Render the Material widget with the physical model layer (#8471)

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.
@@ -205,6 +204,7 @@ class _MaterialState extends State<Material> with TickerProviderStateMixin {
   @override
   Widget build(BuildContext context) {
     Color backgroundColor = _getBackgroundColor(context);
+    assert(backgroundColor != null || config.type == MaterialType.transparency);
     Widget contents = config.child;
     BorderRadius radius = config.borderRadius ?? kMaterialEdges[config.type];
     if (contents != null) {
@@ -228,20 +228,36 @@ class _MaterialState extends State<Material> with TickerProviderStateMixin {
       )
     );
     if (config.type == MaterialType.circle) {
-      contents = new ClipOval(child: contents);
+      contents = new PhysicalModel(
-    } else if (kMaterialEdges[config.type] != null) {
+        shape: BoxShape.circle,
+        elevation: config.elevation,
+        color: backgroundColor,
+        child: contents,
+      );
+    } else if (config.type == MaterialType.transparency) {
+      if (radius == null) {
+        contents = new ClipRect(child: contents);
+      } else {
         contents = new ClipRRect(
           borderRadius: radius,
           child: contents
         );
       }
+    } else {
+      contents = new PhysicalModel(
+        shape: BoxShape.rectangle,
+        borderRadius: radius ?? BorderRadius.zero,
+        elevation: config.elevation,
+        color: backgroundColor,
+        child: contents,
+      );
+    }
     if (config.type != MaterialType.transparency) {
       contents = new AnimatedContainer(
         curve: Curves.fastOutSlowIn,
         duration: kThemeChangeDuration,
         decoration: new BoxDecoration(
           borderRadius: radius,
-          boxShadow: config.elevation == 0 ? null : kElevationToShadow[config.elevation],
           shape: config.type == MaterialType.circle ? BoxShape.circle : BoxShape.rectangle
         ),
         child: new Container(

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

@@ -521,3 +521,45 @@ class BackdropFilterLayer extends ContainerLayer {
     builder.pop();
   }
 }
+
+class PhysicalModelLayer extends ContainerLayer {
+  /// Creates a layer with a rounded-rectangular clip.
+  ///
+  /// The [clipRRect] property must be non-null before the compositing phase of
+  /// the pipeline.
+  PhysicalModelLayer({
+    @required this.clipRRect,
+    @required this.elevation,
+    @required this.color,
+  }) {
+    assert(clipRRect != null);
+    assert(elevation != null);
+    assert(color != null);
+  }
+
+  /// The rounded-rect to clip in the parent's coordinate system
+  RRect clipRRect;
+
+  /// The z-coordinate at which to place this physical object.
+  int elevation;
+
+  /// The background color.
+  Color color;
+
+  @override
+  void addToScene(ui.SceneBuilder builder, Offset layerOffset) {
+    builder.pushPhysicalModel(
+      rrect: clipRRect.shift(layerOffset),
+      elevation: elevation,
+      color: color,
+    );
+    addChildrenToScene(builder, layerOffset);
+    builder.pop();
+  }
+
+  @override
+  void debugFillDescription(List<String> description) {
+    super.debugFillDescription(description);
+    description.add('clipRRect: $clipRRect');
+  }
+}

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

@@ -429,6 +429,33 @@ class PaintingContext {
     painter(childContext, offset);
     childContext._stopRecordingIfNeeded();
   }
+
+  /// Clip using a physical model layer.
+  ///
+  /// * `offset` is the offset from the origin of the canvas' coordinate system
+  ///   to the origin of the caller's coordinate system.
+  /// * `bounds` is the region of the canvas (in the caller's coodinate system)
+  ///   into which `painter` will paint in.
+  /// * `clipRRect` is the rounded-rectangle (in the caller's coodinate system)
+  ///   to use to clip the painting done by `painter`.
+  /// * `elevation` is the z-coordinate at which to place this material.
+  /// * `color` is the background color.
+  /// * `painter` is a callback that will paint with the `clipRRect` applied. This
+  ///   function calls the `painter` synchronously.
+  void pushPhysicalModel(Offset offset, Rect bounds, RRect clipRRect, int elevation, Color color, PaintingContextCallback painter) {
+    final Rect offsetBounds = bounds.shift(offset);
+    final RRect offsetClipRRect = clipRRect.shift(offset);
+    _stopRecordingIfNeeded();
+    final PhysicalModelLayer physicalModel = new PhysicalModelLayer(
+      clipRRect: offsetClipRRect,
+      elevation: elevation,
+      color: color,
+    );
+    _appendLayer(physicalModel);
+    final PaintingContext childContext = new PaintingContext._(physicalModel, offsetBounds);
+    painter(childContext, offset);
+    childContext._stopRecordingIfNeeded();
+  }
 }
 
 /// An abstract set of layout constraints.

