function copy(out, a) {
  out[0] = a[0];
  out[1] = a[1];
  out[2] = a[2];
  out[3] = a[3];
  return out;
}
Copy the values from one vec4 to another

@param {vec4} out the receiving vector
@param {vec4} a the source vector
@returns {vec4} out