Expose LottieDelegates to modify animation properties at runtime (#23)

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

@@ -11,7 +11,7 @@ jobs:
     strategy:
       matrix:
         flutter: ['stable', 'dev']
-    runs-on: ubuntu-latest
+    runs-on: macos-latest
     steps:
       - uses: actions/checkout@v2
       - uses: subosito/flutter-action@v1
@@ -19,8 +19,12 @@ jobs:
           channel: ${{ matrix.flutter }}
       - run: flutter doctor
       - run: flutter --version
+      - run: flutter pub get
+        working-directory: example
       - run: flutter analyze
       - run: flutter test test # https://github.com/flutter/flutter/issues/20907
+      - run: flutter test test
+        working-directory: example
       - run: flutter pub run tool/prepare_submit.dart
       - name: "check for uncommitted changes"
         run: |

.gitignore

@@ -4,6 +4,8 @@ _*
 !.gitignore
 !.github
 
+**/failures/*.png
+
 *.iml
 **/doc/api/
 build/

CHANGELOG.md

@@ -1,3 +1,8 @@
+## [0.3.0] - 2020-03-02
+- Add `LottieDelegates` a group of options to customize the lottie animation at runtime.
+  ie: Dynamically modify color, position, size, text... of every elements of the animation.
+- Integrate latest changes from Lottie-android
+
 ## [0.2.2] - 2020-02-21
 - Add a [repeat] parameter to specify if the automatic animation should loop.
 - Add the [animate], [reverse], [repeat] properties on `LottieBuilder`

README.md

@@ -37,7 +37,7 @@ class MyApp extends StatelessWidget {
                 'https://raw.githubusercontent.com/xvrh/lottie-flutter/master/example/assets/Mobilo/A.json'),
 
             // Load an animation and its images from a zip file
-            Lottie.asset('assets/lottiesfiles/angel.zip'),
+            Lottie.asset('assets/lottiefiles/angel.zip'),
           ],
         ),
       ),
@@ -46,15 +46,8 @@ class MyApp extends StatelessWidget {
 }
 ```
 
-To load an animation from the assets folder, we need to add an `assets` section in the `pubspec.yaml`:
-```yaml
-flutter:
-  assets:
-    - assets/
-```
-
 ### Specify a custom `AnimationController`
-This example shows how to have full control over the animation by providing your own `AnimationController`.
+This example shows how to take full control over the animation by providing your own `AnimationController`.
 
 ```dart
 import 'package:flutter/material.dart';
@@ -201,7 +194,9 @@ class _Painter extends CustomPainter {
     var columns = 10;
     for (var i = 0; i < frameCount; i++) {
       var destRect = Offset(i % columns * 50.0, i ~/ 10 * 80.0) & (size / 5);
-      drawable.draw(canvas, destRect, progress: i / frameCount);
+      drawable
+        ..setProgress(i / frameCount)
+        ..draw(canvas, destRect);
     }
   }
 
@@ -212,14 +207,45 @@ class _Painter extends CustomPainter {
 }
 ````
 
+### Modify properties at runtime
+This example shows how to modify some properties of the animation at runtime. Here we change the text,
+the color, the opacity and the position of some layers.
+For each `ValueDelegate` we can either provide a static `value` or a `callback` to compute a value for a each frame.
+
+````dart
+class _Animation extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return Lottie.asset(
+      'assets/Tests/Shapes.json',
+      delegates: LottieDelegates(
+          text: (initialText) => translate(initialText),
+          values: [
+            ValueDelegate.color(
+              const ['Shape Layer 1', 'Rectangle', 'Fill 1'],
+              value: Colors.red,
+            ),
+            ValueDelegate.opacity(
+              const ['Shape Layer 1', 'Rectangle'],
+              callback: (frameInfo) =>
+                  (frameInfo.overallProgress * 100).round(),
+            ),
+            ValueDelegate.position(
+              const ['Shape Layer 1', 'Rectangle'],
+              relative: Offset(100, 200),
+            ),
+          ]),
+    );
+  }
+}
+````
+
 ## Limitations
 This is a new library so usability, documentation and performance are still work in progress.
 
 The following features are not yet implemented:
 - Dash path effects
 - Transforms on gradients (stroke and fills)
-- Expose `Value callback` to modify dynamically some properties of the animation
-- Text in animations has very basic support (unoptimized and buggy) 
 
 ## Flutter Web
 Run the app with `flutter run -d Chrome --dart-define=FLUTTER_WEB_USE_SKIA=true --release`

README.template.md

@@ -20,15 +20,8 @@ The `Lottie` widget will load the json file and run the animation indefinitely.
 import 'example/lib/examples/main.dart';
 ```
 
-To load an animation from the assets folder, we need to add an `assets` section in the `pubspec.yaml`:
-```yaml
-flutter:
-  assets:
-    - assets/
-```
-
 ### Specify a custom `AnimationController`
-This example shows how to have full control over the animation by providing your own `AnimationController`.
+This example shows how to take full control over the animation by providing your own `AnimationController`.
 
 ```dart
 import 'example/lib/examples/animation_controller.dart';
@@ -69,14 +62,21 @@ a specific position and size.
 import 'example/lib/examples/custom_draw.dart#example';
 ````
 
+### Modify properties at runtime
+This example shows how to modify some properties of the animation at runtime. Here we change the text,
+the color, the opacity and the position of some layers.
+For each `ValueDelegate` we can either provide a static `value` or a `callback` to compute a value for a each frame.
+
+````dart
+import 'example/lib/examples/simple_dynamic_properties.dart#example';
+````
+
 ## Limitations
 This is a new library so usability, documentation and performance are still work in progress.
 
 The following features are not yet implemented:
 - Dash path effects
 - Transforms on gradients (stroke and fills)
-- Expose `Value callback` to modify dynamically some properties of the animation
-- Text in animations has very basic support (unoptimized and buggy) 
 
 ## Flutter Web
 Run the app with `flutter run -d Chrome --dart-define=FLUTTER_WEB_USE_SKIA=true --release`

example/lib/examples/custom_draw.dart

@@ -81,7 +81,9 @@ class _Painter extends CustomPainter {
     var columns = 10;
     for (var i = 0; i < frameCount; i++) {
       var destRect = Offset(i % columns * 50.0, i ~/ 10 * 80.0) & (size / 5);
-      drawable.draw(canvas, destRect, progress: i / frameCount);
+      drawable
+        ..setProgress(i / frameCount)
+        ..draw(canvas, destRect);
     }
   }
 

example/lib/examples/dynamic_properties.dart

@@ -0,0 +1,86 @@
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_colorpicker/flutter_colorpicker.dart';
+import 'package:lottie/lottie.dart';
+
+void main() async {
+  runApp(App());
+}
+
+class App extends StatefulWidget {
+  const App({Key key}) : super(key: key);
+
+  @override
+  _AppState createState() => _AppState();
+}
+
+class _AppState extends State<App> with TickerProviderStateMixin {
+  Color _color = Colors.green;
+  double _opacity = 0.5;
+  bool _useDelegates = true;
+
+  @override
+  Widget build(BuildContext context) {
+    var valueDelegates = [
+      ValueDelegate.color(['Shape Layer 1', 'Rectangle', 'Fill 1'],
+          value: _color),
+      ValueDelegate.opacity(['Shape Layer 1', 'Rectangle', 'Fill 1'],
+          callback: (_) => (_opacity * 100).round()),
+    ];
+
+    return MaterialApp(
+      color: Colors.blue,
+      home: Scaffold(
+        backgroundColor: Colors.white,
+        appBar: AppBar(
+          title: Text('Dynamic properties'),
+        ),
+        body: ListView(
+          children: <Widget>[
+            SizedBox(
+              width: 300,
+              height: 300,
+              child: Lottie.asset(
+                'assets/Tests/Shapes.json',
+                delegates: LottieDelegates(
+                    values: _useDelegates ? valueDelegates : null),
+              ),
+            ),
+            Checkbox(
+              value: _useDelegates,
+              onChanged: (newValue) {
+                setState(() {
+                  _useDelegates = newValue;
+                });
+              },
+            ),
+            Slider(
+              value: _opacity,
+              onChanged: (newOpacity) {
+                setState(() {
+                  _opacity = newOpacity;
+                });
+              },
+            ),
+            Center(
+              child: Container(
+                width: 500,
+                child: ColorPicker(
+                  pickerColor: _color,
+                  onColorChanged: (newColor) {
+                    setState(() {
+                      _color = newColor;
+                    });
+                  },
+                  showLabel: false,
+                  enableAlpha: false,
+                  pickerAreaHeightPercent: 0.8,
+                ),
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}

example/lib/examples/dynamic_text.dart

@@ -0,0 +1,72 @@
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+import 'package:lottie/lottie.dart';
+
+void main() async {
+  runApp(App());
+}
+
+class App extends StatefulWidget {
+  const App({Key key}) : super(key: key);
+
+  @override
+  _AppState createState() => _AppState();
+}
+
+class _AppState extends State<App> with TickerProviderStateMixin {
+  TextEditingController _textController;
+
+  @override
+  void initState() {
+    super.initState();
+
+    _textController = TextEditingController(text: /*'🔥Fire🔥'*/ 'Fire');
+  }
+
+  @override
+  void dispose() {
+    _textController.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      color: Colors.blue,
+      home: Scaffold(
+        backgroundColor: Colors.white,
+        appBar: AppBar(
+          title: Text('Dynamic text'),
+        ),
+        body: Center(
+          child: Column(
+            children: <Widget>[
+              SizedBox(
+                width: 300,
+                height: 300,
+                child: Lottie.asset(
+                  'assets/Tests/DynamicText.json',
+                  delegates: LottieDelegates(
+                    text: (animationText) => _textController.text,
+                    textStyle: (font) => TextStyle(
+                        fontFamily: font.fontFamily,
+                        fontStyle: FontStyle.italic),
+                  ),
+                ),
+              ),
+              Container(
+                width: 300,
+                child: CupertinoTextField(
+                  controller: _textController,
+                  onChanged: (newText) {
+                    setState(() {});
+                  },
+                ),
+              )
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}

example/lib/examples/main.dart

@@ -18,7 +18,7 @@ class MyApp extends StatelessWidget {
                 'https://raw.githubusercontent.com/xvrh/lottie-flutter/master/example/assets/Mobilo/A.json'),
 
