Tags和Layers分别表示是Unity引擎里面的标签和层，他们都是用来对GameObject进行标识的属性，Tags常用于单个GameObject，Layers常用于一组的GameObject。添加Tags和Layers的操作如下：
"Edit" -> "Project Settings" -> "Tags and Layers"来打开设置面板。
tag可以理解为一类元素的标记，如hero、enemy、apple-tree等。通过设置tag，可以方便地通过GameObject.FindWithTag()来寻找对象。GameObject.FindWithTag()只返回一个对象，要想获取多个tag为某值的对象，GameObject.FindGameObjectsWithTag()。
每个GameObject的Inspector面板最上方都也有个Layer选项，就在Tag旁边，unity已经有了几个层，我们新建个层，也叫UI，点击Add Layer，可以看到从Layer0到Layer7都灰掉了，那是不能用的，从第八个起可以用，Layer和tag还有一个很大的区别就是layer最多只能有32个层。
在使用过程中，使用Culling Mask、Layer Mask的地方实际指的就是layer。下面我们来看一段使用layer来检测碰撞的代码：
Ray ray1 = nguiCamera.camera.ScreenPointToRay(Input.mousePosition);
RaycastHit hit1;
LayerMask mask = << LayerMask.NameToLayer("UI");
if (Physics.Raycast(ray1, out hit1, , mask.value))
{
return;
}
LayerMask的NameToLayer是通过层的名称返回该层的索引，如果是8，然后1<<8换算成LayerMask值，再用LayerMask的value就可以了。注意也必须设置collider才能接收碰撞，这里才能判断到。LayerMask实际上是一个位码操作，在Unity中Layers一共有32层，这个是不能增加或者减少的: 1 << LayerMask.NameToLayer("UI") 这一句实际上表示射线查询只在UI所在这个层级查找是返回的该名字所定义的层的层索引，注意是从0开始。
下面我们来看一个玩家控制的脚本，利用 Physics2D.Linecast检测物体是否碰撞到地面。
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.
// 在子对象里面找到groundCheck
groundCheck = transform.Find("groundCheck");
// 获取当前的动画控制器
anim = GetComponent<Animator>();
} void Update()
{
// 是为能随时检测到groundCheck这个物体，添加一个名叫Ground的Layer，然后把场景中的所有代表地面的物体的Layer设为Ground
// 这里用到了2D射线检测Physics2D.Linecast()
// LayerMask实际上是一个位码操作，在Unity3d中Layers一共有32层，这个是不能增加或者减少的:
// 1 << LayerMask.NameToLayer("Ground") 这一句实际上表示射线查询只在Ground所在这个层级查找 是返回的该名字所定义的层的层索引，注意是从0开始
// 每个GameObject的Inspector面板最上方都也有个Layer选项，就在Tag旁边，unity3d已经有了几个层，我们新建个层，也叫UI，点击Add Layer，可以看到从Layer0到Layer7都灰掉了，那是不能用的，从第八个起可以用，所以在第八个建个UI的层。
// 一般情况下我们只用前两个参数，distance表示射线距离，默认是无限远，重点是最后一个参数layerMask，专门处理layer过滤的，是个整型，怎么用呢，是靠layer的二进制位来操作的
// LayerMask的NameToLayer是通过层的名称返回该层的索引，这里是8，然后1<<8换算成LayerMask值，再用LayerMask的value就可以了。
// 注意也必须设置collider才能接收碰撞，这里才能判断到。
grounded = Physics2D.Linecast(transform.position, groundCheck.position, << LayerMask.NameToLayer("Ground")); // If the jump button is pressed and the player is grounded then the player should jump.
// 如果点击了跳的按键，并且已经着陆，那么就可以跳起来
if(Input.GetButtonDown("Jump") && grounded)
jump = true;
} // 因为主角游戏对象要使用到刚体力，所以一定要写在FixedUpdate里面，不能放在Update上
void FixedUpdate ()
{
// Cache the horizontal input.
// 换取水平方向的移动距离
float h = Input.GetAxis("Horizontal"); // The Speed animator parameter is set to the absolute value of the horizontal input.
// 设置动画的速度变量
anim.SetFloat("Speed", Mathf.Abs(h)); // 给物体添加一个水平的力，让它移动的时候会产生惯性的效果
// If the player is changing direction (h has a different sign to velocity.x) or hasn't reached maxSpeed yet...
// 如果速度小于最大的速度
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); // 转身
// If the input is moving the player right and the player is facing left...
if(h > && !facingRight)
// ... flip the player.
Flip();
// Otherwise if the input is moving the player left and the player is facing right...
else if(h < && facingRight)
// ... flip the player.
Flip(); // If the player should jump...
if(jump)
{
// Set the Jump animator trigger parameter.
// 触发跳的动画
anim.SetTrigger("Jump"); // Play a random jump audio clip.
int i = Random.Range(, jumpClips.Length);
AudioSource.PlayClipAtPoint(jumpClips[i], transform.position); // Add a vertical force to the player.
// 添加一个垂直的力
rigidbody2D.AddForce(new Vector2(0f, jumpForce)); // Make sure the player can't jump again until the jump conditions from Update are satisfied.
jump = false;
}
} // 转身
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 *= -;
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(, 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;
}
}