QChart 如何放大缩小？

#if 0 //QChart 放大缩小
    double z = 1.0;
    QPoint numDegrees = e->angleDelta()/8;
    double zi = qAbs(0.1*numDegrees.ry()/15);
    if(e->angleDelta().y()>0){
        z -= zi;
    }else{
        z += zi;
    }
    m_chart->zoom(z);
#endif