How to combine multiple window?

I want to combine multiple windows.

In picture, i have two windows and i want to combine both frame1 and frame2.

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OF CODE:

VideoCapture capture0(0);
VideoCapture capture1(1);

void ofApp::update(){
if (!capture0.isOpened())
{
printf(“첫번째 카메라를 열수 없습니다. \n”);
}

if (!capture1.isOpened())
{
	printf("두번째 카메라를 열수 없습니다. \n");
}

Mat frame_original, frame_1, frame_2;
//capture0 >> frame_original; // get a new frame from webcam
capture0 >> frame_1;
capture1 >> frame_2;
//flip(frame_original, frame_original, 1); // image flip

Mat frame_gray1, frame_gray2;
cvtColor(frame_1, frame_gray1, CV_RGB2GRAY);
cvtColor(frame_2, frame_gray2, CV_RGB2GRAY);
threshold(frame_gray2, frame_gray2, 100, 255, THRESH_BINARY);
//equalizeHist(frame_gray, frame_gray);
//connectedComponents(frame_gray,frame_gray,4,CV_16U);

Mat img_labels, stats, centroids;
int numOfLables = connectedComponentsWithStats(frame_gray2, img_labels, stats, centroids, 8, CV_32S);

//라벨링 된 이미지에 각각 직사각형으로 둘러싸기  
for (int j = 1; j < numOfLables; j++) {
	int area = stats.at<int>(j, CC_STAT_AREA);
	int left = stats.at<int>(j, CC_STAT_LEFT);
	int top = stats.at<int>(j, CC_STAT_TOP);
	int width = stats.at<int>(j, CC_STAT_WIDTH);
	int height = stats.at<int>(j, CC_STAT_HEIGHT);
	
	//double *centroid = centroids.at<double>(j, 0); //중심좌표  
	int x = centroids.at<double>(j,0);
	int y = centroids.at<double>(j,1);

	circle(frame_gray2, Point(x, y), 5, Scalar(255, 0, 0), 1);
	putText(frame_gray2, to_string(x)+ ", " +to_string(y), Point(left + 20, top + 20), FONT_HERSHEY_SIMPLEX,	1, Scalar(255, 255, 0), 2);

	//rectangle(frame_gray, Point(left, top), Point(left + width, top + height),Scalar(0, 0, 255), 1);

	//putText(frame_gray, to_string(j), Point(left + 20, top + 20), FONT_HERSHEY_SIMPLEX,1, Scalar(255, 0, 0), 2);
}

double D2R = PI / 180;
double R2D = 180 / PI;
double IRX2DEG = 46, IRY2DEG = 36;
double Ax=320, Ay=240, Bx=320, By=240, Wx=0,Wy=0,Wz=0;
double ADeg=60, BDeg=120, Am=0, Bm=0;
double Lxz=0,WA_UDDeg=0;

ADeg = 60 - (Ax - 320) * IRX2DEG;
Am = tan(ADeg * D2R);
BDeg = 60 - (Bx - 320) * IRX2DEG;
Bm = tan(BDeg * D2R);

Wx = ((-Bm) * 500) / (Am+1 - Bm);
Wz = Am * Wx;
cout << Wx << endl;

Lxz = sqrt(Wx*Wx + Wz*Wz);
WA_UDDeg = 0 - (Ax - 240)*IRY2DEG;
Wy = -tan(WA_UDDeg*D2R)*Lxz;
   DrawMatchesFlags::DRAW_RICH_KEYPOINTS);

imshow("frame1", frame_gray1);
imshow("frame2", frame_gray2);

}