这是一个简单的类,绘制一个圆形半透明窗口,红色背景50％alpha.

TranslucentRoundWindow.h：

#include <QWidget>

class TranslucentRoundWindow : public QWidget
{
    public:
        TranslucentRoundWindow(QWidget *parent = 0);
        virtual QSize sizeHint() const;

    protected:
        virtual void paintEvent(QPaintEvent *paintEvent);
};

TranslucentRoundWindow.cpp：

#include <QtGui>

#include "TranslucentRoundWindow.h"

TranslucentRoundWindow::TranslucentRoundWindow(QWidget *parent) : QWidget(parent,Qt::FramelessWindowHint)
{
    setAttribute(Qt::WA_TranslucentBackground);
}

QSize TranslucentRoundWindow::sizeHint() const
{
    return QSize(300,300);
}

void TranslucentRoundWindow::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing);
    painter.setPen(Qt::NoPen);
    painter.setBrush(QColor(255,127));

    painter.drawEllipse(0,width(),height());
}

如果您想要使用鼠标移动此窗口,则必须覆盖mousePressEvent,mouseMoveEvent和mouseReleaseEvent.