pars_vertex,

			SPE.shaderChunks.branchAvoidanceFunctions,
			SPE.shaderChunks.unpackColor,
			SPE.shaderChunks.unpackRotationAxis,
			SPE.shaderChunks.floatOverLifetime,
			SPE.shaderChunks.colorOverLifetime,
			SPE.shaderChunks.paramFetchingFunctions,
			SPE.shaderChunks.forceFetchingFunctions,
			SPE.shaderChunks.rotationFunctions,


			'void main() {',


			//
			// Setup...
			//
			'    highp float age = getAge();',
			'    highp float alive = getAlive();',
			'    highp float maxAge = getMaxAge();',
			'    highp float positionInTime = (age / maxAge);',
			'    highp float isAlive = when_gt( alive, 0.0 );',

			'    #ifdef SHOULD_WIGGLE_PARTICLES',
			'        float wiggleAmount = positionInTime * getWiggle();',
			'        float wiggleSin = isAlive * sin( wiggleAmount );',
			'        float wiggleCos = isAlive * cos( wiggleAmount );',
			'    #endif',

			//
			// Forces
			//

			// Get forces & position
			'    vec3 vel = getVelocity( age );',
			'    vec3 accel = getAcceleration( age );',
			'    vec3 force = vec3( 0.0 );',
			'    vec3 pos = vec3( position );',

			// Calculate the required drag to apply to the forces.
			'    float drag = 1.0 - (positionInTime * 0.5) * acceleration.w;',

			// Integrate forces...
			'    force += vel;',
			'    force *= drag;',
			'    force += accel * age;',
			'    pos += force;',


			// Wiggly wiggly wiggle!
			'    #ifdef SHOULD_WIGGLE_PARTICLES',
			'        pos.x += wiggleSin;',
			'        pos.y += wiggleCos;',
			'        pos.z += wiggleSin;',
			'    #endif',


			// Rotate the emitter around it's central point
			'    #ifdef SHOULD_ROTATE_PARTICLES',
			'        pos = getRotation( pos, positionInTime );',
			'    #endif',

			// Convert pos to a world-space value
			'    vec4 mvPosition = modelViewMatrix * vec4( pos, 1.0 );',

			// Determine point size.
			'    highp float pointSize = getFloatOverLifetime( positionInTime, size ) * isAlive;',

			// Determine perspective
			'    #ifdef HAS_PERSPECTIVE',
			'        float perspective = scale / length( mvPosition.xyz );',
			'    #else',
			'        float perspective = 1.0;',
			'    #endif',

			// Apply perpective to pointSize value
			'    float pointSizePerspective = pointSize * perspective;',


			//
			// Appearance
			//

			// Determine color and opacity for this particle
			'    #ifdef COLORIZE',
			'       vec3 c = isAlive * getColorOverLifetime(',
			'           positionInTime,',
			'           unpackColor( color.x ),',
			'           unpackColor( color.y ),',
			'           unpackColor( color.z ),',
			'           unpackColor( color.w )',
			'       );',
			'    #else',
			'       vec3 c = vec3(1.0);',
			'    #endif',

			'    float o = isAlive * getFloatOverLifetime( positionInTime, opacity );',

			// Assign color to vColor varying.
			'    vColor = vec4( c, o );',

			// Determine angle
			'    #ifdef SHOULD_ROTATE_TEXTURE',
			'        vAngle = isAlive * getFloatOverLifetime( positionInTime, angle );',
			'    #endif',

			// If this particle is using a sprite-sheet as a texture, we'll have to figure out
			// what frame of the texture the particle is using at it's current position in time.
			'    #ifdef SHOULD_CALCULATE_SPRITE',
			'        float framesX = textureAnimation.x;',
			'        float framesY = textureAnimation.y;',
			'        float loopCount = textureAnimation.w;',
			'        float totalFrames = textureAnimation.z;',
			'        float frameNumber = mod( (positionInTime * loopCount) * totalFrames, totalFrames );',

			'        float column = floor(mod( frameNumber, framesX ));',
			'        float row = floor( (frameNumber - column) / framesX );',

			'        float columnNorm = column / framesX;',
			'        float rowNorm = row / framesY;',

			'        vSpriteSheet.x = 1.0 / framesX;',
			'        vSpriteSheet.y = 1.0 / framesY;',
			'        vSpriteSheet.z = columnNorm;',
			'        vSpriteSheet.w = rowNorm;',
			'    #endif',

			//
			// Write values
			//

			// Set PointSize according to size at current point in time.
			'    gl_PointSize = pointSizePerspective;',
			'    gl_Position = projectionMatrix * mvPosition;',

			THREE.ShaderChunk.logdepthbuf_vertex,
			THREE.ShaderChunk.fog_vertex,

			'}'
		].join( '\n' ),

		fragment: [
			SPE.shaderChunks.uniforms,

			THREE.ShaderChunk.common,
			THREE.ShaderChunk.fog_pars_fragment,
			THREE.ShaderChunk.logdepthbuf_pars_fragment,

			SPE.shaderChunks.varyings,

			SPE.shaderChunks.branchAvoidanceFunctions,

			'void main() {',
			'    vec3 outgoingLight = vColor.xyz;',
			'    ',
			'    #ifdef ALPHATEST',
			'       if ( vColor.w < float(ALPHATEST) ) discard;',
			'    #endif',

			SPE.shaderChunks.rotateTexture,

			THREE.ShaderChunk.logdepthbuf_fragment,

			'    outgoingLight = vColor.xyz * rotatedTexture.xyz;',
			'    gl_FragColor = vec4( outgoingLight.xyz, rotatedTexture.w * vColor.w );',

			THREE.ShaderChunk.fog_fragment,

			'}'
		].join( '\n' )
	};


	/**
	 * A bunch of utility functions used throughout the library.
	 * @namespace
	 * @type {Object}
	 */
	SPE.utils = {
	    /**
	     * A map of types used by `SPE.utils.ensureTypedArg` and
	     * `SPE.utils.ensureArrayTypedArg` to compare types against.
	     *
	     * @enum {String}
	     */
	    types: {
	        /**
	         * Boolean type.
	         * @type {String}
	         */
	        BOOLEAN: 'boolean',

	        /**
	         * String type.
	         * @type {String}
	         */
	        STRING: 'string',

	        /**
	         * Number type.
	         * @type {String}
	         */
	        NUMBER: 'number',

	        /**
	         * Object type.
	         * @type {String}
	         */
	        OBJECT: 'object'
	    },

	    /**
	     * Given a value, a type, and a default value to fallback to,
	     * ensure the given argument adheres to the type requesting,
	     * returning the default value if type check is false.
	     *
	     * @param  {(boolean|string|number|object)} arg          The value to perform a type-check on.
	     * @param  {String} type         The type the `arg` argument should adhere to.
	     * @param  {(boolean|string|number|object)} defaultValue A default value to fallback on if the type check fails.
	     * @return {(boolean|string|number|object)}              The given value if type check passes, or the default value if it fails.
	     */
	    ensureTypedArg: function( arg, type, defaultValue ) {
	        'use strict';

	        if ( typeof arg === type ) {
	            return arg;
	        }
	        else {
	            return defaultValue;
	        }
	    },

	    /**
	     * Given an array of values, a type, and a default value,
	     * ensure the given array's contents ALL adhere to the provided type,
	     * returning the default value if type check fails.
	     *
	     * If the given value to check isn't an Array, delegates to SPE.utils.ensureTypedArg.
	     *
	     * @param  {Array|boolean|string|number|object} arg          The array of values to check type of.
	     * @param  {String} type         The type that should be adhered to.
	     * @param  {(boolean|string|number|object)} defaultValue A default fallback value.
	     * @return {(boolean|string|number|object)}              The given value if type check passes, or the default value if it fails.
	     */
	    ensureArrayTypedArg: function( arg, type, defaultValue ) {
	        'use strict';

	        // If the argument being checked is an array, loop through
	        // it and ensure all the values are of the correct type,
	        // falling back to the defaultValue if any aren't.
	        if ( Array.isArray( arg ) ) {
	            for ( var i = arg.length - 1; i >= 0; --i ) {
	                if ( typeof arg[ i ] !== type ) {
	                    return defaultValue;
	                }
	            }

	            return arg;
	        }

	        // If the arg isn't an array then just fallback to
	        // checking the type.
	        return this.ensureTypedArg( arg, type, defaultValue );
	    },

	    /**
	     * Ensures the given value is an instance of a constructor function.
	     *
	     * @param  {Object} arg          The value to check instance of.
	     * @param  {Function} instance     The constructor of the instance to check against.
	     * @param  {Object} defaultValue A default fallback value if instance check fails
	     * @return {Object}              The given value if type check passes, or the default value if it fails.
	     */
	    ensureInstanceOf: function( arg, instance, defaultValue ) {
	        'use strict';

	        if ( instance !== undefined && arg instanceof instance ) {
	            return arg;
	        }
	        else {
	            return defaultValue;
	        }
	    },

	    /**
	     * Given an array of values, ensure the instances of all items in the array
	     * matches the given instance constructor falling back to a default value if
	     * the check fails.
	     *
	     * If given value isn't an Array, delegates to `SPE.utils.ensureInstanceOf`.
	     *
	     * @param  {Array|Object} arg          The value to perform the instanceof check on.
	     * @param  {Function} instance     The constructor of the instance to check against.
	     * @param  {Object} defaultValue A default fallback value if instance check fails
	     * @return {Object}              The given value if type check passes, or the default value if it fails.
	     */
	    ensureArrayInstanceOf: function( arg, instance, defaultValue ) {
	        'use strict';

	        // If the argument being checked is an array, loop through
	        // it and ensure all the values are of the correct type,
	        // falling back to the defaultValue if any aren't.
	        if ( Array.isArray( arg ) ) {
	            for ( var i = arg.length - 1; i >= 0; --i ) {
	                if ( instance !== undefined && arg[ i ] instanceof instance === false ) {
	                    return defaultValue;
	                }
	            }

	            return arg;
	        }

	        // If the arg isn't an array then just fallback to
	        // checking the type.
	        return this.ensureInstanceOf( arg, instance, defaultValue );
	    },

	    /**
	     * Ensures that any "value-over-lifetime" properties of an emitter are
	     * of the correct length (as dictated by `SPE.valueOverLifetimeLength`).
	     *
	     * Delegates to `SPE.utils.interpolateArray` for array resizing.
	     *
	     * If properties aren't arrays, then property values are put into one.
	     *
	     * @param  {Object} property  The property of an SPE.Emitter instance to check compliance of.
	     * @param  {Number} minLength The minimum length of the array to create.
	     * @param  {Number} maxLength The maximum length of the array to create.
	     */
	    ensureValueOverLifetimeCompliance: function( property, minLength, maxLength ) {
	        'use strict';

	        minLength = minLength || 3;
	        maxLength = maxLength || 3;

	        // First, ensure both properties are arrays.
	        if ( Array.isArray( property._value ) === false ) {
	            property._value = [ property._value ];
	        }

	        if ( Array.isArray( property._spread ) === false ) {
	            property._spread = [ property._spread ];
	        }

	        var valueLength = this.clamp( property._value.length, minLength, maxLength ),
	            spreadLength = this.clamp( property._spread.length, minLength, maxLength ),
	            desiredLength = Math.max( valueLength, spreadLength );

	        if ( property._value.length !== desiredLength ) {
	            property._value = this.interpolateArray( property._value, desiredLength );
	        }

	        if ( property._spread.length !== desiredLength ) {
	            property._spread = this.interpolateArray( property._spread, desiredLength );
	        }
	    },

