Enable physical model shadows (with animation) and change elevation to a double (#9756)

Fixes https://github.com/flutter/flutter/issues/9342

dev/benchmarks/complex_layout/lib/main.dart

@@ -66,7 +66,7 @@ class TileScrollLayout extends StatelessWidget {
           return new Padding(
             padding:const EdgeInsets.all(5.0),
             child: new Material(
-              elevation: index % 5 + 1,
+              elevation: (index % 5 + 1).toDouble(),
               color: Colors.white,
               child: new IconBar(),
             ),

examples/flutter_gallery/lib/demo/calculator/home.dart

@@ -116,7 +116,7 @@ class _CalculatorState extends State<Calculator> {
     return new Scaffold(
       appBar: new AppBar(
         backgroundColor: Theme.of(context).canvasColor,
-        elevation: 0
+        elevation: 0.0
       ),
       body: new Column(
         crossAxisAlignment: CrossAxisAlignment.stretch,

examples/flutter_gallery/lib/demo/colors_demo.dart

@@ -127,7 +127,7 @@ class ColorsDemo extends StatelessWidget {
       length: allPalettes.length,
       child: new Scaffold(
         appBar: new AppBar(
-          elevation: 0,
+          elevation: 0.0,
           title: const Text('Colors'),
           bottom: new TabBar(
             isScrollable: true,

examples/flutter_gallery/lib/demo/shrine/shrine_order.dart

@@ -162,7 +162,7 @@ class _Heading extends StatelessWidget {
       height: (screenSize.height - kToolbarHeight) * 1.35,
       child: new Material(
         type: MaterialType.card,
-        elevation: 0,
+        elevation: 0.0,
         child: new Padding(
           padding: const EdgeInsets.only(left: 16.0, top: 18.0, right: 16.0, bottom: 24.0),
           child: new CustomMultiChildLayout(
@@ -302,7 +302,7 @@ class _OrderPageState extends State<OrderPage> {
                   .where((Product product) => product != widget.order.product)
                   .map((Product product) {
                     return new Card(
-                      elevation: 1,
+                      elevation: 1.0,
                       child: new Image.asset(
                         product.imageAsset,
                         fit: BoxFit.contain,

examples/flutter_gallery/lib/demo/shrine/shrine_page.dart

@@ -39,10 +39,10 @@ class ShrinePage extends StatefulWidget {
 
 /// Defines the Scaffold, AppBar, etc that the demo pages have in common.
 class ShrinePageState extends State<ShrinePage> {
-  int _appBarElevation = 0;
+  double _appBarElevation = 0.0;
 
   bool _handleScrollNotification(ScrollNotification notification) {
-    final int elevation = notification.metrics.extentBefore <= 0.0 ? 0 : 1;
+    final double elevation = notification.metrics.extentBefore <= 0.0 ? 0.0 : 1.0;
     if (elevation != _appBarElevation) {
       setState(() {
         _appBarElevation = elevation;

examples/stocks/lib/stock_home.dart

@@ -193,7 +193,7 @@ class StockHomeState extends State<StockHome> {
 
   Widget buildAppBar() {
     return new AppBar(
-      elevation: 0,
+      elevation: 0.0,
       title: new Text(StockStrings.of(context).title()),
       actions: <Widget>[
         new IconButton(

packages/flutter/lib/src/material/app_bar.dart

@@ -157,7 +157,7 @@ class AppBar extends StatefulWidget implements PreferredSizeWidget {
     this.actions,
     this.flexibleSpace,
     this.bottom,
-    this.elevation: 4,
+    this.elevation: 4.0,
     this.backgroundColor,
     this.brightness,
     this.iconTheme,
@@ -236,10 +236,8 @@ class AppBar extends StatefulWidget implements PreferredSizeWidget {
 
   /// The z-coordinate at which to place this app bar.
   ///
-  /// The following elevations have defined shadows: 1, 2, 3, 4, 6, 8, 9, 12, 16, 24
-  ///
   /// Defaults to 4, the appropriate elevation for app bars.
-  final int elevation;
+  final double elevation;
 
