Desktop : OpenCV Ellipse2Poly

<h5>Goal</h5>
Test OpenCV Ellipse2Poly.

```OpenCV_Ellipse2Poly.java
import org.opencv.core.*;
import org.opencv.imgproc.Imgproc;

import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import org.opencv.core.Point;

public class OpenCV_Ellipse2Poly {

    static{System.loadLibrary(Core.NATIVE_LIBRARY_NAME);}
    private JFrame frmjavaSwing;

    /**
     *  Launch the application.
     */
    public static void main(String[] args){
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try{
                    OpenCV_Ellipse2Poly window = new OpenCV_Ellipse2Poly();
                    window.frmjavaSwing.setVisible(true);
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     *  Create the application.
     */
    public OpenCV_Ellipse2Poly(){
        init();
    }

    /**
     *  Init the contents of the frame.
     */
    private void init(){
        Mat source =  paint();
        BufferedImage image=matToBufferedImage(source);

        frmjavaSwing = new JFrame();
        frmjavaSwing.setTitle("opencv 橢圓內近似多邊形練習");
        frmjavaSwing.setBounds(100, 100, 300, 300);
        frmjavaSwing.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frmjavaSwing.getContentPane().setLayout(null);

        final JLabel lblNewLabel = new JLabel("");
        lblNewLabel.setBounds(5, 5, image.getHeight()+10, image.getWidth()+10);
        lblNewLabel.setIcon(new ImageIcon(image));
        frmjavaSwing.getContentPane().add(lblNewLabel);
    }

    public Mat paint(){

        Mat source = new Mat(250,250, CvType.CV_8UC3, new Scalar(255,255,255));
        Point pt1=new Point(125,125);
        //原橢圓形
        Imgproc.ellipse(source,pt1,new Size(120,50),50,0,360,new Scalar(255,0,0),4);
        MatOfPoint pts=new MatOfPoint();

        //原橢圓形的近似多邊形
        Imgproc.ellipse2Poly(pt1,new Size(120,50),50,0,360,60, pts);
        Point[] allPoint=pts.toArray();

        for(int i=1;i<allPoint.length;i++){

            Imgproc.line(source, allPoint[i-1], allPoint[i], new Scalar(0,0,0),2);

        }
        return source;
    }

    public BufferedImage matToBufferedImage(Mat matrix) {
        int cols = matrix.cols();
        int rows = matrix.rows();
        int elemSize = (int)matrix.elemSize();
        byte[] data = new byte[cols * rows * elemSize];
        int type;
        matrix.get(0, 0, data);
        switch (matrix.channels()) {
            case 1:
                type = BufferedImage.TYPE_BYTE_GRAY;
                break;
            case 3:
                type = BufferedImage.TYPE_3BYTE_BGR;
                // bgr to rgb
                byte b;
                for(int i=0; i<data.length; i=i+3) {
                    b = data[i];
                    data[i] = data[i+2];
                    data[i+2] = b;
                }
                break;
            default:
                return null;
        }
        BufferedImage image2 = new BufferedImage(cols, rows, type);
        image2.getRaster().setDataElements(0, 0, cols, rows, data);
        return image2;
    }

}
```
<h5>Result</h5>
![opencv_ellipse2poly.JPG](https://qiita-image-store.s3.ap-northeast-1.amazonaws.com/0/276243/6d0aabab-5f9e-9ab8-8210-611d9fa4fa02.jpeg)