用滑鼠畫框框。。

#include <opencv2/opencv.hpp>
#include <opencv2/opencv_modules.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <cstdio>
using namespace cv;

Mat org,dst,img,tmp;

void on_mouse(int event,int x,int y,int flags,void *ustc){
    static Point pre_pt=Point(-1,-1);
    static
 
 Point cur_pt=Point(-1,-1);
    char temp[16];
    if (event==CV_EVENT_LBUTTONDOWN){
        org.copyTo(img);
        sprintf(temp,"(%d,%d)",x,y);
        pre_pt=Point(x,y);
        putText(img,temp,pre_pt,FONT_HERSHEY_SIMPLEX,0.5,Scalar(0,0,0,255),1,8);
        circle(img,pre_pt,2,Scalar(255,0,0,0),CV_FILLED,CV_AA,0
 
); // BGR
        imshow("img",img);
    }
    else if (event==CV_EVENT_MOUSEMOVE&&!(flags&CV_EVENT_FLAG_LBUTTON)){
        img.copyTo(tmp);
        sprintf(temp,"(%d,%d)",x,y);
        cur_pt=Point(x,y);
        putText(tmp,temp,cur_pt,FONT_HERSHEY_SIMPLEX,0.5,Scalar(0,0,0,255));
        imshow("img"
 
,tmp);
    }
    else if (event==CV_EVENT_MOUSEMOVE&&(flags&CV_EVENT_FLAG_LBUTTON)){
        img.copyTo(tmp);
        sprintf(temp,"(%d,%d)",x,y);
        cur_pt=Point(x,y);
        putText(tmp,temp,cur_pt,FONT_HERSHEY_SIMPLEX,0.5,Scalar(0,0,0,255));
        rectangle(tmp,pre_pt,cur_pt,Scalar(0,255,0,0),1,8,0);
        imshow("img",tmp);
    }
    else if (event==CV_EVENT_LBUTTONUP){
        org.copyTo(img);
        sprintf(temp,"(%d,%d)",x,y);
        cur_pt=Point(x,y);
        putText(img,temp,cur_pt,FONT_HERSHEY_SIMPLEX,0.5,Scalar(0,0,0,255));
        circle(img,pre_pt,2,Scalar(255,0,0,0),CV_FILLED,CV_AA,0);
        rectangle(img,pre_pt,cur_pt,Scalar(0,255,0,0),1,8,0);
        imshow("img",img);
        img.copyTo(tmp);
        int width=abs(pre_pt.x-cur_pt.x);
        int height=abs(pre_pt.y-cur_pt.y);
        if (width==0||height==0){
            printf("width==0||height==0");
            return;
        }
        dst=org(Rect(min(cur_pt.x,pre_pt.x),min(cur_pt.y,pre_pt.y),width,height));
        namedWindow("dst",WINDOW_AUTOSIZE);
        imshow("dst",dst);
        waitKey(0);
    }
}

int main(){
    org=imread("/Users/hxh/Desktop/1.jpg");
    org.copyTo(img);
    org.copyTo(tmp);
    namedWindow("img");
    setMouseCallback("img",on_mouse,0);
    imshow("img",img);
    waitKey(0);
    return 0;
}