相机组件结构：

一般是相机根节点处理，相机跟随，旋转。

mainCamera处理相机距离。

当角色靠近墙壁，墙壁处于摄像机和角色之间时，会遮挡角色，处理方法是，把相机距离拉近。

public class Test : MonoBehaviour {

	protected bool isHadCol; //外部调用 是否相机被遮挡

	public Transform m_camera; //相机
	public Transform m_camera_parent; //相机父控件
	public Transform m_target; //相机跟随目标

	public float m_clipMoveTime = 0.2f; //剪裁速度
	public float m_backMoveTime = 0.5f; //回归速度

	public string[] m_raycastLayerName = { "CameraCollide" };
	private int m_raycastLayer = 0;		
	private float m_raycastDistance = 33.0f;    //射线长度

	private float m_defaultDistance;
	private float m_curDistance;

	RaycastHit[] m_raycastHitsArray = new RaycastHit[8];
	private List<float> m_dist = new List<float>();
	private Ray m_ray = new Ray();
	private float m_MoveVelocity;

	void Start () {
		if (!m_camera) {
			m_camera = GetComponentInChildren<Camera>().transform;
		}
		m_camera_parent = m_camera.parent;

		m_raycastLayer = 0;
		for (int i = 0; i < m_raycastLayerName.Length; i++) {
			m_raycastLayer |= 1 << LayerMask.NameToLayer(m_raycastLayerName[i]);
		}

		m_defaultDistance = m_camera.localPosition.magnitude;
		m_curDistance = m_defaultDistance;
	}
	
	void LateUpdate () {
		if (!m_target) return;

		float m_targetDistance = m_defaultDistance;
		
		m_ray.origin = m_target.position;
		m_ray.direction = -m_camera.forward.normalized;

		var hitCount = Physics.RaycastNonAlloc(m_ray, m_raycastHitsArray, m_raycastDistance, m_raycastLayer);
		m_dist.Clear();
		for (int i = 0; i < hitCount; i++) {
			var hitGo = m_raycastHitsArray[i].collider.gameObject;
			//todo 其他条件
			m_dist.Add(m_camera_parent.InverseTransformPoint(m_raycastHitsArray[i].point).z);
		}

		if (m_dist.Count > 0)
		{
			m_dist.Reverse();
			m_targetDistance = m_dist[0];
			isHadCol = true;
		}
		else {
			isHadCol = false;
		}

		Debug.DrawRay(m_ray.origin, m_ray.direction * m_raycastDistance, Color.red);

		m_curDistance = Mathf.SmoothDamp(m_curDistance, m_targetDistance, ref m_MoveVelocity,
			m_curDistance <= m_targetDistance ? m_clipMoveTime : m_backMoveTime);
		m_curDistance = Mathf.Clamp(m_curDistance, 0, 10);
		m_camera.localPosition = Vector3.forward * m_curDistance;

	}
}