code: func ToBitmapBytes(bit C.MMBitmapRef) []byte {
  	var len C.size_t
  	ptr := C.saveMMBitmapAsBytes(bit, &len)
  	if int(len) < 0 {
  		return nil
  	}
  
  	bs := C.GoBytes(unsafe.Pointer(ptr), C.int(len))
  	C.free(unsafe.Pointer(ptr))
  	return bs
  }
docs: // ToBitmapBytes saves Bitmap to bitmap format in bytes