Generating large pdf files when using pen with zero width

QPdfWriter *writer = new QPdfWriter("c:/a.pdf");

QPainter *painter = new QPainter(writer);

QPen pen(QBrush(Qt::black), 0, Qt::DashLine);

painter->setPen(pen);

for (int i = 0; i < 1000; i++) 
{ 
     painter->drawLine(100, i, 500, i); 
}

delete painter;

delete writer;