Image RTL (#12230)

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

@@ -321,9 +321,20 @@ class _BoxDecorationPainter extends BoxPainter {
   ImageInfo _image;
 
   void _paintBackgroundImage(Canvas canvas, Rect rect, ImageConfiguration configuration) {
+    // TODO(ianh): factor this out into a DecorationImage.paint method.
     final DecorationImage backgroundImage = _decoration.image;
     if (backgroundImage == null)
       return;
+
+    bool flipHorizontally = false;
+    if (backgroundImage.matchTextDirection) {
+      // We check this first so that the assert will fire immediately, not just when the
+      // image is ready.
+      assert(configuration.textDirection != null, 'matchTextDirection can only be used when a TextDirection is available.');
+      if (configuration.textDirection == TextDirection.rtl)
+        flipHorizontally = true;
+    }
+
     final ImageStream newImageStream = backgroundImage.image.resolve(configuration);
     if (newImageStream.key != _imageStream?.key) {
       _imageStream?.removeListener(_imageListener);
@@ -350,9 +361,10 @@ class _BoxDecorationPainter extends BoxPainter {
       image: image,
       colorFilter: backgroundImage.colorFilter,
       fit: backgroundImage.fit,
-      alignment: backgroundImage.alignment,
+      alignment: backgroundImage.alignment.resolve(configuration.textDirection),
       centerSlice: backgroundImage.centerSlice,
       repeat: backgroundImage.repeat,
+      flipHorizontally: flipHorizontally,
     );
 
     if (clipPath != null)

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

@@ -35,15 +35,20 @@ enum ImageRepeat {
 class DecorationImage {
   /// Creates an image to show in a [BoxDecoration].
   ///
-  /// The [image] argument must not be null.
+  /// The [image], [alignment], [repeat], and [matchTextDirection] arguments
+  /// must not be null.
   const DecorationImage({
     @required this.image,
     this.colorFilter,
     this.fit,
-    this.alignment,
+    this.alignment: FractionalOffset.center,
     this.centerSlice,
     this.repeat: ImageRepeat.noRepeat,
-  }) : assert(image != null);
+    this.matchTextDirection: false,
+  }) : assert(image != null),
+       assert(alignment != null),
+       assert(repeat != null),
+       assert(matchTextDirection != null);
 
   /// The image to be painted into the decoration.
   ///
@@ -64,12 +69,23 @@ class DecorationImage {
 
   /// How to align the image within its bounds.
   ///
-  /// An alignment of (0.0, 0.0) aligns the image to the top-left corner of its
-  /// layout bounds.  An alignment of (1.0, 0.5) aligns the image to the middle
-  /// of the right edge of its layout 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
+  /// 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
+  /// 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
+  /// when the image is painted.
   ///
   /// Defaults to [FractionalOffset.center].
-  final FractionalOffset alignment;
+  final FractionalOffsetGeometry alignment;
 
   /// The center slice for a nine-patch image.
   ///
@@ -92,6 +108,15 @@ class DecorationImage {
   /// by the image.
   final ImageRepeat repeat;
 
+  /// Whether to paint the image in the direction of the [TextDirection].
+  ///
+  /// If this is true, then in [TextDirection.ltr] contexts, the image will be
+  /// drawn with its origin in the top left (the "normal" painting direction for
+  /// images); and in [TextDirection.rtl] contexts, the image will be drawn with
+  /// a scaling factor of -1 in the horizontal direction so that the origin is
+  /// in the top right.
+  final bool matchTextDirection;
+
   @override
   bool operator ==(dynamic other) {
     if (identical(this, other))
@@ -104,11 +129,12 @@ class DecorationImage {
         && fit == typedOther.fit
         && alignment == typedOther.alignment
         && centerSlice == typedOther.centerSlice
-        && repeat == typedOther.repeat;
+        && repeat == typedOther.repeat
+        && matchTextDirection == typedOther.matchTextDirection;
   }
 
   @override
-  int get hashCode => hashValues(image, colorFilter, fit, alignment, centerSlice, repeat);
+  int get hashCode => hashValues(image, colorFilter, fit, alignment, centerSlice, repeat, matchTextDirection);
 
   @override
   String toString() {
@@ -120,33 +146,44 @@ class DecorationImage {
         !(fit == BoxFit.fill && centerSlice != null) &&
         !(fit == BoxFit.scaleDown && centerSlice == null))
       properties.add('$fit');
-    if (alignment != null)
     properties.add('$alignment');
     if (centerSlice != null)
       properties.add('centerSlice: $centerSlice');
     if (repeat != ImageRepeat.noRepeat)
       properties.add('$repeat');
+    if (matchTextDirection)
+      properties.add('match text direction');
     return '$runtimeType(${properties.join(", ")})';
   }
 }
 
 /// Paints an image into the given rectangle on the canvas.
 ///
+/// The arguments have the following meanings:
+///
 ///  * `canvas`: The canvas onto which the image will be painted.
+///
 ///  * `rect`: The region of the canvas into which the image will be painted.
 ///    The image might not fill the entire rectangle (e.g., depending on the
 ///    `fit`). If `rect` is empty, nothing is painted.
+///
 ///  * `image`: The image to paint onto the canvas.
+///
 ///  * `colorFilter`: If non-null, the color filter to apply when painting the
 ///    image.
+///
 ///  * `fit`: How the image should be inscribed into `rect`. If null, the
 ///    default behavior depends on `centerSlice`. If `centerSlice` is also null,
 ///    the default behavior is [BoxFit.scaleDown]. If `centerSlice` is
 ///    non-null, the default behavior is [BoxFit.fill]. See [BoxFit] for
 ///    details.
-///  * `repeat`: If the image does not fill `rect`, whether and how the image
-///    should be repeated to fill `rect`. By default, the image is not repeated.
-///    See [ImageRepeat] for details.
+///
+///  * `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
+///    as possible within `rect` and placed with its bottom right corner at the
+///    bottom right corner of `rect`. Defaults to [FractionalOffset.center].
+///
 ///  * `centerSlice`: The image is drawn in nine portions described by splitting
 ///    the image by drawing two horizontal lines and two vertical lines, where
 ///    `centerSlice` describes the rectangle formed by the four points where
@@ -157,11 +194,19 @@ class DecorationImage {
 ///    remaining five regions are drawn by stretching them to fit such that they
 ///    exactly cover the destination rectangle while maintaining their relative
 ///    positions.
-///  * `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
-///    as possible within `rect` and placed with its bottom right corner at the
-///    bottom right corner of `rect`.
+///
+///  * `repeat`: If the image does not fill `rect`, whether and how the image
+///    should be repeated to fill `rect`. By default, the image is not repeated.
+///    See [ImageRepeat] for details.
+///
+///  * `flipHorizontally`: Whether to flip the image horizontally. This is
+///    occasionally used with images in right-to-left environments, for images
+///    that were designed for left-to-right locales (or vice versa). Be careful,
+///    when using this, to not flip images with integral shadows, text, or other
+///    effects that will look incorrect when flipped.
+///
+/// The `canvas`, `rect`, `image`, `alignment`, `repeat`, and `flipHorizontally`
+/// arguments must not be null.
 ///
 /// See also:
 ///
@@ -174,12 +219,16 @@ void paintImage({
   @required ui.Image image,
   ColorFilter colorFilter,
   BoxFit fit,
-  FractionalOffset alignment,
+  FractionalOffset alignment: FractionalOffset.center,
   Rect centerSlice,
   ImageRepeat repeat: ImageRepeat.noRepeat,
+  bool flipHorizontally: false,
 }) {
   assert(canvas != null);
   assert(image != null);
+  assert(alignment != null);
+  assert(repeat != null);
+  assert(flipHorizontally != null);
   if (rect.isEmpty)
     return;
   Size outputSize = rect.size;
@@ -219,16 +268,23 @@ void paintImage({
     // to nearest-neighbor.
     paint.filterQuality = FilterQuality.low;
   }
-  final double dx = (outputSize.width - destinationSize.width) * (alignment?.dx ?? 0.5);
-  final double dy = (outputSize.height - destinationSize.height) * (alignment?.dy ?? 0.5);
+  final double dx = (outputSize.width - destinationSize.width) * (flipHorizontally ? 1.0 - alignment.dx : alignment.dx);
+  final double dy = (outputSize.height - destinationSize.height) * alignment.dy;
   final Offset destinationPosition = rect.topLeft.translate(dx, dy);
   final Rect destinationRect = destinationPosition & destinationSize;
-  if (repeat != ImageRepeat.noRepeat) {
+  final bool needSave = repeat != ImageRepeat.noRepeat || flipHorizontally;
+  if (needSave)
     canvas.save();
+  if (repeat != ImageRepeat.noRepeat)
     canvas.clipRect(rect);
+  if (flipHorizontally) {
+    final double dx = -(rect.left + rect.width / 2.0);
+    canvas.translate(-dx, 0.0);
+    canvas.scale(-1.0, 1.0);
+    canvas.translate(dx, 0.0);
   }
   if (centerSlice == null) {
-    final Rect sourceRect = (alignment ?? FractionalOffset.center).inscribe(
+    final Rect sourceRect = alignment.inscribe(
       fittedSizes.source, Offset.zero & inputSize
     );
     for (Rect tileRect in _generateImageTileRects(rect, destinationRect, repeat))
@@ -237,7 +293,7 @@ void paintImage({
     for (Rect tileRect in _generateImageTileRects(rect, destinationRect, repeat))
       canvas.drawImageNine(image, centerSlice, tileRect, paint);
   }
-  if (repeat != ImageRepeat.noRepeat)
+  if (needSave)
     canvas.restore();
 }
 

