`CupertinoAlertDialog` fading in/out leaves a temporary black square

[dkwingsmt]

Steps to reproduce

1. Run the dialog example app on iOS simulator examples/api/lib/cupertino/route/show_cupertino_dialog.0.dart
2. Opens and closes the dialog. Notice then fading animation

Expected results

Smooth fading transiting (shot on c56ab6b, the parent of 35b0349)

before.mp4

Actual results

A temporary black square (shot on 35b0349)

after.mp4

Code sample

import 'package:flutter/cupertino.dart';

Widget createAppWithButtonThatLaunchesDialog({
  required WidgetBuilder dialogBuilder,
  bool? useMaterial3,
}) {
  return CupertinoApp(
    home: CupertinoPageScaffold(
      child: Center(
        child: Builder(builder: (BuildContext context) {
          return CupertinoButton(
            onPressed: () {
              showCupertinoDialog<void>(
                context: context,
                builder: dialogBuilder,
              );
            },
            child: const Text('After PR'),
          );
        }),
      ),
    ),
  );
}

void main() => runApp(const ActionSheetApp());

class ActionSheetApp extends StatelessWidget {
  const ActionSheetApp({super.key});

  @override
  Widget build(BuildContext context) {
    return createAppWithButtonThatLaunchesDialog(
        dialogBuilder: (BuildContext context) {
          return CupertinoAlertDialog(
            title: const Text('The title'),
            actions: <Widget>[
              CupertinoDialogAction(
                child: Text('Enabled'),
                onPressed: () { Navigator.pop(context); },
              ),
              CupertinoDialogAction(
                child: Text('Disabled'),
              ),
            ],
          );
        },
      );
  }
}

Screenshots or Video

No response

Logs

No response

Flutter Doctor output

Doctor output

[!] Flutter (Channel [user-branch], 3.25.0-1.0.pre.287, on macOS 14.6.1 23G93 darwin-arm64, locale en-US)
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      Currently on an unknown channel. Run `flutter channel` to switch to an official channel.
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    ! Upstream repository unknown source is not a standard remote.
      Set environment variable "FLUTTER_GIT_URL" to unknown source to dismiss this error.
    • Framework revision 35b0349294 (3 days ago), 2024-09-06 11:47:11 -0400
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[✓] Connected device (5 available)
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    • All expected network resources are available.

! Doctor found issues in 3 categories.

[dkwingsmt]

cc @davidhicks980

This regression is pretty severe to me that I suggest reverting #151430.

[davidhicks980]

@dkwingsmt So I ran a few tests and it appears to be the blend mode parameter that's causing the issue. I'm okay with either reverting for further investigation, or providing a patch that removes the blendMode line. Let me know if I should do either.

if (filter != null) {
      return ClipRRect(
        borderRadius: _clipper,
        child: BackdropFilter(
          blendMode: BlendMode.src, // THIS LINE
          filter: filter,
          child: contents,
        ),
      );
    }

[dkwingsmt]

Unless you can do some immediate investigation, let's revert it for now. We can always reland it once you resolve the problem.

[danagbemava-nc]

Reproducible using the code sample provided above.

flutter doctor -v

[✓] Flutter (Channel stable, 3.24.2, on macOS 14.6.1 23G93 darwin-arm64, locale en-US)
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• No issues found!

[!] Flutter (Channel master, 3.25.0-1.0.pre.320, on macOS 14.6.1 23G93 darwin-arm64, locale en-US)
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    • Upstream repository https://github.com/flutter/flutter.git
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[✓] Connected device (5 available)
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    • Nexus (mobile)                  • 00008020-001875E83A38002E • ios            • iOS 17.6.1 21G93
    • macOS (desktop)                 • macos                     • darwin-arm64   • macOS 14.6.1 23G93 darwin-arm64
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! Doctor found issues in 1 category.