Qt5:在X11根屏幕上绘制(并更改现有QWidget的WId

#include <QtWidgets>

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

protected:
    void paintEvent(QPaintEvent *event) override {
        QPainter painter(this);
        painter.drawText(rect(), Qt::AlignCenter, "Hello, World!");
    }
};

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

    MainWindow window;
    window.show();

    // 获取根窗口的WId
    WId rootWId = QX11Info::appRootWindow();

    // 创建一个新的QWidget对象，并将其WId设置为根窗口的WId
    QWidget rootWidget;
    rootWidget.create((WId)rootWId);

    // 在根窗口上绘制
    QPainter painter(&rootWidget);
    painter.drawText(rootWidget.rect(), Qt::AlignCenter, "Hello, World!");

    return app.exec();
}