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

@@ -20,6 +20,10 @@ export 'package:flutter/painting.dart' show
 /// various fields on this class in more detail.
 class RenderImage extends RenderBox {
   /// Creates a render box that displays an image.
+  ///
+  /// The [scale], [alignment], [repeat], and [matchTextDirection] arguments
+  /// must not be null. The [textDirection] argument must not be null if
+  /// [alignment] will need resolving or if [matchTextDirection] is true.
   RenderImage({
     ui.Image image,
     double width,
@@ -28,10 +32,16 @@ class RenderImage extends RenderBox {
     Color color,
     BlendMode colorBlendMode,
     BoxFit fit,
-    FractionalOffset alignment,
+    FractionalOffsetGeometry alignment: FractionalOffset.center,
     ImageRepeat repeat: ImageRepeat.noRepeat,
-    Rect centerSlice
-  }) : _image = image,
+    Rect centerSlice,
+    bool matchTextDirection: false,
+    TextDirection textDirection,
+  }) : assert(scale != null),
+       assert(repeat != null),
+       assert(alignment != null),
+       assert(matchTextDirection != null),
+       _image = image,
        _width = width,
        _height = height,
        _scale = scale,
@@ -40,10 +50,28 @@ class RenderImage extends RenderBox {
        _fit = fit,
        _alignment = alignment,
        _repeat = repeat,
-      _centerSlice = centerSlice {
+       _centerSlice = centerSlice,
+       _matchTextDirection = matchTextDirection,
+       _textDirection = textDirection {
     _updateColorFilter();
   }
 
+  FractionalOffset _resolvedAlignment;
+  bool _flipHorizontally;
+
+  void _resolve() {
+    if (_resolvedAlignment != null)
+      return;
+    _resolvedAlignment = alignment.resolve(textDirection);
+    _flipHorizontally = matchTextDirection && textDirection == TextDirection.rtl;
+  }
+
+  void _markNeedResolution() {
+    _resolvedAlignment = null;
+    _flipHorizontally = null;
+    markNeedsPaint();
+  }
+
   /// The image to display.
   ui.Image get image => _image;
   ui.Image _image;
@@ -147,19 +175,24 @@ class RenderImage extends RenderBox {
   }
 
   /// How to align the image within its bounds.
-  FractionalOffset get alignment => _alignment;
-  FractionalOffset _alignment;
-  set alignment(FractionalOffset value) {
+  ///
+  /// 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) {
+    assert(value != null);
     if (value == _alignment)
       return;
     _alignment = value;
-    markNeedsPaint();
+    _markNeedResolution();
   }
 
   /// How to repeat this image if it doesn't fill its layout bounds.
   ImageRepeat get repeat => _repeat;
   ImageRepeat _repeat;
   set repeat(ImageRepeat value) {
+    assert(value != null);
     if (value == _repeat)
       return;
     _repeat = value;
@@ -182,6 +215,44 @@ class RenderImage extends RenderBox {
     markNeedsPaint();
   }
 
+  /// Whether to paint the image in the direction of the [TextDirection].
+  ///
+  /// If this is true, then in [TextDirection.ltr] contexts, the image will be
+  /// drawn with its origin in the top left (the "normal" painting direction for
+  /// images); and in [TextDirection.rtl] contexts, the image will be drawn with
+  /// a scaling factor of -1 in the horizontal direction so that the origin is
+  /// in the top right.
+  ///
+  /// This is occasionally used with images in right-to-left environments, for
+  /// images that were designed for left-to-right locales. Be careful, when
+  /// using this, to not flip images with integral shadows, text, or other
+  /// effects that will look incorrect when flipped.
+  ///
+  /// If this is set to true, [textDirection] must not be null.
+  bool get matchTextDirection => _matchTextDirection;
+  bool _matchTextDirection;
+  set matchTextDirection(bool value) {
+    assert(value != null);
+    if (value == _matchTextDirection)
+      return;
+    _matchTextDirection = value;
+    _markNeedResolution();
+  }
+
+  /// The text direction with which to resolve [alignment].
+  ///
+  /// This may be changed to null, but only after the [alignment] and
+  /// [matchTextDirection] properties have been changed to values that do not
+  /// depend on the direction.
+  TextDirection get textDirection => _textDirection;
+  TextDirection _textDirection;
+  set textDirection(TextDirection value) {
+    if (_textDirection == value)
+      return;
+    _textDirection = value;
+    _markNeedResolution();
+  }
+
   /// Find a size for the render image within the given constraints.
   ///
   ///  - The dimensions of the RenderImage must fit within the constraints.
@@ -246,15 +317,19 @@ class RenderImage extends RenderBox {
   void paint(PaintingContext context, Offset offset) {
     if (_image == null)
       return;
+    _resolve();
+    assert(_resolvedAlignment != null);
+    assert(_flipHorizontally != null);
     paintImage(
       canvas: context.canvas,
       rect: offset & size,
       image: _image,
       colorFilter: _colorFilter,
       fit: _fit,
-      alignment: _alignment,
+      alignment: _resolvedAlignment,
       centerSlice: _centerSlice,
-      repeat: _repeat
+      repeat: _repeat,
+      flipHorizontally: _flipHorizontally,
     );
   }
 
@@ -271,5 +346,7 @@ class RenderImage extends RenderBox {
     description.add(new DiagnosticsProperty<FractionalOffset>('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'));
+    description.add(new EnumProperty<TextDirection>('textDirection', textDirection, defaultValue: null));
   }
 }

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

@@ -17,7 +17,7 @@ import 'layer.dart';
 import 'node.dart';
 import 'semantics.dart';
 
-export 'package:flutter/foundation.dart' show FlutterError, InformationCollector, DiagnosticsNode, DiagnosticsProperty, StringProperty, DoubleProperty, EnumProperty, IntProperty, DiagnosticPropertiesBuilder;
+export 'package:flutter/foundation.dart' show FlutterError, InformationCollector, DiagnosticsNode, DiagnosticsProperty, StringProperty, DoubleProperty, EnumProperty, FlagProperty, IntProperty, DiagnosticPropertiesBuilder;
 export 'package:flutter/gestures.dart' show HitTestEntry, HitTestResult;
 export 'package:flutter/painting.dart';
 

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

@@ -98,20 +98,20 @@ class RenderPadding extends RenderShiftedBox {
        assert(padding.isNonNegative),
        _textDirection = textDirection,
        _padding = padding,
-       super(child) {
-    _applyUpdate();
-  }
+       super(child);
 
-  // The resolved absolute insets.
   EdgeInsets _resolvedPadding;
 
-  void _applyUpdate() {
-    final EdgeInsets resolvedPadding = padding.resolve(textDirection);
-    assert(resolvedPadding.isNonNegative);
-    if (_resolvedPadding != resolvedPadding) {
-      _resolvedPadding = resolvedPadding;
-      markNeedsLayout();
+  void _resolve() {
+    if (_resolvedPadding != null)
+      return;
+    _resolvedPadding = padding.resolve(textDirection);
+    assert(_resolvedPadding.isNonNegative);
   }
+
+  void _markNeedResolution() {
+    _resolvedPadding = null;
+    markNeedsLayout();
   }
 
   /// The amount to pad the child in each dimension.
@@ -126,21 +126,25 @@ class RenderPadding extends RenderShiftedBox {
     if (_padding == value)
       return;
     _padding = value;
-    _applyUpdate();
+    _markNeedResolution();
   }
 
   /// The text direction with which to resolve [padding].
+  ///
+  /// This may be changed to null, but only after the [padding] has been changed
+  /// to a value that does not depend on the direction.
   TextDirection get textDirection => _textDirection;
   TextDirection _textDirection;
   set textDirection(TextDirection value) {
     if (_textDirection == value)
       return;
     _textDirection = value;
-    _applyUpdate();
+    _markNeedResolution();
   }
 
   @override
   double computeMinIntrinsicWidth(double height) {
+    _resolve();
     final double totalHorizontalPadding = _resolvedPadding.left + _resolvedPadding.right;
     final double totalVerticalPadding = _resolvedPadding.top + _resolvedPadding.bottom;
     if (child != null) // next line relies on double.INFINITY absorption
@@ -150,6 +154,7 @@ class RenderPadding extends RenderShiftedBox {
 
