OPENCV POLYLINE

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how to draw polyline? actually poly function contain (&Mat,Pts,npts etc...)

how to set pts and npts values? i tried but error:cv mat to cv arr and then i don't know about the these arguments finally i got pixel position in image but how to connect and draw polyline? here i have attached example code but i can't understand and idon,t know about how to set arguments in list

example code::

void polylines(cv::Mat& img, const std::list<std::listcv::Point2i>& polylines)
{
    for (auto& polyline : polylines)
    {
        auto current = polyline.begin();
        auto next = std::next(current, 1);
        for (; next != polyline.end(); current++, next++)
        {
            cv::line(img, *current, *next, cv::Scalar(255));
        }
    }
}