             // Load an animation and its images from a zip file
-            Lottie.asset('assets/lottiesfiles/angel.zip'),
+            Lottie.asset('assets/lottiefiles/angel.zip'),
           ],
         ),
       ),

example/lib/examples/simple_dynamic_properties.dart

@@ -0,0 +1,47 @@
+import 'package:flutter/material.dart';
+import 'package:lottie/lottie.dart';
+
+void main() => runApp(MyApp());
+
+class MyApp extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      home: Scaffold(
+        body: ListView(
+          children: [_Animation()],
+        ),
+      ),
+    );
+  }
+}
+
+String translate(String input) => '**$input**';
+
+//--- example
+class _Animation extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return Lottie.asset(
+      'assets/Tests/Shapes.json',
+      delegates: LottieDelegates(
+          text: (initialText) => translate(initialText),
+          values: [
+            ValueDelegate.color(
+              const ['Shape Layer 1', 'Rectangle', 'Fill 1'],
+              value: Colors.red,
+            ),
+            ValueDelegate.opacity(
+              const ['Shape Layer 1', 'Rectangle'],
+              callback: (frameInfo) =>
+                  (frameInfo.overallProgress * 100).round(),
+            ),
+            ValueDelegate.position(
+              const ['Shape Layer 1', 'Rectangle'],
+              relative: Offset(100, 200),
+            ),
+          ]),
+    );
+  }
+}
+//---

example/lib/main.dart

@@ -66,7 +66,6 @@ class _Item extends StatelessWidget {
       child: Container(
         decoration: BoxDecoration(
             color: Colors.white,
-            //border: Border.all(color: Colors.black12),
             borderRadius: BorderRadius.all(Radius.circular(10)),
             boxShadow: [
               BoxShadow(

example/pubspec.lock

@@ -29,6 +29,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "1.0.5"
+  characters:
+    dependency: transitive
+    description:
+      name: characters
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.5.0"
   charcode:
     dependency: transitive
     description:
@@ -62,11 +69,25 @@ packages:
     description: flutter
     source: sdk
     version: "0.0.0"
+  flutter_colorpicker:
+    dependency: "direct main"
+    description:
+      name: flutter_colorpicker
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.3.2"
   flutter_test:
     dependency: "direct dev"
     description: flutter
     source: sdk
     version: "0.0.0"
+  golden_toolkit:
+    dependency: "direct dev"
+    description:
+      name: golden_toolkit
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.2.1"
   image:
     dependency: transitive
     description:
@@ -87,7 +108,7 @@ packages:
       path: ".."
       relative: true
     source: path
-    version: "0.2.2"
+    version: "0.3.0"
   matcher:
     dependency: transitive
     description:
@@ -200,3 +221,4 @@ packages:
     version: "3.5.0"
 sdks:
   dart: ">=2.7.0 <3.0.0"
+  flutter: ">=1.5.4 <2.0.0"

example/pubspec.yaml

@@ -10,10 +10,12 @@ dependencies:
     sdk: flutter
   lottie:
     path: ../
+  flutter_colorpicker:
 
 dev_dependencies:
   flutter_test:
     sdk: flutter
+  golden_toolkit:
 
 dependency_overrides:
   pedantic: ^1.9.0
@@ -34,33 +36,25 @@ flutter:
     - assets/Images/
     - assets/Images/WeAccept/
 
-  # To add assets to your package, add an assets section, like this:
-  # assets:
-  #  - images/a_dot_burr.jpeg
-  #  - images/a_dot_ham.jpeg
-  #
-  # For details regarding assets in packages, see
-  # https://flutter.dev/assets-and-images/#from-packages
-  #
-  # An image asset can refer to one or more resolution-specific "variants", see
-  # https://flutter.dev/assets-and-images/#resolution-aware.
-
-  # To add custom fonts to your package, add a fonts section here,
-  # in this "flutter" section. Each entry in this list should have a
-  # "family" key with the font family name, and a "fonts" key with a
-  # list giving the asset and other descriptors for the font. For
-  # example:
-  # fonts:
-  #   - family: Schyler
-  #     fonts:
-  #       - asset: fonts/Schyler-Regular.ttf
-  #       - asset: fonts/Schyler-Italic.ttf
-  #         style: italic
-  #   - family: Trajan Pro
-  #     fonts:
-  #       - asset: fonts/TrajanPro.ttf
-  #       - asset: fonts/TrajanPro_Bold.ttf
-  #         weight: 700
-  #
-  # For details regarding fonts in packages, see
-  # https://flutter.dev/custom-fonts/#from-packages
+  fonts:
+    - family: Comic Neue
+      fonts:
+        - asset: assets/fonts/Comic-Neue.ttf
+    - family: Helvetica
+      fonts:
+        - asset: assets/fonts/Helvetica.ttf
+    - family: Helvetica Neue
+      fonts:
+        - asset: assets/fonts/Helvetica-Neue.ttf
+    - family: Open Sans
+      fonts:
+        - asset: assets/fonts/Open-Sans.ttf
+    - family: PT Serif
+      fonts:
+        - asset: assets/fonts/PT-Serif.ttf
+    - family: Roboto
+      fonts:
+        - asset: assets/fonts/Roboto.ttf
+    - family: Noto Emoji
+      fonts:
+        - asset: assets/fonts/NotoEmoji-Regular.ttf

example/test/dynamic_properties_test.dart

@@ -0,0 +1,293 @@
+import 'dart:io';
+import 'dart:ui';
+import 'package:flutter/material.dart';
+import 'package:flutter/painting.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:lottie/lottie.dart';
+
+void main() {
+  LottieComposition composition;
+
+  setUpAll(() async {
+    composition = await LottieComposition.fromBytes(
+        File('assets/Tests/Shapes.json').readAsBytesSync());
+  });
+
+  void testGolden(String description, ValueDelegate delegate,
+      {double progress}) async {
+    var screenshotName = description
+        .toLowerCase()
+        .replaceAll(RegExp('[^a-z0-9 ]'), '')
+        .replaceAll(' ', '_');
+
+    testWidgets(description, (tester) async {
+      var animation =
+          AnimationController(vsync: tester, duration: composition.duration);
+      if (progress != null) {
+        animation.value = progress;
+      }
+
+      await tester.pumpWidget(
+        Lottie(
+          composition: composition,
+          controller: animation,
+          delegates: LottieDelegates(values: [delegate]),
+        ),
+      );
+      await tester.pump();
+      await expectLater(find.byType(Lottie),
+          matchesGoldenFile('goldens/dynamic/$screenshotName.png'));
+
+      if (progress == null || progress == 0) {
+        await tester.pumpWidget(
+          Lottie(
+            composition: composition,
+            controller: animation,
+            delegates: LottieDelegates(values: []),
+          ),
+        );
+        await tester.pump();
+        await expectLater(find.byType(Lottie),
+            matchesGoldenFile('goldens/dynamic_without_delegate.png'));
+      }
+    });
+  }
+
+  testGolden(
+    'Fill color (Green)',
+    ValueDelegate.color(['Shape Layer 1', 'Rectangle', 'Fill 1'],
+        value: Colors.green),
+  );
+
+  testGolden(
+    'Fill color (Yellow)',
+    ValueDelegate.color(['Shape Layer 1', 'Rectangle', 'Fill 1'],
+        value: Colors.yellow),
+  );
+
+  testGolden(
+    'Fill opacity',
+    ValueDelegate.opacity(['Shape Layer 1', 'Rectangle', 'Fill 1'], value: 50),
+  );
+
+  testGolden(
+    'Stroke color',
+    ValueDelegate.strokeColor(['Shape Layer 1', 'Rectangle', 'Stroke 1'],
+        value: Colors.green),
+  );
+
+  testGolden(
+    'Stroke width',
+    ValueDelegate.strokeWidth(['Shape Layer 1', 'Rectangle', 'Stroke 1'],
+        value: 50),
+  );
+
+  testGolden(
+    'Stroke opacity',
+    ValueDelegate.opacity(['Shape Layer 1', 'Rectangle', 'Stroke 1'],
+        value: 50),
+  );
+
+  testGolden(
+    'Transform anchor point',
+    ValueDelegate.transformAnchorPoint(['Shape Layer 1', 'Rectangle'],
+        value: Offset(20, 20)),
+  );
+
+  testGolden(
+    'Transform position',
+    ValueDelegate.transformPosition(['Shape Layer 1', 'Rectangle'],
+        value: Offset(20, 20)),
+  );
+
+  testGolden(
+    'Transform position (relative)',
+    ValueDelegate.transformPosition(['Shape Layer 1', 'Rectangle'],
+        relative: Offset(20, 20)),
+  );
+
+  testGolden(
+    'Transform opacity',
+    ValueDelegate.transformOpacity(['Shape Layer 1', 'Rectangle'], value: 50),
+  );
+
+  testGolden(
+    'Transform rotation',
+    ValueDelegate.transformRotation(['Shape Layer 1', 'Rectangle'], value: 45),
+  );
+
+  testGolden(
+    'Transform scale',
+    ValueDelegate.transformScale(['Shape Layer 1', 'Rectangle'],
+        value: Offset(0.5, 0.5)),
+  );
+
+  testGolden(
+    'Rectangle corner roundedness',
+    ValueDelegate.cornerRadius(
+        ['Shape Layer 1', 'Rectangle', 'Rectangle Path 1'],
+        value: 7),
+  );
+
+  testGolden(
+    'Rectangle position',
+    ValueDelegate.position(['Shape Layer 1', 'Rectangle', 'Rectangle Path 1'],
+        relative: Offset(20, 20)),
+  );
+
+  testGolden(
+    'Rectangle size',
+    ValueDelegate.rectangleSize(
+        ['Shape Layer 1', 'Rectangle', 'Rectangle Path 1'],
+        relative: Offset(30, 40)),
+  );
+
+  testGolden(
+    'Ellipse position',
+    ValueDelegate.position(['Shape Layer 1', 'Ellipse', 'Ellipse Path 1'],
+        relative: Offset(20, 20)),
+  );
+
+  testGolden(
+    'Ellipse size',
+    ValueDelegate.ellipseSize(['Shape Layer 1', 'Ellipse', 'Ellipse Path 1'],
+        relative: Offset(40, 60)),
+  );
+
+  testGolden(
+    'Star points',
+    ValueDelegate.polystarPoints(['Shape Layer 1', 'Star', 'Polystar Path 1'],
+        value: 8),
+  );
+
+  testGolden(
+    'Star rotation',
+    ValueDelegate.polystarRotation(['Shape Layer 1', 'Star', 'Polystar Path 1'],
+        value: 10),
+  );
+
+  testGolden(
+    'Star position',
+    ValueDelegate.position(['Shape Layer 1', 'Star', 'Polystar Path 1'],
+        relative: Offset(20, 20)),
+  );
+
+  testGolden(
+    'Star inner radius',
+    ValueDelegate.polystarInnerRadius(
+        ['Shape Layer 1', 'Star', 'Polystar Path 1'],
+        value: 10),
+  );
+
+  testGolden(
+    'Star inner roundedness',
+    ValueDelegate.polystarInnerRoundedness(
+        ['Shape Layer 1', 'Star', 'Polystar Path 1'],
+        value: 100),
+  );
+
+  testGolden(
+    'Star outer radius',
+    ValueDelegate.polystarOuterRadius(
+        ['Shape Layer 1', 'Star', 'Polystar Path 1'],
+        value: 60),
+  );
+
+  testGolden(
+    'Star outer roundedness',
+    ValueDelegate.polystarOuterRoundedness(
+        ['Shape Layer 1', 'Star', 'Polystar Path 1'],
+        value: 100),
+  );
+
+  testGolden(
+    'Polygon points',
+    ValueDelegate.polystarPoints(['Shape Layer 1', 'Star', 'Polystar Path 1'],
+        value: 8),
+  );
+
+  testGolden(
+    'Polygon rotation',
+    ValueDelegate.polystarRotation(['Shape Layer 1', 'Star', 'Polystar Path 1'],
+        value: 10),
+  );
+
+  testGolden(
+    'Polygon position',
+    ValueDelegate.position(['Shape Layer 1', 'Star', 'Polystar Path 1'],
+        relative: Offset(20, 20)),
+  );
+
+  testGolden(
+    'Polygon radius',
+    ValueDelegate.polystarOuterRadius(
+        ['Shape Layer 1', 'Star', 'Polystar Path 1'],
+        relative: 60),
+  );
+
+  testGolden(
+    'Polygon roundedness',
+    ValueDelegate.polystarOuterRoundedness(
+        ['Shape Layer 1', 'Star', 'Polystar Path 1'],
+        value: 100),
+  );
+
+  testGolden(
+    'Repeater transform position',
+    ValueDelegate.transformPosition(
+        ['Shape Layer 1', 'Repeater Shape', 'Repeater 1'],
+        relative: Offset(100, 100)),
+  );
+
+  testGolden(
+    'Repeater transform start opacity',
+    ValueDelegate.transformStartOpacity(
+        ['Shape Layer 1', 'Repeater Shape', 'Repeater 1'],
+        value: 25),
+  );
+
+  testGolden(
+    'Repeater transform end opacity',
+    ValueDelegate.transformEndOpacity(
+        ['Shape Layer 1', 'Repeater Shape', 'Repeater 1'],
+        value: 25),
+  );
+
+  testGolden(
+    'Repeater transform rotation',
+    ValueDelegate.transformRotation(
+        ['Shape Layer 1', 'Repeater Shape', 'Repeater 1'],
+        value: 45),
+  );
+
+  testGolden(
+    'Repeater transform scale',
+    ValueDelegate.transformScale(
+        ['Shape Layer 1', 'Repeater Shape', 'Repeater 1'],
+        value: Offset(2, 2)),
+  );
+
+  testGolden('Time remapping', ValueDelegate.timeRemap(['Circle 1'], value: 1),
+      progress: 0.1);
+
+  testGolden(
+    'Color Filter',
+    ValueDelegate.colorFilter(['**'],
+        value: ColorFilter.mode(Colors.green, BlendMode.srcATop)),
+  );
+
+  testGolden(
+    'Null Color Filter',
+    ValueDelegate.colorFilter(['**'], value: null),
+  );
+
+  for (var progress in [0.0, 0.5, 1.0]) {
+    testGolden(
+        'Opacity interpolation ($progress)',
+        ValueDelegate.transformOpacity(['Shape Layer 1', 'Rectangle'],
+            callback: (frameInfo) => lerpDouble(
+                    10, 100, Curves.linear.transform(frameInfo.overallProgress))
+                .round()),
+        progress: progress);
+  }
+}

