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###
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  Particle system wrapper/helper
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  @class bkcore.threejs.Particles
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  @author Thibaut 'BKcore' Despoulain <http://bkcore.com>
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###
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class Particles
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  ###
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    Creates a new particle system using given parameters
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    @param {Object{max, spawnRate, spawn, velocity, randomness,
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    force, spawnRadius, life, friction, color, color2, tint,
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    texture, size, blending, depthTest, transparent, opacity}} opts
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  ###
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  constructor: (opts)->
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    @black = new THREE.Color(0x000000)
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    @white = new THREE.Color(0xffffff)
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    @material = new THREE.ParticleBasicMaterial(
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      color: opts.tint ? 0xffffff
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      map: opts.texture ? null
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      size: opts.size ? 4
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      blending: opts.blending ? THREE.AdditiveBlending
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      depthTest: opts.depthTest ? false
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      transparent: opts.transparent ? true
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      vertexColors: true
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      opacity: opts.opacity ? 1.0
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      sizeAttenuation: true
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    )
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    @max = opts.max ? 1000
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    @spawnRate = opts.spawnRate ? 0
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    @spawn = opts.spawn ? new THREE.Vector3()
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    @velocity = opts.velocity ? new THREE.Vector3()
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    @randomness = opts.randomness ? new THREE.Vector3()
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    @force = opts.force ? new THREE.Vector3()
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    @spawnRadius = opts.spawnRadius ? new THREE.Vector3()
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    @life = opts.life ? 60
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    @ageing = 1 / @life
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    @friction = opts.friction ? 1.0
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    @color = new THREE.Color(opts.color ? 0xffffff)
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    @color2 = if opts.color2? then new THREE.Color(opts.color2) else null
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    @position = opts.position ? new THREE.Vector3()
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    @rotation = opts.rotation ? new THREE.Vector3()
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    @sort = opts.sort ? false
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    @pool = []
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    @buffer = []
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    @geometry = null
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    @system = null
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    @build()
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  ###
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    Emits given number of particles
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    @param  int count
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  ###
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  emit: (count)->
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    emitable = Math.min(count, @pool.length)
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    for i in [0..emitable]
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      p = @pool.pop()
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      p.available = false
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      p.position.copy(@spawn).addSelf(
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        @randomVector().multiplySelf(@spawnRadius)
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      )
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      p.velocity.copy(@velocity).addSelf(
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        @randomVector().multiplySelf(@randomness)
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      )
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      p.force.copy(@force)
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      p.basecolor.copy(@color)
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      if @color2?
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        p.basecolor.lerpSelf(@color2, Math.random())
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      p.life = 1.0
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  ###
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    @private
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  ###
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  build: ()->
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    @geometry = new THREE.Geometry()
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    @geometry.dynamic = true
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    @pool = []
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    @buffer = []
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    for i in [0..@max]
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      p = new bkcore.threejs.Particle()
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      @pool.push(p)
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      @buffer.push(p)
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      @geometry.vertices.push(p.position)
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      @geometry.colors.push(p.color)
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    @system = new THREE.ParticleSystem(@geometry, @material)
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    @system.position = @position
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    @system.rotation = @rotation
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    @system.sort = @sort
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  ###
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    @private
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  ###
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  randomVector: ()->
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    return new THREE.Vector3(
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      Math.random()*2-1,
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      Math.random()*2-1,
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      Math.random()*2-1
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    )
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  ###
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    Updates particles (should be call in a RAF loop)
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    @param  float dt time delta ~1.0
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  ###
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  update: (dt)->
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    df = new THREE.Vector3()
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    dv = new THREE.Vector3()
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    for i in [0..@buffer.length]
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      p = @buffer[i]
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      continue if p.available
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      p.life -= @ageing
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      if p.life <= 0
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        p.reset()
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        @pool.push(p)
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        continue
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      l = if p.life > 0.5 then 1.0 else p.life + 0.5
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      p.color.setRGB(
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        l * p.basecolor.r,
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        l * p.basecolor.g,
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        l * p.basecolor.b
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      )
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      if @friction != 1.0
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        p.velocity.multiplyScalar(@friction)
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      df.copy(p.force).multiplyScalar(dt)
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      p.velocity.addSelf(df)
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      dv.copy(p.velocity).multiplyScalar(dt)
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      p.position.addSelf(dv)
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    if @spawnRate > 0
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      @emit(@spawnRate)
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    @geometry.verticesNeedUpdate = true
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    @geometry.colorsNeedUpdate = true
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###
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  Particle sub class
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  @class bkcore.threejs.Particle
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  @author Thibaut 'BKcore' Despoulain <http://bkcore.com>
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###
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class Particle
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  constructor: ()->
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    @position = new THREE.Vector3(-10000,-10000,-10000)
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    @velocity = new THREE.Vector3()
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    @force = new THREE.Vector3()
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    @color = new THREE.Color(0x000000)
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    @basecolor = new THREE.Color(0x000000)
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    @life = 0.0
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    @available = true
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  reset: ()->
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    @position.set(0,-100000,0)
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    @velocity.set(0,0,0)
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    @force.set(0,0,0)
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    @color.setRGB(0,0,0)
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    @basecolor.setRGB(0,0,0)
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    @life = 0.0
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    @available = true
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###
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  Exports
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  @package bkcore.threejs
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###
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exports = exports ? @
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exports.bkcore ||= {}
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exports.bkcore.threejs ||= {}
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exports.bkcore.threejs.Particle = Particle
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exports.bkcore.threejs.Particles = Particles
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