Add Alignment, which will replace FractionalOffset (#12342)

Unlike FractionalOffset, Alignment uses the center as the zero of the
coordinate system, which makes the RTL math work out much cleaner.

Also, make FractionalOffset into a subclass of Alignment so that clients
can continue to use FractionalOffset.

packages/flutter/lib/painting.dart

@@ -17,6 +17,7 @@
 ///    painting boxes.
 library painting;
 
+export 'src/painting/alignment.dart';
 export 'src/painting/basic_types.dart';
 export 'src/painting/border_radius.dart';
 export 'src/painting/borders.dart';

packages/flutter/lib/src/cupertino/nav_bar.dart

@@ -416,7 +416,7 @@ class _CupertinoLargeTitleNavigationBarSliverDelegate extends SliverPersistentHe
               child: new OverflowBox(
                 minHeight: 0.0,
                 maxHeight: double.INFINITY,
-                alignment: FractionalOffsetDirectional.bottomStart,
+                alignment: AlignmentDirectional.bottomStart,
                 child: new Padding(
                   padding: const EdgeInsetsDirectional.only(
                     start: _kNavBarEdgePadding,

packages/flutter/lib/src/cupertino/route.dart

@@ -11,21 +11,21 @@ const double _kBackGestureWidth = 20.0;
 const double _kMinFlingVelocity = 1.0; // Screen widths per second.
 
 // Fractional offset from offscreen to the right to fully on screen.
-final FractionalOffsetTween _kRightMiddleTween = new FractionalOffsetTween(
-  begin: FractionalOffset.topRight,
-  end: FractionalOffset.topLeft,
+final AlignmentTween _kRightMiddleTween = new AlignmentTween(
+  begin: Alignment.centerRight * 2.0,
+  end: Alignment.center,
 );
 
 // Fractional offset from fully on screen to 1/3 offscreen to the left.
-final FractionalOffsetTween _kMiddleLeftTween = new FractionalOffsetTween(
-  begin: FractionalOffset.topLeft,
-  end: const FractionalOffset(-1.0/3.0, 0.0),
+final AlignmentTween _kMiddleLeftTween = new AlignmentTween(
+  begin: Alignment.center,
+  end: const Alignment(-2.0/3.0, 0.0),
 );
 
 // Fractional offset from offscreen below to fully on screen.
-final FractionalOffsetTween _kBottomUpTween = new FractionalOffsetTween(
-  begin: FractionalOffset.bottomLeft,
-  end: FractionalOffset.topLeft,
+final AlignmentTween _kBottomUpTween = new AlignmentTween(
+  begin: Alignment.bottomCenter * 2.0,
+  end: Alignment.center,
 );
 
 // Custom decoration from no shadow to page shadow mimicking iOS page
@@ -35,8 +35,8 @@ final DecorationTween _kGradientShadowTween = new DecorationTween(
   end: const _CupertinoEdgeShadowDecoration(
     edgeGradient: const LinearGradient(
       // Spans 5% of the page.
-      begin: const FractionalOffset(0.95, 0.0),
-      end: FractionalOffset.topRight,
+      begin: const Alignment(0.90, 0.0),
+      end: Alignment.centerRight,
       // Eyeballed gradient used to mimic a drop shadow on the left side only.
       colors: const <Color>[
         const Color(0x00000000),
@@ -318,9 +318,9 @@ class CupertinoPageTransition extends StatelessWidget {
       super(key: key);
 
   // When this page is coming in to cover another page.
-  final Animation<FractionalOffset> _primaryPositionAnimation;
+  final Animation<Alignment> _primaryPositionAnimation;
   // When this page is becoming covered by another page.
-  final Animation<FractionalOffset> _secondaryPositionAnimation;
+  final Animation<Alignment> _secondaryPositionAnimation;
   final Animation<Decoration> _primaryShadowAnimation;
 
   /// The widget below this widget in the tree.
@@ -361,7 +361,7 @@ class CupertinoFullscreenDialogTransition extends StatelessWidget {
        ),
        super(key: key);
 
-  final Animation<FractionalOffset> _positionAnimation;
+  final Animation<Alignment> _positionAnimation;
 
   /// The widget below this widget in the tree.
   final Widget child;
@@ -562,7 +562,7 @@ class _CupertinoEdgeShadowDecoration extends Decoration {
       const _CupertinoEdgeShadowDecoration();
 
   /// A gradient to draw to the left of the box being decorated.
-  /// FractionalOffsets are relative to the original box translated one box
+  /// Alignments are relative to the original box translated one box
   /// width to the left.
   final LinearGradient edgeGradient;
 

packages/flutter/lib/src/cupertino/tab_scaffold.dart

@@ -145,7 +145,7 @@ class _CupertinoTabScaffoldState extends State<CupertinoTabScaffold> {
 
     if (widget.tabBar != null) {
       stacked.add(new Align(
-        alignment: FractionalOffset.bottomCenter,
+        alignment: Alignment.bottomCenter,
         // Override the tab bar's currentIndex to the current tab and hook in
         // our own listener to update the _currentPage on top of a possibly user
         // provided callback.

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

@@ -448,7 +448,7 @@ class _AppBarState extends State<AppBar> {
     }
 
     appBar = new Align(
-      alignment: FractionalOffset.topCenter,
+      alignment: Alignment.topCenter,
       child: appBar,
     );
 

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

@@ -215,14 +215,14 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
     return (leftWeights + _flex(_animations[index]) / 2.0) / allWeights;
   }
 
-  FractionalOffset _circleOffset(int index) {
+  Alignment _circleOffset(int index) {
     final double iconSize = widget.iconSize;
     final Tween<double> yOffsetTween = new Tween<double>(
       begin: (18.0 + iconSize / 2.0) / kBottomNavigationBarHeight, // 18dp + icon center
       end: (6.0 + iconSize / 2.0) / kBottomNavigationBarHeight     // 6dp + icon center
     );
 
-    return new FractionalOffset(
+    return new Alignment(
       _xOffset(index),
       yOffsetTween.evaluate(_animations[index])
     );
@@ -283,10 +283,10 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
                     widget.onTap(i);
                 },
                 child: new Stack(
-                  alignment: FractionalOffset.center,
+                  alignment: Alignment.center,
                   children: <Widget>[
                     new Align(
-                      alignment: FractionalOffset.topCenter,
+                      alignment: Alignment.topCenter,
                       child: new Container(
                         margin: new EdgeInsets.only(
                           top: new Tween<double>(
@@ -304,7 +304,7 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
                       ),
                     ),
                     new Align(
-                      alignment: FractionalOffset.bottomCenter,
+                      alignment: Alignment.bottomCenter,
                       child: new Container(
                         margin: const EdgeInsets.only(bottom: 10.0),
                         child: DefaultTextStyle.merge(
@@ -319,7 +319,7 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
                                 end: 1.0,
                               ).evaluate(_animations[i]),
                             )),
-                            alignment: FractionalOffset.bottomCenter,
+                            alignment: Alignment.bottomCenter,
                             child: widget.items[i].title,
                           ),
                         ),
@@ -352,10 +352,10 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
                     widget.onTap(i);
                 },
                 child: new Stack(
-                  alignment: FractionalOffset.center,
+                  alignment: Alignment.center,
                   children: <Widget>[
                     new Align(
-                      alignment: FractionalOffset.topCenter,
+                      alignment: Alignment.topCenter,
                       child: new Container(
                         margin: new EdgeInsets.only(
                           top: new Tween<double>(
@@ -373,7 +373,7 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
                       ),
                     ),
                     new Align(
-                      alignment: FractionalOffset.bottomCenter,
+                      alignment: Alignment.bottomCenter,
                       child: new Container(
                         margin: const EdgeInsets.only(bottom: 10.0),
                         child: new FadeTransition(
@@ -465,7 +465,7 @@ class _Circle {
   AnimationController controller;
   CurvedAnimation animation;
 
-  FractionalOffset get offset {
+  Alignment get offset {
     return state._circleOffset(index);
   }
 
@@ -487,11 +487,13 @@ class _RadialPainter extends CustomPainter {
   // bounding rectangle's corners touches the egde of the circle. Drawing a
   // circle beyond this radius is futile since there is no perceivable
   // difference within the cropped rectangle.
-  double _maxRadius(FractionalOffset offset, Size size) {
-    final double dx = offset.dx;
-    final double dy = offset.dy;
-    final double x = (dx > 0.5 ? dx : 1.0 - dx) * size.width;
-    final double y = (dy > 0.5 ? dy : 1.0 - dy) * size.height;
+  double _maxRadius(Alignment alignment, Size size) {
+    final double dx = alignment.x;
+    final double dy = alignment.y;
+    final double halfWidth = size.width / 2.0;
+    final double halfHeight = size.height / 2.0;
+    final double x = halfWidth + dx.abs() * halfWidth;
+    final double y = halfHeight + dy.abs() * halfHeight;
     return math.sqrt(x * x + y * y);
   }
 
@@ -517,20 +519,22 @@ class _RadialPainter extends CustomPainter {
     for (_Circle circle in circles) {
       final Tween<double> radiusTween = new Tween<double>(
         begin: 0.0,
-        end: _maxRadius(circle.offset, size)
+        end: _maxRadius(circle.offset, size),
       );
       final Paint paint = new Paint()..color = circle.color;
       final Rect rect = new Rect.fromLTWH(0.0, 0.0, size.width, size.height);
       canvas.clipRect(rect);
       final double navWidth = math.min(bottomNavMaxWidth, size.width);
+      final double halfNavWidth = navWidth / 2.0;
+      final double halfHeight = size.height / 2.0;
       final Offset center = new Offset(
-        (size.width - navWidth) / 2.0 + circle.offset.dx * navWidth,
-        circle.offset.dy * size.height
+        (size.width - navWidth) / 2.0 + halfNavWidth + circle.offset.x * halfNavWidth,
+        halfHeight + circle.offset.y * halfHeight,
       );
       canvas.drawCircle(
         center,
         radiusTween.lerp(circle.animation.value),
-        paint
+        paint,
       );
     }
   }

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

@@ -408,7 +408,7 @@ class DataTable extends StatelessWidget {
     label = new Container(
       padding: padding,
       height: _kHeadingRowHeight,
-      alignment: numeric ? FractionalOffset.centerRight : FractionalOffsetDirectional.centerStart,
+      alignment: numeric ? Alignment.centerRight : AlignmentDirectional.centerStart,
       child: new AnimatedDefaultTextStyle(
         style: new TextStyle(
           // TODO(ianh): font family should be Roboto; see https://github.com/flutter/flutter/issues/3116
@@ -460,7 +460,7 @@ class DataTable extends StatelessWidget {
     label = new Container(
       padding: padding,
       height: _kDataRowHeight,
-      alignment: numeric ? FractionalOffset.centerRight : FractionalOffsetDirectional.centerStart,
+      alignment: numeric ? Alignment.centerRight : AlignmentDirectional.centerStart,
       child: new DefaultTextStyle(
         style: new TextStyle(
           // TODO(ianh): font family should be Roboto; see https://github.com/flutter/flutter/issues/3116
@@ -774,7 +774,7 @@ class _SortArrowState extends State<_SortArrow> with TickerProviderStateMixin {
       child: new Transform(
         transform: new Matrix4.rotationZ(_orientationOffset + _orientationAnimation.value)
                              ..setTranslationRaw(0.0, _kArrowIconBaselineOffset, 0.0),
-        alignment: FractionalOffset.center,
+        alignment: Alignment.center,
         child: new Icon(
           Icons.arrow_downward,
           size: _kArrowIconSize,

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

@@ -267,7 +267,7 @@ class DrawerControllerState extends State<DrawerController> with SingleTickerPro
   Widget _buildDrawer(BuildContext context) {
     if (_controller.status == AnimationStatus.dismissed) {
       return new Align(
-        alignment: FractionalOffsetDirectional.centerStart,
+        alignment: AlignmentDirectional.centerStart,
         child: new GestureDetector(
           key: _gestureDetectorKey,
           onHorizontalDragUpdate: _move,
@@ -299,9 +299,9 @@ class DrawerControllerState extends State<DrawerController> with SingleTickerPro
                 ),
               ),
               new Align(
-                alignment: FractionalOffsetDirectional.centerStart,
+                alignment: AlignmentDirectional.centerStart,
                 child: new Align(
-                  alignment: FractionalOffsetDirectional.centerEnd,
+                  alignment: AlignmentDirectional.centerEnd,
                   widthFactor: _controller.value,
                   child: new RepaintBoundary(
                     child: new FocusScope(

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

@@ -361,7 +361,7 @@ class DropdownMenuItem<T> extends StatelessWidget {
   Widget build(BuildContext context) {
     return new Container(
       height: _kMenuItemHeight,
-      alignment: FractionalOffset.centerLeft,
+      alignment: Alignment.centerLeft,
       child: child,
     );
   }
@@ -589,7 +589,7 @@ class _DropdownButtonState<T> extends State<DropdownButton<T>> with WidgetsBindi
             // the hint or nothing at all.
             new IndexedStack(
               index: _selectedIndex ?? hintIndex,
-              alignment: FractionalOffset.centerLeft,
+              alignment: Alignment.centerLeft,
               children: items,
             ),
             new Icon(Icons.arrow_drop_down,

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

@@ -92,16 +92,16 @@ class _FlexibleSpaceBarState extends State<FlexibleSpaceBar> {
     return null;
   }
 
-  FractionalOffset _getTitleAlignment(bool effectiveCenterTitle) {
+  Alignment _getTitleAlignment(bool effectiveCenterTitle) {
     if (effectiveCenterTitle)
-      return FractionalOffset.bottomCenter;
+      return Alignment.bottomCenter;
     final TextDirection textDirection = Directionality.of(context);
     assert(textDirection != null);
     switch (textDirection) {
       case TextDirection.rtl:
-        return FractionalOffset.bottomRight;
+        return Alignment.bottomRight;
       case TextDirection.ltr:
-        return FractionalOffset.bottomLeft;
+        return Alignment.bottomLeft;
     }
     return null;
   }
@@ -152,7 +152,7 @@ class _FlexibleSpaceBarState extends State<FlexibleSpaceBar> {
         final double scaleValue = new Tween<double>(begin: 1.5, end: 1.0).lerp(t);
         final Matrix4 scaleTransform = new Matrix4.identity()
           ..scale(scaleValue, scaleValue, 1.0);
-        final FractionalOffset titleAlignment = _getTitleAlignment(effectiveCenterTitle);
+        final Alignment titleAlignment = _getTitleAlignment(effectiveCenterTitle);
         children.add(new Container(
           padding: new EdgeInsetsDirectional.only(
             start: effectiveCenterTitle ? 0.0 : 72.0,

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

@@ -73,7 +73,7 @@ class IconButton extends StatelessWidget {
     Key key,
     this.iconSize: 24.0,
     this.padding: const EdgeInsets.all(8.0),
-    this.alignment: FractionalOffset.center,
+    this.alignment: Alignment.center,
     @required this.icon,
     this.color,
     this.highlightColor,
@@ -107,8 +107,8 @@ class IconButton extends StatelessWidget {
 
   /// Defines how the icon is positioned within the IconButton.
   ///
-  /// This property must not be null. It defaults to [FractionalOffset.center].
-  final FractionalOffsetGeometry alignment;
+  /// This property must not be null. It defaults to [Alignment.center].
+  final AlignmentGeometry alignment;
 
   /// The icon to display inside the button.
   ///

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

@@ -397,7 +397,7 @@ class ListTile extends StatelessWidget {
         child: new Container(
           margin: const EdgeInsetsDirectional.only(end: 16.0),
           width: 40.0,
-          alignment: FractionalOffsetDirectional.centerStart,
+          alignment: AlignmentDirectional.centerStart,
           child: leading,
         ),
       ));
@@ -432,7 +432,7 @@ class ListTile extends StatelessWidget {
         data: iconThemeData,
         child: new Container(
           margin: const EdgeInsetsDirectional.only(start: 16.0),
-          alignment: FractionalOffsetDirectional.centerEnd,
+          alignment: AlignmentDirectional.centerEnd,
           child: trailing,
         ),
       ));

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

@@ -9,9 +9,9 @@ import 'package:flutter/widgets.dart';
 import 'theme.dart';
 
 // Fractional offset from 1/4 screen below the top to fully on screen.
-final FractionalOffsetTween _kBottomUpTween = new FractionalOffsetTween(
-  begin: FractionalOffset.bottomLeft,
-  end: FractionalOffset.topLeft
+final AlignmentTween _kBottomUpTween = new AlignmentTween(
+  begin: Alignment.bottomCenter * 0.5,
+  end: Alignment.center
 );
 
 // Used for Android and Fuchsia.
@@ -26,7 +26,7 @@ class _MountainViewPageTransition extends StatelessWidget {
        )),
        super(key: key);
 
-  final Animation<FractionalOffset> _positionAnimation;
+  final Animation<Alignment> _positionAnimation;
   final Widget child;
 
   @override

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

@@ -447,7 +447,7 @@ class _PopupMenu<T> extends StatelessWidget {
             type: MaterialType.card,
             elevation: route.elevation,
             child: new Align(
-              alignment: FractionalOffset.topRight,
+              alignment: Alignment.topRight,
               widthFactor: width.evaluate(route.animation),
               heightFactor: height.evaluate(route.animation),
               child: child,

