Draw Dashed/Dotted line in OpenCV

opencv_draw_dashed_dotted_line.cc

// reference: https://ddorobot.tistory.com/entry/OpenCV-Draw-DotDash-Line

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

#include "opencv2/opencv.hpp"

void DrawDashedLine(cv::Mat& img, cv::Point pt1, cv::Point pt2,
                    cv::Scalar color, int thickness, std::string style,
                    int gap) {
  float dx = pt1.x - pt2.x;
  float dy = pt1.y - pt2.y;
  float dist = std::hypot(dx, dy);

  std::vector<cv::Point> pts;
  for (int i = 0; i < dist; i += gap) {
    float r = static_cast<float>(i / dist);
    int x = static_cast<int>((pt1.x * (1.0 - r) + pt2.x * r) + .5);
    int y = static_cast<int>((pt1.y * (1.0 - r) + pt2.y * r) + .5);
    pts.emplace_back(x, y);
  }

  int pts_size = pts.size();

  if (style == "dotted") {
    for (int i = 0; i < pts_size; ++i) {
      cv::circle(img, pts[i], thickness, color, -1);
    }
  } else {
    cv::Point s = pts[0];
    cv::Point e = pts[0];

    for (int i = 0; i < pts_size; ++i) {
      s = e;
      e = pts[i];
      if (i % 2 == 1) {
        cv::line(img, s, e, color, thickness);
      }
    }
  }
}

int main(int argc, char **argv) {
  cv::Mat img(200, 200, CV_8UC3, cv::Scalar(0, 0, 0));
  // dotted
  DrawDashedLine(img, cv::Point(10, 10), cv::Point(100,100), cv::Scalar(0, 0, 255), 2, "dotted", 10);

  // dashed
  DrawDashedLine(img, cv::Point(199, 10), cv::Point(100,100), cv::Scalar(0, 255, 0), 2, "", 10);

  cv::imshow("dotted dashed", img);
  cv::waitKey(0);
  return 0;
}