unity使用UGUI创建摇杆

1.现在unity做一个项目，各种插件各种包，于是项目资源就无限变大了，其实一些简单的功能可以自己写，这里就是试着使用UGUI编写一个摇杆功能

2.脚本如下:

using UnityEngine;

using UnityEngine.UI;

using UnityEngine.EventSystems;

using System.Collections;

public class UGUIJoystick : MonoBehaviour,IDragHandler{

    public RectTransform joystickImage;

    public Vector3 startPos;

    public int maxDis = 70;

    public float speed = 5;

	// Use this for initialization

	void Start () {

        startPos = joystickImage.position;

	}

	// Update is called once per frame

	void Update () {

        if (Application.platform == RuntimePlatform.Android)

        {

            if (Input.touchCount <= 0)

            {

                if (Vector3.Distance(joystickImage.position, startPos) > 0.01f)

                {

                    joystickImage.position = joystickImage.position - (joystickImage.position - startPos).normalized * speed;

                }

            }

        }

        else

        {

            if (!Input.GetMouseButton(0))

            {

                if (Vector3.Distance(joystickImage.position, startPos) > 0.01f)

                {

                    joystickImage.position = joystickImage.position - (joystickImage.position - startPos).normalized * speed;

                }

            }

        }

	}

   public void OnDrag(PointerEventData eventData)

    {

        Vector3 wordPos;

        //将UGUI的坐标转为世界坐标

        if (RectTransformUtility.ScreenPointToWorldPointInRectangle(joystickImage, eventData.position, eventData.pressEventCamera, out wordPos))

            joystickImage.position = wordPos;

        Vector3 dir = (joystickImage.position - startPos).normalized;

        if (Vector3.Distance(joystickImage.position, startPos) >= maxDis)

        {

            joystickImage.position = startPos + dir * maxDis;

        }

    }

}

3.这里除了一个简单的接口实现，就是坐标的转换，让摇杆一直跟着手指移动，这里就需要一个函数RectTransformUtility.ScreenPointToWorldPointInRectangle

4.将这个脚本绑定在摇杆用于移动的图片上，效果如下:

5.摇杆常用移动端，但是我并未在移动端测试​