   /// The color to use for the app bar's material. Typically this should be set
   /// along with [brightness], [iconTheme], [textTheme].
@@ -566,7 +564,7 @@ class _SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
   final List<Widget> actions;
   final Widget flexibleSpace;
   final PreferredSizeWidget bottom;
-  final int elevation;
+  final double elevation;
   final bool forceElevated;
   final Color backgroundColor;
   final Brightness brightness;
@@ -607,7 +605,7 @@ class _SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
         actions: actions,
         flexibleSpace: flexibleSpace,
         bottom: bottom,
-        elevation: forceElevated || overlapsContent || (pinned && shrinkOffset > maxExtent - minExtent) ? elevation ?? 4 : 0,
+        elevation: forceElevated || overlapsContent || (pinned && shrinkOffset > maxExtent - minExtent) ? elevation ?? 4.0 : 0.0,
         backgroundColor: backgroundColor,
         brightness: brightness,
         iconTheme: iconTheme,
@@ -774,15 +772,13 @@ class SliverAppBar extends StatefulWidget {
   /// The z-coordinate at which to place this app bar when it is above other
   /// content.
   ///
-  /// The following elevations have defined shadows: 1, 2, 3, 4, 6, 8, 9, 12, 16, 24
-  ///
   /// Defaults to 4, the appropriate elevation for app bars.
   ///
   /// If [forceElevated] is false, the elevation is ignored when the app bar has
   /// no content underneath it. For example, if the app bar is [pinned] but no
   /// content is scrolled under it, or if it scrolls with the content, then no
   /// shadow is drawn, regardless of the value of [elevation].
-  final int elevation;
+  final double elevation;
 
   /// Whether to show the shadow appropriate for the [elevation] even if the
   /// content is not scrolled under the [AppBar].

packages/flutter/lib/src/material/bottom_navigation_bar.dart

@@ -448,7 +448,7 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
       children: <Widget>[
         new Positioned.fill(
           child: new Material( // Casts shadow.
-            elevation: 8,
+            elevation: 8.0,
             color: widget.type == BottomNavigationBarType.shifting ? _backgroundColor : null
           )
         ),

packages/flutter/lib/src/material/button.dart

@@ -192,17 +192,13 @@ class MaterialButton extends StatefulWidget {
 
   /// The z-coordinate at which to place this button.
   ///
-  /// The following elevations have defined shadows: 1, 2, 3, 4, 6, 8, 9, 12, 16, 24
-  ///
   /// Defaults to 0.
-  final int elevation;
+  final double elevation;
 
   /// The z-coordinate at which to place this button when highlighted.
   ///
-  /// The following elevations have defined shadows: 1, 2, 3, 4, 6, 8, 9, 12, 16, 24
-  ///
   /// Defaults to 0.
-  final int highlightElevation;
+  final double highlightElevation;
 
   /// The smallest horizontal extent that the button will occupy.
   ///
@@ -290,7 +286,7 @@ class _MaterialButtonState extends State<MaterialButton> {
     final TextStyle style = theme.textTheme.button.copyWith(color: textColor);
     final ButtonTheme buttonTheme = ButtonTheme.of(context);
     final double height = widget.height ?? buttonTheme.height;
-    final int elevation = (_highlight ? widget.highlightElevation : widget.elevation) ?? 0;
+    final double elevation = (_highlight ? widget.highlightElevation : widget.elevation) ?? 0.0;
     final bool hasColorOrElevation = (widget.color != null || elevation > 0);
     Widget contents = IconTheme.merge(
       data: new IconThemeData(

packages/flutter/lib/src/material/card.dart

@@ -23,7 +23,7 @@ class Card extends StatelessWidget {
   const Card({
     Key key,
     this.color,
-    this.elevation: 2,
+    this.elevation: 2.0,
     this.child
   }) : super(key: key);
 
@@ -35,10 +35,8 @@ class Card extends StatelessWidget {
 
   /// The z-coordinate at which to place this card.
   ///
-  /// The following elevations have defined shadows: 1, 2, 3, 4, 6, 8, 9, 12, 16, 24
-  ///
   /// Defaults to 2, the appropriate elevation for cards.
-  final int elevation;
+  final double elevation;
 
