Select a few rectangles in an image using C++11 and OpenCV 2.4

rect_selector.cc

#include "opencv2/opencv.hpp"

#include <vector>
#include <iostream>

using cv::WINDOW_NORMAL;
using cv::imread;
using cv::waitKey;
using cv::setMouseCallback;
using cv::imshow;
using cv::Rect;
using cv::Point;
using cv::Scalar;
using cv::rectangle;
using cv::Mat;

Mat source_image;
Mat img;

// Current rectangle and start&end points
Rect rect (0, 0, 0, 0);
Point P1 (0, 0);
Point P2 (0, 0);

// Rectangles to be outputted
std::vector<Rect> rects;

static const char* WINDOW_NAME = "Tracking Info Generator";
static bool clicked = false;


void fixBoundaries () {
	if (rect.width > img.cols - rect.x)
		rect.width = img.cols - rect.x;

	if (rect.height > img.rows - rect.y)
		rect.height = img.rows - rect.y;

	if (rect.x < 0)
		rect.x = 0;

	if (rect.y < 0)
		rect.height = 0;
}

void draw (){
	img = source_image.clone();
	fixBoundaries();

	for (const auto& r : rects)
		rectangle(img, r, Scalar(0,255,0), 1, 8, 0 );
	rectangle(img, rect, Scalar(0,255,0), 1, 8, 0 );

	imshow(WINDOW_NAME, img);
}


void onMouse(int event, int x, int y, int f, void*){
	switch(event){
		case CV_EVENT_LBUTTONDOWN:
			clicked = true;
			P1.x = x;
			P1.y = y;
			P2.x = x;
			P2.y = y;
			break;

		case  CV_EVENT_LBUTTONUP:
			clicked = false;
			P2.x = x;
			P2.y = y;
			break;

		case CV_EVENT_MOUSEMOVE:
			if (clicked) {
				P2.x=x;
				P2.y=y;
			}
			break;

		default:
			break;
	}

	if (P1.x > P2.x) {
		rect.x = P2.x;
		rect.width = P1.x - P2.x;
	} else {
		rect.x=P1.x;
		rect.width = P2.x - P1.x;
	}

	if (P1.y > P2.y) {
		rect.y = P2.y;
		rect.height = P1.y - P2.y;
	} else {
		rect.y = P1.y;
		rect.height = P2.y - P1.y;
	}

	draw();
}

int main()
{
	source_image = imread("../assets/face/faces.png", 1);

	namedWindow(WINDOW_NAME, WINDOW_NORMAL);
	setMouseCallback(WINDOW_NAME, onMouse, NULL );
	imshow(WINDOW_NAME, source_image);

	while (1) {
		char c = waitKey();

		switch (c) {
			case 's':
				if (rects.empty()) {
					std::cerr << "No rect added." << std::endl
						<< "Select an area and press 'a' to add!" << std::endl;
					continue;
				}

				for (const auto& r : rects) {
					std::cout << r.x + r.width/2 << " "
						<< r.y + r.height/2 << std::endl;
				}
				break;
			case 'a':
				rects.push_back(rect);
				rect = Rect(0, 0, 0, 0);
				break;
		}
	}

	return 0;
}