角度范围检测方法之一

关于Dot和Cross都能用于角度检测
一般Dot用于计算角度，Cross计算方法

关于介绍，参考：
一、Unity3D之Vector3.Dot和Vector3.Cross的使用
https://blog.csdn.net/wingfourever/article/details/27714311
二、Unity 点乘（Dot）、叉乘（Cross）判断移动方向、朝向等向量问题
https://blog.csdn.net/LIQIANGEASTSUN/article/details/50331933?spm=1001.2101.3001.6650.1&utm_medium=distribute.pc_relevant.none-task-blog-2~default~CTRLIST~Rate-1-50331933-blog-27714311.pc_relevant_recovery_v2&depth_1-utm_source=distribute.pc_relevant.none-task-blog-2~default~CTRLIST~Rate-1-50331933-blog-27714311.pc_relevant_recovery_v2&utm_relevant_index=2

三、国外有个教程用Dot方法做了个小测试

`using UnityEngine;

public class EnemyController : MonoBehaviour
{
public float detectionRadius = 10.0f;
public float detectionAngle = 90.0f;

private void Update()
{
    LookForPlayer();
}

private PlayerController LookForPlayer()
{
    if (PlayerController.Instance == null)
    {
        return null;
    }

    Vector3 enemyPosition = transform.position;
    Vector3 toPlayer = PlayerController.Instance.transform.position - enemyPosition;
    toPlayer.y = 0;

    if (toPlayer.magnitude <= detectionRadius)
    {
        if (Vector3.Dot(toPlayer.normalized, transform.forward) >
            Mathf.Cos(detectionAngle * 0.5f * Mathf.Deg2Rad)) {

            Debug.Log("Player has been detected!");
            return PlayerController.Instance;
        }
    }


    return null;
}

//#if UNITY_EDITOR
private void OnDrawGizmosSelected()
{
Color c = new Color(0.8f, 0, 0, 0.4f);
UnityEditor.Handles.color = c;

    Vector3 rotatedForward = Quaternion.Euler(
        0,
        -detectionAngle * 0.5f,
        0) * transform.forward;

    UnityEditor.Handles.DrawSolidArc(
        transform.position,
        Vector3.up,
        rotatedForward,
        detectionAngle,
        detectionRadius);

}

//#endif
}
`