Opencv C++ Code for drawing Rectangle

Draws a simple, thick, or filled up-right rectangle.

Syntax:
C++ :void rectangle(Mat& img, Point pt1, Point pt2, const Scalar& color, int thickness=1, int lineType=8, int shift=0)

Parameters:
img – Image.
pt1 – Vertex of the rectangle.
pt2 – Vertex of the rectangle opposite to pt1.
rec – Alternative specification of the drawn rectangle.
color – Rectangle color or brightness (grayscale image).
thickness – Thickness of lines that make up the rectangle. Negative values, like CV_FILLED , mean that the function has to draw a filled rectangle.
lineType – Type of the line. See the line() description.
shift – Number of fractional bits in the point coordinates.

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#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
using namespace cv;
  
int main( )
{    
  // Create black empty images
  Mat image = Mat::zeros( 400, 400, CV_8UC3 );
    
  // Draw a rectangle 
  rectangle(image , Point (100,100), Point (300,300), Scalar( 0, 0, 255 ), 1, 8);
  imshow("Image",image);
  
  waitKey( 0 );
  return(0);
}