using UnityEngine;
using UnityEngine.UI;
 
public class TouchJoystick : MonoBehaviour
{
 
  public GameObject go;//需要通过虚拟摇杆控制的目标物体
  public float moveSpeed = 3;//移动速度
 
  public Image touchPoint;//摇杆轴对象
 
  private Vector3 OriginalPos_TP;//摇杆轴的初始位置
  private RectTransform rectTransform_TP;//摇杆轴的位置组件
 
  private float radius;//摇杆轴移动的最大半径
 
  void Start()
  {
    radius = this.GetComponent().rect.width*0.5f;
    rectTransform_TP = touchPoint.GetComponent();
    OriginalPos_TP = rectTransform_TP.position;
  }
 
  void Update()
  {
    //第一次触摸屏幕时，整个虚拟摇杆的位置更新
    if (Input.GetMouseButtonDown(0))
    {
      this.GetComponent().position = Input.mousePosition;
      OriginalPos_TP = rectTransform_TP.position;
    }
 
    if (Input.GetMouseButton(0))
    {
      //取得触摸点与虚拟轴初始点的距离
      float distance = Vector3.Distance(Input.mousePosition, OriginalPos_TP);
      //取得一个初始轴点指向触摸点的向量
      Vector3 pos = Input.mousePosition - OriginalPos_TP;
      //如果距离大于可移动半径
      if (distance > radius)
        rectTransform_TP.position = OriginalPos_TP + pos.normalized*radius;//设置轴点到最大半径位置
      else
        rectTransform_TP.position = Input.mousePosition;//否则轴点在当前触摸位置
      
      //以（0,1,0）为参考点，计算单位轴向量与之夹角
      float angle = Vector3.Angle(new Vector3(0, 1, 0), new Vector3(pos.normalized.x, pos.normalized.y, 0));
      //移动物体
      go.transform.Translate(new Vector3(0, 0, pos.normalized.magnitude*moveSpeed)*Time.deltaTime);
      //更新控制物体的旋转与轴向方向一致
      if (pos.normalized.x > 0)
        go.transform.rotation = Quaternion.AngleAxis(angle, Vector3.up);
      else
        go.transform.rotation = Quaternion.AngleAxis(-angle, Vector3.up);
    }
    else
      rectTransform_TP.position = OriginalPos_TP;//没有触摸时回到初始位置
  }
}