coffeescript 时空穿梭

html {
  background: #000;
}

canvas {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}

'use strict'

Math.DEG = 180 / Math.PI
Math.RAD = Math.PI / 180
Math.TAU = Math.PI * 2
Math.PHI = 0.5 + 0.5 * Math.sqrt 5

LorenzAttractor = (σ, ρ, β) ->
  (v, t) ->
    [ x, y, z ] = v
    v[0] += t * (σ*(y-x))
    v[1] += t * (x*(ρ-z)-y)
    v[2] += t * (x*y-β*z)

@addEventListener 'load', ->

  lorenz  = LorenzAttractor 10, 28, 8/3
  canvas  = document.createElement 'canvas'
  context = canvas.getContext '2d'
  document.body.appendChild canvas

  model      = mat4.create()
  view       = mat4.create()
  projection = mat4.create()
  mvp        = mat4.create()

  v = vec4.fromValues 1, 0, 0, 1
  u = vec4.create()
  p = vec4.create()

  do render = ->
    requestAnimationFrame render

    T = 1e-3 * Date.now()
    W = canvas.clientWidth
    H = canvas.clientHeight

    if W isnt canvas.width or H isnt canvas.height
      canvas.width  = W
      canvas.height = H
      context.globalCompositeOperation = 'screen'
      context.strokeStyle = 'rgb(30,15,80)'

    mat4.identity model
    mat4.rotateY model, model, 0.05 * T
    mat4.rotateX model, model, 1.89 * Math.PI
    mat4.rotateZ model, model, 1.66 * Math.PI
    mat4.translate model, model, [0, 0, -27]
    mat4.lookAt view, [0, 3, 25], [0, -2, 0], [0, 1, 0]
    mat4.perspective projection, 45 * Math.RAD, W/H, 1e-3, 1e3
    mat4.scale projection, projection, [HW = W/2, HH = H/2, 1]
    [ model, view, projection ].reduce (a, b) -> mat4.mul mvp, b, a

    context.setTransform 1, 0, 0, -1, HW, HH
    for i in [0...100e3]
      vec3.copy u, v if i is 1e2
      lorenz v, 5e-3
      vec4.transformMat4 p, v, mvp
      vec3.scale p, p, 1/p[3]
      [ x, y, z ] = p
      if -1<z<1 and -HH<y<HH and -HW<x<HW
        if outside
          outside = no
          context.moveTo lastX, lastY
        context.lineTo x, y
      else
        if not outside
          outside = yes
          context.lineTo x, y
        lastX = x
        lastY = y
    vec3.copy v, u

    context.setTransform 1, 0, 0, 1, 0, 0
    context.clearRect 0, 0, W, H
    context.stroke()
    context.beginPath()