基于opencv的用cvSetMouseCallback画正方形

#include<cv.h>
#include<highgui.hpp>
#include"highgui.h"
using namespace std;
#include <iostream>
using namespace cv;
//回调函数：
void my_mouse_callback(
	int event,int x,int y,int flag,void *para
	);
CvRect box;
bool drawing_box = false;
void draw_box(IplImage * img, CvRect rect) {
	cvRectangle(
		img,
		CvPoint(rect.x, rect.y),
		CvPoint(rect.x + rect.width, rect.y + rect.height),
		CvScalar(0, 0, 255)
	);
}

int main()
{
	box = CvRect(-1, -1, 0, 0);

	IplImage *rect = cvCreateImage(
		CvSize(200, 200),
		IPL_DEPTH_8U,
		3
	);

	cvZero(0);
	IplImage *temp = cvCloneImage(rect);

	cvNamedWindow("Box Example",CV_WINDOW_AUTOSIZE);
	//注册回调函数
	cvSetMouseCallback("Box Example", my_mouse_callback, (void *)rect);

	while (1) {
		cvCopy(rect, temp);
		if (drawing_box)draw_box(temp, box);
		cvShowImage("Box Example", temp);
		if(cvWaitKey(15)==27)break;
	}

	cvReleaseImage(&rect);
	cvReleaseImage(&temp);

	cvDestroyWindow("Box Example");

}
void my_mouse_callback(int event, int x, int y, int flag, void *para) {
	IplImage * img = (IplImage *)para;

	switch (event)
	{
	case CV_EVENT_MOUSEMOVE: {
		if (drawing_box) {
			box.width = x - box.x;
			box.height = y - box.y;
		}
		break;
	}
	case CV_EVENT_LBUTTONDOWN: {
		drawing_box = true;
		box = CvRect(x, y, 0, 0);
	}
		 break;
	case CV_EVENT_LBUTTONUP: {
		drawing_box = false;
		if (box.width < 0) {
			box.x += box.width;
			box.width *= -1;
		}
		if (box.height < 0) {
			box.y += box.width;
			box.height *= -1;
		}
		draw_box(img, box);
	}
	     break;
	default:
		break;
	}
}