SwiftOpenUI

Write SwiftUI, run anywhere.

A cross-platform SwiftUI framework that renders natively on macOS, Linux, Windows, and the Web — from a single Swift codebase.

Color Studio — one codebase, four platforms

macOS (SwiftUI)	Linux (GTK4)
Windows (Win32)	Web (Wasm)

Same Swift code. Native rendering on each platform. No electron, no webview wrappers.

SimplePaint — Canvas, Path, and gesture input

A MacPaint-class drawing app with pencil, eraser, line, rectangle, and ellipse tools. Demonstrates Canvas rendering, Path-based drawing, drag gestures, and undo/redo — all from a single main.swift.

Layout Stress Test — advanced composition patterns

macOS (SwiftUI)	Linux (GTK4)	Windows (Win32)

Settings rows, dashboard cards, sidebar/detail split, nested frame alignment, and status bars — the composition patterns real apps use. Layout parity is verified by a 50-scenario test suite that compares each platform's output against macOS SwiftUI reference fixtures.

Platform Support

Platform	Backend	Status	Views	Modifiers
macOS	SwiftUI (native)	Reference	All	All
Linux	GTK4	Stable	44/45	38/40
Windows	Win32 + D2D	Stable	43/45	38/40
Web	Wasm + DOM	Near-parity	42/45	36/40
Android	Compose	Functional	27/45	23/40

Feature Parity

SwiftOpenUI now tracks parity at two levels:

Doc	Purpose
Feature Parity Matrix	Backend-by-backend behavior status for SwiftUI features, with notes for GTK4, Win32, Web, and Android
API Implementation Tracker	SwiftUI API-surface coverage, availability, and current vs partial vs missing status by feature family

Use the matrix when you want to know how a feature behaves on a specific backend. Use the implementation tracker when you want to know whether a SwiftUI view or modifier family exists in SwiftOpenUI at all.

Current examples:

• .searchable() is implemented on GTK4, Win32, and Web, with fallback-level placement and lightweight token/suggestion/scope UI documented in the matrix.
• .safeAreaInset() and .safeAreaPadding() exist on GTK4, Win32, and Web, with synthetic or partial backend behavior documented in the matrix.
• .toolbar() and .sheet() have working GTK4, Win32, and Web support, while the tracker shows which overload families are implemented vs still pending.

Android support is functional via Jetpack Compose. Core form components, collection views, and precision layout are implemented.

Quick Start

# Clone
git clone https://github.com/codelynx/SwiftOpenUI.git
cd SwiftOpenUI
# Run on macOS (uses real SwiftUI)
swift run HelloWorld
swift run ColorMixer
# Run on Linux (GTK4)
sudo apt install libgtk-4-dev
swift run ColorMixer
# Run in browser (Wasm)
./web/run.sh ColorMixer
# Run on Android (Emulator/Device)
./android/renderer/build-so.sh
cd android/renderer/app && ./gradlew installDebug

For detailed per-platform setup (prerequisites, toolchains, Vite, GTK4 packages, Visual Studio), see the Getting Started Guide.

App Packaging

Package any executable as a .app bundle using the built-in SPM plugin:

swift package create-bundle HelloWorld --allow-writing-to-package-directory
# Output: .build/bundles/HelloWorld.app

Creates a platform-appropriate bundle (macOS: Contents/MacOS/ + Info.plist; Linux: Info.json + lib/; Windows: Info.json + .exe). Resources from Resources/ at the package root are copied automatically.

During development (swift run), AppBundle.main discovers resources from Resources/ at the package root without needing a packaged bundle.

See the App Bundle Packaging Guide for details.

Examples

Showcase

Polished mini-apps demonstrating what you can build:

Example	Command	Description
HelloWorld	swift run HelloWorld	Minimal app — Text with padding
Stopwatch	swift run Stopwatch	Timer, start/stop, lap times
ColorMixer	swift run ColorMixer	Color picker with sliders, swatches, harmony
Calculator	swift run Calculator	Grid/GridRow calculator with arithmetic logic
SimplePaint	swift run SimplePaint	Drawing app with tools, color palette, undo/redo
LayoutStress	swift run LayoutStress	Settings rows, dashboard cards, sidebar/detail, nested alignment, status bar

Parity

Matrix-backed coverage screens — one per feature category:

swift run ParityViewsBasic # Text, Button, TextField, Color, Spacer, Divider
swift run ParityViewsLayout # VStack, HStack, ZStack, ForEach, Group
swift run ParityViewsContainers # Toggle, Slider, Image, ScrollView, List
swift run ParityModifiers # padding, frame, colors, font, border, opacity
swift run ParityStateData # @State, @Binding, @ObservedObject, @StateObject
swift run ParityNavigation # NavigationStack, NavigationLink, NavigationPath
swift run ParityEnvironment # @Environment, @EnvironmentObject, custom keys
swift run ParityGestures # onTapGesture, onLongPressGesture, onDrag
swift run ParityAnimation # .animation(), withAnimation()
swift run ParityFocus # @FocusState, .focused()
swift run ParityAppStructure # App, Scene, WindowGroup, @ViewBuilder

