利用欧拉角和四元素（Quaternion）camera围绕物体旋

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class CameraRotateAround : MonoBehaviour
{

    public Transform target;//相机要围绕其旋转的物体  
    public float distance = 7.0f;//相机与目标物体之间的距离  
    private float eulerAngles_x;
    private float eulerAngles_y;
    private bool isRotating = false;//鼠标水平滑动


    //水平滚动相关  
    public int distanceMax = 10;//相机与目标物体之间的最大距离  
    public int distanceMin = 3;//相机与目标物体之间的最小距离  
    public float xSpeed = 70.0f;//相机水平方向旋转速度  



    //垂直滚动相关  
    public int yMaxLimit = 60;//最大y（单位是角度）  
    public int yMinLimit = -10;//最小y（单位是角度）  
    public float ySpeed = 70.0f;//相机纵向旋转速度  

    //滚轮相关  
    public float MouseScrollWheelSensitivity = 1.0f;//鼠标滚轮灵敏度（备注：鼠标滚轮滚动后将调整相机与目标物体之间的距离）  
    public LayerMask CollisionLayerMask;

    void Start()
    {
        Vector3 eulerAngles = this.transform.eulerAngles;//当前物体的欧拉角  
        this.eulerAngles_x = eulerAngles.y;
        this.eulerAngles_y = eulerAngles.x;
    }

    // Update is called once per frame  
    void LateUpdate()
    {
        RotateView();

    }

    void RotateView()
    {
        if (Input.GetMouseButtonDown(1))
        {
            isRotating = true;
        }

        if (Input.GetMouseButtonUp(1))
        {
            isRotating = false;
        }

        if (isRotating)
        {
            if (this.target != null)
            {
                this.eulerAngles_x += ((Input.GetAxis("Mouse X") * this.xSpeed) * this.distance) * 0.02f;
                this.eulerAngles_y -= (Input.GetAxis("Mouse Y") * this.ySpeed) * 0.02f;
                this.eulerAngles_y = ClampAngle(this.eulerAngles_y, (float)this.yMinLimit, (float)this.yMaxLimit);
                Quaternion quaternion = Quaternion.Euler(this.eulerAngles_y, this.eulerAngles_x, (float)0);
                this.distance = Mathf.Clamp(this.distance - (Input.GetAxis("Mouse ScrollWheel") * MouseScrollWheelSensitivity), (float)this.distanceMin, (float)this.distanceMax);
                //从目标物体处，到当前脚本所依附的对象（相机）发射一个射线，如果中间有物体阻隔，则更改this.distance（这样做的目的是为了物体不被挡住）  
                RaycastHit hitInfo = new RaycastHit();
                if (Physics.Linecast(this.target.position, this.transform.position, out hitInfo, this.CollisionLayerMask))
                {
                    this.distance = hitInfo.distance - 0.05f;
                }
                Vector3 vector = ((Vector3)(quaternion * new Vector3((float)0, (float)0, -this.distance))) + this.target.position;
                //更改相机的旋转角度和位置  
                this.transform.rotation = quaternion;
                this.transform.position = vector;
            }
        }
    }

    //把角度限制到给定范围内  

    public float ClampAngle(float angle, float min, float max)
    {
        while (angle < -360)
        {
            angle += 360;
        }

        while (angle > 360)
        {
            angle -= 360;
        }
        return Mathf.Clamp(angle, min, max);

    }
}