鼠标操作和响应

示例代码如下：

Point sp(-1, -1);
Point st(-1, -1);
Mat temp;
static void on_draw(int event, int x, int y, int flags, void* userdata)
{
    Mat image = *((Mat*)userdata);
    if (event == EVENT_LBUTTONDOWN)
    {
        sp.x = x;
        sp.y = y;
        cout << sp << endl;
    }
    else if (event == EVENT_LBUTTONUP)
    {
        
        st.x = x - sp.x;
        st.y = y - sp.y;
        int x1 = st.x;
        int y1 = st.y;
        Rect rec(sp.x, sp.y, x1, y1);
        if (st.x > 0 && st.y > 0)
        {
            rectangle(image,rec, Scalar(255, 0, 0), 2, 8, 0);
            imshow("鼠标绘制", image);
            imshow("ROI区域", image(rec));
        }
        sp.x = -1;
        sp.y = -1;//鼠标左键弹起时，不再画矩形
    }
    else if (event == EVENT_MOUSEMOVE)
    {
        if (sp.x > 0 && sp.y > 0)//和394，395代码配合使用
        {
            st.x = x - sp.x;
            st.y = y - sp.y;
            int x1 = st.x;
            int y1 = st.y;
            Rect rec(sp.x, sp.y, x1, y1);
            if (st.x > 0 && st.y > 0)
            {
                temp.copyTo(image);//把temp复制到image
                rectangle(image, rec, Scalar(255, 0, 0), 2, 8, 0);
                imshow("鼠标绘制", image);
            }
        }
    }
}
void demo::mouse_demo(Mat& image)
{
    namedWindow("鼠标绘制", WINDOW_AUTOSIZE);
    temp = image.clone();
    setMouseCallback("鼠标绘制", on_draw, (void*)(&image));
    
}

这里的难点是setMouseCallback()函数，声明在highgui.hpp

CV_EXPORTS void setMouseCallback(const String& winname, MouseCallback onMouse, void* userdata = 0);

1.window_name，窗口的名字

2.on_Mouse，指定窗口里每次鼠标事件发生时，被调用的函数指针。

     这个函数的原型大概形式为 void XXX(int event, int x, int y, int flags, void* param) .

     其中 event 是 EVENT_XXX 类型数据，代表鼠标操作事件：

enum MouseEventTypes {
       EVENT_MOUSEMOVE      = 0, //!< indicates that the mouse pointer has moved over the window.
       EVENT_LBUTTONDOWN    = 1, //!< indicates that the left mouse button is pressed.
       EVENT_RBUTTONDOWN    = 2, //!< indicates that the right mouse button is pressed.
       EVENT_MBUTTONDOWN    = 3, //!< indicates that the middle mouse button is pressed.
       EVENT_LBUTTONUP      = 4, //!< indicates that left mouse button is released.
       EVENT_RBUTTONUP      = 5, //!< indicates that right mouse button is released.
       EVENT_MBUTTONUP      = 6, //!< indicates that middle mouse button is released.
       EVENT_LBUTTONDBLCLK  = 7, //!< indicates that left mouse button is double clicked.
       EVENT_RBUTTONDBLCLK  = 8, //!< indicates that right mouse button is double clicked.
       EVENT_MBUTTONDBLCLK  = 9, //!< indicates that middle mouse button is double clicked.
       EVENT_MOUSEWHEEL     = 10,//!< positive and negative values mean forward and backward scrolling, respectively.
       EVENT_MOUSEHWHEEL    = 11 //!< positive and negative values mean right and left scrolling, respectively.
     };

     x 和 y 是鼠标指针在图像坐标系（不是窗口坐标系）中的坐标值，

     flags 是 EVENT_FLAG_XXX 类型数据，也代表鼠标操作事件

enum MouseEventFlags {
       EVENT_FLAG_LBUTTON   = 1, //!< indicates that the left mouse button is down.
       EVENT_FLAG_RBUTTON   = 2, //!< indicates that the right mouse button is down.
       EVENT_FLAG_MBUTTON   = 4, //!< indicates that the middle mouse button is down.
       EVENT_FLAG_CTRLKEY   = 8, //!< indicates that CTRL Key is pressed.
       EVENT_FLAG_SHIFTKEY  = 16,//!< indicates that SHIFT Key is pressed.
       EVENT_FLAG_ALTKEY    = 32 //!< indicates that ALT Key is pressed.
     };

     param 是用户定义的传递到 setMouseCallback 函数调用的参数。

3.userdata，用户定义的传递到回调函数的参数，有默认值 0。注意类型转换。

结果如下：

 over!!!