Backends

Every Nucleus window is a Compose composable. The backend is the layer beneath it: it runs the OS event loop, owns the native window handle, and presents Skia's GPU surface on screen. Nucleus 2.0 uses Tao as its backend behind the same DecoratedWindow API.

The Tao backend

Tao is the Rust windowing layer that also underpins Tauri 2. Nucleus makes it the default for new projects. Tao replaces the toolkit entirely, so the JVM never loads AWT.

The Tao backend adds:

• Native Wayland. No XWayland fallback, with fractional scaling and gestures.
• Multi-touch and gestures. Pinch, swipe, and rotate arrive as Compose pointer events that carry pressure, tilt, and source.
• Pen and stylus. Pressure-sensitive input from devices such as Wacom tablets, the Surface Pen, and Apple Pencil.
• Per-monitor HiDPI. Mixed-DPI setups are handled as you drag a window between displays.
• NativeView. Embed any platform-native view inside a Compose window — NSView on macOS, HWND on Windows, GtkWidget on Linux (SwiftUI, Win32/WinUI, WebView2, GTK, and anything else that exposes those handles).

See Tao for the full surface.

Select a backend

import dev.nucleusframework.application.NucleusBackend
import dev.nucleusframework.application.nucleusApplication

fun main() = nucleusApplication(backend = NucleusBackend.Tao) {
    DecoratedWindow(onCloseRequest = ::exitApplication, title = "MyApp") {
        // your Compose UI
    }
}

NucleusBackend has three values:

• Auto uses Tao when decorated-window-tao is on the classpath, otherwise the deprecated AWT backend. This is the default.
• Tao forces the Tao backend.
• Awt forces the deprecated AWT backend, using JBR or JNI depending on which is resolved.

Reach the native window

The DecoratedWindow composable is identical across backends. When you need a backend-specific call, reach the underlying handle through the window's escape hatches:

• nucleusWindow.unsafe.taoWindow returns the Tao-owned TaoWindow.
• nucleusWindow.unsafe.awtWindow returns the AWT ComposeWindow (deprecated backend only).

Each returns null on the other backend.

What's next

• Tao — the full backend surface: gestures, pen, Wayland, and NativeView.
• Decorated Window — the window you compose on top of a backend.
• Migrating from JBR to Tao — a checklist for existing apps.