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[framework] lerp images in a save layer. (#131703)
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Without a saveLayer, the BlendMode.plus will add itself to the backdrop and not just the previous image. Pushing without tests to see if existing goldens fail, but otherwise I have some good examples locally.

This is necessary uncondtionally, and lerping lerped images has the same issue.

Fixes flutter/flutter#131617

### Before

![flutter_02](https://github.com/flutter/flutter/assets/8975114/1e783285-2fc2-429f-9fd8-6d04d4a155e1)

### After

![flutter_03](https://github.com/flutter/flutter/assets/8975114/3d08b187-26aa-4471-926d-e9ed5946a206)
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@jonahwilliams
jonahwilliams authored Aug 2, 2023
1 parent 5720dea commit 253bd3d
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2 changes: 2 additions & 0 deletions packages/flutter/lib/src/painting/decoration_image.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -815,8 +815,10 @@ class _BlendedDecorationImagePainter implements DecorationImagePainter {

@override
void paint(Canvas canvas, Rect rect, Path? clipPath, ImageConfiguration configuration, { double blend = 1.0, BlendMode blendMode = BlendMode.srcOver }) {
canvas.saveLayer(null, Paint());
a?.paint(canvas, rect, clipPath, configuration, blend: blend * (1.0 - t), blendMode: blendMode);
b?.paint(canvas, rect, clipPath, configuration, blend: blend * t, blendMode: a != null ? BlendMode.plus : blendMode);
canvas.restore();
}

@override
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163 changes: 163 additions & 0 deletions packages/flutter/test/painting/decoration_image_lerp_test.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -405,6 +405,169 @@ void main() {
expect(getPixelFromBlock(19, 19, 19), const Color(0xFF000000));
}
}, skip: kIsWeb); // TODO(ianh): https://github.com/flutter/flutter/issues/130612, https://github.com/flutter/flutter/issues/130609

testWidgets('ImageDecoration.lerp with colored background', (WidgetTester tester) async {
final MemoryImage cmyk = MemoryImage(Uint8List.fromList(<int>[
0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d, 0x49, 0x48, 0x44, 0x52,
0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00, 0x04, 0x02, 0x03, 0x00, 0x00, 0x00, 0xd4, 0x9f, 0x76,
0xed, 0x00, 0x00, 0x00, 0x0c, 0x50, 0x4c, 0x54, 0x45, 0x00, 0xff, 0xff, 0xff, 0x00, 0xff, 0xff,
0xff, 0x00, 0x00, 0x00, 0x00, 0x3b, 0x4c, 0x59, 0x13, 0x00, 0x00, 0x00, 0x0e, 0x49, 0x44, 0x41,
0x54, 0x08, 0xd7, 0x63, 0x60, 0x05, 0xc2, 0xf5, 0x0c, 0xeb, 0x01, 0x03, 0x00, 0x01, 0x69, 0x19,
0xea, 0x34, 0x7b, 0x00, 0x00, 0x00, 0x00, 0x49, 0x45, 0x4e, 0x44, 0xae, 0x42, 0x60, 0x82,
]));
final MemoryImage wrgb = MemoryImage(Uint8List.fromList(<int>[
0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d, 0x49, 0x48, 0x44, 0x52,
0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00, 0x04, 0x02, 0x03, 0x00, 0x00, 0x00, 0xd4, 0x9f, 0x76,
0xed, 0x00, 0x00, 0x00, 0x0c, 0x50, 0x4c, 0x54, 0x45, 0xff, 0xff, 0xff, 0x00, 0x00, 0xff, 0x00,
0xff, 0x00, 0xff, 0x00, 0x00, 0x1e, 0x46, 0xbb, 0x1c, 0x00, 0x00, 0x00, 0x0e, 0x49, 0x44, 0x41,
0x54, 0x08, 0xd7, 0x63, 0xe0, 0x07, 0xc2, 0xa5, 0x0c, 0x4b, 0x01, 0x03, 0x50, 0x01, 0x69, 0x4a,
0x78, 0x1d, 0x41, 0x00, 0x00, 0x00, 0x00, 0x49, 0x45, 0x4e, 0x44, 0xae, 0x42, 0x60, 0x82,
]));