   @override
   double computeMaxIntrinsicWidth(double height) {
+    _resolve();
     final double totalHorizontalPadding = _resolvedPadding.left + _resolvedPadding.right;
     final double totalVerticalPadding = _resolvedPadding.top + _resolvedPadding.bottom;
     if (child != null) // next line relies on double.INFINITY absorption
@@ -159,6 +164,7 @@ class RenderPadding extends RenderShiftedBox {
 
   @override
   double computeMinIntrinsicHeight(double width) {
+    _resolve();
     final double totalHorizontalPadding = _resolvedPadding.left + _resolvedPadding.right;
     final double totalVerticalPadding = _resolvedPadding.top + _resolvedPadding.bottom;
     if (child != null) // next line relies on double.INFINITY absorption
@@ -168,6 +174,7 @@ class RenderPadding extends RenderShiftedBox {
 
   @override
   double computeMaxIntrinsicHeight(double width) {
+    _resolve();
     final double totalHorizontalPadding = _resolvedPadding.left + _resolvedPadding.right;
     final double totalVerticalPadding = _resolvedPadding.top + _resolvedPadding.bottom;
     if (child != null) // next line relies on double.INFINITY absorption
@@ -177,6 +184,7 @@ class RenderPadding extends RenderShiftedBox {
 
   @override
   void performLayout() {
+    _resolve();
     assert(_resolvedPadding != null);
     if (child == null) {
       size = constraints.constrain(new Size(
@@ -226,19 +234,19 @@ abstract class RenderAligningShiftedBox extends RenderShiftedBox {
   }) : assert(alignment != null),
        _alignment = alignment,
        _textDirection = textDirection,
-       super(child) {
-    _applyUpdate();
-  }
+       super(child);
 
-  // The resolved absolute alignment.
   FractionalOffset _resolvedAlignment;
 
-  void _applyUpdate() {
-    final FractionalOffset resolvedAlignment = alignment.resolve(textDirection);
-    if (_resolvedAlignment != resolvedAlignment) {
-      _resolvedAlignment = resolvedAlignment;
-      markNeedsLayout();
+  void _resolve() {
+    if (_resolvedAlignment != null)
+      return;
+    _resolvedAlignment = alignment.resolve(textDirection);
   }
+
+  void _markNeedResolution() {
+    _resolvedAlignment = null;
+    markNeedsLayout();
   }
 
   /// How to align the child.
@@ -251,7 +259,7 @@ abstract class RenderAligningShiftedBox extends RenderShiftedBox {
   /// For example, a value of 0.5 means that the center of the child is aligned
   /// with the center of the parent.
   ///
-  /// If this is set to an [FractionalOffsetDirectional] object, then
+  /// If this is set to a [FractionalOffsetDirectional] object, then
   /// [textDirection] must not be null.
   FractionalOffsetGeometry get alignment => _alignment;
   FractionalOffsetGeometry _alignment;
@@ -263,17 +271,20 @@ abstract class RenderAligningShiftedBox extends RenderShiftedBox {
     if (_alignment == value)
       return;
     _alignment = value;
-    _applyUpdate();
+    _markNeedResolution();
   }
 
   /// The text direction with which to resolve [alignment].
+  ///
+  /// This may be changed to null, but only after [alignment] has been changed
+  /// to a value that does not depend on the direction.
   TextDirection get textDirection => _textDirection;
   TextDirection _textDirection;
   set textDirection(TextDirection value) {
     if (_textDirection == value)
       return;
     _textDirection = value;
-    _applyUpdate();
+    _markNeedResolution();
   }
 
   /// Apply the current [alignment] to the [child].
@@ -285,10 +296,12 @@ abstract class RenderAligningShiftedBox extends RenderShiftedBox {
   /// This method must be called after the child has been laid out and
   /// this object's own size has been set.
   void alignChild() {
+    _resolve();
     assert(child != null);
     assert(!child.debugNeedsLayout);
     assert(child.hasSize);
     assert(hasSize);
+    assert(_resolvedAlignment != null);
     final BoxParentData childParentData = child.parentData;
     childParentData.offset = _resolvedAlignment.alongOffset(size - child.size);
   }

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

@@ -37,22 +37,26 @@ class RenderSliverPadding extends RenderSliver with RenderObjectWithChildMixin<R
        _padding = padding,
        _textDirection = textDirection {
     this.child = child;
-    _applyUpdate();
   }
 
-  // The resolved absolute insets.
   EdgeInsets _resolvedPadding;
 
-  void _applyUpdate() {
-    final EdgeInsets resolvedPadding = padding.resolve(textDirection);
-    assert(resolvedPadding.isNonNegative);
-    if (_resolvedPadding != resolvedPadding) {
-      _resolvedPadding = resolvedPadding;
-      markNeedsLayout();
+  void _resolve() {
+    if (_resolvedPadding != null)
+      return;
+    _resolvedPadding = padding.resolve(textDirection);
+    assert(_resolvedPadding.isNonNegative);
   }
+
+  void _markNeedResolution() {
+    _resolvedPadding = null;
+    markNeedsLayout();
   }
 
   /// The amount to pad the child in each dimension.
+  ///
+  /// If this is set to an [EdgeInsetsDirectional] object, then [textDirection]
+  /// must not be null.
   EdgeInsetsGeometry get padding => _padding;
   EdgeInsetsGeometry _padding;
   set padding(EdgeInsetsGeometry value) {
@@ -61,17 +65,20 @@ class RenderSliverPadding extends RenderSliver with RenderObjectWithChildMixin<R
     if (_padding == value)
       return;
     _padding = value;
-    _applyUpdate();
+    _markNeedResolution();
   }
 
   /// The text direction with which to resolve [padding].
+  ///
+  /// This may be changed to null, but only after the [padding] has been changed
+  /// to a value that does not depend on the direction.
   TextDirection get textDirection => _textDirection;
   TextDirection _textDirection;
   set textDirection(TextDirection value) {
     if (_textDirection == value)
       return;
     _textDirection = value;
-    _applyUpdate();
+    _markNeedResolution();
   }
 
   /// The padding in the scroll direction on the side nearest the 0.0 scroll direction.
@@ -82,6 +89,7 @@ class RenderSliverPadding extends RenderSliver with RenderObjectWithChildMixin<R
     assert(constraints != null);
     assert(constraints.axisDirection != null);
     assert(constraints.growthDirection != null);
+    assert(_resolvedPadding != null);
     switch (applyGrowthDirectionToAxisDirection(constraints.axisDirection, constraints.growthDirection)) {
       case AxisDirection.up:
         return _resolvedPadding.bottom;
@@ -103,6 +111,7 @@ class RenderSliverPadding extends RenderSliver with RenderObjectWithChildMixin<R
     assert(constraints != null);
     assert(constraints.axisDirection != null);
     assert(constraints.growthDirection != null);
+    assert(_resolvedPadding != null);
     switch (applyGrowthDirectionToAxisDirection(constraints.axisDirection, constraints.growthDirection)) {
       case AxisDirection.up:
         return _resolvedPadding.top;
@@ -125,6 +134,7 @@ class RenderSliverPadding extends RenderSliver with RenderObjectWithChildMixin<R
   double get mainAxisPadding {
     assert(constraints != null);
     assert(constraints.axis != null);
+    assert(_resolvedPadding != null);
     return _resolvedPadding.along(constraints.axis);
   }
 
@@ -137,6 +147,7 @@ class RenderSliverPadding extends RenderSliver with RenderObjectWithChildMixin<R
   double get crossAxisPadding {
     assert(constraints != null);
     assert(constraints.axis != null);
+    assert(_resolvedPadding != null);
     switch (constraints.axis) {
       case Axis.horizontal:
         return _resolvedPadding.vertical;
@@ -154,6 +165,8 @@ class RenderSliverPadding extends RenderSliver with RenderObjectWithChildMixin<R
 
   @override
   void performLayout() {
+    _resolve();
+    assert(_resolvedPadding != null);
     final double beforePadding = this.beforePadding;
     final double afterPadding = this.afterPadding;
     final double mainAxisPadding = this.mainAxisPadding;
@@ -248,6 +261,7 @@ class RenderSliverPadding extends RenderSliver with RenderObjectWithChildMixin<R
     assert(constraints != null);
     assert(constraints.axisDirection != null);
     assert(constraints.growthDirection != null);
+    assert(_resolvedPadding != null);
     switch (applyGrowthDirectionToAxisDirection(constraints.axisDirection, constraints.growthDirection)) {
       case AxisDirection.up:
       case AxisDirection.down:

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

@@ -309,7 +309,6 @@ class RenderStack extends RenderBox
        _fit = fit,
        _overflow = overflow {
     addAll(children);
-    _applyUpdate();
   }
 
   bool _hasVisualOverflow = false;
@@ -320,15 +319,17 @@ class RenderStack extends RenderBox
       child.parentData = new StackParentData();
   }
 