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

@@ -384,15 +384,15 @@ class RefreshIndicatorState extends State<RefreshIndicator> with TickerProviderS
           left: 0.0,
           right: 0.0,
           child: new SizeTransition(
-            axisAlignment: _isIndicatorAtTop ? 1.0 : 0.0,
+            axisAlignment: _isIndicatorAtTop ? 1.0 : -1.0,
             sizeFactor: _positionFactor, // this is what brings it down
             child: new Container(
               padding: _isIndicatorAtTop
                 ? new EdgeInsets.only(top: widget.displacement)
                 : new EdgeInsets.only(bottom: widget.displacement),
               alignment: _isIndicatorAtTop
-                ? FractionalOffset.topCenter
-                : FractionalOffset.bottomCenter,
+                ? Alignment.topCenter
+                : Alignment.bottomCenter,
               child: new ScaleTransition(
                 scale: _scaleFactor,
                 child: new AnimatedBuilder(

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

@@ -898,7 +898,7 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
         bottomSheets.add(_currentBottomSheet._widget);
       final Widget stack = new Stack(
         children: bottomSheets,
-        alignment: FractionalOffset.bottomCenter,
+        alignment: Alignment.bottomCenter,
       );
       _addIfNonNull(
         children,
@@ -1053,7 +1053,7 @@ class _PersistentBottomSheetState extends State<_PersistentBottomSheet> {
       animation: widget.animationController,
       builder: (BuildContext context, Widget child) {
         return new Align(
-          alignment: FractionalOffsetDirectional.topStart,
+          alignment: AlignmentDirectional.topStart,
           heightFactor: widget.animationController.value,
           child: child
         );

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

@@ -82,7 +82,7 @@ class SnackBarAction extends StatefulWidget {
   const SnackBarAction({
     Key key,
     @required this.label,
-    @required this.onPressed
+    @required this.onPressed,
   }) : assert(label != null),
        assert(onPressed != null),
        super(key: key);
@@ -117,7 +117,7 @@ class _SnackBarActionState extends State<SnackBarAction> {
   Widget build(BuildContext context) {
     return new FlatButton(
       onPressed: _haveTriggeredAction ? null : _handlePressed,
-      child: new Text(widget.label)
+      child: new Text(widget.label),
     );
   }
 }
@@ -192,7 +192,7 @@ class SnackBar extends StatelessWidget {
     final ThemeData darkTheme = new ThemeData(
       brightness: Brightness.dark,
       accentColor: theme.accentColor,
-      accentColorBrightness: theme.accentColorBrightness
+      accentColorBrightness: theme.accentColorBrightness,
     );
     final List<Widget> children = <Widget>[
       const SizedBox(width: _kSnackBarPadding),
@@ -202,15 +202,15 @@ class SnackBar extends StatelessWidget {
           child: new DefaultTextStyle(
             style: darkTheme.textTheme.subhead,
             child: content,
-          )
-        )
-      )
+          ),
+        ),
+      ),
     ];
     if (action != null) {
       children.add(new ButtonTheme.bar(
         padding: const EdgeInsets.symmetric(horizontal: _kSnackBarPadding),
         textTheme: ButtonTextTheme.accent,
-        child: action
+        child: action,
       ));
     } else {
       children.add(const SizedBox(width: _kSnackBarPadding));
@@ -222,9 +222,9 @@ class SnackBar extends StatelessWidget {
         animation: heightAnimation,
         builder: (BuildContext context, Widget child) {
           return new Align(
-            alignment: FractionalOffsetDirectional.topStart,
+            alignment: AlignmentDirectional.topStart,
             heightFactor: heightAnimation.value,
-            child: child
+            child: child,
           );
         },
         child: new Semantics(
@@ -245,14 +245,14 @@ class SnackBar extends StatelessWidget {
                   opacity: fadeAnimation,
                   child: new Row(
                     children: children,
-                    crossAxisAlignment: CrossAxisAlignment.center
-                  )
-                )
-              )
-            )
-          )
-        )
-      )
+                    crossAxisAlignment: CrossAxisAlignment.center,
+                  ),
+                ),
+              ),
+            ),
+          ),
+        ),
+      ),
     );
   }
 
@@ -278,7 +278,7 @@ class SnackBar extends StatelessWidget {
       backgroundColor: backgroundColor,
       action: action,
       duration: duration,
-      animation: newAnimation
+      animation: newAnimation,
     );
   }
 }

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

@@ -297,7 +297,7 @@ class _StepperState extends State<Stepper> with TickerProviderStateMixin {
               color: _isDark() ? _kErrorDark : _kErrorLight,
             ),
             child: new Align(
-              alignment: const FractionalOffset(0.5, 0.9), // 0.9 looks better than the geometrical 0.66.
+              alignment: const Alignment(0.0, 0.8), // 0.8 looks better than the geometrical 0.33.
               child: _buildCircleChild(index, oldState && widget.steps[index].state != StepState.error),
             ),
           ),

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

@@ -70,7 +70,7 @@ class _AccountDetails extends StatelessWidget {
   Widget addDropdownIcon(Widget line) {
     final Widget icon = new Expanded(
       child: new Align(
-        alignment: FractionalOffsetDirectional.centerEnd,
+        alignment: AlignmentDirectional.centerEnd,
         child: new Icon(
           isOpen ? Icons.arrow_drop_up : Icons.arrow_drop_down,
           color: Colors.white

packages/flutter/lib/src/painting/box_fit.dart

@@ -98,9 +98,9 @@ class FittedSizes {
 /// This method does not express an opinion regarding the alignment of the
 /// source and destination sizes within the input and output rectangles.
 /// Typically they are centered (this is what [BoxDecoration] does, for
-/// instance, and is how [BoxFit] is defined). The [FractionalOffset] class
-/// provides a convenience function, [FractionalOffset.inscribe], for resolving
-/// the sizes to rects, as shown in the example below.
+/// instance, and is how [BoxFit] is defined). The [Alignment] class provides a
+/// convenience function, [Alignment.inscribe], for resolving the sizes to
+/// rects, as shown in the example below.
 ///
 /// ## Sample code
 ///
@@ -112,8 +112,8 @@ class FittedSizes {
 /// void paintImage(ui.Image image, Rect outputRect, Canvas canvas, Paint paint, BoxFit fit) {
 ///   final Size imageSize = new Size(image.width.toDouble(), image.height.toDouble());
 ///   final FittedSizes sizes = applyBoxFit(fit, imageSize, outputRect.size);
-///   final Rect inputSubrect = FractionalOffset.center.inscribe(sizes.source, Offset.zero & imageSize);
-///   final Rect outputSubrect = FractionalOffset.center.inscribe(sizes.destination, outputRect);
+///   final Rect inputSubrect = Alignment.center.inscribe(sizes.source, Offset.zero & imageSize);
+///   final Rect outputSubrect = Alignment.center.inscribe(sizes.destination, outputRect);
 ///   canvas.drawImageRect(image, inputSubrect, outputSubrect, paint);
 /// }
 /// ```

packages/flutter/lib/src/painting/flutter_logo.dart

@@ -9,11 +9,11 @@ import 'dart:ui' as ui show Gradient, TextBox, lerpDouble;
 import 'package:flutter/services.dart';
 import 'package:flutter/foundation.dart';
 
+import 'alignment.dart';
 import 'basic_types.dart';
 import 'box_fit.dart';
 import 'decoration.dart';
 import 'edge_insets.dart';
-import 'fractional_offset.dart';
 import 'text_painter.dart';
 import 'text_span.dart';
 import 'text_style.dart';
@@ -397,7 +397,7 @@ class _FlutterLogoPainter extends BoxPainter {
     }
     final FittedSizes fittedSize = applyBoxFit(BoxFit.contain, logoSize, canvasSize);
     assert(fittedSize.source == logoSize);
-    final Rect rect = FractionalOffset.center.inscribe(fittedSize.destination, offset & canvasSize);
+    final Rect rect = Alignment.center.inscribe(fittedSize.destination, offset & canvasSize);
     final double centerSquareHeight = canvasSize.shortestSide;
     final Rect centerSquare = new Rect.fromLTWH(
       offset.dx + (canvasSize.width - centerSquareHeight) / 2.0,

packages/flutter/lib/src/painting/gradient.dart

@@ -6,8 +6,8 @@ import 'dart:ui' as ui show Gradient, lerpDouble;
 
 import 'package:flutter/foundation.dart';
 
+import 'alignment.dart';
 import 'basic_types.dart';
-import 'fractional_offset.dart';
 
 /// A 2D gradient.
 ///
@@ -27,7 +27,7 @@ abstract class Gradient {
   /// Creates a [Shader] for this gradient to fill the given rect.
   ///
   /// If the gradient's configuration is text-direction-dependent, for example
-  /// it uses [FractionalOffsetDirectional] objects instead of [FractionalOffset]
+  /// it uses [AlignmentDirectional] objects instead of [Alignment]
   /// objects, then the `textDirection` argument must not be null.
   Shader createShader(Rect rect, { TextDirection textDirection });
 }
@@ -64,8 +64,8 @@ abstract class Gradient {
 /// new Container(
 ///   decoration: new BoxDecoration(
 ///     gradient: new LinearGradient(
-///       begin: FractionalOffset.topLeft,
-///       end: new FractionalOffset(0.1, 0.0), // 10% of the width, so there are ten blinds.
+///       begin: Alignment.topLeft,
+///       end: new Alignment(0.8, 0.0), // 10% of the width, so there are ten blinds.
 ///       colors: [const Color(0xFFFFFFEE), const Color(0xFF999999)], // whitish to gray
 ///       tileMode: TileMode.repeated, // repeats the gradient over the canvas
 ///     ),
@@ -85,8 +85,8 @@ class LinearGradient extends Gradient {
   /// The [colors] argument must not be null. If [stops] is non-null, it must
   /// have the same length as [colors].
   const LinearGradient({
-    this.begin: FractionalOffset.centerLeft,
-    this.end: FractionalOffset.centerRight,
+    this.begin: Alignment.centerLeft,
+    this.end: Alignment.centerRight,
     @required this.colors,
     this.stops,
     this.tileMode: TileMode.clamp,
@@ -97,35 +97,33 @@ class LinearGradient extends Gradient {
 
   /// The offset at which stop 0.0 of the gradient is placed.
   ///
-  /// If this is a [FractionalOffset], then it is expressed as a vector from
-  /// coordinate (0.0,0.0), in a coordinate space that maps the top left of the
-  /// paint box at (0.0,0.0) and the bottom right at (1.0,1.0).
+  /// If this is a [Alignment], then it is expressed as a vector from
+  /// coordinate (0.0, 0.0), in a coordinate space that maps the center of the
+  /// paint box at (0.0, 0.0) and the bottom right at (1.0, 1.0).
   ///
-  /// For example, a begin offset of (0.0,0.5) is half way down the
+  /// For example, a begin offset of (-1.0, 0.0) is half way down the
   /// left side of the box.
   ///
-  /// It can also be a [FractionalOffsetDirectional], in which case it is
-  /// expressed as a vector from the top start corner, where the start is the
+  /// It can also be a [AlignmentDirectional], where the start is the
   /// left in left-to-right contexts and the right in right-to-left contexts. If
   /// a text-direction-dependent value is provided here, then the [createShader]
   /// method will need to be given a [TextDirection].
-  final FractionalOffsetGeometry begin;
+  final AlignmentGeometry begin;
 
   /// The offset at which stop 1.0 of the gradient is placed.
   ///
-  /// If this is a [FractionalOffset], then it is expressed as a vector from
-  /// coordinate (0.0,0.0), in a coordinate space that maps the top left of the
-  /// paint box at (0.0,0.0) and the bottom right at (1.0,1.0).
+  /// If this is a [Alignment], then it is expressed as a vector from
+  /// coordinate (0.0, 0.0), in a coordinate space that maps the center of the
+  /// paint box at (0.0, 0.0) and the bottom right at (1.0, 1.0).
   ///
-  /// For example, a begin offset of (1.0,0.5) is half way down the
+  /// For example, a begin offset of (1.0, 0.0) is half way down the
   /// right side of the box.
   ///
-  /// It can also be a [FractionalOffsetDirectional], in which case it is
-  /// expressed as a vector from the top start corner, where the start is the
-  /// left in left-to-right contexts and the right in right-to-left contexts. If
-  /// a text-direction-dependent value is provided here, then the [createShader]
+  /// It can also be a [AlignmentDirectional], where the start is the left in
+  /// left-to-right contexts and the right in right-to-left contexts. If a
+  /// text-direction-dependent value is provided here, then the [createShader]
   /// method will need to be given a [TextDirection].
-  final FractionalOffsetGeometry end;
+  final AlignmentGeometry end;
 
   /// The colors the gradient should obtain at each of the stops.
   ///
@@ -215,8 +213,8 @@ class LinearGradient extends Gradient {
       interpolatedStops = a.stops ?? b.stops;
     }
     return new LinearGradient(
-      begin: FractionalOffsetGeometry.lerp(a.begin, b.begin, t),
-      end: FractionalOffsetGeometry.lerp(a.end, b.end, t),
+      begin: AlignmentGeometry.lerp(a.begin, b.begin, t),
+      end: AlignmentGeometry.lerp(a.end, b.end, t),
       colors: interpolatedColors,
       stops: interpolatedStops,
       tileMode: t < 0.5 ? a.tileMode : b.tileMode,
@@ -295,7 +293,7 @@ class LinearGradient extends Gradient {
 /// ```dart
 /// void paintSky(Canvas canvas, Rect rect) {
 ///   var gradient = new RadialGradient(
-///     center: const FractionalOffset(0.7, 0.2), // near the top right
+///     center: const Alignment(0.7, -0.6), // near the top right
 ///     radius: 0.2,
 ///     colors: [
 ///       const Color(0xFFFFFF00), // yellow sun
@@ -324,7 +322,7 @@ class RadialGradient extends Gradient {
   /// The [colors] argument must not be null. If [stops] is non-null, it must
   /// have the same length as [colors].
   const RadialGradient({
-    this.center: FractionalOffset.center,
+    this.center: Alignment.center,
     this.radius: 0.5,
     @required this.colors,
     this.stops,
@@ -334,22 +332,21 @@ class RadialGradient extends Gradient {
        assert(colors != null),
        assert(tileMode != null);
 
-  /// The center of the gradient, as an offset into the unit square
-  /// describing the gradient which will be mapped onto the paint box.
+  /// The center of the gradient, as an offset into the (-1.0, -1.0) x (1.0, 1.0)
+  /// square describing the gradient which will be mapped onto the paint box.
   ///
-  /// For example, an offset of (0.5,0.5) will place the radial
+  /// For example, an alignment of (0.0, 0.0) will place the radial
   /// gradient in the center of the box.
   ///
-  /// If this is a [FractionalOffset], then it is expressed as a vector from
-  /// coordinate (0.0,0.0), in a coordinate space that maps the top left of the
-  /// paint box at (0.0,0.0) and the bottom right at (1.0,1.0).
+  /// If this is a [Alignment], then it is expressed as a vector from
+  /// coordinate (0.0, 0.0), in a coordinate space that maps the center of the
+  /// paint box at (0.0, 0.0) and the bottom right at (1.0, 1.0).
   ///
-  /// It can also be a [FractionalOffsetDirectional], in which case it is
-  /// expressed as a vector from the top start corner, where the start is the
-  /// left in left-to-right contexts and the right in right-to-left contexts. If
-  /// a text-direction-dependent value is provided here, then the [createShader]
+  /// It can also be a [AlignmentDirectional], where the start is the left in
+  /// left-to-right contexts and the right in right-to-left contexts. If a
+  /// text-direction-dependent value is provided here, then the [createShader]
   /// method will need to be given a [TextDirection].
-  final FractionalOffsetGeometry center;
+  final AlignmentGeometry center;
 
   /// The radius of the gradient, as a fraction of the shortest side
   /// of the paint box.

packages/flutter/lib/src/painting/images.dart

@@ -7,10 +7,10 @@ import 'dart:ui' as ui show Image;
 import 'package:flutter/foundation.dart';
 import 'package:flutter/services.dart';
 
+import 'alignment.dart';
 import 'basic_types.dart';
 import 'borders.dart';
 import 'box_fit.dart';
-import 'fractional_offset.dart';
 
 /// How to paint any portions of a box not covered by an image.
 enum ImageRepeat {
@@ -41,7 +41,7 @@ class DecorationImage {
     @required this.image,
     this.colorFilter,
     this.fit,
-    this.alignment: FractionalOffset.center,
+    this.alignment: Alignment.center,
     this.centerSlice,
     this.repeat: ImageRepeat.noRepeat,
     this.matchTextDirection: false,
@@ -70,22 +70,22 @@ class DecorationImage {
   /// How to align the image within its bounds.
   ///
   /// The alignment aligns the given position in the image to the given position
-  /// in the layout bounds. For example, a [FractionalOffset] alignment of (0.0,
-  /// 0.0) aligns the image to the top-left corner of its layout bounds, while a
-  /// [FractionalOffset] alignment of (1.0, 1.0) aligns the bottom right of the
+  /// in the layout bounds. For example, a [Alignment] alignment of (-1.0,
+  /// -1.0) aligns the image to the top-left corner of its layout bounds, while a
+  /// [Alignment] alignment of (1.0, 1.0) aligns the bottom right of the
   /// image with the bottom right corner of its layout bounds. Similarly, an
-  /// alignment of (0.5, 1.0) aligns the bottom middle of the image with the
+  /// alignment of (0.0, 1.0) aligns the bottom middle of the image with the
   /// middle of the bottom edge of its layout bounds.
   ///
   /// To display a subpart of an image, consider using a [CustomPainter] and
   /// [Canvas.drawImageRect].
   ///
   /// If the [alignment] is [TextDirection]-dependent (i.e. if it is a
-  /// [FractionalOffsetDirectional]), then a [TextDirection] must be available
+  /// [AlignmentDirectional]), then a [TextDirection] must be available
   /// when the image is painted.
   ///
-  /// Defaults to [FractionalOffset.center].
-  final FractionalOffsetGeometry alignment;
+  /// Defaults to [Alignment.center].
+  final AlignmentGeometry alignment;
 
