code: func SetData(pointer uintptr, atom gdk.Atom, data []byte) {
  	c := (*C.GValue)(unsafe.Pointer(pointer))
  	p := (*C.GtkSelectionData)(unsafe.Pointer(c))
  	C.gtk_selection_data_set(p, C.GdkAtom(unsafe.Pointer(atom)), C.gint(8), (*C.guchar)(unsafe.Pointer(&data[0])), C.gint(len(data)))
  }
docs: //for "drag-data-get"