Fix Flutter web compilation error (#109)

This PR improves some fill performance issues I found with various Lottie animations.
I think the real issue comes down to the render performance of Path.addPath(). The performance issue happens in the Render thread and seems directly related to how large the animation is on-screen. Flutter might be caching pre-rendered textures and running out of memory.

I've changed how Path.addPath() is called and how the path is rendered for fill_content.dart and gradient_fill_content.dart.

Just as an example, the example/assets/Tests/bm.json animation gets ~60 fps with this fix, compared to 34-52 fps with the lottie-flutter 0.6.0 release. (This is on a Pixel 3 XL)

There are a couple of other changes:

- I fixed a bug with the casing of "weather" in pubspec.yaml. Without this fix, the examples don't build on Ubuntu Linux.
The debugging class MeanCalculator wasn't initializing its fields, causing a null pointer exception when debugging.
- I added antiAliasingSuggested to LottieDrawable to allow fill paints to be anti-aliased. It is off by default. It also provides some minor performance improvements without any noticeable loss in quality. It is only applied to fills right now.
- I added PathFactory to create Paths rather than just new-ing them. path_factory.dart allows you to switch out the normal Path creation with a debug logging implementation so you can see all of the Path calls that are performed during a frame. Just create a DebugPath in the factory rather than Path.

.github/workflows/analyze-and-test.yaml

@@ -10,7 +10,7 @@ jobs:
     name: Flutter analyze
     strategy:
       matrix:
-        flutter: ['stable', 'dev']
+        flutter: ['stable']
     runs-on: macos-latest
     steps:
       - uses: actions/checkout@v2

CHANGELOG.md

@@ -1,3 +1,9 @@
+## [0.7.0+1]
+- Fix Flutter Web compilation error
+
+## [0.7.0]
+- Performance improvement for complex animations.
+
 ## [0.6.0]
 - Runs the animation at the frame rate specified in the json file (ie. An animation encoded with a 20 FPS will only
   be paint 20 times per seconds even though the AnimationController will invalidate the widget 60 times per seconds).  

README.md

@@ -8,7 +8,7 @@ animations exported as json with [Bodymovin](https://github.com/airbnb/lottie-we
 
 This repository is a unofficial conversion of the [Lottie-android](https://github.com/airbnb/lottie-android) library in pure Dart. 
 
-It works on Android, iOS and macOS and web.
+It works on Android, iOS, macOS, linux, windows and web.
 
 ## Usage
 

README.template.md

@@ -8,7 +8,7 @@ animations exported as json with [Bodymovin](https://github.com/airbnb/lottie-we
 
 This repository is a unofficial conversion of the [Lottie-android](https://github.com/airbnb/lottie-android) library in pure Dart. 
 
-It works on Android, iOS and macOS and web.
+It works on Android, iOS, macOS, linux, windows and web.
 
