QGraphicsScene, QGraphicsItem and QGraphicsView trouble

1)How can I make QGraphicsScene to start from top-left not from center? I tried to do this mathematically, but failed:

Code:

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QPoint temp( view->pos() ); // Coords pos in the window( qDialog )
        QPoint correct( view->rect().width() / 2, view->rect().height() / 2 );
        if( lineButClicked )
        {
 
            items.push_back( scene->addLine( QLine( // items - QVector of QGraphicItem
                  geom[index][0] - temp - correct, // geom - a matrix of QPoint
                  geom[index][1] - temp - correct   ), pen ) );
 
            items[index]->setFlag( QGraphicsItem::ItemIsMovable );
 
            index++; // just an int don't worry about it
            pointsNum = 0; // another int
        }

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2) I tried to separate different graphics items( f.e. lines, rects and ellipses ) in separate classes, but again failed. First I get an error while creating an instance of mygraphicsitem in qdialog class, because it says it's abstract. How can I manage to go through it? Second, I get a bunch of errors from qt libs somelike this: 'staticMetaObject' is not a member of QGraphicsItem, error: 'QScopedPointer<QObjectData> QObject::d_ptr' is protected QScopedPointer<QObjectData> d_ptr,
etc.
Here's my code for line:
lineitem.h

Code:

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#ifndef LINEITEM_H
#define LINEITEM_H
 
#include <QGraphicsItem>
#include <QPaintEvent>
#include <QPainter>
#include <QPen>
 
class LineItem : public QGraphicsItem
{
public:
    LineItem();
    QRectF boundingRect() const;
    void SetRect( QPoint p1, QPoint p2 );
    void paint( QPainter* painter, const QStyleOptionGraphicsItem *option, QWidget* widget );
 
private:
 
 
private:
    QPoint point1;
    QPoint point2;
 
    QPen pen;
 
};
 
#endif // LINEITEM_H

---

lineitem.cpp

Code:

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#include "lineitem.h"
 
LineItem::LineItem() : QGraphicsItem()
{
}
 
QRectF LineItem::boundingRect() const
{
    return QRectF( 0, 0, 10, 10 );
}
 
void LineItem::SetRect(QPoint p1, QPoint p2)
{
    point1 = p1;
    point2 = p2;
}
 
void LineItem::paint(QPainter *painter, const QStyleOptionGraphicsItem* option, QWidget *widget)
{
    painter->drawRect( QRect( point1, point2 ) );
}

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You can find hole project without QGraphicsItem classes, here https://github.com/Vyivrain/ProjectFiles if needed.