Add a PhysicalShape widget and a render object for it. (#13682)

This CL also refactors common logic for RenderPhysicalModel and
RenderPhysicalShape into a base class _RenderPhysicalModelBase.

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

@@ -642,6 +642,9 @@ class ClipPath extends SingleChildRenderObjectWidget {
 /// Physical layers cast shadows based on an [elevation] which is nominally in
 /// logical pixels, coming vertically out of the rendering surface.
 ///
+/// For shapes that cannot be expressed as a rectangle with rounded corners use
+/// [PhysicalShape].
+///
 /// See also:
 ///
 ///  * [DecoratedBox], which can apply more arbitrary shadow effects.
@@ -717,6 +720,73 @@ class PhysicalModel extends SingleChildRenderObjectWidget {
   }
 }
 
+/// A widget representing a physical layer that clips its children to a path.
+///
+/// Physical layers cast shadows based on an [elevation] which is nominally in
+/// logical pixels, coming vertically out of the rendering surface.
+///
+/// [PhysicalModel] does the same but only supports shapes that can be expressed
+/// as rectangles with rounded corners.
+class PhysicalShape extends SingleChildRenderObjectWidget {
+  /// Creates a physical model with an arbitrary shape clip.
+  ///
+  /// The [color] is required; physical things have a color.
+  ///
+  /// The [clipper], [elevation], [color], and [shadowColor] must not be null.
+  const PhysicalShape({
+    Key key,
+    @required this.clipper,
+    this.elevation: 0.0,
+    @required this.color,
+    this.shadowColor: const Color(0xFF000000),
+    Widget child,
+  }) : assert(clipper != null),
+       assert(elevation != null),
+       assert(color != null),
+       assert(shadowColor != null),
+       super(key: key, child: child);
+
+  /// Determines which clip to use.
+  final CustomClipper<Path> clipper;
+
+  /// The z-coordinate at which to place this physical object.
+  final double elevation;
+
+  /// The background color.
+  final Color color;
+
+  /// When elevation is non zero the color to use for the shadow color.
+  final Color shadowColor;
+
+  @override
+  RenderPhysicalShape createRenderObject(BuildContext context) {
+    return new RenderPhysicalShape(
+      clipper: clipper,
+      elevation: elevation,
+      color: color,
+      shadowColor: shadowColor
+    );
+  }
+
+  @override
+  void updateRenderObject(BuildContext context, RenderPhysicalShape renderObject) {
+    renderObject
+      ..clipper = clipper
+      ..elevation = elevation
+      ..color = color
+      ..shadowColor = shadowColor;
+  }
+
+  @override
+  void debugFillProperties(DiagnosticPropertiesBuilder description) {
+    super.debugFillProperties(description);
+    description.add(new EnumProperty<CustomClipper<Path>>('clipper', clipper));
+    description.add(new DoubleProperty('elevation', elevation));
+    description.add(new DiagnosticsProperty<Color>('color', color));
+    description.add(new DiagnosticsProperty<Color>('shadowColor', shadowColor));
+  }
+}
+
 // POSITIONING AND SIZING NODES
 
 /// A widget that applies a transformation before painting its child.

packages/flutter/test/rendering/proxy_box_test.dart

@@ -91,4 +91,47 @@ void main() {
     expect(config.getActionHandler(SemanticsAction.scrollLeft), isNotNull);
     expect(config.getActionHandler(SemanticsAction.scrollRight), isNull);
   });
+
+  group('RenderPhysicalShape', () {
+    setUp(() {
+      debugDefaultTargetPlatformOverride = TargetPlatform.iOS;
+    });
+
+    test('shape change triggers repaint', () {
+      final RenderPhysicalShape root = new RenderPhysicalShape(
+        color: const Color(0xffff00ff),
+        clipper: const ShapeBorderClipper(shapeBorder: const CircleBorder()),
+      );
+      layout(root, phase: EnginePhase.composite);
+      expect(root.debugNeedsPaint, isFalse);
+
+      // Same shape, no repaint.
+      root.clipper = const ShapeBorderClipper(shapeBorder: const CircleBorder());
+      expect(root.debugNeedsPaint, isFalse);
+
+      // Different shape triggers repaint.
+      root.clipper = const ShapeBorderClipper(shapeBorder: const StadiumBorder());
+      expect(root.debugNeedsPaint, isTrue);
+    });
+
+    test('compositing on non-Fuchsia', () {
+      final RenderPhysicalShape root = new RenderPhysicalShape(
+        color: const Color(0xffff00ff),
+        clipper: const ShapeBorderClipper(shapeBorder: const CircleBorder()),
+      );
+      layout(root, phase: EnginePhase.composite);
+      expect(root.needsCompositing, isFalse);
+
+      // On non-Fuchsia platforms, Flutter draws its own shadows.
+      root.elevation = 1.0;
+      pumpFrame(phase: EnginePhase.composite);
+      expect(root.needsCompositing, isFalse);
+
+      root.elevation = 0.0;
+      pumpFrame(phase: EnginePhase.composite);
+      expect(root.needsCompositing, isFalse);
+
+      debugDefaultTargetPlatformOverride = null;
+    });
+  });
 }

