using UnityEngine;
using UnityEngine.EventSystems;
 
public class UIJoystick : MonoBehaviour, IDragHandler, IEndDragHandler
{  
  /// <summary>
 /// 被用戶拖動的操縱桿
  /// </summary>
  public Transform target;
 
  /// <summary>
 /// 操縱桿可移動的最大半徑
  /// </summary>
  public float radius = 50f;
  
  /// <summary>
 /// 當(dāng)前操縱桿在2D空間的x,y位置
  /// 搖桿按鈕的值【-1，1】之間
  /// </summary>
  public Vector2 position;
    
 //操縱桿的RectTransform組件
 private RectTransform thumb;
 
 void Start()
 {
 thumb = target.GetComponent<RectTransform>();
 }
 
  /// <summary>
 /// 當(dāng)操縱桿被拖動時觸發(fā)
  /// </summary>
  public void OnDrag(PointerEventData data)
 {
 //獲取搖桿的RectTransform組件，以檢測操縱桿是否在搖桿內(nèi)移動
 RectTransform draggingPlane = transform as RectTransform;
 Vector3 mousePos;
 
 //檢查拖動的位置是否在拖動rect內(nèi)，
 //然后設(shè)置全局鼠標(biāo)位置并將其分配給操縱桿
 if (RectTransformUtility.ScreenPointToWorldPointInRectangle (draggingPlane, data.position, data.pressEventCamera, out mousePos)) {
  thumb.position = mousePos;
 }
  
 //觸摸向量的長度（大?。?
 //計算操作桿的相對位置
 float length = target.localPosition.magnitude;
 
 //如果操縱桿超過了搖桿的范圍，則將操縱桿設(shè)置為最大半徑
 if (length > radius) {
  target.localPosition = Vector3.ClampMagnitude (target.localPosition, radius);
 }
  
 //在Inspector顯示操縱桿位置
 position = target.localPosition;
 //將操縱桿相對位置映射到【-1，1】之間
 position = position / radius * Mathf.InverseLerp (radius, 2, 1);
 }
  /// <summary>
 /// 當(dāng)操縱桿結(jié)束拖動時觸發(fā)
  /// </summary>
  public void OnEndDrag(PointerEventData data)
 {
 //拖拽結(jié)束，將操縱桿恢復(fù)到默認(rèn)位置
 position = Vector2.zero;
 target.position = transform.position;
 }
}

using System;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;
 
 
// 
// Joystick component for controlling player movement and actions using Unity UI events.
// There can be multiple joysticks on the screen at the same time, implementing different callbacks.
// 
public class UIJoystick : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{
  /// 
  /// Callback triggered when joystick starts moving by user input.
  /// 
  public event Action onDragBegin;
  
  /// 
  /// Callback triggered when joystick is moving or hold down.
  /// 
  public event Action onDrag;
  
  /// 
  /// Callback triggered when joystick input is being released.
  /// 
  public event Action onDragEnd;
 
  /// 
  /// The target object i.e. jostick thumb being dragged by the user.
  /// 
  public Transform target;
 
  /// 
  /// Maximum radius for the target object to be moved in distance from the center.
  /// 
  public float radius = 50f;
  
  /// 
  /// Current position of the target object on the x and y axis in 2D space.
  /// Values are calculated in the range of [-1, 1] translated to left/down right/up.
  /// 
  public Vector2 position;
  
  //keeping track of current drag state
  private bool isDragging = false;
  
  //reference to thumb being dragged around
 private RectTransform thumb;
 
  //initialize variables
 void Start()
 {
 thumb = target.GetComponent();
 
 //in the editor, disable input received by joystick graphics:
    //we want them to be visible but not receive or block any input
 #if UNITY_EDITOR
  Graphic[] graphics = GetComponentsInChildren();
 // for(int i = 0; i < graphics.Length; i++)
 // graphics[i].raycastTarget = false;
 #endif
 }
 
  /// 
  /// Event fired by UI Eventsystem on drag start.
  /// 
  public void OnBeginDrag(PointerEventData data)
  {
    isDragging = true;
    if(onDragBegin != null)
      onDragBegin();
  }
 
  /// 
  /// Event fired by UI Eventsystem on drag.
  /// 
  public void OnDrag(PointerEventData data)
  {
    //get RectTransforms of involved components
    RectTransform draggingPlane = transform as RectTransform;
    Vector3 mousePos;
 
    //check whether the dragged position is inside the dragging rect,
    //then set global mouse position and assign it to the joystick thumb
    if (RectTransformUtility.ScreenPointToWorldPointInRectangle(draggingPlane, data.position, data.pressEventCamera, out mousePos))
    {
      thumb.position = mousePos;
    }
 
    //length of the touch vector (magnitude)
    //calculated from the relative position of the joystick thumb
    float length = target.localPosition.magnitude;
 
    //if the thumb leaves the joystick's boundaries,
    //clamp it to the max radius
    if (length > radius)
    {
      target.localPosition = Vector3.ClampMagnitude(target.localPosition, radius);
    }
 
    //set the Vector2 thumb position based on the actual sprite position
    position = target.localPosition;
    //smoothly lerps the Vector2 thumb position based on the old positions
    position = position / radius * Mathf.InverseLerp(radius, 2, 1);
  }
  
  //set joystick thumb position to drag position each frame
  void Update()
  {
    //in the editor the joystick position does not move, we have to simulate it
 //mirror player input to joystick position and calculate thumb position from that
 #if UNITY_EDITOR
  target.localPosition = position * radius;
  target.localPosition = Vector3.ClampMagnitude(target.localPosition, radius);
 #endif
 
    //check for actual drag state and fire callback. We are doing this in Update(),
    //not OnDrag, because OnDrag is only called when the joystick is moving. But we
    //actually want to keep moving the player even though the jostick is being hold down
    if(isDragging && onDrag != null)
      onDrag(position);
  }
 
  /// 
  /// Event fired by UI Eventsystem on drag end.
  /// 
  public void OnEndDrag(PointerEventData data)
  {
    //we aren't dragging anymore, reset to default position
    position = Vector2.zero;
    target.position = transform.position;
    
    //set dragging to false and fire callback
    isDragging = false;
    if (onDragEnd != null)
      onDragEnd();
  }
}