参考https://www.cnblogs.com/itrena/p/5938341.html

    QRectF rect = event->rect();
    QPainterPath path;

    path.moveTo(rect.center());
    path.arcTo(rect, 90, 120);

    int arcHeight = 50;
    QPainterPath subPath;
    subPath.addEllipse(rect.adjusted(arcHeight, arcHeight, -arcHeight, -arcHeight));

    // path为扇形 subPath为椭圆
    path -= subPath;

   QBrush brush = painter.brush();
   brush.setColor(QColor("#ff00ff"));
   painter.setBrush(brush);
//    painter->setPen(Qt::NoPen);
    painter.drawPath(path);

    painter.fillPath(path, QColor("#ff00ff") );