First remotely working WFC

lib/assets.dart

@@ -1,5 +1,7 @@
 import 'dart:ui' as ui;
 
+import 'package:dartterm/wfc/template.dart';
+import 'package:dartterm/world/level.dart';
 import 'package:flutter/services.dart';
 
 class Assets {
@@ -12,28 +14,35 @@ class Assets {
     return image;
   });
 
+  final _Table<WfcTemplate<LevelTile>> _wfcLevelTemplates =
+      _Table(loadLevelWfcAsync);
+
   ui.Image? getImageIfAvailable(String name) {
     return _images.getIfAvailable(name);
   }
+
+  WfcTemplate<LevelTile>? getWfcLevelTemplateIfAvailable(String name) {
+    return _wfcLevelTemplates.getIfAvailable(name);
+  }
 }
 
 class _Table<T> {
   final Map<String, T> _loaded = {};
   final Set<String> _waiting = {};
-  final Future<T> Function(String) _getAsync;
+  final Future<T> Function(String) _loadAsync;
 
-  _Table(this._getAsync);
+  _Table(this._loadAsync);
 
   T? getIfAvailable(String name) {
     if (!_waiting.contains(name)) {
       _waiting.add(name);
-      _spawnGetAsync(name);
+      _spawnLoadAsync(name);
     }
     return _loaded[name];
   }
 
-  Future<void> _spawnGetAsync(String name) async {
+  Future<void> _spawnLoadAsync(String name) async {
-    final asset = await _getAsync(name);
+    final asset = await _loadAsync(name);
     _loaded[name] = asset;
   }
 }
@@ -43,3 +52,7 @@ final assets = Assets();
 ui.Image? getImageIfAvailable(String name) {
   return assets.getImageIfAvailable(name);
 }
+
+WfcTemplate<LevelTile>? getWfcLevelTemplateIfAvailable(String name) {
+  return assets.getWfcLevelTemplateIfAvailable(name);
+}

lib/game.dart

@@ -1,8 +1,56 @@
 import 'dart:developer';
 
+import 'package:dartterm/assets.dart';
 import 'package:dartterm/colors.dart';
 import 'package:dartterm/terminal.dart';
+import 'package:dartterm/wfc/template.dart';
+import 'package:dartterm/world/level.dart';
 
+void main() async {
+  WfcTemplate<LevelTile> template;
+  while (true) {
+    log("about to load template");
+    at(0, 0).clear();
+    at(0, 0).puts("Loading template!");
+    WfcTemplate<LevelTile>? maybeTemplate =
+        getWfcLevelTemplateIfAvailable("assets/images/wfc/bighouse2.png");
+
+    if (maybeTemplate != null) {
+      log("wasn't null!");
+      template = maybeTemplate;
+      break;
+    }
+    await zzz(0.1);
+  }
+
+  at(0, 0).clear();
+  at(0, 0).puts("Loaded! $template");
+
+  var W = 16;
+  var H = 16;
+
+  var wfc = Wfc(template, W, H);
+  wfc.run(0, -1);
+  var output = wfc.extractPartial();
+  for (var y = 0; y < W; y++) {
+    for (var x = 0; x < H; x++) {
+      var cursor = at(x * 2, y * 2).big();
+      switch (output[x + y * W]) {
+        case LevelTile.floor:
+          cursor.puts(" ");
+        case LevelTile.door:
+          cursor.puts("d");
+        case LevelTile.wall:
+          cursor.puts("#");
+        case LevelTile.exit:
+          cursor.puts("X");
+        case null:
+          cursor.puts("?");
+      }
+    }
+  }
+}
+/*
 void main() async {
   var descriptor = "generic";
   while (true) {
@@ -35,3 +83,4 @@ void main() async {
     await waitMenu();
   }
 }
+*/

lib/main.dart

@@ -6,6 +6,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter/scheduler.dart';
 
 void main() {
+  WidgetsFlutterBinding.ensureInitialized();
   game.main();
   runApp(const App());
 }

lib/wfc/model.dart.old

@@ -3,13 +3,13 @@ import 'dart:math';
 abstract class Model {
   static var dx = [-1, 0, 1, 0];
   static var dy = [0, 1, 0, -1];
-  static var _opposite = [2, 3, 0, 1];
+  static var opposite = [2, 3, 0, 1];
 
   bool _initialized = false;
   List<List<bool>> _wave = [];
   List<List<List<int>>> propagator = [];
   List<List<List<int>>> _compatible = [];
-  List<int> _observed = [];
+  List<int?> _observed = [];
 