 ## Usage
 

example/pubspec.lock

@@ -21,42 +21,42 @@ packages:
       name: async
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.4.2"
+    version: "2.5.0-nullsafety.1"
   boolean_selector:
     dependency: transitive
     description:
       name: boolean_selector
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.0"
+    version: "2.1.0-nullsafety.1"
   characters:
     dependency: transitive
     description:
       name: characters
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.0-nullsafety"
+    version: "1.1.0-nullsafety.3"
   charcode:
     dependency: transitive
     description:
       name: charcode
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.3"
+    version: "1.2.0-nullsafety.1"
   clock:
     dependency: transitive
     description:
       name: clock
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.0.1"
+    version: "1.1.0-nullsafety.1"
   collection:
     dependency: transitive
     description:
       name: collection
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.15.0-nullsafety"
+    version: "1.15.0-nullsafety.3"
   convert:
     dependency: transitive
     description:
@@ -77,7 +77,14 @@ packages:
       name: fake_async
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.0"
+    version: "1.2.0-nullsafety.1"
+  ffi:
+    dependency: transitive
+    description:
+      name: ffi
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.1.3"
   file:
     dependency: transitive
     description:
@@ -143,35 +150,35 @@ packages:
       path: ".."
       relative: true
     source: path
-    version: "0.6.0"
+    version: "0.7.0+1"
   matcher:
     dependency: transitive
     description:
       name: matcher
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.12.8"
+    version: "0.12.10-nullsafety.1"
   meta:
     dependency: transitive
     description:
       name: meta
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.3.0-nullsafety"
+    version: "1.3.0-nullsafety.3"
   path:
     dependency: transitive
     description:
       name: path
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.7.0"
+    version: "1.8.0-nullsafety.1"
   path_provider:
     dependency: "direct main"
     description:
       name: path_provider
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.6.11"
+    version: "1.6.21"
   path_provider_linux:
     dependency: transitive
     description:
@@ -185,14 +192,21 @@ packages:
       name: path_provider_macos
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.0.4+3"
+    version: "0.0.4+4"
   path_provider_platform_interface:
     dependency: transitive
     description:
       name: path_provider_platform_interface
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.0.2"
+    version: "1.0.3"
+  path_provider_windows:
+    dependency: transitive
+    description:
+      name: path_provider_windows
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.0.4+1"
   pedantic:
     dependency: transitive
     description:
@@ -213,7 +227,7 @@ packages:
       name: plugin_platform_interface
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.0.2"
+    version: "1.0.3"
   process:
     dependency: transitive
     description:
@@ -232,63 +246,70 @@ packages:
       name: source_span
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.7.0"
+    version: "1.8.0-nullsafety.2"
   stack_trace:
     dependency: transitive
     description:
       name: stack_trace
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.9.5"
+    version: "1.10.0-nullsafety.1"
   stream_channel:
     dependency: transitive
     description:
       name: stream_channel
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.0"
+    version: "2.1.0-nullsafety.1"
   string_scanner:
     dependency: transitive
     description:
       name: string_scanner
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.0.5"
+    version: "1.1.0-nullsafety.1"
   term_glyph:
     dependency: transitive
     description:
       name: term_glyph
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.0"
+    version: "1.2.0-nullsafety.1"
   test_api:
     dependency: transitive
     description:
       name: test_api
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.17"
+    version: "0.2.19-nullsafety.2"
   typed_data:
     dependency: transitive
     description:
       name: typed_data
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.3.0-nullsafety"
+    version: "1.3.0-nullsafety.3"
   vector_math:
     dependency: transitive
     description:
       name: vector_math
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.0-nullsafety"
+    version: "2.1.0-nullsafety.3"
+  win32:
+    dependency: transitive
+    description:
+      name: win32
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.7.3"
   xdg_directories:
     dependency: transitive
     description:
       name: xdg_directories
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.1.0"
+    version: "0.1.2"
 sdks:
-  dart: ">=2.9.0-18.0 <2.9.0"
+  dart: ">=2.10.0-110 <2.11.0"
   flutter: ">=1.12.13+hotfix.5 <2.0.0"

example/pubspec.yaml

@@ -8,11 +8,11 @@ environment:
 dependencies:
   flutter:
     sdk: flutter
+  flutter_colorpicker:
+  http:
   lottie:
     path: ../
-  flutter_colorpicker:
   path_provider:
-  http:
 
 dev_dependencies:
   flutter_test:
@@ -34,7 +34,7 @@ flutter:
     - assets/Logo/
     - assets/Images/
     - assets/Images/WeAccept/
-    - assets/Weather/
+    - assets/weather/
     - assets/example_with_images/
     - assets/example_with_images/images/
 

lib/src/animation/content/base_stroke_content.dart

@@ -13,6 +13,7 @@ import '../../model/layer/base_layer.dart';
 import '../../utils.dart';
 import '../../utils/dash_path.dart';
 import '../../utils/misc.dart';
+import '../../utils/path_factory.dart';
 import '../../utils/utils.dart';
 import '../../value/lottie_value_callback.dart';
 import '../keyframe/base_keyframe_animation.dart';
@@ -25,8 +26,8 @@ import 'trim_path_content.dart';
 
