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 = 1 << LayerMask.NameToLayer("UI"); if (Physics.Raycast(ray1, out hit1, 600, 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, 1 << 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 > 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. // 触发跳的动画 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 *= -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; } }