Tags和Layers分別表示是Unity引擎裏面的標籤和層，他們都是用來對GameObject進行標識的屬性，Tags常用於單個GameObject，Layers常用於一組的GameObject。添加Tags和Layers的操作如下：
"Edit" -> "Project Settings" -> "Tags and Layers"來打開設置面板。
tag可以理解爲一類元素的標記，如hero、enemy、apple-tree等。通過設置tag，可以方便地通過GameObject.FindWithTag()來尋找對象。GameObject.FindWithTag()只返回一個對象，要想獲取多個tag爲某值的對象，GameObject.FindGameObjectsWithTag()。
每個GameObject的Inspector面板最上方都也有個Layer選項，就在Tag旁邊，unity已經有了幾個層，我們新建個層，也叫UI，點擊Add Layer，可以看到從Layer0到Layer7都灰掉了，那是不能用的，從第八個起可以用，Layer和tag還有一個很大的區別就是layer最多只能有32個層。
在使用過程中，使用Culling Mask、Layer Mask的地方實際指的就是layer。下面我們來看一段使用layer來檢測碰撞的代碼：
Ray ray1 = nguiCamera.camera.ScreenPointToRay(Input.mousePosition);
RaycastHit hit1;
LayerMask mask = 1 << LayerMask.NameToLayer("UI");
if (Physics.Raycast(ray1, out hit1, 600, mask.value))
{
return;
} LayerMask的NameToLayer是通過層的名稱返回該層的索引，如果是8，然後1<<8換算成LayerMask值，再用LayerMask的value就可以了。注意也必須設置collider才能接收碰撞，這裏才能判斷到。LayerMask實際上是一個位碼操作，在Unity中Layers一共有32層，這個是不能增加或者減少的: 1 << LayerMask.NameToLayer("UI") 這一句實際上表示射線查詢只在UI所在這個層級查找是返回的該名字所定義的層的層索引，注意是從0開始。
下面我們來看一個玩家控制的腳本，利用 Physics2D.Linecast檢測物體是否碰撞到地面。
using UnityEngine;
using System.Collections;
public class PlayerControl : MonoBehaviour
{
[HideInInspector]
public bool facingRight = true; // For determining which way the player is currently facing.
[HideInInspector]
public bool jump = false; // Condition for whether the player should jump.
public float moveForce = 365f; // Amount of force added to move the player left and right.
public float maxSpeed = 5f; // The fastest the player can travel in the x axis.
public AudioClip[] jumpClips; // Array of clips for when the player jumps.
public float jumpForce = 1000f; // Amount of force added when the player jumps.
public AudioClip[] taunts; // Array of clips for when the player taunts.
public float tauntProbability = 50f; // Chance of a taunt happening.
public float tauntDelay = 1f; // Delay for when the taunt should happen.
private int tauntIndex; // The index of the taunts array indicating the most recent taunt.
private Transform groundCheck; // A position marking where to check if the player is grounded.
private bool grounded = false; // Whether or not the player is grounded.
private Animator anim; // Reference to the player's animator component.
void Awake()
{
// Setting up references.
// 在子對象裏面找到groundCheck
groundCheck = transform.Find("groundCheck");
// 獲取當前的動畫控制器
anim = GetComponent<Animator>();
}
void Update()
{
// 是爲能隨時檢測到groundCheck這個物體，添加一個名叫Ground的Layer，然後把場景中的所有代表地面的物體的Layer設爲Ground
// 這裏用到了2D射線檢測Physics2D.Linecast()
// LayerMask實際上是一個位碼操作，在Unity3d中Layers一共有32層，這個是不能增加或者減少的:
// 1 << LayerMask.NameToLayer("Ground") 這一句實際上表示射線查詢只在Ground所在這個層級查找 是返回的該名字所定義的層的層索引，注意是從0開始
// 每個GameObject的Inspector面板最上方都也有個Layer選項，就在Tag旁邊，unity3d已經有了幾個層，我們新建個層，也叫UI，點擊Add Layer，可以看到從Layer0到Layer7都灰掉了，那是不能用的，從第八個起可以用，所以在第八個建個UI的層。
// 一般情況下我們只用前兩個參數，distance表示射線距離，默認是無限遠，重點是最後一個參數layerMask，專門處理layer過濾的，是個整型，怎麼用呢，是靠layer的二進制位來操作的
// LayerMask的NameToLayer是通過層的名稱返回該層的索引，這裏是8，然後1<<8換算成LayerMask值，再用LayerMask的value就可以了。
// 注意也必須設置collider才能接收碰撞，這裏才能判斷到。
grounded = Physics2D.Linecast(transform.position, groundCheck.position, 1 << LayerMask.NameToLayer("Ground"));
// If the jump button is pressed and the player is grounded then the player should jump.