 abstract class BaseStrokeContent
     implements KeyPathElementContent, DrawingContent {
-  final Path _path = Path();
+  final Path _path = PathFactory.create();
-  final Path _trimPathPath = Path();
+  final Path _trimPathPath = PathFactory.create();
   final LottieDrawable lottieDrawable;
   final BaseLayer layer;
   final List<_PathGroup> _pathGroups = <_PathGroup>[];

lib/src/animation/content/content_group.dart

@@ -9,6 +9,7 @@ import '../../model/key_path.dart';
 import '../../model/key_path_element.dart';
 import '../../model/layer/base_layer.dart';
 import '../../utils.dart';
+import '../../utils/path_factory.dart';
 import '../../value/lottie_value_callback.dart';
 import '../keyframe/transform_keyframe_animation.dart';
 import 'content.dart';
@@ -43,7 +44,7 @@ class ContentGroup implements DrawingContent, PathContent, KeyPathElement {
   }
 
   final Matrix4 _matrix = Matrix4.identity();
-  final Path _path = Path();
+  final Path _path = PathFactory.create();
 
   @override
   final String name;

lib/src/animation/content/ellipse_content.dart

@@ -7,6 +7,7 @@ import '../../model/key_path.dart';
 import '../../model/layer/base_layer.dart';
 import '../../utils.dart';
 import '../../utils/misc.dart';
+import '../../utils/path_factory.dart';
 import '../../value/lottie_value_callback.dart';
 import '../keyframe/base_keyframe_animation.dart';
 import 'compound_trim_path_content.dart';
@@ -18,7 +19,7 @@ import 'trim_path_content.dart';
 class EllipseContent implements PathContent, KeyPathElementContent {
   static final double _ellipseControlPointPercentage = 0.55228;
 
-  final Path _path = Path();
+  final Path _path = PathFactory.create();
 
   @override
   final String name;

lib/src/animation/content/fill_content.dart

@@ -8,6 +8,7 @@ import '../../model/key_path.dart';
 import '../../model/layer/base_layer.dart';
 import '../../utils.dart';
 import '../../utils/misc.dart';
+import '../../utils/path_factory.dart';
 import '../../value/lottie_value_callback.dart';
 import '../keyframe/base_keyframe_animation.dart';
 import '../keyframe/value_callback_keyframe_animation.dart';
@@ -17,7 +18,7 @@ import 'key_path_element_content.dart';
 import 'path_content.dart';
 
 class FillContent implements DrawingContent, KeyPathElementContent {
-  final Path _path = Path();
+  final Path _path = PathFactory.create();
   final Paint _paint = Paint();
   final BaseLayer layer;
   @override
@@ -70,6 +71,9 @@ class FillContent implements DrawingContent, KeyPathElementContent {
     var alpha =
         ((parentAlpha / 255.0 * _opacityAnimation.value / 100.0) * 255).round();
     _paint.setAlpha(alpha.clamp(0, 255).toInt());
+    if (lottieDrawable.antiAliasingSuggested) {
+      _paint.isAntiAlias = true;
+    }
 
     if (_colorFilterAnimation != null) {
       _paint.colorFilter = _colorFilterAnimation.value;
@@ -77,11 +81,13 @@ class FillContent implements DrawingContent, KeyPathElementContent {
 
     _path.reset();
     for (var i = 0; i < _paths.length; i++) {
-      _path.addPath(_paths[i].getPath(), Offset.zero,
+      _path.addPath(_paths[i].getPath(), Offset.zero);
-          matrix4: parentMatrix.storage);
     }
 
+    canvas.save();
+    canvas.transform(parentMatrix.storage);
     canvas.drawPath(_path, _paint);
+    canvas.restore();
 
