Qwt中鼠标获取坐标点

void getPoint(QwtPlot *plot)
{
      QPoint point = plot->canvas()->mapFromGlobal(QCursor::pos());   
      QString info.sprintf("x = %g, y = %g",
                     plot ->invTransFrom(Qwtplot::xBottom,point.x()),
                     plot ->invTransFrom(Qwtplot::yLeft,point.y() 
                      );   
}