-  // The resolved absolute insets.
   FractionalOffset _resolvedAlignment;
 
-  void _applyUpdate() {
-    final FractionalOffset resolvedAlignment = alignment.resolve(textDirection);
-    if (_resolvedAlignment != resolvedAlignment) {
-      _resolvedAlignment = resolvedAlignment;
-      markNeedsLayout();
+  void _resolve() {
+    if (_resolvedAlignment != null)
+      return;
+    _resolvedAlignment = alignment.resolve(textDirection);
   }
+
+  void _markNeedResolution() {
+    _resolvedAlignment = null;
+    markNeedsLayout();
   }
 
   /// How to align the non-positioned children in the stack.
@@ -337,24 +338,30 @@ class RenderStack extends RenderBox
   /// the points determined by [alignment] are co-located. For example, if the
   /// [alignment] is [FractionalOffset.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) {
     assert(value != null);
-    if (_alignment != value) {
+    if (_alignment == value)
+      return;
     _alignment = value;
-      _applyUpdate();
-    }
+    _markNeedResolution();
   }
 
   /// The text direction with which to resolve [alignment].
+  ///
+  /// This may be changed to null, but only after the [alignment] has been changed
+  /// to a value that does not depend on the direction.
   TextDirection get textDirection => _textDirection;
   TextDirection _textDirection;
   set textDirection(TextDirection value) {
-    if (_textDirection != value) {
+    if (_textDirection == value)
+      return;
     _textDirection = value;
-      _applyUpdate();
-    }
+    _markNeedResolution();
   }
 
   /// How to size the non-positioned children in the stack.
@@ -426,6 +433,8 @@ class RenderStack extends RenderBox
 
   @override
   void performLayout() {
+    _resolve();
+    assert(_resolvedAlignment != null);
     _hasVisualOverflow = false;
     bool hasNonPositionedChildren = false;
 

packages/flutter/lib/src/services/image_provider.dart

@@ -6,7 +6,7 @@ import 'dart:async';
 import 'dart:io' show File;
 import 'dart:typed_data';
 import 'dart:ui' as ui show Image;
-import 'dart:ui' show Size, Locale, hashValues;
+import 'dart:ui' show Size, Locale, TextDirection, hashValues;
 
 import 'package:flutter/foundation.dart';
 import 'package:http/http.dart' as http;
@@ -36,8 +36,9 @@ class ImageConfiguration {
     this.bundle,
     this.devicePixelRatio,
     this.locale,
+    this.textDirection,
     this.size,
-    this.platform
+    this.platform,
   });
 
   /// Creates an object holding the configuration information for an [ImageProvider].
@@ -48,15 +49,17 @@ class ImageConfiguration {
     AssetBundle bundle,
     double devicePixelRatio,
     Locale locale,
+    TextDirection textDirection,
     Size size,
-    String platform
+    String platform,
   }) {
     return new ImageConfiguration(
       bundle: bundle ?? this.bundle,
       devicePixelRatio: devicePixelRatio ?? this.devicePixelRatio,
       locale: locale ?? this.locale,
+      textDirection: textDirection ?? this.textDirection,
       size: size ?? this.size,
-      platform: platform ?? this.platform
+      platform: platform ?? this.platform,
     );
   }
 
@@ -70,6 +73,9 @@ class ImageConfiguration {
   /// The language and region for which to select the image.
   final Locale locale;
 
+  /// The reading direction of the language for which to select the image.
+  final TextDirection textDirection;
+
   /// The size at which the image will be rendered.
   final Size size;
 
@@ -92,6 +98,7 @@ class ImageConfiguration {
     return typedOther.bundle == bundle
         && typedOther.devicePixelRatio == devicePixelRatio
         && typedOther.locale == locale
+        && typedOther.textDirection == textDirection
         && typedOther.size == size
         && typedOther.platform == platform;
   }
@@ -122,6 +129,12 @@ class ImageConfiguration {
       result.write('locale: $locale');
       hasArguments = true;
     }
+    if (textDirection != null) {
+      if (hasArguments)
+        result.write(', ');
+      result.write('textDirection: $textDirection');
+      hasArguments = true;
+    }
     if (size != null) {
       if (hasArguments)
         result.write(', ');

packages/flutter/lib/src/services/image_resolution.dart

@@ -224,8 +224,9 @@ class AssetImage extends AssetBundleImageProvider {
     final SplayTreeMap<double, String> mapping = new SplayTreeMap<double, String>();
     for (String candidate in candidates)
       mapping[_parseScale(candidate)] = candidate;
-    // TODO(ianh): implement support for config.locale, config.size, config.platform
-    // (then document this over in the Image.asset docs)
+    // TODO(ianh): implement support for config.locale, config.textDirection,
+    // config.size, config.platform (then document this over in the Image.asset
+    // docs)
     return _findNearest(mapping, config.devicePixelRatio);
   }
 

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

@@ -161,8 +161,8 @@ class AnimatedList extends StatefulWidget {
   /// AnimatedListState animatedList = AnimatedList.of(context);
   /// ```
   static AnimatedListState of(BuildContext context, { bool nullOk: false }) {
-    assert(nullOk != null);
     assert(context != null);
+    assert(nullOk != null);
     final AnimatedListState result = context.ancestorStateOfType(const TypeMatcher<AnimatedListState>());
     if (nullOk || result != null)
       return result;

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

@@ -3826,7 +3826,8 @@ class RichText extends LeafRenderObjectWidget {
 class RawImage extends LeafRenderObjectWidget {
   /// Creates a widget that displays an image.
   ///
-  /// The [scale] and [repeat] arguments must not be null.
+  /// The [scale], [alignment], [repeat], and [matchTextDirection] arguments must
+  /// not be null.
   const RawImage({
     Key key,
     this.image,
@@ -3836,11 +3837,14 @@ class RawImage extends LeafRenderObjectWidget {
     this.color,
     this.colorBlendMode,
     this.fit,
-    this.alignment,
+    this.alignment: FractionalOffset.center,
     this.repeat: ImageRepeat.noRepeat,
-    this.centerSlice
+    this.centerSlice,
+    this.matchTextDirection: false,
   }) : assert(scale != null),
+       assert(alignment != null),
        assert(repeat != null),
+       assert(matchTextDirection != null),
        super(key: key);
 
   /// The image to display.
@@ -3884,10 +3888,23 @@ class RawImage extends LeafRenderObjectWidget {
 
   /// How to align the image within its bounds.
   ///
-  /// An alignment of (0.0, 0.0) aligns the image to the top-left corner of its
-  /// layout bounds.  An alignment of (1.0, 0.5) aligns the image to the middle
-  /// of the right edge of its layout bounds.
-  final FractionalOffset alignment;
+  /// 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
+  /// 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
+  /// 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
+  /// must be in scope.
+  ///
+  /// Defaults to [FractionalOffset.center].
+  final FractionalOffsetGeometry alignment;
 
   /// How to paint any portions of the layout bounds not covered by the image.
   final ImageRepeat repeat;
@@ -3901,8 +3918,26 @@ class RawImage extends LeafRenderObjectWidget {
   /// the center slice will be stretched only vertically.
   final Rect centerSlice;
 
+  /// Whether to paint the image in the direction of the [TextDirection].
+  ///
+  /// If this is true, then in [TextDirection.ltr] contexts, the image will be
+  /// drawn with its origin in the top left (the "normal" painting direction for
+  /// images); and in [TextDirection.rtl] contexts, the image will be drawn with
+  /// a scaling factor of -1 in the horizontal direction so that the origin is
+  /// in the top right.
+  ///
+  /// This is occasionally used with images in right-to-left environments, for
+  /// images that were designed for left-to-right locales. Be careful, when
+  /// using this, to not flip images with integral shadows, text, or other
+  /// effects that will look incorrect when flipped.
+  ///
+  /// If this is true, there must be an ambient [Directionality] widget in
+  /// scope.
+  final bool matchTextDirection;
+
   @override
   RenderImage createRenderObject(BuildContext context) {
+    assert((!matchTextDirection && alignment is FractionalOffset) || debugCheckHasDirectionality(context));
     return new RenderImage(
       image: image,
       width: width,
@@ -3913,7 +3948,9 @@ class RawImage extends LeafRenderObjectWidget {
       fit: fit,
       alignment: alignment,
       repeat: repeat,
-      centerSlice: centerSlice
+      centerSlice: centerSlice,
+      matchTextDirection: matchTextDirection,
+      textDirection: matchTextDirection || alignment is! FractionalOffset ? Directionality.of(context) : null,
     );
   }
 
@@ -3929,7 +3966,9 @@ class RawImage extends LeafRenderObjectWidget {
       ..alignment = alignment
       ..fit = fit
       ..repeat = repeat
-      ..centerSlice = centerSlice;
+      ..centerSlice = centerSlice
+      ..matchTextDirection = matchTextDirection
+      ..textDirection = matchTextDirection || alignment is! FractionalOffset ? Directionality.of(context) : null;
   }
 
