Dynamic Difficulty

A feedBack plugin that keeps a song's difficulty matched to how well you're actually playing it, and shows upcoming sections as a row of glass-filling difficulty indicators.

What it does

Generate missing difficulty ladders

• Most charts (GP imports, plain single-level sloppaks) have no phrase-level Easy/Medium/Hard data at all — highway.hasPhraseData() is false and the mastery slider has nothing to filter. The "⚙️ Generate Difficulties" button (shown automatically whenever the current song lacks phrase data) analyzes the arrangement's note/chord density, fret complexity, and technique load per section, and writes a fresh multi-tier phrase ladder directly into the sloppak on disk (routes.py's /generate route) — after which the button reconnects the highway so the new data streams in immediately.
• A /generate-library route does the same as a best-effort sweep over every sloppak in the DLC folder, for filling in a whole library at once.
• Never touches an arrangement that already has phrase data unless force is set — existing hand-authored difficulty ladders are never clobbered.
• This is a fresh implementation against feedBack's own arrangement wire format (lib/song.py) — it does not port code from, or share a runtime with, the Slopsmith arrangement editor's differently-scoped difficulty feature; only the general "score note groups, bucket into tiers" heuristic approach was used as design inspiration.

Instrument coverage

Instrument	Supported?	Notes
Guitar / bass (fretted)	✅	Fret complexity, span, technique (bend/slide/hammer-on/tremolo/harmonic), density, sustain-ease.
Keys / piano	✅	Separate pitch-based heuristic (polyphony, hand-span, density, sustain-ease) — keys notes encode midi = string*24 + fret, so the fretted heuristic doesn't apply and never runs against them. No fret anchors/hand-shapes generated (the piano renderer doesn't consume them).
Drums	❌	Drum parts are a drum_tab.json pointer, not a notes/chords file — outside this generator's data model entirely. Detected and skipped cleanly (unsupported-instrument-drums), never mis-scored.

Arrangement type is detected the same way core does: the manifest's type field ("piano"/"keys"/"drums"), falling back to the same /^(keys|piano|keyboard|synth)/i name match the piano-roll chart mode uses.

Per-song difficulty memory

• Core persists master-difficulty as a single global value (whatever the mastery slider was last set to, for any song). This plugin additionally remembers each song's own last-used difficulty (keyed by filename + arrangement, in localStorage) and restores it whenever you come back to that song — so switching between a song you've mastered and one you're still working through no longer carries one song's difficulty into the other. Captures both manual slider moves and this plugin's own auto-adjustments, for songs with phrase-level difficulty data only.

Live auto-adjustment

• Reads live per-note hit/miss judgments from whichever note-detection scorer is active (e.g. the note_detect plugin) via highway.getNoteStateProvider() — this plugin doesn't score notes itself, it observes an existing scorer.
• Tracks a rolling accuracy average per song section (phrase) and nudges the master-difficulty slider (window.setMastery) up after a run of clean sections, or down after a rough one.
• Only ever changes difficulty at section boundaries — never mid-phrase.
• Stands down the instant you move the difficulty slider yourself. Manual action always wins; auto-adjust must be explicitly re-enabled afterward.
• No-ops entirely for songs without a phrase-level difficulty ladder (highway.hasPhraseData() === false — GP imports, legacy sloppak).

Glass-filling section HUD

• Renders upcoming sections in the player as "glasses" — taller glass = a harder section (scaled by that section's peak authored difficulty), fill level = how much of that section's difficulty range the current master-difficulty setting reaches.
• Purely a visualization; can be toggled independently of auto-adjust.

Requirements

• Target Host: feedBack core implementing plugin-spec-v1.md with the v3 player chrome (window.feedBack.ui.playerControlSlot()). The player-controls buttons (Auto-Difficulty, Generate Difficulties) are v3-only today — see COMPLIANCE.md for the tracked v2 gap. The glass-filling HUD itself does not depend on uiVersion and renders on either chrome.
• feedBack core with the note-detection capability / setNoteStateProvider contract (spec 009) and phrase-level difficulty data (feedBack#48).
• A note-detection scorer plugin installed and active for auto-adjust to have any signal to react to. Without one, the HUD still renders (using only authored difficulty + the manual mastery slider), but auto-adjust has nothing to observe and stays idle.

Settings

Exposed via Settings → Plugins → Dynamic Difficulty:

Setting	Effect
Auto-adjust difficulty	Master on/off switch for automatic setMastery() calls.
Glass-filling section HUD	Show/hide the in-player glass row.
Sensitivity (1-3)	How confident auto-adjust must be (hit-rate thresholds) before it moves the slider, and how big a step it takes.
Reaction speed (1-3)	How much weight a single section's result carries in the rolling accuracy average (EMA_ALPHA) — independent of Sensitivity. Default (2) reproduces this plugin's original, pre-#5 behavior.
Min / Max %	Hard bounds auto-adjust will never cross.

Library card badge — songs with a remembered per-song difficulty (see above) show a small indicator on their library card via window.feedBack.libraryCardActions (placement: 'overlay', never a MutationObserver). The exact saved percentage is available via the action's click result/title rather than as on-card text — see this repo's COMPLIANCE.md-adjacent note in screen.js (registerLibraryCardBadge) for why: the card-actions capability's label/icon are static per registration, not computed per song, so a literal "shows N%" on-card text isn't expressible through it as it exists today.

All settings persist in localStorage, prefixed dynamic_difficulty..

Plugin metadata

Field	Value
id	dynamic_difficulty
version	0.1.0
category	practice

Design notes

This plugin is a fresh, feedBack-native implementation. It does not port code or assumptions from the Slopsmith arrangement editor's own (differently scoped) difficulty-generation feature — Slopsmith and feedBack are separate apps with separate plugin contracts, and the two shouldn't be assumed compatible just because they share a similar plugin-loader lineage.