   @override
   Widget build(BuildContext context) {

packages/flutter/lib/src/material/dialog.dart

@@ -51,7 +51,7 @@ class Dialog extends StatelessWidget {
         child: new ConstrainedBox(
           constraints: const BoxConstraints(minWidth: 280.0),
           child: new Material(
-            elevation: 24,
+            elevation: 24.0,
             color: _getColor(context),
             type: MaterialType.card,
             child: child

packages/flutter/lib/src/material/drawer.dart

@@ -68,16 +68,14 @@ class Drawer extends StatelessWidget {
   /// Typically used in the [Scaffold.drawer] property.
   const Drawer({
     Key key,
-    this.elevation: 16,
+    this.elevation: 16.0,
     this.child
   }) : super(key: key);
 
   /// The z-coordinate at which to place this drawer.
   ///
-  /// The following elevations have defined shadows: 1, 2, 3, 4, 6, 8, 9, 12, 16, 24
-  ///
   /// Defaults to 16, the appropriate elevation for drawers.
-  final int elevation;
+  final double elevation;
 
   /// The widget below this widget in the tree.
   ///

packages/flutter/lib/src/material/floating_action_button.dart

@@ -48,8 +48,8 @@ class FloatingActionButton extends StatefulWidget {
     this.tooltip,
     this.backgroundColor,
     this.heroTag,
-    this.elevation: 6,
-    this.highlightElevation: 12,
+    this.elevation: 6.0,
+    this.highlightElevation: 12.0,
     @required this.onPressed,
     this.mini: false
   }) : super(key: key);
@@ -80,18 +80,14 @@ class FloatingActionButton extends StatefulWidget {
 
   /// The z-coordinate at which to place this button.
   ///
-  /// The following elevations have defined shadows: 1, 2, 3, 4, 6, 8, 9, 12, 16, 24
-  ///
   /// Defaults to 6, the appropriate elevation for floating action buttons.
-  final int elevation;
+  final double elevation;
 
   /// The z-coordinate at which to place this button when the user is touching the button.
   ///
-  /// The following elevations have defined shadows: 1, 2, 3, 4, 6, 8, 9, 12, 16, 24
-  ///
   /// Defaults to 12, the appropriate elevation for floating action buttons
   /// while they are being touched.
-  final int highlightElevation;
+  final double highlightElevation;
 
   /// Controls the size of this button.
   ///

packages/flutter/lib/src/material/material.dart

@@ -7,7 +7,6 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
 import 'constants.dart';
-import 'shadows.dart';
 import 'theme.dart';
 
 /// Signature for the callback used by ink effects to obtain the rectangle for the effect.
@@ -113,7 +112,7 @@ class Material extends StatefulWidget {
   const Material({
     Key key,
     this.type: MaterialType.canvas,
-    this.elevation: 0,
+    this.elevation: 0.0,
     this.color,
     this.textStyle,
     this.borderRadius,
@@ -133,10 +132,8 @@ class Material extends StatefulWidget {
 
   /// The z-coordinate at which to place this material.
   ///
-  /// The following elevations have defined shadows: 1, 2, 3, 4, 6, 8, 9, 12, 16, 24
-  ///
   /// Defaults to 0.
-  final int elevation;
+  final double elevation;
 
   /// The color to paint the material.
   ///
@@ -189,9 +186,6 @@ class Material extends StatefulWidget {
 
   /// The default radius of an ink splash in logical pixels.
   static const double defaultSplashRadius = 35.0;
-
-  /// Temporary flag used to enable the PhysicalModel shadow implementation.
-  static bool debugEnablePhysicalModel = false;
 }
 
 class _MaterialState extends State<Material> with TickerProviderStateMixin {
@@ -237,12 +231,14 @@ class _MaterialState extends State<Material> with TickerProviderStateMixin {
       )
     );
 