What's Implemented

Views (44 of 45)

Text, Button, TextField, Toggle, Slider, Image, Color, Spacer, Divider, VStack, HStack, ZStack, Group, ForEach, List, ScrollView, ScrollViewReader, AnyView, EmptyView, NavigationStack, NavigationLink, NavigationSplitView, SecureField, TextEditor, ProgressView, Stepper, Label, Link, TabView, Grid, GridRow, DisclosureGroup, OutlineGroup, Form, Section, LazyVStack, LazyHStack, LazyVGrid, LazyHGrid, Picker, DatePicker, GeometryReader, ViewThatFits, Menu, ConfirmationDialog, Canvas, Path, Circle, Rectangle, RoundedRectangle, Capsule, Ellipse, LinearGradient, RadialGradient

Modifiers (43+)

.padding(), .frame(), .foregroundColor(), .foregroundStyle(), .background(), .font(), .border(), .opacity(), .offset(), .scaleEffect(), .animation(), .imageScale(), .onTapGesture(), .onLongPressGesture(), .onDrag(), .disabled(), .environmentObject(), .environment(), .navigationTitle(), .navigationDestination(), .focused(), .modifier(), withAnimation(), .clipShape(), .clipped(), .hidden(), .blur(), .cornerRadius(), .shadow(), .rotationEffect(), .overlay(), .sheet(), .alert(), .confirmationDialog(), .onAppear(), .onDisappear(), .searchable(), .toolbar(), .gridCellColumns(), .buttonStyle(), .toggleStyle(), .textFieldStyle(), .onChange(), .contextMenu(), .position(), .layoutPriority(), .fixedSize(), .popover(), .id(), .tag(), .onSubmit(), .bold(), .italic(), .fontWeight(), .underline(), .strikethrough(), .textCase(), .aspectRatio(), .scaledToFit(), .scaledToFill(), .fullScreenCover(), .pickerStyle(), .navigationSplitViewColumnWidth(), .ignoresSafeArea(), .safeAreaInset(), .lineLimit(), .truncationMode(), .lineSpacing(), .multilineTextAlignment(), .keyboardShortcut(), .focusedValue(), .help(), .resizable(), .labelsHidden()

Scenes & App Structure

WindowGroup, Window (GTK/Win32), OpenWindowAction, Commands (CommandGroup, CommandMenuItem — native menu bar on GTK/Win32), @SceneBuilder, @ViewBuilder

State Management

@State, @Binding, @Bindable, @ObservedObject, @StateObject, @EnvironmentObject, @Published, @Environment, @FocusState, @FocusedValue (active-window scoped), @Observable, ObservableObject

Architecture

+-----------------------------------------------------+
| Examples (import SwiftUI on macOS, SwiftOpenUI else)|
+-----------------------------------------------------+
| SwiftOpenUI Core |
| View, State, Layout, Modifiers, Environment |
+--------------+---------------+---------------+-------------+
| BackendGTK4 | BackendWin32 | BackendWeb | BackendDroid|
| GTKRenderer | WinRenderer | WebRenderer | AndroidRend.|
| GTKViewHost | Win32ViewHost| WebViewHost | AndroidHost |
+--------------+---------------+---------------+-------------+
| CGTK | CWin32 | JavaScriptKit| JNI |
| CGTKBridge | CWin32Bridge | (DOM API) | Compose |
+--------------+---------------+---------------+-------------+

The core library (Sources/SwiftOpenUI/) is platform-independent with zero platform imports. All GTK/Win32/Web code lives in Sources/Backend/. Backends implement rendering via protocol extensions (GTKRenderable, WinRenderable, WebRenderable).

Building

Platform	Prerequisites	Build	Test
macOS	Xcode CLI tools	swift build	swift test
Linux	libgtk-4-dev	swift build	swift test
Windows	Swift toolchain	swift build	swift test
Web	swiftly + Wasm SDK	./web/run.sh HelloWorld	N/A

Xcode

brew install xcodegen
cd apple/Examples && xcodegen generate
open Examples.xcodeproj

Documentation

Doc	Description
Feature Parity Matrix	Per-backend implementation status
API Implementation Tracker	SwiftUI API-surface coverage and generated feature-family status
Running Examples	Build and run on all platforms
Adding a Backend	How to implement a new backend
Web Setup	Wasm build, Vite, DOM mapping
App Bundle Format	Cross-platform .app bundle spec
App Bundle Packaging	Packaging guide + SPM plugin
Platform Notes	Platform quirks and workarounds
Web Parity Plan	Web backend gap analysis

Contributing

1. Pick a view or modifier from the parity matrix
2. Add the core definition in Sources/SwiftOpenUI/Views/ or Modifiers/
3. Add backend rendering in each renderer (see adding a backend)
4. Add tests in Tests/SwiftOpenUITests/
5. Add coverage to the appropriate parity example

License

MIT License. See LICENSE for details.