feuerwerk/src/core/instrument/chipPresets.ts

import { edgesInto, type Graph, type GraphEdge, type GraphNode } from '../graph/Graph';
import { asNumber } from '../graph/values';
import { newId } from '../ids';
import type { PropertyBag } from '../model/Properties';
import type { FlatDef } from '../properties/PropertySchema';
import type { ChipWave } from '../soundfx/chip';
import {
  CRUSH_ROWS,
  FILTER_ROWS,
  FLAT_Q,
  type FxPassFilter,
  passOf,
  SoundFxBitcrusher,
  FLANGER_ROWS,
  PHASER_ROWS,
  SoundFxDelay,
  SoundFxFilter,
  SoundFxFlanger,
  SoundFxMix,
  SoundFxPhaser,
  SoundFxPitch,
} from '../soundfx/nodes';
import {
  CHIP_ROWS,
  ENVELOPE_ROWS,
  INSTRUMENT_CHIP,
  INSTRUMENT_ENVELOPE,
  INSTRUMENT_NOTES,
  INSTRUMENT_OUTPUT,
  noteNameKey,
  noteOutputKey,
} from './nodes';
import { HIGHEST_NOTE, LOWEST_NOTE } from './notes';

/**
 * The Preset menu, Randomize and Mutate of the Instrument tab (#329), the way sfxr makes its sounds:
 * its generators and its randomizer draw sfxr's settings, 0 to 1 as its sliders have them, which are
 * then worked out into the numbers of a Chip, an Envelope, a Filter, a Bitcrusher and a Flanger (#341),
 * which sfxr calls its phaser. sfxr is
 * Copyright (c) 2007 Tomas Pettersson, MIT licence.
 *
 * Next to those sounds the menu has instruments to play tunes on: Chips that follow the note and hold
 * it while it is held, the same every time they are picked.
 */
export type EffectPreset = 'pickup' | 'laser' | 'explosion' | 'powerup' | 'hit' | 'jump' | 'blip';
export type TonePreset =
  | 'squareLead'
  | 'pulseLead'
  | 'echoLead'
  | 'octaveArp'
  | 'brass'
  | 'detunedSaws'
  | 'stringPad'
  | 'phasedPad'
  | 'organ'
  | 'flute'
  | 'bell'
  | 'pluck'
  | 'triangleBass'
  | 'pluckBass'
  | 'drumKit';
export type ChipPreset = EffectPreset | TonePreset;

export const TONE_PRESETS: readonly { value: TonePreset; label: string }[] = [
  { value: 'squareLead', label: 'Square Lead' },
  { value: 'pulseLead', label: 'Pulse Lead' },
  { value: 'echoLead', label: 'Echo Lead' },
  { value: 'octaveArp', label: 'Octave Arp' },
  { value: 'brass', label: 'Synth Brass' },
  { value: 'detunedSaws', label: 'Detuned Saws' },
  { value: 'stringPad', label: 'String Pad' },
  { value: 'phasedPad', label: 'Phased Pad' },
  { value: 'organ', label: 'Organ' },
  { value: 'flute', label: 'Flute' },
  { value: 'bell', label: 'Bell' },
  { value: 'pluck', label: 'Pluck' },
  { value: 'triangleBass', label: 'Triangle Bass' },
  { value: 'pluckBass', label: 'Pluck Bass' },
  { value: 'drumKit', label: 'Drum Kit' },
];

export const EFFECT_PRESETS: readonly { value: EffectPreset; label: string }[] = [
  { value: 'pickup', label: 'Pickup' },
  { value: 'laser', label: 'Laser' },
  { value: 'explosion', label: 'Explosion' },
  { value: 'powerup', label: 'Powerup' },
  { value: 'hit', label: 'Hit' },
  { value: 'jump', label: 'Jump' },
  { value: 'blip', label: 'Blip' },
];

/** Every preset, the instruments first, as the menu has them. */
export const CHIP_PRESETS: readonly { value: ChipPreset; label: string }[] = [
  ...TONE_PRESETS,
  ...EFFECT_PRESETS,
];

const isTone = (preset: ChipPreset): preset is TonePreset =>
  TONE_PRESETS.some((option) => option.value === preset);

type Random = () => number;

