Support multiple asset types

lib/assets.dart

@@ -3,26 +3,39 @@ import 'dart:ui' as ui;
 import 'package:flutter/services.dart';
 
 class Assets {
-  final Map<String, ui.Image> _loaded = {};
+  final _Table<ui.Image> _images = _Table((name) async {
-  final Set<String> _waiting = {};
-
-  Future<ui.Image> _getImageAsync(String name) async {
     final assetImageByteData = await rootBundle.load(name);
     final codec =
         await ui.instantiateImageCodec(assetImageByteData.buffer.asUint8List());
     final image = (await codec.getNextFrame()).image;
 
-    _loaded[name] = image;
     return image;
-  }
+  });
 
   ui.Image? getImageIfAvailable(String name) {
+    return _images.getIfAvailable(name);
+  }
+}
+
+class _Table<T> {
+  final Map<String, T> _loaded = {};
+  final Set<String> _waiting = {};
+  final Future<T> Function(String) _getAsync;
+
+  _Table(this._getAsync);
+
+  T? getIfAvailable(String name) {
     if (!_waiting.contains(name)) {
       _waiting.add(name);
-      _getImageAsync(name);
+      _spawnGetAsync(name);
     }
     return _loaded[name];
   }
+
+  Future<void> _spawnGetAsync(String name) async {
+    final asset = await _getAsync(name);
+    _loaded[name] = asset;
+  }
 }
 
 final assets = Assets();