Mouse operation and response

The sample code is as follows ：

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(" Mouse drawing ", image);
            imshow("ROI Area ", image(rec));
        }
        sp.x = -1;
        sp.y = -1;// When the left mouse button pops up , No more rectangles
    }
    else if (event == EVENT_MOUSEMOVE)
    {
        if (sp.x > 0 && sp.y > 0)// and 394,395 Code used together
        {
            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);// hold temp Copied to the image
                rectangle(image, rec, Scalar(255, 0, 0), 2, 8, 0);
                imshow(" Mouse drawing ", image);
            }
        }
    }
}
void demo::mouse_demo(Mat& image)
{
    namedWindow(" Mouse drawing ", WINDOW_AUTOSIZE);
    temp = image.clone();
    setMouseCallback(" Mouse drawing ", on_draw, (void*)(&image));
    
}

The difficulty here is setMouseCallback() function , The statement in highgui.hpp

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

1.window_name, The name of the window

2.on_Mouse, Each time a mouse event occurs in the specified window , Pointer to the called function .

      The prototype of this function is roughly in the form of  void XXX(int event, int x, int y, int flags, void* param) .

      among event yes EVENT_XXX Type data , Represents mouse operation events ：

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 and y Is the mouse pointer in the image coordinate system （ It's not a window coordinate system ） The coordinate values in ,

     flags yes  EVENT_FLAG_XXX Type data , It also represents mouse operation events

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 It's user-defined and passed to setMouseCallback The parameters of the function call .

3.userdata, User defined parameters passed to the callback function , Have default values 0. Pay attention to type conversion .

give the result as follows ：

 over!!!