for (int x=-10, y=0;x<=0 && y>=-10;x++,  y--)
    {
        line->draw(painter, QLineF(0,0,x*10,y*10), pixel_size, Qt::red);
    }

    for (int x=0, y=-10;x<=10 && y<=0;x++,  y++)
    {
        line->draw(painter, QLineF(0,0,x*10,y*10), pixel_size, Qt::red);
    }

    for (int x=10, y=0;x>=0 && y<=10;x--,  y++)
    {
        line->draw(painter, QLineF(0,0,x*10,y*10), pixel_size, Qt::red);
    }

    for (int x=0, y=10;x>=-10 && y>=0;x--,  y--)
    {
        line->draw(painter, QLineF(0,0,x*10,y*10), pixel_size, Qt::red);
    }


    line->draw(painter, QLineF(-100,0,0,-100), pixel_size, Qt::red);
    line->draw(painter, QLineF(0,-100,100,0), pixel_size, Qt::red);
    line->draw(painter, QLineF(100,0,0,100), pixel_size, Qt::red);
    line->draw(painter, QLineF(0,100,-100,0), pixel_size, Qt::red);