   List<(int, int)> _stack = [];
   int _stacksize = 0, _observedSoFar = 0;
@@ -51,7 +51,7 @@ abstract class Model {
         ]
     ];
     _distribution = [for (var t = 0; t < cT; t++) 0.0];
-    _observed = [for (var r = 0; r < cMx * cMy; r++) 0];
+    _observed = [for (var r = 0; r < cMx * cMy; r++) null];
 
     _weightLogWeights = [
       for (var t = 0; t < cT; t++) weights[t] * log(weights[t])
@@ -175,7 +175,7 @@ abstract class Model {
 
         if (x2 < 0) {
           x2 += cMx;
-        } else if (x2 >= 0) {
+        } else if (x2 >= cMx) {
           x2 -= cMx;
         }
 
@@ -226,7 +226,7 @@ abstract class Model {
       for (var t = 0; t < cT; t++) {
         _wave[i][t] = true;
         for (var d = 0; d < 4; d++) {
-          _compatible[i][t][d] = propagator[_opposite[d]][t].length;
+          _compatible[i][t][d] = propagator[opposite[d]][t].length;
         }
       }
 

lib/wfc/overlapping.dart

@@ -1,133 +0,0 @@
-import 'dart:ui' as ui;
-
-import 'package:dartterm/wfc/model.dart';
-
-class Bitmap<T> {
-  final int sx;
-  final int sy;
-  final List<T> data;
-
-  const Bitmap(this.sx, this.sy, this.data);
-}
-
-class OverlappingModel<T> extends Model {
-  List<List<int>> _patterns = [];
-  List<T> _colors = [];
-  Map<T, int> _colorOf = {};
-
-  OverlappingModel(
-      Bitmap<T> bitmap,
-      int n,
-      int width,
-      int height,
-      bool periodicInput,
-      bool periodic,
-      int symmetry,
-      bool ground,
-      Heuristic heuristic)
-      : super(width, height, n, periodic, heuristic) {
-    List<int> sample = [];
-    for (var i = 0; i < bitmap.data.length; i++) {
-      var existing = bitmap.data[i];
-      var color = _colorOf[existing];
-      if (color == null) {
-        color = _colors.length;
-        _colorOf[existing] = color;
-        _colors.add(existing);
-      }
-      sample[i] = color;
-    }
-
-    var c = _colors.length;
-
-    List<int> pattern(int Function(int, int) f) {
-      return [
-        for (var y = 0; y < n; y++)
-          for (var x = 0; x < n; x++) f(x, y)
-      ];
-    }
-
-    List<int> rotate(List<int> p) {
-      return pattern((x, y) => p[n - 1 - y + x * n]);
-    }
-
-    List<int> reflect(List<int> p) {
-      return pattern((x, y) => p[n - 1 - x + y * n]);
-    }
-
-    int hash(List<int> p) {
-      var result = 0, power = 1;
-      for (var i = 0; i < p.length; i++) {
-        result += p[p.length - 1 - i] * power;
-        power *= c;
-      }
-      return result;
-    }
-
-    var sx = bitmap.sx;
-    var sy = bitmap.sy;
-    Map<int, int> patternIndices = {};
-    List<double> weightList = [];
-    var xmax = periodicInput ? sx : sx - n + 1;
-    var ymax = periodicInput ? sy : sy - n + 1;
-    for (var y = 0; y < ymax; y++) {
-      for (var x = 0; x < xmax; x++) {
-        var ps = [
-          pattern((dx, dy) => sample[(x + dx) % sx + (y + dy) % sy * sx])
-        ];
-        ps.add(reflect(ps[0]));
-        ps.add(rotate(ps[0]));
-        ps.add(reflect(ps[2]));
-        ps.add(rotate(ps[2]));
-        ps.add(reflect(ps[4]));
-        ps.add(rotate(ps[4]));
-        ps.add(reflect(ps[6]));
-
-        for (var k = 0; k < symmetry; k++) {
-          var p = ps[k];
-          var h = hash(p);
-          var ix = patternIndices[h];
-          if (ix != null) {
-            weightList[ix] = weightList[ix] + 1;
-          } else {
-            patternIndices[h] = weightList.length;
-            weightList.add(1.0);
-            _patterns.add(p);
-          }
-        }
-      }
-    }
-
-    weights = weightList;
-    cT = weights.length;
-    this.ground = ground;
-
-    bool agrees(List<int> p1, List<int> p2, int dx, int dy) {
-      int xmin = dx < 0 ? 0 : dx;
-      int xmax = dx < 0 ? dx + n : n;
-      int ymin = dy < 0 ? 0 : dy;
-      int ymax = dy < 0 ? dy + n : n;
-      for (var y = ymin; y < ymax; y++) {
-        for (var x = xmin; x < xmax; x++) {
-          if (p1[x + n * y] != p2[x - dx + n * (y - dy)]) {
-            return false;
-          }
-        }
-      }
-      return true;
-    }
-
-    propagator = [
-      for (var d = 0; d < 4; d++)
-        [
-          for (var t = 0; t < cT; t++)
-            [
-              for (var t2 = 0; t2 < cT; t2++)
-                if (agrees(
-                    _patterns[t], _patterns[t2], Model.dx[d], Model.dy[d]))
-                  t2
-            ]
-        ]
-    ];
-  }
-}

