Add extracted source directory and README navigation

extracted-source/node_modules/qrcode/lib/renderer/png.js

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+const fs = require('fs')
+const PNG = require('pngjs').PNG
+const Utils = require('./utils')
+
+exports.render = function render (qrData, options) {
+  const opts = Utils.getOptions(options)
+  const pngOpts = opts.rendererOpts
+  const size = Utils.getImageWidth(qrData.modules.size, opts)
+
+  pngOpts.width = size
+  pngOpts.height = size
+
+  const pngImage = new PNG(pngOpts)
+  Utils.qrToImageData(pngImage.data, qrData, opts)
+
+  return pngImage
+}
+
+exports.renderToDataURL = function renderToDataURL (qrData, options, cb) {
+  if (typeof cb === 'undefined') {
+    cb = options
+    options = undefined
+  }
+
+  exports.renderToBuffer(qrData, options, function (err, output) {
+    if (err) cb(err)
+    let url = 'data:image/png;base64,'
+    url += output.toString('base64')
+    cb(null, url)
+  })
+}
+
+exports.renderToBuffer = function renderToBuffer (qrData, options, cb) {
+  if (typeof cb === 'undefined') {
+    cb = options
+    options = undefined
+  }
+
+  const png = exports.render(qrData, options)
+  const buffer = []
+
+  png.on('error', cb)
+
+  png.on('data', function (data) {
+    buffer.push(data)
+  })
+
+  png.on('end', function () {
+    cb(null, Buffer.concat(buffer))
+  })
+
+  png.pack()
+}
+
+exports.renderToFile = function renderToFile (path, qrData, options, cb) {
+  if (typeof cb === 'undefined') {
+    cb = options
+    options = undefined
+  }
+
+  let called = false
+  const done = (...args) => {
+    if (called) return
+    called = true
+    cb.apply(null, args)
+  }
+  const stream = fs.createWriteStream(path)
+
+  stream.on('error', done)
+  stream.on('close', done)
+
+  exports.renderToFileStream(stream, qrData, options)
+}
+
+exports.renderToFileStream = function renderToFileStream (stream, qrData, options) {
+  const png = exports.render(qrData, options)
+  png.pack().pipe(stream)
+}