   @override
@@ -3942,9 +3981,10 @@ class RawImage extends LeafRenderObjectWidget {
     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<FractionalOffsetGeometry>('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/container.dart

@@ -71,7 +71,7 @@ class DecoratedBox extends SingleChildRenderObjectWidget {
     return new RenderDecoratedBox(
       decoration: decoration,
       position: position,
-      configuration: createLocalImageConfiguration(context)
+      configuration: createLocalImageConfiguration(context),
     );
   }
 

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

@@ -60,7 +60,8 @@ class FadeInImage extends StatefulWidget {
   /// then cross-fades to display the [image].
   ///
   /// The [placeholder], [image], [fadeOutDuration], [fadeOutCurve],
-  /// [fadeInDuration], [fadeInCurve] and [repeat] arguments must not be null.
+  /// [fadeInDuration], [fadeInCurve], [alignment], [repeat], and
+  /// [matchTextDirection] arguments must not be null.
   const FadeInImage({
     Key key,
     @required this.placeholder,
@@ -72,15 +73,18 @@ class FadeInImage extends StatefulWidget {
     this.width,
     this.height,
     this.fit,
-    this.alignment,
+    this.alignment: FractionalOffset.center,
     this.repeat: ImageRepeat.noRepeat,
+    this.matchTextDirection: false,
   }) : assert(placeholder != null),
        assert(image != null),
        assert(fadeOutDuration != null),
        assert(fadeOutCurve != null),
        assert(fadeInDuration != null),
        assert(fadeInCurve != null),
+       assert(alignment != null),
        assert(repeat != null),
+       assert(matchTextDirection != null),
        super(key: key);
 
   /// Creates a widget that uses a placeholder image stored in memory while
@@ -94,8 +98,9 @@ class FadeInImage extends StatefulWidget {
   /// [ImageProvider]s (see also [ImageInfo.scale]).
   ///
   /// The [placeholder], [image], [placeholderScale], [imageScale],
-  /// [fadeOutDuration], [fadeOutCurve], [fadeInDuration], [fadeInCurve] and
-  /// [repeat] arguments must not be null.
+  /// [fadeOutDuration], [fadeOutCurve], [fadeInDuration], [fadeInCurve],
+  /// [alignment], [repeat], and [matchTextDirection] arguments must not be
+  /// null.
   ///
   /// See also:
   ///
@@ -116,8 +121,9 @@ class FadeInImage extends StatefulWidget {
     this.width,
     this.height,
     this.fit,
-    this.alignment,
+    this.alignment: FractionalOffset.center,
     this.repeat: ImageRepeat.noRepeat,
+    this.matchTextDirection: false,
   }) : assert(placeholder != null),
        assert(image != null),
        assert(placeholderScale != null),
@@ -126,7 +132,9 @@ class FadeInImage extends StatefulWidget {
        assert(fadeOutCurve != null),
        assert(fadeInDuration != null),
        assert(fadeInCurve != null),
+       assert(alignment != null),
        assert(repeat != null),
+       assert(matchTextDirection != null),
        placeholder = new MemoryImage(placeholder, scale: placeholderScale),
        image = new NetworkImage(image, scale: imageScale),
        super(key: key);
@@ -146,8 +154,8 @@ class FadeInImage extends StatefulWidget {
   /// exact asset specified will be used.
   ///
   /// The [placeholder], [image], [imageScale], [fadeOutDuration],
-  /// [fadeOutCurve], [fadeInDuration], [fadeInCurve] and [repeat] arguments
-  /// must not be null.
+  /// [fadeOutCurve], [fadeInDuration], [fadeInCurve], [alignment], [repeat],
+  /// and [matchTextDirection] arguments must not be null.
   ///
   /// See also:
   ///
@@ -169,8 +177,9 @@ class FadeInImage extends StatefulWidget {
     this.width,
     this.height,
     this.fit,
-    this.alignment,
+    this.alignment: FractionalOffset.center,
     this.repeat: ImageRepeat.noRepeat,
+    this.matchTextDirection: false,
   }) : assert(placeholder != null),
        assert(image != null),
        placeholder = placeholderScale != null
@@ -181,7 +190,9 @@ class FadeInImage extends StatefulWidget {
        assert(fadeOutCurve != null),
        assert(fadeInDuration != null),
        assert(fadeInCurve != null),
+       assert(alignment != null),
        assert(repeat != null),
+       assert(matchTextDirection != null),
        image = new NetworkImage(image, scale: imageScale),
        super(key: key);
 
@@ -227,14 +238,41 @@ class FadeInImage extends StatefulWidget {
 
   /// How to align the image within its bounds.
   ///
-  /// An alignment of (0.0, 0.0) aligns the image to the top-left corner of its
-  /// layout bounds.  An alignment of (1.0, 0.5) aligns the image to the middle
-  /// of the right edge of its layout bounds.
-  final FractionalOffset alignment;
+  /// 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
+  /// 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
+  /// 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
+  /// must be in scope.
+  ///
+  /// Defaults to [FractionalOffset.center].
+  final FractionalOffsetGeometry alignment;
 
   /// How to paint any portions of the layout bounds not covered by the image.
   final ImageRepeat repeat;
 
+  /// Whether to paint the image in the direction of the [TextDirection].
+  ///
+  /// If this is true, then in [TextDirection.ltr] contexts, the image will be
+  /// drawn with its origin in the top left (the "normal" painting direction for
+  /// images); and in [TextDirection.rtl] contexts, the image will be drawn with
+  /// a scaling factor of -1 in the horizontal direction so that the origin is
+  /// in the top right.
+  ///
+  /// This is occasionally used with images in right-to-left environments, for
+  /// images that were designed for left-to-right locales. Be careful, when
+  /// using this, to not flip images with integral shadows, text, or other
+  /// effects that will look incorrect when flipped.
+  ///
+  /// If this is true, there must be an ambient [Directionality] widget in
+  /// scope.
+  final bool matchTextDirection;
+
   @override
   State<StatefulWidget> createState() => new _FadeInImageState();
 }
@@ -456,6 +494,7 @@ class _FadeInImageState extends State<FadeInImage> with TickerProviderStateMixin
       fit: widget.fit,
       alignment: widget.alignment,
       repeat: widget.repeat,
+      matchTextDirection: widget.matchTextDirection,
     );
   }
 

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

@@ -11,6 +11,7 @@ import 'package:flutter/services.dart';
 
 import 'basic.dart';
 import 'framework.dart';
+import 'localizations.dart';
 import 'media_query.dart';
 
 export 'package:flutter/services.dart' show
@@ -39,7 +40,8 @@ ImageConfiguration createLocalImageConfiguration(BuildContext context, { Size si
   return new ImageConfiguration(
     bundle: DefaultAssetBundle.of(context),
     devicePixelRatio: MediaQuery.of(context, nullOk: true)?.devicePixelRatio ?? 1.0,
-    // TODO(ianh): provide the locale
+    locale: Localizations.localeOf(context, nullOk: true),
+    textDirection: Directionality.of(context),
     size: size,
     platform: defaultTargetPlatform,
   );
@@ -101,7 +103,8 @@ class Image extends StatefulWidget {
   /// To show an image from the network or from an asset bundle, consider using
   /// [new Image.network] and [new Image.asset] respectively.
   ///
-  /// The [image] and [repeat] arguments must not be null.
+  /// The [image], [alignment], [repeat], and [matchTextDirection] arguments
+  /// must not be null.
   const Image({
     Key key,
     @required this.image,
@@ -110,12 +113,16 @@ class Image extends StatefulWidget {
     this.color,
     this.colorBlendMode,
     this.fit,
-    this.alignment,
+    this.alignment: FractionalOffset.center,
     this.repeat: ImageRepeat.noRepeat,
     this.centerSlice,
+    this.matchTextDirection: false,
     this.gaplessPlayback: false,
     this.package,
   }) : assert(image != null),
+       assert(alignment != null),
+       assert(repeat != null),
+       assert(matchTextDirection != null),
        super(key: key);
 
   /// Creates a widget that displays an [ImageStream] obtained from the network.
@@ -129,12 +136,16 @@ class Image extends StatefulWidget {
     this.color,
     this.colorBlendMode,
     this.fit,
-    this.alignment,
+    this.alignment: FractionalOffset.center,
     this.repeat: ImageRepeat.noRepeat,
     this.centerSlice,
+    this.matchTextDirection: false,
     this.gaplessPlayback: false,
     this.package,
   }) : image = new NetworkImage(src, scale: scale),
+       assert(alignment != null),
+       assert(repeat != null),
+       assert(matchTextDirection != null),
        super(key: key);
 
   /// Creates a widget that displays an [ImageStream] obtained from a [File].
@@ -151,12 +162,16 @@ class Image extends StatefulWidget {
     this.color,
     this.colorBlendMode,
     this.fit,
-    this.alignment,
+    this.alignment: FractionalOffset.center,
     this.repeat: ImageRepeat.noRepeat,
     this.centerSlice,
+    this.matchTextDirection: false,
     this.gaplessPlayback: false,
     this.package,
   }) : image = new FileImage(file, scale: scale),
+       assert(alignment != null),
+       assert(repeat != null),
+       assert(matchTextDirection != null),
        super(key: key);
 
