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want to select the coke cans boundaries using mouse clicks and crop them.

So need a solution to draw multiple polygons to select objects:

I am able to draw single polygon but not multiples. here is the code:

void mouseHandler(int event, int x, int y, int, void*)
{

    if (event == EVENT_LBUTTONDOWN && !drag)
    {
        if (flag1 == 0)
        {
            if (var == 0)
                img1 = img0.clone();
            point = Point(x, y);
            circle(img1, point, 2, Scalar(0, 0, 255), -1, 8, 0);
            pts[var] = point;
            var++;
            drag = 1;
            if (var>1)
                line(img1, pts[var - 2], point, Scalar(0, 0, 255), 2, 8, 0);

            imshow("Source", img1);
        }
    }

    if (event == EVENT_LBUTTONUP && drag)
    {
        imshow("Source", img1);

        drag = 0;
    }
    if (event == EVENT_RBUTTONDOWN)
    {
        flag1 = 1;
        img1 = img0.clone();
        for (int i = var; i < numpts; i++)
            pts[i] = point;

        if (var != 0)
        {
            const Point* pts3[1] = { &pts[0] };
            polylines(img1, pts3, &numpts, 1, 1, Scalar(0, 0, 0), 2, 8, 0);
        }

        for (int i = 0; i<var; i++)
        {
            minx = min(minx, pts[i].x);
            maxx = max(maxx, pts[i].x);
            miny = min(miny, pts[i].y);
            maxy = max(maxy, pts[i].y);
        }
        lenx = maxx - minx;
        leny = maxy - miny;

        imshow("Source", img1);
    }

    if (event == EVENT_RBUTTONUP)
    {
        flag = var;

        final = Mat::zeros(img0.size(), CV_8UC3);
        res1 = Mat::zeros(img0.size(), CV_8UC1);
        const Point* pts4[1] = { &pts[0] };

        fillPoly(res1, pts4, &numpts, 1, Scalar(255, 255, 255), 8, 0);
        bitwise_and(img0, img0, final, res1);
        imshow("mask", res1);
        imwrite("mask.png", res1);

        imshow("Source", img1);



    }
    if (event == EVENT_MBUTTONDOWN)
    {
        for (int i = 0; i < numpts; i++)
        {
            pts[i].x = 0;
            pts[i].y = 0;
        }
        var = 0;
        flag1 = 0;
        minx = INT_MAX; miny = INT_MAX; maxx = INT_MIN; maxy = INT_MIN;
        imshow("Source", img0);
        drag = 0;
    }
}

int main()
{

    Mat src = imread("coke.jpg");

    minx = INT_MAX; miny = INT_MAX; maxx = INT_MIN; maxy = INT_MIN;

    img0 = src;

    channel = img0.channels();

    res1 = Mat::zeros(img0.size(), CV_8UC1);
    final = Mat::zeros(img0.size(), CV_8UC3);
    //////////// source image ///////////////////

    namedWindow("Source", 1);
    setMouseCallback("Source", mouseHandler, NULL);
    imshow("Source", img0);
    //imshow("mask", res1);
    waitKey(0);
    namedWindow("Source", 1);
    setMouseCallback("Source", mouseHandler, NULL);
    imshow("Source", img0);
    waitKey(0);

    img0.release();
    img1.release();
}