Make upscaling images opt-in

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

@@ -71,26 +71,37 @@ mixin PaintingBinding on BindingBase, ServicesBinding {
   @protected
   ImageCache createImageCache() => ImageCache();
 
-  /// Calls through to [dart:ui] with [decodedCacheRatioCap] from [ImageCache].
+  /// Calls through to [dart:ui] from [ImageCache].
   ///
-  /// The [cacheWidth] and [cacheHeight] parameters, when specified, indicate the
-  /// size to decode the image to.
+  /// The `cacheWidth` and `cacheHeight` parameters, when specified, indicate
+  /// the size to decode the image to.
   ///
-  /// Both [cacheWidth] and [cacheHeight] must be positive values greater than or
-  /// equal to 1 or null. It is valid to specify only one of [cacheWidth] and
-  /// [cacheHeight] with the other remaining null, in which case the omitted
-  /// dimension will decode to its original size. When both are null or omitted,
-  /// the image will be decoded at its native resolution.
+  /// Both `cacheWidth` and `cacheHeight` must be positive values greater than
+  /// or equal to 1, or null. It is valid to specify only one of `cacheWidth`
+  /// and `cacheHeight` with the other remaining null, in which case the omitted
+  /// dimension will be scaled to maintain the aspect ratio of the original
+  /// dimensions. When both are null or omitted, the image will be decoded at
+  /// its native resolution.
+  ///
+  /// The `allowUpscaling` parameter determines whether the `cacheWidth` or
+  /// `cacheHeight` parameters are clamped to the intrinsic width and height of
+  /// the original image. By default, the dimensions are clamped to avoid
+  /// unnecessary memory usage for images. Callers that wish to display an image
+  /// above its native resolution should prefer scaling the canvas the image is
+  /// drawn into.
   Future<ui.Codec> instantiateImageCodec(Uint8List bytes, {
     int cacheWidth,
     int cacheHeight,
+    bool allowUpscaling = false,
   }) {
     assert(cacheWidth == null || cacheWidth > 0);
     assert(cacheHeight == null || cacheHeight > 0);
+    assert(allowUpscaling != null);
     return ui.instantiateImageCodec(
       bytes,
       targetWidth: cacheWidth,
       targetHeight: cacheHeight,
+      allowUpscaling: allowUpscaling,
     );
   }
 

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

@@ -162,13 +162,15 @@ class ImageConfiguration {
 
 /// Performs the decode process for use in [ImageProvider.load].
 ///
-/// This callback allows decoupling of the `cacheWidth` and `cacheHeight`
-/// parameters from implementations of [ImageProvider] that do not use them.
+/// This callback allows decoupling of the `cacheWidth`, `cacheHeight`, and
+/// `allowUpscaling` parameters from implementations of [ImageProvider] that do
+/// not expose them.
 ///
 /// See also:
 ///
-///  * [ResizeImage], which uses this to override the `cacheWidth` and `cacheHeight` parameters.
-typedef DecoderCallback = Future<ui.Codec> Function(Uint8List bytes, {int cacheWidth, int cacheHeight});
+///  * [ResizeImage], which uses this to override the `cacheWidth`,
+///    `cacheHeight`, and `allowUpscaling` parameters.
+typedef DecoderCallback = Future<ui.Codec> Function(Uint8List bytes, {int cacheWidth, int cacheHeight, bool allowUpscaling});
 
 /// Identifies an image without committing to the precise final asset. This
 /// allows a set of images to be identified and for the precise image to later
@@ -718,7 +720,9 @@ class ResizeImage extends ImageProvider<_SizeAwareCacheKey> {
     this.imageProvider, {
     this.width,
     this.height,
-  }) : assert(width != null || height != null);
+    this.allowUpscaling = false,
+  }) : assert(width != null || height != null),
+       assert(allowUpscaling != null);
 
   /// The [ImageProvider] that this class wraps.
   final ImageProvider imageProvider;
@@ -729,6 +733,15 @@ class ResizeImage extends ImageProvider<_SizeAwareCacheKey> {
   /// The height the image should decode to and cache.
   final int height;
 
+  /// Whether the [width] and [height] parameters should be clamped to the
+  /// intrinsic width and height of the image.
+  ///
+  /// In general, it is better for memory usage to avoid scaling the image
+  /// beyond its intrinsic dimensions when decoding it. If there is a need to
+  /// scale an image larger, it is better to apply a scale to the canvas, or
+  /// to use an appropriate [Image.fit].
+  final bool allowUpscaling;
+
   /// Composes the `provider` in a [ResizeImage] only when `cacheWidth` and
   /// `cacheHeight` are not both null.
   ///
@@ -743,12 +756,13 @@ class ResizeImage extends ImageProvider<_SizeAwareCacheKey> {
 
