Animate TextStyle.fontVariations (#138881)

Fixes https://github.com/flutter/flutter/issues/105120

I also exposed the relevant dart:ui types which had the effect of removing a large number of dart:ui imports from examples.

examples/api/lib/ui/text/font_feature.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/material.dart';
 
 /// Flutter code sample for [FontFeature].

examples/api/lib/ui/text/font_feature.font_feature_alternative.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.alternative].

examples/api/lib/ui/text/font_feature.font_feature_alternative_fractions.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.alternativeFractions].

examples/api/lib/ui/text/font_feature.font_feature_case_sensitive_forms.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.caseSensitiveForms].

examples/api/lib/ui/text/font_feature.font_feature_character_variant.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.characterVariant].

examples/api/lib/ui/text/font_feature.font_feature_contextual_alternates.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.contextualAlternates].

examples/api/lib/ui/text/font_feature.font_feature_denominator.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.denominator].

examples/api/lib/ui/text/font_feature.font_feature_fractions.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.fractions].

examples/api/lib/ui/text/font_feature.font_feature_historical_forms.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.historicalForms].

examples/api/lib/ui/text/font_feature.font_feature_historical_ligatures.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.historicalLigatures].

examples/api/lib/ui/text/font_feature.font_feature_lining_figures.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.liningFigures].

examples/api/lib/ui/text/font_feature.font_feature_notational_forms.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.notationalForms].

examples/api/lib/ui/text/font_feature.font_feature_numerators.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.numerators].

examples/api/lib/ui/text/font_feature.font_feature_oldstyle_figures.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.oldstyleFigures].

examples/api/lib/ui/text/font_feature.font_feature_ordinal_forms.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.ordinalForms].

examples/api/lib/ui/text/font_feature.font_feature_proportional_figures.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.proportionalFigures].

examples/api/lib/ui/text/font_feature.font_feature_scientific_inferiors.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.scientificInferiors].

examples/api/lib/ui/text/font_feature.font_feature_slashed_zero.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.slashedZero].

examples/api/lib/ui/text/font_feature.font_feature_stylistic_alternates.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.stylisticAlternates].

examples/api/lib/ui/text/font_feature.font_feature_stylistic_set.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.stylisticSet].

examples/api/lib/ui/text/font_feature.font_feature_stylistic_set.1.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.stylisticSet].

examples/api/lib/ui/text/font_feature.font_feature_subscripts.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.subscripts].

examples/api/lib/ui/text/font_feature.font_feature_superscripts.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.superscripts].

examples/api/lib/ui/text/font_feature.font_feature_swash.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [FontFeature.FontFeature.swash].

examples/api/lib/ui/text/font_feature.font_feature_tabular_figures.0.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/widgets.dart';
 
 /// Flutter code sample for [dart]:ui FontFeature.FontFeature.tabularFigures.

examples/api/test/ui/text/font_feature.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_alternative.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_alternative.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_alternative_fractions.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_alternative_fractions.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_case_sensitive_forms.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_case_sensitive_forms.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_character_variant.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_character_variant.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_contextual_alternates.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_contextual_alternates.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_denominator.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_denominator.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_fractions.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_fractions.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_historical_forms.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_historical_forms.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_historical_ligatures.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_historical_ligatures.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_lining_figures.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_lining_figures.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_notational_forms.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_notational_forms.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_numerators.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_numerators.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_oldstyle_figures.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_oldstyle_figures.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_ordinal_forms.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_ordinal_forms.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_proportional_figures.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_proportional_figures.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_scientific_inferiors.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_scientific_inferiors.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_slashed_zero.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_slashed_zero.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_stylistic_alternates.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_stylistic_alternates.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_stylistic_set.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_stylistic_set.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_stylistic_set.1_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_stylistic_set.1.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_subscripts.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_subscripts.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_superscripts.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_superscripts.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_swash.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_swash.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

examples/api/test/ui/text/font_feature.font_feature_tabular_figures.0_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
 import 'package:flutter/material.dart';
 import 'package:flutter_api_samples/ui/text/font_feature.font_feature_tabular_figures.0.dart' as example;
 import 'package:flutter_test/flutter_test.dart';

