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获得视口宽高

拖动视口会改变屏幕宽高数值

MousePosition

屏幕坐标系的原点在左下角，MousePosition返回Z为0也就是纵深为0的Vector3

但是如果鼠标超出屏幕范围不会做限制，所以可能出现负数或者大于屏幕宽高的情况，做鼠标拖拽物体时需要注意是否需要跟随超出屏幕

下面这个写法是不对的，获得鼠标的屏幕位置纵深将一直为0，屏幕坐标转世界坐标其实是根据距离摄像机的平面确定的（z轴），所以需要先确定z轴后转世界坐标系

GetMouseWorldPosition = Camera.main.ScreenToWorldPoint(GetMousePosition);

利用射线检测物体转屏幕坐标

不会出现超出屏幕坐标系的情况

if (Physics.Raycast(Camera.main.ScreenPointToRay(Input.mousePosition), out RaycastHit hit))
{GetObjectPosition = Camera.main.WorldToScreenPoint(hit.point);
}

获得带纵深的屏幕坐标系，xy值为根据屏幕大小决定，z为距离摄像机的位置与本身的世界坐标系z无关

UI坐标

Canvas的世界坐标z值是距离摄像机的距离，那么子物体的世界坐标z值也是与摄像机的距离

实现拖曳UI

屏幕坐标XY是根据屏幕宽高决定，Z是相对摄像机的距离，将屏幕坐标看成一个个屏幕即可
世界坐标是根据世界原点确定，与屏幕坐标的Z值参考不一样

using UnityEngine;
using UnityEngine.EventSystems;[RequireComponent(typeof(EventTrigger))]
public class DragUI : MonoBehaviour
{private EventTrigger m_eventTrigger;private RectTransform m_rectTransform;private Vector3 m_targetPosition;private Vector3 m_offsetPosition;void Start(){m_eventTrigger = GetComponent<EventTrigger>();m_rectTransform = GetComponent<RectTransform>();EventTrigger.Entry onDragEntry = new EventTrigger.Entry();onDragEntry.eventID = EventTriggerType.Drag;onDragEntry.callback.AddListener((data) => { OnDrag(); });EventTrigger.Entry enterDragEntry = new EventTrigger.Entry();enterDragEntry.eventID = EventTriggerType.BeginDrag;enterDragEntry.callback.AddListener((data) => { EnterDrag(); });m_eventTrigger.triggers.Add(onDragEntry);m_eventTrigger.triggers.Add(enterDragEntry);}private void EnterDrag(){m_offsetPosition = GetScreenMousePosition() - m_rectTransform.transform.position;}// 拖拽时移动UIprivate void OnDrag(){// 屏幕坐标转世界坐标m_targetPosition = GetScreenMousePosition();m_rectTransform.transform.position = m_targetPosition - m_offsetPosition;}// 获得鼠标世界坐标private Vector3 GetScreenMousePosition(){// 与摄像机的距离float distanceCamera = m_rectTransform.transform.position.z;// 鼠标位置（确定了平面的Z）Vector3 screenMousePos = Input.mousePosition + new Vector3(0f, 0f, distanceCamera);// 屏幕坐标转世界坐标Vector3 worldMousePos = Camera.main.ScreenToWorldPoint(screenMousePos);Debug.Log(worldMousePos);return worldMousePos;}
}