   /// Creates a widget that displays an [ImageStream] obtained from an asset
@@ -181,8 +196,9 @@ class Image extends StatefulWidget {
   // ///   size-aware asset resolution will be attempted also, with the given
   // ///   dimensions interpreted as logical pixels.
   // ///
-  // /// * If the images have platform or locale variants, the current platform
-  // ///   and locale is taken into account during asset resolution as well.
+  // /// * If the images have platform, locale, or directionality variants, the
+  // ///   current platform, locale, and directionality are taken into account
+  // ///   during asset resolution as well.
   ///
   /// The [name] and [repeat] arguments must not be null.
   ///
@@ -277,14 +293,18 @@ class Image extends StatefulWidget {
     this.color,
     this.colorBlendMode,
     this.fit,
-    this.alignment,
+    this.alignment: FractionalOffset.center,
     this.repeat: ImageRepeat.noRepeat,
     this.centerSlice,
+    this.matchTextDirection: false,
     this.gaplessPlayback: false,
     this.package,
   }) : image = scale != null
          ? new ExactAssetImage(name, bundle: bundle, scale: scale, package: package)
          : new AssetImage(name, bundle: bundle, package: package),
+       assert(alignment != null),
+       assert(repeat != null),
+       assert(matchTextDirection != null),
        super(key: key);
 
   /// Creates a widget that displays an [ImageStream] obtained from a [Uint8List].
@@ -298,12 +318,16 @@ class Image extends StatefulWidget {
     this.color,
     this.colorBlendMode,
     this.fit,
-    this.alignment,
+    this.alignment: FractionalOffset.center,
     this.repeat: ImageRepeat.noRepeat,
     this.centerSlice,
+    this.matchTextDirection: false,
     this.gaplessPlayback: false,
     this.package,
   }) : image = new MemoryImage(bytes, scale: scale),
+       assert(alignment != null),
+       assert(repeat != null),
+       assert(matchTextDirection != null),
        super(key: key);
 
   /// The image to display.
@@ -342,10 +366,23 @@ class Image extends StatefulWidget {
 
   /// How to align the image within its bounds.
   ///
-  /// An alignment of (0.0, 0.0) aligns the image to the top-left corner of its
-  /// layout bounds.  An alignment of (1.0, 0.5) aligns the image to the middle
-  /// of the right edge of its layout bounds.
-  final FractionalOffset alignment;
+  /// 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
+  /// 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
+  /// 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
+  /// must be in scope.
+  ///
+  /// Defaults to [FractionalOffset.center].
+  final FractionalOffsetGeometry alignment;
 
   /// How to paint any portions of the layout bounds not covered by the image.
   final ImageRepeat repeat;
@@ -359,6 +396,23 @@ class Image extends StatefulWidget {
   /// the center slice will be stretched only vertically.
   final Rect centerSlice;
 
+  /// Whether to paint the image in the direction of the [TextDirection].
+  ///
+  /// If this is true, then in [TextDirection.ltr] contexts, the image will be
+  /// drawn with its origin in the top left (the "normal" painting direction for
+  /// images); and in [TextDirection.rtl] contexts, the image will be drawn with
+  /// a scaling factor of -1 in the horizontal direction so that the origin is
+  /// in the top right.
+  ///
+  /// This is occasionally used with images in right-to-left environments, for
+  /// images that were designed for left-to-right locales. Be careful, when
+  /// using this, to not flip images with integral shadows, text, or other
+  /// effects that will look incorrect when flipped.
+  ///
+  /// If this is true, there must be an ambient [Directionality] widget in
+  /// scope.
+  final bool matchTextDirection;
+
   /// Whether to continue showing the old image (true), or briefly show nothing
   /// (false), when the image provider changes.
   final bool gaplessPlayback;
@@ -379,9 +433,10 @@ 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<FractionalOffset>('alignment', alignment, defaultValue: null));
+    description.add(new DiagnosticsProperty<FractionalOffsetGeometry>('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'));
   }
 }
 
@@ -448,7 +503,8 @@ class _ImageState extends State<Image> {
       fit: widget.fit,
       alignment: widget.alignment,
       repeat: widget.repeat,
-      centerSlice: widget.centerSlice
+      centerSlice: widget.centerSlice,
+      matchTextDirection: widget.matchTextDirection,
     );
   }
 

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

@@ -385,9 +385,16 @@ class Localizations extends StatefulWidget {
 
   /// The locale of the Localizations widget for the widget tree that
   /// corresponds to [BuildContext] `context`.
-  static Locale localeOf(BuildContext context) {
+  ///
+  /// If no [Localizations] widget is in scope then the [Localizations.localeOf]
+  /// method will throw an exception, unless the `nullOk` argument is set to
+  /// true, in which case it returns null.
+  static Locale localeOf(BuildContext context, { bool nullOk: false }) {
     assert(context != null);
+    assert(nullOk != null);
     final _LocalizationsScope scope = context.inheritFromWidgetOfExactType(_LocalizationsScope);
+    if (nullOk && scope == null)
+      return null;
     assert(scope != null, 'a Localizations ancestor was not found');
     return scope.localizationsState.locale;
   }

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

@@ -173,6 +173,8 @@ class MediaQuery extends InheritedWidget {
   /// If you use this from a widget (e.g. in its build function), consider
   /// calling [debugCheckHasMediaQuery].
   static MediaQueryData of(BuildContext context, { bool nullOk: false }) {
+    assert(context != null);
+    assert(nullOk != null);
     final MediaQuery query = context.inheritFromWidgetOfExactType(MediaQuery);
     if (query != null)
       return query.data;

packages/flutter/test/rendering/image_test.dart

@@ -74,6 +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'
       ),
     );
 

packages/flutter/test/rendering/mock_canvas.dart

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui' as ui show Paragraph;
+import 'dart:ui' as ui show Paragraph, Image;
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/rendering.dart';
@@ -278,6 +278,24 @@ abstract class PaintPattern {
   /// If no call to [Canvas.drawParagraph] was made, then this results in failure.
   void paragraph({ ui.Paragraph paragraph, Offset offset });
 
+  /// Indicates that an image is expected next.
+  ///
+  /// The next call to [Canvas.drawImageRect] is examined, and its arguments
+  /// compared to those passed to _this_ method.
+  ///
+  /// If no call to [Canvas.drawImageRect] was made, then this results in
+  /// failure.
+  ///
+  /// Any calls made between the last matched call (if any) and the
+  /// [Canvas.drawImageRect] call are ignored.
+  ///
+  /// The [Paint]-related arguments (`color`, `strokeWidth`, `hasMaskFilter`,
+  /// `style`) are compared against the state of the [Paint] object after the
+  /// painting has completed, not at the time of the call. If the same [Paint]
+  /// object is reused multiple times, then this may not match the actual
+  /// arguments as they were seen by the method.
+  void drawImageRect({ ui.Image image, Rect source, Rect destination, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style });
+
   /// Provides a custom matcher.
   ///
   /// Each method call after the last matched call (if any) will be passed to
@@ -472,6 +490,11 @@ class _TestRecordingCanvasPatternMatcher extends _TestRecordingCanvasMatcher imp
     _predicates.add(new _FunctionPaintPredicate(#drawParagraph, <dynamic>[paragraph, offset]));
   }
 
+  @override
+  void drawImageRect({ ui.Image image, Rect source, Rect destination, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) {
+    _predicates.add(new _DrawImageRectPaintPredicate(image: image, source: source, destination: destination, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style));
+  }
+
   @override
   void something(PaintPatternPredicate predicate) {
     _predicates.add(new _SomethingPaintPredicate(predicate));
@@ -800,6 +823,41 @@ class _ArcPaintPredicate extends _DrawCommandPaintPredicate {
   );
 }
 
