electron/atom/browser/lib/desktop-capturer.coffee

ipc = require 'ipc'

# The browser module manages all desktop-capturer moduels in renderer process.
desktopCapturer = process.atomBinding('desktop_capturer').desktopCapturer

isOptionsEqual = (opt1, opt2) ->
  return JSON.stringify opt1 is JSON.stringify opt2

# A queue for holding all requests from renderer process.
requestsQueue = []

ipc.on 'ATOM_BROWSER_DESKTOP_CAPTURER_GET_SOURCES', (event, options) ->
  request = { options: options, webContents: event.sender }
  desktopCapturer.startHandling options if requestsQueue.length is 0
  requestsQueue.push request
  # If the WebContents is destroyed before receiving result, just remove the
  # reference from requestsQueue to make the module not send the result to it.
  event.sender.once 'destroyed', () ->
    request.webContents = null

desktopCapturer.emit = (event_name, event, sources) ->
  # Receiving sources result from main process, now send them back to renderer.
  handledRequest = requestsQueue.shift 0
  result = ({ id: source.id, name: source.name, thumbnail: source.thumbnail.toDataUrl() } for source in sources)
  handledRequest.webContents?.send 'ATOM_RENDERER_DESKTOP_CAPTURER_RESULT', result

  # Check the queue to see whether there is other same request. If has, handle
  # it for reducing redunplicated `desktopCaptuer.startHandling` calls.
  unhandledRequestsQueue = []
  for request in requestsQueue
    if isOptionsEqual handledRequest.options, request.options
      request.webContents?.send 'ATOM_RENDERER_DESKTOP_CAPTURER_RESULT', result
    else
      unhandledRequestsQueue.push request
  requestsQueue = unhandledRequestsQueue
  # If the requestsQueue is not empty, start a new request handling.
  if requestsQueue.length > 0
    desktopCapturer.startHandling requestsQueue[0].options