Refactor CheckedModeBanner into something more reusable.

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

@@ -9,9 +9,9 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 
 import 'asset_vendor.dart';
+import 'banner.dart';
 import 'basic.dart';
 import 'binding.dart';
-import 'checked_mode_banner.dart';
 import 'framework.dart';
 import 'locale_query.dart';
 import 'media_query.dart';

packages/flutter/lib/src/widgets/checked_mode_banner.dart → packages/flutter/lib/src/widgets/banner.dart

@@ -7,16 +7,25 @@ import 'dart:math' as math;
 import 'basic.dart';
 import 'framework.dart';
 
-class _CheckedModeBannerPainter extends CustomPainter {
-  const _CheckedModeBannerPainter();
+enum BannerLocation { topRight, topLeft, bottomRight, bottomLeft }
+
+class BannerPainter extends CustomPainter {
+  const BannerPainter({
+    this.message,
+    this.location
+  });
+
+  final String message;
+  final BannerLocation location;
 
   static const Color kColor = const Color(0xA0B71C1C);
-  static const double kOffset = 40.0; // distance to bottom of banner, at a 45 degree angle inwards from the top right corner
+  static const double kOffset = 40.0; // distance to bottom of banner, at a 45 degree angle inwards
   static const double kHeight = 12.0; // height of banner
+  static const double kBottomOffset = kOffset + 0.707 * kHeight; // offset plus sqrt(2)/2 * banner height
   static const Offset kTextAlign = const Offset(0.0, -3.0); // offset to move text up
   static const double kFontSize = kHeight * 0.85;
   static const double kShadowBlur = 4.0; // shadow blur sigma
-  static final Rect kRect = new Rect.fromLTWH(-kOffset, kOffset-kHeight, kOffset * 2.0, kHeight);
+  static final Rect kRect = new Rect.fromLTWH(-kOffset, kOffset - kHeight, kOffset * 2.0, kHeight);
   static const TextStyle kTextStyles = const TextStyle(
     color: const Color(0xFFFFFFFF),
     fontSize: kFontSize,
@@ -24,12 +33,6 @@ class _CheckedModeBannerPainter extends CustomPainter {
     textAlign: TextAlign.center
   );
 
-  static final TextPainter textPainter = new TextPainter()
-    ..text = new TextSpan(style: kTextStyles, text: 'SLOW MODE')
-    ..maxWidth = kOffset * 2.0
-    ..maxHeight = kHeight
-    ..layout();
-
   @override
   void paint(Canvas canvas, Size size) {
     final Paint paintShadow = new Paint()
@@ -38,21 +41,84 @@ class _CheckedModeBannerPainter extends CustomPainter {
     final Paint paintBanner = new Paint()
       ..color = kColor;
     canvas
-     ..translate(size.width, 0.0)
-     ..rotate(math.PI/4)
-     ..drawRect(kRect, paintShadow)
-     ..drawRect(kRect, paintBanner);
+      ..translate(_translationX(size.width), _translationY(size.height))
+      ..rotate(_rotation)
+      ..drawRect(kRect, paintShadow)
+      ..drawRect(kRect, paintBanner);
+
+    final TextPainter textPainter = new TextPainter()
+      ..text = new TextSpan(style: kTextStyles, text: message)
+      ..maxWidth = kOffset * 2.0
+      ..maxHeight = kHeight
+      ..layout();
+
     textPainter.paint(canvas, kRect.topLeft.toOffset() + kTextAlign);
   }
 
   @override
-  bool shouldRepaint(_CheckedModeBannerPainter oldPainter) => false;
+  bool shouldRepaint(BannerPainter oldPainter) => false;
 
   @override
   bool hitTest(Point position) => false;
+
+  double _translationX(double width) {
+    switch (location) {
+      case BannerLocation.bottomRight:
+        return width - kBottomOffset;
+      case BannerLocation.topRight:
+        return width;
+      case BannerLocation.bottomLeft:
+        return kBottomOffset;
+      case BannerLocation.topLeft:
+        return 0.0;
+    }
+  }
+
+  double _translationY(double height) {
+    switch (location) {
+      case BannerLocation.bottomRight:
+      case BannerLocation.bottomLeft:
+        return height - kBottomOffset;
+      case BannerLocation.topRight:
+      case BannerLocation.topLeft:
+        return 0.0;
+    }
+  }
+
+  double get _rotation {
+    switch (location) {
+      case BannerLocation.bottomLeft:
+      case BannerLocation.topRight:
+        return math.PI / 4.0;
+      case BannerLocation.bottomRight:
+      case BannerLocation.topLeft:
+        return -math.PI / 4.0;
+    }
+  }
+}
+
+class Banner extends StatelessWidget {
+  Banner({
+    Key key,
+    this.child,
+    this.message,
+    this.location
+  }) : super(key: key);
+
+  final Widget child;
+  final String message;
+  final BannerLocation location;
+
+  @override
+  Widget build(BuildContext context) {
+    return new CustomPaint(
+      foregroundPainter: new BannerPainter(message: message, location: location),
+      child: child
+    );
+  }
 }
 
-/// Displays a banner saying "CHECKED" when running in checked mode.
+/// Displays a banner saying "SLOW MODE" when running in checked mode.
 /// Does nothing in release mode.
 class CheckedModeBanner extends StatelessWidget {
   CheckedModeBanner({
@@ -60,17 +126,16 @@ class CheckedModeBanner extends StatelessWidget {
     this.child
   }) : super(key: key);
 