	    /**
	     * Performs linear interpolation (lerp) on an array.
	     *
	     * For example, lerping [1, 10], with a `newLength` of 10 will produce [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].
	     *
	     * Delegates to `SPE.utils.lerpTypeAgnostic` to perform the actual
	     * interpolation.
	     *
	     * @param  {Array} srcArray  The array to lerp.
	     * @param  {Number} newLength The length the array should be interpolated to.
	     * @return {Array}           The interpolated array.
	     */
	    interpolateArray: function( srcArray, newLength ) {
	        'use strict';

	        var sourceLength = srcArray.length,
	            newArray = [ typeof srcArray[ 0 ].clone === 'function' ? srcArray[ 0 ].clone() : srcArray[ 0 ] ],
	            factor = ( sourceLength - 1 ) / ( newLength - 1 );


	        for ( var i = 1; i < newLength - 1; ++i ) {
	            var f = i * factor,
	                before = Math.floor( f ),
	                after = Math.ceil( f ),
	                delta = f - before;

	            newArray[ i ] = this.lerpTypeAgnostic( srcArray[ before ], srcArray[ after ], delta );
	        }

	        newArray.push(
	            typeof srcArray[ sourceLength - 1 ].clone === 'function' ?
	            srcArray[ sourceLength - 1 ].clone() :
	            srcArray[ sourceLength - 1 ]
	        );

	        return newArray;
	    },

	    /**
	     * Clamp a number to between the given min and max values.
	     * @param  {Number} value The number to clamp.
	     * @param  {Number} min   The minimum value.
	     * @param  {Number} max   The maximum value.
	     * @return {Number}       The clamped number.
	     */
	    clamp: function( value, min, max ) {
	        'use strict';

	        return Math.max( min, Math.min( value, max ) );
	    },

	    /**
	     * If the given value is less than the epsilon value, then return
	     * a randomised epsilon value if specified, or just the epsilon value if not.
	     * Works for negative numbers as well as positive.
	     *
	     * @param  {Number} value     The value to perform the operation on.
	     * @param  {Boolean} randomise Whether the value should be randomised.
	     * @return {Number}           The result of the operation.
	     */
	    zeroToEpsilon: function( value, randomise ) {
	        'use strict';

	        var epsilon = 0.00001,
	            result = value;

	        result = randomise ? Math.random() * epsilon * 10 : epsilon;

	        if ( value < 0 && value > -epsilon ) {
	            result = -result;
	        }

	        // if ( value === 0 ) {
	        //     result = randomise ? Math.random() * epsilon * 10 : epsilon;
	        // }
	        // else if ( value > 0 && value < epsilon ) {
	        //     result = randomise ? Math.random() * epsilon * 10 : epsilon;
	        // }
	        // else if ( value < 0 && value > -epsilon ) {
	        //     result = -( randomise ? Math.random() * epsilon * 10 : epsilon );
	        // }

	        return result;
	    },

	    /**
	     * Linearly interpolates two values of various types. The given values
	     * must be of the same type for the interpolation to work.
	     * @param  {(number|Object)} start The start value of the lerp.
	     * @param  {(number|object)} end   The end value of the lerp.
	     * @param  {Number} delta The delta posiiton of the lerp operation. Ideally between 0 and 1 (inclusive).
	     * @return {(number|object|undefined)}       The result of the operation. Result will be undefined if
	     *                                               the start and end arguments aren't a supported type, or
	     *                                               if their types do not match.
	     */
	    lerpTypeAgnostic: function( start, end, delta ) {
	        'use strict';

	        var types = this.types,
	            out;

	        if ( typeof start === types.NUMBER && typeof end === types.NUMBER ) {
	            return start + ( ( end - start ) * delta );
	        }
	        else if ( start instanceof THREE.Vector2 && end instanceof THREE.Vector2 ) {
	            out = start.clone();
	            out.x = this.lerp( start.x, end.x, delta );
	            out.y = this.lerp( start.y, end.y, delta );
	            return out;
	        }
	        else if ( start instanceof THREE.Vector3 && end instanceof THREE.Vector3 ) {
	            out = start.clone();
	            out.x = this.lerp( start.x, end.x, delta );
	            out.y = this.lerp( start.y, end.y, delta );
	            out.z = this.lerp( start.z, end.z, delta );
	            return out;
	        }
	        else if ( start instanceof THREE.Vector4 && end instanceof THREE.Vector4 ) {
	            out = start.clone();
	            out.x = this.lerp( start.x, end.x, delta );
	            out.y = this.lerp( start.y, end.y, delta );
	            out.z = this.lerp( start.z, end.z, delta );
	            out.w = this.lerp( start.w, end.w, delta );
	            return out;
	        }
	        else if ( start instanceof THREE.Color && end instanceof THREE.Color ) {
	            out = start.clone();
	            out.r = this.lerp( start.r, end.r, delta );
	            out.g = this.lerp( start.g, end.g, delta );
	            out.b = this.lerp( start.b, end.b, delta );
	            return out;
	        }
	        else {
	            console.warn( 'Invalid argument types, or argument types do not match:', start, end );
	        }
	    },

	    /**
	     * Perform a linear interpolation operation on two numbers.
	     * @param  {Number} start The start value.
	     * @param  {Number} end   The end value.
	     * @param  {Number} delta The position to interpolate to.
	     * @return {Number}       The result of the lerp operation.
	     */
	    lerp: function( start, end, delta ) {
	        'use strict';
	        return start + ( ( end - start ) * delta );
	    },

	    /**
	     * Rounds a number to a nearest multiple.
	     *
	     * @param  {Number} n        The number to round.
	     * @param  {Number} multiple The multiple to round to.
	     * @return {Number}          The result of the round operation.
	     */
	    roundToNearestMultiple: function( n, multiple ) {
	        'use strict';

	        var remainder = 0;

	        if ( multiple === 0 ) {
	            return n;
	        }

	        remainder = Math.abs( n ) % multiple;

	        if ( remainder === 0 ) {
	            return n;
	        }

	        if ( n < 0 ) {
	            return -( Math.abs( n ) - remainder );
	        }

	        return n + multiple - remainder;
	    },

	    /**
	     * Check if all items in an array are equal. Uses strict equality.
	     *
	     * @param  {Array} array The array of values to check equality of.
	     * @return {Boolean}       Whether the array's values are all equal or not.
	     */
	    arrayValuesAreEqual: function( array ) {
	        'use strict';

	        for ( var i = 0; i < array.length - 1; ++i ) {
	            if ( array[ i ] !== array[ i + 1 ] ) {
	                return false;
	            }
	        }

	        return true;
	    },

	    // colorsAreEqual: function() {
	    //     var colors = Array.prototype.slice.call( arguments ),
	    //         numColors = colors.length;

	    //     for ( var i = 0, color1, color2; i < numColors - 1; ++i ) {
	    //         color1 = colors[ i ];
	    //         color2 = colors[ i + 1 ];

	    //         if (
	    //             color1.r !== color2.r ||
	    //             color1.g !== color2.g ||
	    //             color1.b !== color2.b
	    //         ) {
	    //             return false
	    //         }
	    //     }

	    //     return true;
	    // },


	    /**
	     * Given a start value and a spread value, create and return a random
	     * number.
	     * @param  {Number} base   The start value.
	     * @param  {Number} spread The size of the random variance to apply.
	     * @return {Number}        A randomised number.
	     */
	    randomFloat: function( base, spread ) {
	        'use strict';
	        return base + spread * ( Math.random() - 0.5 );
	    },



	    /**
	     * Given an SPE.ShaderAttribute instance, and various other settings,
	     * assign values to the attribute's array in a `vec3` format.
	     *
	     * @param  {Object} attribute   The instance of SPE.ShaderAttribute to save the result to.
	     * @param  {Number} index       The offset in the attribute's TypedArray to save the result from.
	     * @param  {Object} base        THREE.Vector3 instance describing the start value.
	     * @param  {Object} spread      THREE.Vector3 instance describing the random variance to apply to the start value.
	     * @param  {Object} spreadClamp THREE.Vector3 instance describing the multiples to clamp the randomness to.
	     */
	    randomVector3: function( attribute, index, base, spread, spreadClamp ) {
	        'use strict';

	        var x = base.x + ( Math.random() * spread.x - ( spread.x * 0.5 ) ),
	            y = base.y + ( Math.random() * spread.y - ( spread.y * 0.5 ) ),
	            z = base.z + ( Math.random() * spread.z - ( spread.z * 0.5 ) );

	        // var x = this.randomFloat( base.x, spread.x ),
	        // y = this.randomFloat( base.y, spread.y ),
	        // z = this.randomFloat( base.z, spread.z );

	        if ( spreadClamp ) {
	            x = -spreadClamp.x * 0.5 + this.roundToNearestMultiple( x, spreadClamp.x );
	            y = -spreadClamp.y * 0.5 + this.roundToNearestMultiple( y, spreadClamp.y );
	            z = -spreadClamp.z * 0.5 + this.roundToNearestMultiple( z, spreadClamp.z );
	        }

	        attribute.typedArray.setVec3Components( index, x, y, z );
	    },

	    /**
	     * Given an SPE.Shader attribute instance, and various other settings,
	     * assign Color values to the attribute.
	     * @param  {Object} attribute The instance of SPE.ShaderAttribute to save the result to.
	     * @param  {Number} index     The offset in the attribute's TypedArray to save the result from.
	     * @param  {Object} base      THREE.Color instance describing the start color.
	     * @param  {Object} spread    THREE.Vector3 instance describing the random variance to apply to the start color.
	     */
	    randomColor: function( attribute, index, base, spread ) {
	        'use strict';

	        var r = base.r + ( Math.random() * spread.x ),
	            g = base.g + ( Math.random() * spread.y ),
	            b = base.b + ( Math.random() * spread.z );

	        r = this.clamp( r, 0, 1 );
	        g = this.clamp( g, 0, 1 );
	        b = this.clamp( b, 0, 1 );


	        attribute.typedArray.setVec3Components( index, r, g, b );
	    },


	    randomColorAsHex: ( function() {
	        'use strict';

	        var workingColor = new THREE.Color();

	        /**
	         * Assigns a random color value, encoded as a hex value in decimal
	         * format, to a SPE.ShaderAttribute instance.
	         * @param  {Object} attribute The instance of SPE.ShaderAttribute to save the result to.
	         * @param  {Number} index     The offset in the attribute's TypedArray to save the result from.
	         * @param  {Object} base      THREE.Color instance describing the start color.
	         * @param  {Object} spread    THREE.Vector3 instance describing the random variance to apply to the start color.
	         */
	        return function( attribute, index, base, spread ) {
	            var numItems = base.length,
	                colors = [];

	            for ( var i = 0; i < numItems; ++i ) {
	                var spreadVector = spread[ i ];

	                workingColor.copy( base[ i ] );

	                workingColor.r += ( Math.random() * spreadVector.x ) - ( spreadVector.x * 0.5 );
	                workingColor.g += ( Math.random() * spreadVector.y ) - ( spreadVector.y * 0.5 );
	                workingColor.b += ( Math.random() * spreadVector.z ) - ( spreadVector.z * 0.5 );

	                workingColor.r = this.clamp( workingColor.r, 0, 1 );
	                workingColor.g = this.clamp( workingColor.g, 0, 1 );
	                workingColor.b = this.clamp( workingColor.b, 0, 1 );

	                colors.push( workingColor.getHex() );
	            }

	            attribute.typedArray.setVec4Components( index, colors[ 0 ], colors[ 1 ], colors[ 2 ], colors[ 3 ] );
	        };
	    }() ),

	    /**
	     * Given an SPE.ShaderAttribute instance, and various other settings,
	     * assign values to the attribute's array in a `vec3` format.
	     *
	     * @param  {Object} attribute   The instance of SPE.ShaderAttribute to save the result to.
	     * @param  {Number} index       The offset in the attribute's TypedArray to save the result from.
	     * @param  {Object} start       THREE.Vector3 instance describing the start line position.
	     * @param  {Object} end         THREE.Vector3 instance describing the end line position.
	     */
	    randomVector3OnLine: function( attribute, index, start, end ) {
	        'use strict';
	        var pos = start.clone();

	        pos.lerp( end, Math.random() );

	        attribute.typedArray.setVec3Components( index, pos.x, pos.y, pos.z );
	    },

	    /**
	     * Given an SPE.Shader attribute instance, and various other settings,
	     * assign Color values to the attribute.
	     * @param  {Object} attribute The instance of SPE.ShaderAttribute to save the result to.
	     * @param  {Number} index     The offset in the attribute's TypedArray to save the result from.
	     * @param  {Object} base      THREE.Color instance describing the start color.
	     * @param  {Object} spread    THREE.Vector3 instance describing the random variance to apply to the start color.
	     */

	    /**
	     * Assigns a random vector 3 value to an SPE.ShaderAttribute instance, projecting the
	     * given values onto a sphere.
	     *
	     * @param  {Object} attribute The instance of SPE.ShaderAttribute to save the result to.
	     * @param  {Number} index     The offset in the attribute's TypedArray to save the result from.
	     * @param  {Object} base              THREE.Vector3 instance describing the origin of the transform.
	     * @param  {Number} radius            The radius of the sphere to project onto.
	     * @param  {Number} radiusSpread      The amount of randomness to apply to the projection result
	     * @param  {Object} radiusScale       THREE.Vector3 instance describing the scale of each axis of the sphere.
	     * @param  {Number} radiusSpreadClamp What numeric multiple the projected value should be clamped to.
	     */
	    randomVector3OnSphere: function(
	        attribute, index, base, radius, radiusSpread, radiusScale, radiusSpreadClamp, distributionClamp
	    ) {
	        'use strict';

	        var depth = 2 * Math.random() - 1,
	            t = 6.2832 * Math.random(),
	            r = Math.sqrt( 1 - depth * depth ),
	            rand = this.randomFloat( radius, radiusSpread ),
	            x = 0,
	            y = 0,
	            z = 0;


	        if ( radiusSpreadClamp ) {
	            rand = Math.round( rand / radiusSpreadClamp ) * radiusSpreadClamp;
	        }