packages/flutter/lib/src/painting/basic_types.dart

@@ -12,7 +12,9 @@ export 'dart:ui' show
   Color,
   ColorFilter,
   FilterQuality,
+  FontFeature,
   FontStyle,
+  FontVariation,
   FontWeight,
   ImageShader,
   Locale,
@@ -28,6 +30,7 @@ export 'dart:ui' show
   Radius,
   Rect,
   Shader,
+  Shadow,
   Size,
   StrokeCap,
   StrokeJoin,
@@ -38,6 +41,8 @@ export 'dart:ui' show
   TextDecoration,
   TextDecorationStyle,
   TextDirection,
+  TextHeightBehavior,
+  TextLeadingDistribution,
   TextPosition,
   TileMode,
   VertexMode,

packages/flutter/lib/src/painting/strut_style.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui' show TextLeadingDistribution;
-
 import 'package:flutter/foundation.dart';
 
 import 'basic_types.dart';

packages/flutter/lib/src/painting/text_painter.dart

@@ -12,7 +12,6 @@ import 'dart:ui' as ui show
   ParagraphConstraints,
   ParagraphStyle,
   PlaceholderAlignment,
-  TextHeightBehavior,
   TextStyle;
 
 import 'package:flutter/foundation.dart';
@@ -488,7 +487,7 @@ class TextPainter {
     Locale? locale,
     StrutStyle? strutStyle,
     TextWidthBasis textWidthBasis = TextWidthBasis.parent,
-    ui.TextHeightBehavior? textHeightBehavior,
+    TextHeightBehavior? textHeightBehavior,
   }) : assert(text == null || text.debugAssertIsValid()),
        assert(maxLines == null || maxLines > 0),
        assert(textScaleFactor == 1.0 || identical(textScaler, TextScaler.noScaling), 'Use textScaler instead.'),
@@ -537,7 +536,7 @@ class TextPainter {
     Locale? locale,
     StrutStyle? strutStyle,
     TextWidthBasis textWidthBasis = TextWidthBasis.parent,
-    ui.TextHeightBehavior? textHeightBehavior,
+    TextHeightBehavior? textHeightBehavior,
     double minWidth = 0.0,
     double maxWidth = double.infinity,
   }) {
@@ -589,7 +588,7 @@ class TextPainter {
     Locale? locale,
     StrutStyle? strutStyle,
     TextWidthBasis textWidthBasis = TextWidthBasis.parent,
-    ui.TextHeightBehavior? textHeightBehavior,
+    TextHeightBehavior? textHeightBehavior,
     double minWidth = 0.0,
     double maxWidth = double.infinity,
   }) {
@@ -894,9 +893,9 @@ class TextPainter {
   }
 
   /// {@macro dart.ui.textHeightBehavior}
-  ui.TextHeightBehavior? get textHeightBehavior => _textHeightBehavior;
-  ui.TextHeightBehavior? _textHeightBehavior;
-  set textHeightBehavior(ui.TextHeightBehavior? value) {
+  TextHeightBehavior? get textHeightBehavior => _textHeightBehavior;
+  TextHeightBehavior? _textHeightBehavior;
+  set textHeightBehavior(TextHeightBehavior? value) {
     if (_textHeightBehavior == value) {
       return;
     }

packages/flutter/lib/src/painting/text_style.dart

@@ -2,14 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:collection';
 import 'dart:ui' as ui show
-  FontFeature,
-  FontVariation,
   ParagraphStyle,
-  Shadow,
   StrutStyle,
-  TextHeightBehavior,
-  TextLeadingDistribution,
   TextStyle,
   lerpDouble;
 
@@ -680,7 +676,7 @@ class TextStyle with Diagnosticable {
   ///
   /// Defaults to null, which defers to the paragraph's
   /// `ParagraphStyle.textHeightBehavior`'s [leadingDistribution].
-  final ui.TextLeadingDistribution? leadingDistribution;
+  final TextLeadingDistribution? leadingDistribution;
 
   /// The locale used to select region-specific glyphs.
   ///
@@ -800,7 +796,7 @@ class TextStyle with Diagnosticable {
   ///
   /// Shadows must be in the same order for [TextStyle] to be considered as
   /// equivalent as order produces differing transparency.
-  final List<ui.Shadow>? shadows;
+  final List<Shadow>? shadows;
 
