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and here is, how to get your image Mat into the callback function:

void CallBackFunc(int event, int x, int y, int flags, void* userdata) { Mat& image = ((Mat)userdata); // 1st cast, then deref. if (event == EVENT_LBUTTONDOWN) // or rather, buttonup ? { cout << "Left button of the mouse is clicked - position (" << x << ", " << y << ")" << endl; rectangle(img, ? ? ? ?); // your task ! } }

in main, pass your image to the callback:

setMouseCallback("Display window", CallBackFunc, &image);

and here is, how to get your image Mat into the callback function:

in main, pass (the address of) your image to the callback:

setMouseCallback("Display window", CallBackFunc, &image);

inside the callback function, unwrap it:

void CallBackFunc(int event, int x, int y, int flags, void* userdata)
{
    Mat& image = ((Mat)userdata); *((Mat*)userdata); // 1st cast, then deref.
    if (event == EVENT_LBUTTONDOWN) // or rather, buttonup ?
    {
        cout << "Left button of the mouse is clicked - position (" << x << ", " << y << ")" << endl;
        rectangle(img, ? ? ? ?); // your task !
    }
}
 
in main, pass your image to the callback:
 
setMouseCallback("Display window", CallBackFunc, &image);
 }

you should use the opencv headers like this:

#include "opencv2/core.hpp"  // forward slashes, please, and no subfolder
#include "opencv2/highgui.hpp"

you also need the imgproc header:

#include "opencv2/imgproc.hpp"

and here is, how to get your image Mat into the callback function:

in main, pass (the address of) your image to the callback:

setMouseCallback("Display window", CallBackFunc, &image);

inside the callback function, unwrap it:

void CallBackFunc(int event, int x, int y, int flags, void* userdata)
{
    Mat& image = *((Mat*)userdata); // 1st cast, then deref.
    if (event == EVENT_LBUTTONDOWN) // or rather, buttonup ?
    {
        cout << "Left button of the mouse is clicked - position (" << x << ", " << y << ")" << endl;
        rectangle(img, rectangle(image, ? ? ? ?); // your task !
    }
}

you should use the opencv headers like this:

#include "opencv2/core.hpp"  // forward slashes, please, and no subfolder
#include "opencv2/highgui.hpp"

you also need the imgproc header:

#include "opencv2/imgproc.hpp"

and here is, how to get your image Mat into the callback function:

in main, pass (the address of) your image to the callback:

setMouseCallback("Display window", CallBackFunc, &image);

inside the callback function, unwrap it:

void CallBackFunc(int event, int x, int y, int flags, void* userdata)
{
    Mat& image = *((Mat*)userdata); // 1st cast, then deref.
    if (event == EVENT_LBUTTONDOWN) // or rather, buttonup ?
    {
        cout << "Left button of the mouse is clicked - position (" << x << ", " << y << ")" << endl;
        rectangle(image, ? ? ? ?); // your task !
    }
}

you should use the opencv headers like this:

#include "opencv2/core.hpp"  // forward slashes, please, and no subfolder
#include "opencv2/highgui.hpp"

you also need the imgproc header:header (for any of the drawing calls):

#include "opencv2/imgproc.hpp"

and here is, how to get your image Mat into the callback function:

in main, pass (the address of) your image to the callback:

setMouseCallback("Display window", CallBackFunc, &image);

inside the callback function, unwrap it:

void CallBackFunc(int event, int x, int y, int flags, void* userdata)
{
    Mat& image = *((Mat*)userdata); // 1st cast, then deref.
    if (event == EVENT_LBUTTONDOWN) // or rather, buttonup ?
    {
        cout << "Left button of the mouse is clicked - position (" << x << ", " << y << ")" << endl;
        rectangle(image, ? ? ? ?); // your task !
        imshow("Display window", image); // update our image.

    }
}

you should use the opencv headers like this:

#include "opencv2/core.hpp"  // forward slashes, please, and no subfolder
#include "opencv2/highgui.hpp"

you also need the imgproc header (for any of the drawing calls):

#include "opencv2/imgproc.hpp"