Qt 圆角矩形+鼠标左键拖动窗口

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

protected:
    void paintEvent(QPaintEvent *event);
    void mousePressEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);
    void mouseReleaseEvent(QMouseEvent *event);

private:
    Ui::MainWindow *ui;

    QPoint m_pos;
    bool m_drag;
};

#endif // MAINWINDOW_H

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <QPainter>
#include <QBitmap>
#include <QMouseEvent>

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent),
      ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    ui->menuBar->close();
    ui->mainToolBar->close();
    ui->statusBar->close();

    setFixedSize(400, 300);
    setWindowFlags(Qt::FramelessWindowHint);

    m_drag = false;
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::paintEvent(QPaintEvent *event)
{
    Q_UNUSED(event);
    QBitmap bitmap(this->size());
    QPainter painter(&bitmap);
    painter.fillRect(this->rect(), Qt::white);
    painter.setBrush(QColor(0, 0, 0));
    painter.setRenderHint(QPainter::Antialiasing);
    painter.setPen(QPen(Qt::blue, 1, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));
    painter.drawRoundedRect(this->rect(), 4, 4);
    this->setMask(bitmap);
}

void MainWindow::mousePressEvent(QMouseEvent *event)
{
    if (Qt::LeftButton == event->button()) {
        m_drag = true;
        m_pos = event->pos();
    }
}

void MainWindow::mouseMoveEvent(QMouseEvent *event)
{
    Q_UNUSED(event);

    if (m_drag) {
        this->move(event->globalPos() - m_pos);
    }
}

void MainWindow::mouseReleaseEvent(QMouseEvent *event)
{
    Q_UNUSED(event);
    m_drag = false;
}