   /// The center slice for a nine-patch image.
   ///
@@ -180,9 +180,9 @@ class DecorationImage {
 ///
 ///  * `alignment`: How the destination rectangle defined by applying `fit` is
 ///    aligned within `rect`. For example, if `fit` is [BoxFit.contain] and
-///    `alignment` is [FractionalOffset.bottomRight], the image will be as large
+///    `alignment` is [Alignment.bottomRight], the image will be as large
 ///    as possible within `rect` and placed with its bottom right corner at the
-///    bottom right corner of `rect`. Defaults to [FractionalOffset.center].
+///    bottom right corner of `rect`. Defaults to [Alignment.center].
 ///
 ///  * `centerSlice`: The image is drawn in nine portions described by splitting
 ///    the image by drawing two horizontal lines and two vertical lines, where
@@ -219,7 +219,7 @@ void paintImage({
   @required ui.Image image,
   ColorFilter colorFilter,
   BoxFit fit,
-  FractionalOffset alignment: FractionalOffset.center,
+  Alignment alignment: Alignment.center,
   Rect centerSlice,
   ImageRepeat repeat: ImageRepeat.noRepeat,
   bool flipHorizontally: false,
@@ -268,8 +268,10 @@ void paintImage({
     // to nearest-neighbor.
     paint.filterQuality = FilterQuality.low;
   }
-  final double dx = (outputSize.width - destinationSize.width) * (flipHorizontally ? 1.0 - alignment.dx : alignment.dx);
-  final double dy = (outputSize.height - destinationSize.height) * alignment.dy;
+  final double halfWidthDelta = (outputSize.width - destinationSize.width) / 2.0;
+  final double halfHeightDelta = (outputSize.height - destinationSize.height) / 2.0;
+  final double dx = halfWidthDelta + (flipHorizontally ? -alignment.x : alignment.x) * halfWidthDelta;
+  final double dy = halfHeightDelta + alignment.y * halfHeightDelta;
   final Offset destinationPosition = rect.topLeft.translate(dx, dy);
   final Rect destinationRect = destinationPosition & destinationSize;
   final bool needSave = repeat != ImageRepeat.noRepeat || flipHorizontally;

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

@@ -72,7 +72,7 @@ class RenderAnimatedSize extends RenderAligningShiftedBox {
     @required TickerProvider vsync,
     @required Duration duration,
     Curve curve: Curves.linear,
-    FractionalOffsetGeometry alignment: FractionalOffset.center,
+    AlignmentGeometry alignment: Alignment.center,
     TextDirection textDirection,
     RenderBox child,
   }) : assert(vsync != null),

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

@@ -32,7 +32,7 @@ class RenderImage extends RenderBox {
     Color color,
     BlendMode colorBlendMode,
     BoxFit fit,
-    FractionalOffsetGeometry alignment: FractionalOffset.center,
+    AlignmentGeometry alignment: Alignment.center,
     ImageRepeat repeat: ImageRepeat.noRepeat,
     Rect centerSlice,
     bool matchTextDirection: false,
@@ -56,7 +56,7 @@ class RenderImage extends RenderBox {
     _updateColorFilter();
   }
 
-  FractionalOffset _resolvedAlignment;
+  Alignment _resolvedAlignment;
   bool _flipHorizontally;
 
   void _resolve() {
@@ -178,9 +178,9 @@ class RenderImage extends RenderBox {
   ///
   /// If this is set to a text-direction-dependent value, [textDirection] must
   /// not be null.
-  FractionalOffsetGeometry get alignment => _alignment;
-  FractionalOffsetGeometry _alignment;
-  set alignment(FractionalOffsetGeometry value) {
+  AlignmentGeometry get alignment => _alignment;
+  AlignmentGeometry _alignment;
+  set alignment(AlignmentGeometry value) {
     assert(value != null);
     if (value == _alignment)
       return;
@@ -343,7 +343,7 @@ class RenderImage extends RenderBox {
     description.add(new DiagnosticsProperty<Color>('color', color, defaultValue: null));
     description.add(new EnumProperty<BlendMode>('colorBlendMode', colorBlendMode, defaultValue: null));
     description.add(new EnumProperty<BoxFit>('fit', fit, defaultValue: null));
-    description.add(new DiagnosticsProperty<FractionalOffset>('alignment', alignment, defaultValue: null));
+    description.add(new DiagnosticsProperty<AlignmentGeometry>('alignment', alignment, defaultValue: null));
     description.add(new EnumProperty<ImageRepeat>('repeat', repeat, defaultValue: ImageRepeat.noRepeat));
     description.add(new DiagnosticsProperty<Rect>('centerSlice', centerSlice, defaultValue: null));
     description.add(new FlagProperty('matchTextDirection', value: matchTextDirection, ifTrue: 'match text direction'));

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

@@ -1599,11 +1599,10 @@ class RenderTransform extends RenderProxyBox {
   RenderTransform({
     @required Matrix4 transform,
     Offset origin,
-    FractionalOffset alignment,
+    Alignment alignment,
     this.transformHitTests: true,
     RenderBox child
   }) : assert(transform != null),
-       assert(alignment == null || (alignment.dx != null && alignment.dy != null)),
        super(child) {
     this.transform = transform;
     this.alignment = alignment;
@@ -1628,10 +1627,10 @@ class RenderTransform extends RenderProxyBox {
   ///
   /// This is equivalent to setting an origin based on the size of the box.
   /// If it is specified at the same time as an offset, both are applied.
-  FractionalOffset get alignment => _alignment;
-  FractionalOffset _alignment;
-  set alignment(FractionalOffset value) {
-    assert(value == null || (value.dx != null && value.dy != null));
+  Alignment get alignment => _alignment;
+  Alignment _alignment;
+  set alignment(Alignment value) {
+    assert(value == null || (value.x != null && value.y != null));
     if (_alignment == value)
       return;
     _alignment = value;
@@ -1751,7 +1750,7 @@ class RenderTransform extends RenderProxyBox {
     super.debugFillProperties(description);
     description.add(new TransformProperty('transform matrix', _transform));
     description.add(new DiagnosticsProperty<Offset>('origin', origin));
-    description.add(new DiagnosticsProperty<FractionalOffset>('alignment', alignment));
+    description.add(new DiagnosticsProperty<Alignment>('alignment', alignment));
     description.add(new DiagnosticsProperty<bool>('transformHitTests', transformHitTests));
   }
 }
@@ -1764,9 +1763,9 @@ class RenderFittedBox extends RenderProxyBox {
   RenderFittedBox({
     RenderBox child,
     BoxFit fit: BoxFit.contain,
-    FractionalOffset alignment: FractionalOffset.center
+    Alignment alignment: Alignment.center
   }) : assert(fit != null),
-       assert(alignment != null && alignment.dx != null && alignment.dy != null),
+       assert(alignment != null),
        _fit = fit,
        _alignment = alignment,
        super(child);
@@ -1788,10 +1787,10 @@ class RenderFittedBox extends RenderProxyBox {
   /// An alignment of (0.0, 0.0) aligns the child to the top-left corner of its
   /// parent's bounds.  An alignment of (1.0, 0.5) aligns the child to the middle
   /// of the right edge of its parent's bounds.
-  FractionalOffset get alignment => _alignment;
-  FractionalOffset _alignment;
-  set alignment(FractionalOffset value) {
-    assert(value != null && value.dx != null && value.dy != null);
+  Alignment get alignment => _alignment;
+  Alignment _alignment;
+  set alignment(Alignment value) {
+    assert(value != null && value.x != null && value.y != null);
     if (_alignment == value)
       return;
     _alignment = value;
@@ -1891,13 +1890,13 @@ class RenderFittedBox extends RenderProxyBox {
   void debugFillProperties(DiagnosticPropertiesBuilder description) {
     super.debugFillProperties(description);
     description.add(new EnumProperty<BoxFit>('fit', fit));
-    description.add(new DiagnosticsProperty<FractionalOffset>('alignment', alignment));
+    description.add(new DiagnosticsProperty<Alignment>('alignment', alignment));
   }
 }
 
 /// Applies a translation transformation before painting its child.
 ///
-/// The translation is expressed as a [FractionalOffset] relative to the
+/// The translation is expressed as a [Alignment] relative to the
 /// RenderFractionalTranslation box's size. Hit tests will only be detected
 /// inside the bounds of the RenderFractionalTranslation, even if the contents
 /// are offset such that they overflow.
@@ -1906,18 +1905,18 @@ class RenderFractionalTranslation extends RenderProxyBox {
   ///
   /// The [translation] argument must not be null.
   RenderFractionalTranslation({
-    FractionalOffset translation,
+    Alignment translation,
     this.transformHitTests: true,
     RenderBox child
-  }) : assert(translation == null || (translation.dx != null && translation.dy != null)),
+  }) : assert(translation == null || (translation.x != null && translation.y != null)),
        _translation = translation,
        super(child);
 
-  /// The translation to apply to the child, as a multiple of the size.
-  FractionalOffset get translation => _translation;
-  FractionalOffset _translation;
-  set translation(FractionalOffset value) {
-    assert(value == null || (value.dx != null && value.dy != null));
+  /// The translation to apply to the child, relative to the child's center.
+  Alignment get translation => _translation;
+  Alignment _translation;
+  set translation(Alignment value) {
+    assert(value == null || (value.x != null && value.y != null));
     if (_translation == value)
       return;
     _translation = value;
@@ -1935,27 +1934,41 @@ class RenderFractionalTranslation extends RenderProxyBox {
   @override
   bool hitTest(HitTestResult result, { Offset position }) {
     assert(!debugNeedsLayout);
-    if (transformHitTests)
-      position = new Offset(position.dx - translation.dx * size.width, position.dy - translation.dy * size.height);
+    if (transformHitTests) {
+      final double halfWidth = size.width / 2.0;
+      final double halfHeight = size.height / 2.0;
+      position = new Offset(
+        position.dx - translation.x * halfWidth,
+        position.dy - translation.y * halfHeight,
+      );
+    }
     return super.hitTest(result, position: position);
   }
 
   @override
   void paint(PaintingContext context, Offset offset) {
     assert(!debugNeedsLayout);
-    if (child != null)
-      super.paint(context, offset + translation.alongSize(size));
+    if (child != null) {
+      final double halfWidth = size.width / 2.0;
+      final double halfHeight = size.height / 2.0;
+      super.paint(context, new Offset(
+        offset.dx + translation.x * halfWidth,
+        offset.dy + translation.y * halfHeight,
+      ));
+    }
   }
 
   @override
   void applyPaintTransform(RenderBox child, Matrix4 transform) {
-    transform.translate(translation.dx * size.width, translation.dy * size.height);
+    final double halfWidth = size.width / 2.0;
+    final double halfHeight = size.height / 2.0;
+    transform.translate(translation.x * halfWidth, translation.y * halfHeight);
   }
 
   @override
   void debugFillProperties(DiagnosticPropertiesBuilder description) {
     super.debugFillProperties(description);
-    description.add(new DiagnosticsProperty<FractionalOffset>('translation', translation));
+    description.add(new DiagnosticsProperty<Alignment>('translation', translation));
     description.add(new DiagnosticsProperty<bool>('transformHitTests', transformHitTests));
   }
 }
@@ -1997,7 +2010,7 @@ class RenderFractionalTranslation extends RenderProxyBox {
 ///   void paint(Canvas canvas, Size size) {
 ///     var rect = Offset.zero & size;
 ///     var gradient = new RadialGradient(
-///       center: const FractionalOffset(0.7, 0.2),
+///       center: const Alignment(0.7, -0.6),
 ///       radius: 0.2,
 ///       colors: [const Color(0xFFFFFF00), const Color(0xFF0099FF)],
 ///       stops: [0.4, 1.0],

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

@@ -222,13 +222,13 @@ class RenderPadding extends RenderShiftedBox {
 }
 
 /// Abstract class for one-child-layout render boxes that use a
-/// [FractionalOffsetGeometry] to align their children.
+/// [AlignmentGeometry] to align their children.
 abstract class RenderAligningShiftedBox extends RenderShiftedBox {
   /// Initializes member variables for subclasses.
   ///
   /// The [alignment] argument must not be null.
   RenderAligningShiftedBox({
-    FractionalOffsetGeometry alignment: FractionalOffset.center,
+    AlignmentGeometry alignment: Alignment.center,
     TextDirection textDirection,
     RenderBox child,
   }) : assert(alignment != null),
@@ -236,7 +236,7 @@ abstract class RenderAligningShiftedBox extends RenderShiftedBox {
        _textDirection = textDirection,
        super(child);
 
-  FractionalOffset _resolvedAlignment;
+  Alignment _resolvedAlignment;
 
   void _resolve() {
     if (_resolvedAlignment != null)
@@ -252,21 +252,21 @@ abstract class RenderAligningShiftedBox extends RenderShiftedBox {
   /// How to align the child.
   ///
   /// The x and y values of the alignment control the horizontal and vertical
-  /// alignment, respectively.  An x value of 0.0 means that the left edge of
+  /// alignment, respectively. An x value of -1.0 means that the left edge of
   /// the child is aligned with the left edge of the parent whereas an x value
   /// of 1.0 means that the right edge of the child is aligned with the right
   /// edge of the parent. Other values interpolate (and extrapolate) linearly.
-  /// For example, a value of 0.5 means that the center of the child is aligned
+  /// For example, a value of 0.0 means that the center of the child is aligned
   /// with the center of the parent.
   ///
-  /// If this is set to a [FractionalOffsetDirectional] object, then
+  /// If this is set to a [AlignmentDirectional] object, then
   /// [textDirection] must not be null.
-  FractionalOffsetGeometry get alignment => _alignment;
-  FractionalOffsetGeometry _alignment;
+  AlignmentGeometry get alignment => _alignment;
+  AlignmentGeometry _alignment;
   /// Sets the alignment to a new value, and triggers a layout update.
   ///
   /// The new alignment must not be null or have any null properties.
-  set alignment(FractionalOffsetGeometry value) {
+  set alignment(AlignmentGeometry value) {
     assert(value != null);
     if (_alignment == value)
       return;
@@ -309,16 +309,16 @@ abstract class RenderAligningShiftedBox extends RenderShiftedBox {
   @override
   void debugFillProperties(DiagnosticPropertiesBuilder description) {
     super.debugFillProperties(description);
-    description.add(new DiagnosticsProperty<FractionalOffsetGeometry>('alignment', alignment));
+    description.add(new DiagnosticsProperty<AlignmentGeometry>('alignment', alignment));
     description.add(new EnumProperty<TextDirection>('textDirection', textDirection, defaultValue: null));
   }
 }
 
-/// Positions its child using a [FractionalOffset].
+/// Positions its child using a [AlignmentGeometry].
 ///
 /// For example, to align a box at the bottom right, you would pass this box a
 /// tight constraint that is bigger than the child's natural size,
-/// with an alignment of [FractionalOffset.bottomRight].
+/// with an alignment of [Alignment.bottomRight].
 ///
 /// By default, sizes to be as big as possible in both axes. If either axis is
 /// unconstrained, then in that direction it will be sized to fit the child's
@@ -330,7 +330,7 @@ class RenderPositionedBox extends RenderAligningShiftedBox {
     RenderBox child,
     double widthFactor,
     double heightFactor,
-    FractionalOffsetGeometry alignment: FractionalOffset.center,
+    AlignmentGeometry alignment: Alignment.center,
     TextDirection textDirection,
   }) : assert(widthFactor == null || widthFactor >= 0.0),
        assert(heightFactor == null || heightFactor >= 0.0),
@@ -475,7 +475,7 @@ class RenderConstrainedOverflowBox extends RenderAligningShiftedBox {
     double maxWidth,
     double minHeight,
     double maxHeight,
-    FractionalOffsetGeometry alignment: FractionalOffset.center,
+    AlignmentGeometry alignment: Alignment.center,
     TextDirection textDirection,
   }) : _minWidth = minWidth,
        _maxWidth = maxWidth,
@@ -571,7 +571,7 @@ class RenderSizedOverflowBox extends RenderAligningShiftedBox {
   RenderSizedOverflowBox({
     RenderBox child,
     @required Size requestedSize,
-    FractionalOffset alignment: FractionalOffset.center,
+    Alignment alignment: Alignment.center,
     TextDirection textDirection,
   }) : assert(requestedSize != null),
        _requestedSize = requestedSize,
@@ -643,7 +643,7 @@ class RenderFractionallySizedOverflowBox extends RenderAligningShiftedBox {
     RenderBox child,
     double widthFactor,
     double heightFactor,
-    FractionalOffset alignment: FractionalOffset.center,
+    Alignment alignment: Alignment.center,
     TextDirection textDirection,
   }) : _widthFactor = widthFactor,
        _heightFactor = heightFactor,