await tester.runAsync(() async {
await load(cmyk);
await load(wrgb);
});

await tester.pumpWidget(
ColoredBox(
color: Colors.pink,
child: Align(
alignment: Alignment.topLeft,
child: Wrap(
textDirection: TextDirection.ltr,
children: <Widget>[
TestImage(DecorationImage.lerp(
DecorationImage(image: wrgb, fit: BoxFit.contain),
DecorationImage(image: cmyk, fit: BoxFit.contain),
0.0,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: wrgb, fit: BoxFit.contain),
DecorationImage(image: cmyk, fit: BoxFit.contain),
0.1,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: wrgb, fit: BoxFit.contain),
DecorationImage(image: cmyk, fit: BoxFit.contain),
0.2,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: wrgb, fit: BoxFit.contain),
DecorationImage(image: cmyk, fit: BoxFit.contain),
0.5,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: wrgb, fit: BoxFit.contain),
DecorationImage(image: cmyk, fit: BoxFit.contain),
0.8,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: wrgb, fit: BoxFit.contain),
DecorationImage(image: cmyk, fit: BoxFit.contain),
0.9,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: wrgb, fit: BoxFit.contain),
DecorationImage(image: cmyk, fit: BoxFit.contain),
1.0,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: wrgb, fit: BoxFit.cover),
DecorationImage(image: cmyk, repeat: ImageRepeat.repeat),
0.5,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: wrgb, repeat: ImageRepeat.repeat),
DecorationImage(image: cmyk, repeat: ImageRepeat.repeatY),
0.5,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: wrgb, repeat: ImageRepeat.repeatX),
DecorationImage(image: cmyk, repeat: ImageRepeat.repeat),
0.5,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: wrgb, repeat: ImageRepeat.repeat, opacity: 0.2),
DecorationImage(image: cmyk, repeat: ImageRepeat.repeat, opacity: 0.2),
0.25,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: wrgb, repeat: ImageRepeat.repeat, opacity: 0.2),
DecorationImage(image: cmyk, repeat: ImageRepeat.repeat, opacity: 0.2),
0.5,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: wrgb, repeat: ImageRepeat.repeat, opacity: 0.2),
DecorationImage(image: cmyk, repeat: ImageRepeat.repeat, opacity: 0.2),
0.75,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: wrgb, scale: 0.5, repeat: ImageRepeat.repeatX),
DecorationImage(image: cmyk, scale: 0.25, repeat: ImageRepeat.repeatY),
0.5,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(2.0, 2.0, 1.0, 1.0)),
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(2.0, 2.0, 1.0, 1.0)),
0.0,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(2.0, 2.0, 1.0, 1.0)),
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(2.0, 2.0, 1.0, 1.0)),
0.25,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(2.0, 2.0, 1.0, 1.0)),
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(2.0, 2.0, 1.0, 1.0)),
0.5,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(2.0, 2.0, 1.0, 1.0)),
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(2.0, 2.0, 1.0, 1.0)),
0.75,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(2.0, 2.0, 1.0, 1.0)),
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(2.0, 2.0, 1.0, 1.0)),
1.0,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(0.0, 0.0, 1.0, 1.0)),
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(2.0, 2.0, 1.0, 1.0)),
0.0,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(0.0, 0.0, 1.0, 1.0)),
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(2.0, 2.0, 1.0, 1.0)),
0.25,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(0.0, 0.0, 1.0, 1.0)),
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(2.0, 2.0, 1.0, 1.0)),
0.5,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(0.0, 0.0, 1.0, 1.0)),
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(2.0, 2.0, 1.0, 1.0)),
0.75,
)),
TestImage(DecorationImage.lerp(
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(0.0, 0.0, 1.0, 1.0)),
DecorationImage(image: cmyk, centerSlice: const Rect.fromLTWH(2.0, 2.0, 1.0, 1.0)),
1.0,
)),
],
),
),
),
);

await expectLater(
find.byType(Wrap),
matchesGoldenFile('decoration_image.lerp.2.png'),
);
}, skip: kIsWeb); // TODO(ianh): https://github.com/flutter/flutter/issues/130612, https://github.com/flutter/flutter/issues/130609
}

Future<void> load(MemoryImage image) {
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