hide rectangle when template not appear

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C++

OpenCV

i made template matching software using opencv and c++. now i need hide rectangle when the template image not appear.and when the template image infront of screen should track the template and draw rectangle. this is my code. sorry for bad english

#include <iostream>
#include "opencv2/opencv.hpp"
#include 
#include 
#include 
#include <windows.h>

#include <sstream>


using namespace cv;
using namespace std;

Point point1, point2; /* vertical points of the bounding box */
int drag = 0;
Rect rect; /* bounding box */
Mat img, roiImg; /* roiImg - the part of the image in the bounding box */
int select_flag = 0;
bool go_fast = false;

Mat mytemplate;
HANDLE hSerial = CreateFile(L"\\\\.\\COM10", GENERIC_READ | GENERIC_WRITE, 0, 0, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0);
char outputChars[5] = {};
	DWORD btsIO;




///------- template matching -----------------------------------------------------------------------------------------------

Mat TplMatch( Mat &img, Mat &mytemplate )
{
  Mat result;

  matchTemplate( img, mytemplate, result, CV_TM_SQDIFF_NORMED );
  normalize( result, result, 0, 1, NORM_MINMAX, -1, Mat() );

  return result;
}


///------- Localizing the best match with minMaxLoc ------------------------------------------------------------------------

Point minmax( Mat &result )
{
  double minVal, maxVal;
  Point  minLoc, maxLoc, matchLoc;

  minMaxLoc( result, &minVal, &maxVal, &minLoc, &maxLoc, Mat() );
  matchLoc = minLoc;

  return matchLoc;
}


///------- tracking --------------------------------------------------------------------------------------------------------

void track()
{
    if (select_flag)
    {
        //roiImg.copyTo(mytemplate);
//         select_flag = false;
        go_fast = true;
    }

//     imshow( "mytemplate", mytemplate ); waitKey(0);

    Mat result  =  TplMatch( img, mytemplate );
    Point match =  minmax( result ); 

    rectangle( img, match, Point( match.x + mytemplate.cols , match.y + mytemplate.rows ), CV_RGB(255, 0, 255), 1 );
	char test[32];
sprintf(test, "x%dy%d\n", (int)match.x, (int)match.y);
		//WriteFile(hSerial, "kjl" ,4,&btsIO,NULL);
WriteFile(hSerial, test, strlen(test), &btsIO, NULL);



    std::cout << "match: " << match << endl;

    /// latest match is the new template
  /*  Rect ROI = cv::Rect( match.x, match.y, mytemplate.cols, mytemplate.rows );
    roiImg = img( ROI );
    roiImg.copyTo(mytemplate);
    imshow( "roiImg", roiImg ); //waitKey(0);*/
}


///------- MouseCallback function ------------------------------------------------------------------------------------------

void mouseHandler(int event, int x, int y, int flags, void *param)
{
    if (event == CV_EVENT_LBUTTONDOWN && !drag)
    {
        /// left button clicked. ROI selection begins
        point1 = Point(x, y);
        drag = 1;
    }

    if (event == CV_EVENT_MOUSEMOVE && drag)
    {
        /// mouse dragged. ROI being selected
        Mat img1 = img.clone();
        point2 = Point(x, y);
        rectangle(img1, point1, point2, CV_RGB(255, 0, 0), 3, 8, 0);
        imshow("image", img1);
    }

    if (event == CV_EVENT_LBUTTONUP && drag)
    {
        point2 = Point(x, y);
        rect = Rect(point1.x, point1.y, x - point1.x, y - point1.y);
        drag = 0;
        roiImg = img(rect);
        roiImg.copyTo(mytemplate);
//  imshow("MOUSE roiImg", roiImg); waitKey(0);
    }

    if (event == CV_EVENT_LBUTTONUP)
    {
        /// ROI selected
        select_flag = 1;
        drag = 0;
    }

}



///------- Main() ----------------------------------------------------------------------------------------------------------

int main()
{


if (hSerial !=INVALID_HANDLE_VALUE)
    {
        printf("Port opened! \n");

        DCB dcbSerialParams;
        GetCommState(hSerial,&dcbSerialParams);

        dcbSerialParams.BaudRate = CBR_9600;
        dcbSerialParams.ByteSize = 8;
        dcbSerialParams.Parity = NOPARITY;
        dcbSerialParams.StopBits = ONESTOPBIT;

        SetCommState(hSerial, &dcbSerialParams);
	}
	else
	{
		if (GetLastError() == ERROR_FILE_NOT_FOUND)
		{
			printf("Serial port doesn't exist! \n");
		}

		printf("Error while setting up serial port! \n");
	}



    int k;
   
///open webcam
    VideoCapture cap(0);
    if (!cap.isOpened())
      return 1;

    ///open video file
   // VideoCapture cap;
    //cap.open( "Megamind.avi" );
    if ( !cap.isOpened() )
    {   cout << "Unable to open video file" << endl;    return -1;    }
/*    
    /// Set video to 320x240
     cap.set(CV_CAP_PROP_FRAME_WIDTH, 320);
     cap.set(CV_CAP_PROP_FRAME_HEIGHT, 240);*/

    cap >> img;
    GaussianBlur( img, img, Size(7,7), 3.0 );
    imshow( "image", img );

	

    while (1)
    {

		


        cap >> img;
        if ( img.empty() )
            break;

    // Flip the frame horizontally and add blur
    cv::flip( img, img, 1 );
    GaussianBlur( img, img, Size(7,7), 3.0 );

        if ( rect.width == 0 && rect.height == 0 )
            cvSetMouseCallback( "image", mouseHandler, NULL );
        else
            track();

        imshow("image", img);
//  waitKey(100);   k = waitKey(75);
    k = waitKey(go_fast ? 30 : 10000);
        if (k == 27)
            break;
    }
	  CloseHandle(hSerial);

    return 0;
}