text: #include <iostream>
  #include <vector>
  #include <iomanip>
  
  #include "opencv2/core/utility.hpp"
  #include "opencv2/highgui/highgui.hpp"
  #include "opencv2/core/ocl.hpp"
  #include "opencv2/video/video.hpp"
  
  using namespace std;
  using namespace cv;
  
  typedef unsigned char uchar;
  #define LOOP_NUM 10
  int64 work_begin = 0;
  int64 work_end = 0;
  
  static void workBegin()
  {
      work_begin = getTickCount();
  }
  static void workEnd()
  {
      work_end += (getTickCount() - work_begin);
  }
  static double getTime()
  {
      return work_end * 1000. / getTickFrequency();
  }
  
  static void drawArrows(UMat& _frame, const vector<Point2f>& prevPts, const vector<Point2f>& nextPts, const vector<uchar>& status,
                         Scalar line_color = Scalar(0, 0, 255))
  {
      Mat frame = _frame.getMat(ACCESS_WRITE);
      for (size_t i = 0; i < prevPts.size(); ++i)
      {
          if (status[i])
          {
              int line_thickness = 1;
  
              Point p = prevPts[i];
              Point q = nextPts[i];
  
              double angle = atan2((double) p.y - q.y, (double) p.x - q.x);
  
              double hypotenuse = sqrt( (double)(p.y - q.y)*(p.y - q.y) + (double)(p.x - q.x)*(p.x - q.x) );
  
              if (hypotenuse < 1.0)
                  continue;
  
              // Here we lengthen the arrow by a factor of three.
              q.x = (int) (p.x - 3 * hypotenuse * cos(angle));
              q.y = (int) (p.y - 3 * hypotenuse * sin(angle));
  
              // Now we draw the main line of the arrow.
              line(frame, p, q, line_color, line_thickness);
  
              // Now draw the tips of the arrow. I do some scaling so that the
              // tips look proportional to the main line of the arrow.
  
              p.x = (int) (q.x + 9 * cos(angle + CV_PI / 4));
              p.y = (int) (q.y + 9 * sin(angle + CV_PI / 4));
              line(frame, p, q, line_color, line_thickness);
  
              p.x = (int) (q.x + 9 * cos(angle - CV_PI / 4));
              p.y = (int) (q.y + 9 * sin(angle - CV_PI / 4));
              line(frame, p, q, line_color, line_thickness);
          }
      }
  }
  
  
  int main(int argc, const char* argv[])
  {
      const char* keys =
          "{ h help           | false           | print help message }"
          "{ l left           |                 | specify left image }"
          "{ r right          |                 | specify right image }"
          "{ c camera         | 0               | enable camera capturing }"
          "{ v video          |                 | use video as input }"
          "{ o output         | pyrlk_output.jpg| specify output save path when input is images }"
          "{ points           | 1000            | specify points count [GoodFeatureToTrack] }"
          "{ min_dist         | 0               | specify minimal distance between points [GoodFeatureToTrack] }"
          "{ m cpu_mode       | false           | run without OpenCL }";
  
      CommandLineParser cmd(argc, argv, keys);
  
      if (cmd.has("help"))
      {
          cout << "Usage: pyrlk_optical_flow [options]" << endl;
          cout << "Available options:" << endl;
          cmd.printMessage();
          return EXIT_SUCCESS;
      }
  
      bool defaultPicturesFail = true;
      string fname0 = cmd.get<string>("left");
      string fname1 = cmd.get<string>("right");
      string vdofile = cmd.get<string>("video");
      string outfile = cmd.get<string>("output");
      int points = cmd.get<int>("points");
      double minDist = cmd.get<double>("min_dist");
      int inputName = cmd.get<int>("c");
  
      UMat frame0;
      imread(fname0, cv::IMREAD_GRAYSCALE).copyTo(frame0);
      UMat frame1;
      imread(fname1, cv::IMREAD_GRAYSCALE).copyTo(frame1);
  
      vector<cv::Point2f> pts(points);
      vector<cv::Point2f> nextPts(points);
      vector<unsigned char> status(points);
      vector<float> err;
  
      cout << "Points count : " << points << endl << endl;
  
      if (frame0.empty() || frame1.empty())
      {
          VideoCapture capture;
          UMat frame, frameCopy;
          UMat frame0Gray, frame1Gray;
          UMat ptr0, ptr1;
  
          if(vdofile.empty())
              capture.open( inputName );
          else
              capture.open(vdofile.c_str());
  
          int c = inputName ;
          if(!capture.isOpened())
          {
              if(vdofile.empty())
                  cout << "Capture from CAM " << c << " didn't work" << endl;
              else
                  cout << "Capture from file " << vdofile << " failed" <<endl;
              if (defaultPicturesFail)
                  return EXIT_FAILURE;
              goto nocamera;
          }
  
          cout << "In capture ..." << endl;
          for(int i = 0;; i++)
          {
              if( !capture.read(frame) )
                  break;
  
              if (i == 0)
              {
                  frame.copyTo( frame0 );
                  cvtColor(frame0, frame0Gray, COLOR_BGR2GRAY);
              }
              else
              {
                  if (i%2 == 1)
                  {
                      frame.copyTo(frame1);
                      cvtColor(frame1, frame1Gray, COLOR_BGR2GRAY);
                      ptr0 = frame0Gray;
                      ptr1 = frame1Gray;
                  }
                  else
                  {
                      frame.copyTo(frame0);
                      cvtColor(frame0, frame0Gray, COLOR_BGR2GRAY);
                      ptr0 = frame1Gray;
                      ptr1 = frame0Gray;
                  }
  
  
                  pts.clear();
                  goodFeaturesToTrack(ptr0, pts, points, 0.01, 0.0);
                  if(pts.size() == 0)
                      continue;
                  calcOpticalFlowPyrLK(ptr0, ptr1, pts, nextPts, status, err);
  
                  if (i%2 == 1)
                      frame1.copyTo(frameCopy);
                  else
                      frame0.copyTo(frameCopy);
                  drawArrows(frameCopy, pts, nextPts, status, Scalar(255, 0, 0));
                  imshow("PyrLK [Sparse]", frameCopy);
              }
              char key = (char)waitKey(10);
  
              if (key == 27)
                  break;
              else if (key == 'm' || key == 'M')
              {
                  ocl::setUseOpenCL(!cv::ocl::useOpenCL());
                  cout << "Switched to " << (ocl::useOpenCL() ? "OpenCL" : "CPU") << " mode\n";
              }
          }
          capture.release();
      }
      else
      {
  nocamera:
          if (cmd.has("cpu_mode"))
          {
              ocl::setUseOpenCL(false);
              std::cout << "OpenCL was disabled" << std::endl;
          }
          for(int i = 0; i <= LOOP_NUM; i ++)
          {
              cout << "loop" << i << endl;
              if (i > 0) workBegin();
  
              goodFeaturesToTrack(frame0, pts, points, 0.01, minDist);
              calcOpticalFlowPyrLK(frame0, frame1, pts, nextPts, status, err);
  
              if (i > 0 && i <= LOOP_NUM)
                  workEnd();
  
              if (i == LOOP_NUM)
              {
                  cout << "average time (noCamera) : ";
  
                  cout << getTime() / LOOP_NUM << " ms" << endl;
  
                  drawArrows(frame0, pts, nextPts, status, Scalar(255, 0, 0));
                  imshow("PyrLK [Sparse]", frame0);
                  imwrite(outfile, frame0);
              }
          }
      }
  
      waitKey();
  
      return EXIT_SUCCESS;
  }
  