-    if (Material.debugEnablePhysicalModel) {
     if (widget.type == MaterialType.circle) {
-        contents = new PhysicalModel(
+      contents = new AnimatedPhysicalModel(
+        curve: Curves.fastOutSlowIn,
+        duration: kThemeChangeDuration,
         shape: BoxShape.circle,
         elevation: widget.elevation,
         color: backgroundColor,
+        animateColor: false,
         child: contents,
       );
     } else if (widget.type == MaterialType.transparency) {
@@ -255,45 +251,18 @@ class _MaterialState extends State<Material> with TickerProviderStateMixin {
         );
       }
     } else {
-        contents = new PhysicalModel(
+      contents = new AnimatedPhysicalModel(
+        curve: Curves.fastOutSlowIn,
+        duration: kThemeChangeDuration,
         shape: BoxShape.rectangle,
         borderRadius: radius ?? BorderRadius.zero,
         elevation: widget.elevation,
         color: backgroundColor,
+        animateColor: false,
         child: contents,
       );
     }
-    } else {
-      if (widget.type == MaterialType.circle) {
-        contents = new ClipOval(child: contents);
-      } else if (kMaterialEdges[widget.type] != null) {
-        contents = new ClipRRect(
-          borderRadius: radius,
-          child: contents
-        );
-      }
-    }
 
-    if (widget.type != MaterialType.transparency) {
-      contents = new AnimatedContainer(
-        curve: Curves.fastOutSlowIn,
-        duration: kThemeChangeDuration,
-        decoration: new BoxDecoration(
-          borderRadius: radius,
-          boxShadow: widget.elevation == 0 || Material.debugEnablePhysicalModel ?
-              null : kElevationToShadow[widget.elevation],
-          shape: widget.type == MaterialType.circle ? BoxShape.circle : BoxShape.rectangle
-        ),
-        child: new Container(
-          decoration: new BoxDecoration(
-            borderRadius: radius,
-            color: backgroundColor,
-            shape: widget.type == MaterialType.circle ? BoxShape.circle : BoxShape.rectangle
-          ),
-          child: contents
-        )
-      );
-    }
     return contents;
   }
 }

packages/flutter/lib/src/material/popup_menu.dart

@@ -379,7 +379,7 @@ class _PopupMenuRoute<T> extends PopupRoute<T> {
   final RelativeRect position;
   final List<PopupMenuEntry<T>> items;
   final dynamic initialValue;
-  final int elevation;
+  final double elevation;
   final ThemeData theme;
 
   @override
@@ -433,15 +433,14 @@ class _PopupMenuRoute<T> extends PopupRoute<T> {
 /// a [Theme] to use for the menu.
 ///
 /// The `elevation` argument specifies the z-coordinate at which to place the
-/// menu. The following elevations have defined shadows: 1, 2, 3, 4, 6, 8, 9,
-/// 12, 16, 24. The elevation defaults to 8, the appropriate elevation for popup
+/// menu. The elevation defaults to 8, the appropriate elevation for popup
 /// menus.
 Future<T> showMenu<T>({
   @required BuildContext context,
   RelativeRect position,
   @required List<PopupMenuEntry<T>> items,
   T initialValue,
-  int elevation: 8
+  double elevation: 8.0
 }) {
   assert(context != null);
   assert(items != null && items.isNotEmpty);
@@ -481,7 +480,7 @@ class PopupMenuButton<T> extends StatefulWidget {
     this.initialValue,
     this.onSelected,
     this.tooltip: 'Show menu',
-    this.elevation: 8,
+    this.elevation: 8.0,
     this.padding: const EdgeInsets.all(8.0),
     this.child
   }) : assert(itemBuilder != null),
@@ -503,9 +502,7 @@ class PopupMenuButton<T> extends StatefulWidget {
   final String tooltip;
 
   /// The z-coordinate at which to place the menu when open.
-  ///
-  /// The following elevations have defined shadows: 1, 2, 3, 4, 6, 8, 9, 12, 16, 24
-  final int elevation;
+  final double elevation;
 