/** sfxr's settings by its own names, with the wave as ours. */
interface Sfxr {
  wave: ChipWave;
  baseFreq: number;
  freqLimit: number;
  freqRamp: number;
  freqDramp: number;
  duty: number;
  dutyRamp: number;
  vibStrength: number;
  vibSpeed: number;
  envAttack: number;
  envSustain: number;
  envDecay: number;
  lpfFreq: number;
  lpfResonance: number;
  hpfFreq: number;
  repeatSpeed: number;
  arpSpeed: number;
  arpMod: number;
  phaOffset: number;
  phaRamp: number;
}

const reset = (): Sfxr => ({
  wave: 'square',
  baseFreq: 0.3,
  freqLimit: 0,
  freqRamp: 0,
  freqDramp: 0,
  duty: 0,
  dutyRamp: 0,
  vibStrength: 0,
  vibSpeed: 0,
  envAttack: 0,
  envSustain: 0.3,
  envDecay: 0.4,
  lpfFreq: 1,
  lpfResonance: 0,
  hpfFreq: 0,
  repeatSpeed: 0,
  arpSpeed: 0,
  arpMod: 0,
  phaOffset: 0,
  phaRamp: 0,
});

/** sfxr's waves by their number there. */
const SFXR_WAVES: readonly ChipWave[] = ['square', 'saw', 'sine', 'noise'];

/** sfxr's generators, one per button. */
function presetSfxr(preset: EffectPreset, random: Random): Sfxr {
  const p = reset();
  // sfxr's `frnd`: 0 up to `range`, and `rnd`: a whole number from 0 to `n`, both included.
  const f = (range: number) => random() * range;
  const r = (n: number) => Math.floor(random() * (n + 1));
  switch (preset) {
    case 'pickup':
      p.baseFreq = 0.4 + f(0.5);
      p.envSustain = f(0.1);
      p.envDecay = 0.1 + f(0.4);
      if (r(1)) {
        p.arpSpeed = 0.5 + f(0.2);
        p.arpMod = 0.2 + f(0.4);
      }
      break;
    case 'laser': {
      let wave = r(2);
      if (wave === 2 && r(1)) wave = r(1);
      p.wave = SFXR_WAVES[wave]!;
      p.baseFreq = 0.5 + f(0.5);
      p.freqLimit = Math.max(0.2, p.baseFreq - 0.2 - f(0.6));
      p.freqRamp = -0.15 - f(0.2);
      if (r(2) === 0) {
        p.baseFreq = 0.3 + f(0.6);
        p.freqLimit = f(0.1);
        p.freqRamp = -0.35 - f(0.3);
      }
      if (r(1)) {
        p.duty = f(0.5);
        p.dutyRamp = f(0.2);
      } else {
        p.duty = 0.4 + f(0.5);
        p.dutyRamp = -f(0.7);
      }
      p.envSustain = 0.1 + f(0.2);
      p.envDecay = f(0.4);
      if (r(1)) p.hpfFreq = f(0.3);
      break;
    }
    case 'explosion':
      p.wave = 'noise';
      if (r(1)) {
        p.baseFreq = 0.1 + f(0.4);
        p.freqRamp = -0.1 + f(0.4);
      } else {
        p.baseFreq = 0.2 + f(0.7);
        p.freqRamp = -0.2 - f(0.2);
      }
      p.baseFreq *= p.baseFreq;
      if (r(4) === 0) p.freqRamp = 0;
      if (r(2) === 0) p.repeatSpeed = 0.3 + f(0.5);
      p.envSustain = 0.1 + f(0.3);
      p.envDecay = f(0.5);
      if (r(1)) {
        p.phaOffset = -0.3 + f(0.9);
        p.phaRamp = -f(0.3);
      }
      if (r(1)) {
        p.vibStrength = f(0.7);
        p.vibSpeed = f(0.6);
      }
      if (r(2) === 0) {
        p.arpSpeed = 0.6 + f(0.3);
        p.arpMod = 0.8 - f(1.6);
      }
      break;
    case 'powerup':
      if (r(1)) p.wave = 'saw';
      else p.duty = f(0.6);
      p.baseFreq = 0.2 + f(0.3);
      if (r(1)) {
        p.freqRamp = 0.1 + f(0.4);
        p.repeatSpeed = 0.4 + f(0.4);
      } else {
        p.freqRamp = 0.05 + f(0.2);
        if (r(1)) {
          p.vibStrength = f(0.7);
          p.vibSpeed = f(0.6);
        }
      }
      p.envSustain = f(0.4);
      p.envDecay = 0.1 + f(0.4);
      break;
    case 'hit': {
      const wave = r(2);
      p.wave = SFXR_WAVES[wave === 2 ? 3 : wave]!;
      if (p.wave === 'square') p.duty = f(0.6);
      p.baseFreq = 0.2 + f(0.6);
      p.freqRamp = -0.3 - f(0.4);
      p.envSustain = f(0.1);
      p.envDecay = 0.1 + f(0.2);
      if (r(1)) p.hpfFreq = f(0.3);
      break;
    }
    case 'jump':
      p.duty = f(0.6);
      p.baseFreq = 0.3 + f(0.3);
      p.freqRamp = 0.1 + f(0.2);
      p.envSustain = 0.1 + f(0.3);
      p.envDecay = 0.1 + f(0.2);
      if (r(1)) p.hpfFreq = f(0.3);
      if (r(1)) p.lpfFreq = 1 - f(0.6);
      break;
    case 'blip':
      p.wave = SFXR_WAVES[r(1)]!;
      if (p.wave === 'square') p.duty = f(0.6);
      p.baseFreq = 0.2 + f(0.4);
      p.envSustain = 0.1 + f(0.1);
      p.envDecay = f(0.2);
      p.hpfFreq = 0.1;
      break;
  }
  return p;
}

