Avalonia Pro Max/preview Server

Preview Server — Visual Variant Picker for Avalonia

What this does

Lets the agent show the user 2–3 design alternatives as actual rendered Avalonia screens (not HTML mockups), in a browser-based side-by-side comparison gallery. The user picks one and the agent then builds the chosen design out into the real app.

Why "real Avalonia" matters: HTML mockups misrepresent how Avalonia's Skia renderer, FluentTheme, ControlThemes, acrylic, shadows and font rendering actually look. A user who approves an HTML mockup is often disappointed by the real app. Rendering the actual XAML guarantees fidelity.

When to use

Must use

• User says: "show me some options", "what would this look like", "give me a few designs", "preview", "mockup"
• Building a new screen/window where there are valid stylistic alternatives
• Choosing between theme libraries (Fluent vs Suki vs Semi vs Material)
• Big visual refactor before committing to one direction

Skip

• User has already specified an exact design
• Tiny tweaks to existing UI (just edit it)
• Pure backend / non-visual changes

High-level flow

1. Agent reads requirements        (uses brainstorming skill if unclear)
2. Agent generates 3 variant       .axaml files in .preview/variants/{1,2,3}/
3. Agent runs render script         renders each variant via Avalonia.Headless
                                    → .preview/output/{variant}/{viewport}-{theme}.png
                                    (e.g. 1/wide-light.png, 1/wide-dark.png,
                                          1/compact-light.png, 1/compact-dark.png)
4. Agent runs serve script          starts python http.server, builds index.html
                                    gallery, prints URL: http://localhost:PORT
5. User reviews in browser, replies "I like variant 2"
6. Agent stops the server, copies   .preview/variants/2/* into the real project
   the chosen variant into the
   actual app

The user never has to install anything beyond what's already needed for Avalonia development plus Python (already required by ui-ux-pro-max).

Prerequisites

• .NET 8 / 9 SDK (Avalonia 12 target)
• Python 3.8+ (for the gallery server)
• A scratch project at .preview/AvaloniaPreviewHost/ — the agent creates this on first use

The scratch project is a bare Avalonia console app referencing:

• Avalonia 12.x
• Avalonia.Themes.Fluent
• Avalonia.Headless
• Avalonia.Skia (transitively required by Headless for image output)

Optional packages added per variant if it uses them: FluentAvalonia, SukiUI, Semi.Avalonia, Material.Avalonia, Lucide.Avalonia, Material.Icons.Avalonia, Svg.Skia.

Variant generation rules

Generate exactly 3 variants that are meaningfully different, not three shades of the same idea. Use this matrix:

| Slot | Variant identity | Typical theme combo | |---|---|---| | A — Conservative | Safe, professional, native-feeling. Lowest risk pick. | FluentTheme + FluentAvalonia | | B — Modern Flat | Opinionated, low-chrome, accent-driven. "Linear/Vercel" energy. | SukiUI or Semi.Avalonia + custom tokens | | C — Distinctive | A bigger swing — bold accent, heavier type, denser layout, or a Material-spec take. | Material.Avalonia or Semi.Avalonia + bold accent or SukiUI dark with neon accent |

If the user has already constrained the choice ("we're using Material"), generate 3 variants within that theme that differ in palette, density, or layout instead.

Each variant must include:

• The same target screen/window (so comparison is apples-to-apples)
• A Resources.axaml with the variant's tokens
• A Styles.axaml with shared component styles
• The screen .axaml (e.g. MainWindow.axaml or DashboardView.axaml)
• A short README.md explaining the design intent in 3–5 bullets

Reference the design-system, themes, and components sub-skills for the actual XAML content.

Workflow for the agent

Step 1 — Confirm scope

Before generating variants, confirm with the user:

• Which screen(s) do you want previewed? (single window / specific page / whole shell)
• Target window size? (default: 1280×800)
• Any hard constraints? (must be dark, must be Fluent, etc.)
• Mobile/tablet preview needed? (default: no — just desktop compact 800×600 + wide 1280×800)

Skip if the user has already given enough detail.

Step 2 — Scaffold the preview host (once per project)

python3 skills/avalonia/avalonia-pro-max/preview-server/scripts/scaffold_host.py

Creates .preview/AvaloniaPreviewHost/ if missing. Idempotent.

Step 3 — Write the 3 variants

Author the XAML files under .preview/variants/{1,2,3}/. The structure for each:

.preview/variants/1/
├── README.md              # 3-5 bullet design intent
├── Resources.axaml        # tokens (theme dictionaries)
├── Styles.axaml           # component styles
├── PreviewScene.axaml     # the screen to render
└── packages.txt           # optional: extra NuGet refs needed (one per line)

The render script will inject Resources.axaml + Styles.axaml into the host App and load PreviewScene.axaml as the window content.

