1.Hierarchy

2.Main Camera Inspector

3.控制脚本

using UnityEngine;
using UnityEngine.UIElements;
/// <summary>
/// 鼠标控制摄像机环绕某点运动
/// </summary>
public class CameraAroundController : MonoBehaviour
{
    //环绕点
    [SerializeField]
    private Transform aroundTransform;
    //摄像机
    [SerializeField]
    private Transform cameraTransform;
    //旋转速度
    [SerializeField]
    private float m_Speed = 5.0f;
    //鼠标滚轮灵敏度
    [SerializeField]
    private float m_ScrollWheelSensitivity = 40f;
    //是否开启鼠标滚轮
    [SerializeField]
    private bool m_ScrollWheelEnabled = true;
    private Vector3 lastPosition;

    public Transform AroundTransform 
    {
        get { return aroundTransform; }
        set { aroundTransform = value; }
    }

    public Transform CameraTransform
    {
        get { return cameraTransform; }
        set { cameraTransform = value; }
    }

    void Update()
    {
        if (aroundTransform == null || cameraTransform == null)
            return;
        MouseRotation();
        MouseScrollWheel();
    }

    // 鼠标控制旋转
    private void MouseRotation()
    {
        if (Input.GetMouseButtonDown(0))
        {
            lastPosition = Input.mousePosition;
            return;
        }

        if (!Input.GetMouseButton(0))
            return;

        if (UGUITool.IsPointerOverUI())
            return;

        Vector3 mousePosition = Input.mousePosition;
        Vector3 offset = mousePosition - lastPosition;
        lastPosition = mousePosition;

        //绕X轴旋转角度
        float angleX = -offset.y * Time.deltaTime * m_Speed;
        //绕Y轴旋转角度
        float angleY = offset.x * Time.deltaTime * m_Speed;
        //绕X轴旋转四元数
        Quaternion quaternionX = Quaternion.AngleAxis(angleX, cameraTransform.right);
        //绕Y轴旋转四元数
        Quaternion quaternionY = Quaternion.AngleAxis(angleY, Vector3.up);
        //综合旋转四元数
        Quaternion quaternion = quaternionX * quaternionY;

        //旋转向量到新的位置
        Vector3 point = aroundTransform.position;
        Vector3 vector = cameraTransform.position;
        Vector3 vector2 = vector - point;
        vector2 = quaternion * vector2;
        Vector3 new_vector = point + vector2;

        //旋转前的方向向量
        Vector3 before_forward = point - vector;
        //旋转后的方向向量
        Vector3 after_forward = point - new_vector;

        //限制摄像机最小俯视视角为0度
        float angle = Vector3.Angle(after_forward, Vector3.up);
        if (angle < 90)//小于90度将变成仰视角度
            return;

        //将before_forward投影到z平面上
        Vector3 zforward = before_forward;
        zforward.y = 0f;
        //限制摄像机最大俯视视角为90度
        angle = Vector3.Angle(zforward, after_forward);
        if (angle > 90)
            return;

        cameraTransform.position = new_vector;
        cameraTransform.LookAt(point);
    }

    // 鼠标滚轮
    private void MouseScrollWheel()
    {
        if (!m_ScrollWheelEnabled)
            return;
        float scrollWheel = Input.GetAxis("Mouse ScrollWheel");
        if (scrollWheel == 0f) return;
        Vector3 direction = cameraTransform.position - aroundTransform.position;
        direction.Normalize();
        cameraTransform.position -= direction * scrollWheel * m_ScrollWheelSensitivity;
    }
}

运行效果