CustomPainter: saveLayer with ImageFilter.blur gives unexpected offset from the edge

### Steps to reproduce

Please use the code sample.

### Expected results

I'm trying to draw a blurred red rectangle that is partially outside the CustomPainter/Canvas edge. Like this:

![Image](https://github.com/user-attachments/assets/3d309de5-d028-452b-9e67-6e2207eb3ca7)

This is a very  simple task with many possible implementations.

### Actual results

I ran into a problem when I tried to implement this using negative scale (canvas.scale(-1, 1)) and saveLayer with ImageFilter.blur. Please see the code sample. Only 46 lines of code.

**In DartPad, everything looks exactly as it should!** The screenshot above is from DartPad. However, in the iOS simulator, the same code produces an unexpected offset from the edge of the canvas:

![Image](https://github.com/user-attachments/assets/357c82aa-832c-4010-87ac-f1cc5ec74550)

I can't find an explanation for this behavior. Is it a bug?

### Code sample

<details closed><summary>Code sample</summary>

```dart
import 'dart:ui';
import 'package:flutter/material.dart';

void main() {
  runApp(
    Container(
      alignment: Alignment.center,
      color: Colors.grey,
      child: Container(
        color: Colors.black,
        padding: EdgeInsetsGeometry.all(1),
        width: 352,
        height: 352,
        child: ClipRect(
          child: CustomPaint(size: Size(350, 350), painter: TestPainter()),
        ),
      ),
    ),
  );
}

class TestPainter extends CustomPainter {
  const TestPainter();

  @override
  void paint(Canvas canvas, Size size) {
    canvas.drawRect(
      Rect.fromLTWH(0, 0, 350, 350),
      Paint()..color = Colors.white,
    );

    canvas.scale(-1, 1);
    canvas.saveLayer(
      Rect.fromLTWH(-150, 100, 300, 100),
      Paint()..imageFilter = ImageFilter.blur(sigmaX: 10, sigmaY: 10),
    );
    canvas.drawRect(
      Rect.fromLTWH(-150, 0, 300, 300),
      Paint()..color = Colors.red,
    );
    canvas.restore();
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) => true;
}
```

</details>


### Screenshots or Video




### Logs




### Flutter Doctor output

<details closed><summary>Doctor output</summary>

```console
[✓] Flutter (Channel stable, 3.41.5, on macOS 26.2 25C56 darwin-arm64, locale xx) [546ms]
    • Flutter version 3.41.5 on channel stable at /Users/xxxxx/Development/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 2c9eb20739 (2 days ago), 2026-03-17 16:14:01 -0700
    • Engine revision 052f31d115
    • Dart version 3.11.3
    • DevTools version 2.54.2
    • Feature flags: enable-web, enable-linux-desktop, enable-macos-desktop, enable-windows-desktop, enable-android, enable-ios, cli-animations,
      enable-native-assets, omit-legacy-version-file, enable-lldb-debugging, enable-uiscene-migration

[✓] Android toolchain - develop for Android devices (Android SDK version 36.1.0) [2,7s]
    • Android SDK at /Users/xxxxx/Library/Android/sdk
    • Emulator version 36.2.12.0 (build_id 14214601) (CL:N/A)
    • Platform android-36, build-tools 36.1.0
    • Java binary at: /Users/xxxxx/Library/Java/JavaVirtualMachines/corretto-22.0.2/Contents/Home/bin/java
      This JDK is specified in your Flutter configuration.
      To change the current JDK, run: `flutter config --jdk-dir="path/to/jdk"`.
    • Java version OpenJDK Runtime Environment Corretto-22.0.2.9.1 (build 22.0.2+9-FR)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 26.3) [1 109ms]
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 17C529
    • CocoaPods version 1.16.2

[✓] Chrome - develop for the web [5ms]
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Connected device (4 available) [10,8s]
    • iPhone 16e (mobile)              • F0F08FFB-1780-4D9E-9638-2DB271A7E24F • ios            • com.apple.CoreSimulator.SimRuntime.iOS-26-2
      (simulator)
    • macOS (desktop)                  • macos                                • darwin-arm64   • macOS 26.2 25C56 darwin-arm64
    • Chrome (web)                     • chrome                               • web-javascript • Google Chrome 146.0.7680.153

[✓] Network resources [677ms]
    • All expected network resources are available.

• No issues found!
```

</details>


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CustomPainter: saveLayer with ImageFilter.blur gives unexpected offset from the edge #183884

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Uh oh!

CustomPainter: saveLayer with ImageFilter.blur gives unexpected offset from the edge #183884

Description

Steps to reproduce

Expected results

Actual results

Code sample

Screenshots or Video

Logs

Flutter Doctor output

Metadata

Metadata

Assignees

Labels

Type

Fields

Projects

Milestone

Relationships

Development

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