     L.endSection('FillContent#draw');
   }

lib/src/animation/content/gradient_fill_content.dart

@@ -10,6 +10,7 @@ import '../../model/key_path.dart';
 import '../../model/layer/base_layer.dart';
 import '../../utils.dart';
 import '../../utils/misc.dart';
+import '../../utils/path_factory.dart';
 import '../../value/lottie_value_callback.dart';
 import '../keyframe/base_keyframe_animation.dart';
 import '../keyframe/value_callback_keyframe_animation.dart';
@@ -25,7 +26,7 @@ class GradientFillContent implements DrawingContent, KeyPathElementContent {
   final GradientFill _fill;
   final _linearGradientCache = <int, Gradient>{};
   final _radialGradientCache = <int, Gradient>{};
-  final _path = Path();
+  final _path = PathFactory.create();
   final _paint = Paint();
   final _paths = <PathContent>[];
   final BaseKeyframeAnimation<GradientColor, GradientColor> _colorAnimation;
@@ -85,15 +86,14 @@ class GradientFillContent implements DrawingContent, KeyPathElementContent {
     L.beginSection('GradientFillContent#draw');
     _path.reset();
     for (var i = 0; i < _paths.length; i++) {
-      _path.addPath(_paths[i].getPath(), Offset.zero,
+      _path.addPath(_paths[i].getPath(), Offset.zero);
-          matrix4: parentMatrix.storage);
     }
 
     Gradient gradient;
     if (_fill.gradientType == GradientType.linear) {
-      gradient = _getLinearGradient(parentMatrix);
+      gradient = _getLinearGradient();
     } else {
-      gradient = _getRadialGradient(parentMatrix);
+      gradient = _getRadialGradient();
     }
 
     _paint.shader = gradient;
@@ -105,8 +105,14 @@ class GradientFillContent implements DrawingContent, KeyPathElementContent {
     var alpha =
         ((parentAlpha / 255.0 * _opacityAnimation.value / 100.0) * 255).round();
     _paint.setAlpha(alpha.clamp(0, 255).toInt());
+    if (lottieDrawable.antiAliasingSuggested) {
+      _paint.isAntiAlias = true;
+    }
 
+    canvas.save();
+    canvas.transform(parentMatrix.storage);
     canvas.drawPath(_path, _paint);
+    canvas.restore();
     L.endSection('GradientFillContent#draw');
   }
 
@@ -124,8 +130,8 @@ class GradientFillContent implements DrawingContent, KeyPathElementContent {
         outBounds.right + 1, outBounds.bottom + 1);
   }
 
-  Gradient _getLinearGradient(Matrix4 parentMatrix) {
+  Gradient _getLinearGradient() {
-    var gradientHash = _getGradientHash(parentMatrix);
+    var gradientHash = _getGradientHash();
     var gradient = _linearGradientCache[gradientHash];
     if (gradient != null) {
       return gradient;
@@ -135,14 +141,14 @@ class GradientFillContent implements DrawingContent, KeyPathElementContent {
     var gradientColor = _colorAnimation.value;
     var colors = _applyDynamicColorsIfNeeded(gradientColor.colors);
     var positions = gradientColor.positions;
-    gradient = Gradient.linear(startPoint, endPoint, colors, positions,
+    gradient = Gradient.linear(
-        TileMode.clamp, parentMatrix.storage);
+        startPoint, endPoint, colors, positions, TileMode.clamp);
     _linearGradientCache[gradientHash] = gradient;
     return gradient;
   }
 
-  Gradient _getRadialGradient(Matrix4 parentMatrix) {
+  Gradient _getRadialGradient() {
-    var gradientHash = _getGradientHash(parentMatrix);
+    var gradientHash = _getGradientHash();
     var gradient = _radialGradientCache[gradientHash];
     if (gradient != null) {
       return gradient;
@@ -160,13 +166,13 @@ class GradientFillContent implements DrawingContent, KeyPathElementContent {
     if (radius <= 0) {
       radius = 0.001;
     }
-    gradient = Gradient.radial(startPoint, radius, colors, positions,
+    gradient =
-        TileMode.clamp, parentMatrix.storage);
+        Gradient.radial(startPoint, radius, colors, positions, TileMode.clamp);
     _radialGradientCache[gradientHash] = gradient;
     return gradient;
   }
 
