code: func (v *Pattern) AddColorStopRGBA(offset, red, green, blue, alpha float64) error {
  	C.cairo_pattern_add_color_stop_rgba(v.native(), C.double(offset),
  		C.double(red), C.double(green), C.double(blue), C.double(alpha))
  	return v.Status().ToError()
  }
docs: // AddColorStopRGBA is a wrapper around cairo_pattern_add_color_stop_rgba().