/** sfxr's Randomize: every setting drawn, most of them leaning towards 0. */
function randomSfxr(random: Random): Sfxr {
  const signed = () => random() * 2 - 1;
  const p = reset();
  p.baseFreq = signed() ** 2;
  if (random() < 0.5) p.baseFreq = signed() ** 3 + 0.5;
  p.freqRamp = signed() ** 5;
  if (p.baseFreq > 0.7 && p.freqRamp > 0.2) p.freqRamp = -p.freqRamp;
  if (p.baseFreq < 0.2 && p.freqRamp < -0.05) p.freqRamp = -p.freqRamp;
  p.freqDramp = signed() ** 3;
  p.duty = signed();
  p.dutyRamp = signed() ** 3;
  p.vibStrength = signed() ** 3;
  p.vibSpeed = signed();
  p.envAttack = signed() ** 3;
  p.envSustain = signed() ** 2;
  p.envDecay = signed();
  if (p.envAttack + p.envSustain + p.envDecay < 0.2) {
    p.envSustain += 0.2 + random() * 0.3;
    p.envDecay += 0.2 + random() * 0.3;
  }
  p.lpfResonance = signed();
  p.lpfFreq = 1 - random() ** 3;
  p.hpfFreq = random() ** 5;
  p.repeatSpeed = signed();
  p.arpSpeed = signed();
  p.arpMod = signed();
  // Drawn last, not where sfxr has them, so the numbers before stay as they were.
  p.phaOffset = signed() ** 3;
  p.phaRamp = signed() ** 3;
  return p;
}

const SFXR_RATE = 44100;
/** sfxr counts a period in samples taken 8 times over: its frequency is `f² + 0.001` of 3528 Hz. */
const hzOf = (f: number) => 3528 * (f * f + 0.001);
/** How long sfxr waits before an arpeggio or a repeat, at a speed from 0 to 1. */
const waitOf = (speed: number) => ((1 - speed) ** 2 * 20000 + 32) / SFXR_RATE;
/** A stage of sfxr's envelope: its setting squared, in 100000 samples. */
const stageOf = (value: number) => (value * value * 100000) / SFXR_RATE;

function chipNumbers(p: Sfxr): Record<keyof typeof CHIP_ROWS, number> {
  const slide = 1 - p.freqRamp ** 3 * 0.01;
  const arpeggio = p.arpMod >= 0 ? 1 - p.arpMod ** 2 * 0.9 : 1 + p.arpMod ** 2 * 10;
  return {
    frequency: hzOf(p.baseFreq),
    duty: 0.5 - p.duty * 0.5,
    dutySweep: -p.dutyRamp * 0.00005 * SFXR_RATE,
    slide: -12 * Math.log2(slide) * SFXR_RATE,
    deltaSlide: (12 / Math.LN2) * SFXR_RATE ** 2 * p.freqDramp ** 3 * 1e-6,
    minFrequency: p.freqLimit > 0 ? hzOf(p.freqLimit) : 0,
    vibratoDepth: 12 * Math.log2(1 + Math.abs(p.vibStrength) * 0.5),
    vibratoSpeed: (p.vibSpeed ** 2 * 0.01 * SFXR_RATE) / (2 * Math.PI),
    arpeggio: p.arpSpeed === 1 || p.arpMod === 0 ? 0 : -12 * Math.log2(arpeggio),
    arpeggioTime: waitOf(p.arpSpeed),
    repeat: p.repeatSpeed === 0 ? 0 : waitOf(p.repeatSpeed),
  };
}

/**
 * sfxr holds a sound at full for its sustain, then lets it fall in a straight line; an Envelope
 * falls away as a struck string does, quick at first. Three times the whole of sfxr's keeps about
 * as much of it heard. Sustain 0 ends the note once it has fallen.
 */
const FALL = 3;
const RELEASE = 0.02;

function envelopeNumbers(p: Sfxr): Record<'attack' | 'decay' | 'sustain' | 'release', number> {
  return {
    attack: stageOf(p.envAttack),
    decay: FALL * (stageOf(p.envSustain) + stageOf(p.envDecay)),
    sustain: 0,
    release: RELEASE,
  };
}