   /// A list of [FontFeature]s that affect how the font selects glyphs.
   ///
@@ -809,7 +805,13 @@ class TextStyle with Diagnosticable {
   /// tabular numbers, or it might offer versions of the zero digit with
   /// and without slashes. [FontFeature]s can be used to select which of
   /// these variants will be used for rendering.
-  final List<ui.FontFeature>? fontFeatures;
+  ///
+  /// Font features are not interpolated by [lerp].
+  ///
+  /// See also:
+  ///
+  ///  * [fontVariations], for font features that have continuous parameters.
+  final List<FontFeature>? fontFeatures;
 
   /// A list of [FontVariation]s that affect how a variable font is rendered.
   ///
@@ -823,10 +825,18 @@ class TextStyle with Diagnosticable {
   /// ```dart
   /// const TextStyle(
   ///   fontFamily: 'RobotoSlab',
-  ///   fontVariations: <ui.FontVariation>[ui.FontVariation('wght', 900.0)]
+  ///   fontVariations: <FontVariation>[FontVariation('wght', 900.0)]
   /// )
   /// ```
-  final List<ui.FontVariation>? fontVariations;
+  ///
+  /// Font variations can be interpolated via [lerp]. This is fastest when the
+  /// same font variation axes are specified, in the same order, in both
+  /// [TextStyle] objects. See [lerpFontVariations].
+  ///
+  /// See also:
+  ///
+  ///  * [fontFeatures], for font variations that have discrete values.
+  final List<FontVariation>? fontVariations;
 
   /// How visual text overflow should be handled.
   final TextOverflow? overflow;
@@ -862,13 +872,13 @@ class TextStyle with Diagnosticable {
     double? wordSpacing,
     TextBaseline? textBaseline,
     double? height,
-    ui.TextLeadingDistribution? leadingDistribution,
+    TextLeadingDistribution? leadingDistribution,
     Locale? locale,
     Paint? foreground,
     Paint? background,
-    List<ui.Shadow>? shadows,
-    List<ui.FontFeature>? fontFeatures,
-    List<ui.FontVariation>? fontVariations,
+    List<Shadow>? shadows,
+    List<FontFeature>? fontFeatures,
+    List<FontVariation>? fontVariations,
     TextDecoration? decoration,
     Color? decorationColor,
     TextDecorationStyle? decorationStyle,
@@ -967,11 +977,11 @@ class TextStyle with Diagnosticable {
     double heightFactor = 1.0,
     double heightDelta = 0.0,
     TextBaseline? textBaseline,
-    ui.TextLeadingDistribution? leadingDistribution,
+    TextLeadingDistribution? leadingDistribution,
     Locale? locale,
-    List<ui.Shadow>? shadows,
-    List<ui.FontFeature>? fontFeatures,
-    List<ui.FontVariation>? fontVariations,
+    List<Shadow>? shadows,
+    List<FontFeature>? fontFeatures,
+    List<FontVariation>? fontVariations,
     String? package,
