using UnityEngine;
using UnityEngine.EventSystems;
public class JoyStick : MonoBehaviour, IDragHandler, IEndDragHandler
{
 Transform point;
 Vector3 startPos;//开始位置
 Vector3 dir;//方向
 float radius = 0;//需要移动的半径
 void Start()
 {
 point = transform.GetChild(0);
 radius = (transform as RectTransform).sizeDelta.x * 0.5f;
 startPos = point.position;
 }
 public void OnDrag(PointerEventData eventData)
 {
 point.position = eventData.position;
 dir = (point.position - startPos).normalized;
 if (Vector3.SqrMagnitude(point.position - startPos) > radius * radius)
 point.position = startPos + dir * radius;
 }
 public void OnEndDrag(PointerEventData eventData)
 {
 point.localPosition = Vector3.zero;
 }
}

public class JoyStick : MonoBehaviour, IDragEvent
{
 private Canvas canvas;
 private RectTransform rectTransform;//坐标
 private static Quaternion amendAngle;
 private static float mRadius = 0,v=0, h=0;
 private static Transform point;
 private static Vector3 initPos;
 private static Vector2 startPos;
 private void Start()
 {
 point = transform.GetChild(0);
 canvas = GameObject.Find("UIRoot").GetComponent();
 rectTransform = transform as RectTransform; //也可以写成this.GetComponent(),但是不建议；
 mRadius = (transform as RectTransform).sizeDelta.x * 0.5f;
 initPos = point.localPosition;
 h = v = 0;
 }
 
 public void OnBeginDrag(PointerEventData eventData)
 {
 RectTransformUtility.ScreenPointToLocalPointInRectangle(rectTransform, eventData.position, canvas.worldCamera, out startPos);
 startPos = eventData.position - startPos;
 h = v = 0; 
 }
 
 public void OnDrag(PointerEventData eventData)
 {
 point.localPosition = eventData.position - startPos;
 Vector3 dir = (point.localPosition - initPos).normalized;
 v = dir.normalized.x; h = dir.normalized.y;
 if (Vector3.SqrMagnitude(point.localPosition - initPos) > mRadius * mRadius)
 point.localPosition = initPos + dir * mRadius;
 }
 
 public void OnEndDrag(PointerEventData eventData)
 {
 point.localPosition = Vector3.zero;
 h = v = 0; 
 }
}