/**
 * The Q a Filter had at a resonance from 0 to 1 before it took a Q (#318): from no bump up to a
 * 20 dB ring for a low- or high-pass, from about two octaves wide to a narrow ring for a band-pass.
 */
function resonanceQ(filter: FxPassFilter, resonance: number): number {
  const r = Math.max(0, Math.min(1, resonance));
  if (filter === 'bandpass') return 0.7 * (20 / 0.7) ** r;
  return FLAT_Q * (10 / FLAT_Q) ** r;
}

/** Where sfxr's filters come out, run 8 times a sample: about 17.8 kHz times `f^1.5` low, 5.6 kHz times `f²` high. */
function filterNumbers(p: Sfxr, filter: FxPassFilter): Record<'cutoff' | 'q', number> {
  if (filter === 'highpass') return { cutoff: 5615 * p.hpfFreq ** 2, q: FLAT_Q };
  // Wide open, as far as the row goes.
  if (p.lpfFreq >= 1) return { cutoff: Infinity, q: FLAT_Q };
  return { cutoff: 17756 * Math.max(0, p.lpfFreq) ** 1.5, q: resonanceQ(filter, Math.abs(p.lpfResonance)) };
}

/**
 * sfxr's phaser as a Flanger: its delay is `offset²` of 1020 samples taken 8 times over, and moves
 * `ramp²` of one of them every sample. Mirrored at 0 as it is, a sweep towards 0 is one with the
 * other sign than the offset.
 */
function flangerNumbers(p: Sfxr): Record<'offset' | 'sweep', number> {
  const taken = 8 * SFXR_RATE;
  const away = Math.sign(p.phaOffset || 1) * Math.sign(p.phaRamp);
  return {
    offset: ((p.phaOffset ** 2 * 1020) / taken) * 1000,
    sweep: (away * p.phaRamp ** 2 * SFXR_RATE * 1000) / taken,
  };
}

/** A number held to its row and rounded to as many places as its step has. */
function heldTo(value: number, row: FlatDef<'number'>): number {
  const places = Math.max(0, -Math.floor(Math.log10(row.step ?? 0.01)));
  const inside = Math.max(row.min ?? -Infinity, Math.min(row.max ?? Infinity, value));
  return Number(inside.toFixed(places)) + 0;
}

function held<K extends string>(
  values: Record<K, number>,
  rows: Record<NoInfer<K>, FlatDef<'number'>>,
): Record<K, number> {
  const out = {} as Record<K, number>;
  for (const key of Object.keys(values) as K[]) out[key] = heldTo(values[key], rows[key]);
  return out;
}

/** Room between the nodes of a preset, left to right and top to bottom: a Chip is a tall node. */
const COLUMN = 240;
const ROW = 340;

/** A node to make: its type and its params. */
type Step = readonly [type: string, params: PropertyBag];

/** A graph laid out on a grid while it is made. */
class Sketch {
  readonly nodes: GraphNode[] = [];
  readonly edges: GraphEdge[] = [];

  add(type: string, column: number, row: number, params: PropertyBag): GraphNode {
    const node: GraphNode = { id: newId(), type, x: column * COLUMN, y: row * ROW, params };
    this.nodes.push(node);
    return node;
  }

  wire(from: GraphNode, out: string, to: GraphNode, into: string): void {
    this.edges.push({ id: newId(), from: { node: from.id, port: out }, to: { node: to.id, port: into } });
  }

  /** Nodes one after another to the right of `from`, each taking the sound of the one before. */
  line(from: GraphNode, ...steps: readonly Step[]): GraphNode {
    let last = from;
    for (const [type, params] of steps) {
      const next = this.add(type, last.x / COLUMN + 1, last.y / ROW, params);
      this.wire(last, 'out', next, 'in');
      last = next;
    }
    return last;
  }

  /** The Output, right of what it plays. */
  end(last: GraphNode): Graph {
    this.line(last, [INSTRUMENT_OUTPUT, {}]);
    return { nodes: this.nodes, edges: this.edges };
  }
}

const everyNote: PropertyBag = { from: String(LOWEST_NOTE), to: String(HIGHEST_NOTE) };

