There is a border when painting two adjacent QPolygonF

#include <QtGui>

class Widget : public QWidget {
public:
    Widget() {
        resize(750, 500);
    }
    void paintEvent(QPaintEvent* e) {

        QWidget::paintEvent(e);
        QPixmap pix(750, 500);
        QPainter painter(&pix);

        painter.setPen(Qt::NoPen);

        painter.setBrush(Qt::white);
        painter.drawRect(0, 0, 750, 500);

        QPolygonF array;
        painter.setBrush(Qt::black);
        float height = 5.049f;
        for(float x = 0; x < 750; x += 11) {
            for(float y = 0; y < 500; y += height) {
                array.clear();
                array << QPointF(x, y);
                array << QPointF(x + 10, y);
                array << QPointF(x + 10, y + height);
                array << QPointF(x, y + height);
                painter.drawPolygon(array);
            }
            height += 0.0013f;
        }

        painter.end();

        QPainter painter2(this);
        painter2.drawPixmap(0, 0, pix);

    }

};

int main( int argc, char ** argv )
{
    QApplication a( argc, argv );

    Widget win;;
    win.show();

    return a.exec();
}