Unity editor project window folder icon modification

ProjectIcons.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Text.RegularExpressions;

using UnityEditor;
using UnityEngine;

[UnityEditor.InitializeOnLoad]
public class ProjectIcons : Editor
{
    static string basePath = "Assets/Unity Chan Run Run/Editor/Icons/";

    static ProjectIcons()
    {
        EditorApplication.projectWindowItemOnGUI += ProjectIcons.MyCallback();
    }

    static EditorApplication.ProjectWindowItemCallback MyCallback()
    {
        EditorApplication.ProjectWindowItemCallback myCallback = new EditorApplication.ProjectWindowItemCallback(IconGUI);
	return myCallback;
    }

    static void IconGUI(string s, Rect r)
    {
        Regex rootGameFolderPathRegex = new Regex(@"Assets/Unity Chan Run Run$");

	    string fileName = AssetDatabase.GUIDToAssetPath(s);

        MatchThenDraw(r, rootGameFolderPathRegex, fileName, Path.Combine(basePath, "game.png"));
    }
    
    static void MatchThenDraw(Rect r, Regex regexPattern, String fileName, String texturePath)
    {
        Match match = regexPattern.Match(fileName);
        if (match.Success)
        {
            r.width = r.height;
            Texture2D icon = (Texture2D)AssetDatabase.LoadAssetAtPath(texturePath, typeof(Texture2D));
            if (icon != null)
            {
                GUI.DrawTexture(r, icon);
            }
        }
    }
}

ProjectIcons2.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Text.RegularExpressions;

using UnityEditor;
using UnityEngine;

[UnityEditor.InitializeOnLoad]
public class ProjectIcons : Editor
{
    static string basePath = "Assets/Unity Chan Run Run/Editor/Icons/";

    static ProjectIcons()
    {
        EditorApplication.projectWindowItemOnGUI += ProjectIcons.MyCallback();
    }

    static EditorApplication.ProjectWindowItemCallback MyCallback()
    {
        EditorApplication.ProjectWindowItemCallback myCallback = new EditorApplication.ProjectWindowItemCallback(IconGUI);
        return myCallback;
    }

    static void IconGUI(string s, Rect r)
    {
        Regex rootGameFolderPathRegex = new Regex(@"Assets/Unity Chan Run Run$");
        Regex editorFolderPathRegex = new Regex(@"Assets/Unity Chan Run Run[//a-zA-Z0-9]*/Editor$");
        Regex resourcesFolderPathRegex = new Regex(@"Assets/Unity Chan Run Run[//a-zA-Z0-9]*/Resources$");

		string fileName = AssetDatabase.GUIDToAssetPath(s);

        MatchThenDraw(r, rootGameFolderPathRegex, fileName, Path.Combine(basePath, "game.png"));
        MatchThenDraw(r, editorFolderPathRegex, fileName, Path.Combine(basePath, "editor.png"));
        MatchThenDraw(r, resourcesFolderPathRegex, fileName, Path.Combine(basePath, "resources.png"));
    }

    static void MatchThenDraw(Rect r, Regex regexPattern, string fileName, string texturePath)
    {
        Func<Rect, Rect> adjustedRect = new Func<Rect, Rect>(rect =>
            {
                bool minimized = Mathf.Approximately(rect.height, 16.0f);
                if (minimized)
                {
                    rect.width = r.height;
                }
                else
                {
                    rect.height -= 16.0f;
                }

                return rect;
            });

        Match match = regexPattern.Match(fileName);
        if (match.Success)
        {
            r = adjustedRect(r);
            Texture2D icon = (Texture2D)AssetDatabase.LoadAssetAtPath(texturePath, typeof(Texture2D));
            if (icon != null)
            {
                GUI.DrawTexture(r, icon);
            }
        }
    }
}