/**
 * An effect preset as a whole graph (#329): every note plays one Chip, which ends by itself through
 * an Envelope, a Filter, sfxr's phaser where it has one, and a Bitcrusher. The Chip keeps to the preset's own frequency, as sfxr does,
 * so every key plays the same sound until "follow note" is turned on. Each call draws it anew.
 */
function effectGraph(preset: EffectPreset, random: Random): Graph {
  const p = presetSfxr(preset, random);
  const filter: FxPassFilter = p.lpfFreq >= 1 && p.hpfFreq > 0 ? 'highpass' : 'lowpass';
  const crushed = random() < 0.5;
  const s = new Sketch();
  const notes = s.add(INSTRUMENT_NOTES, 0, 0, everyNote);
  const chip = s.add(INSTRUMENT_CHIP, 1, 0, {
    wave: p.wave,
    followNote: false,
    ...held(chipNumbers(p), CHIP_ROWS),
  });
  s.wire(notes, 'any', chip, 'trigger');
  const flanged: Step[] =
    p.phaOffset !== 0 || p.phaRamp !== 0
      ? [
          [
            SoundFxFlanger.type,
            held({ ...flangerNumbers(p), rate: 0, depth: 0, feedback: 0, mix: 1 }, FLANGER_ROWS),
          ],
        ]
      : [];
  return s.end(
    s.line(
      chip,
      [INSTRUMENT_ENVELOPE, held(envelopeNumbers(p), ENVELOPE_ROWS)],
      [SoundFxFilter.type, { filter, ...held(filterNumbers(p, filter), FILTER_ROWS) }],
      ...flanged,
      [
        SoundFxBitcrusher.type,
        held({ bits: crushed ? 8 : 16, rate: crushed ? 22050 : 44100, mix: 1 }, CRUSH_ROWS),
      ],
    ),
  );
}

type ChipNumbers = Partial<Record<keyof typeof CHIP_ROWS, number>>;

/** A Chip, triggered by `out` of the Notes: at the pitch of the note, unless it has a frequency of its own. */
function chipOn(
  s: Sketch,
  notes: GraphNode,
  row: number,
  wave: ChipWave,
  numbers: ChipNumbers = {},
  { out = 'any', column = 1 } = {},
): GraphNode {
  const defaults = Object.fromEntries(Object.values(CHIP_ROWS).map((r) => [r.key, r.default])) as Record<
    keyof typeof CHIP_ROWS,
    number
  >;
  const chip = s.add(INSTRUMENT_CHIP, column, row, {
    wave,
    followNote: numbers.frequency === undefined,
    ...held({ ...defaults, ...numbers }, CHIP_ROWS),
  });
  s.wire(notes, out, chip, 'trigger');
  return chip;
}

const envelope = (attack: number, decay: number, sustain: number, release: number) =>
  [INSTRUMENT_ENVELOPE, held({ attack, decay, sustain, release }, ENVELOPE_ROWS)] as const;
const pass = (filter: FxPassFilter, cutoff: number, resonance = 0) =>
  [SoundFxFilter.type, { filter, cutoff, q: heldTo(resonanceQ(filter, resonance), FILTER_ROWS.q) }] as const;
const pitch = (semitones: number) => [SoundFxPitch.type, { semitones }] as const;
const phaser = (stages: number, frequency: number, rate: number, depth: number, feedback: number) =>
  [SoundFxPhaser.type, { stages: String(stages), frequency, rate, depth, feedback, mix: 1 }] as const;
const echo = (time: number, feedback: number, mix: number, pingPong = false) =>
  [SoundFxDelay.type, { time, sync: 'beats', feedback, damping: 0.4, mix, pingPong }] as const;

/** Two ways into one Mix, a column right of the further one; `b` weighs `share`. */
function mixed(s: Sketch, a: GraphNode, b: GraphNode, share: number, curve = 'crossfade'): GraphNode {
  const mix = s.add(SoundFxMix.type, Math.max(a.x, b.x) / COLUMN + 1, Math.min(a.y, b.y) / ROW, {
    curve,
    mix: share,
  });
  s.wire(a, 'out', mix, 'a');
  s.wire(b, 'out', mix, 'b');
  return mix;
}

/**
 * A low-pass whose cutoff an Envelope of its own sweeps, from `from` Hz at rest up to `to` and down
 * to the sustain between them, as a synth's filter envelope does. The Envelope sits under the Filter.
 */
function swept(
  s: Sketch,
  from: GraphNode,
  resonance: number,
  sweep: { from: number; to: number; attack: number; decay: number; sustain: number; release: number },
): GraphNode {
  const filter = s.line(from, pass('lowpass', sweep.from, resonance));
  const { from: low, to: high, ...curve } = sweep;
  const moves = s.add(INSTRUMENT_ENVELOPE, filter.x / COLUMN, filter.y / ROW + 1, {
    ...held(curve, ENVELOPE_ROWS),
    from: low,
    to: high,
  });
  s.wire(moves, 'value', filter, 'cutoff');
  return filter;
}

