feat(scoring): Rock Band-style drums scoring from a YARG engine port

CHANGELOG.md

@@ -0,0 +1,26 @@
+# Changelog
+
+All notable changes to the Drum Highway plugin. The format follows
+[Keep a Changelog](https://keepachangelog.com/en/1.1.0/); versions follow `plugin.json`.
+
+## [4.1.0] - Unreleased
+
+### Added
+- **Rock Band-style scoring** from a JavaScript port of YARG.Core's drums engine (`assets/engine.js`,
+  LGPL-3.0, see `NOTICE.md`): ±70 ms hit window, multiplier up to x4 (x8 in star power), pro-drums
+  cymbal/tom lanes, accent/ghost dynamics bonus, stars, and star power with fill activation. Driven
+  through `assets/session.js`, which also adds spot-on timing, roll and drum-solo bonuses. The 2D view
+  marks hits / misses from the engine and shows a score HUD when **Score** is on.
+- **Difficulty per player** — Easy, Medium, Hard, Expert, Expert+ (`drums_difficulty_v1`), from the
+  settings panel, the HUD badge or D / Shift+D; Expert drops the double-kick notes. Easier levels, star
+  power, fills and solos come from the drum tab's feedpak 1.20.0 gameplay metadata; without it the song
+  plays Expert only, without star power.
+- **Assists** — auto kick / auto cymbals up to a chosen difficulty (played on the drum sound at their own
+  volume), hit-timing presets (Relaxed / Forgiving / Normal / Precision), **Pro cymbals** toggle and an
+  input **Offset** (ms) for audio / MIDI latency.
+
+### Changed
+- A drum-tab hit is an accent only when the tab marks it (`a`, feedpak 1.20.0) or, for older tabs, when it
+  has a written velocity of 100 or more; a hit with no velocity is no longer drawn as an accent. A kick
+  marked `x2` is a double kick (GM 35).
+- The "Hits" checkbox is now **Score**.

LICENSE.LGPL-3.0

@@ -0,0 +1,165 @@
+                   GNU LESSER GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+
+  This version of the GNU Lesser General Public License incorporates
+the terms and conditions of version 3 of the GNU General Public
+License, supplemented by the additional permissions listed below.
+
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NOTICE.md

@@ -0,0 +1,25 @@
+# Licensing notice for the drums plugin
+
+Most of this plugin is original code under the **MIT** license (see `README.md`). That includes
+`screen.js`, `assets/session.js`, `plugin.json`, the other assets and the tests other than
+`tests/engine.test.js`.
+
+Two files are ports of [YARG.Core](https://github.com/YARC-Official/YARG.Core) and are licensed under the
+**GNU Lesser General Public License v3.0** (full text in [`LICENSE.LGPL-3.0`](LICENSE.LGPL-3.0); the LGPL
+builds on the GNU GPL v3.0, whose text is in [`LICENSE.GPL-3.0`](LICENSE.GPL-3.0)):
+
+| File | Status |
+|------|--------|
+| `assets/engine.js` | LGPL-3.0. JavaScript port, with modifications, of YARG.Core's drums engine (`Engine/Drums/DrumsEngine.cs`, `Engine/Drums/Engines/YargDrumsEngine.cs`, `DrumsEngineParameters.cs`, `DrumsStats.cs`, `Engine/BaseEngine*.cs`, `BaseStats.cs`, `HitWindowSettings.cs`, `Chart/Notes/DrumNote.cs`, `Note.cs`, drum activation flags from `InstrumentDifficultyExtensions.cs`, and defaults from `Game/Presets/EnginePreset*.cs`). It also takes the drum star thresholds from YARG's `DrumsPlayer.cs` (LGPL-3.0). Copyright (c) YARC (YARG) contributors. |
+| `tests/engine.test.js` | LGPL-3.0. Tests for `engine.js`, partly ported from `YARG.Core.UnitTests/Engine/DrumEngineTester.cs` and `DrumsStatsTests.cs`. |
+
+`assets/engine.js` is a standalone, unminified script with no dependencies, shipped as its own file and
+loaded at runtime. `screen.js` and `assets/session.js` only use it through its public API
+(`window.DrumsEngine` / `require('./engine.js')`), so they remain separate MIT works that use the Library
+as described in LGPL-3.0 section 4 ("Combined Works"). You may replace `assets/engine.js` with a modified
+version. If you distribute changes to `assets/engine.js`, they must stay under LGPL-3.0 and their source
+must stay available. Combining an LGPL-3.0 file with MIT code this way is permitted by both licenses, and
+both are compatible with feedBack's AGPL-3.0.
+
+The header of `assets/engine.js` lists every behaviour that deviates from YARG ("Deviations from YARG").
+The scoring look and feel imitates rhythm-game drum tracks but uses no artwork, fonts or logos from them.

README.md

@@ -16,7 +16,9 @@ A plugin for [Slopsmith](https://github.com/got-feedback/feedback) that replaces
 - **MIDI drum pad input** — connect any MIDI drum pad, electronic kit, or controller via Web MIDI API
 - **Custom MIDI mapping** — "Learn" mode to assign any MIDI note to any lane, for non-standard drum pads
 - **Built-in drum sounds** — WebAudioFont-powered GM drum kit playback on MIDI hit
-- **Accuracy scoring** — hit detection with tight +/-50ms timing window, accuracy %, streak counter
+- **Rock Band-style scoring** — score, multiplier, streak, stars and star power from a port of the YARG drums engine (`assets/engine.js`). See [Scoring](#scoring).
+- **Difficulty** — Easy, Medium, Hard, Expert or Expert+ per player (browser), changeable mid-song. See [Difficulty](#difficulty).
+- **Assists** — auto kick, auto cymbals (each up to a chosen difficulty) and hit-timing presets. See [Assists](#assists).
 - **Inline settings** — MIDI device, volume, channel filter, lane labels, hit detection, and mapping table
 
