struct MouseParam
{
    int m_WinWidth; //窗口大小
    int m_WinHeight;

    cv::String m_WinName;//窗口名称

    cv::Point m_RoiLeftUp; //Roi区域左上角在原图中的坐标，初始值为（0，0）
    cv::Mat m_Roi; //最终显示出来的Roi区域的图像矩阵

    cv::Mat m_Src; //原始图像

    cv::Point m_StartDrag;
    cv::Point m_EndDrag;
    bool m_Dragging;

    cv::Point m_PrevMouse;
};

void onMouse(int event, int x, int y, int flags, void* param)
{
    MouseParam * mp = (MouseParam*)param;

    cv::Point &prevMouse = mp->m_PrevMouse;
    int &roi_width = mp->m_WinWidth;
    int &roi_height = mp->m_WinHeight; // 可以根据自己的显示屏分辨率自行设置
    cv::Point &roi_lt = mp->m_RoiLeftUp; // roi区域左上角在原图中的坐标，初始值为（0，0）
    cv::Mat &roi = mp->m_Roi; // 最终显示出来的roi区域的图像矩阵
    
    cv::Point &startDrag = mp->m_StartDrag;
    cv::Point &endDrag = mp->m_EndDrag;
    bool &dragging = mp->m_Dragging;

    cv::Mat disp = mp->m_Src.clone();

    cv::String &winName = mp->m_WinName;

    if (event == cv::EVENT_LBUTTONDOWN)
    {// 如果鼠标左键按下，则为开始拖动，记录下拖动起始点，并将dragging标志位设为true
        startDrag = cv::Point(x, y);
        prevMouse = startDrag;
        dragging = true;
    }
    else if (event == cv::EVENT_LBUTTONUP)
    {// 如果鼠标左键松开，则为结束拖动，记录下拖动结束点，并将其与拖动起始点的差值加在roi_lt上，并将dragging标志位设为false
        //cv::Mat disp = (*(cv::Mat*)param).clone();
        endDrag = cv::Point(x, y);
        roi_lt += (startDrag - endDrag);
        // 判断拖动终点是否超出边界
        if (roi_lt.x < 0) roi_lt.x = 0;
        if (roi_lt.y < 0) roi_lt.y = 0;
        if (roi_lt.x > (disp.cols - roi_width)) roi_lt.x = disp.cols - roi_width;
        if (roi_lt.y > (disp.rows - roi_height))roi_lt.y = disp.rows - roi_height;
        dragging = false;
        // 在原图disp上裁剪出roi区域内的像素并显示
        cv::Rect roiRect(roi_lt.x, roi_lt.y, roi_width, roi_height);
        roi = disp(roiRect).clone();
        cv::imshow(winName, roi);
    }
    else if (event == cv::EVENT_MOUSEMOVE && dragging)
    {// 如果鼠标在按住左键的状态下移动，则一直更新画面
        //cv::Mat disp = (*(cv::Mat*)param).clone();
        cv::Point mousePos(x, y);
        roi_lt += (prevMouse - mousePos);
        if (roi_lt.x < 0) roi_lt.x = 0;
        if (roi_lt.y < 0) roi_lt.y = 0;
        if (roi_lt.x > (disp.cols - roi_width)) roi_lt.x = disp.cols - roi_width;
        if (roi_lt.y > (disp.rows - roi_height))roi_lt.y = disp.rows - roi_height;
        prevMouse = mousePos;
        cv::Rect roiRect(roi_lt.x, roi_lt.y, roi_width, roi_height);
        roi = disp(roiRect).clone();
        cv::imshow(winName, roi);
    }
}

void MatShow(const cv::String &winname,cv::Mat &mat)
{
    MouseParam * mp = new MouseParam;
    mp->m_WinWidth = 1000;
    mp->m_WinHeight= 800;
    mp->m_WinName = winname;
    mp->m_Src = mat.clone();

    cv::Rect roiRect(mp->m_RoiLeftUp.x, mp->m_RoiLeftUp.y, mp->m_WinWidth, mp->m_WinHeight);
    mp->m_Roi = mat(roiRect).clone(); // roi

    cv::namedWindow(winname);
    cv::resizeWindow(winname, cv::Size(mp->m_WinWidth, mp->m_WinHeight));
    cv::setMouseCallback(winname, onMouse, mp); // whole display image
    
    cv::imshow(winname, mp->m_Roi);
}