Platform backends

One rendering core, three swappable hosts.

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 host is abstracted behind a small seam so Majorsilence.Forms can run on more than one toolkit:

The core Majorsilence.Forms assembly references no windowing toolkit — only SkiaSharp. Backends are separate assemblies that depend on the core and reach into its internal render/input plumbing.

The seam

Two interfaces define everything a host must provide:

• IPlatformBackend — application + process services: the dispatcher, timers, clipboard, screens, and the modal loop.
• IWindowBackend — one native window: location/size, show/hide/close, cursor, decorations, file dialogs, and — pushed the other way — paint requests and input delivered straight to the window’s neutral Render/Handle* methods.

All coordinates crossing the seam are System.Drawing value types and Majorsilence.Forms enums — no toolkit type ever leaks into the core.

Selecting a backend

A desktop app just references Majorsilence.Forms.Avalonia and calls Application.Run(new MyForm()) with zero configuration. To use a different backend, set it before the first window is created:

Majorsilence.Forms.Backends.Platform.Backend = new Majorsilence.Forms.Headless.HeadlessPlatformBackend ();

The Avalonia backend

The default backend, and the one a new desktop app gets with zero configuration. It targets Windows, macOS, and Linux desktop out of the box. Avalonia itself isn’t desktop-only, though — it ships its own Android, iOS, and Browser (WebAssembly) targets, so wiring Majorsilence.Forms.Avalonia up to one of those is a second path to mobile and web, alongside the dedicated Uno backend below — worth reaching for if your app (or team) is already invested in Avalonia’s mobile/browser tooling.

The Headless backend

The simplest possible backend, and the reference implementation to copy when building a new one: a work-queue message loop, an in-memory clipboard, a virtual screen, and offscreen rendering to an SKSurface. It needs no display, so it powers the unit test suite and can render the ControlGallery headlessly for CI and pixel-diff verification.

The Uno backend

Implements the seam on Uno Platform’s Skia target, hosting a SKXamlCanvas and translating Uno pointer/key/character events into the neutral input path. It needs a Uno app head — see samples/Gallery.Uno — and has been verified launching and rendering a full MainForm on macOS.

Window drag/resize for Majorsilence.Forms’ self-drawn chrome is handled declaratively rather than imperatively on this backend: resize comes for free from a borderless presenter that keeps the OS resize margins, and title-bar drag uses WinUI’s caption-region API on the Windows desktop head. On macOS the native decorations own drag/resize; on X11 title-bar drag is unavailable and UseSystemDecorations is the fallback.

Adding another backend

A new backend is a new assembly referencing Majorsilence.Forms (core) plus the target toolkit, implementing IPlatformBackend and IWindowBackend — mirror the Avalonia/Headless/Uno trio: drive the dispatcher and lifecycle in IPlatformBackend, and present a Skia surface plus translate input in IWindowBackend.

See docs/backends.md in the repository for the full interface listing.