packages/flutter/test/widgets/basic_test.dart

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter/rendering.dart';
+
+
+void main() {
+  group('PhysicalShape', () {
+    testWidgets('properties', (WidgetTester tester) async {
+      await tester.pumpWidget(
+        const PhysicalShape(
+          clipper: const ShapeBorderClipper(shapeBorder: const CircleBorder()),
+          elevation: 2.0,
+          color: const Color(0xFF0000FF),
+          shadowColor: const Color(0xFF00FF00),
+        )
+      );
+      final RenderPhysicalShape renderObject = tester.renderObject(find.byType(PhysicalShape));
+      expect(renderObject.clipper, const ShapeBorderClipper(shapeBorder: const CircleBorder()));
+      expect(renderObject.color, const Color(0xFF0000FF));
+      expect(renderObject.shadowColor, const Color(0xFF00FF00));
+      expect(renderObject.elevation, 2.0);
+    });
+
+    testWidgets('hit test', (WidgetTester tester) async {
+      await tester.pumpWidget(
+        new PhysicalShape(
+          clipper: const ShapeBorderClipper(shapeBorder: const CircleBorder()),
+          elevation: 2.0,
+          color: const Color(0xFF0000FF),
+          shadowColor: const Color(0xFF00FF00),
+          child: new Container(color: const Color(0xFF0000FF)),
+        )
+      );
+
+      final RenderPhysicalShape renderPhysicalShape =
+        tester.renderObject(find.byType(PhysicalShape));
+
+      // The viewport is 800x600, the CircleBorder is centered and fits
+      // the shortest edge, so we get a circle of radius 300, centered at
+      // (400, 300).
+      //
+      // We test by sampling a few points around the left-most point of the
+      // circle (100, 300).
+
+      expect(tester.hitTestOnBinding(const Offset(99.0, 300.0)), doesNotHit(renderPhysicalShape));
+      expect(tester.hitTestOnBinding(const Offset(100.0, 300.0)), hits(renderPhysicalShape));
+      expect(tester.hitTestOnBinding(const Offset(100.0, 299.0)), doesNotHit(renderPhysicalShape));
+      expect(tester.hitTestOnBinding(const Offset(100.0, 301.0)), doesNotHit(renderPhysicalShape));
+    });
+
+  });
+
+}
+
+HitsRenderBox hits(RenderBox renderBox) => new HitsRenderBox(renderBox);
+
+class HitsRenderBox extends Matcher {
+  const HitsRenderBox(this.renderBox);
+
+  final RenderBox renderBox;
+
+  @override
+  Description describe(Description description) =>
+    description.add('hit test result contains ').addDescriptionOf(renderBox);
+
+  @override
+  bool matches(dynamic item, Map<dynamic, dynamic> matchState) {
+    final HitTestResult hitTestResult = item;
+    return hitTestResult.path.where(
+      (HitTestEntry entry) => entry.target == renderBox
+    ).isNotEmpty;
+  }
+}
+
+DoesNotHitRenderBox doesNotHit(RenderBox renderBox) => new DoesNotHitRenderBox(renderBox);
+
+class DoesNotHitRenderBox extends Matcher {
+  const DoesNotHitRenderBox(this.renderBox);
+
+  final RenderBox renderBox;
+
+  @override
+  Description describe(Description description) =>
+    description.add('hit test result doesn\'t contain ').addDescriptionOf(renderBox);
+
+  @override
+  bool matches(dynamic item, Map<dynamic, dynamic> matchState) {
+    final HitTestResult hitTestResult = item;
+    return hitTestResult.path.where(
+      (HitTestEntry entry) => entry.target == renderBox
+    ).isEmpty;
+  }
+}