feat: add UniformPadding (#46)

packages/fleet/README.md

@@ -150,6 +150,10 @@ for animating with Fleet:
 - ASliverPadding
 - ATransform
 
+The following provided widgets are specific to Fleet:
+
+- UniformPadding
+
 ---
 
 **Gabriel Terwesten** • **GitHub**

packages/fleet/example/lib/simple_declarative_animation.dart

@@ -35,10 +35,13 @@ class _MyHomePageState extends State<MyHomePage> {
         style: TextButton.styleFrom(foregroundColor: Colors.white),
         child: const Text('Toggle'),
       )
+          .uniformPadding(Edges.all, _expanded ? null : 32)
+          .animation(Curves.easeInOutCubic.animation(1.s))
+          .boxColor(Colors.orange)
           .center()
           .boxColor(_expanded ? Colors.green : Colors.blue)
           .sizeWith(_expanded ? const Size.square(400) : const Size.square(200))
-          .animation(Curves.ease.animation(1.s), value: _expanded)
+          .animation(Curves.ease.animation(1.s))
           .center(),
     );
   }

packages/fleet/lib/fleet.dart

@@ -22,6 +22,7 @@ export 'src/animate.dart' show Animated, withAnimation, AnimatingStateMixin;
 export 'src/animation.dart' show AnimationSpec, AnimationFromCurveExtension;
 export 'src/common.dart' show Block;
 export 'src/duration.dart' show DurationFromIntExtension;
+export 'src/environment.dart' show EnvironmentKey, EnvironmentValueModifiers;
 export 'src/parameter.dart'
     show
         AnimatableAlignmentGeometry,
@@ -50,3 +51,10 @@ export 'src/parameter.dart'
         AnimatableParameterHostMixin,
         AnimatableParameterHost;
 export 'src/widget_extension.dart' show FleetWidgetExtension;
+export 'src/widgets/uniform_padding.dart'
+    show
+        Edge,
+        Edges,
+        UniformPadding,
+        defaultUniformPadding,
+        UniformPaddingModifiers;

packages/fleet/lib/src/animate.dart

@@ -1,10 +1,13 @@
 import 'package:flutter/widgets.dart' hide Animation;
 
 import 'animatable_flutter_widgets.dart';
+import 'animatable_render_object_widget.dart';
+import 'animatable_stateless_widget.dart';
 import 'animatable_widget_state.dart';
 import 'animation.dart';
 import 'common.dart';
 import 'transaction.dart';
+import 'widgets/uniform_padding.dart';
 
 /// Applies an [animation] to the state changes caused by calling [block].
 ///
@@ -140,8 +143,9 @@ mixin AnimatingStateMixin<T extends StatefulWidget> on State<T> {
 /// {@template fleet.Animated.widgets}
 ///
 /// Only widgets that support animating with Fleet will animate changes. To
-/// implement support for this in your own widgets use [AnimatableStateMixin] or
-/// [AnimatableState].
+/// implement support for this in your own widgets use [AnimatableStateMixin],
+/// [AnimatableState], [AnimatableStatelessWidget] or
+/// [AnimatableSingleChildRenderObjectWidgetMixin].
 ///
 /// The following provided widgets support animating with Fleet:
 ///
@@ -157,6 +161,10 @@ mixin AnimatingStateMixin<T extends StatefulWidget> on State<T> {
 /// - [ASliverPadding]
 /// - [ATransform]
 ///
+/// The following provided widgets are specific to Fleet:
+///
+/// - [UniformPadding]
+///
 /// {@endtemplate}
 ///
 /// State changes are only animated if they happen at the same time that [value]

