devtool script to tile images into a single image

tile-folder.js

// install with:
//    npm i -g devtool
//    npm i img javascript-natural-sort electron-canvas-to-buffer 
//
// run:
//    devtool tile-folder.js -qch

var fs = require('fs')
var path = require('path')
var loadImage = require('img')
var natural = require('javascript-natural-sort')
var canvasToBuffer = require('electron-canvas-to-buffer')

// Your input/output settings
var folder = path.resolve(__dirname, 'tmp')
var output = path.resolve(__dirname, 'output')
var tileScale = 1
var padding = 0
var rows = 6

var files = fs.readdirSync(folder).filter(function (x) {
  return /\.(png|jpg|jpeg|gif|bmp|tiff)$/.test(x)
}).map(function (x) {
  return 'tmp/' + x
})
files.sort(natural)

var loadFiles = files.map(function (src) {
  return new Promise(function (resolve, reject) {
    loadImage(src, function (err, img) {
      if (err) return reject(err)
      resolve(img)
    })
  })
})

Promise.all(loadFiles)
  .then(render)

function render (images) {
  var imageSize = [
    Math.floor(images[0].width * tileScale),
    Math.floor(images[0].height * tileScale)
  ]

  var canvas = document.createElement('canvas')
  var ctx = canvas.getContext('2d')
  var count = images.length
  var cols = Math.ceil(count / rows)
  canvas.width = imageSize[0] * cols + padding * (cols + 1)
  canvas.height = imageSize[1] * rows + padding * (rows + 1)

  images.forEach(function (img, i) {
    var x = Math.floor(i % cols)
    var y = Math.floor(i / cols)
    ctx.drawImage(img,
      padding + x * (padding + imageSize[0]),
      padding + y * (padding + imageSize[1]),
      imageSize[0],
      imageSize[1])
  })

  var buffer = canvasToBuffer(canvas, 'image/png')
  var outfile = path.resolve(output, 'image.png')
  fs.writeFile(outfile, buffer, function (err) {
    if (err) throw err
    window.close()
  })
}