[Mini-Mechanisms#1] State-Driven Camera Motion

== Intro ==

use case: 假设一个棋牌游戏的房间，玩家进入房间后处于站立视角，点击座位后，玩家入座，视角切换，开始游戏
Mechanism: State-Driven Camera Motion

== Problems ==

[1] Locate UI

将UI部件根据世界坐标下物件放置到屏幕上对应位置

[2] Smooth Camera Motion

需要进行平滑的相机移动
总共有四种视角：Stand Up视角 * 1， Sit Down视角 * 3。
根据玩家选择的不同，镜头移动到不同的Sit Down视角
点击Stand Up Btn 后，回到Stand Up视角

== Solutions ==

[1] Locate UI

使用Camera.WorldToScreenPoint

https://docs.unity3d.com/ScriptReference/Camera.WorldToScreenPoint.html
为Take Seat Btn添加一个Component
为该Component指出跟随目标的Transform
Btn UI在Update中不断Locate()，移动到对应屏幕位置

[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
  - 设置一个Fellow Target Transform（代表Player），在Player移动时，Camera在指定的Dolly Track上跟随Player移动
  - 效果不太理想，实现略复杂。原因在于本例的重点不在跟随，需要关注的是State Change（Stand up、Sit Down 0/1/2）
- #2 使用State-Driven Cameras
  - https://www.youtube.com/watch?v=2X00qXErxIM&t=163s
  - 设置Player Animator和State（Stand up、Sit Down 0/1/2），状态迁移可以简单的通过Seat Id equals xxx来实现（Stand up处seat id = -1）
  - 为对应的State创建对应的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);
        }
    }
}