鼠标在屏幕上的移动来控制相机水平，垂直旋转

using UnityEngine;
using System.Collections;
public class CameraController : MonoBehaviour {
    public float distance_v;
    public float distance_h;
    public float rotation_H_speed=1;
    public float rotation_V_speed=1;
    public float max_up_angle = 80;              //越大，头抬得越高
    public float max_down_angle =-60;            //越小，头抬得越低
    public Transform follow_obj;        //player


    private float current_rotation_H;      //水平旋转结果
    private float current_rotation_V;  //垂直旋转结果
    void LateUpdate()      
    {
        //控制旋转
        current_rotation_H+= Input.GetAxis("Mouse X")*rotation_H_speed;
        current_rotation_V += Input.GetAxis("Mouse Y")*rotation_V_speed;
        current_rotation_V=Mathf.Clamp(current_rotation_V, max_down_angle, max_up_angle);       //限制垂直旋转角度
        transform.localEulerAngles = new Vector3(-current_rotation_V,current_rotation_H,0f);
        
        //改变位置，以跟踪的目标为视野中心，且视野中心总是面向follow_obj
        transform.position =follow_obj.position;
        transform.Translate(Vector3.back * distance_h, Space.Self);
        transform.Translate(Vector3.up * distance_v, Space.World);          //相对于世界坐标y轴向上
    }
}