maia-util/es6/convert_1st_bar2anacrusis_val.js

Utility math and music functions supporting various applications by Music Artificial Intelligence Algorithms, Inc.

export default function convert_1st_bar2anacrusis_val(bar_1, divisions){
  // Tom Collins 25/2/2015.
  // In
  // bar_1 Object mandatory
  // divisions Integer mandatory
  // Out Array
  // This function works out how long an anacrusis contained in bar_1 should
  // last.

  // Get top and bottom number from time signature, to work out how long a full
  // first bar should last.
  if (bar_1.attributes){
    var attributes = bar_1.attributes;
    for (let j = 0; j < attributes.length; j++){
      if (attributes[j].time){
        // Assuming there is only one time per attribute...
        var time_sig_1 = {};
        time_sig_1.topNo = parseInt(attributes[j].time[0].beats[0]);
        time_sig_1.bottomNo = parseInt(attributes[j].time[0]['beat-type'][0]);
        }
    }
  }
  if (time_sig_1 == undefined) {
    console.log('It was not possible to find a time signature in the first ' +
                'bar of the top staff.');
    console.log('Returning default values for the anacrusis and crotchets '+
                'bar, which may be wrong.');
    return [0, 4];
  }

  var anacrusis = 0;
  var crotchets_per_bar = 4*time_sig_1.topNo/time_sig_1.bottomNo;
  var dur_in_1st_bar_should_be = divisions*crotchets_per_bar;
  var ontime = 0;

  // Get backup value.
  if (bar_1.backup){
    var backups = bar_1.backup;
    }
  else{
    backups = [];
  }

  // Increment over the notes.
  if (bar_1.note){
    var notes = bar_1.note;
    for (let note_index = 0; note_index < notes.length; note_index++){
      if (notes[note_index].grace == undefined){
        // This is the integer duration expressed in MusicXML.
        var duration = parseInt(notes[note_index].duration[0]);
        var offtime = ontime + duration;
        // Correct rounding errors in the offtime values.
        // If the note is a second, third, etc. note of a chord, then do
        // not increment the ontime variable.
        if (note_index < notes.length - 1 && notes[note_index + 1].chord){
        }
        else { // Do increment the ontime value.
          ontime = offtime;
        }
      }
    }
  }
  var compar = ontime/(backups.length + 1);
  if (compar != dur_in_1st_bar_should_be){
    anacrusis = -compar/divisions;
  }
  return [anacrusis, crotchets_per_bar];
}