例4-1：用滑鼠在視窗中畫方形的程式

#include"pch.h"//看情況加
#include <cv.h>
#include <highgui.h>

CvRect box;	//定義繪製的矩形
bool drawing_box = false;	//狀態-滑鼠正在移動

void draw_box(IplImage* img, CvRect rect){
	//繪製矩形
	cvRectangle(
	img, cvPoint(rect.x, rect.y), cvPoint(rect.x+ rect.width, rect.y+ rect.height),
	cvScalar(0xff,0xf0,0x0f));
}

//滑鼠響應函式-回撥函式
void my_mouse_callback(
	int event, int x, int y, int flags, void* param)
{
	IplImage* img = (IplImage*)param;

	switch (event)
	{
	case CV_EVENT_MOUSEMOVE: 	//mouse move 
		if (drawing_box) {
			box.width = x - box.x;
			box.height = y - box.y;
		}

		break;
	case CV_EVENT_LBUTTONDOWN: 	//left button be pressed
		drawing_box = true;		//drawing flag set 1
		box = cvRect(x, y, 0, 0);

		break;
	case CV_EVENT_LBUTTONUP: 	//left button be released
		drawing_box = false;
		// redefine the left position of box
		if (box.width < 0) {
			box.x += box.width;
			box.width *= -1;
		}
		if (box.height < 0) {
			box.y += box.height;
			box.height *= -1;
		}
		draw_box(img, box);	// draw the box ,the img is a inside var

		break;
	}
}



int main(int argc, char** argv[])
{
	box = cvRect(-1, -1, 0, 0);//設定一個矩形，被隱藏

	IplImage *img = cvCreateImage(cvSize(2000, 2000), IPL_DEPTH_8U, 3);//建立一個影象
	cvZero(img);//資料設定為0
	IplImage* temp = cvCloneImage(img);	//copy image,copy the struction
	cvNamedWindow("Box Example");	//build a windown with box example
	
	//set mouse callback function 
	cvSetMouseCallback(
		"Box Example",
		my_mouse_callback,//the second para. only need pointer address 
		(void*)img);
	
	while (1){
		cvCopy(img, temp);//copy image from imag to temp
		if (drawing_box)	
			draw_box(temp, box);
		cvShowImage("Box Example", temp);
		
		if (cvWaitKey(15) == 27) break;
	}
	cvReleaseImage( &img );
	cvReleaseImage( &temp );
	cvDestroyWindow("Box Example");
}