July 21, 2026 · 5 min read

Platform backends: Avalonia, Uno, and Headless

Majorsilence.Forms does all of its own drawing with SkiaSharp. Every control paints into an SKSurface/SKCanvas; the windowing toolkit underneath is only a host — it creates native windows, runs the message loop, delivers input, and presents the Skia surface to the screen. That separation is what lets the exact same control set run on three very different toolkits today.

The seam

Two interfaces define everything a host must provide:

IPlatformBackend covers application-level services — the dispatcher (Post/Invoke), timers, clipboard, screen enumeration, and the modal loop. IWindowBackend covers a single native window — size and position, show/hide/close, cursor, decorations, file dialogs. Input and paint requests flow the other direction: the backend calls the window’s neutral RenderFrame(SKCanvas, …) and Handle* methods directly. No platform type — no Avalonia type, no WinUI type — ever crosses into core Majorsilence.Forms code.

Three backends today

Majorsilence.Forms.Avalonia is the default — Avalonia 12, giving Windows, macOS, and Linux desktop with zero configuration. Reference it and Application.Run(new MyForm()) just works. It’s not limited to desktop, either: Avalonia ships its own Android, iOS, and Browser (WASM) targets, so this same backend is a second path to mobile and web, alongside the dedicated Uno backend below.

Majorsilence.Forms.Headless is the simplest possible backend and doubles as the reference template for writing a new one: a work-queue message loop, an in-memory clipboard, a virtual screen, and offscreen rendering. It needs no display, so it’s what the unit test suite runs on, and it can render the ControlGallery sample straight to a PNG for CI pixel-diffing:

dotnet run --project samples/ControlGallery -- --render-headless out.png 1100 750 --select-row 0

Majorsilence.Forms.Uno targets Uno Platform’s Skia renderer, hosting a SKXamlCanvas and reaching desktop, iOS, Android, and WebAssembly. It’s been verified end-to-end on macOS: the Uno host launches, the backend creates the window, and the ControlGallery’s full MainForm renders into the canvas. Because it needs an interactive session, it runs through a dedicated app head — samples/Gallery.Uno — rather than the headless CI build.

One detail worth calling out: Uno has no programmatic “begin a window drag” API, so move/resize for Majorsilence.Forms’ self-drawn window chrome is handled declaratively instead — a borderless presenter keeps the OS resize margins for free, and title-bar drag rides WinUI’s caption-region API on the Windows desktop head. On macOS, native decorations own drag/resize instead.

Adding your own

A new backend is just another assembly: reference core Majorsilence.Forms plus your toolkit, implement IPlatformBackend and IWindowBackend, and mirror the Avalonia/Headless/Uno trio — drive the dispatcher in the platform backend, and present a Skia surface plus translate input in the window backend. See Platform backends for the full interface listing.