Нарисовать дугу в QGraphicsItem

Edge::Edge(Node *sourceNode, Node *destNode)
    : id(_idStatic++), arrowSize(15)
{
    setFlag(QGraphicsItem::ItemIsSelectable);
    source = sourceNode;
    dest = destNode;
    source->addEdge(this);
    if(source != dest)
        dest->addEdge(this);
    adjust();
}

QPolygonF Edge::nPolygonMath() const {
    QPolygonF nPolygon;
    if (source != dest) {
        QLineF line = QLineF(sourcePoint.x(), sourcePoint.y(), destPoint.x(), destPoint.y());
        qreal radAngle = line.angle() * M_PI / 180;
        qreal selectionOffset = 3;
        qreal dx = selectionOffset * sin(radAngle);
        qreal dy = selectionOffset * cos(radAngle);
        QPointF offset1 = QPointF(dx, dy);
        QPointF offset2 = QPointF(-dx, -dy);
        nPolygon << line.p1() + offset1
                 << line.p1() + offset2
                 << line.p2() + offset2
                 << line.p2() + offset1;
    } else {
        nPolygon << mapFromItem(source, -Node::Radius, -Node::Radius)
                 << mapFromItem(source, Node::Radius, -Node::Radius)
                 << mapFromItem(source, Node::Radius, Node::Radius)
                 << mapFromItem(source, -Node::Radius, Node::Radius);
    }
    return nPolygon;
}

QRectF Edge::boundingRect() const
{
    if (!source || !dest)
        return QRectF();

    return nPolygonMath().boundingRect();

}

QPainterPath Edge::shape() const{
    QPainterPath ret;
    ret.addPolygon(nPolygonMath());
    return ret;
}

void Edge::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *)
{
    if (!source || !dest)
        return;

    painter->setPen(QPen((option->state & QStyle::State_Selected ? Qt::cyan: Qt::black), 2, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));
    if (source != dest) {
        QLineF line(sourcePoint, destPoint);
        if (qFuzzyCompare(line.length(), qreal(0.)))
            return;

        // Draw the line itself
        painter->drawLine(line);

        // Draw the arrows
        double angle = std::atan2(-line.dy(), line.dx());

        QPointF destArrowP1 = destPoint + QPointF(sin(angle - M_PI / 1.8) * qMin(arrowSize, line.length()),
                                                  cos(angle - M_PI / 1.8) * qMin(arrowSize, line.length()));
        QPointF destArrowP2 = destPoint + QPointF(sin(angle - M_PI + M_PI / 1.8) * qMin(arrowSize, line.length()),
                                                  cos(angle - M_PI + M_PI / 1.8) * qMin(arrowSize, line.length()));

        painter->setBrush((option->state & QStyle::State_Selected ? Qt::cyan: Qt::black));
        painter->drawPolygon(QPolygonF() << line.p2() << destArrowP1 << destArrowP2);
    } else {
        painter->drawArc(mapFromItem(source, Node::Radius, 0).x(),
                         mapFromItem(source, Node::Radius, 0).y(),
                         2 * Node::Radius, 2 * Node::Radius, 16 * -90, 16 * 180);

    }
}