void Kreis::paintEvent(QPaintEvent *event)
{
    QPainter painter(ui.Circle);
    painter.setRenderHint(QPainter::Antialiasing);
    painter.setPen(QPen(QBrush(QColor::fromRgbF(0, 1, 0, 1)), 1));
    painter.drawEllipse(100, 100, -10, -10);
}