writeMidiFile: emit PART DRUMS instrument tracks#104
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This was referenced Apr 20, 2026
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Builds a minimal valid ParsedChart from scratch: default 480 resolution, 120 BPM at tick 0, 4/4 time signature at tick 0, empty tracks/sections/ metadata/vocal parts/unrecognized events. chartBytes defaults to an empty Uint8Array (no source bytes), format defaults to 'chart', iniChartModifiers to the library defaults. Options let callers override resolution, bpm, timeSignature, and format. Useful for programmatic chart generation (e.g. downstream code that builds charts up from scratch rather than parsing source bytes).
Serializes IniMetadata (Partial<typeof defaultMetadata> + extraIniFields) back to song.ini text with: - [song] header - Known fields emitted in the canonical defaultMetadata order - Undefined values skipped - Booleans as True/False (Clone Hero convention) - extraIniFields appended in insertion order - CRLF line endings Derives its field order from Object.keys(defaultMetadata) rather than hardcoding a separate FIELD_ORDER list, so new fields added to defaultMetadata automatically participate in writing. Tests exercise writeIniFile only via round-trip through parseChartAndIni, per reviewer feedback: build a metadata object, write it, re-parse, and assert on parsedChart.metadata. No assertions about the serialized ini text itself (CRLF, field order, True/False formatting, quoting) — those are implementation details.
…emission Port of the non-instrument-track half of the chart writer into scan-chart: - [Song] emits the subset of metadata the chart body supports (Name, Artist, Charter, Album, Genre, Year, Resolution, Offset, PreviewStart, Difficulty). Other fields live exclusively in song.ini. - [SyncTrack] emits tempos as `B millibeats` and time signatures as `TS numerator [denominator-exponent]`, sorted by tick with TS before B at the same tick. - [Events] emits section markers (wrapped as [section name] to survive the parser's greedy trailing-\] regex), end events, unrecognized global events (with bracket-stripping when source is .mid so round-trip to .chart emits naked text), and vocal phrase_start/phrase_end/lyric events from the normalized vocalTracks.parts.vocals. - Unrecognized chart sections are re-emitted verbatim. Instrument tracks ([ExpertSingle] etc.) land in a follow-up PR.
Completes writeChartFile with per-track section emission: - [ExpertSingle], [HardDrums], etc. named from instrument + difficulty. - Drum tracks: base notes (N 0..4 or 0..5 for 5-lane), cymbal markers (N 66/67/68) only in fourLanePro, accent (N 34..38) and ghost (N 40..44) markers matching the emitted note's eventType, one N 109 flam per group, double kick as N 32 only. - 5-lane round-trip: greenDrum+cymbal emits as N 4 (orange) while plain greenDrum stays at N 5; blueDrums coinciding with greenDrum+cymbal emit as N 5 to keep the parser's drumType detection on fiveLane. - Fret/GHL tracks: notes via the 5-fret and 6-fret maps, tap as N 6, forceUnnatural (N 5) when the note's hopo/strum flag disagrees with the natural-HOPO state. - Star power S 2, activation lanes S 64, flex lanes S 65/66, versus phrases S 0/1, solo sections as E 'solo'/'soloend' (tick + length - 1 for soloend to round-trip). - Per-track text events (including disco flip mix markers). - Disco-flip state transitions per difficulty from red/yellow drum disco/discoNoflip flags → 'mix <diff> drums0[d|dnoflip]' text events. - Coda events: if no 'coda' in unrecognizedEvents, synthesize from drumFreestyleSections where isCoda=true. - hasForcedNotes backstop: if hasForcedNotes is set but no forceUnnatural emitted, append N 5 0 at a vacant tick in the first fret track to preserve the flag on round-trip.
Port of the core MIDI writer infrastructure: - writeMidiFile(chart) entry point: builds a Format-1 MIDI and returns Uint8Array via midi-file's writeMidi - TEMPO TRACK: trackName + setTempo (from chart.tempos) + timeSignature (from chart.timeSignatures), all at their absolute ticks - EVENTS track: trackName + section text events (unwrapped so YARG's NormalizeTextEvent doesn't strip names containing ]) + [end] events + global events (bracket-wrap when source is .chart so MIDI output follows convention) + [coda] derived from drumFreestyleSections when not already present in unrecognizedEvents - Unrecognized MIDI tracks: verbatim pass-through with abs-tick → delta-tick conversion; duplicate track names suffixed to keep the internal trackMap unique - finalizeMidiTrack helper: sorts by tick with a type-priority tiebreaker, converts absolute ticks to delta times, appends endOfTrack Instrument tracks (PART DRUMS, PART GUITAR, …) and vocal tracks (PART VOCALS, HARM1/2/3) land in follow-up PRs.
