private LineRenderer line;
//画线
line = this.gameObject.AddComponent<LineRenderer>();
//只有设置了材质 setColor才有作用
line.material = new Material(Shader.Find("Particles/Additive"));
line.SetVertexCount(2);//设置两点
line.SetColors(Color.yellow, Color.red); //设置直线颜色
line.SetWidth(0.01f, 0.01f);//设置直线宽度
//设置指示线的起点和终点
line.SetPosition(0, initPosition);
line.SetPosition(1, newPosition);

 public float R;//半径
 public int N;//不要超过45
 line.SetVertexCount(N+1);//这里要加1,达成闭合曲线
 for (int i = 0; i < N + 1; i++)
{
  float x = R * Mathf.Cos((360 / N * i) * Mathf.Deg2Rad) + transform.position.x; //确定x坐标
  float z = R * Mathf.Sin((360 / N * i) * Mathf.Deg2Rad) + transform.position.z; //确定z坐标
  line.SetPosition(i, new Vector3(x, transform.position.y, z));         
}

using System.Collections;
using System.Collections.Generic;
using UnityEngine; 
public class DrawLineByMouse : MonoBehaviour { 
    //画线组件预制体
    public Transform gestureOnScreenPrefab; 
    private int strokeId = -1; 
    private Vector3 virtualKeyPosition = Vector2.zero;
    private Rect drawArea;
    private RuntimePlatform platform;
    private int vertexCount = 0; 
    private List<LineRenderer> gestureLinesRenderer = new List<LineRenderer>();
    private LineRenderer currentGestureLineRenderer; 
    //GUI
    private string message="what is this ?";
    private bool recognized;
    private string newGestureName = ""; 
    void Start()
    {
        platform = Application.platform;
        drawArea = new Rect(0, 0, Screen.width - Screen.width / 3, Screen.height);
    } 
    void Update()
    { 
        if (platform == RuntimePlatform.Android || platform == RuntimePlatform.IPhonePlayer)
        {
            if (Input.touchCount > 0)
            {
                virtualKeyPosition = new Vector3(Input.GetTouch(0).position.x, Input.GetTouch(0).position.y);
            }
        }
        else
        {
            if (Input.GetMouseButton(0))
            {
                virtualKeyPosition = new Vector3(Input.mousePosition.x, Input.mousePosition.y);
            }
        }
 
        if (drawArea.Contains(virtualKeyPosition))
        {
 
            if (Input.GetMouseButtonDown(0))
            {
               ++strokeId;
 
               // Transform tmpGesture = Instantiate(gestureOnScreenPrefab, transform.position, transform.rotation) as Transform;
               // currentGestureLineRenderer = tmpGesture.GetComponent<LineRenderer>();
 
                GameObject go = new GameObject("LineRenderer");
                go.transform.position = Camera.main.transform.position;
                go.transform.rotation = Camera.main.transform.rotation;
                currentGestureLineRenderer = go.AddComponent<LineRenderer>();              
                currentGestureLineRenderer.startWidth = 0.1f; 
                gestureLinesRenderer.Add(currentGestureLineRenderer); 
                vertexCount = 0;
            }
 
            if (Input.GetMouseButton(0))
            {            
                currentGestureLineRenderer.SetVertexCount(++vertexCount);
                currentGestureLineRenderer.SetPosition(vertexCount - 1, Camera.main.ScreenToWorldPoint(new Vector3(virtualKeyPosition.x, virtualKeyPosition.y, 10)));
            }
        }
    } 
    void OnGUI()
    {
 
        GUI.Box(drawArea, "Draw Area"); 
        GUI.Label(new Rect(10, Screen.height - 40, 500, 50), message); 
        if (GUI.Button(new Rect(Screen.width - 100, 10, 100, 30), "clear line"))
        {
            foreach (LineRenderer lineRenderer in gestureLinesRenderer)
            {
                lineRenderer.SetVertexCount(0);
                Destroy(lineRenderer.gameObject);
            }
            gestureLinesRenderer.Clear();
            recognized = true;
 
        }
    }
}