launchpad-mini/lib/brightness.js

JavaScript library for interacting with the Novation’s midi board LAUNCHPAD MINI.

'use strict';

/*
 Launchpad describes brightness levels as a “duty cycle” fraction described by
 f = num/den. num is a number between 1 and 16, den is a number between 3 and 18.
 */

const num = (new Array( 16 )).fill( 0 ).map( ( el, ix ) => ix + 1 );
const den = (new Array( 16 )).fill( 0 ).map( ( el, ix ) => ix + 3 );

let arr = num.map( nu => den.map( de => [ nu, de ] ) )
    .reduce( ( acc, cur ) => acc.concat( cur ), [] )
    .filter( pair => pair[ 0 ] <= pair[ 1 ] ) // Remove all numbers where the fraction is > 1
    .map( pair => [ pair[ 0 ], pair[ 1 ], pair[ 0 ] / pair[ 1 ] ] ) // now contains all [ num, den, f ] pairs
    .sort( ( a, b ) => a[ 2 ] - b[ 2 ] ) // Sort by size
    .filter( ( el, ix, arr ) => !(ix > 0 && arr[ ix - 1 ][ 2 ] === el[ 2 ]) ); // Remove all duplicates

/**
 * This method finds the best duty cycle match for the given brightness.
 * @param {Number} t Brightness level between 0 and 1
 * @returns {Array.<Number>} Array [ numerator, denominator, fraction ]
 */
const getNumDen = function ( t ) {
    return arr[ Math.min( arr.length - 1, Math.max( 0, Math.round( t * arr.length ) ) ) ];
};

module.exports = {
    getNumDen
};