pan view of QGraphicsView

hi friends,

Please help me to get the basic method of showing the panview of QGraphicsView

on following the the forum code .
http://qtcenter.org/wiki/index.php?t...ng_and_Zooming
Code:
{
    QBrush m_background_brush;
    m_background_brush.setStyle(Qt::SolidPattern);
    m_background_brush.setColor(QColor(3, 24, 39));
    Scene->setBackgroundBrush(m_background_brush);
 
 
    //Set-up the view
    setSceneRect(-500, -500, 1000, 1000);
}
 
void MyGraphicsView::SetCenter(const QPointF& centerPoint) {
    //Get the rectangle of the visible area in scene coords
    QRectF visibleArea = mapToScene(rect()).boundingRect();
 
    //Get the scene area
    QRectF sceneBounds = sceneRect();
    double boundX, boundY, boundWidth, boundHeight;
 
    if(centerPoint.x() >= 0)
    {
        boundX = visibleArea.width() / 2.0;
        boundY = visibleArea.height() / 2.0;
        boundWidth = (sceneBounds.width() - 2.0 * boundX);
        boundHeight = (sceneBounds.height() - 2.0 * boundY);
    } else
    {
        boundX = visibleArea.width() / 2.0;
        boundY = visibleArea.height() / 2.0;
        boundWidth = (sceneBounds.width() + 2.0 * boundX);
        boundHeight = (sceneBounds.height() + 2.0 * boundY);
    }
 
    //The max boundary that the centerPoint can be to
    QRectF bounds(boundX, boundY, boundWidth, boundHeight);
 
    if(bounds.contains(centerPoint)) {
 
        CurrentCenterPoint = centerPoint;
    } else {
 
        if(visibleArea.contains(sceneBounds)) {
 
            CurrentCenterPoint = sceneBounds.center();
        } else {
 
            CurrentCenterPoint = centerPoint;
 
 
            if(centerPoint.x() > bounds.x() + bounds.width()) {
                qDebug()<<"The Clamping on the min X"<<bounds <<" and the clamp:"<< centerPoint;
                CurrentCenterPoint.setX(bounds.x() + bounds.width());
            } else if(centerPoint.x() < bounds.x()) {
                CurrentCenterPoint.setX(bounds.x() );
            }
 
            if(centerPoint.y() > bounds.y() + bounds.height()) {
                qDebug()<<"The Clamping on the min Y";
                CurrentCenterPoint.setY(bounds.y() + bounds.height());
            } else if(centerPoint.y() < bounds.y()) {
                CurrentCenterPoint.setY(bounds.y() );
            }
 
        }
    }
 
    qDebug() <<"Update the scrollbars:" << CurrentCenterPoint;
    centerOn(CurrentCenterPoint);
}
 
 
  */
void MyGraphicsView::mousePressEvent(QMouseEvent* event) {
    //For panning the view
    LastPanPoint = event->pos();
    setCursor(Qt::ClosedHandCursor);
}
 
/**
  * Handles when the mouse button is released
  */
void MyGraphicsView::mouseReleaseEvent(QMouseEvent* event) {
    setCursor(Qt::OpenHandCursor);
    LastPanPoint = QPoint();
}
 
/**
*Handles the mouse move event
*/
void MyGraphicsView::mouseMoveEvent(QMouseEvent* event) {
    if(!LastPanPoint.isNull()) {
        //Get how much we panned
        QPointF delta = mapToScene(LastPanPoint) - mapToScene(event->pos());
        qDebug()<<"The Wheel Delta value:"<< delta;
        LastPanPoint = event->pos();
 
        //Update the center ie. do the pan
        if(delta.x() < 0 )
        {
            SetCenter(GetCenter() - delta);
        } else
            SetCenter(GetCenter() + delta);
    }
}
 
/**
  * Zoom the view in and out.
  */
void MyGraphicsView::wheelEvent(QWheelEvent* event) {
 
    //Get the position of the mouse before scaling, in scene coords
    QPointF pointBeforeScale(mapToScene(event->pos()));
 
    //Get the original screen centerpoint
    QPointF screenCenter = GetCenter(); //CurrentCenterPoint; //(visRect.center());
 
    //Scale the view ie. do the zoom
    double scaleFactor = 1.15; //How fast we zoom
    if(event->delta() > 0) {
        //Zoom in
        scale(scaleFactor, scaleFactor);
    } else {
        //Zooming out
        scale(1.0 / scaleFactor, 1.0 / scaleFactor);
    }
 
    //Get the position after scaling, in scene coords
    QPointF pointAfterScale(mapToScene(event->pos()));
 
    //Get the offset of how the screen moved
    QPointF offset = pointBeforeScale - pointAfterScale;
 
    //Adjust to the new center for correct zooming
    QPointF newCenter = screenCenter + offset;
    SetCenter(newCenter);
}
 
void MyGraphicsView::resizeEvent(QResizeEvent* event) {
    QRectF visibleArea = mapToScene(rect()).boundingRect();
    SetCenter(visibleArea.center());
 
    //Call the subclass resize so the scrollbars are updated correctly
    QGraphicsView::resizeEvent(event);
}
but this code pans only on the positive direction of the zoom area ..

.. if i set the sceneRect to (0, 0, 1000, 1000) panning view was clear and perfect ..
please help me to solve this problem ..

Thnks in advance ..