IconGUI.cs

/*
 * このスクリプトを Assets/Editor/ 以下に置く。
 * また PSD のアイコンに使う画像を Assets/Editor/PSD.png として置く。
 */
using UnityEditor;
using UnityEngine;

// code stolen from: https://discussions.unity.com/t/editor-changing-an-items-icon-in-the-project-window/552493/6

[UnityEditor.InitializeOnLoad]
public class ProjectIcons : Editor {
    static ProjectIcons () {
        EditorApplication.projectWindowItemOnGUI += MyCallback();
    }

    [MenuItem( "EDITORS/ProjectIcons/Enable" )]
    private static void EnableIcons () {
        EditorApplication.projectWindowItemOnGUI -= ProjectIcons.MyCallback();
        EditorApplication.projectWindowItemOnGUI += ProjectIcons.MyCallback();
    }

    [MenuItem( "EDITORS/ProjectIcons/Disable" )]
    private static void DisableIcons () {
        EditorApplication.projectWindowItemOnGUI -= ProjectIcons.MyCallback();
    }

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

    private static void IconGUI ( string s, Rect r ) {
        var fileName = AssetDatabase.GUIDToAssetPath( s );
        var index = fileName.LastIndexOf( '.' );
        if ( index == -1 ) return;
        var fileType = fileName[(index + 1)..];
        switch ( fileType ) {
            case "psd":
                r.x += r.width - r.width / 3;
                r.y += r.height - r.height / 3 - EditorGUIUtility.singleLineHeight;
                r.width /= 3;
                r.height /= 3;
                GUI.DrawTexture( r, (Texture2D) AssetDatabase.LoadAssetAtPath( "Assets/Editor/PSD.png", typeof( Texture2D ) ) );
                break;
        }
    }
}