Added mouse event callback example

examples/window/01_MouseEventCallback.cpp

@@ -0,0 +1,75 @@
+#include <iostream>
+#include <opencv2/highgui.hpp>
+#include <opencv2/imgproc/imgproc.hpp>
+
+using namespace cv;
+using namespace std;
+
+/**
+ * Struct used later as a `userdata`
+ */
+struct Object {
+	int id = 100;
+};
+
+ostream& operator<<(std::ostream& stream, const Object& obj) {
+	stream << "ID=" << obj.id;
+	return stream;
+}
+
+int main( int argc, char** argv ) {
+
+	// Create matrix from image
+	Mat image = imread("lena1.png", CV_LOAD_IMAGE_COLOR);
+
+	// Create window
+	namedWindow("My Image", WINDOW_AUTOSIZE);
+
+	// Show image in window
+	imshow("My Image", image);
+
+	// Create an object
+	Object *objptr = new Object;
+
+	// Set callback function on mouse event
+	setMouseCallback("My Image", [](int event, int x, int y, int flags, void* userdata) {
+		cout << "=================================" << endl;
+		cout << "X: " << x << ", Y: " << y << endl;
+		cout << "Event type: " << event << endl;
+		/**
+		 * cv::EVENT_MOUSEMOVE = 0,
+		 * cv::EVENT_LBUTTONDOWN = 1,
+		 * cv::EVENT_RBUTTONDOWN = 2,
+		 * cv::EVENT_MBUTTONDOWN = 3,
+		 * cv::EVENT_LBUTTONUP = 4,
+		 * cv::EVENT_RBUTTONUP = 5,
+		 * cv::EVENT_MBUTTONUP = 6,
+		 * cv::EVENT_LBUTTONDBLCLK = 7,
+		 * cv::EVENT_RBUTTONDBLCLK = 8,
+		 * cv::EVENT_MBUTTONDBLCLK = 9,
+		 * cv::EVENT_MOUSEWHEEL = 10,
+		 * cv::EVENT_MOUSEHWHEEL = 11
+		 */
+
+		cout << "Flag: " << flags << endl;
+		/**
+		 * cv::EVENT_FLAG_LBUTTON = 1,
+		 * cv::EVENT_FLAG_RBUTTON = 2,
+		 * cv::EVENT_FLAG_MBUTTON = 4,
+		 * cv::EVENT_FLAG_CTRLKEY = 8,
+		 * cv::EVENT_FLAG_SHIFTKEY = 16,
+		 * cv::EVENT_FLAG_ALTKEY = 32
+		 */
+
+		// User defined value
+		cout << "Userdata: " << *(Object*)userdata << endl;
+	}, objptr /*extra pointer parameter*/);
+
+	// Wait for user input
+	waitKey(0);
+
+	// Delete pointer
+	delete objptr;
+	return 0;
+}
+