lc0 0.1.0

Lc0 Flutter no GPU

dart-lc0

A Flutter plugin that embeds the Lc0 (Leela Chess Zero) chess engine for iOS and Android. CPU-only — no GPU required.

Features

• Runs Lc0 v0.32.1 in-process via Dart FFI
• Communicates with the engine using the UCI protocol
• Non-blocking: engine runs in a Dart isolate
• Supports any .pb.gz neural network weights file (e.g. Maia)

Platform Support

Android	iOS
✓	✓

Installation

Add to your pubspec.yaml:

dependencies:
  lc0:
    git:
      url: https://github.com/lichess-org/dart-lc0.git

Usage

An engine is a handle: Lc0.create() starts one and completes once it has answered uciok, and dispose() releases it.

import 'package:lc0/lc0.dart';

// Start the engine. Completes when it is ready for commands.
final engine = await Lc0.create();

// Listen to engine output. Pass `onStdout` to `create` instead if you need the
// lines it writes while starting.
engine.stdout.listen((line) => print(line));

// Load neural network weights (required before analysis)
engine.stdin = 'setoption name WeightsFile value /path/to/weights.pb.gz';

// Analyze a position
engine.stdin = 'position startpos moves e2e4 e7e5';
engine.stdin = 'go movetime 3000';

// Release it. The handle is single-use: call create() again for a fresh engine.
await engine.dispose();

One engine at a time. lc0 keeps its command line, its option registry and its backend factories in process globals, so create() throws a StateError while another engine is live. This plugin does not takes the process's stdin and stdout over, so an lc0 engine and another engine can be resident side by side.

When something goes wrong

The engine runs on a thread Dart does not own, so engine.diagnostics reports what the native side is doing — which phase it is in, which step of it, and for how long. Attach it to any report of an engine that would not start or would not quit; Lc0Diagnostics.looksStuck says when a transition has taken far longer than it should.

final engine = await Lc0.create();
print(engine.diagnostics);  // phase=uciLoop step=uci_loop for 12ms

Check the example/ directory for a complete Flutter app that bundles and loads Maia weights.

Building

The engine and Eigen are vendored under ios/lc0/Sources/lc0/, so a checkout builds without fetching anything. The plugin ships both a Swift Package (ios/lc0/Package.swift) and a podspec; Flutter picks the package when Swift Package Manager is enabled for the host app.

tool/update_engine.sh re-vendors the engine from upstream and re-applies lc0.patch. It is a maintainer's tool — its output is committed.

Weights

The engine requires a neural network weights file at runtime. You can use any Lc0-compatible .pb.gz weights file. The example app ships with maia1500.pb.gz from the Maia Chess project.

License

GPL — see LICENSE.