Adds drum emission to writeMidiFile: - buildDrumTrack: groups one or more ParsedTrackData entries (one per difficulty) into a single PART DRUMS MIDI track. Emits trackName, delegates per-difficulty notes to emitDrumNotes, collects and dedupes instrument-wide star power (MIDI 116) / solo (MIDI 103) / activation lanes (MIDI 120), emits flex lanes (MIDI 126/127 with per-difficulty LDS velocity), passes through per-track text events and unrecognizedMidiEvents from the first difficulty. - emitDrumNotes: per-difficulty note emission with full modifier support: base drum notes (MIDI 96..100 expert / 84..88 hard / 72..76 medium / 60..64 easy); double-kick as MIDI 95 only, emitted AFTER regular kick at the same tick (YARG insertion order quirk); tom markers (MIDI 110/111/112) only in fourLanePro; accent (velocity 127) / ghost (velocity 1) encoding; one flam marker (MIDI 109) per group; 5-lane green+cymbal remapped to offset 4 (orange pad); blue-at-same-tick-as- green+cymbal remapped to offset 5 so fiveLane detection succeeds; fourLanePro green+tom fallback to offset 5 when a conflicting green+cymbal exists at the same tick across difficulties; disco-flip state-transition text events (`[mix <diff> drums0[d|dnoflip]]`). - fourLanePro sentinel greenTomMarker: when drumType=1 but no tom markers were emitted (all yellow/blue defaulted to cymbal, green-toms used offset-5 encoding), emit a MIDI 112 at a safe tick so scan-chart's drumType detection still picks fourLanePro. - [ENABLE_CHART_DYNAMICS] text event at tick 0 when any accent or ghost was emitted. - computeLengthOverrides: prevents scan-chart's trimSustains from collapsing adjacent short-sustain drum-note chains by attributing the combined chain length to the first note. - Shared helpers: addNoteOnOff, addNoteOnOffWithChannel (with zero-length seq-pairing to survive finalizeMidiTrack's sort), deduplicateSections, instrumentTrackNames table. Fret tracks (PART GUITAR, GHL) and vocal tracks (PART VOCALS, HARM1/2/3) remain no-ops until the follow-up PRs land — the writeMidiFile entry iterates trackData but skips any non-drum instrument group.
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Context
Adds drum emission to `writeMidiFile` — the largest single piece of the MIDI writer.
Features
`buildDrumTrack`: groups multi-difficulty drum entries into one PART DRUMS track. Emits trackName, delegates per-difficulty notes to `emitDrumNotes`, collects and dedupes instrument-wide sections (star power / solo / activation), emits flex lanes with per-difficulty LDS velocities, passes through per-track text events + unrecognizedMidiEvents from the first difficulty.
`emitDrumNotes`: full per-difficulty emission:
fourLanePro sentinel greenTomMarker: when drumType=1 but no tom markers were emitted (all yellow/blue default cymbal, green-toms encoded at offset 5), emit a MIDI 112 at a safe tick so scan-chart's drumType detection picks fourLanePro on re-parse.
`[ENABLE_CHART_DYNAMICS]` text event at tick 0 when any accent or ghost velocity was emitted.
`computeLengthOverrides`: prevents `trimSustains` from collapsing adjacent short-sustain drum-note chains by attributing combined chain length to the first note.
Shared helpers: `addNoteOnOff`, `addNoteOnOffWithChannel` (with zero-length seq-pairing to survive `finalizeMidiTrack`'s priority sort), `deduplicateSections`, `instrumentTrackNames` table.
Tests
20 new test cases: track layout, multi-difficulty grouping, note-number mapping, velocity encoding, tom markers (emit/skip/sentinel), flam, instrument-wide sections, flex lanes, drum round-trip through `parseChartAndIni`, all-flag round-trip (accent/ghost/flam/doubleKick). 38 drum tests in total on the `midi-writer` test file, 382 tests passing across the scan-chart suite at the tip.
Deferred to follow-up PRs
Depends on
PRs #97 + #98 + #99 + #100 + #101 + #102 + #103 — stacked above the writer chain.