dartterm/lib/assets.dart

import 'dart:ui' as ui;

import 'package:flutter/services.dart';

class Assets {
  final _Table<ui.Image> _images = _Table((name) async {
    final assetImageByteData = await rootBundle.load(name);
    final codec =
        await ui.instantiateImageCodec(assetImageByteData.buffer.asUint8List());
    final image = (await codec.getNextFrame()).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);
      _spawnGetAsync(name);
    }
    return _loaded[name];
  }

  Future<void> _spawnGetAsync(String name) async {
    final asset = await _getAsync(name);
    _loaded[name] = asset;
  }
}

final assets = Assets();

ui.Image? getImageIfAvailable(String name) {
  return assets.getImageIfAvailable(name);
}