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

public class MoveOnSphere : MonoBehaviour {
    public GameObject sphere;
    public GameObject target;
	// Use this for initialization
    
	void Start () {
        if (sphere == null)
		{
            Debug.Log("球為空");
            return;
		}       
	}	
	// Update is called once per frame
	void Update () {
        if (Input.GetMouseButton(0))
        {
            Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
            RaycastHit hit;
            if (Physics.Raycast(ray, out hit, 1000, 1 << 8))//8層，球的層級
            {          
				//膠囊體在一個父級空物件下
                transform.parent.position = hit.point;
				
                //計算球上一點的法線向量
                Vector3 normal = transform.position-sphere.transform.position;
				
				//球心到目標點的向量
                Vector3 SphereToTarget = target.transform.position - sphere.transform.position;
				
				//計算次法線的向量（即與切線和法線所在平面垂直的向量）
                Vector3 binormal = Vector3.Cross(normal,SphereToTarget).normalized;
				
				//計算出指向目標物的切線向量
                Vector3 tangent = Vector3.Cross(binormal,normal);
				
				//計算父級的前方向和目標切線的角度
                float angle = Vector3.Angle(transform.parent.forward,tangent);
				
				//膠囊體旋轉相反的角度對準目標物體
                transform.localEulerAngles = new Vector3(0,-angle,0);
				
				//將UP向量朝向法線
                transform.parent.up = normal;
                
            }
        }
	}
}