gistfile1.txt

void paintEvent (QPaintEvent * event)
{
    qDebug()<<__PRETTY_FUNCTION__;
    QPainter p1(this);
    {
        QPainter p(this);
        p.setCompositionMode(QPainter::CompositionMode_Clear);
        p.fillRect(QRect(0,0,100,100),Qt::transparent);
    }
    p1.setCompositionMode(QPainter::CompositionMode_Clear);
    p1.fillRect(QRect(0,0,100,100),Qt::transparent);

}