鼠标画矩形openCV

#include <cv.h>  
#include <highgui.h>  
#include <stdio.h>  
/*鼠标画矩形*/
    void my_mouse_callback(
        int event,int x,int y,int flag,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(500,500),
            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);
        cvDestroyAllWindows();


    }

    void my_mouse_callback(
        int event,int x,int y,int flag,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;
        }
    }