当检测到眼镜即Camera的碰撞事件时，启动眼镜视图的淡入淡出。
PlayArea对象上挂在此脚本；

参数：

    public float timeTillFade = 0f;//等待淡入的时间
    public float blinkTransitionSpeed = 0.1f;//碰撞时的闪烁速度
    public Color fadeColor = Color.black;//指定颜色
    public VRTK_PolicyList targetListPolicy;//类
    public VRTK_HeadsetCollision headsetCollision;    //类   
    public VRTK_HeadsetFade headsetFade;//类

protected修饰的方法：

OnEnable()
获取这两个类：headsetFade headsetCollision
headsetCollision注册两个事件
OnDisable()
headsetCollision移除两个事件

事件绑定的方法：

OnHeadsetCollisionDetect()： 里面执行 Invoke("StartFade", timeTillFade);
OnHeadsetCollisionEnded(): 里面执行CancelInvoke("StartFade");
headsetFade.Unfade(blinkTransitionSpeed);

StartFade() 开始颜色变黑，调用的VRTK_HeadsetFade类里的Fade方法
ValidTarget() 返回bool值，判断碰撞后是否需要颜色变黑

    // Headset Collision Fade|Presence|70030
     namespace VRTK
   {
  using UnityEngine;
/// <summary>
/// Initiates a fade of the headset view when a headset collision event is detected.
/// </summary>
/// <remarks>
/// **Required Components:**
///  * `VRTK_HeadsetCollision` - A Headset Collision script to determine when the HMD has collided with valid geometry.
///  * `VRTK_HeadsetFade` - A Headset Fade script to alter the visible colour on the HMD view.
///
/// **Script Usage:**
///  * Place the `VRTK_HeadsetCollisionFade` script on any active scene GameObject.
/// </remarks>
/// <example>
/// `VRTK/Examples/011_Camera_HeadSetCollisionFading` has collidable walls around the play area and if the user puts their head into any of the walls then the headset will fade to black.
/// </example>
[AddComponentMenu("VRTK/Scripts/Presence/VRTK_HeadsetCollisionFade")]
public class VRTK_HeadsetCollisionFade : MonoBehaviour
{
    [Header("Collision Fade Settings")]

    [Tooltip("The amount of time to wait until a fade occurs.")]
    public float timeTillFade = 0f;//等待淡入的时间
    [Tooltip("The fade blink speed on collision.")]
    public float blinkTransitionSpeed = 0.1f;//碰撞时的闪烁速度
    [Tooltip("The colour to fade the headset to on collision.")]
    public Color fadeColor = Color.black;//碰撞后的颜色
    [Tooltip("A specified VRTK_PolicyList to use to determine whether any objects will be acted upon by the Headset Collision Fade.")]
    public VRTK_PolicyList targetListPolicy;//指定的VRTK_PolicyList类，用于确定耳机冲突是否会对任何对象起作用

    [Header("Custom Settings")]

    [Tooltip("The VRTK Headset Collision script to use when determining headset collisions. If this is left blank then the script will need to be applied to the same GameObject.")]
    public VRTK_HeadsetCollision headsetCollision;//确定耳机碰撞的类 determining headset collisions
    [Tooltip("The VRTK Headset Fade script to use when fading the headset. If this is left blank then the script will need to be applied to the same GameObject.")]
    public VRTK_HeadsetFade headsetFade;//负责褪色的类

    protected virtual void OnEnable()
    {
        headsetFade = (headsetFade != null ? headsetFade : FindObjectOfType<VRTK_HeadsetFade>());
        headsetCollision = (headsetCollision != null ? headsetCollision : FindObjectOfType<VRTK_HeadsetCollision>());

        if (headsetFade == null)
        {
            VRTK_Logger.Error(VRTK_Logger.GetCommonMessage(VRTK_Logger.CommonMessageKeys.REQUIRED_COMPONENT_MISSING_FROM_GAMEOBJECT, "VRTK_HeadsetCollisionFade", "VRTK_HeadsetFade", "the same or child"));
            return;
        }

        if (headsetCollision == null)
        {
            VRTK_Logger.Error(VRTK_Logger.GetCommonMessage(VRTK_Logger.CommonMessageKeys.REQUIRED_COMPONENT_MISSING_FROM_GAMEOBJECT, "VRTK_HeadsetCollisionFade", "VRTK_HeadsetCollision", "the same or child"));
            return;
        }

        headsetCollision.HeadsetCollisionDetect += new HeadsetCollisionEventHandler(OnHeadsetCollisionDetect);
        headsetCollision.HeadsetCollisionEnded += new HeadsetCollisionEventHandler(OnHeadsetCollisionEnded);
    }

    protected virtual void OnDisable()
    {
        if (headsetCollision != null)
        {
            headsetCollision.HeadsetCollisionDetect -= new HeadsetCollisionEventHandler(OnHeadsetCollisionDetect);
            headsetCollision.HeadsetCollisionEnded -= new HeadsetCollisionEventHandler(OnHeadsetCollisionEnded);
        }
    }

    protected virtual void OnHeadsetCollisionDetect(object sender, HeadsetCollisionEventArgs e)
    {
        if (ValidTarget(e.collider))
        {
            Invoke("StartFade", timeTillFade);
        }
    }

    protected virtual void OnHeadsetCollisionEnded(object sender, HeadsetCollisionEventArgs e)
    {
        if (ValidTarget(e.collider))
        {
            CancelInvoke("StartFade");
            headsetFade.Unfade(blinkTransitionSpeed);
        }
    }

    protected virtual void StartFade()
    {
        headsetFade.Fade(fadeColor, blinkTransitionSpeed);
    }

    protected virtual bool ValidTarget(Collider target)
    {
        return (target != null && !(VRTK_PolicyList.Check(target.gameObject, targetListPolicy)));
    }
}

}