LeelaChessZero (lc0) #

The Leela Chess Zero (lc0) neural network chess engine for Flutter.

About #

Leela Chess Zero (lc0) is an open-source chess engine that uses deep neural networks to evaluate positions. It's based on the same approach as AlphaZero, using Monte Carlo Tree Search (MCTS) guided by a neural network.

Requirements #

• iOS: IPHONEOS_DEPLOYMENT_TARGET >= 13.0
• Android: minSdkVersion >= 24
• Neural network weights file (see below)

Installation #

Add dependency to pubspec.yaml:

dependencies:
  LeelaChessZero: ^1.0.0

Usage #

Initialize engine #

import 'package:LeelaChessZero/lc0.dart';

// create a new instance
final lc0 = Lc0();

// state is a ValueListenable<Lc0State>
print(lc0.state.value); // Lc0State.starting

// the engine takes a few moments to start
await Future.delayed(...)
print(lc0.state.value); // Lc0State.ready

Async initialization #

// Wait for engine to be ready
final lc0 = await lc0Async();

UCI commands #

Waits until the state is ready before sending commands.

lc0.stdin = 'uci';
lc0.stdin = 'setoption name WeightsFile value /path/to/weights.pb.gz';
lc0.stdin = 'position startpos moves e2e4 e7e5';
lc0.stdin = 'go nodes 1000';
lc0.stdin = 'stop';

Engine output is directed to a Stream<String>:

lc0.stdout.listen((line) {
  print(line);
});

Dispose / Hot reload #

// sends the UCI quit command
lc0.stdin = 'quit';

// or even easier...
lc0.dispose();

Note: Only one instance can be created at a time. The factory method Lc0() will throw StateError if called when an existing instance is active.

Neural Network Weights #

Unlike Stockfish which embeds evaluation weights at compile time, lc0 requires you to provide a neural network weights file at runtime.

Bundled Weights #

This package includes Maia-1900 weights (~1.2MB) - a neural network trained to play like a ~1900 rated human player. Maia networks are from the maia-chess project.

To use the bundled weights, first copy them from assets to a writable location:

import 'dart:io';
import 'package:flutter/services.dart';
import 'package:path_provider/path_provider.dart';

Future<String> extractWeights() async {
  final dir = await getApplicationDocumentsDirectory();
  final weightsPath = '${dir.path}/maia-1900.pb.gz';

  if (!await File(weightsPath).exists()) {
    final data = await rootBundle.load('assets/weights/maia-1900.pb.gz');
    await File(weightsPath).writeAsBytes(data.buffer.asUint8List());
  }

  return weightsPath;
}

// Then configure lc0:
final weightsPath = await extractWeights();
lc0.stdin = 'setoption name WeightsFile value $weightsPath';

Loading custom weights #

lc0.stdin = 'setoption name WeightsFile value /path/to/weights.pb.gz';

Other recommended networks #

Download networks from lczero.org or maiachess.com.

Differences from Stockfish #

Credits #

• Leela Chess Zero - The lc0 project and team
• LeelaChessZero/lc0 - Source repository