How to use org.bytedeco.opencv.global.opencv_imgproc.polylines method

[NicolasDrapier]

Hello,

Since yesterday I'm trying to make this code work. The expected result is a polyline on my image (the mat parameter).
Actually, I'm not sure how to use the polylines function.

What is sure is that this does not work. It shows me a result after 2min for just 10 points.

    private fun drawAVPolyline(mat: Mat) {
    // Some other code with coords lists
        val size = 10L
        val pts = Point(size)
        for (i in 0 until size) {
            pts.position(i).apply { x(list[i.toInt()]); y(list[i.toInt()]) }
        }

        polylines(mat, pts, IntPointer(size.toInt()), 1, false, Scalar(255,255,255), 2, 8, 0)
    }

I don't quite understand what to pass for the points parameter (is what I did right?), and what to pass for the npts and ncontours parameters.

Could someone help me?
Nicolas

[saudet]

It's usually easier to look at some sample code in C++ and port that, for example:
https://github.com/opencv/opencv/blob/master/samples/dnn/scene_text_detection.cpp#L109
But I see that uses std::vector<std::vector<cv::Point>>, which isn't mapped... We should be able to get this working pretty easily with MatVector though. If you want to draw a single polygon with those points, something like this should work:

polylines(mat, new MatVector(new Mat(pts.position(0))), false, ...)

[NicolasDrapier]

Indeed, I had read this piece of code and I had seen that it used vectors. So I also thought of using MatVectors but not in this way. I will try it on Monday and I will make a quick feedback.
Anyway, thank you for your quick response.

[NicolasDrapier]

It's perfect, many thanks @saudet !