Unity 屏幕坐标到UGUI RectTransform本地坐标的转换

public static bool ScreenPointToLocalPointInRectangle(RectTransform rect, Vector2 screenPoint, Camera cam, out Vector2 localPoint);

rect: 对应的 RectTransform 的引用
screenPoint: 位置，基于屏幕坐标系
cam: 相机的引用，如果Canvas的Render Mode 为 Screen Space - Camera 模式，则需要填入 Render Camera 对应的引用
localPoint: rect 本地坐标系下的坐标（原点(0,0)位置受Anchor的影响）
参考：
https://docs.unity3d.com/ScriptReference/RectTransformUtility.ScreenPointToLocalPointInRectangle.html

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

public class GlobalTest : MonoBehaviour
{
    public Canvas canvas;
    Text uiText;
    RectTransform canvasRect;
    RectTransform textRect;
    void Start()
    {
        uiText = canvas.GetComponentInChildren<Text>();
        canvasRect = canvas.GetComponent<RectTransform>();
        textRect = uiText.GetComponent<RectTransform>();

        Debug.Log(textRect.anchoredPosition);

    }

    void Update()
    {
        if (Input.GetMouseButtonUp())
        {
            Vector2 outVec;
            if (RectTransformUtility.ScreenPointToLocalPointInRectangle(canvasRect,Input.mousePosition,null,out outVec))
            {
                Debug.Log("Setting anchored positiont to: " + outVec);
                textRect.anchoredPosition = outVec;
            }
        }

    }
}

参考：
https://forum.unity.com/threads/issues-with-recttransformutility-screenpointtolocalpointinrectangle.437246/
再说一句
也可以从UGUI的EventSystem中获得鼠标基于屏幕坐标系的点击位置

    public void OnPointerDown(PointerEventData pointerEventData)
    {
        //Output the name of the GameObject that is being clicked
        Debug.Log(name + "Game Object Click in Progress");
    }

参考：
https://docs.unity3d.com/ScriptReference/EventSystems.IPointerDownHandler.html