#include <iostream>
#include <opencv2\opencv.hpp>
using namespace std;
using namespace cv;
void on_MouseHandle(int event, int x, int y, int flags, void* param);
void DrawRectangle(Mat& img, Rect box);
Rect g_rectangle;
bool g_bDrawingBox = false;
RNG g_rng(12345);
int main()
{
    g_rectangle = Rect(-1, -1, 0, 0);
    Mat srcImage(600, 800, CV_8UC3), tempImage;
    srcImage.copyTo(tempImage);
    srcImage = Scalar::all(0);
    namedWindow("Window");
    setMouseCallback("Window", on_MouseHandle, (void*)& srcImage);
    while (1)
    {
        srcImage.copyTo(tempImage);
        if (g_bDrawingBox)
            DrawRectangle(tempImage, g_rectangle);
        imshow("Window", tempImage);
        if (waitKey(10) == 27)
            break;
    }
    return 0;

}
void on_MouseHandle(int event, int x, int y, int flags, void* param)
{
    Mat& image = *(Mat*)param;
    switch (event)
    {
    case EVENT_LBUTTONDOWN:
    {
        g_bDrawingBox = true;
        g_rectangle=Rect(x, y, 0, 0);
    }
    break;
    case EVENT_MOUSEMOVE:
    {
        if (g_bDrawingBox)
        {
            g_rectangle.width = x - g_rectangle.x;
            g_rectangle.height = y - g_rectangle.y;
        }

    }
    break;
    case EVENT_LBUTTONUP:
    {
        g_bDrawingBox = true;
        if (g_rectangle.width < 0)
        {
            g_rectangle.x += g_rectangle.width;
            g_rectangle.width *= -1;
        }
        if (g_rectangle.height < 0)
        {
            g_rectangle.y += g_rectangle.height;
            g_rectangle.height *= -1;
        }
        DrawRectangle(image, g_rectangle);

    }
    break;
    }
}
void DrawRectangle(Mat& img, Rect box)
{
    rectangle(img, box.tl(), box.br(), Scalar(g_rng.uniform(0, 255), g_rng.uniform(0, 255), g_rng.uniform(0, 255)));
}