Dash line drawing example source code using openCV
 
* example code
Mat img(500, 500, CV_8UC3);
img.setTo(0);
Mat rImg = DrawDashLine(img, Point(20, 20), Point(300, 300), 10, CV_RGB(255, 0, 0)); 
namedWindow("test", 0);
cv::imshow("test", rImg);
waitKey(0);