Перегрузи метод paint() элемента
C++ (Qt)
void YourGraphicsItem::paint( QPainter* p, const QStyleOptionGraphicsItem* option, QWidget* w )
{
QMatrix wm = p->worldMatrix();
p->setWorldMatrix( QMatrix() );
QRectF rect( boundingRect() );
rect.moveTo( QPointF( wm.dx(), wm.dy() ) );
p->drawRect( rect );
p->setWorldMatrix( wm );
}