-  /// The widget below this widget in the tree.
   final Widget child;
 
   @override
   Widget build(BuildContext context) {
     Widget result = child;
     assert(() {
-      result = new CustomPaint(
-        foregroundPainter: const _CheckedModeBannerPainter(),
-        child: result
-      );
+      result = new Banner(
+        child: result,
+        message: 'SLOW MODE',
+        location: BannerLocation.topRight);
       return true;
     });
     return result;

packages/flutter/lib/widgets.dart

@@ -8,9 +8,9 @@ library widgets;
 export 'src/widgets/app.dart';
 export 'src/widgets/asset_vendor.dart';
 export 'src/widgets/auto_layout.dart';
+export 'src/widgets/banner.dart';
 export 'src/widgets/basic.dart';
 export 'src/widgets/binding.dart';
-export 'src/widgets/checked_mode_banner.dart';
 export 'src/widgets/child_view.dart';
 export 'src/widgets/dismissable.dart';
 export 'src/widgets/drag_target.dart';

packages/flutter/test/widget/banner_test.dart

+// Copyright 2015 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 'dart:math' as math;
+
+import 'package:flutter/widgets.dart';
+import 'package:test/test.dart';
+
+class TestCanvas implements Canvas {
+  final List<Invocation> invocations = <Invocation>[];
+
+  @override
+  void noSuchMethod(Invocation invocation) {
+    invocations.add(invocation);
+  }
+}
+
+void main() {
+  test('A Banner with a location of topLeft paints in the top left', () {
+    BannerPainter bannerPainter = new BannerPainter(
+      message:"foo",
+      location: BannerLocation.topLeft
+    );
+
+    TestCanvas canvas = new TestCanvas();
+
+    bannerPainter.paint(canvas, new Size(1000.0, 1000.0));
+
+    Invocation translateCommand = canvas.invocations.firstWhere((Invocation invocation) {
+      return invocation.memberName == #translate;
+    });
+
+    expect(translateCommand, isNotNull);
+    expect(translateCommand.positionalArguments[0], lessThan(100.0));
+    expect(translateCommand.positionalArguments[1], lessThan(100.0));
+
+    Invocation rotateCommand = canvas.invocations.firstWhere((Invocation invocation) {
+      return invocation.memberName == #rotate;
+    });
+
+    expect(rotateCommand, isNotNull);
+    expect(rotateCommand.positionalArguments[0], equals(-math.PI / 4.0));
+  });
+
+  test('A Banner with a location of topRight paints in the top right', () {
+    BannerPainter bannerPainter = new BannerPainter(
+      message:"foo",
+      location: BannerLocation.topRight
+    );
+
+    TestCanvas canvas = new TestCanvas();
+
+    bannerPainter.paint(canvas, new Size(1000.0, 1000.0));
+
+    Invocation translateCommand = canvas.invocations.firstWhere((Invocation invocation) {
+      return invocation.memberName == #translate;
+    });
+
+    expect(translateCommand, isNotNull);
+    expect(translateCommand.positionalArguments[0], greaterThan(900.0));
+    expect(translateCommand.positionalArguments[1], lessThan(100.0));
+
+    Invocation rotateCommand = canvas.invocations.firstWhere((Invocation invocation) {
+      return invocation.memberName == #rotate;
+    });
+
+    expect(rotateCommand, isNotNull);
+    expect(rotateCommand.positionalArguments[0], equals(math.PI / 4.0));
+  });
+
+  test('A Banner with a location of bottomLeft paints in the bottom left', () {
+    BannerPainter bannerPainter = new BannerPainter(
+      message:"foo",
+      location: BannerLocation.bottomLeft
+    );
+
+    TestCanvas canvas = new TestCanvas();
+
+    bannerPainter.paint(canvas, new Size(1000.0, 1000.0));
+
+    Invocation translateCommand = canvas.invocations.firstWhere((Invocation invocation) {
+      return invocation.memberName == #translate;
+    });
+
+    expect(translateCommand, isNotNull);
+    expect(translateCommand.positionalArguments[0], lessThan(100.0));
+    expect(translateCommand.positionalArguments[1], greaterThan(900.0));
+
+    Invocation rotateCommand = canvas.invocations.firstWhere((Invocation invocation) {
+      return invocation.memberName == #rotate;
+    });
+
+    expect(rotateCommand, isNotNull);
+    expect(rotateCommand.positionalArguments[0], equals(math.PI / 4.0));
+  });
+
+  test('A Banner with a location of bottomRight paints in the bottom right', () {
+    BannerPainter bannerPainter = new BannerPainter(
+      message:"foo",
+      location: BannerLocation.bottomRight
+    );
+
+    TestCanvas canvas = new TestCanvas();
+
+    bannerPainter.paint(canvas, new Size(1000.0, 1000.0));
+
+    Invocation translateCommand = canvas.invocations.firstWhere((Invocation invocation) {
+      return invocation.memberName == #translate;
+    });
+
+    expect(translateCommand, isNotNull);
+    expect(translateCommand.positionalArguments[0], greaterThan(900.0));
+    expect(translateCommand.positionalArguments[1], greaterThan(900.0));
+
+    Invocation rotateCommand = canvas.invocations.firstWhere((Invocation invocation) {
+      return invocation.memberName == #rotate;
+    });
+
+    expect(rotateCommand, isNotNull);
+    expect(rotateCommand.positionalArguments[0], equals(-math.PI / 4.0));
+  });
+}