mirror of
https://codeberg.org/uzu/strudel
synced 2026-09-05 06:57:35 -04:00
Felix Roos
72 lines
2.2 KiB
JavaScript
72 lines
2.2 KiB
JavaScript
const steps = [1, 0, 2, 0, 3, 4, 0, 5, 0, 6, 0, 7];
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const notes = ['C', '', 'D', '', 'E', 'F', '', 'G', '', 'A', '', 'B'];
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const noteLetters = ['C', 'D', 'E', 'F', 'G', 'A', 'B'];
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const accidentalOffset = (accidentals) => {
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return accidentals.split('#').length - accidentals.split('b').length;
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};
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const accidentalString = (offset) => {
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if (offset < 0) {
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return 'b'.repeat(-offset);
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}
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if (offset > 0) {
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return '#'.repeat(offset);
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}
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return '';
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};
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export const Step = {
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tokenize(step) {
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const [accidentals, stepNumber] = step.match(/^([#b]*)([1-9]+)$/).slice(1);
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return [accidentals, parseInt(stepNumber)];
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},
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accidentals(step) {
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return accidentalOffset(Step.tokenize(step)[0]);
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},
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};
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Step.tokenize('#11');
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Step.tokenize('b13');
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Step.tokenize('bb6');
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Step.accidentals('3');
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Step.accidentals('b3');
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export const Note = {
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// TODO: support octave numbers
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tokenize(note) {
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return [note[0], note.slice(1)];
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},
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accidentals(note) {
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return accidentalOffset(this.tokenize(note)[1]);
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},
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};
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Note.tokenize('C##');
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Note.accidentals('C#');
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Note.accidentals('C##');
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Note.accidentals('Eb');
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Note.accidentals('Bbb');
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// TODO: support octave numbers
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function transpose(note, step) {
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// example: E, 3
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const stepNumber = Step.tokenize(step)[1]; // 3
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const noteLetter = Note.tokenize(note)[0]; // E
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const noteIndex = noteLetters.indexOf(noteLetter); // 2 "E is C+2"
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const targetNote = noteLetters[(noteIndex + stepNumber - 1) % 8]; // G "G is a third above E"
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const rootIndex = notes.indexOf(noteLetter); // 4 "E is 4 semitones above C"
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const targetIndex = notes.indexOf(targetNote); // 7 "G is 7 semitones above C"
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const indexOffset = targetIndex - rootIndex; // 3 (E to G is normally a 3 semitones)
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const stepIndex = steps.indexOf(stepNumber); // 4 ("3" is normally 4 semitones)
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const offsetAccidentals = accidentalString(Step.accidentals(step) + Note.accidentals(note) + stepIndex - indexOffset); // "we need to add a # to to the G to make it a major third from E"
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return [targetNote, offsetAccidentals].join('');
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}
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transpose('F#', '3');
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transpose('C', '3');
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transpose('D', '3');
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transpose('E', '3');
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transpose('Eb', '3');
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transpose('Ebb', '3');
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