   /// Matches IconButton's 8 dps padding by default. In some cases, notably where
   /// this button appears as the trailing element of a list item, it's useful to be able

packages/flutter/lib/src/material/progress_indicator.dart

@@ -480,7 +480,7 @@ class _RefreshProgressIndicatorState extends _CircularProgressIndicatorState {
       child: new Material(
         type: MaterialType.circle,
         color: widget.backgroundColor ?? Theme.of(context).canvasColor,
-        elevation: 2,
+        elevation: 2.0,
         child: new Padding(
           padding: const EdgeInsets.all(12.0),
           child: new CustomPaint(

packages/flutter/lib/src/material/raised_button.dart

@@ -43,9 +43,9 @@ class RaisedButton extends StatelessWidget {
     this.highlightColor,
     this.splashColor,
     this.disabledColor,
-    this.elevation: 2,
-    this.highlightElevation: 8,
-    this.disabledElevation: 0,
+    this.elevation: 2.0,
+    this.highlightElevation: 8.0,
+    this.disabledElevation: 0.0,
     this.colorBrightness,
     this.child
   }) : super(key: key);
@@ -97,25 +97,19 @@ class RaisedButton extends StatelessWidget {
 
   /// The z-coordinate at which to place this button.
   ///
-  /// The following elevations have defined shadows: 1, 2, 3, 4, 6, 8, 9, 12, 16, 24
-  ///
   /// Defaults to 2, the appropriate elevation for raised buttons.
-  final int elevation;
+  final double elevation;
 
   /// The z-coordinate at which to place this button when highlighted.
   ///
-  /// The following elevations have defined shadows: 1, 2, 3, 4, 6, 8, 9, 12, 16, 24
-  ///
   /// Defaults to 8, the appropriate elevation for raised buttons while they are
   /// being touched.
-  final int highlightElevation;
+  final double highlightElevation;
 
   /// The z-coordinate at which to place this button when disabled.
   ///
-  /// The following elevations have defined shadows: 1, 2, 3, 4, 6, 8, 9, 12, 16, 24
-  ///
   /// Defaults to 0, the appropriate elevation for disabled raised buttons.
-  final int disabledElevation;
+  final double disabledElevation;
 
   /// The theme brightness to use for this button.
   ///

packages/flutter/lib/src/material/snack_bar.dart

@@ -237,7 +237,7 @@ class SnackBar extends StatelessWidget {
               Scaffold.of(context).removeCurrentSnackBar(reason: SnackBarClosedReason.swipe);
             },
             child: new Material(
-              elevation: 6,
+              elevation: 6.0,
               color: backgroundColor ?? _kSnackBackground,
               child: new Theme(
                 data: darkTheme,

packages/flutter/lib/src/material/stepper.dart

@@ -591,7 +591,7 @@ class _StepperState extends State<Stepper> with TickerProviderStateMixin {
     return new Column(
       children: <Widget>[
         new Material(
-          elevation: 2,
+          elevation: 2.0,
           child: new Container(
             margin: const EdgeInsets.symmetric(horizontal: 24.0),
             child: new Row(

packages/flutter/lib/src/material/text_selection.dart

@@ -41,7 +41,7 @@ class _TextSelectionToolbar extends StatelessWidget {
     }
 
     return new Material(
-      elevation: 1,
+      elevation: 1.0,
       child: new Container(
         height: 44.0,
         child: new Row(mainAxisSize: MainAxisSize.min, children: items)

packages/flutter/lib/src/rendering/layer.dart

@@ -645,7 +645,7 @@ class PhysicalModelLayer extends ContainerLayer {
   ///
   /// The scene must be explicitly recomposited after this property is changed
   /// (as described at [Layer]).
-  int elevation;
+  double elevation;
 
   /// The background color.
   ///
@@ -657,7 +657,7 @@ class PhysicalModelLayer extends ContainerLayer {
   void addToScene(ui.SceneBuilder builder, Offset layerOffset) {
     builder.pushPhysicalModel(
       rrect: clipRRect.shift(layerOffset),
-      elevation: elevation.toDouble(),
+      elevation: elevation,
       color: color,
     );
     addChildrenToScene(builder, layerOffset);