     TextOverflow? overflow,
   }) {
@@ -1136,7 +1146,7 @@ class TextStyle with Diagnosticable {
         background: t < 0.5 ? null : b.background,
         shadows: t < 0.5 ? null : b.shadows,
         fontFeatures: t < 0.5 ? null : b.fontFeatures,
-        fontVariations: t < 0.5 ? null : b.fontVariations,
+        fontVariations: lerpFontVariations(null, b.fontVariations, t),
         decoration: t < 0.5 ? null : b.decoration,
         decorationColor: Color.lerp(null, b.decorationColor, t),
         decorationStyle: t < 0.5 ? null : b.decorationStyle,
@@ -1167,7 +1177,7 @@ class TextStyle with Diagnosticable {
         background: t < 0.5 ? a.background : null,
         shadows: t < 0.5 ? a.shadows : null,
         fontFeatures: t < 0.5 ? a.fontFeatures : null,
-        fontVariations: t < 0.5 ? a.fontVariations : null,
+        fontVariations: lerpFontVariations(a.fontVariations, null, t),
         decoration: t < 0.5 ? a.decoration : null,
         decorationColor: Color.lerp(a.decorationColor, null, t),
         decorationStyle: t < 0.5 ? a.decorationStyle : null,
@@ -1267,7 +1277,7 @@ class TextStyle with Diagnosticable {
         : null,
       shadows: t < 0.5 ? a.shadows : b.shadows,
       fontFeatures: t < 0.5 ? a.fontFeatures : b.fontFeatures,
-      fontVariations: t < 0.5 ? a.fontVariations : b.fontVariations,
+      fontVariations: lerpFontVariations(a.fontVariations, b.fontVariations, t),
       decoration: t < 0.5 ? a.decoration : b.decoration,
       decorationColor: Color.lerp(a.decorationColor, b.decorationColor, t),
       decorationStyle: t < 0.5 ? a.decorationStyle : b.decorationStyle,
@@ -1342,7 +1352,7 @@ class TextStyle with Diagnosticable {
     TextScaler textScaler = TextScaler.noScaling,
     String? ellipsis,
     int? maxLines,
-    ui.TextHeightBehavior? textHeightBehavior,
+    TextHeightBehavior? textHeightBehavior,
     Locale? locale,
     String? fontFamily,
     double? fontSize,
@@ -1352,9 +1362,9 @@ class TextStyle with Diagnosticable {
     StrutStyle? strutStyle,
   }) {
     assert(maxLines == null || maxLines > 0);
-    final ui.TextLeadingDistribution? leadingDistribution = this.leadingDistribution;
-    final ui.TextHeightBehavior? effectiveTextHeightBehavior = textHeightBehavior
-      ?? (leadingDistribution == null ? null : ui.TextHeightBehavior(leadingDistribution: leadingDistribution));
+    final TextLeadingDistribution? leadingDistribution = this.leadingDistribution;
+    final TextHeightBehavior? effectiveTextHeightBehavior = textHeightBehavior
+      ?? (leadingDistribution == null ? null : TextHeightBehavior(leadingDistribution: leadingDistribution));
 
