using namespace std;

namespace cv {
struct Point2d
 {
    double x;
    double y;
 };
}
void smooth_DEMA(vector<cv::Point2d>& points, bool left_to_right = true)
{
 if(points.size() > 0){
   // DEMA filter
   double k1 = 0.2;
   double k2 = 0.8;
   vector<cv::Point2d>::iterator start;
   if(left_to_right){
     start = next(points.begin());
   }else{
     //start = next(points.rbegin());
   }
   double tmp_val = start->y;
   for(size_t i = 1; i < points.size(); i++)
   {
     tmp_val = k1 * prev(start)->y + (1 - k1) * tmp_val;
     start->y = k2 * tmp_val + (1 - k2) * (start->y);
   }
 }
}

int main()
{
 vector<cv::Point2d> points = {cv::Point2d{1,1}, cv::Point2d{2,2}, cv::Point2d{3,2}};
 smooth_DEMA(points);
 smooth_DEMA(points, false);
 for(const auto& i : points)
 {
   cout << i.x << " " << i.y << endl;  
 }
 return 0;
}