Arranging Contour Points in Clockwise order

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I will simply guide you to the resources to find your solution.

First, familiarise yourself with the return orientation of findContours

Then this blog post explains how to do a clockwise order of points

MatOfPoint2f orderPointsClockwise(MatOfPoint2f screenCnt2f) {
    System.out.println(screenCnt2f.dump());

    List<Point> points = screenCnt2f.toList();
    // # initialize a list of coordinates that will be ordered
    // # such that the first entry in the list is the top-left,
    // # the second entry is the top-right, the third is the
    // # bottom-right, and the fourth is the bottom-left
    Collections.sort(points, new Comparator<Point>() {
        @Override
        public int compare(Point p1, Point p2) {
            double s1 = p1.x + p1.y;
            double s2 = p2.x + p2.y;
            return Double.compare(s1, s2);
        }
    });
    Point topLeft = points.get(0);
    Point bottomRight = points.get(3);


    // # now, compute the difference between the points, the
    // # top-right point will have the smallest difference,
    // # whereas the bottom-left will have the largest difference
    Collections.sort(points, new Comparator<Point>() {
        @Override
        public int compare(Point p1, Point p2) {
            double s1 = p1.y - p1.x  ;
            double s2 = p2.y - p2.x;
            return Double.compare(s1, s2);
        }
    });
    Point topRight = points.get(0);
    Point bottomLeft = points.get(3);

    Point[] pts = new Point[]{topLeft,topRight, bottomRight, bottomLeft};

    screenCnt2f = new MatOfPoint2f(pts);
    // System.out.println(screenCnt2f.dump());
    return screenCnt2f;
}