example/test/dynamic_text_test.dart

@@ -0,0 +1,29 @@
+import 'dart:io';
+import 'dart:ui';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:lottie/lottie.dart';
+
+void main() {
+  testWidgets('Dynamic test', (tester) async {
+    var composition = await LottieComposition.fromBytes(
+        File('assets/Tests/DynamicText.json').readAsBytesSync());
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Lottie(
+          composition: composition,
+          animate: false,
+          delegates: LottieDelegates(
+              text: (input) => '🔥c️🔥👮🏿‍🔥',
+              textStyle: (font) => TextStyle(
+                  fontFamily: 'Roboto', fontFamilyFallback: ['Noto Emoji']),
+              values: []),
+        ),
+      ),
+    );
+
+    await expectLater(
+        find.byType(Lottie), matchesGoldenFile('goldens/dynamic_text.png'));
+  });
+}

example/test/flutter_test_config.dart

@@ -0,0 +1,7 @@
+import 'dart:async';
+import 'package:golden_toolkit/golden_toolkit.dart';
+
+Future<void> main(FutureOr<void> Function() testMain) async {
+  await loadAppFonts();
+  return testMain();
+}

example/test/widget_test.dart

@@ -1,12 +1,9 @@
-// This is a basic Flutter widget test.
-//
-// To perform an interaction with a widget in your test, use the WidgetTester
-// utility that Flutter provides. For example, you can send tap and scroll
-// gestures. You can also use WidgetTester to find child widgets in the widget
-// tree, read text, and verify that the values of widget properties are correct.
-
 import 'package:flutter_test/flutter_test.dart';
+import 'package:lottie_example/main.dart';
 
 void main() {
-  testWidgets('Counter increments smoke test', (WidgetTester tester) async {});
+  testWidgets('Main sample', (tester) async {
+    await tester.pumpWidget(App());
+    await tester.pump();
+  });
 }

lib/lottie.dart

@@ -1,6 +1,8 @@
 export 'src/composition.dart' show LottieComposition;
 export 'src/lottie.dart' show Lottie;
 export 'src/lottie_builder.dart' show LottieBuilder;
-export 'src/lottie_drawable.dart' show LottieDrawable;
+export 'src/lottie_delegates.dart' show LottieDelegates;
+export 'src/lottie_drawable.dart' show LottieDrawable, LottieFontStyle;
 export 'src/lottie_image_asset.dart' show LottieImageAsset;
 export 'src/raw_lottie.dart' show RawLottie;
+export 'src/value_delegate.dart' show ValueDelegate;

lib/src/animation/content/gradient_fill_content.dart

@@ -132,7 +132,7 @@ class GradientFillContent implements DrawingContent, KeyPathElementContent {
   }
 
   LinearGradient _getLinearGradient() {
-    var gradientHash = getGradientHash();
+    var gradientHash = _getGradientHash();
     var gradient = _linearGradientCache[gradientHash];
     if (gradient != null) {
       return gradient;
@@ -152,7 +152,7 @@ class GradientFillContent implements DrawingContent, KeyPathElementContent {
   }
 
   RadialGradient _getRadialGradient() {
-    var gradientHash = getGradientHash();
+    var gradientHash = _getGradientHash();
     var gradient = _radialGradientCache[gradientHash];
     if (gradient != null) {
       return gradient;
@@ -176,7 +176,7 @@ class GradientFillContent implements DrawingContent, KeyPathElementContent {
     return gradient;
   }
 
-  int getGradientHash() {
+  int _getGradientHash() {
     var startPointProgress =
         (_startPointAnimation.progress * _cacheSteps).round();
     var endPointProgress = (_endPointAnimation.progress * _cacheSteps).round();

lib/src/animation/keyframe/scale_keyframe_animation.dart

@@ -1,32 +0,0 @@
-import '../../value/keyframe.dart';
-import '../../value/scale_xy.dart';
-import 'keyframe_animation.dart';
-
-class ScaleKeyframeAnimation extends KeyframeAnimation<ScaleXY> {
-  ScaleKeyframeAnimation(List<Keyframe<ScaleXY>> keyframes) : super(keyframes);
-
-  @override
-  ScaleXY getValue(Keyframe<ScaleXY> keyframe, double keyframeProgress) {
-    if (keyframe.startValue == null || keyframe.endValue == null) {
-      throw StateError('Missing values for keyframe.');
-    }
-    var startTransform = keyframe.startValue;
-    var endTransform = keyframe.endValue;
-
-    if (valueCallback != null) {
-      var value = valueCallback.getValueInternal(
-          keyframe.startFrame,
-          keyframe.endFrame,
-          startTransform,
-          endTransform,
-          keyframeProgress,
-          getLinearCurrentKeyframeProgress(),
-          progress);
-      if (value != null) {
-        return value;
-      }
-    }
-
-    return ScaleXY.lerp(startTransform, endTransform, keyframeProgress);
-  }
-}

lib/src/animation/keyframe/transform_keyframe_animation.dart

@@ -7,7 +7,6 @@ import '../../model/layer/base_layer.dart';
 import '../../utils.dart';
 import '../../value/keyframe.dart';
 import '../../value/lottie_value_callback.dart';
-import '../../value/scale_xy.dart';
 import 'base_keyframe_animation.dart';
 import 'double_keyframe_animation.dart';
 import 'value_callback_keyframe_animation.dart';
@@ -37,7 +36,7 @@ class TransformKeyframeAnimation {
 
   BaseKeyframeAnimation<Offset, Offset> /*?*/ _anchorPoint;
   BaseKeyframeAnimation<dynamic, Offset> /*?*/ _position;
-  BaseKeyframeAnimation<ScaleXY, ScaleXY> /*?*/ _scale;
+  BaseKeyframeAnimation<Offset, Offset> /*?*/ _scale;
   BaseKeyframeAnimation<double, double> /*?*/ _rotation;
   DoubleKeyframeAnimation /*?*/ _skew;
   DoubleKeyframeAnimation /*?*/ _skewAngle;
@@ -141,8 +140,8 @@ class TransformKeyframeAnimation {
 
     if (_scale != null) {
       final scale = _scale.value;
-      if (scale.x != 1 || scale.y != 1) {
-        _matrix.scale(scale.x, scale.y);
+      if (scale.dx != 1 || scale.dy != 1) {
+        _matrix.scale(scale.dx, scale.dy);
       }
     }
 
@@ -169,7 +168,7 @@ class TransformKeyframeAnimation {
     }
 
     if (scale != null) {
-      _matrix.scale(scale.x, scale.y);
+      _matrix.scale(scale.dx, scale.dy);
     }
 
     if (rotation != null) {
@@ -200,9 +199,9 @@ class TransformKeyframeAnimation {
     } else if (property == LottieProperty.transformScale) {
       if (_scale == null) {
         _scale = ValueCallbackKeyframeAnimation(
-            callback as LottieValueCallback<ScaleXY>, ScaleXY.one());
+            callback as LottieValueCallback<Offset>, Offset(1, 1));
       } else {
-        _scale.setValueCallback(callback as LottieValueCallback<ScaleXY>);
+        _scale.setValueCallback(callback as LottieValueCallback<Offset>);
       }
     } else if (property == LottieProperty.transformRotation) {
       if (_rotation == null) {

lib/src/animation/keyframe/value_callback_keyframe_animation.dart

@@ -34,7 +34,8 @@ class ValueCallbackKeyframeAnimation<K, A> extends BaseKeyframeAnimation<K, A> {
   @override
   A get value {
     return valueCallback.getValueInternal(0.0, 0.0, valueCallbackValue,
-        valueCallbackValue, progress, progress, progress);
+            valueCallbackValue, progress, progress, progress) ??
+        valueCallbackValue;
   }
 
