void BackgroundLayer::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget)
{
    painter->drawImage( QRectF(dx1, dy1, dx2-dx1, dy2-dy1), shownImage, QRectF(sx1, sy1, sx2-sx1, sy2-sy1) );
}

void ForegroundLayer::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget)
{
    QPen pen(Qt::red, 3, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin);
    painter->setPen(pen);
    painter->drawLine(p1, p2);
}

Rectangle {
    width: 1920
    height: 1080

    BackgroundLayer{
        id: background_layer
        anchors.fill: parent
    }

    ForegroundLayer {
        id: foreground_layer
        anchors.fill: parent
    }
}