function inverse(out, a) {
  out[0] = 1.0 / a[0]
  out[1] = 1.0 / a[1]
  out[2] = 1.0 / a[2]
  return out
}
Returns the inverse of the components of a vec3

@param {vec3} out the receiving vector
@param {vec3} a vector to invert
@returns {vec3} out