   @override

lib/src/lottie.dart

@@ -23,16 +23,19 @@ class Lottie extends StatefulWidget {
     bool animate,
     bool repeat,
     bool reverse,
+    this.delegates,
   })  : animate = animate ?? true,
         reverse = reverse ?? false,
         repeat = repeat ?? true,
         super(key: key);
 
+  /// Creates a widget that displays an [LottieComposition] obtained from an [AssetBundle].
   static LottieBuilder asset(String name,
           {Animation<double> controller,
           bool animate,
           bool repeat,
           bool reverse,
+          LottieDelegates delegates,
           void Function(LottieComposition) onLoaded,
           LottieImageProviderFactory imageProviderFactory,
           Key key,
@@ -49,6 +52,7 @@ class Lottie extends StatefulWidget {
         animate: animate,
         repeat: repeat,
         reverse: reverse,
+        delegates: delegates,
         imageProviderFactory: imageProviderFactory,
         onLoaded: onLoaded,
         key: key,
@@ -61,12 +65,14 @@ class Lottie extends StatefulWidget {
         package: package,
       );
 
+  /// Creates a widget that displays an [LottieComposition] obtained from a [File].
   static LottieBuilder file(
     File file, {
     Animation<double> controller,
     bool animate,
     bool repeat,
     bool reverse,
+    LottieDelegates delegates,
     LottieImageProviderFactory imageProviderFactory,
     void Function(LottieComposition) onLoaded,
     Key key,
@@ -82,6 +88,7 @@ class Lottie extends StatefulWidget {
         animate: animate,
         repeat: repeat,
         reverse: reverse,
+        delegates: delegates,
         imageProviderFactory: imageProviderFactory,
         onLoaded: onLoaded,
         key: key,
@@ -92,12 +99,14 @@ class Lottie extends StatefulWidget {
         alignment: alignment,
       );
 
+  /// Creates a widget that displays an [LottieComposition] obtained from a [Uint8List].
   static LottieBuilder memory(
     Uint8List bytes, {
     Animation<double> controller,
     bool animate,
     bool repeat,
     bool reverse,
+    LottieDelegates delegates,
     LottieImageProviderFactory imageProviderFactory,
     void Function(LottieComposition) onLoaded,
     Key key,
@@ -113,6 +122,7 @@ class Lottie extends StatefulWidget {
         animate: animate,
         repeat: repeat,
         reverse: reverse,
+        delegates: delegates,
         imageProviderFactory: imageProviderFactory,
         onLoaded: onLoaded,
         key: key,
@@ -123,12 +133,14 @@ class Lottie extends StatefulWidget {
         alignment: alignment,
       );
 
+  /// Creates a widget that displays an [LottieComposition] obtained from the network.
   static LottieBuilder network(
     String url, {
     Animation<double> controller,
     bool animate,
     bool repeat,
     bool reverse,
+    LottieDelegates delegates,
     LottieImageProviderFactory imageProviderFactory,
     void Function(LottieComposition) onLoaded,
     Key key,
@@ -144,6 +156,7 @@ class Lottie extends StatefulWidget {
         animate: animate,
         repeat: repeat,
         reverse: reverse,
+        delegates: delegates,
         imageProviderFactory: imageProviderFactory,
         onLoaded: onLoaded,
         key: key,
@@ -180,13 +193,13 @@ class Lottie extends StatefulWidget {
   /// The property has no effect if [animate] is false, [repeat] is false or [controller] is not null.
   final bool reverse;
 
-  /// If non-null, require the Lottie composition to have this width.
+  /// If non-null, requires the composition to have this width.
   ///
   /// If null, the composition will pick a size that best preserves its intrinsic
   /// aspect ratio.
   final double width;
 
-  /// If non-null, require the Lottie composition to have this height.
+  /// If non-null, require the composition to have this height.
   ///
   /// If null, the composition will pick a size that best preserves its intrinsic
   /// aspect ratio.
@@ -215,6 +228,13 @@ class Lottie extends StatefulWidget {
   ///    relative to text direction.
   final AlignmentGeometry alignment;
 
+  /// A group of options to further customize the lottie animation.
+  /// - A [text] delegate to dynamically change some text displayed in the animation
+  /// - A value callback to change the properties of the animation at runtime.
+  /// - A text style factory to map between a font family specified in the animation
+  ///   and the font family in your assets.
+  final LottieDelegates delegates;
+
   @override
   _LottieState createState() => _LottieState();
 }
@@ -268,6 +288,7 @@ class _LottieState extends State<Lottie> with TickerProviderStateMixin {
       animation: _progressAnimation,
       builder: (context, _) => RawLottie(
         composition: widget.composition,
+        delegates: widget.delegates,
         progress: _progressAnimation.value,
         width: widget.width,
         height: widget.height,

lib/src/lottie_builder.dart

@@ -6,7 +6,6 @@ import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
 import '../lottie.dart';
 import 'lottie.dart';
-import 'lottie_drawable.dart';
 import 'providers/asset_provider.dart';
 import 'providers/file_provider.dart';
 import 'providers/load_image.dart';
@@ -40,6 +39,7 @@ class LottieBuilder extends StatefulWidget {
     this.animate,
     this.reverse,
     this.repeat,
+    this.delegates,
     this.onLoaded,
     this.frameBuilder,
     this.width,
@@ -49,7 +49,7 @@ class LottieBuilder extends StatefulWidget {
   })  : assert(lottie != null),
         super(key: key);
 
-  /// Creates a widget that displays an [LottieStream] obtained from the network.
+  /// Creates a widget that displays an [LottieComposition] obtained from the network.
   LottieBuilder.network(
     String src, {
     Map<String, String> headers,
@@ -57,6 +57,7 @@ class LottieBuilder extends StatefulWidget {
     this.animate,
     this.reverse,
     this.repeat,
+    this.delegates,
     LottieImageProviderFactory imageProviderFactory,
     this.onLoaded,
     Key key,
@@ -69,13 +70,11 @@ class LottieBuilder extends StatefulWidget {
             headers: headers, imageProviderFactory: imageProviderFactory),
         super(key: key);
 
-  /// Creates a widget that displays an [ImageStream] obtained from a [File].
-  ///
-  /// The [file], [scale], and [repeat] arguments must not be null.
+  /// Creates a widget that displays an [LottieComposition] obtained from a [File].
   ///
   /// Either the [width] and [height] arguments should be specified, or the
   /// widget should be placed in a context that sets tight layout constraints.
-  /// Otherwise, the image dimensions will change as the image is loaded, which
+  /// Otherwise, the image dimensions will change as the animation is loaded, which
   /// will result in ugly layout changes.
   ///
   /// On Android, this may require the
@@ -87,6 +86,7 @@ class LottieBuilder extends StatefulWidget {
     this.animate,
     this.reverse,
     this.repeat,
+    this.delegates,
     LottieImageProviderFactory imageProviderFactory,
     this.onLoaded,
     Key key,
@@ -98,12 +98,14 @@ class LottieBuilder extends StatefulWidget {
   })  : lottie = FileLottie(file, imageProviderFactory: imageProviderFactory),
         super(key: key);
 
+  /// Creates a widget that displays an [LottieComposition] obtained from an [AssetBundle].
   LottieBuilder.asset(
     String name, {
     this.controller,
     this.animate,
     this.reverse,
     this.repeat,
+    this.delegates,
     LottieImageProviderFactory imageProviderFactory,
     this.onLoaded,
     Key key,
@@ -120,13 +122,14 @@ class LottieBuilder extends StatefulWidget {
             imageProviderFactory: imageProviderFactory),
         super(key: key);
 
-  /// Creates a widget that displays an [LottieDrawable] obtained from a [Uint8List].
+  /// Creates a widget that displays an [LottieComposition] obtained from a [Uint8List].
   LottieBuilder.memory(
     Uint8List bytes, {
     this.controller,
     this.animate,
     this.reverse,
     this.repeat,
+    this.delegates,
     LottieImageProviderFactory imageProviderFactory,
     this.onLoaded,
     Key key,
@@ -139,7 +142,7 @@ class LottieBuilder extends StatefulWidget {
             MemoryLottie(bytes, imageProviderFactory: imageProviderFactory),
         super(key: key);
 
-  /// The lottie animation to display.
+  /// The lottie animation to load.
   /// Example of providers: [AssetLottie], [NetworkLottie], [FileLottie], [MemoryLottie]
   final LottieProvider lottie;
 
@@ -170,6 +173,13 @@ class LottieBuilder extends StatefulWidget {
   /// The property has no effect if [animate] is false, [repeat] is false or [controller] is not null.
   final bool reverse;
 
+  /// A group of options to further customize the lottie animation.
+  /// - A [text] delegate to dynamically change some text displayed in the animation
+  /// - A value callback to change the properties of the animation at runtime.
+  /// - A text style factory to map between a font family specified in the animation
+  ///   and the font family in your assets.
+  final LottieDelegates delegates;
+
   /// A builder function responsible for creating the widget that represents
   /// this lottie animation.
   ///
@@ -368,6 +378,7 @@ class _LottieBuilderState extends State<LottieBuilder> {
           animate: widget.animate,
           reverse: widget.reverse,
           repeat: widget.repeat,
+          delegates: widget.delegates,
           width: widget.width,
           height: widget.height,
           fit: widget.fit,

lib/src/lottie_delegates.dart

@@ -0,0 +1,64 @@
+import 'package:flutter/widgets.dart';
+import 'lottie_drawable.dart';
+import 'value_delegate.dart';
+
+// TODO(xha): recognize style Bold, Medium, Regular, SemiBold, etc...
+TextStyle _defaultTextStyleDelegate(LottieFontStyle font) =>
+    TextStyle(fontFamily: font.fontFamily);
+
+@immutable
+class LottieDelegates {
+  /// Specify a callback to dynamically changes the text displayed in the lottie
+  /// animation.
+  /// For instance, this is useful when you want to translate the text in the animation.
+  final String Function(String) /*?*/ text;
+
+  /// A callback to map between a font family specified in the json animation
+  /// with the font family in your assets.
+  /// This is useful either if:
+  ///  - the name of the font in your asset doesn't match the one in the json file.
+  ///  - you want to use an other font than the one declared in the json
+  ///
+  /// If the callback is null, the font family from the json is used as it.
+  ///
+  /// Given an object containing the font family and style specified in the json
+  /// return a configured `TextStyle` that will be used as the base style when
+  /// painting the text.
+  final TextStyle Function(LottieFontStyle) textStyle;
+
+  /// A list of value delegates to dynamically modify the animation
+  /// properties at runtime.
+  ///
+  /// Example:
+  /// ```dart
+  /// Lottie.asset(
+  ///   'lottiefile.json',
+  ///   delegates: LottieDelegates(
+  ///     value: [
+  ///       ValueDelegate.color(['lake', 'fill'], value: Colors.blue),
+  ///       ValueDelegate.opacity(['**', 'fill'], callback: (frameInfo) => 0.5 * frameInfo.overallProgress),
+  ///     ],
+  ///   ),
+  /// );
+  /// ```
+  final List<ValueDelegate> values;
+
+  //TODO(xha): imageDelegate to change the image to display?
+
+  LottieDelegates({
+    this.text,
+    TextStyle Function(LottieFontStyle) textStyle,
+    this.values,
+  }) : textStyle = textStyle ?? _defaultTextStyleDelegate;
+
+  @override
+  bool operator ==(Object other) =>
+      identical(this, other) ||
+      other is LottieDelegates &&
+          text == other.text &&
+          textStyle == other.textStyle &&
+          values == other.values;
+
+  @override
+  int get hashCode => hashValues(text, textStyle, values);
+}

