QMainWindow透明背景

#include <QApplication>
#include <QMainWindow>
#include <QPainter>

class CMainWindow : public QMainWindow
{
public:
    CMainWindow(QWidget* parent = 0) : QMainWindow(parent)
    {
        setAutoFillBackground(false);
//        setWindowFlags(Qt::FramelessWindowHint);
        setAttribute(Qt::WA_TranslucentBackground, true);
    }

protected:
    void paintEvent(QPaintEvent*)
    {
        QPainter pt(this);
        QColor c(Qt::gray);
        c.setAlpha(100);
        pt.fillRect(rect(), c);
    }
};


int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    CMainWindow w;
    w.show();
    return a.exec();
}