lib/wfc/template.dart

@@ -0,0 +1,498 @@
+import 'dart:developer';
+import 'dart:math' as math;
+import 'dart:typed_data';
+import 'dart:ui' as ui;
+import 'dart:ui';
+
+import 'package:flutter/services.dart';
+
+class Wfc<T> {
+  // parameters
+  final WfcTemplate<T> _template;
+  final int _mx, _my;
+
+  // constants
+  int get _n => _mx * _my;
+  int get _nShingles => _template._shingles.n;
+  int get _order => _template._order;
+  double _weight(int shingleIx) =>
+      _template._shingles._shingleWeights[shingleIx];
+
+  // overall algo state
+  List<List<bool>> _wave = [];
+  List<List<List<int>>> _compatible = [];
+  List<int?> _observed = [];
+
+  // computationally expensive stuff that we keep in an incremental way
+  List<double> _weightLogWeights = [];
+  double _sumOfWeights = 0.0, _sumOfWeightLogWeights = 0.0;
+  double _startingEntropy = 0.0;
+
+  List<int> _sumsOfOnes = [];
+  List<double> _sumsOfWeights = [];
+  List<double> _sumsOfWeightLogWeights = [];
+  List<double> _entropies = [];
+
+  // temporaries
+  List<double> _distribution = [];
+  List<(int, int)> _stack = [];
+  int _stacksize = 0;
+
+  Wfc(this._template, this._mx, this._my) {
+    _wave = [
+      for (var r = 0; r < _n; r++) [for (var t = 0; t < _nShingles; t++) false]
+    ];
+
+    _compatible = [
+      for (var r = 0; r < _n; r++)
+        [
+          for (var t = 0; t < _nShingles; t++) [0, 0, 0, 0]
+        ]
+    ];
+
+    _distribution = [for (var t = 0; t < _nShingles; t++) 0.0];
+    _observed = [for (var r = 0; r < _n; r++) null];
+
+    _weightLogWeights = [
+      for (var t = 0; t < _nShingles; t++) _weight(t) * math.log(_weight(t))
+    ];
+    _sumOfWeights = 0.0;
+    _sumOfWeightLogWeights = 0.0;
+    for (var t = 0; t < _nShingles; t++) {
+      _sumOfWeights += _weight(t);
+      _sumOfWeightLogWeights += _weightLogWeights[t];
+    }
+    _startingEntropy =
+        math.log(_sumOfWeights) - _sumOfWeightLogWeights / _sumOfWeights;
+
+    _sumsOfOnes = [for (var r = 0; r < _n; r++) 0];
+    _sumsOfWeights = [for (var r = 0; r < _n; r++) 0.0];
+    _sumsOfWeightLogWeights = [for (var r = 0; r < _n; r++) 0.0];
+    _entropies = [for (var r = 0; r < _n; r++) 0.0];
+
+    _stack = [for (var r = 0; r < _n * _nShingles; r++) (0, 0)];
+    _stacksize = 0;
+  }
+
+  void clear() {
+    for (var i = 0; i < _wave.length; i++) {
+      for (var t = 0; t < _nShingles; t++) {
+        _wave[i][t] = true;
+        for (var d = 0; d < 4; d++) {
+          _compatible[i][t][d] = _template
+              ._shingles._metadata._propagators[_opposite[d]][t].length;
+        }
+      }
+
+      _sumsOfOnes[i] = _nShingles;
+      _sumsOfWeights[i] = _sumOfWeights;
+      _sumsOfWeightLogWeights[i] = _sumOfWeightLogWeights;
+      _entropies[i] = _startingEntropy;
+      _observed[i] = null;
+    }
+  }
+
+  bool run(int? seed, int limit) {
+    clear();
+
+    var random = math.Random(seed);
+    for (var l = 0; l < limit || limit < 0; l++) {
+      var node = _nextUnobservedNode(random);
+      if (node != null) {
+        _observe(node, random);
+        var success = _propagate();
+        if (!success) {
+          return false;
+        }
+      } else {
+        for (var i = 0; i < _n; i++) {
+          for (var t = 0; t < _nShingles; t++) {
+            if (_wave[i][t]) {
+              _observed[i] = t;
+              break;