	        // Set position on sphere
	        x = r * Math.cos( t ) * rand;
	        y = r * Math.sin( t ) * rand;
	        z = depth * rand;

	        // Apply radius scale to this position
	        x *= radiusScale.x;
	        y *= radiusScale.y;
	        z *= radiusScale.z;

	        // Translate to the base position.
	        x += base.x;
	        y += base.y;
	        z += base.z;

	        // Set the values in the typed array.
	        attribute.typedArray.setVec3Components( index, x, y, z );
	    },

	    seededRandom: function( seed ) {
	        var x = Math.sin( seed ) * 10000;
	        return x - ( x | 0 );
	    },



	    /**
	     * Assigns a random vector 3 value to an SPE.ShaderAttribute instance, projecting the
	     * given values onto a 2d-disc.
	     *
	     * @param  {Object} attribute The instance of SPE.ShaderAttribute to save the result to.
	     * @param  {Number} index     The offset in the attribute's TypedArray to save the result from.
	     * @param  {Object} base              THREE.Vector3 instance describing the origin of the transform.
	     * @param  {Number} radius            The radius of the sphere to project onto.
	     * @param  {Number} radiusSpread      The amount of randomness to apply to the projection result
	     * @param  {Object} radiusScale       THREE.Vector3 instance describing the scale of each axis of the disc. The z-component is ignored.
	     * @param  {Number} radiusSpreadClamp What numeric multiple the projected value should be clamped to.
	     */
	    randomVector3OnDisc: function( attribute, index, base, radius, radiusSpread, radiusScale, radiusSpreadClamp ) {
	        'use strict';

	        var t = 6.2832 * Math.random(),
	            rand = Math.abs( this.randomFloat( radius, radiusSpread ) ),
	            x = 0,
	            y = 0,
	            z = 0;

	        if ( radiusSpreadClamp ) {
	            rand = Math.round( rand / radiusSpreadClamp ) * radiusSpreadClamp;
	        }

	        // Set position on sphere
	        x = Math.cos( t ) * rand;
	        y = Math.sin( t ) * rand;

	        // Apply radius scale to this position
	        x *= radiusScale.x;
	        y *= radiusScale.y;

	        // Translate to the base position.
	        x += base.x;
	        y += base.y;
	        z += base.z;

	        // Set the values in the typed array.
	        attribute.typedArray.setVec3Components( index, x, y, z );
	    },

	    randomDirectionVector3OnSphere: ( function() {
	        'use strict';

	        var v = new THREE.Vector3();

	        /**
	         * Given an SPE.ShaderAttribute instance, create a direction vector from the given
	         * position, using `speed` as the magnitude. Values are saved to the attribute.
	         *
	         * @param  {Object} attribute       The instance of SPE.ShaderAttribute to save the result to.
	         * @param  {Number} index           The offset in the attribute's TypedArray to save the result from.
	         * @param  {Number} posX            The particle's x coordinate.
	         * @param  {Number} posY            The particle's y coordinate.
	         * @param  {Number} posZ            The particle's z coordinate.
	         * @param  {Object} emitterPosition THREE.Vector3 instance describing the emitter's base position.
	         * @param  {Number} speed           The magnitude to apply to the vector.
	         * @param  {Number} speedSpread     The amount of randomness to apply to the magnitude.
	         */
	        return function( attribute, index, posX, posY, posZ, emitterPosition, speed, speedSpread ) {
	            v.copy( emitterPosition );

	            v.x -= posX;
	            v.y -= posY;
	            v.z -= posZ;

	            v.normalize().multiplyScalar( -this.randomFloat( speed, speedSpread ) );

	            attribute.typedArray.setVec3Components( index, v.x, v.y, v.z );
	        };
	    }() ),


	    randomDirectionVector3OnDisc: ( function() {
	        'use strict';

	        var v = new THREE.Vector3();

	        /**
	         * Given an SPE.ShaderAttribute instance, create a direction vector from the given
	         * position, using `speed` as the magnitude. Values are saved to the attribute.
	         *
	         * @param  {Object} attribute       The instance of SPE.ShaderAttribute to save the result to.
	         * @param  {Number} index           The offset in the attribute's TypedArray to save the result from.
	         * @param  {Number} posX            The particle's x coordinate.
	         * @param  {Number} posY            The particle's y coordinate.
	         * @param  {Number} posZ            The particle's z coordinate.
	         * @param  {Object} emitterPosition THREE.Vector3 instance describing the emitter's base position.
	         * @param  {Number} speed           The magnitude to apply to the vector.
	         * @param  {Number} speedSpread     The amount of randomness to apply to the magnitude.
	         */
	        return function( attribute, index, posX, posY, posZ, emitterPosition, speed, speedSpread ) {
	            v.copy( emitterPosition );

	            v.x -= posX;
	            v.y -= posY;
	            v.z -= posZ;

	            v.normalize().multiplyScalar( -this.randomFloat( speed, speedSpread ) );

	            attribute.typedArray.setVec3Components( index, v.x, v.y, 0 );
	        };
	    }() ),

	    getPackedRotationAxis: ( function() {
	        'use strict';

	        var v = new THREE.Vector3(),
	            vSpread = new THREE.Vector3(),
	            c = new THREE.Color(),
	            addOne = new THREE.Vector3( 1, 1, 1 );

	        /**
	         * Given a rotation axis, and a rotation axis spread vector,
	         * calculate a randomised rotation axis, and pack it into
	         * a hexadecimal value represented in decimal form.
	         * @param  {Object} axis       THREE.Vector3 instance describing the rotation axis.
	         * @param  {Object} axisSpread THREE.Vector3 instance describing the amount of randomness to apply to the rotation axis.
	         * @return {Number}            The packed rotation axis, with randomness.
	         */
	        return function( axis, axisSpread ) {
	            v.copy( axis ).normalize();
	            vSpread.copy( axisSpread ).normalize();

	            v.x += ( -axisSpread.x * 0.5 ) + ( Math.random() * axisSpread.x );
	            v.y += ( -axisSpread.y * 0.5 ) + ( Math.random() * axisSpread.y );
	            v.z += ( -axisSpread.z * 0.5 ) + ( Math.random() * axisSpread.z );

	            // v.x = Math.abs( v.x );
	            // v.y = Math.abs( v.y );
	            // v.z = Math.abs( v.z );

	            v.normalize().add( addOne ).multiplyScalar( 0.5 );

	            c.setRGB( v.x, v.y, v.z );

	            return c.getHex();
	        };
	    }() )
	};


	/**
	 * An SPE.Group instance.
	 * @typedef {Object} Group
	 * @see SPE.Group
	 */

	/**
	 * A map of options to configure an SPE.Group instance.
	 * @typedef {Object} GroupOptions
	 *
	 * @property {Object} texture An object describing the texture used by the group.
	 *
	 * @property {Object} texture.value An instance of THREE.Texture.
	 *
	 * @property {Object=} texture.frames A THREE.Vector2 instance describing the number
	 *                                    of frames on the x- and y-axis of the given texture.
	 *                                    If not provided, the texture will NOT be treated as
	 *                                    a sprite-sheet and as such will NOT be animated.
	 *
	 * @property {Number} [texture.frameCount=texture.frames.x * texture.frames.y] The total number of frames in the sprite-sheet.
	 *                                                                   Allows for sprite-sheets that don't fill the entire
	 *                                                                   texture.
	 *
	 * @property {Number} texture.loop The number of loops through the sprite-sheet that should
	 *                                 be performed over the course of a single particle's lifetime.
	 *
	 * @property {Number} fixedTimeStep If no `dt` (or `deltaTime`) value is passed to this group's
	 *                                  `tick()` function, this number will be used to move the particle
	 *                                  simulation forward. Value in SECONDS.
	 *
	 * @property {Boolean} hasPerspective Whether the distance a particle is from the camera should affect
	 *                                    the particle's size.
	 *
	 * @property {Boolean} colorize Whether the particles in this group should be rendered with color, or
	 *                              whether the only color of particles will come from the provided texture.
	 *
	 * @property {Number} blending One of Three.js's blending modes to apply to this group's `ShaderMaterial`.
	 *
	 * @property {Boolean} transparent Whether these particle's should be rendered with transparency.
	 *
	 * @property {Number} alphaTest Sets the alpha value to be used when running an alpha test on the `texture.value` property. Value between 0 and 1.
	 *
	 * @property {Boolean} depthWrite Whether rendering the group has any effect on the depth buffer.
	 *
	 * @property {Boolean} depthTest Whether to have depth test enabled when rendering this group.
	 *
	 * @property {Boolean} fog Whether this group's particles should be affected by their scene's fog.
	 *
	 * @property {Number} scale The scale factor to apply to this group's particle sizes. Useful for
	 *                          setting particle sizes to be relative to renderer size.
	 */


	/**
	 * The SPE.Group class. Creates a new group, containing a material, geometry, and mesh.
	 *
	 * @constructor
	 * @param {GroupOptions} options A map of options to configure the group instance.
	 */
	SPE.Group = function( options ) {
	    'use strict';

	    var utils = SPE.utils,
	        types = utils.types;

	    // Ensure we have a map of options to play with
	    options = utils.ensureTypedArg( options, types.OBJECT, {} );
	    options.texture = utils.ensureTypedArg( options.texture, types.OBJECT, {} );

	    // Assign a UUID to this instance
	    this.uuid = THREE.Math.generateUUID();

	    // If no `deltaTime` value is passed to the `SPE.Group.tick` function,
	    // the value of this property will be used to advance the simulation.
	    this.fixedTimeStep = utils.ensureTypedArg( options.fixedTimeStep, types.NUMBER, 0.016 );

	    // Set properties used in the uniforms map, starting with the
	    // texture stuff.
	    this.texture = utils.ensureInstanceOf( options.texture.value, THREE.Texture, null );
	    this.textureFrames = utils.ensureInstanceOf( options.texture.frames, THREE.Vector2, new THREE.Vector2( 1, 1 ) );
	    this.textureFrameCount = utils.ensureTypedArg( options.texture.frameCount, types.NUMBER, this.textureFrames.x * this.textureFrames.y );
	    this.textureLoop = utils.ensureTypedArg( options.texture.loop, types.NUMBER, 1 );
	    this.textureFrames.max( new THREE.Vector2( 1, 1 ) );

	    this.hasPerspective = utils.ensureTypedArg( options.hasPerspective, types.BOOLEAN, true );
	    this.colorize = utils.ensureTypedArg( options.colorize, types.BOOLEAN, true );

	    this.maxParticleCount = utils.ensureTypedArg( options.maxParticleCount, types.NUMBER, null );


	    // Set properties used to define the ShaderMaterial's appearance.
	    this.blending = utils.ensureTypedArg( options.blending, types.NUMBER, THREE.AdditiveBlending );
	    this.transparent = utils.ensureTypedArg( options.transparent, types.BOOLEAN, true );
	    this.alphaTest = parseFloat( utils.ensureTypedArg( options.alphaTest, types.NUMBER, 0.0 ) );
	    this.depthWrite = utils.ensureTypedArg( options.depthWrite, types.BOOLEAN, false );
	    this.depthTest = utils.ensureTypedArg( options.depthTest, types.BOOLEAN, true );
	    this.fog = utils.ensureTypedArg( options.fog, types.BOOLEAN, true );
	    this.scale = utils.ensureTypedArg( options.scale, types.NUMBER, 300 );

	    // Where emitter's go to curl up in a warm blanket and live
	    // out their days.
	    this.emitters = [];
	    this.emitterIDs = [];

	    // Create properties for use by the emitter pooling functions.
	    this._pool = [];
	    this._poolCreationSettings = null;
	    this._createNewWhenPoolEmpty = 0;

	    // Whether all attributes should be forced to updated
	    // their entire buffer contents on the next tick.
	    //
	    // Used when an emitter is removed.
	    this._attributesNeedRefresh = false;
	    this._attributesNeedDynamicReset = false;

	    this.particleCount = 0;


