unity 刀塔类镜头旋转，缩放，人物控制等

功能：摄像头可以围绕主角进行旋转，放大，缩小，
镜头设置了一个Y轴的旋转极限，保证视角正确。

Update内进行缩放，并且记录offsetposition，用于下次位置更新，
旋转时记得弄清楚围绕哪个对象，哪个轴。

（调用顺序）

private float distance;
private bool isscroll;
public GameObject player;
private Vector3 offsetposition;
// Use this for initialization
void Start () {
    transform.LookAt(player.transform.position);
    offsetposition = this.transform.position - player.transform.position;
    distance = offsetposition.magnitude;
}

// Update is called once per frame
void Update () {

    transform.position = player.transform.position + offsetposition;
    Scrollscreen();
    distance -= Input.GetAxis("Mouse ScrollWheel")*10;
    distance = Mathf.Clamp(distance, 2, 18);
    offsetposition = offsetposition.normalized * distance;

}

void Scrollscreen()
{
    if(Input.GetMouseButtonDown(0)&&!EventSystem.current.IsPointerOverGameObject())
    {
        isscroll = true;
    }
    if(Input.GetMouseButtonUp(0))
    {
        isscroll = false;
    }
    if(isscroll)
    {
        transform.RotateAround(player.transform.position, player.transform.up, (Input.GetAxis("Mouse X") * 5));
        Quaternion quaternion = transform.rotation;
        Vector3 vector3 = transform.position;
        transform.RotateAround(player.transform.position, transform.right, -(Input.GetAxis("Mouse Y") * 5));

        float x = transform.eulerAngles.x;
        
        if(x<10||x>80)
        {
            transform.rotation = quaternion;
            transform.position = vector3;
        }


        offsetposition = this.transform.position - player.transform.position;
    }

}