     return ui.ParagraphStyle(
       textAlign: textAlign,
@@ -1475,9 +1485,9 @@ class TextStyle with Diagnosticable {
       overflow,
     );
 
-    final List<ui.Shadow>? shadows = this.shadows;
-    final List<ui.FontFeature>? fontFeatures = this.fontFeatures;
-    final List<ui.FontVariation>? fontVariations = this.fontVariations;
+    final List<Shadow>? shadows = this.shadows;
+    final List<FontFeature>? fontFeatures = this.fontFeatures;
+    final List<FontVariation>? fontVariations = this.fontVariations;
     return Object.hash(
       inherit,
       color,
@@ -1537,7 +1547,7 @@ class TextStyle with Diagnosticable {
     styles.add(DoubleProperty('${prefix}wordSpacing', wordSpacing, defaultValue: null));
     styles.add(EnumProperty<TextBaseline>('${prefix}baseline', textBaseline, defaultValue: null));
     styles.add(DoubleProperty('${prefix}height', height, unit: 'x', defaultValue: null));
-    styles.add(EnumProperty<ui.TextLeadingDistribution>('${prefix}leadingDistribution', leadingDistribution, defaultValue: null));
+    styles.add(EnumProperty<TextLeadingDistribution>('${prefix}leadingDistribution', leadingDistribution, defaultValue: null));
     styles.add(DiagnosticsProperty<Locale>('${prefix}locale', locale, defaultValue: null));
     styles.add(DiagnosticsProperty<Paint>('${prefix}foreground', foreground, defaultValue: null));
     styles.add(DiagnosticsProperty<Paint>('${prefix}background', background, defaultValue: null));
@@ -1578,3 +1588,95 @@ class TextStyle with Diagnosticable {
     styles.add(EnumProperty<TextOverflow>('${prefix}overflow', overflow, defaultValue: null));
   }
 }
+
+/// Interpolate between two lists of [FontVariation] objects.
+///
+/// Variations are paired by axis, and interpolated using [FontVariation.lerp].
+///
+/// Entries that are only present in one list are animated using a step-function
+/// at t=0.5 that enables or disables the variation. This can be jarring and
+/// largely defeats the point of animating font variations. For best results,
+/// specify the same axes in both lists, and for best performance, specify them
+/// in the same order.
+///
+/// ## Performance details
+///
+/// This algorithm is O(N), but the constant factor varies based on the input,
+/// and that is probably more important (because typically N is going to be
+/// tiny, like 1 or 2; at the time of writing, there are only about five defined
+/// axes that fonts typically use!).
+///
+/// It is fastest when the lists contain the same axes ([FontVariation.axis]) in
+/// the same order. The result is again in the same order, and no attempt is
+/// made to detect or remove duplicates in this process. This is, by far, the
+/// recommended way to use this algorithm.
+///
+/// When the order of items in the two input lists vary, the constant factor
+/// increases substantially, as it involves creating two maps and a set,
+/// inserting every variation in both lists into the maps and the set, and then
+/// iterating over them to recreate the list.
+///
+/// In this case, the resulting order is arbitrary. Duplicates are dropped; in
+/// each list, the last [FontVariation] for any particular axis is the one used
+/// to compute the value for that axis. Values that only appear on one side are
+/// interpolated using [FontVariation.lerp] against a null value, and resulting
+/// null values are omitted from the resulting list.
+///
+/// When the lists begin with matching pairs of axes, the fast algorithm is used
+/// up to the point where the lists diverge, and the more expensive algorithm
+/// is used on the remaining entries.
+///
+/// See also:
+///
+///  * [TextStyle.lerp], which uses this function to handle
+///    [TextStyle.fontVariations].
+List<FontVariation>? lerpFontVariations(List<FontVariation>? a, List<FontVariation>? b, double t) {
+  if (t == 0.0) {
+    return a;
+  }
+  if (t == 1.0) {
+    return b;
+  }
+  if (a == null || a.isEmpty || b == null || b.isEmpty) {
+    // If one side is empty, that means anything on the other
+    // side will use the null-to-something lerp, which is to
+    // say, a step function at t=0.5.
+    return t < 0.5 ? a : b;
+  }
+  assert(a.isNotEmpty && b.isNotEmpty);
+  final List<FontVariation> result = <FontVariation>[];
+  // First, try the efficient O(N) solution in the event that
+  // the lists are compatible.
+  int index = 0;
+  final int minLength = a.length < b.length ? a.length : b.length;
+  for (; index < minLength; index += 1) {
+    if (a[index].axis != b[index].axis) {
+      // The lists aren't compatible.
+      break;
+    }
+    result.add(FontVariation.lerp(a[index], b[index], t)!);
+  }
+  final int maxLength = a.length > b.length ? a.length : b.length;
+  if (index < maxLength) {
+    // If we get here, we have found some case where we cannot
+    // use the efficient approach.
+    final Set<String> axes = HashSet<String>();
+    final Map<String, FontVariation> aVariations = HashMap<String, FontVariation>();
+    for (int indexA = index; indexA < a.length; indexA += 1) {
+      aVariations[a[indexA].axis] = a[indexA];
+      axes.add(a[indexA].axis);
+    }
+    final Map<String, FontVariation> bVariations = HashMap<String, FontVariation>();
+    for (int indexB = index; indexB < b.length; indexB += 1) {
+      bVariations[b[indexB].axis] = b[indexB];
+      axes.add(b[indexB].axis);
+    }
+    for (final String axis in axes) {
+      final FontVariation? variation = FontVariation.lerp(aVariations[axis], bVariations[axis], t);
+      if (variation != null) {
+        result.add(variation);
+      }
+    }
+  }
+  return result;
+}

packages/flutter/lib/src/widgets/icon.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/foundation.dart';
 import 'package:flutter/rendering.dart';
 

packages/flutter/test/painting/text_style_test.dart

@@ -595,4 +595,63 @@ void main() {
     expect(TextStyle.lerp(fromStyle, toStyle, 1), toStyle);
   });
 