   @override
   ImageStreamCompleter load(_SizeAwareCacheKey key, DecoderCallback decode) {
-    final DecoderCallback decodeResize = (Uint8List bytes, {int cacheWidth, int cacheHeight}) {
+    final DecoderCallback decodeResize = (Uint8List bytes, {int cacheWidth, int cacheHeight, bool allowUpscaling}) {
       assert(
-        cacheWidth == null && cacheHeight == null,
-        'ResizeImage cannot be composed with another ImageProvider that applies cacheWidth or cacheHeight.'
+        cacheWidth == null && cacheHeight == null && allowUpscaling == null,
+        'ResizeImage cannot be composed with another ImageProvider that applies '
+        'cacheWidth, cacheHeight, or allowUpscaling.'
       );
-      return decode(bytes, cacheWidth: width, cacheHeight: height);
+      return decode(bytes, cacheWidth: width, cacheHeight: height, allowUpscaling: this.allowUpscaling);
     };
     return imageProvider.load(key.providerCacheKey, decodeResize);
   }

packages/flutter/test/painting/image_data.dart

@@ -4,6 +4,21 @@
 
 // @dart = 2.8
 
+
+/// A 50x50 blue square png.
+const List<int> kBlueSquare = <int>[
+  0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d, 0x49,
+  0x48, 0x44, 0x52, 0x00, 0x00, 0x00, 0x32, 0x00, 0x00, 0x00, 0x32, 0x08, 0x06,
+  0x00, 0x00, 0x00, 0x1e, 0x3f, 0x88, 0xb1, 0x00, 0x00, 0x00, 0x48, 0x49, 0x44,
+  0x41, 0x54, 0x78, 0xda, 0xed, 0xcf, 0x31, 0x0d, 0x00, 0x30, 0x08, 0x00, 0xb0,
+  0x61, 0x63, 0x2f, 0xfe, 0x2d, 0x61, 0x05, 0x34, 0xf0, 0x92, 0xd6, 0x41, 0x23,
+  0x7f, 0xf5, 0x3b, 0x20, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44,
+  0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44,
+  0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44, 0x44,
+  0x44, 0x44, 0x44, 0x36, 0x06, 0x03, 0x6e, 0x69, 0x47, 0x12, 0x8e, 0xea, 0xaa,
+  0x00, 0x00, 0x00, 0x00, 0x49, 0x45, 0x4e, 0x44, 0xae, 0x42, 0x60, 0x82,
+];
+
 const List<int> kTransparentImage = <int>[
   0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A, 0x00, 0x00, 0x00, 0x0D, 0x49,
   0x48, 0x44, 0x52, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01, 0x08, 0x06,

packages/flutter/test/painting/image_provider_and_image_cache_test.dart

@@ -19,8 +19,8 @@ import 'mocks_for_image_cache.dart';
 void main() {
   TestRenderingFlutterBinding();
 
-  final DecoderCallback _basicDecoder = (Uint8List bytes, {int cacheWidth, int cacheHeight}) {
-    return PaintingBinding.instance.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight);
+  final DecoderCallback _basicDecoder = (Uint8List bytes, {int cacheWidth, int cacheHeight, bool allowUpscaling}) {
+    return PaintingBinding.instance.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight, allowUpscaling: allowUpscaling ?? false);
   };
 
   FlutterExceptionHandler oldError;

packages/flutter/test/painting/image_provider_network_image_test.dart

@@ -20,8 +20,8 @@ import 'image_data.dart';
 void main() {
   TestRenderingFlutterBinding();
 
-  final DecoderCallback _basicDecoder = (Uint8List bytes, {int cacheWidth, int cacheHeight}) {
-    return PaintingBinding.instance.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight);
+  final DecoderCallback _basicDecoder = (Uint8List bytes, {int cacheWidth, int cacheHeight, bool allowUpscaling}) {
+    return PaintingBinding.instance.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight, allowUpscaling: allowUpscaling);
   };
 
   _MockHttpClient httpClient;

packages/flutter/test/painting/image_provider_resize_image_test.dart

@@ -21,13 +21,40 @@ void main() {
     PaintingBinding.instance.imageCache.clearLiveImages();
   });
 
