always pass filterQuality specified in the Image widget to canvas (flutter#74854)

Author: yjbanov

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

@@ -473,9 +473,7 @@ void paintImage({
   final Paint paint = Paint()..isAntiAlias = isAntiAlias;
   if (colorFilter != null)
     paint.colorFilter = colorFilter;
-  if (sourceSize != destinationSize) {
-    paint.filterQuality = filterQuality;
-  }
+  paint.filterQuality = filterQuality;
   paint.invertColors = invertColors;
   final double halfWidthDelta = (outputSize.width - destinationSize.width) / 2.0;
   final double halfHeightDelta = (outputSize.height - destinationSize.height) / 2.0;

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

@@ -312,10 +312,9 @@ class Image extends StatefulWidget {
   /// Otherwise, the image dimensions will change as the image is loaded, which
   /// will result in ugly layout changes.
   ///
-  /// Use [filterQuality] to change the quality when scaling an image.
-  /// Use the [FilterQuality.low] quality setting to scale the image,
-  /// which corresponds to bilinear interpolation, rather than the default
-  /// [FilterQuality.none] which corresponds to nearest-neighbor.
+  /// {@template flutter.widgets.image.filterQualityParameter}
+  /// Use [filterQuality] to specify the rendering quality of the image.
+  /// {@endtemplate}
   ///
   /// If [excludeFromSemantics] is true, then [semanticLabel] will be ignored.
   const Image({
@@ -360,10 +359,7 @@ class Image extends StatefulWidget {
   /// An optional [headers] argument can be used to send custom HTTP headers
   /// with the image request.
   ///
-  /// Use [filterQuality] to change the quality when scaling an image.
-  /// Use the [FilterQuality.low] quality setting to scale the image,
-  /// which corresponds to bilinear interpolation, rather than the default
-  /// [FilterQuality.none] which corresponds to nearest-neighbor.
+  /// {@macro flutter.widgets.image.filterQualityParameter}
   ///
   /// If [excludeFromSemantics] is true, then [semanticLabel] will be ignored.
   ///
@@ -424,10 +420,7 @@ class Image extends StatefulWidget {
   /// On Android, this may require the
   /// `android.permission.READ_EXTERNAL_STORAGE` permission.
   ///
-  /// Use [filterQuality] to change the quality when scaling an image.
-  /// Use the [FilterQuality.low] quality setting to scale the image,
-  /// which corresponds to bilinear interpolation, rather than the default
-  /// [FilterQuality.none] which corresponds to nearest-neighbor.
+  /// {@macro flutter.widgets.image.filterQualityParameter}
   ///
   /// If [excludeFromSemantics] is true, then [semanticLabel] will be ignored.
   ///
@@ -520,10 +513,7 @@ class Image extends StatefulWidget {
   /// Otherwise, the image dimensions will change as the image is loaded, which
   /// will result in ugly layout changes.
   ///
-  /// Use [filterQuality] to change the quality when scaling an image.
-  /// Use the [FilterQuality.low] quality setting to scale the image,
-  /// which corresponds to bilinear interpolation, rather than the default
-  /// [FilterQuality.none] which corresponds to nearest-neighbor.
+  /// {@macro flutter.widgets.image.filterQualityParameter}
   ///
   /// {@tool snippet}
   ///
@@ -667,10 +657,7 @@ class Image extends StatefulWidget {
   /// Otherwise, the image dimensions will change as the image is loaded, which
   /// will result in ugly layout changes.
   ///
-  /// Use [filterQuality] to change the quality when scaling an image.
-  /// Use the [FilterQuality.low] quality setting to scale the image,
-  /// which corresponds to bilinear interpolation, rather than the default
-  /// [FilterQuality.none] which corresponds to nearest-neighbor.
+  /// {@macro flutter.widgets.image.filterQualityParameter}
   ///
   /// If [excludeFromSemantics] is true, then [semanticLabel] will be ignored.
   ///
@@ -930,11 +917,22 @@ class Image extends StatefulWidget {
   /// If non-null, this color is blended with each image pixel using [colorBlendMode].
   final Color? color;
 