lib/src/lottie_drawable.dart

@@ -1,42 +1,65 @@
 import 'dart:ui' as ui;
 import 'package:flutter/rendering.dart';
-import 'package:meta/meta.dart';
 import 'package:vector_math/vector_math_64.dart';
 import 'composition.dart';
+import 'lottie_delegates.dart';
+import 'model/key_path.dart';
 import 'model/layer/composition_layer.dart';
 import 'parser/layer_parser.dart';
-import 'text_delegate.dart';
+import 'value_delegate.dart';
 
 class LottieDrawable {
   final LottieComposition composition;
   final _matrix = Matrix4.identity();
   CompositionLayer _compositionLayer;
   final Size size;
-  TextDelegate /*?*/ textDelegate;
+  LottieDelegates _delegates;
+  bool _isDirty = true;
 
-  LottieDrawable(this.composition, {this.textDelegate})
+  LottieDrawable(this.composition, {LottieDelegates delegates})
       : size = Size(composition.bounds.width.toDouble(),
             composition.bounds.height.toDouble()) {
+    this.delegates = delegates;
     _compositionLayer = CompositionLayer(
         this, LayerParser.parse(composition), composition.layers, composition);
   }
 
-  CompositionLayer get compositionLayer => _compositionLayer;
-
   /// Sets whether to apply opacity to the each layer instead of shape.
   ///
-  /// Opacity is normally applied directly to a shape. In cases where translucent shapes overlap, applying opacity to a layer will be more accurate
-  /// at the expense of performance.
+  /// Opacity is normally applied directly to a shape. In cases where translucent
+  /// shapes overlap, applying opacity to a layer will be more accurate at the
+  /// expense of performance.
   ///
   /// The default value is false.
   ///
-  /// Note: This process is very expensive. The performance impact will be reduced when hardware acceleration is enabled.
+  /// Note: This process is very expensive. The performance impact will be reduced
+  /// when hardware acceleration is enabled.
   bool isApplyingOpacityToLayersEnabled = false;
 
-  void invalidateSelf() {}
+  void invalidateSelf() {
+    _isDirty = true;
+  }
+
+  double get progress => _progress;
+  double _progress = 0.0;
+  bool setProgress(double value) {
+    _isDirty = false;
+    _progress = value;
+    _compositionLayer.setProgress(value);
+    return _isDirty;
+  }
+
+  LottieDelegates get delegates => _delegates;
+  set delegates(LottieDelegates delegates) {
+    delegates ??= LottieDelegates();
+    if (_delegates != delegates) {
+      _delegates = delegates;
+      _updateValueDelegates(delegates.values);
+    }
+  }
 
   bool get useTextGlyphs {
-    return textDelegate == null && composition.characters.isNotEmpty;
+    return delegates.text == null && composition.characters.isNotEmpty;
   }
 
   ui.Image getImageAsset(String ref) {
@@ -49,13 +72,54 @@ class LottieDrawable {
   }
 
   TextStyle getTextStyle(String font, String style) {
-    //TODO(xha): allow the user to map Font in the animation with FontFamily loaded for flutter
-    // Support to inherit TextStyle from DefaultTextStyle applied for the Lottie wiget
-    return TextStyle(fontFamily: font);
+    return _delegates
+        .textStyle(LottieFontStyle(fontFamily: font, style: style));
   }
 
-  void draw(ui.Canvas canvas, ui.Rect rect,
-      {@required double progress, BoxFit fit, Alignment alignment}) {
+  List<ValueDelegate> _valueDelegates = <ValueDelegate>[];
+  void _updateValueDelegates(List<ValueDelegate> newDelegates) {
+    if (identical(_valueDelegates, newDelegates)) return;
+
+    newDelegates ??= const [];
+
+    var delegates = <ValueDelegate>[];
+
+    for (var newDelegate in newDelegates) {
+      var existingDelegate = _valueDelegates
+          .firstWhere((f) => f.isSameProperty(newDelegate), orElse: () => null);
+      if (existingDelegate != null) {
+        var resolved = internalResolved(existingDelegate);
+        resolved.updateDelegate(newDelegate);
+        delegates.add(existingDelegate);
+      } else {
+        var keyPaths = _resolveKeyPath(KeyPath(newDelegate.keyPath));
+        var resolvedValueDelegate = internalResolve(newDelegate, keyPaths);
+        resolvedValueDelegate.addValueCallback(this);
+        delegates.add(newDelegate);
+      }
+    }
+    for (var oldDelegate in _valueDelegates) {
+      if (delegates.every((c) => !c.isSameProperty(oldDelegate))) {
+        var resolved = internalResolved(oldDelegate);
+        resolved.clear();
+      }
+    }
+    _valueDelegates = delegates;
+  }
+
+  /// Takes a {@link KeyPath}, potentially with wildcards or globstars and resolve it to a list of
+  /// zero or more actual {@link KeyPath Keypaths} that exist in the current animation.
+  /// <p>
+  /// If you want to set value callbacks for any of these values, it is recommend to use the
+  /// returned {@link KeyPath} objects because they will be internally resolved to their content
+  /// and won't trigger a tree walk of the animation contents when applied.
+  List<KeyPath> _resolveKeyPath(KeyPath keyPath) {
+    var keyPaths = <KeyPath>[];
+    _compositionLayer.resolveKeyPath(keyPath, 0, keyPaths, KeyPath([]));
+    return keyPaths;
+  }
+
+  void draw(ui.Canvas canvas, ui.Rect rect, {BoxFit fit, Alignment alignment}) {
     if (rect.isEmpty) {
       return;
     }
@@ -79,9 +143,12 @@ class LottieDrawable {
     _matrix.translate(destinationRect.left, destinationRect.top);
     _matrix.scale(destinationRect.size.width / sourceRect.width,
         destinationRect.size.height / sourceRect.height);
-    progress ??= 0;
-    _compositionLayer
-      ..setProgress(progress)
-      ..draw(canvas, rect.size, _matrix, parentAlpha: 255);
+    _compositionLayer.draw(canvas, rect.size, _matrix, parentAlpha: 255);
   }
 }
+
+class LottieFontStyle {
+  final String fontFamily, style;
+
+  LottieFontStyle({this.fontFamily, this.style});
+}

lib/src/lottie_property.dart

@@ -1,5 +1,4 @@
 import 'dart:ui';
-import 'value/scale_xy.dart';
 
 /// Property values are the same type as the generic type of their corresponding
 /// {@link LottieValueCallback}. With this, we can use generics to maintain type safety
@@ -62,69 +61,69 @@ abstract class LottieProperty {
   static final int opacity = 4;
 
   /// In Px */
-  static final Offset transformAnchorPoint = Offset.zero;
+  static final Offset transformAnchorPoint = Offset(5, 5);
 
   /// In Px */
-  static final Offset transformPosition = Offset.zero;
+  static final Offset transformPosition = Offset(6, 6);
 
   /// In Px */
-  static final Offset ellipseSize = Offset.zero;
+  static final Offset ellipseSize = Offset(7, 7);
 
   /// In Px */
-  static final Offset rectangleSize = Offset.zero;
+  static final Offset rectangleSize = Offset(8, 8);
 
   /// In degrees */
-  static final double cornerRadius = 0.0;
+  static final double cornerRadius = 9.0;
 
   /// In Px */
-  static final Offset position = Offset.zero;
-  static final ScaleXY transformScale = ScaleXY.one();
+  static final Offset position = Offset(10, 10);
+  static final Offset transformScale = Offset(11, 11);
 
   /// In degrees */
-  static final double transformRotation = 1.0;
+  static final double transformRotation = 12.0;
 
   /// 0-85 */
-  static final double transformSkew = 0.0;
+  static final double transformSkew = 13.0;
 
   /// In degrees */
-  static final double transformSkewAngle = 0.0;
+  static final double transformSkewAngle = 14.0;
 
   /// In Px */
-  static final double strokeWidth = 2.0;
-  static final double textTracking = 3.0;
-  static final double repeaterCopies = 4.0;
-  static final double repeaterOffset = 5.0;
-  static final double polystarPoints = 6.0;
+  static final double strokeWidth = 15.0;
+  static final double textTracking = 16.0;
+  static final double repeaterCopies = 17.0;
+  static final double repeaterOffset = 18.0;
+  static final double polystarPoints = 19.0;
 
   /// In degrees */
-  static final double polystarRotation = 7.0;
+  static final double polystarRotation = 20.0;
 
   /// In Px */
-  static final double polystarInnerRadius = 8.0;
+  static final double polystarInnerRadius = 21.0;
 
   /// In Px */
-  static final double polystarOuterRadius = 9.0;
+  static final double polystarOuterRadius = 22.0;
 
   /// [0,100] */
-  static final double polystarInnerRoundedness = 10.0;
+  static final double polystarInnerRoundedness = 23.0;
 
   /// [0,100] */
-  static final double polystarOuterRoundedness = 11.0;
+  static final double polystarOuterRoundedness = 24.0;
 
   /// [0,100] */
-  static final double transformStartOpacity = 12.0;
+  static final double transformStartOpacity = 25.0;
 
   /// [0,100] */
-  static final double transformEndOpacity = 12.1;
+  static final double transformEndOpacity = 26.0;
 
   /// The time value in seconds */
-  static final double timeRemap = 13.0;
+  static final double timeRemap = 27.0;
 
-  /// In Dp */
-  static final double textSize = 14.0;
+  /// In Dp
+  static final double textSize = 28.0;
 
   static final ColorFilter colorFilter =
       ColorFilter.mode(Color(0xFF000000), BlendMode.dst);
 