	    // Map of uniforms to be applied to the ShaderMaterial instance.
	    this.uniforms = {
	        tex: {
	            type: 't',
	            value: this.texture
	        },
	        textureAnimation: {
	            type: 'v4',
	            value: new THREE.Vector4(
	                this.textureFrames.x,
	                this.textureFrames.y,
	                this.textureFrameCount,
	                Math.max( Math.abs( this.textureLoop ), 1.0 )
	            )
	        },
	        fogColor: {
	            type: 'c',
	            value: this.fog ? new THREE.Color() : null
	        },
	        fogNear: {
	            type: 'f',
	            value: 10
	        },
	        fogFar: {
	            type: 'f',
	            value: 200
	        },
	        fogDensity: {
	            type: 'f',
	            value: 0.5
	        },
	        deltaTime: {
	            type: 'f',
	            value: 0
	        },
	        runTime: {
	            type: 'f',
	            value: 0
	        },
	        scale: {
	            type: 'f',
	            value: this.scale
	        }
	    };

	    // Add some defines into the mix...
	    this.defines = {
	        HAS_PERSPECTIVE: this.hasPerspective,
	        COLORIZE: this.colorize,
	        VALUE_OVER_LIFETIME_LENGTH: SPE.valueOverLifetimeLength,

	        SHOULD_ROTATE_TEXTURE: false,
	        SHOULD_ROTATE_PARTICLES: false,
	        SHOULD_WIGGLE_PARTICLES: false,

	        SHOULD_CALCULATE_SPRITE: this.textureFrames.x > 1 || this.textureFrames.y > 1
	    };

	    // Map of all attributes to be applied to the particles.
	    //
	    // See SPE.ShaderAttribute for a bit more info on this bit.
	    this.attributes = {
	        position: new SPE.ShaderAttribute( 'v3', true ),
	        acceleration: new SPE.ShaderAttribute( 'v4', true ), // w component is drag
	        velocity: new SPE.ShaderAttribute( 'v3', true ),
	        rotation: new SPE.ShaderAttribute( 'v4', true ),
	        rotationCenter: new SPE.ShaderAttribute( 'v3', true ),
	        params: new SPE.ShaderAttribute( 'v4', true ), // Holds (alive, age, delay, wiggle)
	        size: new SPE.ShaderAttribute( 'v4', true ),
	        angle: new SPE.ShaderAttribute( 'v4', true ),
	        color: new SPE.ShaderAttribute( 'v4', true ),
	        opacity: new SPE.ShaderAttribute( 'v4', true )
	    };

	    this.attributeKeys = Object.keys( this.attributes );
	    this.attributeCount = this.attributeKeys.length;

	    // Create the ShaderMaterial instance that'll help render the
	    // particles.
	    this.material = new THREE.ShaderMaterial( {
	        uniforms: this.uniforms,
	        vertexShader: SPE.shaders.vertex,
	        fragmentShader: SPE.shaders.fragment,
	        blending: this.blending,
	        transparent: this.transparent,
	        alphaTest: this.alphaTest,
	        depthWrite: this.depthWrite,
	        depthTest: this.depthTest,
	        defines: this.defines,
	        fog: this.fog
	    } );

	    // Create the BufferGeometry and Points instances, ensuring
	    // the geometry and material are given to the latter.
	    this.geometry = new THREE.BufferGeometry();
	    this.mesh = new THREE.Points( this.geometry, this.material );

	    if ( this.maxParticleCount === null ) {
	        console.warn( 'SPE.Group: No maxParticleCount specified. Adding emitters after rendering will probably cause errors.' );
	    }
	};

	SPE.Group.constructor = SPE.Group;


	SPE.Group.prototype._updateDefines = function() {
	    'use strict';

	    var emitters = this.emitters,
	        i = emitters.length - 1,
	        emitter,
	        defines = this.defines;

	    for ( i; i >= 0; --i ) {
	        emitter = emitters[ i ];

	        // Only do angle calculation if there's no spritesheet defined.
	        //
	        // Saves calculations being done and then overwritten in the shaders.
	        if ( !defines.SHOULD_CALCULATE_SPRITE ) {
	            defines.SHOULD_ROTATE_TEXTURE = defines.SHOULD_ROTATE_TEXTURE || !!Math.max(
	                Math.max.apply( null, emitter.angle.value ),
	                Math.max.apply( null, emitter.angle.spread )
	            );
	        }

	        defines.SHOULD_ROTATE_PARTICLES = defines.SHOULD_ROTATE_PARTICLES || !!Math.max(
	            emitter.rotation.angle,
	            emitter.rotation.angleSpread
	        );

	        defines.SHOULD_WIGGLE_PARTICLES = defines.SHOULD_WIGGLE_PARTICLES || !!Math.max(
	            emitter.wiggle.value,
	            emitter.wiggle.spread
	        );
	    }

	    this.material.needsUpdate = true;
	};

	SPE.Group.prototype._applyAttributesToGeometry = function() {
	    'use strict';

	    var attributes = this.attributes,
	        geometry = this.geometry,
	        geometryAttributes = geometry.attributes,
	        attribute,
	        geometryAttribute;

	    // Loop through all the shader attributes and assign (or re-assign)
	    // typed array buffers to each one.
	    for ( var attr in attributes ) {
	        if ( attributes.hasOwnProperty( attr ) ) {
	            attribute = attributes[ attr ];
	            geometryAttribute = geometryAttributes[ attr ];

	            // Update the array if this attribute exists on the geometry.
	            //
	            // This needs to be done because the attribute's typed array might have
	            // been resized and reinstantiated, and might now be looking at a
	            // different ArrayBuffer, so reference needs updating.
	            if ( geometryAttribute ) {
	                geometryAttribute.array = attribute.typedArray.array;
	            }

	            // // Add the attribute to the geometry if it doesn't already exist.
	            else {
	                geometry.setAttribute( attr, attribute.bufferAttribute );
	            }

	            // Mark the attribute as needing an update the next time a frame is rendered.
	            attribute.bufferAttribute.needsUpdate = true;
	        }
	    }

	    // Mark the draw range on the geometry. This will ensure
	    // only the values in the attribute buffers that are
	    // associated with a particle will be used in THREE's
	    // render cycle.
	    this.geometry.setDrawRange( 0, this.particleCount );
	};

	/**
	 * Adds an SPE.Emitter instance to this group, creating particle values and
	 * assigning them to this group's shader attributes.
	 *
	 * @param {Emitter} emitter The emitter to add to this group.
	 */
	SPE.Group.prototype.addEmitter = function( emitter ) {
	    'use strict';

	    // Ensure an actual emitter instance is passed here.
	    //
	    // Decided not to throw here, just in case a scene's
	    // rendering would be paused. Logging an error instead
	    // of stopping execution if exceptions aren't caught.
	    if ( emitter instanceof SPE.Emitter === false ) {
	        console.error( '`emitter` argument must be instance of SPE.Emitter. Was provided with:', emitter );
	        return;
	    }

	    // If the emitter already exists as a member of this group, then
	    // stop here, we don't want to add it again.
	    else if ( this.emitterIDs.indexOf( emitter.uuid ) > -1 ) {
	        console.error( 'Emitter already exists in this group. Will not add again.' );
	        return;
	    }

	    // And finally, if the emitter is a member of another group,
	    // don't add it to this group.
	    else if ( emitter.group !== null ) {
	        console.error( 'Emitter already belongs to another group. Will not add to requested group.' );
	        return;
	    }

	    var attributes = this.attributes,
	        start = this.particleCount,
	        end = start + emitter.particleCount;

	    // Update this group's particle count.
	    this.particleCount = end;

	    // Emit a warning if the emitter being added will exceed the buffer sizes specified.
	    if ( this.maxParticleCount !== null && this.particleCount > this.maxParticleCount ) {
	        console.warn( 'SPE.Group: maxParticleCount exceeded. Requesting', this.particleCount, 'particles, can support only', this.maxParticleCount );
	    }


	    // Set the `particlesPerSecond` value (PPS) on the emitter.
	    // It's used to determine how many particles to release
	    // on a per-frame basis.
	    emitter._calculatePPSValue( emitter.maxAge._value + emitter.maxAge._spread );
	    emitter._setBufferUpdateRanges( this.attributeKeys );

	    // Store the offset value in the TypedArray attributes for this emitter.
	    emitter._setAttributeOffset( start );

	    // Save a reference to this group on the emitter so it knows
	    // where it belongs.
	    emitter.group = this;

	    // Store reference to the attributes on the emitter for
	    // easier access during the emitter's tick function.
	    emitter.attributes = this.attributes;



	    // Ensure the attributes and their BufferAttributes exist, and their
	    // TypedArrays are of the correct size.
	    for ( var attr in attributes ) {
	        if ( attributes.hasOwnProperty( attr ) ) {
	            // When creating a buffer, pass through the maxParticle count
	            // if one is specified.
	            attributes[ attr ]._createBufferAttribute(
	                this.maxParticleCount !== null ?
	                this.maxParticleCount :
	                this.particleCount
	            );
	        }
	    }

	    // Loop through each particle this emitter wants to have, and create the attributes values,
	    // storing them in the TypedArrays that each attribute holds.
	    for ( var i = start; i < end; ++i ) {
	        emitter._assignPositionValue( i );
	        emitter._assignForceValue( i, 'velocity' );
	        emitter._assignForceValue( i, 'acceleration' );
	        emitter._assignAbsLifetimeValue( i, 'opacity' );
	        emitter._assignAbsLifetimeValue( i, 'size' );
	        emitter._assignAngleValue( i );
	        emitter._assignRotationValue( i );
	        emitter._assignParamsValue( i );
	        emitter._assignColorValue( i );
	    }

	    // Update the geometry and make sure the attributes are referencing
	    // the typed arrays properly.
	    this._applyAttributesToGeometry();

	    // Store this emitter in this group's emitter's store.
	    this.emitters.push( emitter );
	    this.emitterIDs.push( emitter.uuid );

	    // Update certain flags to enable shader calculations only if they're necessary.
	    this._updateDefines( emitter );

	    // Update the material since defines might have changed
	    this.material.needsUpdate = true;
	    this.geometry.needsUpdate = true;
	    this._attributesNeedRefresh = true;

	    // Return the group to enable chaining.
	    return this;
	};

	/**
	 * Removes an SPE.Emitter instance from this group. When called,
	 * all particle's belonging to the given emitter will be instantly
	 * removed from the scene.
	 *
	 * @param {Emitter} emitter The emitter to add to this group.
	 */
	SPE.Group.prototype.removeEmitter = function( emitter ) {
	    'use strict';

	    var emitterIndex = this.emitterIDs.indexOf( emitter.uuid );

	    // Ensure an actual emitter instance is passed here.
	    //
	    // Decided not to throw here, just in case a scene's
	    // rendering would be paused. Logging an error instead
	    // of stopping execution if exceptions aren't caught.
	    if ( emitter instanceof SPE.Emitter === false ) {
	        console.error( '`emitter` argument must be instance of SPE.Emitter. Was provided with:', emitter );
	        return;
	    }

	    // Issue an error if the emitter isn't a member of this group.
	    else if ( emitterIndex === -1 ) {
	        console.error( 'Emitter does not exist in this group. Will not remove.' );
	        return;
	    }

	    // Kill all particles by marking them as dead
	    // and their age as 0.
	    var start = emitter.attributeOffset,
	        end = start + emitter.particleCount,
	        params = this.attributes.params.typedArray;

	    // Set alive and age to zero.
	    for ( var i = start; i < end; ++i ) {
	        params.array[ i * 4 ] = 0.0;
	        params.array[ i * 4 + 1 ] = 0.0;
	    }

	    // Remove the emitter from this group's "store".
	    this.emitters.splice( emitterIndex, 1 );
	    this.emitterIDs.splice( emitterIndex, 1 );

	    // Remove this emitter's attribute values from all shader attributes.
	    // The `.splice()` call here also marks each attribute's buffer
	    // as needing to update it's entire contents.
	    for ( var attr in this.attributes ) {
	        if ( this.attributes.hasOwnProperty( attr ) ) {
	            this.attributes[ attr ].splice( start, end );
	        }
	    }

	    // Ensure this group's particle count is correct.
	    this.particleCount -= emitter.particleCount;

	    // Call the emitter's remove method.
	    emitter._onRemove();

	    // Set a flag to indicate that the attribute buffers should
	    // be updated in their entirety on the next frame.
	    this._attributesNeedRefresh = true;
	};