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

@@ -297,7 +297,7 @@ class RenderStack extends RenderBox
   /// top left corners.
   RenderStack({
     List<RenderBox> children,
-    FractionalOffsetGeometry alignment: FractionalOffsetDirectional.topStart,
+    AlignmentGeometry alignment: AlignmentDirectional.topStart,
     TextDirection textDirection,
     StackFit fit: StackFit.loose,
     Overflow overflow: Overflow.clip,
@@ -319,7 +319,7 @@ class RenderStack extends RenderBox
       child.parentData = new StackParentData();
   }
 
-  FractionalOffset _resolvedAlignment;
+  Alignment _resolvedAlignment;
 
   void _resolve() {
     if (_resolvedAlignment != null)
@@ -336,14 +336,14 @@ class RenderStack extends RenderBox
   ///
   /// The non-positioned children are placed relative to each other such that
   /// the points determined by [alignment] are co-located. For example, if the
-  /// [alignment] is [FractionalOffset.topLeft], then the top left corner of
+  /// [alignment] is [Alignment.topLeft], then the top left corner of
   /// each non-positioned child will be located at the same global coordinate.
   ///
-  /// If this is set to a [FractionalOffsetDirectional] object, then
-  /// [textDirection] must not be null.
-  FractionalOffsetGeometry get alignment => _alignment;
-  FractionalOffsetGeometry _alignment;
-  set alignment(FractionalOffsetGeometry value) {
+  /// If this is set to a [AlignmentDirectional] object, then [textDirection]
+  /// must not be null.
+  AlignmentGeometry get alignment => _alignment;
+  AlignmentGeometry _alignment;
+  set alignment(AlignmentGeometry value) {
     assert(value != null);
     if (_alignment == value)
       return;
@@ -559,7 +559,7 @@ class RenderStack extends RenderBox
   @override
   void debugFillProperties(DiagnosticPropertiesBuilder description) {
     super.debugFillProperties(description);
-    description.add(new DiagnosticsProperty<FractionalOffsetGeometry>('alignment', alignment));
+    description.add(new DiagnosticsProperty<AlignmentGeometry>('alignment', alignment));
     description.add(new EnumProperty<TextDirection>('textDirection', textDirection));
     description.add(new EnumProperty<StackFit>('fit', fit));
     description.add(new EnumProperty<Overflow>('overflow', overflow));
@@ -577,7 +577,7 @@ class RenderIndexedStack extends RenderStack {
   /// If the [index] parameter is null, nothing is displayed.
   RenderIndexedStack({
     List<RenderBox> children,
-    FractionalOffsetGeometry alignment: FractionalOffsetDirectional.topStart,
+    AlignmentGeometry alignment: AlignmentDirectional.topStart,
     TextDirection textDirection,
     int index: 0,
   }) : _index = index, super(

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

@@ -7,15 +7,14 @@ import 'package:flutter/painting.dart';
 
 /// An interpolation between two fractional offsets.
 ///
-/// This class specializes the interpolation of Tween<FractionalOffset> to be
-/// appropriate for rectangles.
+/// This class specializes the interpolation of [Tween<FractionalOffset>] to be
+/// appropriate for fractional offsets.
 ///
 /// See [Tween] for a discussion on how to use interpolation objects.
 ///
 /// See also:
 ///
-///  * [FractionalOffsetGeometryTween], which interpolates between two
-///    [FractionalOffsetGeometry] objects.
+///  * [AlignmentTween], which interpolates between to [Alignment] objects.
 class FractionalOffsetTween extends Tween<FractionalOffset> {
   /// Creates a fractional offset tween.
   ///
@@ -29,28 +28,51 @@ class FractionalOffsetTween extends Tween<FractionalOffset> {
   FractionalOffset lerp(double t) => FractionalOffset.lerp(begin, end, t);
 }
 
-/// An interpolation between two [FractionalOffsetGeometry].
+/// An interpolation between two alignments.
 ///
-/// This class specializes the interpolation of [Tween<FractionalOffsetGeometry>]
-/// to be appropriate for rectangles.
+/// This class specializes the interpolation of [Tween<Alignment>] to be
+/// appropriate for alignments.
 ///
 /// See [Tween] for a discussion on how to use interpolation objects.
 ///
 /// See also:
 ///
-///  * [FractionalOffsetTween], which interpolates between two
-///    [FractionalOffset] objects.
-class FractionalOffsetGeometryTween extends Tween<FractionalOffsetGeometry> {
+///  * [AlignmentGeometryTween], which interpolates between two
+///    [AlignmentGeometry] objects.
+class AlignmentTween extends Tween<Alignment> {
+  /// Creates a fractional offset tween.
+  ///
+  /// The [begin] and [end] properties may be null; the null value
+  /// is treated as meaning the center.
+  AlignmentTween({ Alignment begin, Alignment end })
+    : super(begin: begin, end: end);
+
+  /// Returns the value this variable has at the given animation clock value.
+  @override
+  Alignment lerp(double t) => Alignment.lerp(begin, end, t);
+}
+
+/// An interpolation between two [AlignmentGeometry].
+///
+/// This class specializes the interpolation of [Tween<AlignmentGeometry>]
+/// to be appropriate for alignments.
+///
+/// See [Tween] for a discussion on how to use interpolation objects.
+///
+/// See also:
+///
+///  * [AlignmentTween], which interpolates between two [Alignment] objects.
+class AlignmentGeometryTween extends Tween<AlignmentGeometry> {
   /// Creates a fractional offset geometry tween.
   ///
   /// The [begin] and [end] properties may be null; the null value
   /// is treated as meaning the center.
-  FractionalOffsetGeometryTween({
-    FractionalOffsetGeometry begin,
-    FractionalOffsetGeometry end,
+  AlignmentGeometryTween({
+    AlignmentGeometry begin,
+    AlignmentGeometry end,
   }) : super(begin: begin, end: end);
 
   /// Returns the value this variable has at the given animation clock value.
   @override
-  FractionalOffsetGeometry lerp(double t) => FractionalOffsetGeometry.lerp(begin, end, t);
+  AlignmentGeometry lerp(double t) => AlignmentGeometry.lerp(begin, end, t);
 }

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

@@ -115,7 +115,7 @@ class AnimatedCrossFade extends StatefulWidget {
     this.firstCurve: Curves.linear,
     this.secondCurve: Curves.linear,
     this.sizeCurve: Curves.linear,
-    this.alignment: FractionalOffset.topCenter,
+    this.alignment: Alignment.topCenter,
     @required this.crossFadeState,
     @required this.duration,
     this.layoutBuilder: defaultLayoutBuilder,
@@ -165,8 +165,8 @@ class AnimatedCrossFade extends StatefulWidget {
 
   /// How the children should be aligned while the size is animating.
   ///
-  /// Defaults to [FractionalOffset.topCenter].
-  final FractionalOffsetGeometry alignment;
+  /// Defaults to [Alignment.topCenter].
+  final AlignmentGeometry alignment;
 
   /// A builder that positions the [firstChild] and [secondChild] widgets.
   ///
@@ -218,7 +218,7 @@ class AnimatedCrossFade extends StatefulWidget {
   void debugFillProperties(DiagnosticPropertiesBuilder description) {
     super.debugFillProperties(description);
     description.add(new EnumProperty<CrossFadeState>('crossFadeState', crossFadeState));
-    description.add(new DiagnosticsProperty<FractionalOffsetGeometry>('alignment', alignment, defaultValue: FractionalOffset.topCenter));
+    description.add(new DiagnosticsProperty<AlignmentGeometry>('alignment', alignment, defaultValue: Alignment.topCenter));
   }
 }
 
@@ -356,6 +356,6 @@ class _AnimatedCrossFadeState extends State<AnimatedCrossFade> with TickerProvid
     super.debugFillProperties(description);
     description.add(new EnumProperty<CrossFadeState>('crossFadeState', widget.crossFadeState));
     description.add(new DiagnosticsProperty<AnimationController>('controller', _controller, showName: false));
-    description.add(new DiagnosticsProperty<FractionalOffsetGeometry>('alignment', widget.alignment, defaultValue: FractionalOffset.topCenter));
+    description.add(new DiagnosticsProperty<AlignmentGeometry>('alignment', widget.alignment, defaultValue: Alignment.topCenter));
   }
 }

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

@@ -18,7 +18,7 @@ class AnimatedSize extends SingleChildRenderObjectWidget {
   const AnimatedSize({
     Key key,
     Widget child,
-    this.alignment: FractionalOffset.center,
+    this.alignment: Alignment.center,
     this.curve: Curves.linear,
     @required this.duration,
     @required this.vsync,
@@ -28,13 +28,13 @@ class AnimatedSize extends SingleChildRenderObjectWidget {
   /// the same size as the child.
   ///
   /// The x and y values of the alignment control the horizontal and vertical
-  /// alignment, respectively. An x value of 0.0 means that the left edge of
+  /// alignment, respectively. An x value of -1.0 means that the left edge of
   /// the child is aligned with the left edge of the parent whereas an x value
   /// of 1.0 means that the right edge of the child is aligned with the right
   /// edge of the parent. Other values interpolate (and extrapolate) linearly.
-  /// For example, a value of 0.5 means that the center of the child is aligned
+  /// For example, a value of 0.0 means that the center of the child is aligned
   /// with the center of the parent.
-  final FractionalOffsetGeometry alignment;
+  final AlignmentGeometry alignment;
 
   /// The animation curve when transitioning this widget's size to match the
   /// child's size.

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

@@ -25,7 +25,7 @@ import 'image.dart';
 /// new DecoratedBox(
 ///   decoration: new BoxDecoration(
 ///     gradient: new RadialGradient(
-///       center: const FractionalOffset(0.25, 0.3),
+///       center: const Alignment(-0.5, -0.6),
 ///       radius: 0.15,
 ///       colors: <Color>[
 ///         const Color(0xFFEEEEEE),
@@ -207,7 +207,7 @@ class DecoratedBox extends SingleChildRenderObjectWidget {
 ///   ),
 ///   padding: const EdgeInsets.all(8.0),
 ///   color: Colors.teal.shade700,
-///   alignment: FractionalOffset.center,
+///   alignment: Alignment.center,
 ///   child: new Text('Hello World', style: Theme.of(context).textTheme.display1.copyWith(color: Colors.white)),
 ///   foregroundDecoration: new BoxDecoration(
 ///     image: new DecorationImage(
@@ -278,7 +278,7 @@ class Container extends StatelessWidget {
   /// constraints are unbounded, then the child will be shrink-wrapped instead.
   ///
   /// Ignored if [child] is null.
-  final FractionalOffsetGeometry alignment;
+  final AlignmentGeometry alignment;
 
   /// Empty space to inscribe inside the [decoration]. The [child], if any, is
   /// placed inside this padding.
@@ -362,7 +362,7 @@ class Container extends StatelessWidget {
   @override
   void debugFillProperties(DiagnosticPropertiesBuilder description) {
     super.debugFillProperties(description);
-    description.add(new DiagnosticsProperty<FractionalOffsetGeometry>('alignment', alignment, showName: false, defaultValue: null));
+    description.add(new DiagnosticsProperty<AlignmentGeometry>('alignment', alignment, showName: false, defaultValue: null));
     description.add(new DiagnosticsProperty<EdgeInsetsGeometry>('padding', padding, defaultValue: null));
     description.add(new DiagnosticsProperty<Decoration>('bg', decoration, defaultValue: null));
     description.add(new DiagnosticsProperty<Decoration>('fg', foregroundDecoration, defaultValue: null));

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

@@ -232,7 +232,7 @@ bool debugCheckHasDirectionality(BuildContext context) {
         'determines the ambient reading direction and is used, for example, to '
         'determine how to lay out text, how to interpret "start" and "end" '
         'values, and to resolve EdgeInsetsDirectional, '
-        'FractionalOffsetDirectional, and other *Directional objects.'
+        'AlignmentDirectional, and other *Directional objects.'
       );
     }
     return true;

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

@@ -135,19 +135,21 @@ class _DismissibleClipper extends CustomClipper<Rect> {
        super(reclip: moveAnimation);
 
   final Axis axis;
-  final Animation<FractionalOffset> moveAnimation;
+  final Animation<Alignment> moveAnimation;
 
   @override
   Rect getClip(Size size) {
     assert(axis != null);
     switch (axis) {
       case Axis.horizontal:
-        final double offset = moveAnimation.value.dx * size.width;
+        final double halfWidth = size.width / 2.0;
+        final double offset = halfWidth + moveAnimation.value.x * halfWidth;
         if (offset < 0)
           return new Rect.fromLTRB(size.width + offset, 0.0, size.width, size.height);
         return new Rect.fromLTRB(0.0, 0.0, offset, size.height);
       case Axis.vertical:
-        final double offset = moveAnimation.value.dy * size.height;
+        final double halfHeight = size.height / 2.0;
+        final double offset = halfHeight + moveAnimation.value.y * halfHeight;
         if (offset < 0)
           return new Rect.fromLTRB(0.0, size.height + offset, size.width, size.height);
         return new Rect.fromLTRB(0.0, 0.0, size.width, offset);
@@ -175,7 +177,7 @@ class _DismissibleState extends State<Dismissible> with TickerProviderStateMixin
   }
 
   AnimationController _moveController;
-  Animation<FractionalOffset> _moveAnimation;
+  Animation<Alignment> _moveAnimation;
 
   AnimationController _resizeController;
   Animation<double> _resizeAnimation;
@@ -268,11 +270,10 @@ class _DismissibleState extends State<Dismissible> with TickerProviderStateMixin
   }
 
   void _updateMoveAnimation() {
-    _moveAnimation = new FractionalOffsetTween(
-      begin: FractionalOffset.topLeft,
-      end: _directionIsXAxis ?
-             new FractionalOffset(_dragExtent.sign, 0.0) :
-             new FractionalOffset(0.0, _dragExtent.sign)
+    final double end = _dragExtent.sign * 2.0;
+    _moveAnimation = new AlignmentTween(
+      begin: Alignment.center,
+      end: _directionIsXAxis ? new Alignment(end, 0.0) : new Alignment(0.0, end),
     ).animate(_moveController);
   }
 

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

@@ -73,7 +73,7 @@ class FadeInImage extends StatefulWidget {
     this.width,
     this.height,
     this.fit,
-    this.alignment: FractionalOffset.center,
+    this.alignment: Alignment.center,
     this.repeat: ImageRepeat.noRepeat,
     this.matchTextDirection: false,
   }) : assert(placeholder != null),
@@ -121,7 +121,7 @@ class FadeInImage extends StatefulWidget {
     this.width,
     this.height,
     this.fit,
-    this.alignment: FractionalOffset.center,
+    this.alignment: Alignment.center,
     this.repeat: ImageRepeat.noRepeat,
     this.matchTextDirection: false,
   }) : assert(placeholder != null),
@@ -177,7 +177,7 @@ class FadeInImage extends StatefulWidget {
     this.width,
     this.height,
     this.fit,
-    this.alignment: FractionalOffset.center,
+    this.alignment: Alignment.center,
     this.repeat: ImageRepeat.noRepeat,
     this.matchTextDirection: false,
   }) : assert(placeholder != null),
@@ -239,19 +239,19 @@ class FadeInImage extends StatefulWidget {
   /// How to align the image within its bounds.
   ///
   /// The alignment aligns the given position in the image to the given position
-  /// in the layout bounds. For example, a [FractionalOffset] alignment of (0.0,
-  /// 0.0) aligns the image to the top-left corner of its layout bounds, while a
-  /// [FractionalOffset] alignment of (1.0, 1.0) aligns the bottom right of the
+  /// in the layout bounds. For example, a [Alignment] alignment of (-1.0,
+  /// -1.0) aligns the image to the top-left corner of its layout bounds, while a
+  /// [Alignment] alignment of (1.0, 1.0) aligns the bottom right of the
   /// image with the bottom right corner of its layout bounds. Similarly, an
-  /// alignment of (0.5, 1.0) aligns the bottom middle of the image with the
+  /// alignment of (0.0, 1.0) aligns the bottom middle of the image with the
   /// middle of the bottom edge of its layout bounds.
   ///
   /// If the [alignment] is [TextDirection]-dependent (i.e. if it is a
-  /// [FractionalOffsetDirectional]), then an ambient [Directionality] widget
+  /// [AlignmentDirectional]), then an ambient [Directionality] widget
   /// must be in scope.
   ///
-  /// Defaults to [FractionalOffset.center].
-  final FractionalOffsetGeometry alignment;
+  /// Defaults to [Alignment.center].
+  final AlignmentGeometry alignment;
 
   /// How to paint any portions of the layout bounds not covered by the image.
   final ImageRepeat repeat;

