LEDMatrix/docs/SKIN_SYSTEM.md

Skin System Architecture

Skins are user-installable visual overlays for the sports scoreboards. A skin replaces only the look of a scoreboard — the host plugin keeps doing data fetching, scheduling, caching, dedup, live-priority takeover, and vegas mode. If you only want to build a skin, read CREATING_SKINS.md; this document explains how the system works and why it is shaped this way.

Why skins instead of forks

Before skins, changing a scoreboard's layout meant forking the whole plugin (e.g. the community MLB scoreboard fork). The fork gets the new look but loses everything the maintained plugin keeps earning: duration/scheduling behavior, vegas mode support, caching and background-fetch improvements, bug fixes. It also silently drifts: every upstream improvement now has to be re-ported by hand.

A skin inverts that trade. The plugin remains stock and keeps updating through the store; the skin is ~100 lines of pure rendering code that receives the plugin's already-fetched data each frame. Uninstalling the skin (or the skin crashing) simply restores the built-in look.

              (unchanged)                        (the skin seam)
 ESPN API ──► update() ──► game view model ──► _render_game() ──► display
              fetching        (a dict)          │         │
              caching                           │         └─ built-in
              scheduling                        └─ skin.render_<mode>(ctx, game)
              live priority                        draws onto ctx.canvas

The render funnel

Every sports scoreboard (baseball, football, basketball, hockey — anything built on src/base_classes/sports.py) renders through exactly one seam: SportsCore._render_game(game, force_clear).

1. The mode class's display() (live, SportsUpcoming, SportsRecent) picks self.current_game and calls _render_game.
2. _render_game lazily loads the configured skin (once, on first render — a broken skin can never block plugin startup).
3. If a skin is active, the host builds a SkinContext — a fresh black canvas at the current display size plus layout/font/logo helpers — and calls the skin's render_live / render_recent / render_upcoming with a copy of the game dict.
4. If the skin returns True, the canvas is composited onto the display. If it returns False, isn't implemented for that mode, or raises, the built-in _draw_scorebug_layout runs instead.

Key properties that fall out of this design:

• Per-mode fallback. A skin that only implements render_live gets the stock recent/upcoming screens for free.
• Three strikes. A skin that raises 3 times in a row is disabled for the rest of the session (one loud error log per failure); the display never goes dark. Restarting the service re-arms it.
• Copies, not references. Skins receive a shallow copy of the game dict, so a buggy skin cannot corrupt the plugin's scheduling state.
• Vegas mode works untouched. Vegas capture falls back to grabbing the regular display() output, which is already skin-rendered. Skins can additionally implement render_vegas_card for purpose-built scroll cards, and hosts can call SportsCore.render_skin_card(game, size) to use it.
• Hot-loop caution. render_live runs every display-loop pass during a live game. The host logs a warning when a skin render exceeds 150 ms, and scripts/validate_skin.py enforces a budget at development time — but Python cannot forcibly time-out a stuck render, so a skin that blocks (network I/O, giant image ops) stalls the display. This is why the rules in CREATING_SKINS.md ban I/O in render paths.

The view model contract

The game dict a skin receives is the plugin's already-extracted view model (SportsCore._extract_game_details_common plus per-sport extras from src/base_classes/{baseball,basketball,football,hockey}.py).

• Guaranteed keys (view model v1.0) — always present for every sport: id, game_time, game_date, start_time_utc (a UTC datetime), status_text, is_live, is_final, is_upcoming, is_halftime, home_abbr/away_abbr, home_id/away_id, home_score/away_score (strings), home_logo_path/away_logo_path, home_record/away_record.
• Sport extras — documented per sport in CREATING_SKINS.md (e.g. baseball adds inning, inning_half, balls, strikes, outs, bases_occupied).
• Optional keys (odds, rankings, series_summary, …) are present only when the feature is enabled — skins must always use .get().

Versioning policy: additive changes bump the minor version (VIEW_MODEL_VERSION in src/skin_system/skin_base.py, surfaced to skins as ctx.view_model_version); renaming or removing a guaranteed key requires a major bump plus a compat shim. test/test_skin_system.py::TestViewModelContract fails CI if a guaranteed key disappears from the extractor.

Separately, SKIN_API_VERSION versions the Python API (ScoreboardSkin, SkinContext). The loader refuses a skin whose manifest declares a different major version and falls back to the built-in renderer with a clear "skin needs an update" log line.

Package layout and lifecycle

skins/<skin-id>/
  skin.json      # manifest (required)
  skin.py        # ScoreboardSkin subclass (required)
  preview.png    # optional, shown by the web UI
  assets/        # optional skin-local images
  helpers.py ... # optional extra modules (namespaced per skin at import)

Skins live in the central skins/ directory — deliberately not inside the plugin's directory, because plugin reinstall/update deletes the whole plugin directory and a skin must survive that. One skin can also target several plugins (mlb + milb).

Lifecycle: discovered lazily on first render → manifest validated → API major version gated → module imported under a namespaced sys.modules key (two skins can both ship a helpers.py, same scheme plugins use) → instantiated with (manifest, options). Every failure logs and falls back to built-in.

Skins should be stateless: the live, recent, and upcoming mode classes each hold their own skin instance, so derive everything from (ctx, game).

Selection and configuration

Inside the plugin's own config section in config/config.json:

"baseball-scoreboard": {
  "skin": "retro-baseball",
  "skin_options": { "accent_color": [255, 80, 0] }
}

"skin" is either one id for all modes or a per-mode mapping ({"live": "retro-baseball", "recent": "built-in"}). Absent, empty, or "built-in" means the stock renderer. Because this rides the plugin's config section, it persists across plugin reinstalls like every other setting.

The web UI shows a Visual Skin dropdown for plugins that have matching skins installed: SchemaManager.inject_skin_selector adds an enum to the served schema only. Validation never sees the enum — so a config that references an uninstalled skin stays valid (rendering just falls back), and the currently-configured value is always kept selectable. GET /api/v3/skins lists installed skins (optionally filtered by ?plugin_id=).

Distribution

• Manual: git clone <skin repo> skins/<skin-id> — that's the whole install. No manifest bumps, no update_registry.py; skins are not monorepo plugins.
• Store: registry entries with "type": "skin" install through the same plugins.json pipeline; PluginStoreManager routes them to skins/, validates skin.json (including the API major version) instead of manifest.json, and never installs dependencies — skins are render-only (stdlib + PIL + the provided context, no third-party packages in v1).

Trust model

A skin is Python executing inside the display service — exactly the same trust level as a plugin, even though "skin" sounds cosmetic. Only install skins from sources you'd be willing to install a plugin from.

v2 directions (not in v1)

• A generic BasePlugin opt-in (render_with_skin()) so non-sports plugins (weather, music) can offer skinnable layouts; skin_runtime is already sports-agnostic in anticipation.
• Store UI: preview gallery, one-click install from the skin browser.
• An update path for git-cloned skins (today: re-clone or store reinstall).
• Animation support in skins (today the API is one frame per render call; stateful tricks work but are at-your-own-risk).