With the following code (see QTBUG-81540 for the font), artifacts are visible on the text. Either removing the translation or adding in the 90 degree rotation fixes the issue. It can also be fixed by adding a scale. So it seems to only occur with translation matrices specifically for bitmap fonts.

        QFont bm("GohuNew", 28);
        QPainter p(this);

         p.translate(100, 100);
        //p.rotate(90);
        p.setFont(bm);
        p.drawText(QPointF(100, 100), "Foobar");