Step 4 — Render to PNG

python3 skills/avalonia/avalonia-pro-max/preview-server/scripts/render_variants.py

What it does:

1. For each variants/{N}/:

• Reads packages.txt and adds any new NuGet refs to the host project
• Copies the variant's .axaml files into .preview/AvaloniaPreviewHost/Variant/
• Runs dotnet run --project .preview/AvaloniaPreviewHost -- --variant N --viewport wide --theme light --out .preview/output/1/wide-light.png
• Repeats for: wide-dark, compact-light, compact-dark

1. Outputs total render time + path to gallery script

Default viewports:

• wide: 1280 × 800
• compact: 800 × 600

Mobile viewports if --mobile flag passed:

• phone: 390 × 844 (iPhone 14)
• tablet: 1024 × 1366 (iPad Pro)

Step 5 — Serve the gallery

python3 skills/avalonia/avalonia-pro-max/preview-server/scripts/serve_gallery.py

What it does:

1. Generates .preview/output/index.html from the gallery template — side-by-side cards per variant, with theme toggle (light/dark) and viewport toggle (wide/compact).
2. Starts python -m http.server on a free port (default 8765, falls back if taken).
3. Prints:

`` Preview gallery serving at: http://localhost:8765 Press Ctrl+C to stop. ``

1. Optionally opens the URL via xdg-open / open / start if --open flag passed.

The agent leaves the server running and tells the user:

> I've put 3 design options on http://localhost:8765 — have a look and tell me which one to build (or describe what you'd change about one of them).

Step 6 — Apply the chosen variant

Once the user picks (e.g. "go with variant 2, but with a green accent instead of blue"):

1. Stop the preview server (Ctrl+C or kill the process the agent spawned).
2. Copy .preview/variants/2/Resources.axaml, Styles.axaml, and any necessary .axaml into the real project's Resources/ and Views/ folders.
3. Apply any tweaks the user asked for (accent swap, etc.).
4. Wire up via App.axaml (StyleInclude + ResourceInclude) — see design-system.
5. Optionally clean up .preview/ or leave for next iteration.

Step 7 — Iterate (optional)

If the user says "I like variant 2 but make it tighter", generate 3 new variants based on variant 2 and re-run from Step 4. Keep iterations cheap — the host project is already scaffolded.

File layout summary

/
├── .preview/                                 # gitignored
│   ├── AvaloniaPreviewHost/                  # scratch .NET project (scaffolded once)
│   │   ├── AvaloniaPreviewHost.csproj
│   │   ├── Program.cs                        # CLI: --variant N --viewport X --theme T --out P
│   │   ├── App.axaml
│   │   └── Variant/                          # populated per render run
│   │       ├── Resources.axaml
│   │       ├── Styles.axaml
│   │       └── PreviewScene.axaml
│   ├── variants/
│   │   ├── 1/{Resources,Styles,PreviewScene}.axaml + README.md
│   │   ├── 2/...
│   │   └── 3/...
│   └── output/
│       ├── index.html                        # gallery
│       ├── 1/wide-light.png, wide-dark.png, compact-light.png, compact-dark.png
│       ├── 2/...
│       └── 3/...
└── .gitignore                                # ensure .preview/ is excluded

Add to .gitignore

The agent should ensure .gitignore contains:

.preview/

Limits and honest caveats

• Custom title bars / acrylic / native chrome render but won't show OS-specific behavior (window shadows, traffic lights). The screen content is accurate; the chrome may differ slightly per platform.
• Animation can't be screenshotted. Document motion intent in the variant README.md instead. For motion previews, escalate to the Avalonia WASM live preview approach (not in this sub-skill — see "Future work" below).
• Fonts must be embedded (avares://). System-installed-only fonts may render with fallback under headless Skia.
• First render is slow (~10–30s — restoring NuGet + JIT). Subsequent renders are ~1–3s per PNG.
• Headless rendering uses software Skia by default. Pixel output matches a real Avalonia window 99%+ for static UI; tiny anti-aliasing differences exist but are not user-visible at gallery scale.
• ExperimentalAcrylicBorder works under headless but the blur source is a flat color (no real desktop background to sample), so the effect is approximate.

Future work (not in this sub-skill)

• Live WASM preview — compile each variant to wasm via dotnet publish and serve interactively. Higher fidelity (motion, hover, click) but +30–60s per variant build and requires dotnet workload install wasm-tools.
• Diff overlay — render two variants and produce a pixel diff highlighting changes.
• Auto-screenshot on file change — watch variants/ and re-render on save for fast iteration.

Common mistakes

• Generating three near-identical variants. Defeats the purpose. Use the A/B/C identity matrix above.
• Different content per variant. The variants must show the same screen so the user is judging style, not content.
• Forgetting packages.txt. If variant uses SukiUI, the host won't compile without the reference.
• Not gitignoring .preview/. Pollutes the repo with binary screenshots.
• Telling the user "click the button to pick" when the gallery is purely visual. The user replies in chat — re-read this skill: selection is chat-based, not click-based.
• Leaving the server running after selection. Stop it before continuing implementation.
• Rendering at only one viewport/theme. Always render all four (wide/compact × light/dark) by default — that's the point of the comparison.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: linuxdevel
• Source: linuxdevel/Avalonia-skills
• License: MIT

Install and usage instructions live in the source repository linked above.