在 Ubuntu 20.04 中我无法获取触摸点的面积

Question

在 Ubuntu 20.04 中无法获取触摸点面积，但在 Ubuntu 16.04 中可以获取触摸点面积；该怎么办？以前的方法如下：

bool GraphicsView::viewportEvent(QEvent *event){ QEvent::Type type = event->type();

if(type == QEvent::TouchBegin || type == QEvent::TouchUpdate
   || type == QEvent::TouchEnd){

    QTouchEvent *pTouchEvent = static_cast<QTouchEvent*>(event);
    QList<QTouchEvent::TouchPoint> touchPoints = pTouchEvent->touchPoints();

    int nId = 0;
    QColor penColor;

    foreach (const QTouchEvent::TouchPoint tp, touchPoints) {

        qDebug() << "id" << tp.id() << "触摸区域" << tp.ellipseDiameters() << "触摸点" << tp.pos();
    }
    return true;
}

return QGraphicsView::viewportEvent(event);

}