[Unity2D]Tags和Layers

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;
    }
}