-  static final List<Color> gradientColor = const [];
+  static final List<Color> gradientColor = [];
 }

lib/src/model/animatable/animatable_scale_value.dart

@@ -1,19 +1,19 @@
+import 'dart:ui';
 import '../../animation/keyframe/base_keyframe_animation.dart';
-import '../../animation/keyframe/scale_keyframe_animation.dart';
+import '../../animation/keyframe/point_keyframe_animation.dart';
 import '../../value/keyframe.dart';
-import '../../value/scale_xy.dart';
 import 'base_animatable_value.dart';
 
-class AnimatableScaleValue extends BaseAnimatableValue<ScaleXY, ScaleXY> {
-  AnimatableScaleValue.one() : this(ScaleXY.one());
+class AnimatableScaleValue extends BaseAnimatableValue<Offset, Offset> {
+  AnimatableScaleValue.one() : this(Offset(1, 1));
 
-  AnimatableScaleValue(ScaleXY value) : super.fromValue(value);
+  AnimatableScaleValue(Offset value) : super.fromValue(value);
 
-  AnimatableScaleValue.fromKeyframes(List<Keyframe<ScaleXY>> keyframes)
+  AnimatableScaleValue.fromKeyframes(List<Keyframe<Offset>> keyframes)
       : super.fromKeyframes(keyframes);
 
   @override
-  BaseKeyframeAnimation<ScaleXY, ScaleXY> createAnimation() {
-    return ScaleKeyframeAnimation(keyframes);
+  BaseKeyframeAnimation<Offset, Offset> createAnimation() {
+    return PointKeyframeAnimation(keyframes);
   }
 }

lib/src/model/layer/text_layer.dart

@@ -1,4 +1,5 @@
 import 'dart:ui';
+import 'package:characters/characters.dart';
 import 'package:flutter/widgets.dart';
 import 'package:vector_math/vector_math_64.dart';
 import '../../animation/content/content_group.dart';
@@ -22,7 +23,6 @@ class TextLayer extends BaseLayer {
   final _matrix = Matrix4.identity();
   final _fillPaint = Paint()..style = PaintingStyle.fill;
   final _strokePaint = Paint()..style = PaintingStyle.stroke;
-  TextStyle _textStyle;
   final _contentsForCharacter = <FontCharacter, List<ContentGroup>>{};
   final TextKeyframeAnimation _textAnimation;
   final LottieComposition _composition;
@@ -227,14 +227,14 @@ class TextLayer extends BaseLayer {
   void _drawTextWithFont(DocumentData documentData, Font font,
       Matrix4 parentMatrix, Canvas canvas) {
     var parentScale = parentMatrix.getScale();
-    _textStyle = lottieDrawable.getTextStyle(font.family, font.style);
-    if (_textStyle == null) {
+    var textStyle = lottieDrawable.getTextStyle(font.family, font.style);
+    if (textStyle == null) {
       return;
     }
     var text = documentData.text;
-    var textDelegate = lottieDrawable.textDelegate;
+    var textDelegate = lottieDrawable.delegates.text;
     if (textDelegate != null) {
-      text = textDelegate.getTextInternal(text);
+      text = textDelegate(text);
     }
     double textSize;
     if (_textSizeCallbackAnimation != null) {
@@ -244,8 +244,8 @@ class TextLayer extends BaseLayer {
     } else {
       textSize = documentData.size;
     }
-    _textStyle =
-        _textStyle.copyWith(fontSize: textSize * window.devicePixelRatio);
+    textStyle =
+        textStyle.copyWith(fontSize: textSize * window.devicePixelRatio);
 
     // Line height
     var lineHeight = documentData.lineHeight * window.devicePixelRatio;
@@ -256,7 +256,7 @@ class TextLayer extends BaseLayer {
     for (var l = 0; l < textLineCount; l++) {
       var textLine = textLines[l];
       var textPainter = TextPainter(
-          text: TextSpan(text: textLine, style: _textStyle),
+          text: TextSpan(text: textLine, style: textStyle),
           textDirection: _textDirection);
       textPainter.layout();
       var textLineWidth = textPainter.width;
@@ -270,7 +270,7 @@ class TextLayer extends BaseLayer {
       canvas.translate(0, translateY);
 
       // Draw each line
-      _drawFontTextLine(textLine, documentData, canvas, parentScale);
+      _drawFontTextLine(textLine, textStyle, documentData, canvas, parentScale);
 
       // Reset canvas
       canvas.transform(parentMatrix.storage);
@@ -284,14 +284,13 @@ class TextLayer extends BaseLayer {
     return textLinesArray;
   }
 
-  void _drawFontTextLine(String text, DocumentData documentData, Canvas canvas,
-      double parentScale) {
-    for (var i = 0; i < text.length;) {
-      var charString = _codePointToString(text, i);
-      i += charString.length;
-      _drawCharacterFromFont(charString, documentData, canvas);
+  void _drawFontTextLine(String text, TextStyle textStyle,
+      DocumentData documentData, Canvas canvas, double parentScale) {
+    for (var char in text.characters) {
+      var charString = char;
+      _drawCharacterFromFont(charString, textStyle, documentData, canvas);
       var textPainter = TextPainter(
-          text: TextSpan(text: charString, style: _textStyle),
+          text: TextSpan(text: charString, style: textStyle),
           textDirection: _textDirection);
       textPainter.layout();
       var charWidth = textPainter.width;
@@ -369,18 +368,19 @@ class TextLayer extends BaseLayer {
     canvas.drawPath(path, paint);
   }
 
-  void _drawCharacterFromFont(
-      String character, DocumentData documentData, Canvas canvas) {
+  void _drawCharacterFromFont(String character, TextStyle textStyle,
+      DocumentData documentData, Canvas canvas) {
     if (documentData.strokeOverFill) {
-      _drawCharacter(character, _fillPaint, canvas);
-      _drawCharacter(character, _strokePaint, canvas);
+      _drawCharacter(character, textStyle, _fillPaint, canvas);
+      _drawCharacter(character, textStyle, _strokePaint, canvas);
     } else {
-      _drawCharacter(character, _strokePaint, canvas);
-      _drawCharacter(character, _fillPaint, canvas);
+      _drawCharacter(character, textStyle, _strokePaint, canvas);
+      _drawCharacter(character, textStyle, _fillPaint, canvas);
     }
   }
 
-  void _drawCharacter(String character, Paint paint, Canvas canvas) {
+  void _drawCharacter(
+      String character, TextStyle textStyle, Paint paint, Canvas canvas) {
     if (paint.color.alpha == 0) {
       return;
     }
@@ -388,18 +388,17 @@ class TextLayer extends BaseLayer {
       return;
     }
 
-    TextStyle textStyle;
     if (paint.style == PaintingStyle.fill) {
-      textStyle = _textStyle.copyWith(foreground: paint);
+      textStyle = textStyle.copyWith(foreground: paint);
     } else if (paint.style == PaintingStyle.stroke) {
-      textStyle = _textStyle.copyWith(background: paint);
+      textStyle = textStyle.copyWith(background: paint);
     }
     var painter = TextPainter(
       text: TextSpan(text: character, style: textStyle),
       textDirection: _textDirection,
     );
     painter.layout();
-    painter.paint(canvas, Offset(0, -_textStyle.fontSize));
+    painter.paint(canvas, Offset(0, -textStyle.fontSize));
   }
 
   List<ContentGroup> _getContentsForCharacter(FontCharacter character) {
@@ -417,11 +416,6 @@ class TextLayer extends BaseLayer {
     return contents;
   }
 
-  //TODO(xha): use package:character to correctly iterate over visual glyphs
-  String _codePointToString(String text, int startIndex) {
-    return text[startIndex];
-  }
-
   @override
   void addValueCallback<T>(T property, LottieValueCallback<T> /*?*/ callback) {
     super.addValueCallback(property, callback);

lib/src/parser/animatable_transform_parser.dart

@@ -170,7 +170,8 @@ class AnimatableTransformParser {
 
   static bool isScaleIdentity(AnimatableScaleValue scale) {
     return scale == null ||
-        (scale.isStatic && scale.keyframes.first.startValue.equals(1.0, 1.0));
+        (scale.isStatic &&
+            scale.keyframes.first.startValue == Offset(1.0, 1.0));
   }
 
   static bool isSkewIdentity(AnimatableDoubleValue skew) {

lib/src/parser/color_parser.dart

@@ -14,7 +14,7 @@ Color colorParser(JsonReader reader, {double scale}) {
     reader.endArray();
   }
 
-  if (r <= 1 && g <= 1 && b <= 11) {
+  if (r <= 1 && g <= 1 && b <= 1) {
     r *= 255;
     g *= 255;
     b *= 255;

lib/src/parser/scale_xy_parser.dart

@@ -1,7 +1,7 @@
-import '../value/scale_xy.dart';
+import 'dart:ui';
 import 'moshi/json_reader.dart';
 
-ScaleXY scaleXYParser(JsonReader reader, {double scale}) {
+Offset scaleXYParser(JsonReader reader, {double scale}) {
   var isArray = reader.peek() == Token.beginArray;
   if (isArray) {
     reader.beginArray();
@@ -14,5 +14,5 @@ ScaleXY scaleXYParser(JsonReader reader, {double scale}) {
   if (isArray) {
     reader.endArray();
   }
-  return ScaleXY(sx / 100.0 * scale, sy / 100.0 * scale);
+  return Offset(sx / 100.0 * scale, sy / 100.0 * scale);
 }

lib/src/raw_lottie.dart

@@ -12,6 +12,7 @@ class RawLottie extends LeafRenderObjectWidget {
   const RawLottie({
     Key key,
     this.composition,
+    this.delegates,
     double progress,
     this.width,
     this.height,
@@ -24,6 +25,9 @@ class RawLottie extends LeafRenderObjectWidget {
   /// The Lottie composition to display.
   final LottieComposition composition;
 
+  /// Allows to modify the Lottie animation at runtime
+  final LottieDelegates delegates;
+
   /// The progress of the Lottie animation (between 0.0 and 1.0).
   final double progress;
 
@@ -66,6 +70,7 @@ class RawLottie extends LeafRenderObjectWidget {
   RenderLottie createRenderObject(BuildContext context) {
     return RenderLottie(
       composition: composition,
+      delegates: delegates,
       progress: progress,
       width: width,
       height: height,
@@ -77,8 +82,7 @@ class RawLottie extends LeafRenderObjectWidget {
   @override
   void updateRenderObject(BuildContext context, RenderLottie renderObject) {
     renderObject
-      ..composition = composition
-      ..progress = progress
+      ..setComposition(composition, progress: progress, delegates: delegates)
       ..width = width
       ..height = height
       ..alignment = alignment

lib/src/render_lottie.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/rendering.dart';
+import 'package:meta/meta.dart';
 import '../lottie.dart';
 import 'lottie_drawable.dart';
 