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

@@ -1181,6 +1181,108 @@ class RenderClipPath extends _RenderCustomClip<Path> {
   }
 }
 
+/// Creates a physical model layer that clips its children to a rounded
+/// rectangle.
+class RenderPhysicalModel extends _RenderCustomClip<RRect> {
+  /// Creates a rounded-rectangular clip.
+  ///
+  /// The [borderRadius] defaults to [BorderRadius.zero], i.e. a rectangle with
+  /// right-angled corners.
+  RenderPhysicalModel({
+    RenderBox child,
+    BoxShape shape,
+    BorderRadius borderRadius: BorderRadius.zero,
+    int elevation,
+    Color color,
+  }) : _shape = shape,
+       _borderRadius = borderRadius,
+       _elevation = elevation,
+       _color = color,
+       super(child: child) {
+    if (shape == BoxShape.rectangle)
+      assert(_borderRadius != null);
+  }
+
+  @override
+  bool get alwaysNeedsCompositing => true;
+
+  /// The shape of the layer.
+  BoxShape get shape => _shape;
+  BoxShape _shape;
+  set shape (BoxShape value) {
+    assert(value != null);
+    if (_shape == value)
+      return;
+    _shape = value;
+    _markNeedsClip();
+  }
+
+  /// The border radius of the rounded corners.
+  ///
+  /// Values are clamped so that horizontal and vertical radii sums do not
+  /// exceed width/height.
+  BorderRadius get borderRadius => _borderRadius;
+  BorderRadius _borderRadius;
+  set borderRadius (BorderRadius value) {
+    assert(value != null);
+    if (_borderRadius == value)
+      return;
+    _borderRadius = value;
+    _markNeedsClip();
+  }
+
+  /// The z-coordinate at which to place this material.
+  int get elevation => _elevation;
+  int _elevation;
+  set elevation (int value) {
+    assert(value != null);
+    if (_elevation == value)
+      return;
+    _elevation = value;
+    markNeedsPaint();
+  }
+
+  /// The background color.
+  Color get color => _color;
+  Color _color;
+  set color (Color value) {
+    assert(value != null);
+    if (_color == value)
+      return;
+    _color = value;
+    markNeedsPaint();
+  }
+
+  @override
+  RRect get _defaultClip {
+    if (_shape == BoxShape.rectangle) {
+      return _borderRadius.toRRect(Point.origin & size);
+    } else {
+      Rect rect = Point.origin & size;
+      return new RRect.fromRectXY(rect, rect.width / 2, rect.height / 2);
+    }
+  }
+
+  @override
+  bool hitTest(HitTestResult result, { Point position }) {
+    if (_clipper != null) {
+      _updateClip();
+      assert(_clip != null);
+      if (!_clip.contains(position))
+        return false;
+    }
+    return super.hitTest(result, position: position);
+  }
+
+  @override
+  void paint(PaintingContext context, Offset offset) {
+    if (child != null) {
+      _updateClip();
+      context.pushPhysicalModel(offset, _clip.outerRect, _clip, _elevation, _color, super.paint);
+    }
+  }
+}
+
 /// Where to paint a box decoration.
 enum DecorationPosition {
   /// Paint the box decoration behind the children.

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

@@ -398,6 +398,51 @@ class ClipPath extends SingleChildRenderObjectWidget {
   }
 }
 
+/// A widget representing a physical layer that clips its children to a shape.
+class PhysicalModel extends SingleChildRenderObjectWidget {
+  /// Creates a physical model with a rounded-rectangular clip.
+  PhysicalModel({
+    Key key,
+    @required this.shape,
+    this.borderRadius: BorderRadius.zero,
+    @required this.elevation,
+    @required this.color,
+    Widget child,
+  }) : super(key: key, child: child) {
+    if (shape == BoxShape.rectangle)
+      assert(borderRadius != null);
+    assert(shape != null);
+    assert(elevation != null);
+    assert(color != null);
+  }
+
+  /// The type of shape.
+  final BoxShape shape;
+
+  /// The border radius of the rounded corners.
+  ///
+  /// Values are clamped so that horizontal and vertical radii sums do not
+  /// exceed width/height.
+  final BorderRadius borderRadius;
+
+  /// The z-coordinate at which to place this physical object.
+  final int elevation;
+
+  /// The background color.
+  final Color color;
+
+  @override
+  RenderPhysicalModel createRenderObject(BuildContext context) => new RenderPhysicalModel(shape: shape, borderRadius: borderRadius, elevation: elevation, color: color);
+
+  @override
+  void updateRenderObject(BuildContext context, RenderPhysicalModel renderObject) {
+    renderObject
+      ..shape = shape
+      ..borderRadius = borderRadius
+      ..elevation = elevation
+      ..color = color;
+  }
+}
 
 // POSITIONING AND SIZING NODES