/** Two saws a tenth of a semitone apart, mixed evenly: a fuller sound than one alone. */
function detuned(s: Sketch, notes: GraphNode, numbers: ChipNumbers = {}): GraphNode {
  const a = chipOn(s, notes, 0, 'saw', numbers);
  const b = s.line(chipOn(s, notes, 1, 'saw', numbers), pitch(0.1));
  return mixed(s, a, b, 0.5);
}

/** The drums of the kit, on the keys General MIDI has them on. */
const KICK = 36;
const SNARE = 38;
const CLOSED_HAT = 42;
const OPEN_HAT = 46;

/**
 * A kit on single notes: a kick that drops in pitch, a snare of a falling triangle and noise, and two
 * hi-hats of bright noise, short and long. Each ends by itself; only one of them plays on a key, so
 * the Mixes that join them pass it on whole.
 */
function drumKit(s: Sketch): GraphNode {
  const notes = s.add(INSTRUMENT_NOTES, 0, 0, {
    from: String(KICK),
    to: String(OPEN_HAT),
    singleNotes: true,
    [noteNameKey(KICK)]: 'Kick',
    [noteNameKey(SNARE)]: 'Snare',
    [noteNameKey(CLOSED_HAT)]: 'Closed hat',
    [noteNameKey(OPEN_HAT)]: 'Open hat',
  });
  const on = (note: number) => ({ out: noteOutputKey(note) });
  const kick = s.line(
    chipOn(s, notes, 0, 'sine', { frequency: 160, slide: -120, minFrequency: 30 }, on(KICK)),
    envelope(0.001, 0.3, 0, 0.02),
  );
  const body = s.line(
    chipOn(s, notes, 1, 'triangle', { frequency: 190, slide: -60 }, on(SNARE)),
    envelope(0.001, 0.1, 0, 0.02),
  );
  const rattle = s.line(
    chipOn(s, notes, 2, 'noise', { frequency: 2500 }, on(SNARE)),
    pass('highpass', 1200),
    envelope(0.001, 0.18, 0, 0.02),
  );
  const closed = s.line(
    chipOn(s, notes, 3, 'noise', { frequency: 4000 }, on(CLOSED_HAT)),
    pass('highpass', 7000, 0.1),
    envelope(0.001, 0.05, 0, 0.01),
  );
  const open = s.line(
    chipOn(s, notes, 4, 'noise', { frequency: 4000 }, on(OPEN_HAT)),
    pass('highpass', 6000, 0.1),
    envelope(0.001, 0.35, 0, 0.05),
  );
  const snare = mixed(s, body, rattle, 0.6);
  const hats = mixed(s, closed, open, 0.5);
  return mixed(s, mixed(s, kick, snare, 0.5), hats, 0.5);
}

