Unity 鼠标拖拽旋转平面内2D物体 解决方案

比如音响的音量旋钮

具体逻辑：鼠标按下时期间每帧记录鼠标位置，算出由2D物体中心到鼠标的向量角度，根据角度变化相等地调节2D物体的旋转。

缺点：无法记录拖拽转了几圈

代码：

using UnityEngine;
using UnityEngine.EventSystems;

public class knob : MonoBehaviour, IBeginDragHandler, IDragHandler
{
    Vector2 knobPos;
    RectTransform knobRT;
    float rotAngle = 0;
    float angleRecord = 0;
    float clickRecord = 0;

    private void Start()
    {
        knobPos = RectTransformUtility.WorldToScreenPoint(null,transform.position);
        knobRT = GetComponent<RectTransform>();
    }
    public void OnBeginDrag(PointerEventData eventData)
    {
        angleRecord = knobRT.localEulerAngles.z;
        clickRecord = Vector2Angle(Input.mousePosition);
    }

    public void OnDrag(PointerEventData eventData)
    {
        rotAngle = Vector2Angle(Input.mousePosition);
        //Debug.Log(rotAngle);
        knobRT.localEulerAngles = new Vector3(0, 0, angleRecord + rotAngle - clickRecord);
    }

    float Vector2Angle(Vector2 vector)
    {
        return Mathf.Atan2(vector.y - knobPos.y, vector.x - knobPos.x) / Mathf.PI * 180;
    }
}