如何在我的Qt窗口中创建一个“洞”？

#include <QtWidgets>

class HoleWidget : public QWidget {
public:
    HoleWidget(QWidget *parent = nullptr) : QWidget(parent) {}

protected:
    void paintEvent(QPaintEvent *event) override {
        QPainter painter(this);
        painter.setRenderHint(QPainter::Antialiasing);

        // 设置绘图模式为清空
        painter.setCompositionMode(QPainter::CompositionMode_Clear);

        // 绘制矩形形状的洞
        QRect holeRect(50, 50, 100, 100);
        painter.fillRect(holeRect, Qt::transparent);
        painter.drawRect(holeRect);

        // 恢复绘图模式为默认
        painter.setCompositionMode(QPainter::CompositionMode_SourceOver);
    }
};

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QWidget window;
    window.resize(400, 300);

    // 创建洞容器
    HoleWidget *holeWidget = new HoleWidget(&window);
    holeWidget->setGeometry(50, 50, 300, 200);

    window.show();
    return app.exec();
}