Как нарисовать половину эллипса с вырезом в QPainter?

#include <QApplication>
#include <QWidget>
#include <QPainter>
#include <QtMath>
class Window: public QWidget
{
  void paintEvent(QPaintEvent *)
  {
    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing, true);
    QPen pen(Qt::black, 10, Qt::SolidLine, Qt::RoundCap);
    painter.setPen(pen);
    const int max = qMin(width(), height());
    const int margin = max/40;
    const int alpha = 75*16;
    const int radius = max/2 - margin;
    const int a = radius * qSin(qDegreesToRadians(alpha/16.0));
    const int b = radius * qCos(qDegreesToRadians(alpha/16.0));
    const QRect rect(margin, margin, radius*2-margin, radius*2-margin);
    painter.drawArc(rect,  90*16,  alpha);
    painter.drawArc(rect, 270*16, -alpha);
    const QPoint points[4] = {
      QPoint(radius-a+margin, radius-b+margin/2),
      QPoint(radius-a+margin+max/4, radius-b+margin/2),
      QPoint(radius-a+margin+max/4, max-radius+b-1.5*margin),
      QPoint(radius-a+margin, max-radius+b-1.5*margin)
    };
    painter.drawPolyline(points, 4);
    painter.drawLine(radius+margin/2, margin, radius+margin/2, radius*2);
  }
};
int main(int argc, char** argv)
{
  QApplication app(argc, argv);
  Window window;
  window.show();
  return app.exec();
}