packages/fleet/lib/src/environment.dart

@@ -0,0 +1,131 @@
+import 'package:flutter/widgets.dart';
+
+/// A key for accessing and modifying associated values from the [BuildContext].
+///
+/// [EnvironmentKey]s are an alternative to using [InheritedWidget]s for passing
+/// values down the widget tree.
+///
+/// An [EnvironmentKey] is less verbose to define than an [InheritedWidget]
+/// since it inherits the [of] and [maybeOf] methods instead of having to define
+/// the equivalent static accessors.
+///
+/// It further incorporates the concept of a [defaultValue] which is used when
+/// no value is provided through the [BuildContext].
+///
+/// # Example
+///
+/// The following example shows how to define a [EnvironmentKey], as well as a
+/// extension method that is typically provided to make it easier to use.
+///
+/// ```dart multi_begin
+/// import 'package:flutter/widgets.dart';
+///
+/// final class _DefaultPaddingKey
+///     extends EnvironmentKey<double, _DefaultPaddingKey> {
+///   const _DefaultPaddingKey();
+///
+///   @override
+///   double defaultValue(BuildContext context) => 8;
+/// }
+///
+/// const defaultPadding = _DefaultPaddingKey();
+///
+/// extension WidgetModifiers on Widget {
+///   @widgetFactory
+///   Widget defaultPadding(double amount) =>
+///       const _DefaultPaddingKey().update(value: amount, child: this);
+/// }
+/// ```
+///
+/// To access the value of an [EnvironmentKey] from the [BuildContext], use the
+/// [of] method:
+///
+/// ```dart multi_end
+/// Widget build(BuildContext context) {
+///   return Padding(
+///     padding: EdgeInsets.all(defaultPadding.of(context)),
+///     child: Container(),
+///   );
+/// }
+/// ```
+abstract base class EnvironmentKey<T, K extends EnvironmentKey<T, K>> {
+  /// Constructor for subclasses.
+  const EnvironmentKey();
+
+  /// Returns the default value for this key, when no value is provided through
+  /// the [BuildContext].
+  T defaultValue(BuildContext context);
+
+  /// Returns the value of this key form the given [BuildContext] or the
+  /// [defaultValue] if no value is provided.
+  T of(BuildContext context) => maybeOf(context) ?? defaultValue(context);
+
+  /// Returns the value of this key based on the given [BuildContext] or `null`
+  /// if no value is provided.
+  T? maybeOf(BuildContext context) => context
+      .dependOnInheritedWidgetOfExactType<_EnvironmentValue<T, K>>()
+      ?.value;
+}
+
+/// Methods on [EnvironmentKey] for modifying the value of the key.
+extension EnvironmentValueModifiers<T, K extends EnvironmentKey<T, K>>
+    on EnvironmentKey<T, K> {
+  /// Returns a widget that provides the given [value] for this key to its
+  /// descendants.
+  @widgetFactory
+  Widget update({required T value, required Widget child}) {
+    return _EnvironmentValue<T, K>(
+      value: value,
+      child: child,
+    );
+  }
+
+  /// Returns a widget that provides the result of [transform] applied to the
+  /// value of this key to its descendants.
+  @widgetFactory
+  Widget transform({
+    required T Function(T value) transform,
+    required Widget child,
+  }) {
+    return _EnvironmentValueTransformer(
+      environmentKey: this,
+      transform: transform,
+      child: child,
+    );
+  }
+}
+
+final class _EnvironmentValue<T, K extends EnvironmentKey<T, K>>
+    extends InheritedWidget {
+  const _EnvironmentValue({
+    required this.value,
+    required super.child,
+  });
+
+  final T value;
+
+  @override
+  bool updateShouldNotify(covariant _EnvironmentValue<T, K> oldWidget) =>
+      value != oldWidget.value;
+}
+
+final class _EnvironmentValueTransformer<T, K extends EnvironmentKey<T, K>>
+    extends StatelessWidget {
+  const _EnvironmentValueTransformer({
+    required this.environmentKey,
+    required this.transform,
+    required this.child,
+  });
+
+  final K environmentKey;
+  final T Function(T value) transform;
+  final Widget child;
+
+  @override
+  Widget build(BuildContext context) {
+    return environmentKey.update(
+      value: transform(environmentKey.of(context)),
+      child: child,
+    );
+  }
+}

packages/fleet/lib/src/widget_extension.dart

@@ -81,7 +81,7 @@ extension FleetWidgetExtension on Widget {
 
   /// Adds [padding] around this widget.
   @widgetFactory
-  Widget padding(EdgeInsets padding) {
+  Widget padding(EdgeInsetsGeometry padding) {
     return APadding(
       padding: padding,
       child: this,

