Draw lines connecting two sub-windows of QMdiArea

[tom701]

Dear All,
I need GUI to show correspondences between points from two images (a computer vision task). But I have problem drawing lines to connect these corresponding points. The QMdiArea has QScrollArea as sub-windows. The problem is: part of the lines drawn is always underneath the QScrollArea (the sub-window). Please see the attached figure, and the code to draw is shown below. How can I draw the lines on top of the sub-windows of QMdiArea? Thank you for help!

Header:

class QMyMdiArea : public QMdiArea
{
    Q_OBJECT
public:
    explicit QMyMdiArea(QWidget *parent = 0);
    bool eventFilter(QObject *o, QEvent *e);
protected:
     void paintEvent(QPaintEvent*);
};

class QMyMdiArea : public QMdiArea
{
    Q_OBJECT
public:
    explicit QMyMdiArea(QWidget *parent = 0);
    bool eventFilter(QObject *o, QEvent *e);
protected:
     void paintEvent(QPaintEvent*);
};

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Implementation:

void QMyMdiArea::paintEvent(QPaintEvent* pe)
{
    QMdiArea::paintEvent(pe);
 
    QPainter p(this->viewport());
    p.setPen(Qt::red);
 
    QPointF pt1;
    QPointF pt2;
 
    p.drawLine(pt1, pt2);
}
 
bool QMyMdiArea::eventFilter(QObject *o, QEvent *e)
{
    if(qobject_cast<QMdiSubWindow*> (o)!=0 && e->type()==QEvent::Move)
       viewport()->update();
return false;
}

void QMyMdiArea::paintEvent(QPaintEvent* pe)
{
    QMdiArea::paintEvent(pe);

    QPainter p(this->viewport());
    p.setPen(Qt::red);

    QPointF pt1;
    QPointF pt2;

    p.drawLine(pt1, pt2);
}

bool QMyMdiArea::eventFilter(QObject *o, QEvent *e)
{
    if(qobject_cast<QMdiSubWindow*> (o)!=0 && e->type()==QEvent::Move)
       viewport()->update();
return false;
}

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[tbscope]

You could use a transparent top widget, but that will make using the widgets underneath it pretty difficult.

I personally would try using QGraphicsView.

[tom701]

Thank you very much for the suggestion! I tried to get the "Handle" to the desktop, and then draw on it, but it seems impossible in MS Widnows using QT. I am going to play with QGraphicsView which seems to be the only solution. Thanks a lot for help!