-  test('ResizeImage resizes to the correct dimensions', () async {
+  test('ResizeImage resizes to the correct dimensions (up)', () async {
     final Uint8List bytes = Uint8List.fromList(kTransparentImage);
     final MemoryImage imageProvider = MemoryImage(bytes);
     final Size rawImageSize = await _resolveAndGetSize(imageProvider);
     expect(rawImageSize, const Size(1, 1));
 
     const Size resizeDims = Size(14, 7);
+    final ResizeImage resizedImage = ResizeImage(MemoryImage(bytes), width: resizeDims.width.round(), height: resizeDims.height.round(), allowUpscaling: true);
+    const ImageConfiguration resizeConfig = ImageConfiguration(size: resizeDims);
+    final Size resizedImageSize = await _resolveAndGetSize(resizedImage, configuration: resizeConfig);
+    expect(resizedImageSize, resizeDims);
+  }, skip: isBrowser); // https://github.com/flutter/flutter/issues/56312
+
+
+  test('ResizeImage resizes to the correct dimensions (down)', () async {
+    final Uint8List bytes = Uint8List.fromList(kBlueSquare);
+    final MemoryImage imageProvider = MemoryImage(bytes);
+    final Size rawImageSize = await _resolveAndGetSize(imageProvider);
+    expect(rawImageSize, const Size(50, 50));
+
+    const Size resizeDims = Size(25, 25);
+    final ResizeImage resizedImage = ResizeImage(MemoryImage(bytes), width: resizeDims.width.round(), height: resizeDims.height.round(), allowUpscaling: true);
+    const ImageConfiguration resizeConfig = ImageConfiguration(size: resizeDims);
+    final Size resizedImageSize = await _resolveAndGetSize(resizedImage, configuration: resizeConfig);
+    expect(resizedImageSize, resizeDims);
+  }, skip: isBrowser); // https://github.com/flutter/flutter/issues/56312
+
+  test('ResizeImage resizes to the correct dimensions - no upscaling', () async {
+    final Uint8List bytes = Uint8List.fromList(kTransparentImage);
+    final MemoryImage imageProvider = MemoryImage(bytes);
+    final Size rawImageSize = await _resolveAndGetSize(imageProvider);
+    expect(rawImageSize, const Size(1, 1));
+
+    const Size resizeDims = Size(1, 1);
     final ResizeImage resizedImage = ResizeImage(MemoryImage(bytes), width: resizeDims.width.round(), height: resizeDims.height.round());
     const ImageConfiguration resizeConfig = ImageConfiguration(size: resizeDims);
     final Size resizedImageSize = await _resolveAndGetSize(resizedImage, configuration: resizeConfig);
@@ -73,10 +100,11 @@ void main() {
     final MemoryImage memoryImage = MemoryImage(bytes);
     final ResizeImage resizeImage = ResizeImage(memoryImage, width: 123, height: 321);
 
-    final DecoderCallback decode = (Uint8List bytes, {int cacheWidth, int cacheHeight}) {
+    final DecoderCallback decode = (Uint8List bytes, {int cacheWidth, int cacheHeight, bool allowUpscaling}) {
       expect(cacheWidth, 123);
       expect(cacheHeight, 321);
-      return PaintingBinding.instance.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight);
+      expect(allowUpscaling, false);
+      return PaintingBinding.instance.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight, allowUpscaling: allowUpscaling);
     };
 
     resizeImage.load(await resizeImage.obtainKey(ImageConfiguration.empty), decode);

packages/flutter/test/painting/painting_utils.dart

@@ -17,7 +17,7 @@ class PaintingBindingSpy extends BindingBase with SchedulerBinding, ServicesBind
   int get instantiateImageCodecCalledCount => counter;
 
   @override
-  Future<ui.Codec> instantiateImageCodec(Uint8List list, {int cacheWidth, int cacheHeight}) {
+  Future<ui.Codec> instantiateImageCodec(Uint8List list, {int cacheWidth, int cacheHeight, bool allowUpscaling = false}) {
     counter++;
     return ui.instantiateImageCodec(list);
   }

packages/flutter/test/widgets/fade_in_image_test.dart

@@ -323,11 +323,12 @@ Future<void> main() async {
         );
 
         bool called = false;
-        final DecoderCallback decode = (Uint8List bytes, {int cacheWidth, int cacheHeight}) {
+        final DecoderCallback decode = (Uint8List bytes, {int cacheWidth, int cacheHeight, bool allowUpscaling}) {
           expect(cacheWidth, 20);
           expect(cacheHeight, 30);
+          expect(allowUpscaling, false);
           called = true;
-          return PaintingBinding.instance.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight);
+          return PaintingBinding.instance.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight, allowUpscaling: allowUpscaling);
         };
         final ImageProvider resizeImage = image.placeholder;
         expect(image.placeholder, isA<ResizeImage>());
@@ -345,9 +346,10 @@ Future<void> main() async {
         );
 
         bool called = false;
-        final DecoderCallback decode = (Uint8List bytes, {int cacheWidth, int cacheHeight}) {
+        final DecoderCallback decode = (Uint8List bytes, {int cacheWidth, int cacheHeight, bool allowUpscaling}) {
           expect(cacheWidth, null);
           expect(cacheHeight, null);
+          expect(allowUpscaling, null);
           called = true;
           return PaintingBinding.instance.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight);
         };