Opencv draw a black rectangle and write the serial number

1、 Draw a black rectangle evenly on the picture
2、 Write a sequence number on each rectangle

#include <iostream>
#include <stdio.h>
#include "opencv2/core.hpp"
#include "opencv2/core/utility.hpp"
#include "opencv2/core/ocl.hpp"
#include "opencv2/imgcodecs.hpp"
#include "opencv2/highgui.hpp"
#include "opencv2/features2d.hpp"
#include "opencv2/calib3d.hpp"
#include "opencv2/imgproc.hpp"
#include "opencv2/xfeatures2d.hpp"
#include<list>
#include<windows.h>
#include <opencv2/highgui/highgui_c.h>
#include<string>
using namespace cv;
using namespace cv::xfeatures2d;
using namespace std;
void func2()
{
    
	int t_width = 3500;
	int t_height = 2474;
	int t_width_all = 9;
	int t_height_all = 9;
		Mat displayMat = cv::Mat(t_height , t_width, CV_8UC3, Scalar(255, 255, 255));
		int t_per_width = t_width / t_width_all;
		int t_per_height = t_height / t_height_all;

		int t_index = 1;
		for (int i = 0; i < t_width_all; )
		{
    
			for (int j = 0; j < t_height_all;)
			{
    
				vector<Point> m1;
				m1.push_back(Point(t_per_width * i, t_per_height * j));
				m1.push_back(Point(t_per_width * (i + 1), t_per_height * j));
				m1.push_back(Point(t_per_width * (i + 1), t_per_height * (j + 1)));
				m1.push_back(Point(t_per_width * i, t_per_height * (j + 1)));
				fillPoly(displayMat, m1, Scalar(0, 0, 0), 8);

				String t_tep_index = to_string(t_index);
				while (t_tep_index.length() != 3)
				{
    
					t_tep_index = "0" + t_tep_index;
				}				
				putText(displayMat, t_tep_index.c_str(), Point(t_per_width * i+ t_per_width/5, t_per_height * j+ t_per_height/3*2), FONT_HERSHEY_SIMPLEX, 4, Scalar(255, 255, 255), 8, 8);
				t_index++;
				j += 2;
			}
			i += 2;
		}
		cv::imshow("displayMat", displayMat);
		imwrite("D:\\11.jpg", displayMat);
		cv::waitKey(0);	
}

int  main()
{
    
	func2();
	return 0;
}

The effect is as follows ：