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

@@ -113,7 +113,7 @@ class Image extends StatefulWidget {
     this.color,
     this.colorBlendMode,
     this.fit,
-    this.alignment: FractionalOffset.center,
+    this.alignment: Alignment.center,
     this.repeat: ImageRepeat.noRepeat,
     this.centerSlice,
     this.matchTextDirection: false,
@@ -136,7 +136,7 @@ class Image extends StatefulWidget {
     this.color,
     this.colorBlendMode,
     this.fit,
-    this.alignment: FractionalOffset.center,
+    this.alignment: Alignment.center,
     this.repeat: ImageRepeat.noRepeat,
     this.centerSlice,
     this.matchTextDirection: false,
@@ -162,7 +162,7 @@ class Image extends StatefulWidget {
     this.color,
     this.colorBlendMode,
     this.fit,
-    this.alignment: FractionalOffset.center,
+    this.alignment: Alignment.center,
     this.repeat: ImageRepeat.noRepeat,
     this.centerSlice,
     this.matchTextDirection: false,
@@ -293,7 +293,7 @@ class Image extends StatefulWidget {
     this.color,
     this.colorBlendMode,
     this.fit,
-    this.alignment: FractionalOffset.center,
+    this.alignment: Alignment.center,
     this.repeat: ImageRepeat.noRepeat,
     this.centerSlice,
     this.matchTextDirection: false,
@@ -318,7 +318,7 @@ class Image extends StatefulWidget {
     this.color,
     this.colorBlendMode,
     this.fit,
-    this.alignment: FractionalOffset.center,
+    this.alignment: Alignment.center,
     this.repeat: ImageRepeat.noRepeat,
     this.centerSlice,
     this.matchTextDirection: false,
@@ -367,22 +367,22 @@ class Image extends StatefulWidget {
   /// How to align the image within its bounds.
   ///
   /// The alignment aligns the given position in the image to the given position
-  /// in the layout bounds. For example, a [FractionalOffset] alignment of (0.0,
-  /// 0.0) aligns the image to the top-left corner of its layout bounds, while a
-  /// [FractionalOffset] alignment of (1.0, 1.0) aligns the bottom right of the
+  /// in the layout bounds. For example, a [Alignment] alignment of (-1.0,
+  /// -1.0) aligns the image to the top-left corner of its layout bounds, while a
+  /// [Alignment] alignment of (1.0, 1.0) aligns the bottom right of the
   /// image with the bottom right corner of its layout bounds. Similarly, an
-  /// alignment of (0.5, 1.0) aligns the bottom middle of the image with the
+  /// alignment of (0.0, 1.0) aligns the bottom middle of the image with the
   /// middle of the bottom edge of its layout bounds.
   ///
   /// To display a subpart of an image, consider using a [CustomPainter] and
   /// [Canvas.drawImageRect].
   ///
   /// If the [alignment] is [TextDirection]-dependent (i.e. if it is a
-  /// [FractionalOffsetDirectional]), then an ambient [Directionality] widget
+  /// [AlignmentDirectional]), then an ambient [Directionality] widget
   /// must be in scope.
   ///
-  /// Defaults to [FractionalOffset.center].
-  final FractionalOffsetGeometry alignment;
+  /// Defaults to [Alignment.center].
+  final AlignmentGeometry alignment;
 
   /// How to paint any portions of the layout bounds not covered by the image.
   final ImageRepeat repeat;
@@ -433,7 +433,7 @@ class Image extends StatefulWidget {
     description.add(new DiagnosticsProperty<Color>('color', color, defaultValue: null));
     description.add(new EnumProperty<BlendMode>('colorBlendMode', colorBlendMode, defaultValue: null));
     description.add(new EnumProperty<BoxFit>('fit', fit, defaultValue: null));
-    description.add(new DiagnosticsProperty<FractionalOffsetGeometry>('alignment', alignment, defaultValue: null));
+    description.add(new DiagnosticsProperty<AlignmentGeometry>('alignment', alignment, defaultValue: null));
     description.add(new EnumProperty<ImageRepeat>('repeat', repeat, defaultValue: ImageRepeat.noRepeat));
     description.add(new DiagnosticsProperty<Rect>('centerSlice', centerSlice, defaultValue: null));
     description.add(new FlagProperty('matchTextDirection', value: matchTextDirection, ifTrue: 'match text direction'));

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

@@ -75,7 +75,7 @@ class ImageIcon extends StatelessWidget {
       height: iconSize,
       color: iconColor,
       fit: BoxFit.scaleDown,
-      alignment: FractionalOffset.center
+      alignment: Alignment.center,
     );
   }
 

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

@@ -391,7 +391,7 @@ class AnimatedContainer extends ImplicitlyAnimatedWidget {
   /// constraints are unbounded, then the child will be shrink-wrapped instead.
   ///
   /// Ignored if [child] is null.
-  final FractionalOffsetGeometry alignment;
+  final AlignmentGeometry alignment;
 
   /// Empty space to inscribe inside the [decoration]. The [child], if any, is
   /// placed inside this padding.
@@ -427,7 +427,7 @@ class AnimatedContainer extends ImplicitlyAnimatedWidget {
   @override
   void debugFillProperties(DiagnosticPropertiesBuilder description) {
     super.debugFillProperties(description);
-    description.add(new DiagnosticsProperty<FractionalOffsetGeometry>('alignment', alignment, showName: false, defaultValue: null));
+    description.add(new DiagnosticsProperty<AlignmentGeometry>('alignment', alignment, showName: false, defaultValue: null));
     description.add(new DiagnosticsProperty<EdgeInsetsGeometry>('padding', padding, defaultValue: null));
     description.add(new DiagnosticsProperty<Decoration>('bg', decoration, defaultValue: null));
     description.add(new DiagnosticsProperty<Decoration>('fg', foregroundDecoration, defaultValue: null));
@@ -438,7 +438,7 @@ class AnimatedContainer extends ImplicitlyAnimatedWidget {
 }
 
 class _AnimatedContainerState extends AnimatedWidgetBaseState<AnimatedContainer> {
-  FractionalOffsetGeometryTween _alignment;
+  AlignmentGeometryTween _alignment;
   EdgeInsetsGeometryTween _padding;
   DecorationTween _decoration;
   DecorationTween _foregroundDecoration;
@@ -448,7 +448,7 @@ class _AnimatedContainerState extends AnimatedWidgetBaseState<AnimatedContainer>
 
   @override
   void forEachTween(TweenVisitor<dynamic> visitor) {
-    _alignment = visitor(_alignment, widget.alignment, (dynamic value) => new FractionalOffsetGeometryTween(begin: value));
+    _alignment = visitor(_alignment, widget.alignment, (dynamic value) => new AlignmentGeometryTween(begin: value));
     _padding = visitor(_padding, widget.padding, (dynamic value) => new EdgeInsetsGeometryTween(begin: value));
     _decoration = visitor(_decoration, widget.decoration, (dynamic value) => new DecorationTween(begin: value));
     _foregroundDecoration = visitor(_foregroundDecoration, widget.foregroundDecoration, (dynamic value) => new DecorationTween(begin: value));
@@ -474,7 +474,7 @@ class _AnimatedContainerState extends AnimatedWidgetBaseState<AnimatedContainer>
   @override
   void debugFillProperties(DiagnosticPropertiesBuilder description) {
     super.debugFillProperties(description);
-    description.add(new DiagnosticsProperty<FractionalOffsetGeometryTween>('alignment', _alignment, showName: false, defaultValue: null));
+    description.add(new DiagnosticsProperty<AlignmentGeometryTween>('alignment', _alignment, showName: false, defaultValue: null));
     description.add(new DiagnosticsProperty<EdgeInsetsGeometryTween>('padding', _padding, defaultValue: null));
     description.add(new DiagnosticsProperty<DecorationTween>('bg', _decoration, defaultValue: null));
     description.add(new DiagnosticsProperty<DecorationTween>('fg', _foregroundDecoration, defaultValue: null));

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

@@ -632,9 +632,9 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
   ///       Widget child,
   ///    ) {
   ///     return new SlideTransition(
-  ///       position: new FractionalOffsetTween(
-  ///         begin: FractionalOffset.bottomLeft,
-  ///         end: FractionalOffset.topLeft
+  ///       position: new AlignmentTween(
+  ///         begin: Alignment.bottomCenter,
+  ///         end: Alignment.topCenter,
   ///       ).animate(animation),
   ///       child: child, // child is the value returned by pageBuilder
   ///     );
@@ -669,14 +669,14 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
   ///       Widget child,
   ///   ) {
   ///     return new SlideTransition(
-  ///       position: new FractionalOffsetTween(
-  ///         begin: FractionalOffset.bottomLeft,
-  ///         end: FractionalOffset.topLeft,
+  ///       position: new AlignmentTween(
+  ///         begin: Alignment.bottomCenter,
+  ///         end: Alignment.topCenter,
   ///       ).animate(animation),
   ///       child: new SlideTransition(
-  ///         position: new FractionalOffsetTween(
-  ///           begin: FractionalOffset.topLeft,
-  ///           end: FractionalOffset.bottomLeft,
+  ///         position: new AlignmentTween(
+  ///           begin: Alignment.topCenter,
+  ///           end: Alignment.bottomCenter,
   ///         ).animate(secondaryAnimation),
   ///         child: child,
   ///       ),

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

@@ -279,7 +279,7 @@ abstract class ScrollView extends StatelessWidget {
 ///       delegate: new SliverChildBuilderDelegate(
 ///         (BuildContext context, int index) {
 ///           return new Container(
-///             alignment: FractionalOffset.center,
+///             alignment: Alignment.center,
 ///             color: Colors.teal[100 * (index % 9)],
 ///             child: new Text('grid item $index'),
 ///           );
@@ -292,7 +292,7 @@ abstract class ScrollView extends StatelessWidget {
 ///       delegate: new SliverChildBuilderDelegate(
 ///         (BuildContext context, int index) {
 ///           return new Container(
-///             alignment: FractionalOffset.center,
+///             alignment: Alignment.center,
 ///             color: Colors.lightBlue[100 * (index % 9)],
 ///             child: new Text('list item $index'),
 ///           );

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

@@ -279,7 +279,7 @@ void _paintMessage(Canvas canvas, SemanticsNode node) {
     ..textAlign = TextAlign.center
     ..layout(maxWidth: rect.width);
 
-  textPainter.paint(canvas, FractionalOffset.center.inscribe(textPainter.size, rect).topLeft);
+  textPainter.paint(canvas, Alignment.center.inscribe(textPainter.size, rect).topLeft);
   canvas.restore();
 }
 

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

@@ -422,7 +422,7 @@ class SliverList extends SliverMultiBoxAdaptorWidget {
 ///   delegate: new SliverChildBuilderDelegate(
 ///     (BuildContext context, int index) {
 ///       return new Container(
-///         alignment: FractionalOffset.center,
+///         alignment: Alignment.center,
 ///         color: Colors.lightBlue[100 * (index % 9)],
 ///         child: new Text('list item $index'),
 ///       );
@@ -489,7 +489,7 @@ class SliverFixedExtentList extends SliverMultiBoxAdaptorWidget {
 ///   delegate: new SliverChildBuilderDelegate(
 ///     (BuildContext context, int index) {
 ///       return new Container(
-///         alignment: FractionalOffset.center,
+///         alignment: Alignment.center,
 ///         color: Colors.teal[100 * (index % 9)],
 ///         child: new Text('grid item $index'),
 ///       );

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

@@ -103,7 +103,7 @@ class SlideTransition extends AnimatedWidget {
   /// The [position] argument must not be null.
   const SlideTransition({
     Key key,
-    @required Animation<FractionalOffsetGeometry> position,
+    @required Animation<Alignment> position,
     this.transformHitTests: true,
     this.child,
   }) : super(key: key, listenable: position);
@@ -112,7 +112,7 @@ class SlideTransition extends AnimatedWidget {
   ///
   /// If the current value of the position animation is (dx, dy), the child will
   /// be translated horizontally by width * dx and vertically by height * dy.
-  Animation<FractionalOffsetGeometry> get position => listenable;
+  Animation<Alignment> get position => listenable;
 
   /// Whether hit testing should be affected by the slide animation.
   ///
@@ -140,11 +140,11 @@ class ScaleTransition extends AnimatedWidget {
   /// Creates a scale transition.
   ///
   /// The [scale] argument must not be null. The [alignment] argument defaults
-  /// to [FractionalOffset.center].
+  /// to [Alignment.center].
   const ScaleTransition({
     Key key,
     @required Animation<double> scale,
-    this.alignment: FractionalOffset.center,
+    this.alignment: Alignment.center,
     this.child,
   }) : super(key: key, listenable: scale);
 
@@ -158,8 +158,8 @@ class ScaleTransition extends AnimatedWidget {
   /// takes place, relative to the size of the box.
   ///
   /// For example, to set the origin of the scale to bottom middle, you can use
-  /// an alignment of (0.5, 1.0).
-  final FractionalOffset alignment;
+  /// an alignment of (0.0, 1.0).
+  final Alignment alignment;
 
   /// The widget below this widget in the tree.
   final Widget child;
@@ -203,7 +203,7 @@ class RotationTransition extends AnimatedWidget {
     final Matrix4 transform = new Matrix4.rotationZ(turnsValue * math.PI * 2.0);
     return new Transform(
       transform: transform,
-      alignment: FractionalOffset.center,
+      alignment: Alignment.center,
       child: child,
     );
   }
@@ -217,13 +217,13 @@ class SizeTransition extends AnimatedWidget {
   /// Creates a size transition.
   ///
   /// The [sizeFactor] argument must not be null. The [axis] argument defaults
-  /// to [Axis.vertical]. The [axisAlignment] defaults to 0.5, which centers the
+  /// to [Axis.vertical]. The [axisAlignment] defaults to 0.0, which centers the
   /// child along the main axis during the transition.
   const SizeTransition({
     Key key,
     this.axis: Axis.vertical,
     @required Animation<double> sizeFactor,
-    this.axisAlignment: 0.5,
+    this.axisAlignment: 0.0,
     this.child,
   }) : assert(axis != null),
        super(key: key, listenable: sizeFactor);
@@ -244,11 +244,11 @@ class SizeTransition extends AnimatedWidget {
 
   @override
   Widget build(BuildContext context) {
-    FractionalOffsetDirectional alignment;
+    AlignmentDirectional alignment;
     if (axis == Axis.vertical)
-      alignment = new FractionalOffsetDirectional(0.0, axisAlignment);
+      alignment = new AlignmentDirectional(-1.0, axisAlignment);
     else
-      alignment = new FractionalOffsetDirectional(axisAlignment, 0.0);
+      alignment = new AlignmentDirectional(axisAlignment, -1.0);
     return new ClipRect(
       child: new Align(
         alignment: alignment,

packages/flutter/test/cupertino/page_test.dart

@@ -33,13 +33,13 @@ void main() {
     Offset widget2TopLeft = tester.getTopLeft(find.text('Page 2'));
 
     // Page 1 is moving to the left.
-    expect(widget1TransientTopLeft.dx < widget1InitialTopLeft.dx, true);
+    expect(widget1TransientTopLeft.dx, lessThan(widget1InitialTopLeft.dx));
     // Page 1 isn't moving vertically.
-    expect(widget1TransientTopLeft.dy == widget1InitialTopLeft.dy, true);
+    expect(widget1TransientTopLeft.dy, equals(widget1InitialTopLeft.dy));
     // iOS transition is horizontal only.
-    expect(widget1InitialTopLeft.dy == widget2TopLeft.dy, true);
+    expect(widget1InitialTopLeft.dy, equals(widget2TopLeft.dy));
     // Page 2 is coming in from the right.
-    expect(widget2TopLeft.dx > widget1InitialTopLeft.dx, true);
+    expect(widget2TopLeft.dx, greaterThan(widget1InitialTopLeft.dx));
 
     await tester.pumpAndSettle();
 
@@ -55,13 +55,13 @@ void main() {
     widget2TopLeft = tester.getTopLeft(find.text('Page 2'));
 
     // Page 1 is coming back from the left.
-    expect(widget1TransientTopLeft.dx < widget1InitialTopLeft.dx, true);
+    expect(widget1TransientTopLeft.dx, lessThan(widget1InitialTopLeft.dx));
     // Page 1 isn't moving vertically.
-    expect(widget1TransientTopLeft.dy == widget1InitialTopLeft.dy, true);
+    expect(widget1TransientTopLeft.dy, equals(widget1InitialTopLeft.dy));
     // iOS transition is horizontal only.
-    expect(widget1InitialTopLeft.dy == widget2TopLeft.dy, true);
+    expect(widget1InitialTopLeft.dy, equals(widget2TopLeft.dy));
     // Page 2 is leaving towards the right.
-    expect(widget2TopLeft.dx > widget1InitialTopLeft.dx, true);
+    expect(widget2TopLeft.dx, greaterThan(widget1InitialTopLeft.dx));
 
     await tester.pumpAndSettle();
 
@@ -71,7 +71,7 @@ void main() {
     widget1TransientTopLeft = tester.getTopLeft(find.text('Page 1'));
 
     // Page 1 is back where it started.
-    expect(widget1InitialTopLeft == widget1TransientTopLeft, true);
+    expect(widget1InitialTopLeft, equals(widget1TransientTopLeft));
   });
 
   testWidgets('test iOS fullscreen dialog transition', (WidgetTester tester) async {
@@ -105,11 +105,11 @@ void main() {
     Offset widget2TopLeft = tester.getTopLeft(find.text('Page 2'));
 