packages/flutter/lib/src/rendering/object.dart

@@ -456,7 +456,7 @@ class PaintingContext {
   /// * `color` is the background color.
   /// * `painter` is a callback that will paint with the `clipRRect` applied. This
   ///   function calls the `painter` synchronously.
-  void pushPhysicalModel(bool needsCompositing, Offset offset, Rect bounds, RRect clipRRect, int elevation, Color color, PaintingContextCallback painter) {
+  void pushPhysicalModel(bool needsCompositing, Offset offset, Rect bounds, RRect clipRRect, double elevation, Color color, PaintingContextCallback painter) {
     final Rect offsetBounds = bounds.shift(offset);
     final RRect offsetClipRRect = clipRRect.shift(offset);
     if (needsCompositing) {

packages/flutter/lib/src/rendering/proxy_box.dart

@@ -1198,7 +1198,7 @@ class RenderPhysicalModel extends _RenderCustomClip<RRect> {
     RenderBox child,
     BoxShape shape,
     BorderRadius borderRadius: BorderRadius.zero,
-    int elevation,
+    double elevation,
     Color color,
   }) : _shape = shape,
        _borderRadius = borderRadius,
@@ -1235,9 +1235,9 @@ class RenderPhysicalModel extends _RenderCustomClip<RRect> {
   }
 
   /// The z-coordinate at which to place this material.
-  int get elevation => _elevation;
-  int _elevation;
-  set elevation(int value) {
+  double get elevation => _elevation;
+  double _elevation;
+  set elevation(double value) {
     assert(value != null);
     if (_elevation == value)
       return;

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

@@ -472,7 +472,7 @@ class PhysicalModel extends SingleChildRenderObjectWidget {
   final BorderRadius borderRadius;
 
   /// The z-coordinate at which to place this physical object.
-  final int elevation;
+  final double elevation;
 
   /// The background color.
   final Color color;

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

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/animation.dart';
 import 'package:flutter/foundation.dart';
 import 'package:vector_math/vector_math_64.dart';
 
@@ -44,6 +45,17 @@ class EdgeInsetsTween extends Tween<EdgeInsets> {
   EdgeInsets lerp(double t) => EdgeInsets.lerp(begin, end, t);
 }
 
+/// An interpolation between two [BorderRadius]s.
+class BorderRadiusTween extends Tween<BorderRadius> {
+  /// Creates a border radius tween.
+  ///
+  /// The [begin] and [end] arguments must not be null.
+  BorderRadiusTween({ BorderRadius begin, BorderRadius end }) : super(begin: begin, end: end);
+
+  @override
+  BorderRadius lerp(double t) => BorderRadius.lerp(begin, end, t);
+}
+
 /// An interpolation between two [Matrix4]s.
 ///
 /// Currently this class works only for translations.
@@ -643,3 +655,86 @@ class _AnimatedDefaultTextStyleState extends AnimatedWidgetBaseState<AnimatedDef
     );
   }
 }
+
+/// Animated version of [PhysicalModel].
+class AnimatedPhysicalModel extends ImplicitlyAnimatedWidget {
+  /// Creates a widget that animates the properties of a [PhysicalModel].
+  ///
+  /// The [child], [shape], [borderRadius], [elevation], [color], [curve], and
+  /// [duration] arguments must not be null.
+  ///
+  /// Animating [color] is optional and is controlled by the [animateColor] flag.
+  const AnimatedPhysicalModel({
+    Key key,
+    @required this.child,
+    @required this.shape,
+    this.borderRadius: BorderRadius.zero,
+    @required this.elevation,
+    @required this.color,
+    this.animateColor: true,
+    Curve curve: Curves.linear,
+    @required Duration duration,
+  }) : assert(child != null),
+       assert(shape != null),
+       assert(borderRadius != null),
+       assert(elevation != null),
+       assert(color != null),
+       super(key: key, curve: curve, duration: duration);
+
+  /// The widget below this widget in the tree.
+  final Widget child;
+
+  /// The type of shape.
+  ///
+  /// This property is not animated.
+  final BoxShape shape;
+
+  /// The target border radius of the rounded corners for a rectangle shape.
+  final BorderRadius borderRadius;
+
+  /// The target z-coordinate at which to place this physical object.
+  final double elevation;
+
+  /// The target background color.
+  final Color color;
+
+  /// Whether the color should be animated.
+  final bool animateColor;
+
+  @override
+  _AnimatedPhysicalModelState createState() => new _AnimatedPhysicalModelState();
+
+  @override
+  void debugFillDescription(List<String> description) {
+    super.debugFillDescription(description);
+    description.add('shape: $shape');
+    description.add('borderRadius: $borderRadius');
+    description.add('elevation: $elevation');
+    description.add('color: $color');
+    description.add('animateColor: $animateColor');
+  }
+}
+
+class _AnimatedPhysicalModelState extends AnimatedWidgetBaseState<AnimatedPhysicalModel> {
+  BorderRadiusTween _borderRadius;
+  Tween<double> _elevation;
+  ColorTween _color;
+
+  @override
+  void forEachTween(TweenVisitor<dynamic> visitor) {
+    _borderRadius = visitor(_borderRadius, widget.borderRadius, (dynamic value) => new BorderRadiusTween(begin: value));
+    _elevation = visitor(_elevation, widget.elevation, (dynamic value) => new Tween<double>(begin: value));
+    _color = visitor(_color, widget.color, (dynamic value) => new ColorTween(begin: value));
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return new PhysicalModel(
+      child: widget.child,
+      shape: widget.shape,
+      borderRadius: _borderRadius.evaluate(animation),
+      elevation: _elevation.evaluate(animation),
+      color: widget.animateColor ? _color.evaluate(animation) : widget.color,
+    );
+  }
+}