@@ -9,6 +10,7 @@ import 'lottie_drawable.dart';
 class RenderLottie extends RenderBox {
   RenderLottie({
     LottieComposition composition,
+    LottieDelegates delegates,
     double progress = 0.0,
     double width,
     double height,
@@ -16,37 +18,49 @@ class RenderLottie extends RenderBox {
     AlignmentGeometry alignment = Alignment.center,
   })  : assert(alignment != null),
         assert(progress != null && progress >= 0.0 && progress <= 1.0),
-        _composition = composition,
-        _progress = progress,
+        _drawable = composition != null
+            ? (LottieDrawable(composition)
+              ..setProgress(progress)
+              ..delegates = delegates)
+            : null,
         _width = width,
         _height = height,
         _fit = fit,
         _alignment = alignment;
 
   /// The lottie composition to display.
-  LottieComposition get composition => _composition;
-  LottieComposition _composition;
-  set composition(LottieComposition value) {
-    if (value == _composition) {
-      return;
-    }
-    _composition = value;
+  LottieComposition get composition => _drawable?.composition;
+  LottieDrawable _drawable;
+  void setComposition(LottieComposition composition,
+      {@required double progress, @required LottieDelegates delegates}) {
+    var needsLayout = false;
+    var needsPaint = false;
+    if (composition == null) {
       _drawable = null;
-    markNeedsPaint();
-    if (_width == null || _height == null) {
-      markNeedsLayout();
+      needsPaint = true;
+      needsLayout = true;
+    } else {
+      if (_drawable?.composition != composition) {
+        _drawable = LottieDrawable(composition);
+        needsLayout = true;
+        needsPaint = true;
+      }
+
+      needsPaint |= _drawable.setProgress(progress);
+
+      if (_drawable.delegates != delegates) {
+        _drawable.delegates = delegates;
+        needsPaint = true;
       }
     }
 
-  double get progress => _progress;
-  double _progress;
-  set progress(double value) {
-    if (value == _progress) {
-      return;
+    if (needsPaint) {
+      markNeedsPaint();
     }
-    _progress = value;
+    if (needsLayout && (_width == null || _height == null)) {
       markNeedsLayout();
     }
+  }
 
   /// If non-null, requires the composition to have this width.
   ///
@@ -116,14 +130,12 @@ class RenderLottie extends RenderBox {
       height: _height,
     ).enforce(constraints);
 
-    if (_composition == null) {
+    if (_drawable == null) {
       return constraints.smallest;
     }
 
-    return constraints.constrainSizeAndAttemptToPreserveAspectRatio(Size(
-      _composition.bounds.width.toDouble(),
-      _composition.bounds.height.toDouble(),
-    ));
+    return constraints
+        .constrainSizeAndAttemptToPreserveAspectRatio(_drawable.size);
   }
 
   @override
@@ -168,17 +180,12 @@ class RenderLottie extends RenderBox {
     size = _sizeForConstraints(constraints);
   }
 
-  LottieDrawable _drawable;
   @override
   void paint(PaintingContext context, Offset offset) {
-    if (_composition == null) return;
-
-    _drawable ??= LottieDrawable(_composition);
+    if (_drawable == null) return;
 
     _drawable.draw(context.canvas, offset & size,
-        progress: _progress,
-        fit: _fit,
-        alignment: _alignment.resolve(TextDirection.ltr));
+        fit: _fit, alignment: _alignment.resolve(TextDirection.ltr));
   }
 
   @override

lib/src/text_delegate.dart

@@ -1,60 +0,0 @@
-import 'lottie_drawable.dart';
-
-/// Extend this class to replace animation text with custom text. This can be useful to handle
-/// translations.
-///
-/// The only method you should have to override is {@link #getText(String)}.
-class TextDelegate {
-  final _stringMap = <String, String>{};
-  final LottieDrawable /*?*/ drawable;
-  bool _cacheText = true;
-
-  TextDelegate(this.drawable);
-
-  /// Override this to replace the animation text with something dynamic. This can be used for
-  /// translations or custom data.
-  String getText(String input) {
-    return input;
-  }
-
-  /// Update the text that will be rendered for the given input text.
-  void setText(String input, String output) {
-    _stringMap[input] = output;
-    _invalidate();
-  }
-
-  /// Sets whether or not {@link TextDelegate} will cache (memoize) the results of getText.
-  /// If this isn't necessary then set it to false.
-  void setCacheText(bool cacheText) {
-    _cacheText = cacheText;
-  }
-
-  /// Invalidates a cached string with the given input.
-  void invalidateText(String input) {
-    _stringMap.remove(input);
-    _invalidate();
-  }
-
-  /// Invalidates all cached strings
-  void invalidateAllText() {
-    _stringMap.clear();
-    _invalidate();
-  }
-
-  String getTextInternal(String input) {
-    if (_cacheText && _stringMap.containsKey(input)) {
-      return _stringMap[input];
-    }
-    var text = getText(input);
-    if (_cacheText) {
-      _stringMap[input] = text;
-    }
-    return text;
-  }
-
-  void _invalidate() {
-    if (drawable != null) {
-      drawable.invalidateSelf();
-    }
-  }
-}

lib/src/value/lottie_relative_double_value_callback.dart

@@ -0,0 +1,12 @@
+import 'dart:ui';
+import 'lottie_frame_info.dart';
+
+double Function(LottieFrameInfo<double>) relativeDoubleValueCallback(
+    double offset) {
+  return (LottieFrameInfo<double> frameInfo) {
+    var originalValue = lerpDouble(frameInfo.startValue, frameInfo.endValue,
+        frameInfo.interpolatedKeyframeProgress);
+
+    return originalValue + offset;
+  };
+}

lib/src/value/lottie_relative_integer_value_callback.dart

@@ -0,0 +1,11 @@
+import 'dart:ui';
+import 'lottie_frame_info.dart';
+
+int Function(LottieFrameInfo<int>) relativeIntegerValueCallback(int offset) {
+  return (LottieFrameInfo<int> frameInfo) {
+    var originalValue = lerpDouble(frameInfo.startValue, frameInfo.endValue,
+        frameInfo.interpolatedKeyframeProgress);
+
+    return (originalValue + offset).round();
+  };
+}

lib/src/value/lottie_relative_point_value_callback.dart

@@ -0,0 +1,12 @@
+import 'dart:ui';
+import 'lottie_frame_info.dart';
+
+Offset Function(LottieFrameInfo<Offset>) relativeOffsetValueCallback(
+    Offset offset) {
+  return (LottieFrameInfo<Offset> frameInfo) {
+    var point = Offset.lerp(frameInfo.startValue, frameInfo.endValue,
+        frameInfo.interpolatedKeyframeProgress);
+
+    return point.translate(offset.dx, offset.dy);
+  };
+}

lib/src/value/lottie_value_callback.dart

@@ -4,26 +4,34 @@ import 'lottie_frame_info.dart';
 /// Allows you to set a callback on a resolved {@link com.airbnb.lottie.model.KeyPath} to modify
 /// its animation values at runtime.
 class LottieValueCallback<T> {
-  BaseKeyframeAnimation /*?*/ animation;
+  LottieValueCallback(this._value);
+
+  BaseKeyframeAnimation /*?*/ _animation;
+  BaseKeyframeAnimation get animation => _animation;
 
   /// This can be set with {@link #setValue(Object)} to use a value instead of deferring
   /// to the callback.
   ///*/
-  T /*?*/ value;
+  T /*?*/ _value;
+  T get value => _value;
 
-  LottieValueCallback(this.value);
+  T Function(LottieFrameInfo<T>) callback;
 
   /// Override this if you haven't set a static value in the constructor or with setValue.
   ///
   /// Return null to resort to the default value.
   T getValue(LottieFrameInfo<T> frameInfo) {
+    if (callback != null) {
+      return callback(frameInfo);
+    }
+
     return value;
   }
 
   void setValue(T /*?*/ value) {
-    this.value = value;
-    if (animation != null) {
-      animation.notifyListeners();
+    _value = value;
+    if (_animation != null) {
+      _animation.notifyListeners();
     }
   }
 
@@ -35,11 +43,17 @@ class LottieValueCallback<T> {
       double linearKeyframeProgress,
       double interpolatedKeyframeProgress,
       double overallProgress) {
-    return getValue(LottieFrameInfo(startFrame, endFrame, startValue, endValue,
-        linearKeyframeProgress, interpolatedKeyframeProgress, overallProgress));
+    return getValue(LottieFrameInfo<T>(
+        startFrame,
+        endFrame,
+        startValue,
+        endValue,
+        linearKeyframeProgress,
+        interpolatedKeyframeProgress,
+        overallProgress));
   }
 
   void setAnimation(BaseKeyframeAnimation /*?*/ animation) {
-    this.animation = animation;
+    _animation = animation;
   }
 }

lib/src/value/scale_xy.dart

@@ -1,23 +0,0 @@
-import 'dart:ui';
-
-//TODO(xha): delete and use Offset
-class ScaleXY {
-  final double x;
-  final double y;
-
-  ScaleXY(this.x, this.y);
-  ScaleXY.one() : this(1, 1);
-
-  @override
-  bool operator ==(other) {
-    return other is ScaleXY && x == other.x && y == other.y;
-  }
-
-  @override
-  int get hashCode => hashValues(x, y);
-
-  bool equals(double x, double y) => this.x == x && this.y == y;
-
-  static ScaleXY lerp(ScaleXY a, ScaleXY b, double t) =>
-      ScaleXY(lerpDouble(a.x, b.x, t), lerpDouble(a.y, b.y, t));
-}