-  /// Used to set the [FilterQuality] of the image.
+  /// The rendering quality of the image.
+  ///
+  /// If the image is of a high quality and its pixels are perfectly aligned
+  /// with the physical screen pixels, extra quality enhancement may not be
+  /// necessary. If so, then [FilterQuality.none] would be the most efficient.
+  ///
+  /// If the pixels are not perfectly aligned with the screen pixels, or if the
+  /// image itself is of a low quality, [FilterQuality.none] may produce
+  /// undesirable artifacts. Consider using other [FilterQuality] values to
+  /// improve the rendered image quality in this case. Pixels may be misaligned
+  /// with the screen pixels as a result of transforms or scaling.
+  ///
+  /// See also:
   ///
-  /// Use the [FilterQuality.low] quality setting to scale the image with
-  /// bilinear interpolation, or the [FilterQuality.none] which corresponds
-  /// to nearest-neighbor.
+  ///  * [FilterQuality], the enum containing all possible filter quality
+  ///    options.
   final FilterQuality filterQuality;
 
   /// Used to combine [color] with this image.

packages/flutter/test/widgets/image_test.dart

@@ -1877,6 +1877,61 @@ void main() {
     expect(tester.widget<Padding>(find.byType(Padding)).child, isA<RawImage>());
     expect(find.byKey(errorKey), findsNothing);
   });
+
+  testWidgets('Image at default filterQuality', (WidgetTester tester) async {
+    await testImageQuality(tester, null);
+  });
+
+  testWidgets('Image at high filterQuality', (WidgetTester tester) async {
+    await testImageQuality(tester, ui.FilterQuality.high);
+  });
+
+  testWidgets('Image at none filterQuality', (WidgetTester tester) async {
+    await testImageQuality(tester, ui.FilterQuality.none);
+  });
+}
+
+Future<void> testImageQuality(WidgetTester tester, ui.FilterQuality? quality) async {
+  await tester.binding.setSurfaceSize(const ui.Size(3, 3));
+  // A 3x3 image encoded as PNG with white background and black pixels on the diagonal:
+  // ┌──────┐
+  // │▓▓    │
+  // │  ▓▓  │
+  // │    ▓▓│
+  // └──────┘
+  // At different levels of quality these pixels are blurred differently.
+  final Uint8List test3x3Image = Uint8List.fromList(<int>[
+    0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d,
+    0x49, 0x48, 0x44, 0x52, 0x00, 0x00, 0x00, 0x03, 0x00, 0x00, 0x00, 0x03,
+    0x08, 0x02, 0x00, 0x00, 0x00, 0xd9, 0x4a, 0x22, 0xe8, 0x00, 0x00, 0x00,
+    0x1b, 0x49, 0x44, 0x41, 0x54, 0x08, 0xd7, 0x63, 0x64, 0x60, 0x60, 0xf8,
+    0xff, 0xff, 0x3f, 0x03, 0x9c, 0xfa, 0xff, 0xff, 0x3f, 0xc3, 0xff, 0xff,
+    0xff, 0x21, 0x1c, 0x00, 0xcb, 0x70, 0x0e, 0xf3, 0x5d, 0x11, 0xc2, 0xf8,
+    0x00, 0x00, 0x00, 0x00, 0x49, 0x45, 0x4e, 0x44, 0xae, 0x42, 0x60, 0x82,
+  ]);
+  final ui.Image image = (await tester.runAsync(() async {
+    final ui.Codec codec = await ui.instantiateImageCodec(test3x3Image);
+    return (await codec.getNextFrame()).image;
+  }))!;
+  expect(image.width, 3);
+  expect(image.height, 3);
+  final TestImageStreamCompleter streamCompleter = TestImageStreamCompleter();
+  streamCompleter.setData(imageInfo: ImageInfo(image: image));
+  final TestImageProvider imageProvider = TestImageProvider(streamCompleter: streamCompleter);
+
+  await tester.pumpWidget(
+    quality == null
+      ? Image(image: imageProvider)
+      : Image(
+          image: imageProvider,
+          filterQuality: quality,
+        ),
+  );
+
+  await expectLater(
+    find.byType(Image),
+    matchesGoldenFile('image_quality_${quality ?? 'default'}.png'),
+  );
 }
 
 class ImagePainter extends CustomPainter {

packages/flutter_test/lib/src/animation_sheet.dart

@@ -169,6 +169,9 @@ class AnimationSheetBuilder {
         image: image.clone(),
         width: frameSize.width,
         height: frameSize.height,
+        // Disable quality enhancement because the point of this class is to
+        // precisely record what the widget looks like.
+        filterQuality: ui.FilterQuality.none,
       )).toList(),
     );
   }