Draw line on image using QPainter

[Qt Coder]

I m using Qt 4.6.2 on windows xp

I need to draw horizontal ,vertical lines and an arc over the image .


My code is

#include <QtGui>
 
     QPixmap pixmap;
     QPainter painter;    
     QPen DarkGray((QColor::QColor(69,86,96)),1);
 
     pixmap.load(QString::fromUtf8(":/BiFold/Images/Plane.PNG"));
     painter.begin(&pixmap);
     painter.setPen(DarkGray);
     painter.drawLine(250,300,500,300);
     painter.end();
    ui->lbl_plane->setGeometry(QRect(100,150,611,301));
     ui->lbl_plane->setPixmap(pixmap);

#include <QtGui>

     QPixmap pixmap;
     QPainter painter;    
     QPen DarkGray((QColor::QColor(69,86,96)),1);
   
     pixmap.load(QString::fromUtf8(":/BiFold/Images/Plane.PNG"));
     painter.begin(&pixmap);
     painter.setPen(DarkGray);
     painter.drawLine(250,300,500,300);
     painter.end();
    ui->lbl_plane->setGeometry(QRect(100,150,611,301));
     ui->lbl_plane->setPixmap(pixmap);

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But only image is displayed ,no line is drawn....