+            }
+          }
+        }
+        return true;
+      }
+    }
+
+    return true;
+  }
+
+  List<T>? extract() {
+    var partial = extractPartial();
+    List<T> out = [];
+    for (var i in partial) {
+      if (i == null) {
+        return null;
+      }
+      out.add(i);
+    }
+    return out;
+  }
+
+  List<T?> extractPartial() {
+    List<T?> result = [];
+    for (int i = 0; i < _n; i++) {
+      result.add(null);
+    }
+
+    for (int y = 0; y < _my; y++) {
+      var dy = y < _my - _order + 1 ? 0 : _order - 1;
+      for (int x = 0; x < _mx; x++) {
+        var dx = x < _mx - _order + 1 ? 0 : _order - 1;
+        var shingleIx = _observed[x - dx + (y - dy) * _mx];
+        if (shingleIx != null) {
+          var shingle = _template._shingles._shingleValues[shingleIx];
+          var content = shingle.content[dx + dy * _order];
+          var real = _template._embedding.decode(content);
+
+          result[x + y * _mx] = real;
+        }
+      }
+    }
+
+    return result;
+  }
+
+  int? _nextUnobservedNode(math.Random random) {
+    double min = 1E+10;
+    int? argmin;
+    for (var i = 0; i < _n; i++) {
+      if (i % _mx + _order > _mx || i ~/ _mx + _order > _my) {
+        continue;
+      }
+      var remainingValues = _sumsOfOnes[i];
+      double entropy = remainingValues.toDouble(); // _entropies[i];
+      if (remainingValues > 1 && entropy <= min) {
+        double noise = 1E-6 * random.nextDouble();
+        if (entropy + noise < min) {
+          min = entropy + noise;
+          argmin = i;
+        }
+      }
+    }
+    return argmin;
+  }
+
+  void _observe(int node, math.Random random) {
+    var w = _wave[node];
+    for (var t = 0; t < _nShingles; t++) {
+      _distribution[t] = w[t] ? _weight(t) : 0.0;
+    }
+
+    int r = _chooseRandom(random, _distribution);
+    for (var t = 0; t < _nShingles; t++) {
+      if (w[t] != (t == r)) {
+        _ban(node, t);
+      }
+    }
+  }
+
+  bool _propagate() {
+    while (_stacksize > 0) {
+      int i1, t1;
+      (i1, t1) = _stack[_stacksize - 1];
+      _stacksize--;
+
+      int x1 = i1 % _mx;
+      int y1 = i1 ~/ _mx;
+
+      for (int d = 0; d < 4; d++) {
+        var x2 = x1 + _dx[d];
+        var y2 = y1 + _dy[d];
+
+        if (x2 < 0 || y2 < 0 || x2 + _order > _mx || y2 + _order > _my) {
+          continue;
+        }
+
+        int i2 = x2 + y2 * _mx;
+        var p = _template._shingles._metadata._propagators[d][t1];
+        var compat = _compatible[i2];
+
+        for (var t2 in p) {
+          var comp = compat[t2];
+          comp[d]--;
+          if (comp[d] == 0) {
+            _ban(i2, t2);
+          }
+        }
+      }
+    }
+
+    return _sumsOfOnes[0] > 0;
+  }
+
+  void _ban(int i, int t) {
+    _wave[i][t] = false;
+
+    var comp = _compatible[i][t];
+    for (var d = 0; d < 4; d++) {
+      comp[d] = 0;
+    }
+    _stack[_stacksize] = (i, t);
+    _stacksize++;
+
+    _sumsOfOnes[i] -= 1;
+    _sumsOfWeights[i] -= _weight(t);
+    _sumsOfWeightLogWeights[i] -= _weightLogWeights[t];
+
+    var sum = _sumsOfWeights[i];
+    _entropies[i] = math.log(sum) - _sumsOfWeightLogWeights[i] / sum;
+  }
+}
+
+class WfcTemplate<T> {
+  final Shingles _shingles;
+  final Embedding<T> _embedding;
+  final int _order;
+
+  WfcTemplate(this._shingles, this._embedding, this._order);
+
+  static Future<WfcTemplate<T>> loadAsync<T>(