     // Page 1 doesn't move.
-    expect(widget1TransientTopLeft == widget1InitialTopLeft, true);
+    expect(widget1TransientTopLeft, equals(widget1InitialTopLeft));
     // Fullscreen dialogs transitions vertically only.
-    expect(widget1InitialTopLeft.dx == widget2TopLeft.dx, true);
+    expect(widget1InitialTopLeft.dx, equals(widget2TopLeft.dx));
     // Page 2 is coming in from the bottom.
-    expect(widget2TopLeft.dy > widget1InitialTopLeft.dy, true);
+    expect(widget2TopLeft.dy, greaterThan(widget1InitialTopLeft.dy));
 
     await tester.pumpAndSettle();
 
@@ -125,11 +125,11 @@ void main() {
     widget2TopLeft = tester.getTopLeft(find.text('Page 2'));
 
     // Page 1 doesn't move.
-    expect(widget1TransientTopLeft == widget1InitialTopLeft, true);
+    expect(widget1TransientTopLeft, equals(widget1InitialTopLeft));
     // Fullscreen dialogs transitions vertically only.
-    expect(widget1InitialTopLeft.dx == widget2TopLeft.dx, true);
+    expect(widget1InitialTopLeft.dx, equals(widget2TopLeft.dx));
     // Page 2 is leaving towards the bottom.
-    expect(widget2TopLeft.dy > widget1InitialTopLeft.dy, true);
+    expect(widget2TopLeft.dy, greaterThan(widget1InitialTopLeft.dy));
 
     await tester.pumpAndSettle();
 
@@ -139,7 +139,7 @@ void main() {
     widget1TransientTopLeft = tester.getTopLeft(find.text('Page 1'));
 
     // Page 1 is back where it started.
-    expect(widget1InitialTopLeft == widget1TransientTopLeft, true);
+    expect(widget1InitialTopLeft, equals(widget1TransientTopLeft));
   });
 
   testWidgets('test only edge swipes work', (WidgetTester tester) async {

packages/flutter/test/material/app_bar_test.dart

@@ -999,8 +999,8 @@ void main() {
             flexibleSpace: new DecoratedBox(
               decoration: new BoxDecoration(
                 gradient: new LinearGradient(
-                  begin: const FractionalOffset(0.50, 0.0),
-                  end: const FractionalOffset(0.48, 1.0),
+                  begin: const Alignment(0.0, -1.0),
+                  end: const Alignment(-0.04, 1.0),
                   colors: <Color>[Colors.blue.shade500, Colors.blue.shade800],
                 ),
               ),
@@ -1029,8 +1029,8 @@ void main() {
             flexibleSpace: new DecoratedBox(
               decoration: new BoxDecoration(
                 gradient: new LinearGradient(
-                  begin: const FractionalOffset(0.50, 0.0),
-                  end: const FractionalOffset(0.48, 1.0),
+                  begin: const Alignment(0.0, -1.0),
+                  end: const Alignment(-0.04, 1.0),
                   colors: <Color>[Colors.blue.shade500, Colors.blue.shade800],
                 ),
               ),

packages/flutter/test/material/dialog_test.dart

@@ -160,7 +160,7 @@ void main() {
       child: new Container(
         width: 100.0,
         height: 100.0,
-        alignment: FractionalOffset.center,
+        alignment: Alignment.center,
         child: const Text('Dialog1'),
       ),
     );
@@ -180,7 +180,7 @@ void main() {
       child: new Container(
         width: 100.0,
         height: 100.0,
-        alignment: FractionalOffset.center,
+        alignment: Alignment.center,
         child: const Text('Dialog2'),
       ),
     );

packages/flutter/test/material/dropdown_test.dart

@@ -24,7 +24,7 @@ Widget buildFrame({
     bool isDense: false,
     Widget hint,
     List<String> items: menuItems,
-    FractionalOffset alignment: FractionalOffset.center,
+    Alignment alignment: Alignment.center,
   }) {
   return new MaterialApp(
     home: new Material(
@@ -219,7 +219,7 @@ void main() {
       new MaterialApp(
         home: new Material(
           child: new Align(
-            alignment: FractionalOffset.topCenter,
+            alignment: Alignment.topCenter,
             child: button,
           ),
         ),
@@ -443,19 +443,19 @@ void main() {
     // so that it fits within the frame.
 
     await popUpAndDown(
-      buildFrame(alignment: FractionalOffset.topLeft, value: menuItems.last)
+      buildFrame(alignment: Alignment.topLeft, value: menuItems.last)
     );
     expect(menuRect.topLeft, Offset.zero);
     expect(menuRect.topRight, new Offset(menuRect.width, 0.0));
 
     await popUpAndDown(
-      buildFrame(alignment: FractionalOffset.topCenter, value: menuItems.last)
+      buildFrame(alignment: Alignment.topCenter, value: menuItems.last)
     );
     expect(menuRect.topLeft, new Offset(buttonRect.left, 0.0));
     expect(menuRect.topRight, new Offset(buttonRect.right, 0.0));
 
     await popUpAndDown(
-      buildFrame(alignment: FractionalOffset.topRight, value: menuItems.last)
+      buildFrame(alignment: Alignment.topRight, value: menuItems.last)
     );
     expect(menuRect.topLeft, new Offset(800.0 - menuRect.width, 0.0));
     expect(menuRect.topRight, const Offset(800.0, 0.0));
@@ -465,19 +465,19 @@ void main() {
     // is selected) and shifted horizontally so that it fits within the frame.
 
     await popUpAndDown(
-      buildFrame(alignment: FractionalOffset.centerLeft, value: menuItems.first)
+      buildFrame(alignment: Alignment.centerLeft, value: menuItems.first)
     );
     expect(menuRect.topLeft, new Offset(0.0, buttonRect.top));
     expect(menuRect.topRight, new Offset(menuRect.width, buttonRect.top));
 
     await popUpAndDown(
-      buildFrame(alignment: FractionalOffset.center, value: menuItems.first)
+      buildFrame(alignment: Alignment.center, value: menuItems.first)
     );
     expect(menuRect.topLeft, buttonRect.topLeft);
     expect(menuRect.topRight, buttonRect.topRight);
 
     await popUpAndDown(
-      buildFrame(alignment: FractionalOffset.centerRight, value: menuItems.first)
+      buildFrame(alignment: Alignment.centerRight, value: menuItems.first)
     );
     expect(menuRect.topLeft, new Offset(800.0 - menuRect.width, buttonRect.top));
     expect(menuRect.topRight, new Offset(800.0, buttonRect.top));
@@ -487,19 +487,19 @@ void main() {
     // so that it fits within the frame.
 
     await popUpAndDown(
-      buildFrame(alignment: FractionalOffset.bottomLeft, value: menuItems.first)
+      buildFrame(alignment: Alignment.bottomLeft, value: menuItems.first)
     );
     expect(menuRect.bottomLeft, const Offset(0.0, 600.0));
     expect(menuRect.bottomRight, new Offset(menuRect.width, 600.0));
 
     await popUpAndDown(
-      buildFrame(alignment: FractionalOffset.bottomCenter, value: menuItems.first)
+      buildFrame(alignment: Alignment.bottomCenter, value: menuItems.first)
     );
     expect(menuRect.bottomLeft, new Offset(buttonRect.left, 600.0));
     expect(menuRect.bottomRight, new Offset(buttonRect.right, 600.0));
 
     await popUpAndDown(
-      buildFrame(alignment: FractionalOffset.bottomRight, value: menuItems.first)
+      buildFrame(alignment: Alignment.bottomRight, value: menuItems.first)
     );
     expect(menuRect.bottomLeft, new Offset(800.0 - menuRect.width, 600.0));
     expect(menuRect.bottomRight, const Offset(800.0, 600.0));

packages/flutter/test/material/tabs_test.dart

@@ -444,7 +444,7 @@ void main() {
     await tester.pumpWidget(
       new MaterialApp(
         home: new Align(
-          alignment: FractionalOffset.topLeft,
+          alignment: Alignment.topLeft,
           child: new SizedBox(
             width: 300.0,
             height: 200.0,

packages/flutter/test/painting/decoration_test.dart

@@ -205,7 +205,7 @@ void main() {
       image: new SynchronousTestImageProvider(),
       colorFilter: colorFilter,
       fit: BoxFit.contain,
-      alignment: FractionalOffset.bottomLeft,
+      alignment: Alignment.bottomLeft,
       centerSlice: new Rect.fromLTWH(10.0, 20.0, 30.0, 40.0),
       repeat: ImageRepeat.repeatY,
     );

packages/flutter/test/painting/gradient_test.dart

@@ -8,8 +8,8 @@ import 'package:flutter/painting.dart';
 void main() {
   test('LinearGradient scale test', () {
     final LinearGradient testGradient = const LinearGradient(
-      begin: FractionalOffset.bottomRight,
-      end: const FractionalOffset(0.7, 1.0),
+      begin: Alignment.bottomRight,
+      end: const Alignment(0.7, 1.0),
       colors: const <Color>[
         const Color(0x00FFFFFF),
         const Color(0x11777777),
@@ -19,8 +19,8 @@ void main() {
     final LinearGradient actual = LinearGradient.lerp(null, testGradient, 0.25);
 
     expect(actual, const LinearGradient(
-      begin: FractionalOffset.bottomRight,
-      end: const FractionalOffset(0.7, 1.0),
+      begin: Alignment.bottomRight,
+      end: const Alignment(0.7, 1.0),
       colors: const <Color>[
         const Color(0x00FFFFFF),
         const Color(0x04777777),
@@ -31,8 +31,8 @@ void main() {
 
   test('LinearGradient lerp test', () {
     final LinearGradient testGradient1 = const LinearGradient(
-      begin: FractionalOffset.topLeft,
-      end: FractionalOffset.bottomLeft,
+      begin: Alignment.topLeft,
+      end: Alignment.bottomLeft,
       colors: const <Color>[
         const Color(0x33333333),
         const Color(0x66666666),
@@ -40,8 +40,8 @@ void main() {
     );
 
     final LinearGradient testGradient2 = const LinearGradient(
-      begin: FractionalOffset.topRight,
-      end: FractionalOffset.topLeft,
+      begin: Alignment.topRight,
+      end: Alignment.topLeft,
       colors: const <Color>[
         const Color(0x44444444),
         const Color(0x88888888),
@@ -50,8 +50,8 @@ void main() {
     final LinearGradient actual = LinearGradient.lerp(testGradient1, testGradient2, 0.5);
 
     expect(actual, const LinearGradient(
-      begin: const FractionalOffset(0.5, 0.0),
-      end: const FractionalOffset(0.0, 0.5),
+      begin: const Alignment(0.0, -1.0),
+      end: const Alignment(-1.0, 0.0),
       colors: const <Color>[
         const Color(0x3B3B3B3B),
         const Color(0x77777777),
@@ -62,24 +62,24 @@ void main() {
   test('LinearGradient toString', () {
     expect(
       const LinearGradient(
-        begin: FractionalOffset.topLeft,
-        end: FractionalOffset.bottomLeft,
+        begin: Alignment.topLeft,
+        end: Alignment.bottomLeft,
         colors: const <Color>[
           const Color(0x33333333),
           const Color(0x66666666),
         ],
       ).toString(),
       equals(
-        'LinearGradient(FractionalOffset.topLeft, FractionalOffset.bottomLeft, [Color(0x33333333), Color(0x66666666)], null, TileMode.clamp)',
+        'LinearGradient(Alignment.topLeft, Alignment.bottomLeft, [Color(0x33333333), Color(0x66666666)], null, TileMode.clamp)',
       ),
     );
   });
 
-  test('LinearGradient with FractionalOffsetDirectional', () {
+  test('LinearGradient with AlignmentDirectional', () {
     expect(
       () {
         return const LinearGradient(
-          begin: FractionalOffsetDirectional.topStart,
+          begin: AlignmentDirectional.topStart,
           colors: const <Color>[ const Color(0xFFFFFFFF), const Color(0xFFFFFFFF) ]
         ).createShader(new Rect.fromLTWH(0.0, 0.0, 100.0, 100.0));
       },
@@ -88,7 +88,7 @@ void main() {
     expect(
       () {
         return const LinearGradient(
-          begin: FractionalOffsetDirectional.topStart,
+          begin: AlignmentDirectional.topStart,
           colors: const <Color>[ const Color(0xFFFFFFFF), const Color(0xFFFFFFFF) ]
         ).createShader(new Rect.fromLTWH(0.0, 0.0, 100.0, 100.0), textDirection: TextDirection.rtl);
       },
@@ -97,7 +97,7 @@ void main() {
     expect(
       () {
         return const LinearGradient(
-          begin: FractionalOffsetDirectional.topStart,
+          begin: AlignmentDirectional.topStart,
           colors: const <Color>[ const Color(0xFFFFFFFF), const Color(0xFFFFFFFF) ]
         ).createShader(new Rect.fromLTWH(0.0, 0.0, 100.0, 100.0), textDirection: TextDirection.ltr);
       },
@@ -106,7 +106,7 @@ void main() {
     expect(
       () {
         return const LinearGradient(
-          begin: FractionalOffset.topLeft,
+          begin: Alignment.topLeft,
           colors: const <Color>[ const Color(0xFFFFFFFF), const Color(0xFFFFFFFF) ]
         ).createShader(new Rect.fromLTWH(0.0, 0.0, 100.0, 100.0));
       },
@@ -114,11 +114,11 @@ void main() {
     );
   });
 
-  test('RadialGradient with FractionalOffsetDirectional', () {
+  test('RadialGradient with AlignmentDirectional', () {
     expect(
       () {
         return const RadialGradient(
-          center: FractionalOffsetDirectional.topStart,
+          center: AlignmentDirectional.topStart,
           colors: const <Color>[ const Color(0xFFFFFFFF), const Color(0xFFFFFFFF) ]
         ).createShader(new Rect.fromLTWH(0.0, 0.0, 100.0, 100.0));
       },
@@ -127,7 +127,7 @@ void main() {
     expect(
       () {
         return const RadialGradient(
-          center: FractionalOffsetDirectional.topStart,
+          center: AlignmentDirectional.topStart,
           colors: const <Color>[ const Color(0xFFFFFFFF), const Color(0xFFFFFFFF) ]
         ).createShader(new Rect.fromLTWH(0.0, 0.0, 100.0, 100.0), textDirection: TextDirection.rtl);
       },
@@ -136,7 +136,7 @@ void main() {
     expect(
       () {
         return const RadialGradient(
-          center: FractionalOffsetDirectional.topStart,
+          center: AlignmentDirectional.topStart,
           colors: const <Color>[ const Color(0xFFFFFFFF), const Color(0xFFFFFFFF) ]
         ).createShader(new Rect.fromLTWH(0.0, 0.0, 100.0, 100.0), textDirection: TextDirection.ltr);
       },
@@ -145,7 +145,7 @@ void main() {
     expect(
       () {
         return const RadialGradient(
-          center: FractionalOffset.topLeft,
+          center: Alignment.topLeft,
           colors: const <Color>[ const Color(0xFFFFFFFF), const Color(0xFFFFFFFF) ]
         ).createShader(new Rect.fromLTWH(0.0, 0.0, 100.0, 100.0));
       },

packages/flutter/test/painting/paint_image_test.dart

@@ -39,7 +39,7 @@ void main() {
       rect: new Rect.fromLTWH(50.0, 75.0, 200.0, 100.0),
       image: image,
       fit: BoxFit.cover,
-      alignment: const FractionalOffset(0.0, 0.5)
+      alignment: const Alignment(-1.0, 0.0),
     );
 
     final Invocation command = canvas.invocations.firstWhere((Invocation invocation) {

packages/flutter/test/rendering/baseline_test.dart

@@ -13,7 +13,7 @@ void main() {
     RenderBaseline parent;
     RenderSizedBox child;
     final RenderBox root = new RenderPositionedBox(
-      alignment: FractionalOffset.topLeft,
+      alignment: Alignment.topLeft,
       child: parent = new RenderBaseline(
         baseline: 0.0,
         baselineType: TextBaseline.alphabetic,

packages/flutter/test/rendering/box_test.dart

@@ -14,7 +14,7 @@ void main() {
       decoration: new BoxDecoration(
         color: const Color(0xFF00FF00),
         gradient: new RadialGradient(
-          center: FractionalOffset.topLeft, radius: 1.8,
+          center: Alignment.topLeft, radius: 1.8,
           colors: <Color>[Colors.yellow[500], Colors.blue[500]],
         ),
         boxShadow: kElevationToShadow[3],

packages/flutter/test/rendering/image_test.dart

@@ -74,7 +74,7 @@ void main() {
         '   constraints: BoxConstraints(25.0<=w<=100.0, 25.0<=h<=100.0)\n'
         '   size: Size(25.0, 25.0)\n'
         '   image: [10×10]\n'
-        '   alignment: FractionalOffset.center\n'
+        '   alignment: Alignment.center\n'
       ),
     );
 

packages/flutter/test/rendering/limited_box_test.dart

@@ -36,7 +36,7 @@ void main() {
         ' │ parentData: <none>\n'
         ' │ constraints: BoxConstraints(w=800.0, h=600.0)\n'
         ' │ size: Size(800.0, 600.0)\n'
-        ' │ alignment: FractionalOffset.center\n'
+        ' │ alignment: Alignment.center\n'
         ' │ minWidth: 0.0\n'
         ' │ maxWidth: Infinity\n'
         ' │ minHeight: 0.0\n'
@@ -122,7 +122,7 @@ void main() {
         ' │ parentData: <none>\n'
         ' │ constraints: BoxConstraints(w=800.0, h=600.0)\n'
         ' │ size: Size(800.0, 600.0)\n'
-        ' │ alignment: FractionalOffset.center\n'
+        ' │ alignment: Alignment.center\n'
         ' │ minWidth: 10.0\n'
         ' │ maxWidth: 500.0\n'
         ' │ minHeight: 0.0\n'
@@ -158,7 +158,7 @@ void main() {
         ' │ parentData: <none>\n'
         ' │ constraints: BoxConstraints(w=800.0, h=600.0)\n'
         ' │ size: Size(800.0, 600.0)\n'
-        ' │ alignment: FractionalOffset.center\n'
+        ' │ alignment: Alignment.center\n'
         ' │ minWidth: 10.0\n'
         ' │ maxWidth: use parent maxWidth constraint\n'
         ' │ minHeight: use parent minHeight constraint\n'

packages/flutter/test/rendering/non_render_object_root_test.dart

@@ -47,7 +47,7 @@ void main() {
     RenderPositionedBox child;
     final RealRoot root = new RealRoot(
       child = new RenderPositionedBox(
-        alignment: FractionalOffset.center,
+        alignment: Alignment.center,
         child: new RenderSizedBox(const Size(100.0, 100.0))
       )
     );

packages/flutter/test/rendering/overflow_test.dart

@@ -23,9 +23,9 @@ void main() {
           onPaint: () {
             baseline1 = child.getDistanceToBaseline(TextBaseline.alphabetic);
             height1 = text.size.height;
-          }
-        )
-      )
+          },
+        ),
+      ),
     );
     layout(root, phase: EnginePhase.paint);
 
