GL_UNPACK_ALIGNMENT cause drawText render corrupted image

class frmMainGLWnd: public  QOpenGLWidget{
...
}

void frmMainGLWnd::paintGL()
{


   glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
   QPainter painter(this);
   painter.setRenderHint(QPainter::Antialiasing);

   painter.save();

   QFont font = QApplication::font();
   font.setPixelSize(22);
   painter.setFont(font);
   painter.drawText(0,0,painter.window().width(),painter.window().height(),Qt::AlignCenter,
                                   tr("Qt by\nThe Qt Company"));
   painter.restore();
}