如何在qt中绘制带有彩色边角的透明矩形？

#include <QtWidgets>

class CustomWidget : public QWidget {
public:
    CustomWidget(QWidget* parent = nullptr) : QWidget(parent) {
        setAttribute(Qt::WA_TranslucentBackground); // 设置背景透明
    }

protected:
    void paintEvent(QPaintEvent* event) override {
        Q_UNUSED(event);

        QPainter painter(this);
        painter.setRenderHint(QPainter::Antialiasing); // 抗锯齿

        // 绘制透明矩形
        painter.setBrush(QBrush(QColor(0, 0, 0, 100))); // 设置透明度为100
        painter.drawRect(rect());

        // 绘制彩色边角
        QPainterPath path;
        path.moveTo(rect().topLeft());
        path.lineTo(rect().topRight());
        path.lineTo(rect().bottomRight());
        path.lineTo(rect().bottomLeft());
        path.closeSubpath();

        painter.setClipPath(path); // 限制绘制区域在路径内

        QPolygonF polygon;
        polygon << QPointF(rect().topLeft() + QPointF(10, 10))
                << QPointF(rect().topLeft() + QPointF(50, 10))
                << QPointF(rect().topLeft() + QPointF(10, 50));

        painter.setBrush(QBrush(Qt::red)); // 设置边角颜色为红色
        painter.drawPolygon(polygon);
    }
};

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

    CustomWidget widget;
    widget.resize(400, 300);
    widget.show();

    return app.exec();
}