	/**
	 * Fetch a single emitter instance from the pool.
	 * If there are no objects in the pool, a new emitter will be
	 * created if specified.
	 *
	 * @return {Emitter|null}
	 */
	SPE.Group.prototype.getFromPool = function() {
	    'use strict';

	    var pool = this._pool,
	        createNew = this._createNewWhenPoolEmpty;

	    if ( pool.length ) {
	        return pool.pop();
	    }
	    else if ( createNew ) {
	        var emitter = new SPE.Emitter( this._poolCreationSettings );

	        this.addEmitter( emitter );

	        return emitter;
	    }

	    return null;
	};


	/**
	 * Release an emitter into the pool.
	 *
	 * @param  {ShaderParticleEmitter} emitter
	 * @return {Group} This group instance.
	 */
	SPE.Group.prototype.releaseIntoPool = function( emitter ) {
	    'use strict';

	    if ( emitter instanceof SPE.Emitter === false ) {
	        console.error( 'Argument is not instanceof SPE.Emitter:', emitter );
	        return;
	    }

	    emitter.reset();
	    this._pool.unshift( emitter );

	    return this;
	};


	/**
	 * Get the pool array
	 *
	 * @return {Array}
	 */
	SPE.Group.prototype.getPool = function() {
	    'use strict';
	    return this._pool;
	};


	/**
	 * Add a pool of emitters to this particle group
	 *
	 * @param {Number} numEmitters      The number of emitters to add to the pool.
	 * @param {EmitterOptions|Array} emitterOptions  An object, or array of objects, describing the options to pass to each emitter.
	 * @param {Boolean} createNew       Should a new emitter be created if the pool runs out?
	 * @return {Group} This group instance.
	 */
	SPE.Group.prototype.addPool = function( numEmitters, emitterOptions, createNew ) {
	    'use strict';

	    var emitter;

	    // Save relevant settings and flags.
	    this._poolCreationSettings = emitterOptions;
	    this._createNewWhenPoolEmpty = !!createNew;

	    // Create the emitters, add them to this group and the pool.
	    for ( var i = 0; i < numEmitters; ++i ) {
	        if ( Array.isArray( emitterOptions ) ) {
	            emitter = new SPE.Emitter( emitterOptions[ i ] );
	        }
	        else {
	            emitter = new SPE.Emitter( emitterOptions );
	        }
	        this.addEmitter( emitter );
	        this.releaseIntoPool( emitter );
	    }

	    return this;
	};



	SPE.Group.prototype._triggerSingleEmitter = function( pos ) {
	    'use strict';

	    var emitter = this.getFromPool(),
	        self = this;

	    if ( emitter === null ) {
	        console.log( 'SPE.Group pool ran out.' );
	        return;
	    }

	    // TODO:
	    // - Make sure buffers are update with thus new position.
	    if ( pos instanceof THREE.Vector3 ) {
	        emitter.position.value.copy( pos );

	        // Trigger the setter for this property to force an
	        // update to the emitter's position attribute.
	        emitter.position.value = emitter.position.value;
	    }

	    emitter.enable();

	    setTimeout( function() {
	        emitter.disable();
	        self.releaseIntoPool( emitter );
	    }, ( Math.max( emitter.duration, ( emitter.maxAge.value + emitter.maxAge.spread ) ) ) * 1000 );

	    return this;
	};


	/**
	 * Set a given number of emitters as alive, with an optional position
	 * vector3 to move them to.
	 *
	 * @param  {Number} numEmitters The number of emitters to activate
	 * @param  {Object} [position=undefined] A THREE.Vector3 instance describing the position to activate the emitter(s) at.
	 * @return {Group} This group instance.
	 */
	SPE.Group.prototype.triggerPoolEmitter = function( numEmitters, position ) {
	    'use strict';

	    if ( typeof numEmitters === 'number' && numEmitters > 1 ) {
	        for ( var i = 0; i < numEmitters; ++i ) {
	            this._triggerSingleEmitter( position );
	        }
	    }
	    else {
	        this._triggerSingleEmitter( position );
	    }

	    return this;
	};



	SPE.Group.prototype._updateUniforms = function( dt ) {
	    'use strict';

	    this.uniforms.runTime.value += dt;
	    this.uniforms.deltaTime.value = dt;
	};

	SPE.Group.prototype._resetBufferRanges = function() {
	    'use strict';

	    var keys = this.attributeKeys,
	        i = this.attributeCount - 1,
	        attrs = this.attributes;

	    for ( i; i >= 0; --i ) {
	        attrs[ keys[ i ] ].resetUpdateRange();
	    }
	};


	SPE.Group.prototype._updateBuffers = function( emitter ) {
	    'use strict';

	    var keys = this.attributeKeys,
	        i = this.attributeCount - 1,
	        attrs = this.attributes,
	        emitterRanges = emitter.bufferUpdateRanges,
	        key,
	        emitterAttr,
	        attr;

	    for ( i; i >= 0; --i ) {
	        key = keys[ i ];
	        emitterAttr = emitterRanges[ key ];
	        attr = attrs[ key ];
	        attr.setUpdateRange( emitterAttr.min, emitterAttr.max );
	        attr.flagUpdate();
	    }
	};


	/**
	 * Simulate all the emitter's belonging to this group, updating
	 * attribute values along the way.
	 * @param  {Number} [dt=Group's `fixedTimeStep` value] The number of seconds to simulate the group's emitters for (deltaTime)
	 */
	SPE.Group.prototype.tick = function( dt ) {
	    'use strict';

	    var emitters = this.emitters,
	        numEmitters = emitters.length,
	        deltaTime = dt || this.fixedTimeStep,
	        keys = this.attributeKeys,
	        i,
	        attrs = this.attributes;

	    // Update uniform values.
	    this._updateUniforms( deltaTime );

	    // Reset buffer update ranges on the shader attributes.
	    this._resetBufferRanges();


	    // If nothing needs updating, then stop here.
	    if (
	        numEmitters === 0 &&
	        this._attributesNeedRefresh === false &&
	        this._attributesNeedDynamicReset === false
	    ) {
	        return;
	    }

	    // Loop through each emitter in this group and
	    // simulate it, then update the shader attribute
	    // buffers.
	    for ( var i = 0, emitter; i < numEmitters; ++i ) {
	        emitter = emitters[ i ];
	        emitter.tick( deltaTime );
	        this._updateBuffers( emitter );
	    }

	    // If the shader attributes have been refreshed,
	    // then the dynamic properties of each buffer
	    // attribute will need to be reset back to
	    // what they should be.
	    if ( this._attributesNeedDynamicReset === true ) {
	        i = this.attributeCount - 1;

	        for ( i; i >= 0; --i ) {
	            attrs[ keys[ i ] ].resetDynamic();
	        }

	        this._attributesNeedDynamicReset = false;
	    }

	    // If this group's shader attributes need a full refresh
	    // then mark each attribute's buffer attribute as
	    // needing so.
	    if ( this._attributesNeedRefresh === true ) {
	        i = this.attributeCount - 1;

	        for ( i; i >= 0; --i ) {
	            attrs[ keys[ i ] ].forceUpdateAll();
	        }

	        this._attributesNeedRefresh = false;
	        this._attributesNeedDynamicReset = true;
	    }
	};


	/**
	 * Dipose the geometry and material for the group.
	 *
	 * @return {Group} Group instance.
	 */
	SPE.Group.prototype.dispose = function() {
	    'use strict';
	    this.geometry.dispose();
	    this.material.dispose();
	    return this;
	};


	/**
	 * An SPE.Emitter instance.
	 * @typedef {Object} Emitter
	 * @see SPE.Emitter
	 */

