problem with pan zooming in QGraphicsView

hi friends,

I just implement the pan zooming of QGraphicsView by following this example in this forum

http://qtcenter.org/wiki/index.php?t...ng_and_Zooming


but this pan zooming was behaving different when i change the coordinates of the scene from (0, 0, 1000, 1000) to ( -500, -500, 1000, 1000)
i tried to identify where to correct but failed

Code:

---

QRectF visibleArea = mapToScene(rect()).boundingRect();
 
    //Get the scene area
    QRectF sceneBounds = sceneRect();
 
    double boundX = visibleArea.width() / 2.0;
    double boundY = visibleArea.height() / 2.0;
    double boundWidth = sceneBounds.width() - 2.0 * boundX;
    double 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)) {
        //We are within the bounds
        CurrentCenterPoint = centerPoint;
    } else {
        //We need to clamp or use the center of the screen
        if(visibleArea.contains(sceneBounds)) {
            //Use the center of scene ie. we can see the whole scene
            CurrentCenterPoint = sceneBounds.center();
        } else {
 
            CurrentCenterPoint = centerPoint;
 
            //We need to clamp the center. The centerPoint is too large
            if(centerPoint.x() > bounds.x() + bounds.width()) {
                CurrentCenterPoint.setX(bounds.x() + bounds.width());
            } else if(centerPoint.x() < bounds.x()) {
                CurrentCenterPoint.setX(bounds.x());
            }
 
            if(centerPoint.y() > bounds.y() + bounds.height()) {
                CurrentCenterPoint.setY(bounds.y() + bounds.height());
            } else if(centerPoint.y() < bounds.y()) {
                CurrentCenterPoint.setY(bounds.y());
            }
 
        }
    }
 
    //Update the scrollbars
    centerOn(CurrentCenterPoint);

---

is where they are centering the viewport but while zooming only positive half was visible and pan is not working

please help me