Musical Arpeggio Pattern Generator

musical-arpeggio-pattern-generator.markdown

Musical Arpeggio Pattern Generator

A Pen by Jake Albaugh on CodePen.

License.

script.babel

/**
  ArpeggioPatterns
  returns arrays of arpeggio patterns for a given length of notes
  @param steps {Integer} number of steps
  @return {Object}
    patterns: {Array} of arpeggiated index patterns
 */

class ArpeggioPatterns {
  constructor(params) {
    this.steps = params.steps;
    this._loadPatterns();
    this.updatePatterns = this.pubUpdatePatterns;
  };
  
  pubUpdatePatterns(params) {
    this.steps = params.steps;
    this._loadPatterns();
  };
  
  _loadPatterns() {
    this.arr = [];
    this.patterns = [];
    for(let i = 0; i < this.steps; i++) { this.arr.push(i); }
    this._used = [];
    this.permutations = this._permute(this.arr);
    this.looped = this._loop();
    this.patterns = {
      straight: this.permutations,
      looped: this.looped
    };
  };
  
  _permute(input, permutations) {
    permutations = permutations || [];
    var i, ch;
    for (i = 0; i < input.length; i++) {
      ch = input.splice(i, 1)[0];
      this._used.push(ch);
      if (input.length === 0) {
        permutations.push(this._used.slice());
      }
      this._permute(input, permutations);
      input.splice(i, 0, ch);
      this._used.pop();
    }
    return permutations;
  };
  
  _loop() {
    let looped = [];
    for(let p = 0; p < this.permutations.length; p++) {
      let perm = this.permutations[p];
      let arr = Array.from(perm);
      for(let x = 1; x < perm.length - 1; x++) {
        arr.push(perm[perm.length - 1 - x]);
      }
      looped.push(arr);
    }
    return looped;
  };
  
};