	/**
	 * A map of options to configure an SPE.Emitter instance.
	 *
	 * @typedef {Object} EmitterOptions
	 *
	 * @property {distribution} [type=BOX] The default distribution this emitter should use to control
	 *                         its particle's spawn position and force behaviour.
	 *                         Must be an SPE.distributions.* value.
	 *
	 *
	 * @property {Number} [particleCount=100] The total number of particles this emitter will hold. NOTE: this is not the number
	 *                                  of particles emitted in a second, or anything like that. The number of particles
	 *                                  emitted per-second is calculated by particleCount / maxAge (approximately!)
	 *
	 * @property {Number|null} [duration=null] The duration in seconds that this emitter should live for. If not specified, the emitter
	 *                                         will emit particles indefinitely.
	 *                                         NOTE: When an emitter is older than a specified duration, the emitter is NOT removed from
	 *                                         it's group, but rather is just marked as dead, allowing it to be reanimated at a later time
	 *                                         using `SPE.Emitter.prototype.enable()`.
	 *
	 * @property {Boolean} [isStatic=false] Whether this emitter should be not be simulated (true).
	 * @property {Boolean} [activeMultiplier=1] A value between 0 and 1 describing what percentage of this emitter's particlesPerSecond should be
	 *                                          emitted, where 0 is 0%, and 1 is 100%.
	 *                                          For example, having an emitter with 100 particles, a maxAge of 2, yields a particlesPerSecond
	 *                                          value of 50. Setting `activeMultiplier` to 0.5, then, will only emit 25 particles per second (0.5 = 50%).
	 *                                          Values greater than 1 will emulate a burst of particles, causing the emitter to run out of particles
	 *                                          before it's next activation cycle.
	 *
	 * @property {Boolean} [direction=1] The direction of the emitter. If value is `1`, emitter will start at beginning of particle's lifecycle.
	 *                                   If value is `-1`, emitter will start at end of particle's lifecycle and work it's way backwards.
	 *
	 * @property {Object} [maxAge={}] An object describing the particle's maximum age in seconds.
	 * @property {Number} [maxAge.value=2] A number between 0 and 1 describing the amount of maxAge to apply to all particles.
	 * @property {Number} [maxAge.spread=0] A number describing the maxAge variance on a per-particle basis.
	 *
	 *
	 * @property {Object} [position={}] An object describing this emitter's position.
	 * @property {Object} [position.value=new THREE.Vector3()] A THREE.Vector3 instance describing this emitter's base position.
	 * @property {Object} [position.spread=new THREE.Vector3()] A THREE.Vector3 instance describing this emitter's position variance on a per-particle basis.
	 *                                                          Note that when using a SPHERE or DISC distribution, only the x-component
	 *                                                          of this vector is used.
	 *                                                          When using a LINE distribution, this value is the endpoint of the LINE.
	 * @property {Object} [position.spreadClamp=new THREE.Vector3()] A THREE.Vector3 instance describing the numeric multiples the particle's should
	 *                                                               be spread out over.
	 *                                                               Note that when using a SPHERE or DISC distribution, only the x-component
	 *                                                               of this vector is used.
	 *                                                               When using a LINE distribution, this property is ignored.
	 * @property {Number} [position.radius=10] This emitter's base radius.
	 * @property {Object} [position.radiusScale=new THREE.Vector3()] A THREE.Vector3 instance describing the radius's scale in all three axes. Allows a SPHERE or DISC to be squashed or stretched.
	 * @property {distribution} [position.distribution=value of the `type` option.] A specific distribution to use when radiusing particles. Overrides the `type` option.
	 * @property {Boolean} [position.randomise=false] When a particle is re-spawned, whether it's position should be re-randomised or not. Can incur a performance hit.
	 *
	 *
	 * @property {Object} [velocity={}] An object describing this particle velocity.
	 * @property {Object} [velocity.value=new THREE.Vector3()] A THREE.Vector3 instance describing this emitter's base velocity.
	 * @property {Object} [velocity.spread=new THREE.Vector3()] A THREE.Vector3 instance describing this emitter's velocity variance on a per-particle basis.
	 *                                                          Note that when using a SPHERE or DISC distribution, only the x-component
	 *                                                          of this vector is used.
	 * @property {distribution} [velocity.distribution=value of the `type` option.] A specific distribution to use when calculating a particle's velocity. Overrides the `type` option.
	 * @property {Boolean} [velocity.randomise=false] When a particle is re-spawned, whether it's velocity should be re-randomised or not. Can incur a performance hit.
	 *
	 *
	 * @property {Object} [acceleration={}] An object describing this particle's acceleration.
	 * @property {Object} [acceleration.value=new THREE.Vector3()] A THREE.Vector3 instance describing this emitter's base acceleration.
	 * @property {Object} [acceleration.spread=new THREE.Vector3()] A THREE.Vector3 instance describing this emitter's acceleration variance on a per-particle basis.
	 *                           Note that when using a SPHERE or DISC distribution, only the x-component
	 *                           of this vector is used.
	 * @property {distribution} [acceleration.distribution=value of the `type` option.] A specific distribution to use when calculating a particle's acceleration. Overrides the `type` option.
	 * @property {Boolean} [acceleration.randomise=false] When a particle is re-spawned, whether it's acceleration should be re-randomised or not. Can incur a performance hit.
	 *
	 *
	 * @property {Object} [drag={}] An object describing this particle drag. Drag is applied to both velocity and acceleration values.
	 * @property {Number} [drag.value=0] A number between 0 and 1 describing the amount of drag to apply to all particles.
	 * @property {Number} [drag.spread=0] A number describing the drag variance on a per-particle basis.
	 * @property {Boolean} [drag.randomise=false] When a particle is re-spawned, whether it's drag should be re-randomised or not. Can incur a performance hit.
	 *
	 *
	 * @property {Object} [wiggle={}] This is quite a fun one! The values of this object will determine whether a particle will wiggle, or jiggle, or wave,
	 *                                or shimmy, or waggle, or... Well you get the idea. The wiggle is calculated over-time, meaning that a particle will
	 *                                start off with no wiggle, and end up wiggling about with the distance of the `value` specified by the time it dies.
	 *                                It's quite handy to simulate fire embers, or similar effects where the particle's position should slightly change over
	 *                                time, and such change isn't easily controlled by rotation, velocity, or acceleration. The wiggle is a combination of sin and cos calculations, so is circular in nature.
	 * @property {Number} [wiggle.value=0] A number describing the amount of wiggle to apply to all particles. It's measured in distance.
	 * @property {Number} [wiggle.spread=0] A number describing the wiggle variance on a per-particle basis.
	 *
	 *
	 * @property {Object} [rotation={}] An object describing this emitter's rotation. It can either be static, or set to rotate from 0radians to the value of `rotation.value`
	 *                                  over a particle's lifetime. Rotation values affect both a particle's position and the forces applied to it.
	 * @property {Object} [rotation.axis=new THREE.Vector3(0, 1, 0)] A THREE.Vector3 instance describing this emitter's axis of rotation.
	 * @property {Object} [rotation.axisSpread=new THREE.Vector3()] A THREE.Vector3 instance describing the amount of variance to apply to the axis of rotation on
	 *                                                              a per-particle basis.
	 * @property {Number} [rotation.angle=0] The angle of rotation, given in radians. If `rotation.static` is true, the emitter will start off rotated at this angle, and stay as such.
	 *                                       Otherwise, the particles will rotate from 0radians to this value over their lifetimes.
	 * @property {Number} [rotation.angleSpread=0] The amount of variance in each particle's rotation angle.
	 * @property {Boolean} [rotation.static=false] Whether the rotation should be static or not.
	 * @property {Object} [rotation.center=The value of `position.value`] A THREE.Vector3 instance describing the center point of rotation.
	 * @property {Boolean} [rotation.randomise=false] When a particle is re-spawned, whether it's rotation should be re-randomised or not. Can incur a performance hit.
	 *
	 *
	 * @property {Object} [color={}] An object describing a particle's color. This property is a "value-over-lifetime" property, meaning an array of values and spreads can be
	 *                               given to describe specific value changes over a particle's lifetime.
	 *                               Depending on the value of SPE.valueOverLifetimeLength, if arrays of THREE.Color instances are given, then the array will be interpolated to
	 *                               have a length matching the value of SPE.valueOverLifetimeLength.
	 * @property {Object} [color.value=new THREE.Color()] Either a single THREE.Color instance, or an array of THREE.Color instances to describe the color of a particle over it's lifetime.
	 * @property {Object} [color.spread=new THREE.Vector3()] Either a single THREE.Vector3 instance, or an array of THREE.Vector3 instances to describe the color variance of a particle over it's lifetime.
	 * @property {Boolean} [color.randomise=false] When a particle is re-spawned, whether it's color should be re-randomised or not. Can incur a performance hit.
	 *
	 *
	 * @property {Object} [opacity={}] An object describing a particle's opacity. This property is a "value-over-lifetime" property, meaning an array of values and spreads can be
	 *                               given to describe specific value changes over a particle's lifetime.
	 *                               Depending on the value of SPE.valueOverLifetimeLength, if arrays of numbers are given, then the array will be interpolated to
	 *                               have a length matching the value of SPE.valueOverLifetimeLength.
	 * @property {Number} [opacity.value=1] Either a single number, or an array of numbers to describe the opacity of a particle over it's lifetime.
	 * @property {Number} [opacity.spread=0] Either a single number, or an array of numbers to describe the opacity variance of a particle over it's lifetime.
	 * @property {Boolean} [opacity.randomise=false] When a particle is re-spawned, whether it's opacity should be re-randomised or not. Can incur a performance hit.
	 *
	 *
	 * @property {Object} [size={}] An object describing a particle's size. This property is a "value-over-lifetime" property, meaning an array of values and spreads can be
	 *                               given to describe specific value changes over a particle's lifetime.
	 *                               Depending on the value of SPE.valueOverLifetimeLength, if arrays of numbers are given, then the array will be interpolated to
	 *                               have a length matching the value of SPE.valueOverLifetimeLength.
	 * @property {Number} [size.value=1] Either a single number, or an array of numbers to describe the size of a particle over it's lifetime.
	 * @property {Number} [size.spread=0] Either a single number, or an array of numbers to describe the size variance of a particle over it's lifetime.
	 * @property {Boolean} [size.randomise=false] When a particle is re-spawned, whether it's size should be re-randomised or not. Can incur a performance hit.
	 *
	 *
	 * @property {Object} [angle={}] An object describing a particle's angle. The angle is a 2d-rotation, measured in radians, applied to the particle's texture.
	 *                               NOTE: if a particle's texture is a sprite-sheet, this value IS IGNORED.
	 *                               This property is a "value-over-lifetime" property, meaning an array of values and spreads can be
	 *                               given to describe specific value changes over a particle's lifetime.
	 *                               Depending on the value of SPE.valueOverLifetimeLength, if arrays of numbers are given, then the array will be interpolated to
	 *                               have a length matching the value of SPE.valueOverLifetimeLength.
	 * @property {Number} [angle.value=0] Either a single number, or an array of numbers to describe the angle of a particle over it's lifetime.
	 * @property {Number} [angle.spread=0] Either a single number, or an array of numbers to describe the angle variance of a particle over it's lifetime.
	 * @property {Boolean} [angle.randomise=false] When a particle is re-spawned, whether it's angle should be re-randomised or not. Can incur a performance hit.
	 *
	 */

	/**
	 * The SPE.Emitter class.
	 *
	 * @constructor
	 *
	 * @param {EmitterOptions} options A map of options to configure the emitter.
	 */
	SPE.Emitter = function( options ) {
	    'use strict';

	    var utils = SPE.utils,
	        types = utils.types,
	        lifetimeLength = SPE.valueOverLifetimeLength;

	    // Ensure we have a map of options to play with,
	    // and that each option is in the correct format.
	    options = utils.ensureTypedArg( options, types.OBJECT, {} );
	    options.position = utils.ensureTypedArg( options.position, types.OBJECT, {} );
	    options.velocity = utils.ensureTypedArg( options.velocity, types.OBJECT, {} );
	    options.acceleration = utils.ensureTypedArg( options.acceleration, types.OBJECT, {} );
	    options.radius = utils.ensureTypedArg( options.radius, types.OBJECT, {} );
	    options.drag = utils.ensureTypedArg( options.drag, types.OBJECT, {} );
	    options.rotation = utils.ensureTypedArg( options.rotation, types.OBJECT, {} );
	    options.color = utils.ensureTypedArg( options.color, types.OBJECT, {} );
	    options.opacity = utils.ensureTypedArg( options.opacity, types.OBJECT, {} );
	    options.size = utils.ensureTypedArg( options.size, types.OBJECT, {} );
	    options.angle = utils.ensureTypedArg( options.angle, types.OBJECT, {} );
	    options.wiggle = utils.ensureTypedArg( options.wiggle, types.OBJECT, {} );
	    options.maxAge = utils.ensureTypedArg( options.maxAge, types.OBJECT, {} );

	    if ( options.onParticleSpawn ) {
	        console.warn( 'onParticleSpawn has been removed. Please set properties directly to alter values at runtime.' );
	    }

	    this.uuid = THREE.Math.generateUUID();

	    this.type = utils.ensureTypedArg( options.type, types.NUMBER, SPE.distributions.BOX );

	    // Start assigning properties...kicking it off with props that DON'T support values over
	    // lifetimes.
	    //
	    // Btw, values over lifetimes are just the new way of referring to *Start, *Middle, and *End.
	    this.position = {
	        _value: utils.ensureInstanceOf( options.position.value, THREE.Vector3, new THREE.Vector3() ),
	        _spread: utils.ensureInstanceOf( options.position.spread, THREE.Vector3, new THREE.Vector3() ),
	        _spreadClamp: utils.ensureInstanceOf( options.position.spreadClamp, THREE.Vector3, new THREE.Vector3() ),
	        _distribution: utils.ensureTypedArg( options.position.distribution, types.NUMBER, this.type ),
	        _randomise: utils.ensureTypedArg( options.position.randomise, types.BOOLEAN, false ),
	        _radius: utils.ensureTypedArg( options.position.radius, types.NUMBER, 10 ),
	        _radiusScale: utils.ensureInstanceOf( options.position.radiusScale, THREE.Vector3, new THREE.Vector3( 1, 1, 1 ) ),
	        _distributionClamp: utils.ensureTypedArg( options.position.distributionClamp, types.NUMBER, 0 ),
	    };

	    this.velocity = {
	        _value: utils.ensureInstanceOf( options.velocity.value, THREE.Vector3, new THREE.Vector3() ),
	        _spread: utils.ensureInstanceOf( options.velocity.spread, THREE.Vector3, new THREE.Vector3() ),
	        _distribution: utils.ensureTypedArg( options.velocity.distribution, types.NUMBER, this.type ),
	        _randomise: utils.ensureTypedArg( options.position.randomise, types.BOOLEAN, false )
	    };

	    this.acceleration = {
	        _value: utils.ensureInstanceOf( options.acceleration.value, THREE.Vector3, new THREE.Vector3() ),
	        _spread: utils.ensureInstanceOf( options.acceleration.spread, THREE.Vector3, new THREE.Vector3() ),
	        _distribution: utils.ensureTypedArg( options.acceleration.distribution, types.NUMBER, this.type ),
	        _randomise: utils.ensureTypedArg( options.position.randomise, types.BOOLEAN, false )
	    };

	    this.drag = {
	        _value: utils.ensureTypedArg( options.drag.value, types.NUMBER, 0 ),
	        _spread: utils.ensureTypedArg( options.drag.spread, types.NUMBER, 0 ),
	        _randomise: utils.ensureTypedArg( options.position.randomise, types.BOOLEAN, false )
	    };

	    this.wiggle = {
	        _value: utils.ensureTypedArg( options.wiggle.value, types.NUMBER, 0 ),
	        _spread: utils.ensureTypedArg( options.wiggle.spread, types.NUMBER, 0 )
	    };

	    this.rotation = {
	        _axis: utils.ensureInstanceOf( options.rotation.axis, THREE.Vector3, new THREE.Vector3( 0.0, 1.0, 0.0 ) ),
	        _axisSpread: utils.ensureInstanceOf( options.rotation.axisSpread, THREE.Vector3, new THREE.Vector3() ),
	        _angle: utils.ensureTypedArg( options.rotation.angle, types.NUMBER, 0 ),
	        _angleSpread: utils.ensureTypedArg( options.rotation.angleSpread, types.NUMBER, 0 ),
	        _static: utils.ensureTypedArg( options.rotation.static, types.BOOLEAN, false ),
	        _center: utils.ensureInstanceOf( options.rotation.center, THREE.Vector3, this.position._value.clone() ),
	        _randomise: utils.ensureTypedArg( options.position.randomise, types.BOOLEAN, false )
	    };


	    this.maxAge = {
	        _value: utils.ensureTypedArg( options.maxAge.value, types.NUMBER, 2 ),
	        _spread: utils.ensureTypedArg( options.maxAge.spread, types.NUMBER, 0 )
	    };