packages/flutter/test/material/material_test.dart

@@ -14,7 +14,7 @@ class NotifyMaterial extends StatelessWidget {
   }
 }
 
-Widget buildMaterial(int elevation) {
+Widget buildMaterial(double elevation) {
   return new Center(
     child: new SizedBox(
       height: 100.0,
@@ -27,10 +27,8 @@ Widget buildMaterial(int elevation) {
   );
 }
 
-List<BoxShadow> getShadow(WidgetTester tester) {
-  final RenderDecoratedBox box = tester.renderObject(find.byType(DecoratedBox).first);
-  final BoxDecoration decoration = box.decoration;
-  return decoration.boxShadow;
+RenderPhysicalModel getShadow(WidgetTester tester) {
+  return tester.renderObject(find.byType(PhysicalModel));
 }
 
 class PaintRecorder extends CustomPainter {
@@ -115,67 +113,27 @@ void main() {
   });
 
   testWidgets('Shadows animate smoothly', (WidgetTester tester) async {
-    await tester.pumpWidget(buildMaterial(0));
-    final List<BoxShadow> shadowA = getShadow(tester);
+    // This code verifies that the PhysicalModel's elevation animates over
+    // a kThemeChangeDuration time interval.
 
-    await tester.pumpWidget(buildMaterial(9));
-    final List<BoxShadow> shadowB = getShadow(tester);
+    await tester.pumpWidget(buildMaterial(0.0));
+    final RenderPhysicalModel modelA = getShadow(tester);
+    expect(modelA.elevation, equals(0.0));
+
+    await tester.pumpWidget(buildMaterial(9.0));
+    final RenderPhysicalModel modelB = getShadow(tester);
+    expect(modelB.elevation, equals(0.0));
 
     await tester.pump(const Duration(milliseconds: 1));
-    final List<BoxShadow> shadowC = getShadow(tester);
+    final RenderPhysicalModel modelC = getShadow(tester);
+    expect(modelC.elevation, closeTo(0.0, 0.001));
 
     await tester.pump(kThemeChangeDuration ~/ 2);
-    final List<BoxShadow> shadowD = getShadow(tester);
+    final RenderPhysicalModel modelD = getShadow(tester);
+    expect(modelD.elevation, isNot(closeTo(0.0, 0.001)));
 
