Add support for playback in Electron apps

[cheap-glitch]

Currently, when trying to create an AlphaSynthWebWorkerApi instance in the renderer process of an Electron app, an error is thrown (Workers not yet supported in Node.js).

But it should be possible to run the alphaSynth APIs in an Electron app, since it's basically a Chromium browser embedded in a desktop app. So this should be as simple as updating the detection logic to include this case, and check it with something like:

typeof window !== 'undefined' && typeof window.process === 'object' && window.process.type === 'renderer'

(source)

FYI, my use case is making an alphaTab plugin for Obsidian. I've tried running the above snippet in the console and it seems the detection logic is working. I can also see the Worker and AudioContext objects are available, so alphaSynth should work out-of-the-box once the detection logic is updated.

[Danielku15]

In electron you have two parts: A node.js backend and a Chromium Frontend. The Node.js backend has no support for Web Audio. For now you likely need to use alphaTab both on the "backend" and "frontend" and communicate through channels.

When using AlphaTabApi there is one main abstraction for integrating with the underlying platform: The IUiFacade and related components.

The IUIFacade takes care of integrating the the User Interface aspects like passing rendered images/SVGs to the UI for display, listening for user inputs, creating background workers, synth outputs etc.. The BrowserUiFacade does this using the DOM and Browser APIs and is not compatible with a node environment.

Likely you are not using AlphaTabApi as the BrowserUiFacade would report an error early:

alphaTab/src/platform/javascript/BrowserUiFacade.ts

Lines 112 to 117 in af692f2

	if (Environment.webPlatform !== WebPlatform.Browser && Environment.webPlatform !== WebPlatform.BrowserModule) {
	throw new AlphaTabError(
	AlphaTabErrorType.General,
	'Usage of AlphaTabApi is only possible in browser environments. For usage in node use the Low Level APIs'
	);
	}

I am not sure if there is a built-in way into Electron to use the Frontend APIs from the Node.js backend (e.g. simply doing a document.createElement()) on the currently loaded page. If that's the case we could reuse the BrowserUiFacade.

There is currently also no "NodeUiFacade" which could be used to run alphaTab (e.g. in a virtual/headless space which could be manually synchronized with an external UI).