Plumix 0.4 beta: the Cupertino port, Android and iOS hosts

Plumix started as an experiment: what if Flutter's architecture — not a look-alike, the actual Widget → Element → RenderObject pipeline — ran on .NET? With 0.4 the experiment becomes a beta. The framework layer, the Material library and now the Cupertino library are strict ports of Flutter 3.47, and the same widget tree runs on desktop, Android, iOS and in the browser.

This post is the human-readable summary. The full list, with the Dart source of every port and every breaking change by name, is in the changelog.

The Cupertino library, ported

Every file in Flutter's cupertino_ui package now has a C# counterpart in Plumix.Cupertino:

• CupertinoApp, the Cupertino theme, colours and text theme, with dynamic colours resolved for light, dark and high-contrast modes;
• page and tab scaffolds, large-title navigation bars, iOS page routes with the swipe-back gesture, and sheets;
• wheel pickers (CupertinoPicker, CupertinoDatePicker, CupertinoTimerPicker), text fields with iOS selection handles, segmented controls and the pull-to-refresh control;
• list sections and tiles, context menus, the menu anchor, action sheets and alert dialogs;
• the icon set and localizations for 116 locales.

The milestone stays open for its last exit criteria: auditing that every Material .Adaptive factory composes the Cupertino widget the way Flutter does, and running the sample gallery's Cupertino tab through CupertinoApp on every host. The Cupertino catalog lists the main widgets.

Hosts are now engine embedders

The biggest change is one you don't see in widget code. A Plumix host used to lay out and paint the render tree itself; now it behaves like a Flutter engine embedder. The framework builds retained Scenes through SceneBuilder, and the host only rasterizes what FlutterView.Render hands it. Pointer data, metrics, locales, accessibility and key events arrive through PlatformDispatcher, and text input, key events and platform calls go over the same flutter/textinput, flutter/keyevent and flutter/platform channels a Flutter engine uses.

That boundary is what makes more hosts cheap. 0.4 ships:

• Desktop — Windows, macOS and Linux through Avalonia, the most mature host;
• Android — the new Plumix.Android package, with PlumixMainActivity and the system back button routed to WidgetsApp;
• iOS and browser (WebAssembly) sample hosts in the repository.

Cross-host stability is the current milestone. The main open item on iOS is an ahead-of-time compilation crash that has to be fixed before a release candidate.

A dart:ui surface underneath

To port Flutter code faithfully you need Flutter's lower layers, not just its widgets. 0.4 adds a dart:ui-shaped API: Canvas, Picture and Paint with blend modes and mask filters, Flutter's own Color type, native Path geometry and metrics, and a Paragraph with SkParagraph-compatible metrics. Anti-aliasing for rounded rectangles and paths now matches Skia exactly — the precondition for comparing every sample screen against a capture of the same screen in real Flutter.

Material, re-ported strictly

Every Material widget family was ported by August; this release re-ports buttons and ButtonStyle, Switch, sliders, ink features, Scaffold, AppBar, the date and time pickers, TextField and InputDecorator, ThemeData and more against the pinned Flutter source. Two large tables come along: the 8,825-icon Icons catalog and GlobalMaterialLocalizations for 119 locales.

Testing like Flutter does

FrameworkDartTester brings flutter_test's finders, matchers and TestTextInput to C#, so Flutter's own widget tests can be ported per subsystem. The suite runs green in Debug, Profile and Release, and CI also runs it against the newest Avalonia release of the supported major version.

Breaking changes

This is a beta, and it breaks things on purpose — almost always to move closer to Flutter. The largest groups:

• Hosts: Avalonia 12.1.4 is the minimum; PlumixHost no longer lays out or paints, it rasterizes scenes; hosts speak the Flutter channels instead of custom key and text-input types.
• Painting: the framework Color replaces Avalonia's Color in every API; Matrix4 replaces the affine pipeline; text styles and paragraphs follow Dart's types.
• Material and Cupertino: many controls were re-ported strictly, and parameters that don't exist in Flutter are gone.

Each one is listed by name in the changelog.

Try it

dotnet add package Plumix --prerelease
dotnet add package Plumix.Material --prerelease

The getting-started guide builds a first app in a few minutes. If you're coming from Flutter, porting a widget line by line shows how directly the code translates.

What's next

The road to 1.0.0-rc.1 is public in the framework plan. The release candidate freezes the public API, and it needs three things first: the Cupertino milestone's last exit criteria, Android and iOS hosts building cleanly with the iOS crash fixed, and every sample route matching its Flutter screenshot or documenting why not.