+  test('lerpFontVariations', () {
+    // nil cases
+    expect(lerpFontVariations(const <FontVariation>[], const <FontVariation>[], 0.0), const <FontVariation>[]);
+    expect(lerpFontVariations(const <FontVariation>[], const <FontVariation>[], 0.5), const <FontVariation>[]);
+    expect(lerpFontVariations(const <FontVariation>[], const <FontVariation>[], 1.0), const <FontVariation>[]);
+    expect(lerpFontVariations(null, const <FontVariation>[], 0.0), null);
+    expect(lerpFontVariations(const <FontVariation>[], null, 0.0), const <FontVariation>[]);
+    expect(lerpFontVariations(null, null, 0.0), null);
+    expect(lerpFontVariations(null, const <FontVariation>[], 0.5), const <FontVariation>[]);
+    expect(lerpFontVariations(const <FontVariation>[], null, 0.5), null);
+    expect(lerpFontVariations(null, null, 0.5), null);
+    expect(lerpFontVariations(null, const <FontVariation>[], 1.0), const <FontVariation>[]);
+    expect(lerpFontVariations(const <FontVariation>[], null, 1.0), null);
+    expect(lerpFontVariations(null, null, 1.0), null);
+
+    const FontVariation w100 = FontVariation.weight(100.0);
+    const FontVariation w120 = FontVariation.weight(120.0);
+    const FontVariation w150 = FontVariation.weight(150.0);
+    const FontVariation w200 = FontVariation.weight(200.0);
+    const FontVariation w300 = FontVariation.weight(300.0);
+    const FontVariation w1000 = FontVariation.weight(1000.0);
+
+    // one axis
+    expect(lerpFontVariations(const <FontVariation>[w100], const <FontVariation>[w200], 0.0), const <FontVariation>[w100]);
+    expect(lerpFontVariations(const <FontVariation>[w100], const <FontVariation>[w200], 0.2), const <FontVariation>[w120]);
+    expect(lerpFontVariations(const <FontVariation>[w100], const <FontVariation>[w200], 0.5), const <FontVariation>[w150]);
+    expect(lerpFontVariations(const <FontVariation>[w100], const <FontVariation>[w200], 2.0), const <FontVariation>[w300]);
+
+    // weird one axis cases
+    expect(lerpFontVariations(const <FontVariation>[w100, w1000], const <FontVariation>[w300], 0.0), const <FontVariation>[w100, w1000]);
+    expect(lerpFontVariations(const <FontVariation>[w100, w1000], const <FontVariation>[w300], 0.5), const <FontVariation>[w200]);
+    expect(lerpFontVariations(const <FontVariation>[w100, w1000], const <FontVariation>[w300], 1.0), const <FontVariation>[w300]);
+    expect(lerpFontVariations(const <FontVariation>[w100, w1000], const <FontVariation>[], 0.5), const <FontVariation>[]);
+
+    const FontVariation sn80 = FontVariation.slant(-80.0);
+    const FontVariation sn40 = FontVariation.slant(-40.0);
+    const FontVariation s0 = FontVariation.slant(0.0);
+    const FontVariation sp40 = FontVariation.slant(40.0);
+    const FontVariation sp80 = FontVariation.slant(80.0);
+
+    // two axis matched order
+    expect(lerpFontVariations(const <FontVariation>[w100, sn80], const <FontVariation>[w300, sp80], 0.5), const <FontVariation>[w200, s0]);
+
+    // two axis unmatched order
+    expect(lerpFontVariations(const <FontVariation>[sn80, w100], const <FontVariation>[w300, sp80], 0.0), const <FontVariation>[sn80, w100]);
+    expect(lerpFontVariations(const <FontVariation>[sn80, w100], const <FontVariation>[w300, sp80], 0.5), unorderedMatches(const <FontVariation>[s0, w200]));
+    expect(lerpFontVariations(const <FontVariation>[sn80, w100], const <FontVariation>[w300, sp80], 1.0), const <FontVariation>[w300, sp80]);
+
+    // two axis with duplicates
+    expect(lerpFontVariations(const <FontVariation>[sn80, w100, sp80], const <FontVariation>[w300, sp80], 0.5), unorderedMatches(const <FontVariation>[sp80, w200]));
+
+    // mixed axis counts
+    expect(lerpFontVariations(const <FontVariation>[sn80, w100], const <FontVariation>[w300], 0.5), const <FontVariation>[w200]);
+    expect(lerpFontVariations(const <FontVariation>[sn80], const <FontVariation>[w300], 0.0), const <FontVariation>[sn80]);
+    expect(lerpFontVariations(const <FontVariation>[sn80], const <FontVariation>[w300], 0.1), const <FontVariation>[sn80]);
+    expect(lerpFontVariations(const <FontVariation>[sn80], const <FontVariation>[w300], 0.9), const <FontVariation>[w300]);
+    expect(lerpFontVariations(const <FontVariation>[sn80], const <FontVariation>[w300], 1.0), const <FontVariation>[w300]);
+    expect(lerpFontVariations(const <FontVariation>[sn40, s0, w100], const <FontVariation>[sp40, w300, sp80], 0.5), anyOf(equals(const <FontVariation>[s0, w200, sp40]), equals(const <FontVariation>[s0, sp40, w200])));
+  });
 }

packages/flutter/test/widgets/icon_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui';
-
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:leak_tracker_flutter_testing/leak_tracker_flutter_testing.dart';