@@ -37,15 +37,15 @@ void main() {
             textDirection: TextDirection.ltr,
           ),
           maxHeight: height1 / 2.0,
-          alignment: const FractionalOffset(0.0, 0.0)
+          alignment: Alignment.topLeft,
         ),
         painter: new TestCallbackPainter(
           onPaint: () {
             baseline2 = child.getDistanceToBaseline(TextBaseline.alphabetic);
             height2 = text.size.height;
-          }
-        )
-      )
+          },
+        ),
+      ),
     );
     layout(root, phase: EnginePhase.paint);
 

packages/flutter/test/rendering/rendering_tester.dart

@@ -57,7 +57,7 @@ TestRenderingFlutterBinding get renderer {
 /// has no build phase.
 void layout(RenderBox box, {
   BoxConstraints constraints,
-  FractionalOffset alignment: FractionalOffset.center,
+  Alignment alignment: Alignment.center,
   EnginePhase phase: EnginePhase.layout,
 }) {
   assert(box != null); // If you want to just repump the last box, call pumpFrame().

packages/flutter/test/rendering/transform_test.dart

@@ -18,10 +18,10 @@ void main() {
     RenderBox inner;
     final RenderBox sizer = new RenderTransform(
       transform: new Matrix4.identity(),
-      alignment: FractionalOffset.center,
+      alignment: Alignment.center,
       child: inner = new RenderSizedBox(const Size(100.0, 100.0)),
     );
-    layout(sizer, constraints: new BoxConstraints.tight(const Size(100.0, 100.0)), alignment: FractionalOffset.topLeft);
+    layout(sizer, constraints: new BoxConstraints.tight(const Size(100.0, 100.0)), alignment: Alignment.topLeft);
     expect(inner.globalToLocal(const Offset(0.0, 0.0)), equals(const Offset(0.0, 0.0)));
     expect(inner.globalToLocal(const Offset(100.0, 100.0)), equals(const Offset(100.0, 100.0)));
     expect(inner.globalToLocal(const Offset(25.0, 75.0)), equals(const Offset(25.0, 75.0)));
@@ -36,13 +36,13 @@ void main() {
     RenderBox inner;
     final RenderBox sizer = new RenderTransform(
       transform: new Matrix4.identity(),
-      alignment: FractionalOffset.center,
+      alignment: Alignment.center,
       child: new RenderPadding(
         padding: const EdgeInsets.only(left: 20.0),
         child: inner = new RenderSizedBox(const Size(80.0, 100.0)),
       ),
     );
-    layout(sizer, constraints: new BoxConstraints.tight(const Size(100.0, 100.0)), alignment: FractionalOffset.topLeft);
+    layout(sizer, constraints: new BoxConstraints.tight(const Size(100.0, 100.0)), alignment: Alignment.topLeft);
     expect(inner.globalToLocal(const Offset(0.0, 0.0)), equals(const Offset(-20.0, 0.0)));
     expect(inner.globalToLocal(const Offset(100.0, 100.0)), equals(const Offset(80.0, 100.0)));
     expect(inner.globalToLocal(const Offset(25.0, 75.0)), equals(const Offset(5.0, 75.0)));
@@ -57,10 +57,10 @@ void main() {
     RenderBox inner;
     final RenderBox sizer = new RenderTransform(
       transform: new Matrix4.translationValues(50.0, 200.0, 0.0),
-      alignment: FractionalOffset.center,
+      alignment: Alignment.center,
       child: inner = new RenderSizedBox(const Size(100.0, 100.0)),
     );
-    layout(sizer, constraints: new BoxConstraints.tight(const Size(100.0, 100.0)), alignment: FractionalOffset.topLeft);
+    layout(sizer, constraints: new BoxConstraints.tight(const Size(100.0, 100.0)), alignment: Alignment.topLeft);
     expect(inner.globalToLocal(const Offset(0.0, 0.0)), equals(const Offset(-50.0, -200.0)));
     expect(inner.globalToLocal(const Offset(100.0, 100.0)), equals(const Offset(50.0, -100.0)));
     expect(inner.globalToLocal(const Offset(25.0, 75.0)), equals(const Offset(-25.0, -125.0)));
@@ -75,13 +75,13 @@ void main() {
     RenderBox inner;
     final RenderBox sizer = new RenderTransform(
       transform: new Matrix4.translationValues(50.0, 200.0, 0.0),
-      alignment: FractionalOffset.center,
+      alignment: Alignment.center,
       child: new RenderPadding(
         padding: const EdgeInsets.only(left: 20.0),
         child: inner = new RenderSizedBox(const Size(80.0, 100.0)),
       ),
     );
-    layout(sizer, constraints: new BoxConstraints.tight(const Size(100.0, 100.0)), alignment: FractionalOffset.topLeft);
+    layout(sizer, constraints: new BoxConstraints.tight(const Size(100.0, 100.0)), alignment: Alignment.topLeft);
     expect(inner.globalToLocal(const Offset(0.0, 0.0)), equals(const Offset(-70.0, -200.0)));
     expect(inner.globalToLocal(const Offset(100.0, 100.0)), equals(const Offset(30.0, -100.0)));
     expect(inner.globalToLocal(const Offset(25.0, 75.0)), equals(const Offset(-45.0, -125.0)));
@@ -96,10 +96,10 @@ void main() {
     RenderBox inner;
     final RenderBox sizer = new RenderTransform(
       transform: new Matrix4.rotationZ(math.PI),
-      alignment: FractionalOffset.center,
+      alignment: Alignment.center,
       child: inner = new RenderSizedBox(const Size(100.0, 100.0)),
     );
-    layout(sizer, constraints: new BoxConstraints.tight(const Size(100.0, 100.0)), alignment: FractionalOffset.topLeft);
+    layout(sizer, constraints: new BoxConstraints.tight(const Size(100.0, 100.0)), alignment: Alignment.topLeft);
     expect(round(inner.globalToLocal(const Offset(0.0, 0.0))), equals(const Offset(100.0, 100.0)));
     expect(round(inner.globalToLocal(const Offset(100.0, 100.0))), equals(const Offset(0.0, 0.0)));
     expect(round(inner.globalToLocal(const Offset(25.0, 75.0))), equals(const Offset(75.0, 25.0)));
@@ -114,13 +114,13 @@ void main() {
     RenderBox inner;
     final RenderBox sizer = new RenderTransform(
       transform: new Matrix4.rotationZ(math.PI),
-      alignment: FractionalOffset.center,
+      alignment: Alignment.center,
       child: new RenderPadding(
         padding: const EdgeInsets.only(left: 20.0),
         child: inner = new RenderSizedBox(const Size(80.0, 100.0)),
       ),
     );
-    layout(sizer, constraints: new BoxConstraints.tight(const Size(100.0, 100.0)), alignment: FractionalOffset.topLeft);
+    layout(sizer, constraints: new BoxConstraints.tight(const Size(100.0, 100.0)), alignment: Alignment.topLeft);
     expect(round(inner.globalToLocal(const Offset(0.0, 0.0))), equals(const Offset(80.0, 100.0)));
     expect(round(inner.globalToLocal(const Offset(100.0, 100.0))), equals(const Offset(-20.0, 0.0)));
     expect(round(inner.globalToLocal(const Offset(25.0, 75.0))), equals(const Offset(55.0, 25.0)));
@@ -135,10 +135,10 @@ void main() {
     RenderBox inner;
     final RenderBox sizer = new RenderTransform(
       transform: rotateAroundXAxis(math.PI * 0.25), // at pi/4, we are about 70 pixels high
-      alignment: FractionalOffset.center,
+      alignment: Alignment.center,
       child: inner = new RenderSizedBox(const Size(100.0, 100.0)),
     );
-    layout(sizer, constraints: new BoxConstraints.tight(const Size(100.0, 100.0)), alignment: FractionalOffset.topLeft);
+    layout(sizer, constraints: new BoxConstraints.tight(const Size(100.0, 100.0)), alignment: Alignment.topLeft);
 
     expect(round(inner.globalToLocal(const Offset(25.0, 50.0))), equals(const Offset(25.0, 50.0)));
     expect(inner.globalToLocal(const Offset(25.0, 17.0)).dy, greaterThan(0.0));
@@ -152,10 +152,10 @@ void main() {
     RenderBox inner;
     final RenderBox sizer = new RenderTransform(
       transform: rotateAroundXAxis(math.PI * 0.4999), // at pi/2, we're seeing the box on its edge,
-      alignment: FractionalOffset.center,
+      alignment: Alignment.center,
       child: inner = new RenderSizedBox(const Size(100.0, 100.0)),
     );
-    layout(sizer, constraints: new BoxConstraints.tight(const Size(100.0, 100.0)), alignment: FractionalOffset.topLeft);
+    layout(sizer, constraints: new BoxConstraints.tight(const Size(100.0, 100.0)), alignment: Alignment.topLeft);
 
     // the inner widget has a height of about half a pixel at this rotation, so
     // everything should end up around the middle of the outer box.

packages/flutter/test/widgets/align_test.dart

@@ -11,34 +11,34 @@ void main() {
     await tester.pumpWidget(
       new Align(
         child: new Container(),
-        alignment: const FractionalOffset(0.75, 0.75),
+        alignment: const Alignment(0.50, 0.50),
       ),
     );
 
     await tester.pumpWidget(
       new Align(
         child: new Container(),
-        alignment: const FractionalOffset(0.5, 0.5),
+        alignment: const Alignment(0.0, 0.0),
       ),
     );
 
     await tester.pumpWidget(
       const Align(
         key: const GlobalObjectKey<Null>(null),
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
       ),
     );
     await tester.pumpWidget(const Directionality(
       textDirection: TextDirection.rtl,
       child: const Align(
         key: const GlobalObjectKey<Null>(null),
-        alignment: FractionalOffsetDirectional.topStart,
+        alignment: AlignmentDirectional.topStart,
       ),
     ));
     await tester.pumpWidget(
       const Align(
         key: const GlobalObjectKey<Null>(null),
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
       ),
     );
   });
@@ -48,7 +48,7 @@ void main() {
       textDirection: TextDirection.ltr,
       child: new Align(
         child: new Container(width: 100.0, height: 80.0),
-        alignment: FractionalOffsetDirectional.topStart,
+        alignment: AlignmentDirectional.topStart,
       ),
     ));
 
@@ -59,7 +59,7 @@ void main() {
       textDirection: TextDirection.ltr,
       child: new Align(
         child: new Container(width: 100.0, height: 80.0),
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
       ),
     ));
 
@@ -72,7 +72,7 @@ void main() {
       textDirection: TextDirection.rtl,
       child: new Align(
         child: new Container(width: 100.0, height: 80.0),
-        alignment: FractionalOffsetDirectional.topStart,
+        alignment: AlignmentDirectional.topStart,
       ),
     ));
 
@@ -83,7 +83,7 @@ void main() {
       textDirection: TextDirection.ltr,
       child: new Align(
         child: new Container(width: 100.0, height: 80.0),
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
       ),
     ));
 
@@ -101,7 +101,7 @@ void main() {
             width: 10.0,
             height: 10.0
           ),
-          alignment: const FractionalOffset(0.50, 0.50),
+          alignment: const Alignment(0.0, 0.0),
         ),
       ),
     );

packages/flutter/test/widgets/animated_container_test.dart

@@ -183,7 +183,7 @@ void main() {
         textDirection: TextDirection.rtl,
         child: new AnimatedContainer(
           duration: const Duration(milliseconds: 200),
-          alignment: FractionalOffset.topRight,
+          alignment: Alignment.topRight,
           child: new SizedBox(key: target, width: 100.0, height: 200.0),
         ),
       ),
@@ -197,7 +197,7 @@ void main() {
         textDirection: TextDirection.rtl,
         child: new AnimatedContainer(
           duration: const Duration(milliseconds: 200),
-          alignment: FractionalOffsetDirectional.bottomStart,
+          alignment: AlignmentDirectional.bottomStart,
           child: new SizedBox(key: target, width: 100.0, height: 200.0),
         ),
       ),

packages/flutter/test/widgets/animated_cross_fade_test.dart

@@ -98,7 +98,7 @@ void main() {
         textDirection: TextDirection.ltr,
         child: new Center(
           child: new AnimatedCrossFade(
-            alignment: FractionalOffset.bottomRight,
+            alignment: Alignment.bottomRight,
             firstChild: new SizedBox(
               key: firstKey,
               width: 100.0,
@@ -121,7 +121,7 @@ void main() {
         textDirection: TextDirection.ltr,
         child: new Center(
           child: new AnimatedCrossFade(
-            alignment: FractionalOffset.bottomRight,
+            alignment: Alignment.bottomRight,
             firstChild: new SizedBox(
               key: firstKey,
               width: 100.0,
@@ -156,7 +156,7 @@ void main() {
         textDirection: TextDirection.ltr,
         child: new Center(
           child: new AnimatedCrossFade(
-            alignment: FractionalOffsetDirectional.bottomEnd,
+            alignment: AlignmentDirectional.bottomEnd,
             firstChild: new SizedBox(
               key: firstKey,
               width: 100.0,
@@ -179,7 +179,7 @@ void main() {
         textDirection: TextDirection.ltr,
         child: new Center(
           child: new AnimatedCrossFade(
-            alignment: FractionalOffsetDirectional.bottomEnd,
+            alignment: AlignmentDirectional.bottomEnd,
             firstChild: new SizedBox(
               key: firstKey,
               width: 100.0,
@@ -214,7 +214,7 @@ void main() {
         textDirection: TextDirection.rtl,
         child: new Center(
           child: new AnimatedCrossFade(
-            alignment: FractionalOffsetDirectional.bottomEnd,
+            alignment: AlignmentDirectional.bottomEnd,
             firstChild: new SizedBox(
               key: firstKey,
               width: 100.0,
@@ -237,7 +237,7 @@ void main() {
         textDirection: TextDirection.rtl,
         child: new Center(
           child: new AnimatedCrossFade(
-            alignment: FractionalOffsetDirectional.bottomEnd,
+            alignment: AlignmentDirectional.bottomEnd,
             firstChild: new SizedBox(
               key: firstKey,
               width: 100.0,

packages/flutter/test/widgets/clip_test.dart

@@ -107,7 +107,7 @@ void main() {
   testWidgets('ClipRect', (WidgetTester tester) async {
     await tester.pumpWidget(
       new Align(
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
         child: new SizedBox(
           width: 100.0,
           height: 100.0,
@@ -131,7 +131,7 @@ void main() {
 
     await tester.pumpWidget(
       new Align(
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
         child: new SizedBox(
           width: 100.0,
           height: 100.0,
@@ -149,7 +149,7 @@ void main() {
 
     await tester.pumpWidget(
       new Align(
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
         child: new SizedBox(
           width: 200.0,
           height: 200.0,
@@ -167,7 +167,7 @@ void main() {
 
     await tester.pumpWidget(
       new Align(
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
         child: new SizedBox(
           width: 200.0,
           height: 200.0,
@@ -185,7 +185,7 @@ void main() {
 
     await tester.pumpWidget(
       new Align(
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
         child: new SizedBox(
           width: 200.0,
           height: 200.0,
@@ -203,7 +203,7 @@ void main() {
 
     await tester.pumpWidget(
       new Align(
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
         child: new SizedBox(
           width: 200.0,
           height: 200.0,

packages/flutter/test/widgets/container_test.dart

@@ -10,7 +10,7 @@ import '../rendering/mock_canvas.dart';
 void main() {
   testWidgets('Container control test', (WidgetTester tester) async {
     final Container container = new Container(
-      alignment: FractionalOffset.bottomRight,
+      alignment: Alignment.bottomRight,
       padding: const EdgeInsets.all(7.0),
       // uses color, not decoration:
       color: const Color(0xFF00FF00),
@@ -37,7 +37,7 @@ void main() {
     expect(container, hasOneLineDescription);
 
     await tester.pumpWidget(new Align(
-      alignment: FractionalOffset.topLeft,
+      alignment: Alignment.topLeft,
       child: container
     ));
 