/** What each instrument is made of, up to what the Output plays. */
const TONES: Record<Exclude<TonePreset, 'drumKit'>, (s: Sketch, notes: GraphNode) => GraphNode> = {
  // The plain square of the NES with a slight vibrato, its harshest top taken off.
  squareLead: (s, notes) =>
    s.line(
      chipOn(s, notes, 0, 'square', { vibratoDepth: 0.2, vibratoSpeed: 5.5 }),
      envelope(0.005, 0.2, 0.6, 0.15),
      pass('lowpass', 6000),
    ),
  // The thin, nasal eighth of a square, as near as the duty's steps of 0.01 come.
  pulseLead: (s, notes) =>
    s.line(
      chipOn(s, notes, 0, 'square', { duty: 0.13, vibratoDepth: 0.1, vibratoSpeed: 6 }),
      envelope(0.002, 0.1, 0.8, 0.08),
    ),
  // A quarter square with dotted-eighth echoes, left and right.
  echoLead: (s, notes) =>
    s.line(
      chipOn(s, notes, 0, 'square', { duty: 0.25 }),
      envelope(0.005, 0.15, 0.5, 0.1),
      echo(0.75, 0.35, 0.35, true),
    ),
  // The note and its octave by turns, 25 times a second: how a console played a chord.
  octaveArp: (s, notes) =>
    s.line(
      chipOn(s, notes, 0, 'square', { duty: 0.25, arpeggio: 12, arpeggioTime: 0.04, repeat: 0.08 }),
      envelope(0.002, 0.1, 0.7, 0.08),
    ),
  // A saw that swells and opens up as it is blown.
  brass: (s, notes) =>
    swept(
      s,
      s.line(
        chipOn(s, notes, 0, 'saw', { vibratoDepth: 0.1, vibratoSpeed: 5 }),
        envelope(0.04, 0.2, 0.8, 0.2),
      ),
      0.15,
      { from: 400, to: 3500, attack: 0.08, decay: 0.4, sustain: 0.5, release: 0.2 },
    ),
  detunedSaws: (s, notes) => s.line(detuned(s, notes), envelope(0.01, 0.3, 0.8, 0.3), pass('lowpass', 7000)),
  // Slow to come and to go, darker, with a little vibrato.
  stringPad: (s, notes) =>
    s.line(
      detuned(s, notes, { vibratoDepth: 0.1, vibratoSpeed: 5 }),
      envelope(0.5, 0.5, 0.8, 1),
      pass('lowpass', 2200, 0.1),
    ),
  // A saw pad, slow to come, swirled by a phaser of six stages.
  phasedPad: (s, notes) =>
    s.line(
      chipOn(s, notes, 0, 'saw', { vibratoDepth: 0.1, vibratoSpeed: 5 }),
      envelope(0.3, 0.5, 0.8, 0.8),
      pass('lowpass', 3000, 0.1),
      phaser(6, 600, 0.3, 2.5, 0.5),
    ),
  // A square and the square an octave up, held at full while the key is.
  organ: (s, notes) => {
    const low = chipOn(s, notes, 0, 'square');
    const high = s.line(chipOn(s, notes, 1, 'square'), pitch(12));
    return s.line(mixed(s, low, high, 0.35), envelope(0.005, 0.05, 1, 0.06), pass('lowpass', 4500));
  },
  // A triangle with vibrato and a breath of noise around 2.5 kHz.
  flute: (s, notes) => {
    const tone = chipOn(s, notes, 0, 'triangle', { vibratoDepth: 0.2, vibratoSpeed: 5 });
    const breath = s.line(chipOn(s, notes, 1, 'noise', { frequency: 2000 }), pass('bandpass', 2500, 0.3));
    return s.line(mixed(s, tone, breath, 0.08), envelope(0.06, 0.1, 0.85, 0.15));
  },
  // Two sines 2.76 times apart, as a bell's partials are, the upper fading first; echoes after.
  bell: (s, notes) => {
    const low = s.line(chipOn(s, notes, 0, 'sine'), envelope(0.001, 2, 0, 0.4));
    const high = s.line(chipOn(s, notes, 1, 'sine'), pitch(17.6), envelope(0.001, 0.6, 0, 0.2));
    return s.line(mixed(s, low, high, 0.35), echo(0.5, 0.3, 0.25));
  },
  // Struck, bright at once and dull soon after, gone in a moment however long it is held.
  pluck: (s, notes) =>
    swept(s, s.line(chipOn(s, notes, 0, 'square', { duty: 0.3 }), envelope(0.001, 0.6, 0, 0.1)), 0.2, {
      from: 600,
      to: 6000,
      attack: 0.001,
      decay: 0.15,
      sustain: 0,
      release: 0.1,
    }),
  // The triangle of the NES as its bass: no fade while it is held.
  triangleBass: (s, notes) => s.line(chipOn(s, notes, 0, 'triangle'), envelope(0.002, 0.05, 1, 0.04)),
  // A saw whose filter snaps open and shut on every note.
  pluckBass: (s, notes) =>
    swept(s, s.line(chipOn(s, notes, 0, 'saw'), envelope(0.002, 0.4, 0.5, 0.08)), 0.35, {
      from: 180,
      to: 2400,
      attack: 0.002,
      decay: 0.25,
      sustain: 0.15,
      release: 0.08,
    }),
};

/** An instrument preset: every note at its own pitch, the same graph each time it is picked. */
function toneGraph(preset: TonePreset): Graph {
  const s = new Sketch();
  if (preset === 'drumKit') return s.end(drumKit(s));
  return s.end(TONES[preset](s, s.add(INSTRUMENT_NOTES, 0, 0, everyNote)));
}

/**
 * A preset as a whole graph (#329): an sfxr sound, drawn anew on every call, or an instrument to
 * play tunes on, which comes out the same every time.
 */
export function chipPresetGraph(preset: ChipPreset, random: Random = Math.random): Graph {
  return isTone(preset) ? toneGraph(preset) : effectGraph(preset, random);
}

/** One number Randomize or Mutate gives a node. */
export interface ParamChange {
  node: string;
  key: string;
  value: number;
}

function rowsOf(type: string): Record<string, FlatDef<'number'>> | null {
  switch (type) {
    case INSTRUMENT_CHIP:
      return CHIP_ROWS;
    case INSTRUMENT_ENVELOPE:
      return ENVELOPE_ROWS;
    case SoundFxFilter.type:
      return FILTER_ROWS;
    case SoundFxBitcrusher.type:
      return CRUSH_ROWS;
    case SoundFxPhaser.type:
      return PHASER_ROWS;
    case SoundFxFlanger.type:
      return FLANGER_ROWS;
    default:
      return null;
  }
}