packages/fleet/lib/src/widgets/uniform_padding.dart

@@ -0,0 +1,173 @@
+// ignore_for_file: library_private_types_in_public_api
+
+import 'package:flutter/rendering.dart';
+import 'package:flutter/widgets.dart';
+
+import '../animatable_render_object_widget.dart';
+import '../environment.dart';
+import '../parameter.dart';
+
+/// An edge of a rectangle.
+enum Edge {
+  /// The beginning edge in the reading direction.
+  start,
+
+  /// The ending edge in the reading direction.
+  end,
+
+  /// The top edge.
+  top,
+
+  /// The bottom edge.
+  bottom;
+}
+
+/// Combinations of [Edge]s.
+abstract final class Edges {
+  /// Set of all edges.
+  static const all = {Edge.top, Edge.bottom, Edge.start, Edge.end};
+
+  /// Set of all edges along the vertical axis.
+  static const vertical = {Edge.top, Edge.bottom};
+
+  /// Set of all edges along the horizontal axis.
+  static const horizontal = {Edge.start, Edge.end};
+
+  /// Set that contains only the [Edge.start] edge.
+  static const start = {Edge.start};
+
+  /// Set that contains only the [Edge.end] edge.
+  static const end = {Edge.end};
+
+  /// Set that contains only the [Edge.top] edge.
+  static const top = {Edge.top};
+
+  /// Set that contains only the [Edge.bottom] edge.
+  static const bottom = {Edge.bottom};
+}
+
+extension on Set<Edge> {
+  EdgeInsetsGeometry uniformEdgeInsets(double amount) {
+    return EdgeInsetsDirectional.only(
+      top: contains(Edge.top) ? amount : 0,
+      bottom: contains(Edge.bottom) ? amount : 0,
+      start: contains(Edge.start) ? amount : 0,
+      end: contains(Edge.end) ? amount : 0,
+    );
+  }
+}
+
+final class _DefaultUniformPaddingKey
+    extends EnvironmentKey<double, _DefaultUniformPaddingKey> {
+  const _DefaultUniformPaddingKey();
+
+  @override
+  double defaultValue(BuildContext context) => 8;
+}
+
+/// [EnvironmentKey] for the default amount of padding to use in
+/// [UniformPadding].
+///
+/// {@template fleet.defaultUniformPadding}
+/// [defaultUniformPadding] is used by [UniformPadding] to determine the amount
+/// of padding to add when [UniformPadding.amount] is `null`.
+///
+/// The default value is `8`.
+/// {@endtemplate}
+const defaultUniformPadding = _DefaultUniformPaddingKey();
+
+typedef _UniformPaddingAnimatableParameters = ({
+  AnimatableEdgeInsetsGeometry padding
+});
+
+/// Adds an equal [amount] of padding to specific [edges] around [child].
+final class UniformPadding extends SingleChildRenderObjectWidget
+    with
+        AnimatableSingleChildRenderObjectWidgetMixin<
+            _UniformPaddingAnimatableParameters> {
+  /// Creates an [UniformPadding] widget.
+  const UniformPadding({
+    super.key,
+    this.edges = Edges.all,
+    this.amount,
+    super.child,
+  });
+
+  /// The edges to add padding to.
+  final Set<Edge> edges;
+
+  /// The amount of padding to add.
+  final double? amount;
+
+  EdgeInsetsGeometry _resolvePadding(BuildContext context) =>
+      edges.uniformEdgeInsets(amount ?? defaultUniformPadding.of(context));
+
+  @override
+  RenderObject createRenderObject(BuildContext context) {
+    return RenderPadding(
+      padding: _resolvePadding(context),
+      textDirection: Directionality.of(context),
+    );
+  }
+
+  @override
+  void updateRenderObject(
+    BuildContext context,
+    covariant RenderPadding renderObject,
+  ) {
+    renderObject
+      ..padding = _resolvePadding(context)
+      ..textDirection = Directionality.of(context);
+  }
+
+  @override
+  _UniformPaddingAnimatableParameters createAnimatableParameters(
+    covariant RenderPadding renderObject,
+    AnimatableParameterHost host,
+  ) {
+    return (
+      padding: AnimatableEdgeInsetsGeometry(
+        renderObject.padding,
+        host: host,
+      )
+    );
+  }
+
+  @override
+  void updateAnimatableParameters(
+    BuildContext context,
+    _UniformPaddingAnimatableParameters parameters,
+  ) {
+    parameters.padding.value = _resolvePadding(context);
+  }
+
+  @override
+  void updateRenderObjectWithAnimatableParameters(
+    BuildContext context,
+    covariant RenderPadding renderObject,
+    _UniformPaddingAnimatableParameters parameters,
+  ) {
+    renderObject.padding = parameters.padding.animatedValue;
+  }
+}
+
+/// Extension-based API for [UniformPadding].
+extension UniformPaddingModifiers on Widget {
+  /// Sets the [defaultUniformPadding] to [amount] for this widget and its
+  /// descendants.
+  ///
+  /// {@macro fleet.defaultUniformPadding}
+  @widgetFactory
+  Widget defaultUniformPadding(double amount) =>
+      const _DefaultUniformPaddingKey().update(value: amount, child: this);
+
+  /// Adds an equal [amount] of padding to specific [edges] of this widget.
+  @widgetFactory
+  Widget uniformPadding([Set<Edge> edges = Edges.all, double? amount]) {
+    return UniformPadding(
+      edges: edges,
+      amount: amount,
+      child: this,
+    );
+  }
+}