-  int _getGradientHash(Matrix4 parentMatrix) {
+  int _getGradientHash() {
     var startPointProgress =
         (_startPointAnimation.progress * _cacheSteps).round();
     var endPointProgress = (_endPointAnimation.progress * _cacheSteps).round();
@@ -181,7 +187,6 @@ class GradientFillContent implements DrawingContent, KeyPathElementContent {
     if (colorProgress != 0) {
       hash = hash * 31 * colorProgress;
     }
-    hash *= 31 * parentMatrix.hashCode;
     return hash;
   }
 

lib/src/animation/content/merge_paths_content.dart

@@ -1,15 +1,16 @@
 import 'dart:ui';
 import '../../model/content/merge_paths.dart';
 import '../../utils.dart';
+import '../../utils/path_factory.dart';
 import 'content.dart';
 import 'content_group.dart';
 import 'greedy_content.dart';
 import 'path_content.dart';
 
 class MergePathsContent implements PathContent, GreedyContent {
-  final Path _firstPath = Path();
+  final Path _firstPath = PathFactory.create();
-  final Path _remainderPath = Path();
+  final Path _remainderPath = PathFactory.create();
-  final Path _path = Path();
+  final Path _path = PathFactory.create();
 
   final List<PathContent> _pathContents = <PathContent>[];
   final MergePaths _mergePaths;

lib/src/animation/content/polystar_content.dart

@@ -8,6 +8,7 @@ import '../../model/content/shape_trim_path.dart';
 import '../../model/key_path.dart';
 import '../../model/layer/base_layer.dart';
 import '../../utils/misc.dart';
+import '../../utils/path_factory.dart';
 import '../../value/lottie_value_callback.dart';
 import '../keyframe/base_keyframe_animation.dart';
 import 'compound_trim_path_content.dart';
@@ -23,7 +24,7 @@ class PolystarContent implements PathContent, KeyPathElementContent {
   /// work otherwise.
   static final _polystarMagicNumber = .47829;
   static final _polygonMagicNumber = .25;
-  final _path = Path();
+  final _path = PathFactory.create();
 
   final LottieDrawable lottieDrawable;
   final PolystarShape _polystarShape;

lib/src/animation/content/rectangle_content.dart

@@ -8,6 +8,7 @@ import '../../model/content/shape_trim_path.dart';
 import '../../model/key_path.dart';
 import '../../model/layer/base_layer.dart';
 import '../../utils/misc.dart';
+import '../../utils/path_factory.dart';
 import '../../value/lottie_value_callback.dart';
 import '../keyframe/base_keyframe_animation.dart';
 import 'compound_trim_path_content.dart';
@@ -17,7 +18,7 @@ import 'path_content.dart';
 import 'trim_path_content.dart';
 
 class RectangleContent implements KeyPathElementContent, PathContent {
-  final _path = Path();
+  final _path = PathFactory.create();
 
   @override
   final String name;

lib/src/animation/content/repeater_content.dart

@@ -7,6 +7,7 @@ import '../../model/key_path.dart';
 import '../../model/layer/base_layer.dart';
 import '../../utils.dart';
 import '../../utils/misc.dart';
+import '../../utils/path_factory.dart';
 import '../../value/lottie_value_callback.dart';
 import '../keyframe/base_keyframe_animation.dart';
 import '../keyframe/transform_keyframe_animation.dart';
@@ -24,7 +25,7 @@ class RepeaterContent
         GreedyContent,
         KeyPathElementContent {
   final Matrix4 _matrix = Matrix4.identity();
-  final _path = Path();
+  final _path = PathFactory.create();
 
   final LottieDrawable lottieDrawable;
   final BaseLayer layer;

lib/src/animation/content/shape_content.dart

@@ -4,6 +4,7 @@ import '../../model/content/shape_path.dart';
 import '../../model/content/shape_trim_path.dart';
 import '../../model/layer/base_layer.dart';
 import '../../utils.dart';
+import '../../utils/path_factory.dart';
 import '../keyframe/base_keyframe_animation.dart';
 import 'compound_trim_path_content.dart';
 import 'content.dart';
@@ -11,7 +12,7 @@ import 'path_content.dart';
 import 'trim_path_content.dart';
 
 class ShapeContent implements PathContent {
-  final _path = Path();
+  final _path = PathFactory.create();
 
