Leela Chess Zero swift framework for iOS

A framework built for iOS to allow use of LeelaChessZero (lc0) chess engine.

See the project lczero.org code here: GITHUB

The majority of the work needed here was crossing the languange boundaries.

• Leela is in C++, so I used uciloop.cc as a template for binding to lc0 callbacks called LeelaConnect.
• C++ doesn't play nice with Objective-C, so I used Objective-C++ as the pass through language. EngineBridge.mm
• LeelaSwift.swift uses the EngineBridge gives a delegate interface for communication.

How it works.

This repo uses lc0 as a submodule, make sure to recurse the submodules so you have all the code needed. This will place the lc0 code where the Xcode project expects it.

• There were 2 changes to the lc0 and lczero-commons. They are in lc0-ios.diff and lczero-common-ios.diff. You can apply them by running these command from the project root directory.

pushd submodules/lc0/libs/lczero-common; git apply ../../../../lczero-common-ios.diff; popd
pushd submodules/lc0; git apply ../../lc0-ios.diff; popd

• You'll have to trigger the generation of the proto/net.pb.cc, proto/net.pb.cc the script build_proto.sh

The other libraries that this framework rely on are libz and libprotobuf-lite

• libz is included with iOS, just go to your app target -> build phases -> link with libraries and find libz.tbd
• libprotobuf is a bit involved to build. My tip is to compile and install the mac libraries first so you can use the protoc built on the mac during the cross compile.

My protobuf configure (after installing the Mac built protobuf first)

./configure --with-sysroot=/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk --with-protoc=/usr/local/bin/protoc --disable-shared --enable-static --host=arm-apple-darwin

Assuming that all goes well, you should be able to open LeelaChessZero.xcodeproj and build LeelaChessZero.framework.

Here's a snippet to use Leela via the framework:

class TestLeela: LeelaChessZeroDelegate {
    var leelaEngine: lczero.UCICommandEngine?

    public init(weightsFile: String) {
        self.init()
        self.leelaEngine = lczero.UCICommandEngine(delegate: self)
        leelaEngine?.setupWeights(filePath: weightsFile)
    }

    func evaluatePosition(fen: String, moves: [String]) {
        self.leelaEngine?.sendCommand(.position(fen: fen, moves: moves))
        let params: lczero.UCIGoParams = lczero.UCIGoParams()
        self.leelaEngine?.sendCommand(.go(params: params))
    }
    
    public func leela(bestMove: LCZero_BestMoveInfo) {
        print("Best Move: \(bestMove)")
    }
    
    public func leela(thoughts: Array<LCZero_Thought>) {
        print("Thoughts: \(thoughts)")
    }
}

// Elsewhere in the app:
let testLeela = TestLeela(weightsFile: filePath)
testLeela.evaluatePosition("6r1/5k2/5p2/p2P1N1R/2Ppp3/1P6/4K3/4b2r w - - 7 50", [])