+      String name, int order, T Function(int) cb) async {
+    final assetImageByteData = await rootBundle.load(name);
+    final codec =
+        await ui.instantiateImageCodec(assetImageByteData.buffer.asUint8List());
+    final image = (await codec.getNextFrame()).image;
+
+    final bytedata =
+        (await image.toByteData(format: ImageByteFormat.rawStraightRgba))!;
+
+    final sx = image.width;
+    final sy = image.height;
+
+    final List<T> bitmap = [];
+    for (var i = 0; i < sx * sy; i++) {
+      var pixel = bytedata.getUint32(i * 4, Endian.little);
+      log("pixel: $pixel");
+      bitmap.add(cb(pixel));
+    }
+
+    return loadBitmap(bitmap, sx, sy, order);
+  }
+
+  static WfcTemplate<T> loadBitmap<T>(
+      List<T> bitmap, int sx, int sy, int order) {
+    if (bitmap.length != sx * sy) {
+      throw Exception("malformed bitmap");
+    }
+    var embedding = Embedding<T>();
+    List<int> sample = [
+      for (var i = 0; i < bitmap.length; i++) embedding.encode(bitmap[i])
+    ];
+    embedding.freeze();
+
+    var shingles = Shingles();
+    var xmax = sx - order + 1;
+    var ymax = sy - order + 1;
+    for (var y = 0; y < ymax; y++) {
+      for (var x = 0; x < xmax; x++) {
+        var ps = [
+          Shingle(order, embedding.c,
+              (dx, dy) => sample[(x + dx) % sx + (y + dy) % sy * sx])
+        ];
+        ps.add(ps[0].reflect());
+        ps.add(ps[0].rotate());
+        ps.add(ps[2].reflect());
+        ps.add(ps[2].rotate());
+        ps.add(ps[4].reflect());
+        ps.add(ps[4].rotate());
+        ps.add(ps[6].reflect());
+        for (var p in ps) {
+          shingles.observe(p, 1.0);
+        }
+      }
+    }
+    shingles.freeze();
+
+    return WfcTemplate(shingles, embedding, order);
+  }
+}
+
+class Shingles {
+  bool _frozen = false;
+  final Map<int, int> _shingleIndices = {};
+  final List<Shingle> _shingleValues = [];
+  final List<double> _shingleWeights = [];
+
+  late ShingleMetadata _metadata;
+
+  int get n {
+    if (!_frozen) {
+      throw StateError("can't use Shingles#get n until frozen");
+    }
+    return _shingleValues.length;
+  }
+
+  void freeze() {
+    if (_frozen) {
+      throw StateError("can't freeze when already frozen");
+    }
+    _frozen = true;
+
+    _metadata = ShingleMetadata(this);
+  }
+
+  void observe(Shingle s, double n) {
+    if (_frozen) {
+      throw StateError("can't observe when already frozen");
+    }
+
+    // double n: weights can be fractional
+    var index = _shingleIndices[s.hashCode];
+    if (index == null) {
+      index = _shingleValues.length;
+      _shingleValues.add(s);
+      _shingleWeights.add(n);
+    } else {
+      _shingleWeights[index] += n;
+    }
+  }
+}
+
+class ShingleMetadata {
+  // [direction][source] => list of agreeing items
+  List<List<List<int>>> _propagators = [];
+
+  ShingleMetadata(Shingles s) {
+    _propagators = [
+      for (var d = 0; d < 4; d++)
+        [
+          for (var t = 0; t < s.n; t++)
+            [
+              for (var t2 = 0; t2 < s.n; t2++)
+                if (s._shingleValues[t]
+                    .agrees(s._shingleValues[t2], _dx[d], _dy[d]))
+                  t2
+            ]
+        ]
+    ];
+  }
+}
+
+class Shingle {
+  int order;
+  int c;
+  List<int> content = [];
+
+  @override
+  int hashCode = 0;
+