lib/src/value_delegate.dart

@@ -0,0 +1,331 @@
+import 'package:collection/collection.dart';
+import 'package:flutter/widgets.dart';
+import 'lottie_drawable.dart';
+import 'lottie_property.dart';
+import 'model/key_path.dart';
+import 'value/lottie_frame_info.dart';
+import 'value/lottie_relative_double_value_callback.dart';
+import 'value/lottie_relative_integer_value_callback.dart';
+import 'value/lottie_relative_point_value_callback.dart';
+import 'value/lottie_value_callback.dart';
+
+class ValueDelegate<T> {
+  final List<String> keyPath;
+  final T property;
+  final T value;
+  final T Function(LottieFrameInfo<T>) callback;
+
+  ValueDelegate._(this.keyPath, this.property, this.value, this.callback)
+      : assert(value == null || callback == null,
+            "Value and callback can't be both specified.");
+
+  static ValueDelegate<Offset> _offset(
+      List<String> keyPath,
+      Offset property,
+      Offset value,
+      Offset Function(LottieFrameInfo<Offset>) callback,
+      Offset relative) {
+    if (relative != null) {
+      assert(callback == null);
+      callback = relativeOffsetValueCallback(relative);
+    }
+    return ValueDelegate<Offset>._(keyPath, property, value, callback);
+  }
+
+  static ValueDelegate<double> _double(
+      List<String> keyPath,
+      double property,
+      double value,
+      double Function(LottieFrameInfo<double>) callback,
+      double relative) {
+    if (relative != null) {
+      assert(callback == null);
+      callback = relativeDoubleValueCallback(relative);
+    }
+    return ValueDelegate<double>._(keyPath, property, value, callback);
+  }
+
+  static ValueDelegate<int> _int(List<String> keyPath, int property, int value,
+      int Function(LottieFrameInfo<int>) callback, int relative) {
+    if (relative != null) {
+      assert(callback == null);
+      callback = relativeIntegerValueCallback(relative);
+    }
+    return ValueDelegate<int>._(keyPath, property, value, callback);
+  }
+
+  static ValueDelegate<Color> color(List<String> keyPath,
+          {Color value, Color Function(LottieFrameInfo<Color>) callback}) =>
+      ValueDelegate._(keyPath, LottieProperty.color, value, callback);
+
+  static ValueDelegate<Color> strokeColor(List<String> keyPath,
+          {Color value, Color Function(LottieFrameInfo<Color>) callback}) =>
+      ValueDelegate._(keyPath, LottieProperty.strokeColor, value, callback);
+
+  /// Opacity value are 0-100 to match after effects
+  static ValueDelegate<int> transformOpacity(List<String> keyPath,
+          {int value,
+          int Function(LottieFrameInfo<int>) callback,
+          int relative}) =>
+      _int(keyPath, LottieProperty.transformOpacity, value, callback, relative);
+
+  /// Opacity value are 0-100 to match after effects
+  static ValueDelegate<int> opacity(List<String> keyPath,
+          {int value,
+          int Function(LottieFrameInfo<int>) callback,
+          int relative}) =>
+      _int(keyPath, LottieProperty.opacity, value, callback, relative);
+
+  static ValueDelegate<Offset> transformAnchorPoint(
+    List<String> keyPath, {
+    Offset value,
+    Offset Function(LottieFrameInfo<Offset>) callback,
+    Offset relative,
+  }) {
+    return _offset(keyPath, LottieProperty.transformAnchorPoint, value,
+        callback, relative);
+  }
+
+  static ValueDelegate<Offset> transformPosition(
+    List<String> keyPath, {
+    Offset value,
+    Offset Function(LottieFrameInfo<Offset>) callback,
+    Offset relative,
+  }) =>
+      _offset(
+          keyPath, LottieProperty.transformPosition, value, callback, relative);
+
+  static ValueDelegate<Offset> ellipseSize(
+    List<String> keyPath, {
+    Offset value,
+    Offset Function(LottieFrameInfo<Offset>) callback,
+    Offset relative,
+  }) =>
+      _offset(keyPath, LottieProperty.ellipseSize, value, callback, relative);
+
+  static ValueDelegate<Offset> rectangleSize(
+    List<String> keyPath, {
+    Offset value,
+    Offset Function(LottieFrameInfo<Offset>) callback,
+    Offset relative,
+  }) =>
+      _offset(keyPath, LottieProperty.rectangleSize, value, callback, relative);
+
+  static ValueDelegate<double> cornerRadius(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(keyPath, LottieProperty.cornerRadius, value, callback, relative);
+
+  static ValueDelegate<Offset> position(
+    List<String> keyPath, {
+    Offset value,
+    Offset Function(LottieFrameInfo<Offset>) callback,
+    Offset relative,
+  }) =>
+      _offset(keyPath, LottieProperty.position, value, callback, relative);
+
+  static ValueDelegate<Offset> transformScale(
+    List<String> keyPath, {
+    Offset value,
+    Offset Function(LottieFrameInfo<Offset>) callback,
+    Offset relative,
+  }) =>
+      _offset(
+          keyPath, LottieProperty.transformScale, value, callback, relative);
+
+  /// In degrees
+  static ValueDelegate<double> transformRotation(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(
+          keyPath, LottieProperty.transformRotation, value, callback, relative);
+
+  static ValueDelegate<double> transformSkew(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(keyPath, LottieProperty.transformSkew, value, callback, relative);
+
+  static ValueDelegate<double> transformSkewAngle(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(keyPath, LottieProperty.transformSkewAngle, value, callback,
+          relative);
+
+  static ValueDelegate<double> strokeWidth(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(keyPath, LottieProperty.strokeWidth, value, callback, relative);
+
+  static ValueDelegate<double> textTracking(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(keyPath, LottieProperty.textTracking, value, callback, relative);
+
+  static ValueDelegate<double> repeaterCopies(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(
+          keyPath, LottieProperty.repeaterCopies, value, callback, relative);
+
+  static ValueDelegate<double> repeaterOffset(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(
+          keyPath, LottieProperty.repeaterOffset, value, callback, relative);
+
+  static ValueDelegate<double> polystarPoints(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(
+          keyPath, LottieProperty.polystarPoints, value, callback, relative);
+
+  /// In degrees
+  static ValueDelegate<double> polystarRotation(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(
+          keyPath, LottieProperty.polystarRotation, value, callback, relative);
+
+  static ValueDelegate<double> polystarInnerRadius(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(keyPath, LottieProperty.polystarInnerRadius, value, callback,
+          relative);
+
+  static ValueDelegate<double> polystarOuterRadius(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(keyPath, LottieProperty.polystarOuterRadius, value, callback,
+          relative);
+
+  static ValueDelegate<double> polystarInnerRoundedness(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(keyPath, LottieProperty.polystarInnerRoundedness, value, callback,
+          relative);
+
+  static ValueDelegate<double> polystarOuterRoundedness(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(keyPath, LottieProperty.polystarOuterRoundedness, value, callback,
+          relative);
+
+  /// Opacity value are 0-100 to match after effects
+  static ValueDelegate<double> transformStartOpacity(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(keyPath, LottieProperty.transformStartOpacity, value, callback,
+          relative);
+
+  /// Opacity value are 0-100 to match after effects
+  static ValueDelegate<double> transformEndOpacity(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(keyPath, LottieProperty.transformEndOpacity, value, callback,
+          relative);
+
+  /// The time value in seconds
+  static ValueDelegate<double> timeRemap(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(keyPath, LottieProperty.timeRemap, value, callback, relative);
+
+  static ValueDelegate<double> textSize(List<String> keyPath,
+          {double value,
+          double Function(LottieFrameInfo<double>) callback,
+          double relative}) =>
+      _double(keyPath, LottieProperty.textSize, value, callback, relative);
+
+  static ValueDelegate<ColorFilter> colorFilter(List<String> keyPath,
+          {ColorFilter value,
+          ColorFilter Function(LottieFrameInfo<ColorFilter>) callback}) =>
+      ValueDelegate._(keyPath, LottieProperty.colorFilter, value, callback);
+
+  static ValueDelegate<List<Color>> gradientColor(List<String> keyPath,
+          {List<Color> value,
+          List<Color> Function(LottieFrameInfo<List<Color>>) callback}) =>
+      ValueDelegate._(keyPath, LottieProperty.gradientColor, value, callback);
+
+  ResolvedValueDelegate<T> _resolved;
+  ResolvedValueDelegate _resolve(List<KeyPath> resolvedPaths) {
+    _resolved = ResolvedValueDelegate<T>(this, resolvedPaths);
+    return _resolved;
+  }
+
+  bool isSameProperty(ValueDelegate other) {
+    if (identical(this, other)) return true;
+    return other is ValueDelegate<T> &&
+        const ListEquality().equals(other.keyPath, keyPath) &&
+        other.property == property;
+  }
+}
+
+ResolvedValueDelegate internalResolved(ValueDelegate valueDelegate) {
+  return valueDelegate._resolved;
+}
+
+ResolvedValueDelegate internalResolve(
+    ValueDelegate delegate, List<KeyPath> resolvedPaths) {
+  return delegate._resolve(resolvedPaths);
+}
+
+class ResolvedValueDelegate<T> {
+  final ValueDelegate<T> valueDelegate;
+  final List<KeyPath> keyPaths;
+  final LottieValueCallback<T> valueCallback;
+
+  ResolvedValueDelegate(this.valueDelegate, this.keyPaths)
+      : valueCallback = LottieValueCallback(valueDelegate.value)
+          ..callback = valueDelegate.callback;
+
+  T get property => valueDelegate.property;
+
+  void updateDelegate(ValueDelegate<T> delegate) {
+    valueCallback
+      ..setValue(delegate.value)
+      ..callback = delegate.callback;
+  }
+
+  void clear() {
+    valueCallback
+      ..setValue(null)
+      ..callback = null;
+  }
+
+  /// Add a property callback for the specified {@link KeyPath}. This {@link KeyPath} can resolve
+  /// to multiple contents. In that case, the callbacks's value will apply to all of them.
+  /// <p>
+  /// Internally, this will check if the {@link KeyPath} has already been resolved with
+  /// {@link #resolveKeyPath(KeyPath)} and will resolve it if it hasn't.
+  void addValueCallback(LottieDrawable drawable) {
+    for (var keyPath in keyPaths) {
+      keyPath.resolvedElement.addValueCallback<T>(property, valueCallback);
+    }
+    if (keyPaths.isNotEmpty) {
+      drawable.invalidateSelf();
+      if (property == LottieProperty.timeRemap) {
+        // Time remapping values are read in setProgress. In order for the new value
+        // to apply, we have to re-set the progress with the current progress so that the
+        // time remapping can be reapplied.
+        drawable.setProgress(drawable.progress);
+      }
+    }
+  }
+}

pubspec.lock

@@ -43,6 +43,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "1.0.5"
+  characters:
+    dependency: "direct main"
+    description:
+      name: characters
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.5.0"
   charcode:
     dependency: "direct main"
     description:
@@ -171,7 +178,7 @@ packages:
       name: package_config
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.0"
+    version: "1.9.1"
   path:
     dependency: "direct main"
     description:
@@ -199,7 +206,7 @@ packages:
       name: pub_semver
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.4.2"
+    version: "1.4.3"
   quiver:
     dependency: transitive
     description:

pubspec.yaml

@@ -1,6 +1,6 @@
 name: lottie
 description: Render After Effects animations natively on Flutter. This package is a pure Dart implementation of a Lottie player.
-version: 0.2.2
+version: 0.3.0
 homepage: https://github.com/xvrh/lottie-flutter
 
 environment:
@@ -10,6 +10,7 @@ dependencies:
   flutter:
     sdk: flutter
   archive: ^2.0.0
+  characters:
   charcode: ^1.0.0
   logging: ^0.11.0
   meta: ^1.1.8

test/compositions_test.dart

@@ -21,8 +21,9 @@ void main() {
       var recorder = PictureRecorder();
       var canvas = Canvas(recorder);
       for (var progress = 0; progress <= 100; progress += 20) {
-        drawable.draw(canvas, Rect.fromLTWH(0, 0, 200, 200),
-            progress: progress / 100);
+        drawable
+          ..setProgress(progress / 100)
+          ..draw(canvas, Rect.fromLTWH(0, 0, 200, 200));
       }
     });
   }