@@ -96,7 +96,7 @@ void main() {
         '           │ parentData: offset=Offset(7.0, 7.0) (can use size)\n'
         '           │ constraints: BoxConstraints(w=39.0, h=64.0)\n'
         '           │ size: Size(39.0, 64.0)\n'
-        '           │ alignment: FractionalOffset.bottomRight\n'
+        '           │ alignment: Alignment.bottomRight\n'
         '           │ widthFactor: expand\n'
         '           │ heightFactor: expand\n'
         '           │\n'
@@ -173,7 +173,7 @@ void main() {
         '           │ parentData: offset=Offset(7.0, 7.0) (can use size)\n'
         '           │ constraints: BoxConstraints(w=39.0, h=64.0)\n'
         '           │ size: Size(39.0, 64.0)\n'
-        '           │ alignment: FractionalOffset.bottomRight\n'
+        '           │ alignment: Alignment.bottomRight\n'
         '           │ widthFactor: expand\n'
         '           │ heightFactor: expand\n'
         '           │\n'
@@ -281,7 +281,7 @@ void main() {
         '           │ layer: null\n'
         '           │ semantics node: null\n'
         '           │ size: Size(39.0, 64.0)\n'
-        '           │ alignment: FractionalOffset.bottomRight\n'
+        '           │ alignment: Alignment.bottomRight\n'
         '           │ textDirection: null\n'
         '           │ widthFactor: expand\n'
         '           │ heightFactor: expand\n'
@@ -412,7 +412,7 @@ void main() {
         '           │ isBlockingSemanticsOfPreviouslyPaintedNodes: false\n'
         '           │ isSemanticBoundary: false\n'
         '           │ size: Size(39.0, 64.0)\n'
-        '           │ alignment: FractionalOffset.bottomRight\n'
+        '           │ alignment: Alignment.bottomRight\n'
         '           │ textDirection: null\n'
         '           │ widthFactor: expand\n'
         '           │ heightFactor: expand\n'

packages/flutter/test/widgets/fractionally_sized_box_test.dart

@@ -14,7 +14,7 @@ void main() {
       maxWidth: 100.0,
       minHeight: 0.0,
       maxHeight: 100.0,
-      alignment: const FractionalOffset(0.0, 0.0),
+      alignment: const Alignment(-1.0, -1.0),
       child: new Center(
         child: new FractionallySizedBox(
           widthFactor: 0.5,

packages/flutter/test/widgets/heroes_test.dart

@@ -312,7 +312,7 @@ void main() {
       routes: <String, WidgetBuilder>{
         '/next': (BuildContext context) {
           return new Align(
-            alignment: FractionalOffset.topLeft,
+            alignment: Alignment.topLeft,
             child: new Hero(
               tag: 'foo',
               child: new GestureDetector(

packages/flutter/test/widgets/image_rtl_test.dart

@@ -49,7 +49,7 @@ void main() {
             decoration: new BoxDecoration(
               image: new DecorationImage(
                 image: new TestImageProvider(),
-                alignment: FractionalOffsetDirectional.topEnd,
+                alignment: AlignmentDirectional.topEnd,
                 repeat: ImageRepeat.repeatX,
                 matchTextDirection: true,
               ),
@@ -88,7 +88,7 @@ void main() {
             decoration: new BoxDecoration(
               image: new DecorationImage(
                 image: new TestImageProvider(),
-                alignment: FractionalOffsetDirectional.topEnd,
+                alignment: AlignmentDirectional.topEnd,
                 repeat: ImageRepeat.repeatX,
                 matchTextDirection: true,
               ),
@@ -124,7 +124,7 @@ void main() {
             decoration: new BoxDecoration(
               image: new DecorationImage(
                 image: new TestImageProvider(),
-                alignment: FractionalOffsetDirectional.topEnd,
+                alignment: AlignmentDirectional.topEnd,
                 repeat: ImageRepeat.repeatX,
               ),
             ),
@@ -159,7 +159,7 @@ void main() {
             decoration: new BoxDecoration(
               image: new DecorationImage(
                 image: new TestImageProvider(),
-                alignment: FractionalOffsetDirectional.topEnd,
+                alignment: AlignmentDirectional.topEnd,
                 repeat: ImageRepeat.repeatX,
               ),
             ),
@@ -194,7 +194,7 @@ void main() {
             decoration: new BoxDecoration(
               image: new DecorationImage(
                 image: new TestImageProvider(),
-                alignment: FractionalOffset.centerRight,
+                alignment: Alignment.centerRight,
                 matchTextDirection: true,
               ),
             ),
@@ -226,7 +226,7 @@ void main() {
             decoration: new BoxDecoration(
               image: new DecorationImage(
                 image: new TestImageProvider(),
-                alignment: FractionalOffset.centerRight,
+                alignment: Alignment.centerRight,
               ),
             ),
           ),
@@ -253,7 +253,7 @@ void main() {
             decoration: new BoxDecoration(
               image: new DecorationImage(
                 image: new TestImageProvider(),
-                alignment: FractionalOffset.centerRight,
+                alignment: Alignment.centerRight,
                 matchTextDirection: true
               ),
             ),
@@ -281,7 +281,7 @@ void main() {
             decoration: new BoxDecoration(
               image: new DecorationImage(
                 image: new TestImageProvider(),
-                alignment: FractionalOffset.centerRight,
+                alignment: Alignment.centerRight,
                 matchTextDirection: true
               ),
             ),
@@ -308,7 +308,7 @@ void main() {
             height: 50.0,
             child: new Image(
               image: new TestImageProvider(),
-              alignment: FractionalOffsetDirectional.topEnd,
+              alignment: AlignmentDirectional.topEnd,
               repeat: ImageRepeat.repeatX,
               matchTextDirection: true,
             ),
@@ -345,7 +345,7 @@ void main() {
             height: 50.0,
             child: new Image(
               image: new TestImageProvider(),
-              alignment: FractionalOffsetDirectional.topEnd,
+              alignment: AlignmentDirectional.topEnd,
               repeat: ImageRepeat.repeatX,
               matchTextDirection: true,
             ),
@@ -379,7 +379,7 @@ void main() {
             height: 50.0,
             child: new Image(
               image: new TestImageProvider(),
-              alignment: FractionalOffsetDirectional.topEnd,
+              alignment: AlignmentDirectional.topEnd,
               repeat: ImageRepeat.repeatX,
             ),
           ),
@@ -412,7 +412,7 @@ void main() {
             height: 50.0,
             child: new Image(
               image: new TestImageProvider(),
-              alignment: FractionalOffsetDirectional.topEnd,
+              alignment: AlignmentDirectional.topEnd,
               repeat: ImageRepeat.repeatX,
             ),
           ),
@@ -445,7 +445,7 @@ void main() {
             height: 50.0,
             child: new Image(
               image: new TestImageProvider(),
-              alignment: FractionalOffset.centerRight,
+              alignment: Alignment.centerRight,
               matchTextDirection: true,
             ),
           ),
@@ -475,7 +475,7 @@ void main() {
             height: 50.0,
             child: new Image(
               image: new TestImageProvider(),
-              alignment: FractionalOffset.centerRight,
+              alignment: Alignment.centerRight,
             ),
           ),
         ),
@@ -500,7 +500,7 @@ void main() {
             height: 50.0,
             child: new Image(
               image: new TestImageProvider(),
-              alignment: FractionalOffset.centerRight,
+              alignment: Alignment.centerRight,
               matchTextDirection: true
             ),
           ),
@@ -526,7 +526,7 @@ void main() {
             height: 50.0,
             child: new Image(
               image: new TestImageProvider(),
-              alignment: FractionalOffset.centerRight,
+              alignment: Alignment.centerRight,
               matchTextDirection: true
             ),
           ),
@@ -548,7 +548,7 @@ void main() {
         textDirection: TextDirection.ltr,
         child: new Image(
           image: new TestImageProvider(),
-          alignment: FractionalOffset.centerRight,
+          alignment: Alignment.centerRight,
           matchTextDirection: false,
         ),
       ),
@@ -560,7 +560,7 @@ void main() {
         textDirection: TextDirection.ltr,
         child: new Image(
           image: new TestImageProvider(),
-          alignment: FractionalOffsetDirectional.centerEnd,
+          alignment: AlignmentDirectional.centerEnd,
           matchTextDirection: true,
         ),
       ),
@@ -572,7 +572,7 @@ void main() {
         textDirection: TextDirection.ltr,
         child: new Image(
           image: new TestImageProvider(),
-          alignment: FractionalOffset.centerRight,
+          alignment: Alignment.centerRight,
           matchTextDirection: false,
         ),
       ),

packages/flutter/test/widgets/overflow_box_test.dart

@@ -10,7 +10,7 @@ void main() {
   testWidgets('OverflowBox control test', (WidgetTester tester) async {
     final GlobalKey inner = new GlobalKey();
     await tester.pumpWidget(new Align(
-      alignment: const FractionalOffset(1.0, 1.0),
+      alignment: const Alignment(1.0, 1.0),
       child: new SizedBox(
         width: 10.0,
         height: 20.0,
@@ -42,7 +42,7 @@ void main() {
         .where((DiagnosticsNode n) => !n.isFiltered(DiagnosticLevel.info))
         .map((DiagnosticsNode n) => n.toString()).toList();
     expect(description, <String>[
-      'alignment: FractionalOffset.center',
+      'alignment: Alignment.center',
       'minWidth: 1.0',
       'maxWidth: 2.0',
       'minHeight: 3.0',

packages/flutter/test/widgets/overlay_test.dart

@@ -46,7 +46,7 @@ void main() {
             ' ╎ │   size)\n'
             ' ╎ │ constraints: BoxConstraints(w=800.0, h=600.0)\n'
             ' ╎ │ size: Size(800.0, 600.0)\n'
-            ' ╎ │ alignment: FractionalOffsetDirectional.topStart\n'
+            ' ╎ │ alignment: AlignmentDirectional.topStart\n'
             ' ╎ │ textDirection: ltr\n'
             ' ╎ │ fit: expand\n'
             ' ╎ │ overflow: clip\n'
@@ -113,7 +113,7 @@ void main() {
         ' ╎ │   size)\n'
         ' ╎ │ constraints: BoxConstraints(w=800.0, h=600.0)\n'
         ' ╎ │ size: Size(800.0, 600.0)\n'
-        ' ╎ │ alignment: FractionalOffsetDirectional.topStart\n'
+        ' ╎ │ alignment: AlignmentDirectional.topStart\n'
         ' ╎ │ textDirection: ltr\n'
         ' ╎ │ fit: expand\n'
         ' ╎ │ overflow: clip\n'

packages/flutter/test/widgets/shader_mask_test.dart

@@ -9,8 +9,8 @@ import 'package:flutter/widgets.dart';
 
 Shader createShader(Rect bounds) {
   return new LinearGradient(
-    begin: FractionalOffset.topLeft,
-    end: FractionalOffset.bottomLeft,
+    begin: Alignment.topCenter,
+    end: Alignment.bottomCenter,
     colors: <Color>[const Color(0x00FFFFFF), const Color(0xFFFFFFFF)],
     stops: <double>[0.1, 0.35]
   ).createShader(bounds);
@@ -31,7 +31,7 @@ void main() {
     }
 
     final Widget widget = new Align(
-      alignment: FractionalOffset.center,
+      alignment: Alignment.center,
       child: new SizedBox(
         width: 400.0,
         height: 400.0,

packages/flutter/test/widgets/sliver_prototype_item_extent_test.dart

@@ -15,7 +15,7 @@ class TestItem extends StatelessWidget {
     return new Container(
       width: width,
       height: height,
-      alignment: FractionalOffset.center,
+      alignment: Alignment.center,
       child: new Text('Item $item', textDirection: TextDirection.ltr),
     );
   }

packages/flutter/test/widgets/stack_test.dart

@@ -41,7 +41,7 @@ void main() {
 
     await tester.pumpWidget(
       new Stack(
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
         children: <Widget>[
           new Positioned(
             left: 10.0,
@@ -69,7 +69,7 @@ void main() {
 
     await tester.pumpWidget(
       new Stack(
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
         children: <Widget>[
           new Positioned(
             right: 10.0,
@@ -140,7 +140,7 @@ void main() {
         textDirection: TextDirection.ltr,
         child: new Center(
           child: new Stack(
-            alignment: FractionalOffset.center,
+            alignment: Alignment.center,
             children: <Widget>[
               new Container(key: child0Key, width: 20.0, height: 20.0),
               new Container(key: child1Key, width: 10.0, height: 10.0),
@@ -163,7 +163,7 @@ void main() {
         textDirection: TextDirection.ltr,
         child: new Center(
           child: new Stack(
-            alignment: FractionalOffsetDirectional.bottomEnd,
+            alignment: AlignmentDirectional.bottomEnd,
             children: <Widget>[
               new Container(key: child0Key, width: 20.0, height: 20.0),
               new Container(key: child1Key, width: 10.0, height: 10.0),
@@ -186,7 +186,7 @@ void main() {
         textDirection: TextDirection.rtl,
         child: new Center(
           child: new Stack(
-            alignment: FractionalOffset.center,
+            alignment: Alignment.center,
             children: <Widget>[
               new Container(key: child0Key, width: 20.0, height: 20.0),
               new Container(key: child1Key, width: 10.0, height: 10.0),
@@ -209,7 +209,7 @@ void main() {
         textDirection: TextDirection.rtl,
         child: new Center(
           child: new Stack(
-            alignment: FractionalOffsetDirectional.bottomEnd,
+            alignment: AlignmentDirectional.bottomEnd,
             children: <Widget>[
               new Container(key: child0Key, width: 20.0, height: 20.0),
               new Container(key: child1Key, width: 10.0, height: 10.0),
@@ -257,7 +257,7 @@ void main() {
       });
       return new Center(
         child: new IndexedStack(
-          alignment: FractionalOffset.topLeft,
+          alignment: Alignment.topLeft,
           children: items,
           index: index,
         ),
@@ -289,7 +289,7 @@ void main() {
       });
       return new Center(
         child: new IndexedStack(
-          alignment: FractionalOffset.topLeft,
+          alignment: Alignment.topLeft,
           children: items,
           key: key,
           index: index,
@@ -614,18 +614,18 @@ void main() {
   testWidgets('Can change the text direction of a Stack', (WidgetTester tester) async {
     await tester.pumpWidget(
       new Stack(
-        alignment: FractionalOffset.center,
+        alignment: Alignment.center,
       ),
     );
     await tester.pumpWidget(
       new Stack(
-        alignment: FractionalOffsetDirectional.topStart,
+        alignment: AlignmentDirectional.topStart,
         textDirection: TextDirection.rtl,
       ),
     );
     await tester.pumpWidget(
       new Stack(
-        alignment: FractionalOffset.center,
+        alignment: Alignment.center,
       ),
     );
   });

packages/flutter/test/widgets/transform_test.dart

@@ -82,7 +82,7 @@ void main() {
                 height: 100.0,
                 child: new Transform(
                   transform: new Matrix4.diagonal3Values(0.5, 0.5, 1.0),
-                  alignment: const FractionalOffset(1.0, 0.5),
+                  alignment: const Alignment(1.0, 0.0),
                   child: new GestureDetector(
                     onTap: () {
                       didReceiveTap = true;
@@ -131,7 +131,7 @@ void main() {
                 child: new Transform(
                   transform: new Matrix4.diagonal3Values(0.5, 0.5, 1.0),
                   origin: const Offset(100.0, 0.0),
-                  alignment: const FractionalOffset(0.0, 0.5),
+                  alignment: const Alignment(-1.0, 0.0),
                   child: new GestureDetector(
                     onTap: () {
                       didReceiveTap = true;

packages/flutter/test/widgets/wrap_test.dart

@@ -585,7 +585,7 @@ void main() {
   testWidgets('Shrink-wrapping Wrap test', (WidgetTester tester) async {
     await tester.pumpWidget(
       new Align(
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
         child: new Wrap(
           alignment: WrapAlignment.end,
           crossAxisAlignment: WrapCrossAlignment.end,
@@ -609,7 +609,7 @@ void main() {
 
     await tester.pumpWidget(
       new Align(
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
         child: new Wrap(
           alignment: WrapAlignment.end,
           crossAxisAlignment: WrapCrossAlignment.end,
@@ -635,7 +635,7 @@ void main() {
   testWidgets('Wrap spacing test', (WidgetTester tester) async {
     await tester.pumpWidget(
       new Align(
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
         child: new Wrap(
           runSpacing: 10.0,
           alignment: WrapAlignment.start,
@@ -662,7 +662,7 @@ void main() {
   testWidgets('Vertical Wrap test with spacing', (WidgetTester tester) async {
     await tester.pumpWidget(
       new Align(
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
         child: new Wrap(
           direction: Axis.vertical,
           spacing: 10.0,
@@ -693,7 +693,7 @@ void main() {
 
     await tester.pumpWidget(
       new Align(
-        alignment: FractionalOffset.topLeft,
+        alignment: Alignment.topLeft,
         child: new Wrap(
           direction: Axis.horizontal,
           spacing: 12.0,