Some pixels are missing when using drawPolygon() with a pen of size 1

On a pixmap, ::drawPolygon() with a pen of size 1 do not draw all pixels.

For example, drawing a line with drawPolygon() is not the same as drawing with drawLine().

Here is the test to reproduce the issue:

#include <QtTest/QtTest>
#include <QPainter>
#include <QPixmap>

class Test : public QObject{
Q_OBJECT

private slots:
void testLineSize_data()

{ QTest::addColumn<int>("penSize"); QTest::newRow("0") << 0; QTest::newRow("1") << 1; }

void testLineSize(){
QPixmap pixmap(20, 1);
pixmap.fill();
QPainter painter(&pixmap);

QPen pen(Qt::black);

QFETCH(int, penSize);
pen.setWidth(penSize);
painter.setPen(pen);

QPolygon polygon;
polygon.putPoints(0, 2, 2, 0, 17, 0);
painter.drawPolygon(polygon);
// painter.drawLine(2, 0, 17, 0); < drawLine is Ok
painter.end();

QImage image = pixmap.toImage();
int nb_pixels = 0;
for(int i=0; i<20; ++i)

{ QRgb pixel = image.pixel(i, 0); if(pixel != QColor(Qt::white).rgb()) ++nb_pixels; }

QCOMPARE(nb_pixels, 16);
}
};

QTEST_MAIN(Test)
#include "test.moc"