opl.js
Javascript wrapper: Copyright 2018 Adam Nielsen <malvineous@shikadi.net>
OPL emulator: Copyright 2002-2015 The DOSBox Team
This is a Javascript wrapper around the OPL3 emulator included in DOSBox. It allows OPL-compatible FM synthesis from within Javascript code, running in Node or in the browser.
The emulator is written in C++ and compiled to Javascript WebAssembly with Emscripten. A small wrapper is provided to simplify the interface between the C++ code and the Javascript code.
Example code is provided, both for the Node environment (with require()) and
for the browser (using <script/>).
Installation
npm install @malvineous/opl
Use
const OPL = require('@malvineous/opl');
OPL.create().then(opl => {
opl.write(0xBD, 0x20);
const samples = opl.generate(512);
// samples now contains 512 16-bit stereo samples as a Uint8Array
});
Examples
In the examples/ folder there are some short demonstrations showing how to
interface with the OPL emulator.
The web example may not work if loading the HTML file directly, as some browsers
do not like loading WebAssembly files from file:// URLs. To run this example,
you can either upload it somewhere or use Node to run serve-demo-web.js which
will use ExpressJS to host the necessary files. You may need to run
npm install --dev to get ExpressJS installed first.
Limitations
The library is only focused on generating the audio. It does not feature any sort of playback or audio mixing mechanism, as this is likely to be very different for different projects. You will need to include another library in your project if you wish to play the generated audio. The web example shows how to use WebAudio for playback in the browser, and the Node example shows how to save the generated audio to a .wav file instead.
8-bit and floating point audio formats are not supported. You can still use these formats, but you'll need to convert the signed 16-bit samples into these formats yourself. The WebAudio sample code shows conversion to floating point.
Contributing
When you install the release with npm the WebAssembly binary is included.
This is not part of the git repository, so if you clone the repo you will need
to install emscripten in order to compile the C++ code into Javascript.
Once emscripten is installed, run:
npm run build
This will compile the C++ code in src/ and put the compiled files into lib/.