docs: function unproject (out, vec, viewport, invProjectionView) {
    var viewX = viewport[0],
      viewY = viewport[1],
      viewWidth = viewport[2],
      viewHeight = viewport[3]
  
    var x = vec[0],
      y = vec[1],
      z = vec[2]
  
    x = x - viewX
    y = viewHeight - y - 1
    y = y - viewY
  
    out[0] = (2 * x) / viewWidth - 1
    out[1] = (2 * y) / viewHeight - 1
    out[2] = 2 * z - 1
    return transform(out, out, invProjectionView)
  }