opencv用鼠标在窗口中画方形的程序

#include <iostream>
#include "cv.h"
#include "highgui.h"

void my_mouse_callback(int event, int x, int y, int flags, void* param);

CvRect box;
bool drawing_box = false;

void draw_box(IplImage* img, CvRect rect)
{
    cvRectangle(img, cvPoint(box.x, box.y), cvPoint(box.x+box.width, box.y+box.height),cvScalar(0xff,0x00,0x00));
}

int main()
{
    box = cvRect(-1,-1,0,0);
    IplImage* image = cvCreateImage(cvSize(200,200), IPL_DEPTH_8U, 3);
    cvZero(image);
    IplImage* temp = cvCloneImage(image);
    cvNamedWindow("Box Example");
    cvSetMouseCallback("Box Example", my_mouse_callback, (void*)image);
    while(1)
    {
        cvCopyImage(image, temp);
        if(drawing_box)
            draw_box(temp, box);
        cvShowImage("Box Example",  temp);
        if(cvWaitKey(15)==27) break;
    }
    cvReleaseImage(&image);
    cvReleaseImage(&temp);
    cvDestroyWindow("Box Example");
}

void my_mouse_callback(int event, int x, int y, int flags, void* param)
{
    IplImage* image = (IplImage*) param;
    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.height;
                box.height*=-1;
            }
            draw_box(image, box);
        }
        break;
    }
}