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Low Level APIs

This guide explains how to use the low level APIs of alphaTab in case the full API object cannot be used or is not needed.

The full API object is usually linked directly to a UI via a IUiFacade. There exist various IUiFacade implementations for the different platforms like for Web, .net WPF and .net WinForms.

In scenarios where none of these UI platforms are used or if not even a UI exists, you will need to use the low level APIs of alphaTab to setup the individual steps manually. The following examples show the most typical scenarios that you will likely need when using alphaTab.

Loading Files via ScoreLoader​

One of the most common tasks is to load a Score object from a binary buffer, the AlphaTab.Importer.ScoreLoader class offers an easy mechanism to take a buffer, and try loading it with the available importers. Internally alphaTab has a list of ScoreImporter implementations for the different file formats which are tried one after another to parse the provided buffer into a Score object. If the buffer cannot be converted a AlphaTab.Importer.UnsupportedFormatError is thrown.

The LoadScoreFromBytes method accepts as first parameter the raw byte buffer and as second optional parameter a AlphaTab.Settings object which might control some aspects of the import sequence. 

const xhr = new XMLHttpRequest();
xhr.open('GET', 'MyFile.gp', true);
xhr.responseType = 'arraybuffer';
xhr.onload = () => {
    const data = new Uint8Array(xhr.response);
    const settings = new alphaTab.Settings();
    let score: Score = alphaTab.importer.ScoreLoader.loadScoreFromBytes(data, settings);
};
xhr.send();

Rendering Files via ScoreRenderer​

The AlphaTab.Rendering.ScoreRenderer is the main component which takes a Score and Settings as input, and then generates a rendered music sheet. Setting up a ScoreRenderer is fairly easy if you know the following basics:

  1. The ScoreRenderer needs to know the target width if you use a Top-To-Bottom Layout
  2. The music sheet is rendered in individual chunks which are provided via the events partialRenderFinished and renderFinished
  3. AlphaTab internally keeps the information about the rendered score when rendering with renderScore, afterwards optimized rendering with resizing can be done via resizeRender

The ScoreRenderer does not provide rendering in a background worker (aka. Thread) out of the box. This logic is part of the AlphaTabApi which wraps a ScoreRenderer into a worker.

// 1. Setup renderer
const score = /* Load score here */;
const settings = new alphaTab.Settings();
settings.core.engine = 'svg';
const renderer = new alphaTab.rendering.ScoreRenderer(settings);
renderer.width = 1200;

// 2. Listen to Events 
let svgChunks = [];
renderer.preRender.on(isResize => {
    svgChunks = []; // clear on new rendering
});
// since 1.2.3 we need to request
// rendering of each chunk layed out. 
// you can defer rendering based on your needs. 
renderer.partialLayoutFinished.on(r => {
    renderer.renderResult(r.id);
});
renderer.partialRenderFinished.on(r => {
    svgChunks.push({
        svg: r.renderResult, // svg string
        width: r.width,
        height: r.height
    });
});
renderer.renderFinished.on(r => {
    displayResult(svgChunks, r.totalWidth, r.totalHeight);
});

// 3. Fire off rendering
renderer.renderScore(score, [0]);

// 4. resize
renderer.width = 800;
renderer.resizeRender();

Generating Midi Files via MidiFileGenerator​

AlphaTab has components for translating a Score object into a MidiFile which can then be passed on to other components to write it to a file or feed it into a Midi Synthesis engine. The main classes related to midi generation are:

  1. The AlphaTab.Midi.MidiFileGenerator which contains all the logic for emitting the right midi events for a Score using an IMidiFileHandler
  2. The AlphaTab.Midi.AlphaSynthMidiFileHandler which fills a AlphaTab.Midi.MidiFile object with events.
  3. The AlphaTab.Midi.MidiFile representing a Sequence of Midi Events that can be passed on to AlphaSynth or be written into a file. 
const score = /* Load score here */;
const settings = new alphaTab.Settings();

// Setup generator and midi file handler
const midiFile = new alphaTab.midi.MidiFile();
const handler = new alphaTab.midi.AlphaSynthMidiFileHandler(midiFile, true /* For SMF1.0 export */);
const generator = new alphaTab.midi.MidiFileGenerator(score, settings, handler);

// start generation
generator.generate();

// use midi file
saveToFile(midiFile);

Playing Files via AlphaSynth​

A midi file as such is not very interesting, but it becomes interesting when you can play it. AlphaTab has a component named AlphaSynth which is a SoundFont2 based midi synthesizer. It can take a SoundFont2 file and a Midi File generated by alphaTab, and play it on the corresponding target platform via an IOutput implementation.

The following examples show how to use the main component AlphaSynth which is usually running within a worker or thread to ensure smooth playback. 

const midifile = /* Load score and convert it to midi here */;
const soundFont = /* Load SoundFont2 as Uint8Array here */;

// Setup player
const player = new alphaTab.synth.AlphaSynth(
    new AlphaSynthWebAudioOutput() // the output to use
);
player.loadSoundFont(soundFont);
player.loadMidiFile(midiFile);
player.play();

For the Web version of alphaTab provides an out-of-the-box implementation for operating alphaSynth within a WebWorker and playing the audio via Web Audio API on the main browser thread: alphaTab.synth.AlphaSynthWebWorkerApi. The API is the same as on the normal AlphaSynth object but it needs a bit more input on creation but then the rest works as above. 

const supportsAudioWorklets: boolean = window.isSecureContext && 'AudioWorkletNode' in window;

const player = new alphaTab.synth.AlphaSynthWebWorkerApi(
    // the output to be used on the main browser thread
    supportsAudioWorklets ? new alphaTab.synth.AlphaSynthAudioWorkletOutput() : new alphaTab.synth.AlphaSynthWebAudioOutput(),
    pathToAlphaSynthScriptFile, // this script will be used to launch the worker, must point to the main file containing alphaTab
    alphaTab.LogLevel.Info // the log level to use
);
player.loadSoundFont(soundFont);
player.loadMidiFile(midiFile);
player.play();

Serialize Data Model from/to JSON​

alphaTab can convert the data model (and also the settings object) from and to Map objects for further serialization via JSON or transmission over wire. The normal data model of alphaTab requires many references to be hooked up and also the right object instances to be created. This graph cannot be simply written to a JSON e.g. via JSON.stringify but requires the right logic to do so.

note

The serialized JSON/Map should not be used for persisting the data model to disk or databases for later loading. The format is not guaranteed to be compatible between different alphaTab versions and might change over time. This data structure can be used to transmit the data model between components using the same version of alphaTab like backends+frontends.

This logic can be accessed via the alphaTab.model.JsonConverter class. It provides 4 main operations for both Score and Settings objects:

  1. *ToJsObject - Convert a Score or Settings object into a Map structure for further serialization
  2. jsObjectTo* - Convert a Map structure back to a Score or Settings object.
  3. *ToJson - Convert a Score or Settings object into JSON encoded string (web only).
  4. jsonTo* - Convert a JSON encoded string back to a Score or Settings object (web only).

For the conversions back to Score objects a Settings object can/should be passed on.

const map = alphaTab.model.JsonConverter.scoreToJsObject(api.score);
const json = alphaTab.model.JsonConverter.scoreToJson(api.score);
const score = alphaTab.model.JsonConverter.jsObjectToScore(map, api.settings);
const json = alphaTab.model.JsonConverter.jsonToScore(json, api.settings);