stockfish_for_flutter 0.1.2

The Stockfish Chess Engine for Flutter. Stockfish is a chess engine written following the UCI protocol.

Stockfish for flutter

The Stockfish Chess Engine for Flutter. This project has been adapted from Stockfish.

Using source code from Stockfish 15

Usages

You can find a description of the UCI protocol here.

Position validity

Be carefull, if you run command "position fen $position" (where position is the value of the position FEN) : you should only send valid positions ! Otherwise your program will crash !

That also means that if you use Chess package, you must do 2 additionnal check:

1. There must be only one king for each player.

2. There is no any pawn on rank 1 and rank 8.

Otherwise you can use the latest version of chess, from its repository, adding something like this in pubspec.yaml:

chess:
    git:
      url: https://github.com/davecom/chess.dart
      ref: 9bc48075ecaab3eb3356c26fee4404a362fe5d54

IOS

iOS project must have IPHONEOS_DEPLOYMENT_TARGET >=11.0.

Example

@PScottZero was kind enough to create a working chess game using this package.

Add dependency

Update dependencies section inside pubspec.yaml:

  stockfish_for_flutter: ^0.1.0

Init engine

import 'package:stockfish_for_flutter/stockfish.dart';

# create a new instance
final stockfish = Stockfish();

# state is a ValueListenable<StockfishState>
print(stockfish.state.value); # StockfishState.starting

# the engine takes a few moment to start
await Future.delayed(...)
print(stockfish.state.value); # StockfishState.ready

UCI command

Waits until the state is ready before sending commands.

stockfish.stdin = 'isready';
stockfish.stdin = 'go movetime 3000';
stockfish.stdin = 'go infinite';
stockfish.stdin = 'stop';

Engine output is directed to a Stream<String>, add a listener to process results.

stockfish.stdout.listen((line) {
  # do something useful
  print(line);
});

Dispose / Hot reload

There are two active isolates when Stockfish engine is running. That interferes with Flutter's hot reload feature so you need to dispose it before attempting to reload.

# sends the UCI quit command
stockfish.stdin = 'quit';

# or even easier...
stockfish.dispose();

Note: only one instance can be created at a time. The factory method Stockfish() will return null if it was called when an existing instance is active.

Generating the Stockfish bindings

1. Run flutter pub get.
2. Uncomment line #define _ffigen on top of src/stockfish_for_flutter.h (for the ffi generation to pass).
3. Run command flutter pub run ffigen --config ffigen.yaml. More on https://pub.dev/packages/ffigen for the prerequesites per OS.
4. Comment line #define _ffigen in src/stockfish_for_flutter.h (otherwise Stockfish engine compilation will pass but be incorrect).

Upgrading

Changing the downloaded NNUE file

1. Go to Stockfish NNUE files page and select a reference from the list.
2. Modify android/CMakeLists.txt, by replacing line starting by set (NNUE_NAME ) by setting your reference name, without any quote.
3. Modify ios/stockfish.podspec and replace both references to nn-XXXXX.nnue (where XXXX is the 'serial' value) by the name of NNUE to download.
4. Modify the reference name in evaluate.h in the line containing #define EvalFileDefaultName , by setting your nnue file name, with the quotes of course.

Updating Stockfish version

Just change the folder /src/stockfish with the sources of the new version, and also adjust the referenced NNUE file, as described above.

If necessary, import the code inside main() function in main.cpp of stockfish source file, into the main() function in cpp/bridge/stockfish.cpp.