QGraphicsView/QGraphicsScene rendering question

[onurozcelik]

I am using QGraphicsScene/QGraphicsView pair in my application. I had subclassed them for my purpose. The code snippet that generate the pair is below:

itsScene = new QGraphicsScene;
itsView = new QGraphicsView;
itsView->setParent(itsCanvas);
 
itsView->setGeometry(20,20,1700,720);
itsView->setBackgroundBrush(Qt::black);
itsView->setAlignment(Qt::AlignTop);
itsView->setScene(itsScene);

itsScene = new QGraphicsScene;
itsView = new QGraphicsView;
itsView->setParent(itsCanvas);

itsView->setGeometry(20,20,1700,720);
itsView->setBackgroundBrush(Qt::black);
itsView->setAlignment(Qt::AlignTop);
itsView->setScene(itsScene);

To copy to clipboard, switch view to plain text mode 

After adding some widgets into QGraphicsScene my application final UI snapshot is below:

Here my question is why there is some free space above the picture? What may cause this? I am using some negative coordinates for my widgets. Is it related with that?