在做道具配置的时候，想要实现在编辑器内有一个和摄像机可视范围同样大小的矩形框，用来告诉我道具放置的边界在哪里，于是想要实现在scene窗口画矩形的一个效果，Unity的Gizmo可以实现类似的效果。

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEditor;

public class ItemGroupGenerator
{
    //ItemGroup是一个空的MonoBehaviour, 用于挂在想要显示Gizmo的物体上
    [DrawGizmo(GizmoType.NonSelected | GizmoType.Active | GizmoType.InSelectionHierarchy)]
    static void DrawItemGizmoType(ItemGroup gameObject, GizmoType gizmoType)
    {
        var transform = gameObject.transform;

        //根据选中的状态做差异化实验
        /*
        //该物体没有选中为绿色
        if ((gizmoType & GizmoType.NonSelected) != 0)
        {
            Gizmos.DrawWireCube(transform.position, Vector3.one);
        }
        //该物体选中时为红色
        if ((gizmoType & GizmoType.Active) != 0)
        {
            Gizmos.DrawWireCube(transform.position, Vector3.one);
        }
        //该物体选中或者该物体的父物体被选中
        if ((gizmoType & GizmoType.InSelectionHierarchy) !=0 )
        {
            Gizmos.DrawWireSphere(transform.position, 0.5f);
        } 
        */

        Vector3 cornerPos = Camera.main.ViewportToWorldPoint(new Vector3(1f, 1f, Mathf.Abs(-Camera.main.transform.position.z)));
        Vector3 leftUp = new Vector3(transform.position.x - cornerPos.x, transform.position.y + cornerPos.y, 0);
        Vector3 rightUp = new Vector3(transform.position.x + cornerPos.x, transform.position.y + cornerPos.y, 0);
        Vector3 leftDown = new Vector3(transform.position.x - cornerPos.x, transform.position.y - cornerPos.y, 0);
        Vector3 rightDown = new Vector3(transform.position.x + cornerPos.x, transform.position.y - cornerPos.y, 0);

        Gizmos.color = Color.green;
        Gizmos.DrawLine(leftUp, rightUp);
        Gizmos.DrawLine(leftUp, leftDown);
        Gizmos.DrawLine(leftDown, rightDown);
        Gizmos.DrawLine(rightUp, rightDown);
    }
}

效果图如下：