FishNet で AR マルチプレイを実装してみた！

// Mirror: 手動で Command → ClientRpc を繋ぐ
[Command]
private void CmdMove(Vector3 pos, Quaternion rot) { ... }

[ClientRpc]
private void RpcSyncedPos(Vector3 pos, Quaternion rot) { ... }

// FishNet: SyncVar に書くだけで全クライアントに自動配信
[ServerRpc]
private void CmdUpdateLocalPos(Vector3 localPos)
{
    _syncedLocalPosition.Value = localPos;
}

// サーバー側: 部屋を作ったら広告開始
_discoveryService.StartAdvertise();

// クライアント側: 探索開始、見つかったら接続
_discoveryService.StartSearch();
_discoveryService.OnServerFound.Subscribe(async address =>
{
    _discoveryService.StopSearch();
    await _networkService.ConnectAsClientAsync(address, port: 7777, ct);
});

async UniTask StartServerAndListenAsync(CancellationToken ct)
{
    // 1. サーバー起動
    _networkManager.TransportManager.Transport.SetPort(7777);
    _networkManager.ServerManager.StartConnection();

    // IsServerStarted になるまでポーリングで待機
    await UniTask.WaitUntil(() => _networkManager.IsServerStarted, cancellationToken: ct);

    // 2. アドバタイズ開始（ゲストが LAN で探索できるようにする）
    _networkDiscovery.AdvertiseServer();

    // 3. ホスト自身もクライアントとして接続（リッスンサーバー）
    _networkManager.TransportManager.Transport.SetClientAddress("127.0.0.1");
    _networkManager.ClientManager.StartConnection();

    await UniTask.WaitUntil(() => _networkManager.IsClientStarted, cancellationToken: ct);

    // 4. 相手の入室を ServerManager のイベントで検知
    _networkManager.ServerManager.OnRemoteConnectionState += OnRemoteConnectionState;
}

void OnRemoteConnectionState(NetworkConnection conn, RemoteConnectionStateArgs args)
{
    if (args.ConnectionState == RemoteConnectionState.Started)
        OnRemotePlayerJoined(); // 5. ボタン有効化
}

void OnBattleStartClicked()
{
    // 6. 全クライアントにゲーム開始を通知
    _networkManager.ServerManager.Broadcast(new GameStartBroadcast());
}

async UniTask FindAndJoinRoomAsync(CancellationToken ct)
{
    // 1. サーバー探索
    string serverAddress = null;
    _networkDiscovery.ServerFoundCallback += endPoint =>
    {
        if (serverAddress == null) serverAddress = endPoint.Address.ToString();
    };
    _networkDiscovery.SearchForServers();

    // 2. アドレスが取得できるまで待機
    await UniTask.WaitUntil(() => serverAddress != null, cancellationToken: ct);
    _networkDiscovery.StopSearchingOrAdvertising();

    // 3. 接続
    var transport = _networkManager.TransportManager.Transport;
    transport.SetClientAddress(serverAddress);
    transport.SetPort(7777);
    _networkManager.ClientManager.StartConnection();

    await UniTask.WaitUntil(() => _networkManager.IsClientStarted, cancellationToken: ct);

    // 4. ホストの開始ブロードキャストを待つ
    _networkManager.ClientManager.RegisterBroadcast<GameStartBroadcast>(OnGameStartReceived);
}

void OnTrackedImagesChanged(ARTrackedImagesChangedEventArgs args)
{
    foreach (var image in args.added.Concat(args.updated))
    {
        if (image.trackingState != TrackingState.Tracking) continue;
        if (image.referenceImage.name != _config.TargetMarkerName) continue;

        // マーカー位置から FieldAnchor のワールド座標を逆算
        var (pos, rot) = _markerAnchor.CalculateFieldAnchorPose(
            image.transform.position,
            image.transform.rotation);

        _fieldAnchorProvider.SetFieldAnchorPosition(pos, rot);
        onUpdated?.Invoke(new CalibrationTransform(pos, rot));
    }
}

public (Vector3 position, Quaternion rotation) CalculateFieldAnchorPose(
    Vector3 markerWorldPosition, Quaternion markerWorldRotation)
{
    // ARFoundation（Y=法線）→ エディタ（Z=法線）に変換
    var correctedRotation = markerWorldRotation * Quaternion.Euler(90f, 0f, 0f);

    var markerWorldMatrix  = Matrix4x4.TRS(markerWorldPosition, correctedRotation, Vector3.one);
    var localOffsetMatrix  = Matrix4x4.TRS(_localPositionOffset, _localRotationOffset, Vector3.one);
    var fieldAnchorMatrix  = markerWorldMatrix * localOffsetMatrix.inverse;

    return (fieldAnchorMatrix.GetPosition(), fieldAnchorMatrix.rotation);
}

protected readonly SyncVar<Vector3> _syncedLocalPosition = new(Vector3.zero);

protected virtual void UpdateOwnerPosition()
{
    var localPos = _fieldAnchorProvider.FieldAnchor
        .InverseTransformPoint(_cameraTransform.position);

    if (Vector3.Distance(localPos, _syncedLocalPosition.Value) > 0.001f)
        CmdUpdateLocalPos(localPos);

    transform.localPosition = localPos; // ローカルは即時反映
}

[ServerRpc]
private void CmdUpdateLocalPos(Vector3 localPos)
{
    _syncedLocalPosition.Value = localPos; // 全クライアントに自動配信
}

protected override void UpdateNonOwnerPosition()
{
    var syncedPos = _syncedLocalPosition.Value;

    // SyncVar の更新を検知して速度を推定
    if (syncedPos != _lastKnownSyncedPos)
    {
        var dt  = Time.time - _drBaseTime;
        _drBaseVel          = dt > 0.001f ? (syncedPos - _drBasePos) / dt : Vector3.zero;
        _drBasePos          = syncedPos;
        _drBaseTime         = Time.time;
        _lastKnownSyncedPos = syncedPos;
    }

    // 最大 0.5 秒分を外挿（それ以上は誤差が大きくなる）
    var timeSince = Mathf.Min(Time.time - _drBaseTime, 0.5f);
    var predicted = _drBasePos + _drBaseVel * timeSince;

    transform.localPosition = Vector3.Lerp(
        transform.localPosition, predicted, Time.deltaTime * 12f);
}

// 座標は FieldAnchor ローカル座標で送る
public struct BulletFiredBroadcast : IBroadcast
{
    public Vector3 LocalPosition;
    public Vector3 LocalDirection;
}

// 自分が発射したら送信
void BroadcastFire(Vector3 localPos, Vector3 localDir)
{
    _networkManager.ClientManager.Broadcast(new BulletFiredBroadcast
    {
        LocalPosition  = localPos,
        LocalDirection = localDir.normalized,
    });
}

// サーバー: 送信元以外の全クライアントへ中継
void OnServerReceive(NetworkConnection conn, BulletFiredBroadcast msg, Channel ch)
{
    foreach (var client in _networkManager.ServerManager.Clients.Values)
    {
        if (client == conn) continue;
        _networkManager.ServerManager.Broadcast(client, msg, channel: ch);
    }
}

// 受信側: ローカル座標 → ワールド座標に戻して弾をスポーン
void OnClientReceive(BulletFiredBroadcast msg, Channel ch)
{
    var worldPos = fieldAnchor.TransformPoint(msg.LocalPosition);
    var worldDir = fieldAnchor.TransformDirection(msg.LocalDirection);
    SpawnBullet(worldPos, worldDir);
}