	    // The following properties can support either single values, or an array of values that change
	    // the property over a particle's lifetime (value over lifetime).
	    this.color = {
	        _value: utils.ensureArrayInstanceOf( options.color.value, THREE.Color, new THREE.Color() ),
	        _spread: utils.ensureArrayInstanceOf( options.color.spread, THREE.Vector3, new THREE.Vector3() ),
	        _randomise: utils.ensureTypedArg( options.position.randomise, types.BOOLEAN, false )
	    };

	    this.opacity = {
	        _value: utils.ensureArrayTypedArg( options.opacity.value, types.NUMBER, 1 ),
	        _spread: utils.ensureArrayTypedArg( options.opacity.spread, types.NUMBER, 0 ),
	        _randomise: utils.ensureTypedArg( options.position.randomise, types.BOOLEAN, false )
	    };

	    this.size = {
	        _value: utils.ensureArrayTypedArg( options.size.value, types.NUMBER, 1 ),
	        _spread: utils.ensureArrayTypedArg( options.size.spread, types.NUMBER, 0 ),
	        _randomise: utils.ensureTypedArg( options.position.randomise, types.BOOLEAN, false )
	    };

	    this.angle = {
	        _value: utils.ensureArrayTypedArg( options.angle.value, types.NUMBER, 0 ),
	        _spread: utils.ensureArrayTypedArg( options.angle.spread, types.NUMBER, 0 ),
	        _randomise: utils.ensureTypedArg( options.position.randomise, types.BOOLEAN, false )
	    };


	    // Assign renaining option values.
	    this.particleCount = utils.ensureTypedArg( options.particleCount, types.NUMBER, 100 );
	    this.duration = utils.ensureTypedArg( options.duration, types.NUMBER, null );
	    this.isStatic = utils.ensureTypedArg( options.isStatic, types.BOOLEAN, false );
	    this.activeMultiplier = utils.ensureTypedArg( options.activeMultiplier, types.NUMBER, 1 );
	    this.direction = utils.ensureTypedArg( options.direction, types.NUMBER, 1 );

	    // Whether this emitter is alive or not.
	    this.alive = utils.ensureTypedArg( options.alive, types.BOOLEAN, true );


	    // The following properties are set internally and are not
	    // user-controllable.
	    this.particlesPerSecond = 0;

	    // The current particle index for which particles should
	    // be marked as active on the next update cycle.
	    this.activationIndex = 0;

	    // The offset in the typed arrays this emitter's
	    // particle's values will start at
	    this.attributeOffset = 0;

	    // The end of the range in the attribute buffers
	    this.attributeEnd = 0;



	    // Holds the time the emitter has been alive for.
	    this.age = 0.0;

	    // Holds the number of currently-alive particles
	    this.activeParticleCount = 0.0;

	    // Holds a reference to this emitter's group once
	    // it's added to one.
	    this.group = null;

	    // Holds a reference to this emitter's group's attributes object
	    // for easier access.
	    this.attributes = null;

	    // Holds a reference to the params attribute's typed array
	    // for quicker access.
	    this.paramsArray = null;

	    // A set of flags to determine whether particular properties
	    // should be re-randomised when a particle is reset.
	    //
	    // If a `randomise` property is given, this is preferred.
	    // Otherwise, it looks at whether a spread value has been
	    // given.
	    //
	    // It allows randomization to be turned off as desired. If
	    // all randomization is turned off, then I'd expect a performance
	    // boost as no attribute buffers (excluding the `params`)
	    // would have to be re-passed to the GPU each frame (since nothing
	    // except the `params` attribute would have changed).
	    this.resetFlags = {
	        // params: utils.ensureTypedArg( options.maxAge.randomise, types.BOOLEAN, !!options.maxAge.spread ) ||
	        //     utils.ensureTypedArg( options.wiggle.randomise, types.BOOLEAN, !!options.wiggle.spread ),
	        position: utils.ensureTypedArg( options.position.randomise, types.BOOLEAN, false ) ||
	            utils.ensureTypedArg( options.radius.randomise, types.BOOLEAN, false ),
	        velocity: utils.ensureTypedArg( options.velocity.randomise, types.BOOLEAN, false ),
	        acceleration: utils.ensureTypedArg( options.acceleration.randomise, types.BOOLEAN, false ) ||
	            utils.ensureTypedArg( options.drag.randomise, types.BOOLEAN, false ),
	        rotation: utils.ensureTypedArg( options.rotation.randomise, types.BOOLEAN, false ),
	        rotationCenter: utils.ensureTypedArg( options.rotation.randomise, types.BOOLEAN, false ),
	        size: utils.ensureTypedArg( options.size.randomise, types.BOOLEAN, false ),
	        color: utils.ensureTypedArg( options.color.randomise, types.BOOLEAN, false ),
	        opacity: utils.ensureTypedArg( options.opacity.randomise, types.BOOLEAN, false ),
	        angle: utils.ensureTypedArg( options.angle.randomise, types.BOOLEAN, false )
	    };

	    this.updateFlags = {};
	    this.updateCounts = {};

	    // A map to indicate which emitter parameters should update
	    // which attribute.
	    this.updateMap = {
	        maxAge: 'params',
	        position: 'position',
	        velocity: 'velocity',
	        acceleration: 'acceleration',
	        drag: 'acceleration',
	        wiggle: 'params',
	        rotation: 'rotation',
	        size: 'size',
	        color: 'color',
	        opacity: 'opacity',
	        angle: 'angle'
	    };

	    for ( var i in this.updateMap ) {
	        if ( this.updateMap.hasOwnProperty( i ) ) {
	            this.updateCounts[ this.updateMap[ i ] ] = 0.0;
	            this.updateFlags[ this.updateMap[ i ] ] = false;
	            this._createGetterSetters( this[ i ], i );
	        }
	    }

	    this.bufferUpdateRanges = {};
	    this.attributeKeys = null;
	    this.attributeCount = 0;


	    // Ensure that the value-over-lifetime property objects above
	    // have value and spread properties that are of the same length.
	    //
	    // Also, for now, make sure they have a length of 3 (min/max arguments here).
	    utils.ensureValueOverLifetimeCompliance( this.color, lifetimeLength, lifetimeLength );
	    utils.ensureValueOverLifetimeCompliance( this.opacity, lifetimeLength, lifetimeLength );
	    utils.ensureValueOverLifetimeCompliance( this.size, lifetimeLength, lifetimeLength );
	    utils.ensureValueOverLifetimeCompliance( this.angle, lifetimeLength, lifetimeLength );
	};

	SPE.Emitter.constructor = SPE.Emitter;

	SPE.Emitter.prototype._createGetterSetters = function( propObj, propName ) {
	    'use strict';

	    var self = this;

	    for ( var i in propObj ) {
	        if ( propObj.hasOwnProperty( i ) ) {

	            var name = i.replace( '_', '' );

	            Object.defineProperty( propObj, name, {
	                get: ( function( prop ) {
	                    return function() {
	                        return this[ prop ];
	                    };
	                }( i ) ),

	                set: ( function( prop ) {
	                    return function( value ) {
	                        var mapName = self.updateMap[ propName ],
	                            prevValue = this[ prop ],
	                            length = SPE.valueOverLifetimeLength;

	                        if ( prop === '_rotationCenter' ) {
	                            self.updateFlags.rotationCenter = true;
	                            self.updateCounts.rotationCenter = 0.0;
	                        }
	                        else if ( prop === '_randomise' ) {
	                            self.resetFlags[ mapName ] = value;
	                        }
	                        else {
	                            self.updateFlags[ mapName ] = true;
	                            self.updateCounts[ mapName ] = 0.0;
	                        }

	                        self.group._updateDefines();

	                        this[ prop ] = value;

	                        // If the previous value was an array, then make
	                        // sure the provided value is interpolated correctly.
	                        if ( Array.isArray( prevValue ) ) {
	                            SPE.utils.ensureValueOverLifetimeCompliance( self[ propName ], length, length );
	                        }
	                    };
	                }( i ) )
	            } );
	        }
	    }
	};

	SPE.Emitter.prototype._setBufferUpdateRanges = function( keys ) {
	    'use strict';

	    this.attributeKeys = keys;
	    this.attributeCount = keys.length;

	    for ( var i = this.attributeCount - 1; i >= 0; --i ) {
	        this.bufferUpdateRanges[ keys[ i ] ] = {
	            min: Number.POSITIVE_INFINITY,
	            max: Number.NEGATIVE_INFINITY
	        };
	    }
	};

	SPE.Emitter.prototype._calculatePPSValue = function( groupMaxAge ) {
	    'use strict';

	    var particleCount = this.particleCount;


	    // Calculate the `particlesPerSecond` value for this emitter. It's used
	    // when determining which particles should die and which should live to
	    // see another day. Or be born, for that matter. The "God" property.
	    if ( this.duration ) {
	        this.particlesPerSecond = particleCount / ( groupMaxAge < this.duration ? groupMaxAge : this.duration );
	    }
	    else {
	        this.particlesPerSecond = particleCount / groupMaxAge;
	    }
	};

	SPE.Emitter.prototype._setAttributeOffset = function( startIndex ) {
	    this.attributeOffset = startIndex;
	    this.activationIndex = startIndex;
	    this.activationEnd = startIndex + this.particleCount;
	};


	SPE.Emitter.prototype._assignValue = function( prop, index ) {
	    'use strict';

	    switch ( prop ) {
	        case 'position':
	            this._assignPositionValue( index );
	            break;

	        case 'velocity':
	        case 'acceleration':
	            this._assignForceValue( index, prop );
	            break;

	        case 'size':
	        case 'opacity':
	            this._assignAbsLifetimeValue( index, prop );
	            break;

	        case 'angle':
	            this._assignAngleValue( index );
	            break;

	        case 'params':
	            this._assignParamsValue( index );
	            break;

	        case 'rotation':
	            this._assignRotationValue( index );
	            break;

	        case 'color':
	            this._assignColorValue( index );
	            break;
	    }
	};

	SPE.Emitter.prototype._assignPositionValue = function( index ) {
	    'use strict';

	    var distributions = SPE.distributions,
	        utils = SPE.utils,
	        prop = this.position,
	        attr = this.attributes.position,
	        value = prop._value,
	        spread = prop._spread,
	        distribution = prop._distribution;

	    switch ( distribution ) {
	        case distributions.BOX:
	            utils.randomVector3( attr, index, value, spread, prop._spreadClamp );
	            break;

	        case distributions.SPHERE:
	            utils.randomVector3OnSphere( attr, index, value, prop._radius, prop._spread.x, prop._radiusScale, prop._spreadClamp.x, prop._distributionClamp || this.particleCount );
	            break;

	        case distributions.DISC:
	            utils.randomVector3OnDisc( attr, index, value, prop._radius, prop._spread.x, prop._radiusScale, prop._spreadClamp.x );
	            break;

	        case distributions.LINE:
	            utils.randomVector3OnLine( attr, index, value, spread );
	            break;
	    }
	};

	SPE.Emitter.prototype._assignForceValue = function( index, attrName ) {
	    'use strict';

	    var distributions = SPE.distributions,
	        utils = SPE.utils,
	        prop = this[ attrName ],
	        value = prop._value,
	        spread = prop._spread,
	        distribution = prop._distribution,
	        pos,
	        positionX,
	        positionY,
	        positionZ,
	        i;

	    switch ( distribution ) {
	        case distributions.BOX:
	            utils.randomVector3( this.attributes[ attrName ], index, value, spread );
	            break;

	        case distributions.SPHERE:
	            pos = this.attributes.position.typedArray.array;
	            i = index * 3;

	            // Ensure position values aren't zero, otherwise no force will be
	            // applied.
	            // positionX = utils.zeroToEpsilon( pos[ i ], true );
	            // positionY = utils.zeroToEpsilon( pos[ i + 1 ], true );
	            // positionZ = utils.zeroToEpsilon( pos[ i + 2 ], true );
	            positionX = pos[ i ];
	            positionY = pos[ i + 1 ];
	            positionZ = pos[ i + 2 ];

	            utils.randomDirectionVector3OnSphere(
	                this.attributes[ attrName ], index,
	                positionX, positionY, positionZ,
	                this.position._value,
	                prop._value.x,
	                prop._spread.x
	            );
	            break;

	        case distributions.DISC:
	            pos = this.attributes.position.typedArray.array;
	            i = index * 3;

	            // Ensure position values aren't zero, otherwise no force will be
	            // applied.
	            // positionX = utils.zeroToEpsilon( pos[ i ], true );
	            // positionY = utils.zeroToEpsilon( pos[ i + 1 ], true );
	            // positionZ = utils.zeroToEpsilon( pos[ i + 2 ], true );
	            positionX = pos[ i ];
	            positionY = pos[ i + 1 ];
	            positionZ = pos[ i + 2 ];

	            utils.randomDirectionVector3OnDisc(
	                this.attributes[ attrName ], index,
	                positionX, positionY, positionZ,
	                this.position._value,
	                prop._value.x,
	                prop._spread.x
	            );
	            break;

	        case distributions.LINE:
	            utils.randomVector3OnLine( this.attributes[ attrName ], index, value, spread );
	            break;
	    }

	    if ( attrName === 'acceleration' ) {
	        var drag = utils.clamp( utils.randomFloat( this.drag._value, this.drag._spread ), 0, 1 );
	        this.attributes.acceleration.typedArray.array[ index * 4 + 3 ] = drag;
	    }
	};

