Flatten Unity SpriteAtlas via Context Menu

FlattenSpriteAtlasContextMenu.cs

#nullable enable

using System.Collections.Generic;
using System.IO;
using System.Linq;
using UnityEditor;
using UnityEditor.U2D;
using UnityEngine;
using UnityEngine.U2D;

/// <summary>
/// This script flattens a SpriteAtlas, i.e. removes all folders and adds all
/// sprites individually. It can be accessed by right-clicking on a SpriteAtlas
/// in the Project window and selecting "Flatten SpriteAtlas".
///
/// Drop this file into any folder named "Editor" and it will be available in
/// the Unity Editor.
///
/// @author Jimmie Tyrrell
/// </summary>
public static class FlattenSpriteAtlasContextMenu {
  public static readonly string[] ImageLikeExtensions = new [] { "png", "jpg", "jpeg", "psd", "gif", "tga" };

  [MenuItem("Assets/Flatten SpriteAtlas", true)]
  private static bool Validate() {
    return Selection.activeObject is SpriteAtlas;
  }

  private static List<string> GetTexturesAtPath(string path) {
    var enumerations = new IEnumerable<string>[ImageLikeExtensions.Length];

    for (int i = 0; i < ImageLikeExtensions.Length; i++) {
      enumerations[i] = Directory.EnumerateFiles(path, $"*.{ImageLikeExtensions[i]}", SearchOption.AllDirectories);
    }

    return enumerations.SelectMany(_ => _).ToList();
  }

  [MenuItem("Assets/Flatten SpriteAtlas")]
  private static void Perform() {
    if (Selection.activeObject is not SpriteAtlas atlas) return;

    // Remove all old sprites + folders from the atlas
    var packables = atlas.GetPackables();

    var packablesToRemove = new List<Object>();
    var spritesToAdd = new List<Sprite>();

    foreach (var packable in packables) {
      var path = AssetDatabase.GetAssetPath(packable);

      // If the packable is not a folder, ignore it
      if (!Directory.Exists(path)) continue;

      // If it is a folder, schedule the packable for removal
      packablesToRemove.Add(packable);

      // Get all sprites in that directory
      var spritePaths = GetTexturesAtPath(path);
      foreach (var spritePath in spritePaths) {
        // Load the sprite and add it to the atlas
        var sprite = AssetDatabase.LoadAssetAtPath<Sprite>(spritePath);
        if (sprite != null) {
          spritesToAdd.Add(sprite);
        }
      }
    }

    // Remove any packables that were folders
    if (packablesToRemove.Count > 0) {
      SpriteAtlasExtensions.Remove(atlas, packablesToRemove.ToArray());
    }

    // Add any sprites that were found in those converted folders
    if (spritesToAdd.Count > 0) {
      SpriteAtlasExtensions.Add(atlas, spritesToAdd.ToArray());
    }

    // Refresh the atlas
    EditorUtility.SetDirty(atlas);
    AssetDatabase.SaveAssets();
  }
}