+class _DrawImageRectPaintPredicate extends _DrawCommandPaintPredicate {
+  _DrawImageRectPaintPredicate({ this.image, this.source, this.destination, Color color, double strokeWidth, bool hasMaskFilter, PaintingStyle style }) : super(
+    #drawImageRect, 'an image', 4, 3, color: color, strokeWidth: strokeWidth, hasMaskFilter: hasMaskFilter, style: style
+  );
+
+  final ui.Image image;
+  final Rect source;
+  final Rect destination;
+
+  @override
+  void verifyArguments(List<dynamic> arguments) {
+    super.verifyArguments(arguments);
+    final ui.Image imageArgument = arguments[0];
+    if (image != null && imageArgument != image)
+      throw 'It called $methodName with an image, $imageArgument, which was not exactly the expected image ($image).';
+    final Rect sourceArgument = arguments[1];
+    if (source != null && sourceArgument != source)
+      throw 'It called $methodName with a source rectangle, $sourceArgument, which was not exactly the expected rectangle ($source).';
+    final Rect destinationArgument = arguments[2];
+    if (destination != null && destinationArgument != destination)
+      throw 'It called $methodName with a destination rectangle, $destinationArgument, which was not exactly the expected rectangle ($destination).';
+  }
+
+  @override
+  void debugFillDescription(List<String> description) {
+    super.debugFillDescription(description);
+    if (image != null)
+      description.add('image $image');
+    if (source != null)
+      description.add('source $source');
+    if (destination != null)
+      description.add('destination $destination');
+  }
+}
+
 class _SomethingPaintPredicate extends _PaintPredicate {
   _SomethingPaintPredicate(this.predicate);
 

packages/flutter/test/widgets/align_test.dart

@@ -21,6 +21,26 @@ void main() {
         alignment: const FractionalOffset(0.5, 0.5),
       ),
     );
+
+    await tester.pumpWidget(
+      const Align(
+        key: const GlobalObjectKey<Null>(null),
+        alignment: FractionalOffset.topLeft,
+      ),
+    );
+    await tester.pumpWidget(const Directionality(
+      textDirection: TextDirection.rtl,
+      child: const Align(
+        key: const GlobalObjectKey<Null>(null),
+        alignment: FractionalOffsetDirectional.topStart,
+      ),
+    ));
+    await tester.pumpWidget(
+      const Align(
+        key: const GlobalObjectKey<Null>(null),
+        alignment: FractionalOffset.topLeft,
+      ),
+    );
   });
 