// 如果點擊了跳的按鍵，並且已經着陸，那麼就可以跳起來
if(Input.GetButtonDown("Jump") && grounded)
jump = true;
}
// 因爲主角遊戲對象要使用到剛體力，所以一定要寫在FixedUpdate裏面，不能放在Update上
void FixedUpdate ()
{
// Cache the horizontal input.
// 換取水平方向的移動距離
float h = Input.GetAxis("Horizontal");
// The Speed animator parameter is set to the absolute value of the horizontal input.
// 設置動畫的速度變量
anim.SetFloat("Speed", Mathf.Abs(h));
// 給物體添加一個水平的力，讓它移動的時候會產生慣性的效果
// If the player is changing direction (h has a different sign to velocity.x) or hasn't reached maxSpeed yet...
// 如果速度小於最大的速度
if(h * rigidbody2D.velocity.x < maxSpeed)
// ... add a force to the player.
rigidbody2D.AddForce(Vector2.right * h * moveForce);
// If the player's horizontal velocity is greater than the maxSpeed...
if(Mathf.Abs(rigidbody2D.velocity.x) > maxSpeed)
// ... set the player's velocity to the maxSpeed in the x axis.
rigidbody2D.velocity = new Vector2(Mathf.Sign(rigidbody2D.velocity.x) * maxSpeed, rigidbody2D.velocity.y);
// 轉身
// If the input is moving the player right and the player is facing left...
if(h > 0 && !facingRight)
// ... flip the player.
Flip();
// Otherwise if the input is moving the player left and the player is facing right...
else if(h < 0 && facingRight)
// ... flip the player.
Flip();
// If the player should jump...
if(jump)
{
// Set the Jump animator trigger parameter.
// 觸發跳的動畫
anim.SetTrigger("Jump");
// Play a random jump audio clip.
int i = Random.Range(0, jumpClips.Length);
AudioSource.PlayClipAtPoint(jumpClips[i], transform.position);
// Add a vertical force to the player.
// 添加一個垂直的力
rigidbody2D.AddForce(new Vector2(0f, jumpForce));
// Make sure the player can't jump again until the jump conditions from Update are satisfied.
jump = false;
}
}
// 轉身
void Flip ()
{
// Switch the way the player is labelled as facing.
facingRight = !facingRight;
// Multiply the player's x local scale by -1.
Vector3 theScale = transform.localScale;
theScale.x *= -1;
transform.localScale = theScale;
}
public IEnumerator Taunt()
{
// Check the random chance of taunting.
float tauntChance = Random.Range(0f, 100f);
if(tauntChance > tauntProbability)
{
// Wait for tauntDelay number of seconds.
yield return new WaitForSeconds(tauntDelay);
// If there is no clip currently playing.
if(!audio.isPlaying)
{
// Choose a random, but different taunt.
tauntIndex = TauntRandom();
// Play the new taunt.
audio.clip = taunts[tauntIndex];
audio.Play();
}
}
}
int TauntRandom()
{
// Choose a random index of the taunts array.
int i = Random.Range(0, taunts.Length);
// If it's the same as the previous taunt...
if(i == tauntIndex)
// ... try another random taunt.
return TauntRandom();
else
// Otherwise return this index.
return i;
}
}