     await tester.pump(kThemeChangeDuration);
-    final List<BoxShadow> shadowE = getShadow(tester);
-
-    // This code verifies the following:
-    //  1. When the elevation is zero, there's no shadow.
-    //  2. When the elevation isn't zero, there's three shadows.
-    //  3. When the elevation changes from 0 to 9, one millisecond later, the
-    //     shadows are still more or less indistinguishable from zero.
-    //  4. Have a kThemeChangeDuration later, they are distinguishable form
-    //     zero.
-    //  5. ...but still distinguishable from the actual 9 elevation.
-    //  6. After kThemeChangeDuration, the shadows are exactly the elevation 9
-    //     shadows.
-    // The point being to verify that the shadows animate, and do so
-    // continually, not in discrete increments (e.g. not jumping from elevation
-    // 0 to 1 to 2 to 3 and so forth).
-
-    // TODO(ianh): Port this test when we turn the physical model back on.
-
-    // 1
-    expect(shadowA, isNull);
-    expect(shadowB, isNull);
-    // 2
-    expect(shadowC, hasLength(3));
-    // 3
-    expect(shadowC[0].offset.dy, closeTo(0.0, 0.001));
-    expect(shadowC[1].offset.dy, closeTo(0.0, 0.001));
-    expect(shadowC[2].offset.dy, closeTo(0.0, 0.001));
-    expect(shadowC[0].blurRadius, closeTo(0.0, 0.001));
-    expect(shadowC[1].blurRadius, closeTo(0.0, 0.001));
-    expect(shadowC[2].blurRadius, closeTo(0.0, 0.001));
-    expect(shadowC[0].spreadRadius, closeTo(0.0, 0.001));
-    expect(shadowC[1].spreadRadius, closeTo(0.0, 0.001));
-    expect(shadowC[2].spreadRadius, closeTo(0.0, 0.001));
-    // 4
-    expect(shadowD[0].offset.dy, isNot(closeTo(0.0, 0.001)));
-    expect(shadowD[1].offset.dy, isNot(closeTo(0.0, 0.001)));
-    expect(shadowD[2].offset.dy, isNot(closeTo(0.0, 0.001)));
-    expect(shadowD[0].blurRadius, isNot(closeTo(0.0, 0.001)));
-    expect(shadowD[1].blurRadius, isNot(closeTo(0.0, 0.001)));
-    expect(shadowD[2].blurRadius, isNot(closeTo(0.0, 0.001)));
-    expect(shadowD[0].spreadRadius, isNot(closeTo(0.0, 0.001)));
-    expect(shadowD[1].spreadRadius, isNot(closeTo(0.0, 0.001)));
-    expect(shadowD[2].spreadRadius, isNot(closeTo(0.0, 0.001)));
-    // 5
-    expect(shadowD[0], isNot(shadowE[0]));
-    expect(shadowD[1], isNot(shadowE[1]));
-    expect(shadowD[2], isNot(shadowE[2]));
-    // 6
-    expect(shadowE, kElevationToShadow[9]);
+    final RenderPhysicalModel modelE = getShadow(tester);
+    expect(modelE.elevation, equals(9.0));
   });
 }

packages/flutter/test/material/mergeable_material_test.dart

@@ -51,11 +51,14 @@ void matches(BorderRadius borderRadius, RadiusType top, RadiusType bottom) {
   }
 }
 
+// Returns the border radius decoration of an item within a MergeableMaterial.
+// This depends on the exact structure of objects built by the Material and
+// MergeableMaterial widgets.
 BorderRadius getBorderRadius(WidgetTester tester, int index) {
   final List<Element> containers = tester.elementList(find.byType(Container))
                                    .toList();
 
-  final Container container = containers[index + 2].widget;
+  final Container container = containers[index].widget;
   final BoxDecoration boxDecoration = container.decoration;
 
   return boxDecoration.borderRadius;
@@ -1095,7 +1098,7 @@ void main() {
     );
 
     List<Widget> boxes = tester.widgetList(find.byType(DecoratedBox)).toList();
-    int offset = 3;
+    int offset = 1;
 
     expect(isDivider(boxes[offset], false, true), isTrue);
     expect(isDivider(boxes[offset + 1], true, true), isTrue);
@@ -1151,7 +1154,7 @@ void main() {
     await tester.pump(const Duration(milliseconds: 200));
 
     boxes = tester.widgetList(find.byType(DecoratedBox)).toList();
-    offset = 3;
+    offset = 1;
 
     expect(isDivider(boxes[offset], false, true), isTrue);
     expect(isDivider(boxes[offset + 1], true, false), isTrue);