   final ShapePath _shape;
 

lib/src/animation/keyframe/shape_keyframe_animation.dart

@@ -1,12 +1,13 @@
 import 'dart:ui';
 import '../../model/content/shape_data.dart';
 import '../../utils/misc.dart';
+import '../../utils/path_factory.dart';
 import '../../value/keyframe.dart';
 import 'base_keyframe_animation.dart';
 
 class ShapeKeyframeAnimation extends BaseKeyframeAnimation<ShapeData, Path> {
   final ShapeData _tempShapeData = ShapeData.empty();
-  final Path _tempPath = Path();
+  final Path _tempPath = PathFactory.create();
 
   ShapeKeyframeAnimation(List<Keyframe<ShapeData>> keyframes)
       : super(keyframes);

lib/src/lottie_drawable.dart

@@ -18,6 +18,9 @@ class LottieDrawable {
   bool _isDirty = true;
   final bool enableMergePaths;
 
+  /// Gives a suggestion whether to paint with anti-aliasing, or not. Default is true.
+  bool antiAliasingSuggested = true;
+
   LottieDrawable(this.composition,
       {LottieDelegates delegates, bool enableMergePaths})
       : size = Size(composition.bounds.width.toDouble(),

lib/src/model/layer/solid_layer.dart

@@ -5,13 +5,14 @@ import '../../animation/keyframe/value_callback_keyframe_animation.dart';
 import '../../lottie_drawable.dart';
 import '../../lottie_property.dart';
 import '../../utils.dart';
+import '../../utils/path_factory.dart';
 import '../../value/lottie_value_callback.dart';
 import 'base_layer.dart';
 import 'layer.dart';
 
 class SolidLayer extends BaseLayer {
   final Paint paint = Paint()..style = PaintingStyle.fill;
-  final Path path = Path();
+  final Path path = PathFactory.create();
   BaseKeyframeAnimation<ColorFilter, ColorFilter> /*?*/ _colorFilterAnimation;
 
   SolidLayer(LottieDrawable lottieDrawable, Layer layerModel)

lib/src/utils/dash_path.dart

@@ -1,6 +1,7 @@
 import 'dart:math';
 import 'dart:ui';
 import 'package:meta/meta.dart';
+import 'path_factory.dart';
 
 Path dashPath(
   Path source, {
@@ -14,7 +15,7 @@ Path dashPath(
   }
   phase ??= 0;
 
-  var dest = Path();
+  var dest = PathFactory.create();
   for (final metric in source.computeMetrics()) {
     for (var dash in _dashes(metric.length, intervals, phase)) {
       dest.addPath(metric.extractPath(dash.left, dash.right), Offset.zero);