	SPE.Emitter.prototype._assignAbsLifetimeValue = function( index, propName ) {
	    'use strict';

	    var array = this.attributes[ propName ].typedArray,
	        prop = this[ propName ],
	        utils = SPE.utils,
	        value;

	    if ( utils.arrayValuesAreEqual( prop._value ) && utils.arrayValuesAreEqual( prop._spread ) ) {
	        value = Math.abs( utils.randomFloat( prop._value[ 0 ], prop._spread[ 0 ] ) );
	        array.setVec4Components( index, value, value, value, value );
	    }
	    else {
	        array.setVec4Components( index,
	            Math.abs( utils.randomFloat( prop._value[ 0 ], prop._spread[ 0 ] ) ),
	            Math.abs( utils.randomFloat( prop._value[ 1 ], prop._spread[ 1 ] ) ),
	            Math.abs( utils.randomFloat( prop._value[ 2 ], prop._spread[ 2 ] ) ),
	            Math.abs( utils.randomFloat( prop._value[ 3 ], prop._spread[ 3 ] ) )
	        );
	    }
	};

	SPE.Emitter.prototype._assignAngleValue = function( index ) {
	    'use strict';

	    var array = this.attributes.angle.typedArray,
	        prop = this.angle,
	        utils = SPE.utils,
	        value;

	    if ( utils.arrayValuesAreEqual( prop._value ) && utils.arrayValuesAreEqual( prop._spread ) ) {
	        value = utils.randomFloat( prop._value[ 0 ], prop._spread[ 0 ] );
	        array.setVec4Components( index, value, value, value, value );
	    }
	    else {
	        array.setVec4Components( index,
	            utils.randomFloat( prop._value[ 0 ], prop._spread[ 0 ] ),
	            utils.randomFloat( prop._value[ 1 ], prop._spread[ 1 ] ),
	            utils.randomFloat( prop._value[ 2 ], prop._spread[ 2 ] ),
	            utils.randomFloat( prop._value[ 3 ], prop._spread[ 3 ] )
	        );
	    }
	};

	SPE.Emitter.prototype._assignParamsValue = function( index ) {
	    'use strict';

	    this.attributes.params.typedArray.setVec4Components( index,
	        this.isStatic ? 1 : 0,
	        0.0,
	        Math.abs( SPE.utils.randomFloat( this.maxAge._value, this.maxAge._spread ) ),
	        SPE.utils.randomFloat( this.wiggle._value, this.wiggle._spread )
	    );
	};

	SPE.Emitter.prototype._assignRotationValue = function( index ) {
	    'use strict';

	    this.attributes.rotation.typedArray.setVec3Components( index,
	        SPE.utils.getPackedRotationAxis( this.rotation._axis, this.rotation._axisSpread ),
	        SPE.utils.randomFloat( this.rotation._angle, this.rotation._angleSpread ),
	        this.rotation._static ? 0 : 1
	    );

	    this.attributes.rotationCenter.typedArray.setVec3( index, this.rotation._center );
	};

	SPE.Emitter.prototype._assignColorValue = function( index ) {
	    'use strict';
	    SPE.utils.randomColorAsHex( this.attributes.color, index, this.color._value, this.color._spread );
	};

	SPE.Emitter.prototype._resetParticle = function( index ) {
	    'use strict';

	    var resetFlags = this.resetFlags,
	        updateFlags = this.updateFlags,
	        updateCounts = this.updateCounts,
	        keys = this.attributeKeys,
	        key,
	        updateFlag;

	    for ( var i = this.attributeCount - 1; i >= 0; --i ) {
	        key = keys[ i ];
	        updateFlag = updateFlags[ key ];

	        if ( resetFlags[ key ] === true || updateFlag === true ) {
	            this._assignValue( key, index );
	            this._updateAttributeUpdateRange( key, index );

	            if ( updateFlag === true && updateCounts[ key ] === this.particleCount ) {
	                updateFlags[ key ] = false;
	                updateCounts[ key ] = 0.0;
	            }
	            else if ( updateFlag == true ) {
	                ++updateCounts[ key ];
	            }
	        }
	    }
	};

	SPE.Emitter.prototype._updateAttributeUpdateRange = function( attr, i ) {
	    'use strict';

	    var ranges = this.bufferUpdateRanges[ attr ];

	    ranges.min = Math.min( i, ranges.min );
	    ranges.max = Math.max( i, ranges.max );
	};

	SPE.Emitter.prototype._resetBufferRanges = function() {
	    'use strict';

	    var ranges = this.bufferUpdateRanges,
	        keys = this.bufferUpdateKeys,
	        i = this.bufferUpdateCount - 1,
	        key;

	    for ( i; i >= 0; --i ) {
	        key = keys[ i ];
	        ranges[ key ].min = Number.POSITIVE_INFINITY;
	        ranges[ key ].max = Number.NEGATIVE_INFINITY;
	    }
	};

	SPE.Emitter.prototype._onRemove = function() {
	    'use strict';
	    // Reset any properties of the emitter that were set by
	    // a group when it was added.
	    this.particlesPerSecond = 0;
	    this.attributeOffset = 0;
	    this.activationIndex = 0;
	    this.activeParticleCount = 0;
	    this.group = null;
	    this.attributes = null;
	    this.paramsArray = null;
	    this.age = 0.0;
	};

	SPE.Emitter.prototype._decrementParticleCount = function() {
	    'use strict';
	    --this.activeParticleCount;

	    // TODO:
	    //  - Trigger event if count === 0.
	};

	SPE.Emitter.prototype._incrementParticleCount = function() {
	    'use strict';
	    ++this.activeParticleCount;

	    // TODO:
	    //  - Trigger event if count === this.particleCount.
	};

	SPE.Emitter.prototype._checkParticleAges = function( start, end, params, dt ) {
	    'use strict';
	    for ( var i = end - 1, index, maxAge, age, alive; i >= start; --i ) {
	        index = i * 4;

	        alive = params[ index ];

	        if ( alive === 0.0 ) {
	            continue;
	        }

	        // Increment age
	        age = params[ index + 1 ];
	        maxAge = params[ index + 2 ];

	        if ( this.direction === 1 ) {
	            age += dt;

	            if ( age >= maxAge ) {
	                age = 0.0;
	                alive = 0.0;
	                this._decrementParticleCount();
	            }
	        }
	        else {
	            age -= dt;

	            if ( age <= 0.0 ) {
	                age = maxAge;
	                alive = 0.0;
	                this._decrementParticleCount();
	            }
	        }

	        params[ index ] = alive;
	        params[ index + 1 ] = age;

	        this._updateAttributeUpdateRange( 'params', i );
	    }
	};

	SPE.Emitter.prototype._activateParticles = function( activationStart, activationEnd, params, dtPerParticle ) {
	    'use strict';
	    var direction = this.direction;

	    for ( var i = activationStart, index, dtValue; i < activationEnd; ++i ) {
	        index = i * 4;

	        // Don't re-activate particles that aren't dead yet.
	        // if ( params[ index ] !== 0.0 && ( this.particleCount !== 1 || this.activeMultiplier !== 1 ) ) {
	        //     continue;
	        // }

	        if ( params[ index ] != 0.0 && this.particleCount !== 1 ) {
	            continue;
	        }

	        // Increment the active particle count.
	        this._incrementParticleCount();

	        // Mark the particle as alive.
	        params[ index ] = 1.0;

	        // Reset the particle
	        this._resetParticle( i );

	        // Move each particle being activated to
	        // it's actual position in time.
	        //
	        // This stops particles being 'clumped' together
	        // when frame rates are on the lower side of 60fps
	        // or not constant (a very real possibility!)
	        dtValue = dtPerParticle * ( i - activationStart )
	        params[ index + 1 ] = direction === -1 ? params[ index + 2 ] - dtValue : dtValue;

	        this._updateAttributeUpdateRange( 'params', i );
	    }
	};

	/**
	 * Simulates one frame's worth of particles, updating particles
	 * that are already alive, and marking ones that are currently dead
	 * but should be alive as alive.
	 *
	 * If the emitter is marked as static, then this function will do nothing.
	 *
	 * @param  {Number} dt The number of seconds to simulate (deltaTime)
	 */
	SPE.Emitter.prototype.tick = function( dt ) {
	    'use strict';

	    if ( this.isStatic ) {
	        return;
	    }

	    if ( this.paramsArray === null ) {
	        this.paramsArray = this.attributes.params.typedArray.array;
	    }

	    var start = this.attributeOffset,
	        end = start + this.particleCount,
	        params = this.paramsArray, // vec3( alive, age, maxAge, wiggle )
	        ppsDt = this.particlesPerSecond * this.activeMultiplier * dt,
	        activationIndex = this.activationIndex;

	    // Reset the buffer update indices.
	    this._resetBufferRanges();

	    // Increment age for those particles that are alive,
	    // and kill off any particles whose age is over the limit.
	    this._checkParticleAges( start, end, params, dt );

	    // If the emitter is dead, reset the age of the emitter to zero,
	    // ready to go again if required
	    if ( this.alive === false ) {
	        this.age = 0.0;
	        return;
	    }

	    // If the emitter has a specified lifetime and we've exceeded it,
	    // mark the emitter as dead.
	    if ( this.duration !== null && this.age > this.duration ) {
	        this.alive = false;
	        this.age = 0.0;
	        return;
	    }


	    var activationStart = this.particleCount === 1 ? activationIndex : ( activationIndex | 0 ),
	        activationEnd = Math.min( activationStart + ppsDt, this.activationEnd ),
	        activationCount = activationEnd - this.activationIndex | 0,
	        dtPerParticle = activationCount > 0 ? dt / activationCount : 0;

	    this._activateParticles( activationStart, activationEnd, params, dtPerParticle );

	    // Move the activation window forward, soldier.
	    this.activationIndex += ppsDt;

	    if ( this.activationIndex > end ) {
	        this.activationIndex = start;
	    }


	    // Increment the age of the emitter.
	    this.age += dt;
	};

	/**
	 * Resets all the emitter's particles to their start positions
	 * and marks the particles as dead if the `force` argument is
	 * true.
	 *
	 * @param  {Boolean} [force=undefined] If true, all particles will be marked as dead instantly.
	 * @return {Emitter}       This emitter instance.
	 */
	SPE.Emitter.prototype.reset = function( force ) {
	    'use strict';

	    this.age = 0.0;
	    this.alive = false;

	    if ( force === true ) {
	        var start = this.attributeOffset,
	            end = start + this.particleCount,
	            array = this.paramsArray,
	            attr = this.attributes.params.bufferAttribute;

	        for ( var i = end - 1, index; i >= start; --i ) {
	            index = i * 4;

	            array[ index ] = 0.0;
	            array[ index + 1 ] = 0.0;
	        }

	        attr.updateRange.offset = 0;
	        attr.updateRange.count = -1;
	        attr.needsUpdate = true;
	    }

	    return this;
	};

	/**
	 * Enables the emitter. If not already enabled, the emitter
	 * will start emitting particles.
	 *
	 * @return {Emitter} This emitter instance.
	 */
	SPE.Emitter.prototype.enable = function() {
	    'use strict';
	    this.alive = true;
	    return this;
	};

	/**
	 * Disables th emitter, but does not instantly remove it's
	 * particles fromt the scene. When called, the emitter will be
	 * 'switched off' and just stop emitting. Any particle's alive will
	 * be allowed to finish their lifecycle.
	 *
	 * @return {Emitter} This emitter instance.
	 */
	SPE.Emitter.prototype.disable = function() {
	    'use strict';

	    this.alive = false;
	    return this;
	};

	/**
	 * Remove this emitter from it's parent group (if it has been added to one).
	 * Delgates to SPE.group.prototype.removeEmitter().
	 *
	 * When called, all particle's belonging to this emitter will be instantly
	 * removed from the scene.
	 *
	 * @return {Emitter} This emitter instance.
	 *
	 * @see SPE.Group.prototype.removeEmitter
	 */
	SPE.Emitter.prototype.remove = function() {
	    'use strict';
	    if ( this.group !== null ) {
	        this.group.removeEmitter( this );
	    }
	    else {
	        console.error( 'Emitter does not belong to a group, cannot remove.' );
	    }

	    return this;
	};

/***/ })
/******/ ]);