@doot-games/charter

Turn an analysis plus a tempo into a playable chart. Pure logic, no DOM, seeded so the same inputs always produce the same chart.

Method

Two stages, after the Dance Dance Convolution decomposition but using classical signal processing rather than a trained net:

1. Placement. Quantize onsets to the difficulty's rhythmic grid, dedupe grid slots keeping the strongest, and thin to a notes-per-second cap.
2. Selection. Walk the placed rows assigning arrows with strict foot alternation. A foot only reaches panels on its own body side, so no crossover appears unless the tier's crossover probability adds one. Footswitches unlock the same way. Low tiers forbid both, which keeps beginner charts forward-facing.

Lane bias drum routes low band energy toward Down and high toward Up so arrows track the drum kit. Lane bias none (Quick) ignores the bands and leans on alternation and the home-side backbone only.

API

• DIFFS the difficulty table: beginner, basic, difficult, expert, challenge, each with a foot rating, allowed subdivisions, and probabilities for jumps, crossovers, footswitches, and holds.
• generate(analysis, tempo, options) returns a chart. options: difficulty, laneBias (drum or none), seed, engine, engineUsed.
• countJumps(notes) count rows carrying two or more arrows.
• nominalRadar(difficulty) a preview radar for a difficulty before a chart exists.

Chart shape

{ bpm, offset, difficulty, foot, meter, duration, engine, engineUsed,
  notes: [{ t, beat, lane, dur, quant, type, endBeat? }], count, radar }

Lanes are 0 Left, 1 Down, 2 Up, 3 Right. t and dur are seconds, beat is the position in beats, quant is the note value (4, 8, 12, 16, 24, 32) used to color the arrow. A jump is two notes sharing a t. A hold sets type: 'hold', a positive dur, and an endBeat.