hi, i use double buffer draw wave(not in the paintEvent fun), first i draw wave in a QPixmap, then i use update fun to invoke paintEvent fun draw QPixmap, because invoke update fun more first, so use CPU more, i see the qt helper, the update fun is use to update the widget, but now i do not want to update the widget, i only want update my drawed picture, so please help have any good methods to show the picture in screen. thanks.