lib/src/utils/debug_path.dart

@@ -0,0 +1,189 @@
+import 'dart:typed_data';
+import 'dart:ui';
+
+class DebugPath extends Path {
+  void _log(String methodName) {
+    print('Path.$methodName');
+  }
+
+  @override
+  void addArc(Rect oval, double startAngle, double sweepAngle) {
+    _log('addArc');
+    super.addArc(oval, startAngle, sweepAngle);
+  }
+
+  @override
+  void addOval(Rect oval) {
+    _log('addOval');
+    super.addOval(oval);
+  }
+
+  @override
+  void addPath(Path path, Offset offset, {Float64List matrix4}) {
+    _log('addPath');
+    super.addPath(path, offset, matrix4: matrix4);
+  }
+
+  @override
+  void addPolygon(List<Offset> points, bool close) {
+    _log('addPolygon');
+    super.addPolygon(points, close);
+  }
+
+  @override
+  void addRRect(RRect rrect) {
+    _log('addRRect');
+    super.addRRect(rrect);
+  }
+
+  @override
+  void addRect(Rect rect) {
+    _log('addRect');
+    super.addRect(rect);
+  }
+
+  @override
+  void arcTo(
+      Rect rect, double startAngle, double sweepAngle, bool forceMoveTo) {
+    _log('arcTo');
+    super.arcTo(rect, startAngle, sweepAngle, forceMoveTo);
+  }
+
+  @override
+  void arcToPoint(Offset arcEnd,
+      {Radius radius = Radius.zero,
+      double rotation = 0.0,
+      bool largeArc = false,
+      bool clockwise = true}) {
+    _log('arcToPoint');
+    super.arcToPoint(arcEnd,
+        radius: radius,
+        rotation: rotation,
+        largeArc: largeArc,
+        clockwise: clockwise);
+  }
+
+  @override
+  void close() {
+    _log('close');
+    super.close();
+  }
+
+  @override
+  PathMetrics computeMetrics({bool forceClosed = false}) {
+    _log('computeMetrics');
+    return super.computeMetrics();
+  }
+
+  @override
+  void conicTo(double x1, double y1, double x2, double y2, double w) {
+    _log('conicTo');
+    super.conicTo(x1, y1, x2, y2, w);
+  }
+
+  @override
+  bool contains(Offset point) {
+    _log('contains');
+    return super.contains(point);
+  }
+
+  @override
+  void cubicTo(
+      double x1, double y1, double x2, double y2, double x3, double y3) {
+    _log('cubicTo');
+    super.cubicTo(x1, y1, x2, y2, x3, y3);
+  }
+
+  @override
+  void extendWithPath(Path path, Offset offset, {Float64List matrix4}) {
+    _log('extendWithPath');
+    super.extendWithPath(path, offset, matrix4: matrix4);
+  }
+
+  @override
+  Rect getBounds() {
+    _log('getBounds');
+    return super.getBounds();
+  }
+
+  @override
+  void lineTo(double x, double y) {
+    _log('lineTo');
+    super.lineTo(x, y);
+  }
+
+  @override
+  void moveTo(double x, double y) {
+    _log('moveTo');
+    super.moveTo(x, y);
+  }
+
+  @override
+  void quadraticBezierTo(double x1, double y1, double x2, double y2) {
+    _log('quadraticBezierTo');
+    super.quadraticBezierTo(x1, y1, x2, y2);
+  }
+
+  @override
+  void relativeArcToPoint(Offset arcEndDelta,
+      {Radius radius = Radius.zero,
+      double rotation = 0.0,
+      bool largeArc = false,
+      bool clockwise = true}) {
+    _log('relativeArcToPoint');
+    super.relativeArcToPoint(arcEndDelta,
+        radius: radius,
+        rotation: rotation,
+        largeArc: largeArc,
+        clockwise: clockwise);
+  }
+
+  @override
+  void relativeConicTo(double x1, double y1, double x2, double y2, double w) {
+    _log('relativeConicTo');
+    super.relativeConicTo(x1, y1, x2, y2, w);
+  }
+
+  @override
+  void relativeCubicTo(
+      double x1, double y1, double x2, double y2, double x3, double y3) {
+    _log('relativeCubicTo');
+    super.relativeCubicTo(x1, y1, x2, y2, x3, y3);
+  }
+
+  @override
+  void relativeLineTo(double dx, double dy) {
+    _log('relativeLineTo');
+    super.relativeLineTo(dx, dy);
+  }
+
+  @override
+  void relativeMoveTo(double dx, double dy) {
+    _log('relativeMoveTo');
+    super.relativeMoveTo(dx, dy);
+  }
+
+  @override
+  void relativeQuadraticBezierTo(double x1, double y1, double x2, double y2) {
+    _log('relativeQuadraticBezierTo');
+    super.relativeQuadraticBezierTo(x1, y1, x2, y2);
+  }
+
+  @override
+  void reset() {
+    _log('reset');
+    super.reset();
+  }
+
+  @override
+  Path shift(Offset offset) {
+    _log('shift');
+    return super.shift(offset);
+  }
+
+  @override
+  Path transform(Float64List matrix4) {
+    _log('transform');
+    return super.transform(matrix4);
+  }
+}

lib/src/utils/mean_calculator.dart

@@ -1,6 +1,6 @@
 class MeanCalculator {
-  double _sum;
+  double _sum = 0;
-  int _n;
+  int _n = 0;
 
   double get mean => _n == 0 ? 0 : _sum / _n;