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

[RequireComponent(typeof(MeshFilter), typeof(MeshRenderer))]
public class TestCircle : MonoBehaviour
{
    private MeshFilter meshFilter;
    [ExecuteInEditMode]
    private void Awake()
    {
        tempSegments = Segments;
        tempRadius = Radius;
        if (Segments <= 0)
        {

        }
        else
        {
            meshFilter = GetComponent<MeshFilter>();
            meshFilter.mesh = CreatCircle();
        }
    }

    private void Update()
    {
        if (tempSegments != Segments || tempRadius != Radius)
        {
            Awake();
        }
    }

    private float tempRadius = 5;
    private int tempSegments = 4;
    [Range(1, 10)]
    public float Radius = 5;    //半径
    [Range(1,200)]
    public int Segments = 4;	//分割数  360/Segments
    Mesh CreatCircle()
    {
        Mesh mesh = new Mesh();
        float dregrees = -Mathf.PI * 2 / Segments;  //每段弧度
        print(Mathf.Cos(dregrees));
        Vector3 tr = transform.position;
        List<Vector3> vector3s = new List<Vector3>();
        vector3s.Add(new Vector3(tr.x, tr.y, tr.z));
        for (int i = 0; i < Segments ; i++)
        {
            vector3s.Add(new Vector3(tr.x + Radius * Mathf.Cos(dregrees * i), tr.y + Radius * Mathf.Sin(dregrees * i), tr.z));
        }

       

        List<int> triangles = new List<int>();
        for (int i = 0; i < Segments - 1; i++)
        {
            triangles.Add(0);
            triangles.Add(i + 1);
            triangles.Add(i + 2);
        }
        triangles.Add(0);
        triangles.Add(Segments);
        triangles.Add(1);

        List<Vector2> uvs = new List<Vector2>();
        for (int i = 0; i < vector3s.Count; i++)
        {
            //uvs.Add(Vector2.zero);
            uvs.Add(new Vector2((vector3s[i].x- tr.x) / Radius / 2 + 0.5f,
                (vector3s[i].y - tr.y) / Radius / 2 + 0.5f));
        }

        mesh.vertices = vector3s.ToArray();
        mesh.triangles = triangles.ToArray();
        mesh.uv = uvs.ToArray(); ;

        return mesh;
    }


    void OnDrawGizmos()
    {
        Gizmos.color = Color.gray;
        DrawMesh();
    }

    void OnDrawGizmosSelected()
    {
        Gizmos.color = Color.green;
        DrawMesh();
    }

    private void DrawMesh()
    {
        if (Segments <= 0)
        {

        }
        else
        {
            Mesh mesh = CreatCircle();

            int[] tris = mesh.triangles;

            //画三角形
            for (int i = 0; i < tris.Length / 3; i++)
            {
                Gizmos.DrawLine(mesh.vertices[tris[i * 3]], mesh.vertices[tris[i * 3 + 1]]);
                Gizmos.DrawLine(mesh.vertices[tris[i * 3 + 1]], mesh.vertices[tris[i * 3 + 2]]);
                Gizmos.DrawLine(mesh.vertices[tris[i * 3 + 2]], mesh.vertices[tris[i * 3]]);
            }

            //在每个顶点处画球
            for (int i = 0; i < mesh.vertices.Length; i++)
            {
                Gizmos.DrawSphere(mesh.vertices[i], 0.2f);
            }
        }
      
    }
}