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;
}