+  Shingle(this.order, this.c, int Function(int, int) f) {
+    content = [
+      for (var y = 0; y < order; y++)
+        for (var x = 0; x < order; x++) f(x, y)
+    ];
+
+    int result = 0, power = 1;
+    for (var i = 0; i < content.length; i++) {
+      result += content[content.length - 1 - i] * power;
+      power *= c;
+    }
+    hashCode = result;
+  }
+
+  Shingle rotate() {
+    return Shingle(order, c, (x, y) => content[order - 1 - y + x * order]);
+  }
+
+  Shingle reflect() {
+    return Shingle(order, c, (x, y) => content[order - 1 - x + y * order]);
+  }
+
+  bool agrees(Shingle other, int dx, int dy) {
+    var p1 = content;
+    var p2 = other.content;
+    var n = order;
+
+    int xmin = dx < 0 ? 0 : dx;
+    int xmax = dx < 0 ? dx + n : n;
+    int ymin = dy < 0 ? 0 : dy;
+    int ymax = dy < 0 ? dy + n : n;
+    for (var y = ymin; y < ymax; y++) {
+      for (var x = xmin; x < xmax; x++) {
+        if (p1[x + n * y] != p2[x - dx + n * (y - dy)]) {
+          return false;
+        }
+      }
+    }
+    return true;
+  }
+
+  @override
+  bool operator ==(Object other) {
+    return (other is Shingle) &&
+        other.hashCode == hashCode &&
+        other.order == order &&
+        other.c == c;
+  }
+}
+
+class Embedding<T> {
+  bool _frozen = false;
+  final List<T> _colorOf = [];
+  final Map<T, int> _codeOf = {};
+
+  void freeze() {
+    if (_frozen) {
+      throw StateError("can't freeze when already frozen");
+    }
+    _frozen = true;
+  }
+
+  int get c {
+    if (!_frozen) {
+      throw StateError("can't use Embedding#get c until frozen");
+    }
+    return _colorOf.length;
+  }
+
+  int encode(T t) {
+    var code = _codeOf[t];
+    if (code == null) {
+      if (_frozen) {
+        throw StateError("can't create new code when frozen");
+      }
+      code = _colorOf.length;
+      _codeOf[t] = code;
+      _colorOf.add(t);
+    }
+    return code;
+  }
+
+  T decode(int i) {
+    return _colorOf[i]!;
+  }
+}
+
+int _chooseRandom(math.Random rand, List<double> distribution) {
+  if (distribution.isEmpty) {
+    throw Exception("can't sample empty distribution");
+  }
+  var sum = 0.0;
+  for (var i = 0; i < distribution.length; i++) {
+    sum += distribution[i];
+  }
+
+  if (sum == 0.0) {
+    return rand.nextInt(distribution.length);
+  }
+
+  var rnd = rand.nextDouble() * sum;
+
+  var i = 0;
+  while (rnd > 0) {
+    rnd -= distribution[i];
+    if (rnd < 0) {
+      return i;
+    }
+    i += 1;
+  }
+  return distribution.length - 1;
+}
+
+final List<int> _dx = [-1, 0, 1, 0];
+final List<int> _dy = [0, 1, 0, -1];
+final List<int> _opposite = [2, 3, 0, 1];

lib/world/level.dart

@@ -1,5 +1,33 @@
-import 'dart:ui';
+import 'package:dartterm/wfc/template.dart';
+
+enum LevelTile {
+  exit,
+  door,
+  floor,
+  wall,
+}
 
 class Level {
   Set<(int, int)> openCells = {};
 }
+
+Future<WfcTemplate<LevelTile>> loadLevelWfcAsync(String name) async {
+  return WfcTemplate.loadAsync(name, 2, (c) {
+    switch (c) {
+      // ABGR
+      case 0xFF000000:
+      case 0xFF707070:
+        return LevelTile.wall;
+      case 0xFFFFFFFF:
+      case 0xFF00FFFF:
+      case 0xFFFF00FF:
+        return LevelTile.floor;
+      case 0xFFFF8700:
+        return LevelTile.door;
+      case 0xFF0000FF:
+        return LevelTile.exit;
+      default:
+        throw Exception("unrecognized pixel: $c");
+    }
+  });
+}