Euclidean Rhythm Generator (ideal for p5.js)

euclidArray.js

// @mkontogiannis's euclidean rhythm calculator
// https://github.com/mkontogiannis/euclidean-rhythms
//
// specifically grok'd from this version:
// https://unpkg.com/[email protected]/dist/bundle.umd.js
//
// see also:
// http://cgm.cs.mcgill.ca/~godfried/publications/banff.pdf
// http://www.atonalmicroshores.com/2014/03/bjorklund-py/
//
// creates binary arrays for rhythmic patterns that work well with p5.js 
// https://p5js.org/reference/#/p5.Part
//

"use strict";


/**
   *  Returns the calculated pattern of equally distributed pulses in total steps
   *  based on the euclidean rhythms algorithm described by Godfried Toussaint
   *
   *  @method  getPattern
   *  @param {Number} pulses Number of pulses in the pattern
   *  @param {Number} steps  Number of steps in the pattern (pattern length)
   */
var getPattern = function getPattern(pulses, steps) {
  if (pulses < 0 || steps < 0 || steps < pulses) {
    return [];
  }

  // Create the two arrays
  var first = new Array(pulses).fill([1]);
  var second = new Array(steps - pulses).fill([0]);

  var firstLength = first.length;
  var minLength = Math.min(firstLength, second.length);

  var loopThreshold = 0;
  // Loop until at least one array has length gt 2 (1 for first loop)
  while (minLength > loopThreshold) {
    // Allow only loopThreshold to be zero on the first loop
    if (loopThreshold === 0) {
      loopThreshold = 1;
    }

    // For the minimum array loop and concat
    for (var x = 0; x < minLength; x++) {
      first[x] = Array.prototype.concat.call(first[x], second[x]);
    }

    // if the second was the bigger array, slice the remaining elements/arrays and update
    if (minLength === firstLength) {
      second = Array.prototype.slice.call(second, minLength);
    }
    // Otherwise update the second (smallest array) with the remainders of the first
    // and update the first array to include onlt the extended sub-arrays
    else {
        second = Array.prototype.slice.call(first, minLength);
        first = Array.prototype.slice.call(first, 0, minLength);
      }
    firstLength = first.length;
    minLength = Math.min(firstLength, second.length);
  }

  // Build the final array
  var pattern = [];
  first.forEach(function (f) {
    pattern = Array.prototype.concat.call(pattern, f);
  });
  second.forEach(function (s) {
    pattern = Array.prototype.concat.call(pattern, s);
  });

  return pattern;
};