mainstage-diatonic-chord-trigger.js

// Diatonic Chord Trigger

var notes = ["C", "C#/Db", "D", "D#/Eb", "E", "F", "F#/Gb", "G", "G#/Ab", "A", "A#/Bb", "B"];
var PluginParameters = [
  { name: "Parent Key", type: "menu", valueStrings:notes, defaultValue: 0 }
];
var debug = true;

function rootKey() {
  return GetParameter("Parent Key");
}

function playChord(events) {
  for (var i = 0; i < events.length; i += 1) {
    if (debug) {
      events[i].trace();
    }
    events[i].send();
  }
}

function copyNote(event) {
  var copy = new event.constructor();
  copy.pitch = event.pitch;
  copy.velocity = event.velocity;
  return copy;
}

function noteAtSemitonesFrom(event, semitones) {
  var note = new event.constructor();
  note.pitch = event.pitch + semitones;
  note.velocity = event.velocity;
  return note;
}

function semitoneDifferenceFromRoot(pitch) {
  var semitones = (pitch - rootKey()) % 12;
  if (debug) {
    Trace(pitch);
    Trace(semitones);
  }
  return semitones;
}

function isMajorInterval(event) {
  return [0, 5, 7].indexOf(semitoneDifferenceFromRoot(event.pitch)) >= 0;
}

function isMinorInterval(event) {
  return [2, 3, 4, 9, 11].indexOf(semitoneDifferenceFromRoot(event.pitch)) >= 0;
}

function majorThirdIntervalFrom(event) {
  return noteAtSemitonesFrom(event, 4);
}

function minorThirdIntervalFrom(event) {
  return noteAtSemitonesFrom(event, 3);
}

function perfectFifthIntervalFrom(event) {
  return noteAtSemitonesFrom(event, 7);
}

function diminishedFifthIntervalFrom(event) {
  return noteAtSemitonesFrom(event, 6);
}

function octaveAbove(event) {
  return noteAtSemitonesFrom(event, 12);
}

function majorChordWithRoot(event) {
  return [
    event,
    majorThirdIntervalFrom(event),
    perfectFifthIntervalFrom(event),
    octaveAbove(event)
  ];
}

function minorChordWithRoot(event) {
  var notes = [
    event,
    minorThirdIntervalFrom(event),
  ];
  
  if (11 === semitoneDifferenceFromRoot(event.pitch)) {
    notes.push(diminishedFifthIntervalFrom(event));
  } else {
    notes.push(perfectFifthIntervalFrom(event));
  }
  
  notes.push(octaveAbove(event));
  return notes;
}

function chordForNote(event) {
  if (isMajorInterval(event)) {
    return majorChordWithRoot(event);
  } else if (isMinorInterval(event)) {
    return minorChordWithRoot(event);
  } else {
    return [event];
  }
}

function HandleMIDI(event) {
  playChord(chordForNote(event));  
}