   testWidgets('Align control test (LTR)', (WidgetTester tester) async {

packages/flutter/test/widgets/image_rtl_test.dart

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:ui' as ui show Image;
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../rendering/mock_canvas.dart';
+
+class TestImageProvider extends ImageProvider<TestImageProvider> {
+  @override
+  Future<TestImageProvider> obtainKey(ImageConfiguration configuration) {
+    return new SynchronousFuture<TestImageProvider>(this);
+  }
+
+  @override
+  ImageStreamCompleter load(TestImageProvider key) {
+    return new OneFrameImageStreamCompleter(
+      new SynchronousFuture<ImageInfo>(new ImageInfo(image: new TestImage()))
+    );
+  }
+}
+
+class TestImage extends ui.Image {
+  @override
+  int get width => 16;
+
+  @override
+  int get height => 9;
+
+  // @override
+  // void dispose() { }
+}
+
+void main() {
+  testWidgets('DecorationImage RTL with alignment topEnd and match', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.rtl,
+        child: new Center(
+          child: new Container(
+            width: 100.0,
+            height: 50.0,
+            decoration: new BoxDecoration(
+              image: new DecorationImage(
+                image: new TestImageProvider(),
+                alignment: FractionalOffsetDirectional.topEnd,
+                repeat: ImageRepeat.repeatX,
+                matchTextDirection: true,
+              ),
+            ),
+          ),
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    expect(find.byType(Container), paints
+      ..clipRect(rect: new Rect.fromLTRB(0.0, 0.0, 100.0, 50.0))
+      ..translate(x: 50.0, y: 0.0)
+      ..scale(x: -1.0, y: 1.0)
+      ..translate(x: -50.0, y: 0.0)
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(-12.0, 0.0, 4.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(4.0, 0.0, 20.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(20.0, 0.0, 36.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(36.0, 0.0, 52.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(52.0, 0.0, 68.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(68.0, 0.0, 84.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(84.0, 0.0, 100.0, 9.0))
+      ..restore()
+    );
+    expect(find.byType(Container), isNot(paints..scale()..scale()));
+  });
+
+  testWidgets('DecorationImage LTR with alignment topEnd (and pointless match)', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new Center(
+          child: new Container(
+            width: 100.0,
+            height: 50.0,
+            decoration: new BoxDecoration(
+              image: new DecorationImage(
+                image: new TestImageProvider(),
+                alignment: FractionalOffsetDirectional.topEnd,
+                repeat: ImageRepeat.repeatX,
+                matchTextDirection: true,
+              ),
+            ),
+          ),
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    expect(find.byType(Container), paints
+      ..clipRect(rect: new Rect.fromLTRB(0.0, 0.0, 100.0, 50.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(-12.0, 0.0, 4.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(4.0, 0.0, 20.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(20.0, 0.0, 36.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(36.0, 0.0, 52.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(52.0, 0.0, 68.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(68.0, 0.0, 84.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(84.0, 0.0, 100.0, 9.0))
+      ..restore()
+    );
+    expect(find.byType(Container), isNot(paints..scale()));
+  });
+
+  testWidgets('DecorationImage RTL with alignment topEnd', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.rtl,
+        child: new Center(
+          child: new Container(
+            width: 100.0,
+            height: 50.0,
+            decoration: new BoxDecoration(
+              image: new DecorationImage(
+                image: new TestImageProvider(),
+                alignment: FractionalOffsetDirectional.topEnd,
+                repeat: ImageRepeat.repeatX,
+              ),
+            ),
+          ),
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    expect(find.byType(Container), paints
+      ..clipRect(rect: new Rect.fromLTRB(0.0, 0.0, 100.0, 50.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(16.0, 0.0, 32.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(32.0, 0.0, 48.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(48.0, 0.0, 64.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(64.0, 0.0, 80.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(80.0, 0.0, 96.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(96.0, 0.0, 112.0, 9.0))
+      ..restore()
+    );
+    expect(find.byType(Container), isNot(paints..scale()));
+  });
+
+  testWidgets('DecorationImage LTR with alignment topEnd', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new Center(
+          child: new Container(
+            width: 100.0,
+            height: 50.0,
+            decoration: new BoxDecoration(
+              image: new DecorationImage(
+                image: new TestImageProvider(),
+                alignment: FractionalOffsetDirectional.topEnd,
+                repeat: ImageRepeat.repeatX,
+              ),
+            ),
+          ),
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    expect(find.byType(Container), paints
+      ..clipRect(rect: new Rect.fromLTRB(0.0, 0.0, 100.0, 50.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(-12.0, 0.0, 4.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(4.0, 0.0, 20.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(20.0, 0.0, 36.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(36.0, 0.0, 52.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(52.0, 0.0, 68.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(68.0, 0.0, 84.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(84.0, 0.0, 100.0, 9.0))
+      ..restore()
+    );
+    expect(find.byType(Container), isNot(paints..scale()));
+  });
+
+  testWidgets('DecorationImage RTL with alignment center-right and match', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.rtl,
+        child: new Center(
+          child: new Container(
+            width: 100.0,
+            height: 50.0,
+            decoration: new BoxDecoration(
+              image: new DecorationImage(
+                image: new TestImageProvider(),
+                alignment: FractionalOffset.centerRight,
+                matchTextDirection: true,
+              ),
+            ),
+          ),
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    expect(find.byType(Container), paints
+      ..translate(x: 50.0, y: 0.0)
+      ..scale(x: -1.0, y: 1.0)
+      ..translate(x: -50.0, y: 0.0)
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(0.0, 20.5, 16.0, 29.5))
+      ..restore()
+    );
+    expect(find.byType(Container), isNot(paints..scale()..scale()));
+    expect(find.byType(Container), isNot(paints..drawImageRect()..drawImageRect()));
+  });
+
+  testWidgets('DecorationImage RTL with alignment center-right and no match', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.rtl,
+        child: new Center(
+          child: new Container(
+            width: 100.0,
+            height: 50.0,
+            decoration: new BoxDecoration(
+              image: new DecorationImage(
+                image: new TestImageProvider(),
+                alignment: FractionalOffset.centerRight,
+              ),
+            ),
+          ),
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    expect(find.byType(Container), paints
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(84.0, 20.5, 100.0, 29.5))
+    );
+    expect(find.byType(Container), isNot(paints..scale()));
+    expect(find.byType(Container), isNot(paints..drawImageRect()..drawImageRect()));
+  });
+
+  testWidgets('DecorationImage LTR with alignment center-right and match', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new Center(
+          child: new Container(
+            width: 100.0,
+            height: 50.0,
+            decoration: new BoxDecoration(
+              image: new DecorationImage(
+                image: new TestImageProvider(),
+                alignment: FractionalOffset.centerRight,
+                matchTextDirection: true
+              ),
+            ),
+          ),
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    expect(find.byType(Container), paints
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(84.0, 20.5, 100.0, 29.5))
+    );
+    expect(find.byType(Container), isNot(paints..scale()));
+    expect(find.byType(Container), isNot(paints..drawImageRect()..drawImageRect()));
+  });
+
+  testWidgets('DecorationImage LTR with alignment center-right and no match', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new Center(
+          child: new Container(
+            width: 100.0,
+            height: 50.0,
+            decoration: new BoxDecoration(
+              image: new DecorationImage(
+                image: new TestImageProvider(),
+                alignment: FractionalOffset.centerRight,
+                matchTextDirection: true
+              ),
+            ),
+          ),
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    expect(find.byType(Container), paints
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(84.0, 20.5, 100.0, 29.5))
+    );
+    expect(find.byType(Container), isNot(paints..scale()));
+    expect(find.byType(Container), isNot(paints..drawImageRect()..drawImageRect()));
+  });
+
+  testWidgets('Image RTL with alignment topEnd and match', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.rtl,
+        child: new Center(
+          child: new Container(
+            width: 100.0,
+            height: 50.0,
+            child: new Image(
+              image: new TestImageProvider(),
+              alignment: FractionalOffsetDirectional.topEnd,
+              repeat: ImageRepeat.repeatX,
+              matchTextDirection: true,
+            ),
+          ),
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    expect(find.byType(Container), paints
+      ..clipRect(rect: new Rect.fromLTRB(0.0, 0.0, 100.0, 50.0))
+      ..translate(x: 50.0, y: 0.0)
+      ..scale(x: -1.0, y: 1.0)
+      ..translate(x: -50.0, y: 0.0)
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(-12.0, 0.0, 4.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(4.0, 0.0, 20.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(20.0, 0.0, 36.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(36.0, 0.0, 52.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(52.0, 0.0, 68.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(68.0, 0.0, 84.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(84.0, 0.0, 100.0, 9.0))
+      ..restore()
+    );
+    expect(find.byType(Container), isNot(paints..scale()..scale()));
+  });
+
+  testWidgets('Image LTR with alignment topEnd (and pointless match)', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new Center(
+          child: new Container(
+            width: 100.0,
+            height: 50.0,
+            child: new Image(
+              image: new TestImageProvider(),
+              alignment: FractionalOffsetDirectional.topEnd,
+              repeat: ImageRepeat.repeatX,
+              matchTextDirection: true,
+            ),
+          ),
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    expect(find.byType(Container), paints
+      ..clipRect(rect: new Rect.fromLTRB(0.0, 0.0, 100.0, 50.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(-12.0, 0.0, 4.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(4.0, 0.0, 20.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(20.0, 0.0, 36.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(36.0, 0.0, 52.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(52.0, 0.0, 68.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(68.0, 0.0, 84.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(84.0, 0.0, 100.0, 9.0))
+      ..restore()
+    );
+    expect(find.byType(Container), isNot(paints..scale()));
+  });
+
+  testWidgets('Image RTL with alignment topEnd', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.rtl,
+        child: new Center(
+          child: new Container(
+            width: 100.0,
+            height: 50.0,
+            child: new Image(
+              image: new TestImageProvider(),
+              alignment: FractionalOffsetDirectional.topEnd,
+              repeat: ImageRepeat.repeatX,
+            ),
+          ),
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    expect(find.byType(Container), paints
+      ..clipRect(rect: new Rect.fromLTRB(0.0, 0.0, 100.0, 50.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(16.0, 0.0, 32.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(32.0, 0.0, 48.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(48.0, 0.0, 64.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(64.0, 0.0, 80.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(80.0, 0.0, 96.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(96.0, 0.0, 112.0, 9.0))
+      ..restore()
+    );
+    expect(find.byType(Container), isNot(paints..scale()));
+  });
+
+  testWidgets('Image LTR with alignment topEnd', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new Center(
+          child: new Container(
+            width: 100.0,
+            height: 50.0,
+            child: new Image(
+              image: new TestImageProvider(),
+              alignment: FractionalOffsetDirectional.topEnd,
+              repeat: ImageRepeat.repeatX,
+            ),
+          ),
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    expect(find.byType(Container), paints
+      ..clipRect(rect: new Rect.fromLTRB(0.0, 0.0, 100.0, 50.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(-12.0, 0.0, 4.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(4.0, 0.0, 20.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(20.0, 0.0, 36.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(36.0, 0.0, 52.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(52.0, 0.0, 68.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(68.0, 0.0, 84.0, 9.0))
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(84.0, 0.0, 100.0, 9.0))
+      ..restore()
+    );
+    expect(find.byType(Container), isNot(paints..scale()));
+  });
+
+  testWidgets('Image RTL with alignment center-right and match', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.rtl,
+        child: new Center(
+          child: new Container(
+            width: 100.0,
+            height: 50.0,
+            child: new Image(
+              image: new TestImageProvider(),
+              alignment: FractionalOffset.centerRight,
+              matchTextDirection: true,
+            ),
+          ),
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    expect(find.byType(Container), paints
+      ..translate(x: 50.0, y: 0.0)
+      ..scale(x: -1.0, y: 1.0)
+      ..translate(x: -50.0, y: 0.0)
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(0.0, 20.5, 16.0, 29.5))
+      ..restore()
+    );
+    expect(find.byType(Container), isNot(paints..scale()..scale()));
+    expect(find.byType(Container), isNot(paints..drawImageRect()..drawImageRect()));
+  });
+
+  testWidgets('Image RTL with alignment center-right and no match', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.rtl,
+        child: new Center(
+          child: new Container(
+            width: 100.0,
+            height: 50.0,
+            child: new Image(
+              image: new TestImageProvider(),
+              alignment: FractionalOffset.centerRight,
+            ),
+          ),
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    expect(find.byType(Container), paints
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(84.0, 20.5, 100.0, 29.5))
+    );
+    expect(find.byType(Container), isNot(paints..scale()));
+    expect(find.byType(Container), isNot(paints..drawImageRect()..drawImageRect()));
+  });
+
+  testWidgets('Image LTR with alignment center-right and match', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new Center(
+          child: new Container(
+            width: 100.0,
+            height: 50.0,
+            child: new Image(
+              image: new TestImageProvider(),
+              alignment: FractionalOffset.centerRight,
+              matchTextDirection: true
+            ),
+          ),
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    expect(find.byType(Container), paints
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(84.0, 20.5, 100.0, 29.5))
+    );
+    expect(find.byType(Container), isNot(paints..scale()));
+    expect(find.byType(Container), isNot(paints..drawImageRect()..drawImageRect()));
+  });
+
+  testWidgets('Image LTR with alignment center-right and no match', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new Center(
+          child: new Container(
+            width: 100.0,
+            height: 50.0,
+            child: new Image(
+              image: new TestImageProvider(),
+              alignment: FractionalOffset.centerRight,
+              matchTextDirection: true
+            ),
+          ),
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    expect(find.byType(Container), paints
+      ..drawImageRect(source: new Rect.fromLTRB(0.0, 0.0, 16.0, 9.0), destination: new Rect.fromLTRB(84.0, 20.5, 100.0, 29.5))
+    );
+    expect(find.byType(Container), isNot(paints..scale()));
+    expect(find.byType(Container), isNot(paints..drawImageRect()..drawImageRect()));
+  });
+
+  testWidgets('Image - Switch needing direction', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new Image(
+          image: new TestImageProvider(),
+          alignment: FractionalOffset.centerRight,
+          matchTextDirection: false,
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new Image(
+          image: new TestImageProvider(),
+          alignment: FractionalOffsetDirectional.centerEnd,
+          matchTextDirection: true,
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new Image(
+          image: new TestImageProvider(),
+          alignment: FractionalOffset.centerRight,
+          matchTextDirection: false,
+        ),
+      ),
+      Duration.ZERO,
+      EnginePhase.layout, // so that we don't try to paint the fake images
+    );
+  });
+}
\ No newline at end of file

packages/flutter/test/widgets/rtl_test.dart

@@ -21,6 +21,26 @@ void main() {
       child: child,
     ));
     expect(tester.getTopLeft(find.byType(Placeholder)), const Offset(0.0, 0.0));
+
+    await tester.pumpWidget(
+      const Padding(
+        key: const GlobalObjectKey<Null>(null),
+        padding: const EdgeInsets.only(left: 1.0),
+      ),
+    );
+    await tester.pumpWidget(const Directionality(
+      textDirection: TextDirection.rtl,
+      child: const Padding(
+        key: const GlobalObjectKey<Null>(null),
+        padding: const EdgeInsetsDirectional.only(start: 1.0),
+      ),
+    ));
+    await tester.pumpWidget(
+      const Padding(
+        key: const GlobalObjectKey<Null>(null),
+        padding: const EdgeInsets.only(left: 1.0),
+      ),
+    );
   });
 
   testWidgets('Container padding/margin RTL', (WidgetTester tester) async {

packages/flutter/test/widgets/stack_test.dart

@@ -610,4 +610,23 @@ void main() {
 
     expect(tester.getTopLeft(find.byKey(key)), const Offset(50.0, 0.0));
   });
+
+  testWidgets('Can change the text direction of a Stack', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new Stack(
+        alignment: FractionalOffset.center,
+      ),
+    );
+    await tester.pumpWidget(
+      new Stack(
+        alignment: FractionalOffsetDirectional.topStart,
+        textDirection: TextDirection.rtl,
+      ),
+    );
+    await tester.pumpWidget(
+      new Stack(
+        alignment: FractionalOffset.center,
+      ),
+    );
+  });
 }