[Mini-Mechanisms#1] State-Driven Camera Motion-有解無憂

== Intro ==

use case: 假設一個棋牌游戲的房間，玩家進入房間后處于站立視角，點擊座位后，玩家入座，視角切換，開始游戲
Mechanism: State-Driven Camera Motion

== Problems == [1] Locate UI

將UI部件根據世界坐標下物件放置到螢屏上對應位置

[2] Smooth Camera Motion

需要進行平滑的相機移動
總共有四種視角：Stand Up視角 * 1， Sit Down視角 * 3，
根據玩家選擇的不同，鏡頭移動到不同的Sit Down視角
點擊Stand Up Btn 后，回到Stand Up視角

== Solutions == [1] Locate UI

使用Camera.WorldToScreenPoint

https://docs.unity3d.com/ScriptReference/Camera.WorldToScreenPoint.html
為Take Seat Btn添加一個Component
為該Component指出跟隨目標的Transform
Btn UI在Update中不斷Locate()，移動到對應螢屏位置

[2] Smooth Camera Motion

使用Unity 提供的Cinemachine
- #1 使用Virtual Camera搭配Dolly Track
  - https://www.youtube.com/watch?v=q1fkx94vHtg&list=PLX2vGYjWbI0TQpl4JdfEDNO1xK_I34y8P&index=2
  - 設定一個Fellow Target Transform（代表Player），在Player移動時，Camera在指定的Dolly Track上跟隨Player移動
  - 效果不太理想，實作略復雜，原因在于本例的重點不在跟隨，需要關注的是State Change（Stand up、Sit Down 0/1/2）
- #2 使用State-Driven Cameras
  - https://www.youtube.com/watch?v=2X00qXErxIM&t=163s
  - 設定Player Animator和State（Stand up、Sit Down 0/1/2），狀態遷移可以簡單的通過Seat Id equals xxx來實作（Stand up處seat id = -1）
  - 為對應的State創建對應的camera

== Locate UI == [1] ScreenPosLocator

using UnityEngine;

namespace CameraMotion.Scripts
{
    public class ScreenPosLocator : MonoBehaviour
    {
        public Transform followTransform;
        public Vector3 offset;
        public bool shouldFellow;
        private Camera camera;
    
        public void Awake()
        {
            camera = Camera.main;
        }

        public void Update()
        {
            Locate();
        }
        
        private void Locate()
        {
            if (shouldFellow)
            {
                transform.position = camera.WorldToScreenPoint(followTransform.position + offset);
            }
        }
    }
}

[2] Seat

using UnityEngine;
using UnityEngine.Events;
using UnityEngine.UI;

namespace CameraMotion.Scripts
{
    public class Seat : MonoBehaviour
    {
        public int seatId;
        public Button btnTakeSeat;
        public UnityEvent<Seat> playerSitDownEvent;
        private bool available;
        
        public void Awake()
        {
            available = true;
            btnTakeSeat.onClick.AddListener(OnOccupied);
        }

        public void Occupy()
        {
            available = false;
        }

        public void Release()
        {
            available = true;
        }
        
        public void Disable()
        {
            btnTakeSeat.gameObject.SetActive(false);
        }
        
        public void TryEnable()
        {
            if (available)
            {
                Enable();
            }
        }
        
        private void Enable()
        {
            btnTakeSeat.gameObject.SetActive(true);
        }
        
        private void OnOccupied()
        {
            playerSitDownEvent?.Invoke(this);
        }
    }
}