/** Whether Randomize and Mutate find anything in a graph to change. */
export const hasChipNumbers = (graph: Graph): boolean =>
  graph.nodes.some((node) => rowsOf(node.type) !== null);

/** An input an edge feeds keeps what it is fed: a number typed in there would do nothing. */
const typedIn = (graph: Graph, node: GraphNode) => (key: string) =>
  edgesInto(graph, node.id, key).length === 0;

function randomNumbers(node: GraphNode, random: Random): Record<string, number> | null {
  switch (node.type) {
    case INSTRUMENT_CHIP:
      return held(chipNumbers(randomSfxr(random)), CHIP_ROWS);
    case INSTRUMENT_ENVELOPE:
      return held(envelopeNumbers(randomSfxr(random)), ENVELOPE_ROWS);
    case SoundFxFilter.type:
      return held(filterNumbers(randomSfxr(random), passOf(node.params)), FILTER_ROWS);
    case SoundFxBitcrusher.type:
      return held({ bits: 4 + random() * 12, rate: 2000 * 24 ** random() }, CRUSH_ROWS);
    case SoundFxPhaser.type:
      return held(
        {
          frequency: 200 * 20 ** random(),
          rate: 0.05 * 100 ** random(),
          depth: 0.5 + random() * 3.5,
          feedback: random() * 0.8,
        },
        PHASER_ROWS,
      );
    case SoundFxFlanger.type:
      return held(
        {
          ...flangerNumbers(randomSfxr(random)),
          rate: 0.05 * 100 ** random(),
          depth: random() * 4,
          feedback: random() * 0.8,
        },
        FLANGER_ROWS,
      );
    default:
      return null;
  }
}

/**
 * Randomize (#329): the numbers of every Chip, Envelope, Filter, Bitcrusher, Phaser and Flanger
 * (#341) drawn anew, as sfxr's randomizer draws them; a Phaser's, and a Flanger's LFO, which sfxr
 * has not, within bounds of their own. Waves, filter types, the stages of a Phaser, every Mix and
 * an Envelope's "from" and "to" stay, and so does everything else in the graph.
 */
export function randomizedParams(graph: Graph, random: Random = Math.random): ParamChange[] {
  const changes: ParamChange[] = [];
  for (const node of graph.nodes) {
    const values = randomNumbers(node, random);
    if (!values) continue;
    const open = typedIn(graph, node);
    for (const [key, value] of Object.entries(values))
      if (open(key)) changes.push({ node: node.id, key, value });
  }
  return changes;
}

/** How far Mutate moves a number at most: a share of an octave where it is heard as a ratio, else a step and a tenth of it. */
const MUTATE: Readonly<Record<string, { octaves: number } | { by: number }>> = {
  frequency: { octaves: 0.25 },
  minFrequency: { octaves: 0.25 },
  cutoff: { octaves: 0.25 },
  rate: { octaves: 0.25 },
  duty: { by: 0.025 },
  dutySweep: { by: 0.1 },
  slide: { by: 5 },
  deltaSlide: { by: 20 },
  vibratoDepth: { by: 0.2 },
  vibratoSpeed: { by: 0.5 },
  arpeggio: { by: 1 },
  arpeggioTime: { by: 0.01 },
  repeat: { by: 0.02 },
  attack: { by: 0.005 },
  decay: { by: 0.02 },
  release: { by: 0.01 },
  q: { octaves: 0.25 },
  gain: { by: 1 },
  bits: { by: 0.5 },
  offset: { by: 0.1 },
  sweep: { by: 2 },
  depth: { by: 0.2 },
  feedback: { by: 0.05 },
};

/**
 * Mutate (#329): as sfxr does, each number of those nodes moves a little or not at all, one in two.
 * A 0 stays 0, so nothing that was off comes on, and an Envelope keeps its sustain.
 */
export function mutatedParams(graph: Graph, random: Random = Math.random): ParamChange[] {
  const changes: ParamChange[] = [];
  for (const node of graph.nodes) {
    const rows = rowsOf(node.type);
    if (!rows) continue;
    const open = typedIn(graph, node);
    for (const row of Object.values(rows)) {
      const how = MUTATE[row.key];
      if (!how || !open(row.key) || random() < 0.5) continue;
      const now = asNumber(node.params[row.key] ?? row.default);
      if (now === 0) continue;
      const u = random() * 2 - 1;
      const moved =
        'octaves' in how ? now * 2 ** (u * how.octaves) : now + u * (how.by + Math.abs(now) * 0.1);
      const value = heldTo(moved, row);
      if (value !== now) changes.push({ node: node.id, key: row.key, value });
    }
  }
  return changes;
}