Ellipse.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Ellipse : MonoBehaviour
{
    Mesh mesh;
    public Vector3 center;
    public float a;
    public float b;
    // Start is called before the first frame update
    void Start()
    {
        mesh = new Mesh
        {
            name = "Ellipse"
        };
    }

    // Update is called once per frame
    void Update()
    {
        
    }

    public void DrawEllipse()
    {
        mesh.Clear();

        Vector3[] vectors = new Vector3[200];
        int k = 0;
        float step = a / 50;
        for (float i = -a; i <= a; i += step)
        {
            float y = 1 - i * i / (a * a);
            y *= (b * b);
            y = Mathf.Sqrt(y);
            vectors[k] = new Vector3(i, y, 0);
            if (y != 0)
            {
                vectors[200 - k] = new Vector3(i, -y, 0);
            }
            k++;
        }
        mesh.vertices = vectors;

        int[] triangle = new int[400];
        for (int i = 0; i < vectors.Length - 1; ++i)
        {
            triangle[2 * i] = i;
            triangle[2 * i + 1] = i + 1;
        }
        triangle[398] = 199;
        triangle[399] = 0;

        mesh.SetIndices(triangle, MeshTopology.Lines, 0);

        GetComponent<MeshFilter>().mesh = mesh;
    }

    public void DrawEllipse3D()
    {
        mesh.Clear();

        Vector3[] vectors = new Vector3[400];
        int k = 0;
        float step = a / 50;
        for (float i = -a; i <= a; i += step)
        {
            float y = 1 - i * i / (a * a);
            y *= (b * b);
            y = Mathf.Sqrt(y);
            vectors[k] = new Vector3(i, y, -5);
            if (y != 0)
            {
                vectors[400 - k] = new Vector3(i, -y, -5);
            }
            k++;
            vectors[k] = new Vector3(i, y, 5);
            if (y != 0)
            {
                if(k % 2 == 0)
                    vectors[400 - k] = new Vector3(i, -y, 5);
                else
                    vectors[402 - k] = new Vector3(i, -y, 5);
            }
            k++;
        }
        mesh.vertices = vectors;

        Vector2[] uvs = new Vector2[vectors.Length];
        for (int i = 0; i < uvs.Length; i++)
        {
            uvs[i] = new Vector2(0, (vectors[i].y + 4) / 8);
        }
        mesh.uv = uvs;

        int[] triangle = new int[1200];
        for (int i = 0; i < 199; ++i)
        {
            triangle[6 * i] = 2 * i;
            triangle[6 * i + 1] = 2 * i + 1;
            triangle[6 * i + 2] = 2 * i + 2;
            triangle[6 * i + 3] = 2 * i + 1;
            triangle[6 * i + 4] = 2 * i + 3;
            triangle[6 * i + 5] = 2 * i + 2;
        }
        triangle[1194] = 398;
        triangle[1195] = 399;
        triangle[1196] = 0;
        triangle[1197] = 399;
        triangle[1198] = 1;
        triangle[1199] = 0;

        mesh.SetIndices(triangle, MeshTopology.Triangles, 0);

        GetComponent<MeshFilter>().mesh = mesh;
    }

    public void MeshClear()
    {
        mesh.Clear();
        GetComponent<MeshFilter>().mesh = mesh;
    }
}