【Unity】一个鼠标控制UI移动和缩放的小组件

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;
[RequireComponent(typeof(RectTransform))]
public class UIMove : MonoBehaviour, IDragHandler, IBeginDragHandler, IScrollHandler
{
    [Header("移动")]
    [SerializeField]
    private bool canMove = true;

    [Header("缩放")]
    [SerializeField]
    private bool canScale = false;

    /// <summary>
    /// 滚轮滚动一个段落缩放的本地大小倍数
    /// </summary>
    [SerializeField]
    [Tooltip("缩放的速度")]
    private float scaleSpeed = 0.1f;

    [SerializeField]
    [Tooltip("x:最小尺寸 y:最大尺寸")]
    private Vector2 limitSize = new Vector2(0.5f,2);

    [Header("聚焦")]
    [Tooltip("在缩放时，使UI中心向光标靠近")]
    [SerializeField]
    private bool isFocusWhenScale = true;

    /// <summary>
    /// 缩放时,靠近的速度
    /// </summary>
    [SerializeField]
    private float focusSpeed = 0.3f;

    [Header("其他")]
    [SerializeField]
    [Tooltip("允许光标超出屏幕后生效")]
    private bool AllowOverScreen = false;

    [SerializeField]
    [Tooltip("非活动（Disable）时复原位置和尺寸")]
    private bool ResetOnDisable = true;

    RectTransform rt;

    //拖拽前UI的位置
    Vector3 startObjectPos;

    //每次拖拽开始前光标的位置
    Vector3 startMousePos;
    
    //每次拖拽过程中光标的位置
    Vector3 nowMousePos;
    
    //UI的原始尺寸的位置，用于复原
    Vector3 _originScale;
    Vector3 _originPoint;

    void Start()
    {
        rt = gameObject.GetComponent<RectTransform>();
        _originPoint = rt.localPosition;
        _originScale = rt.localScale;
    }
    public void OnScroll(PointerEventData eventData)
    {
        if(canScale) SetSize(eventData);
    }
    public void SetSize(PointerEventData eventData)
    {
        float speed = focusSpeed / rt.localScale.x;

        //注意eventData.enterEventCamera与eventData.pressEventCamera的不同，在这里踩了坑，导致第一次缩放出问题
        RectTransformUtility.ScreenPointToWorldPointInRectangle(rt, eventData.position, eventData.enterEventCamera, out nowMousePos);

        float OffsetX = nowMousePos.x - transform.position.x;
        float OffsetY = nowMousePos.y - transform.position.y;
        float PivotX = OffsetX / rt.rect.width / transform.localScale.x;
        float PivotY = OffsetY / rt.rect.height / transform.localScale.y;

        if (isFocusWhenScale)
        {
            rt.pivot += new Vector2(PivotX, PivotY);
            transform.position += new Vector3(OffsetX, OffsetY, 0) * speed;
        }
        if (Input.GetAxis("Mouse ScrollWheel") > 0)
        {
            transform.localScale += (transform.localScale.x >= limitSize.y ? Vector3.zero : Vector3.one * scaleSpeed);
        }
        else if (Input.GetAxis("Mouse ScrollWheel") < 0)
        {
            transform.localScale += (transform.localScale.x <= limitSize.x ? Vector3.zero : Vector3.one * -scaleSpeed);
        }
    }
    public void OnBeginDrag(PointerEventData eventData)
    {
        //记录拖拽前UI位置，鼠标位置
        startObjectPos = rt.position;
        RectTransformUtility.ScreenPointToWorldPointInRectangle(rt, eventData.position, eventData.pressEventCamera, out startMousePos);
    }
    public void OnDrag(PointerEventData eventData)
    {
        if (canMove) SetDraggedPosition(eventData);
    }
    private void SetDraggedPosition(PointerEventData eventData)
    {
        //检测鼠标位置是否在UI内
        if (RectTransformUtility.ScreenPointToWorldPointInRectangle(rt, eventData.position, eventData.pressEventCamera, out nowMousePos))
        {
            //记录光标移动的路程，加到UI上，实现位置跟随
            Vector3 targetPos = startObjectPos + nowMousePos - startMousePos;

            //若光标移动到了屏幕外，根据设AllowOverScreen决定是否跟随
            if (AllowedMove())
            {
                rt.position = targetPos;
            }
        }
    }
    /// <summary>
    /// 检测鼠标是否在屏幕内
    /// </summary>
    /// <param name="targetPos"></param>
    /// <param name="targetlocalScale"></param>
    /// <returns></returns>
    private bool IsOverScreen()
    {
        bool isOver;
        isOver = Input.mousePosition.x > Screen.width || Input.mousePosition.x < 0 
            || Input.mousePosition.y > Screen.height || Input.mousePosition.y < 0;
        return isOver;
    }
    private bool AllowedMove()
    {
        return !IsOverScreen() || AllowOverScreen;
    }
    /// <summary>
    /// 将其位置和尺寸重置到初始状态
    /// </summary>
    public void ResetPosAndScale()
    {
        this.transform.localPosition = _originPoint;
        this.transform.localScale = _originScale;
    }
    /// <summary>
    /// 隐藏时复原位置和尺寸
    /// </summary>
    public void OnDisable()
    {
        if(ResetOnDisable) ResetPosAndScale();
    }
}