虚拟摇杆

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

//用ScrollCircle代替ScrollRect组件，达到在一个圆形范围内拖动的效果
public class ScrollCircle : ScrollRect {

    protected float mRadius = 0f;
    protected float mWidth, bWidth, contentWidth;
    // Use this for initialization
    protected override void Start () {
        base.Start();
        //bWidth 为整个摇杆宽度占画布宽度的比例
        bWidth = (transform as RectTransform).anchorMax.x - (transform as RectTransform).anchorMin.x;
        //contentWidth为摇块宽度占摇杆背景宽度的比例
        contentWidth = content.anchorMax.x - content.anchorMin.x;
        GetRadius();
    }

    // Update is called once per frame
    void Update()
    {
        GetRadius();
    }

    public override void OnDrag(PointerEventData eventData)
    {
        base.OnDrag(eventData);
        var contentPosition = this.content.anchoredPosition;
        if (contentPosition.magnitude > mRadius)
        {
            contentPosition = contentPosition.normalized * (mRadius);
            SetContentAnchoredPosition(contentPosition);
        }
    }

    //获取摇块能够移动的范围
    public void GetRadius()
    {
        //mWidth 为整个摇杆的宽度
        mWidth = transform.GetComponentInParent<Canvas>().pixelRect.width * bWidth;
        //mRadius 为摇块能够移动的最大距离
        mRadius = mWidth * 0.5f * (1 - contentWidth);
    }
}