 ## Drum Lanes
@@ -32,6 +34,68 @@ A plugin for [Slopsmith](https://github.com/got-feedback/feedback) that replaces
 | Ride | Ri | 51, 59 | White | Diamond |
 | Kick | Ki | 35, 36 | Red | Full-width bar |
 
+## Scoring
+
+Turn on **Score** in the settings panel (gear) to see the scoring HUD: multiplier, score, streak, stars
+and the star power meter. Hit notes turn green, missed notes grey, and a pad hit on an empty lane flashes it
+red.
+
+Scoring is a JavaScript port of YARG.Core's drums engine (`assets/engine.js`, LGPL-3.0 — see
+[License](#license)), used through `assets/session.js`:
+
+- **Hit window** ±70 ms (see [Assists](#assists) for wider ones); one pad hit hits at most one note.
+- **Multiplier** grows every 10 notes up to x4, doubled during star power (x8). 60 points per note (pro
+  drums), plus a dynamics bonus for hitting an accent hard or a ghost note soft (needs a velocity-sensitive
+  kit). Pro drums: a cymbal and the tom of the same colour are different notes; with **Pro cymbals** off
+  either one hits that colour's notes.
+- **Star power** — notes in a star power phrase are drawn silver-white; hitting every note of a phrase fills
+  a quarter of the meter. With half a meter, the chart's **fills** are marked green: the hit that ends the
+  fill activates star power.
+- **Bonuses** (shown in the score) — +10 x multiplier for a hit within 25 ms, extra points for snare / tom
+  rolls, and a drum-solo bonus (100 per note hit, doubled for a perfect solo) with a live percentage during
+  a solo.
+- **Offset** (ms) — subtracted from the time of every hit; raise it if your hits register late (audio or
+  MIDI latency). Hits between frames are placed using the playback rate, not quantised to the frame rate.
+- Seeking (or a loop jumping back) restarts scoring from the new position; skipped notes aren't misses.
+
+The scoring files load on first use from core's plugin assets route (`/api/plugins/drums/assets/`). Until
+they have loaded the view shows the chart as it is.
+
+### Difficulty
+
+Each player picks **Easy**, **Medium**, **Hard**, **Expert** or **Expert+**, stored per browser
+(`localStorage` key `drums_difficulty_v1`, default Expert), so in splitscreen / multiplayer every player
+keeps their own. Change it in the settings panel, by clicking the difficulty badge (top-left of the lanes),
+or with **D** (harder) / **Shift+D** (easier) while the view is focused.
+
+- **Expert+** is the drum part as charted, double kicks included; **Expert** drops the double-kick notes
+  (`x2`). **Easy / Medium / Hard** come from the chart's own easier levels; the badge says **AUTO** when a
+  level was reduced by software rather than hand-charted.
+- A level the chart doesn't have is greyed out with the reason; a song without your saved level plays
+  Expert (the badge is dimmed) and your choice is kept for the next song.
+- Changing difficulty mid-song rebuilds the chart from the current position, like a seek.
+
+### Where star power, fills and levels come from
+
+They are part of the song's drum tab (`drum_tab.json`, feedpak 1.20.0 "drum gameplay metadata"): per-hit
+`a` (accent) and `x2` (double kick) flags, `star_power` / `fills` / `solos` as `{start_time, end_time}`
+ranges, and `levels.easy|medium|hard` with their own `hits` and a `generated` marker. feedBack's Rock Band /
+Clone Hero / YARG chart importer writes them, and core streams them to the plugin with the tab
+(`bundle.drumTab`). A tab without them — an older tab, a core that doesn't stream them yet, or drums encoded
+as guitar notes — plays **Expert only, without star power**; everything else works the same.
+
+### Assists
+
+- **Auto kick / Auto cymbals** (`drums_auto_kick_v1`, `drums_auto_cymbals_v1`): `Off`, `Easy only`,
+  `Easy – Medium`, `Easy – Hard` or `Every difficulty` — the assist is on at that difficulty and the ones
+  below it. Those notes are left out of scoring, marked as played when they reach the now line, and pad hits
+  on them are ignored. Cymbals = the chart's hi-hat, ride and crash notes. They are **played on the drum
+  sound** (scheduled ~60 ms ahead on the audio clock) so muting the drum stem leaves no holes, at their own
+  **Auto vol** (`drums_auto_volume_v1`, default 80%), so pads can stay silent when the kit module makes the
+  sound.
+- **Timing** (`drums_timing_v1`): Relaxed ±130 ms, Forgiving ±100 ms, Normal ±70 ms (YARG's default),
+  Precision (YARG's dynamic window that tightens on fast notes).
+
 ## Requirements
 
 - **Chrome or Edge** for MIDI drum pad input (Firefox does not support Web MIDI)
@@ -71,6 +135,14 @@ Different drum pads send different MIDI note numbers. Use the "Learn" mode in se
 
 Click "Reset Map" to return to standard GM mapping.
 
+## Development
+
+Tests run with plain Node (the org CI runs each `tests/*.test.js`): `node tests/engine.test.js`,
+`node tests/session.test.js`, `node tests/screen.test.js`.
+
 ## License
 
-MIT
+MIT, except `assets/engine.js` and `tests/engine.test.js`: they are ports of
+[YARG.Core](https://github.com/YARC-Official/YARG.Core) and stay under the **LGPL-3.0**
+(`LICENSE.LGPL-3.0`, with the GPL-3.0 it builds on in `LICENSE.GPL-3.0`). The engine is a separate,
+replaceable file that the MIT code only calls through its public API. Details in [NOTICE.md](NOTICE.md).