sema-engine
v0.1.4
Published
Module containing Sema's signal engine and compiler for a live coding language ecosystem
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sema-engine
sema-engine is a Javascript library that provides a high-performance audio engine for modern Web applications, with an easy-to-use API. It was extracted from sema, an app developed with @chriskiefer and @thormagnusson, and refactored for the MIMICproject.com.
sema-engine builds upon the following components:
the Maximilian DSP C++ library – from which sema-engine consumes DSP objects, as a git submodule
the Web Audio API Audio Worklet – packs a bespoke Audio Worklet node (src/engine.js) and processor (maxi-processor), which loads Maximilian DSP objects and dynamic program specifications
the Nearley compiler – generates parsers from an EBNF grammar specification
The sema-engine library exposes ES and UMD modules (works on the browser, with modern native JS modules and older JS module formats—amd, cjs for nodejs applications—think electron!).
sema-engine uses Github Actions workflows for build automation and continuous integration. The development builds propagate source maps (.map files)—so you can have modern debugging features like using breakpoints in the context of the client application. The production build ships all formats optimised and minified.
Usage
The sema-engine is published in the Node Package Manager (NPM) registry. If you are developing a Web application in a modern environment, and using a bundler such as Webpack or Rollup, you can easily add sema-engine as a dependency,
npm install sema-engine
For an advanced use, check how sema-engine is integrated in Sema, a full-fledged application from which sema-engine was extracted.
You can use also use the sema-engine library modules in an a HTML file using inline <script>
tags (check the published example which is output by the development build).
<script type="module">
import {
Engine,
compile,
Learner,
getBlock
} from "./sema-engine.mjs";
</script>
Note the that the script tag for the main module sema-engine.mjs
has type = module
.
When initialising sema-engine, you need to pass the origin
URL which points to where package dependencies – e.g. maxi-processor.js and maximilian.wasmmodule.js (check the dist/
folder) – should be served from.
let engine,
analyser = 0,
dspCode,
learner
;
let origin = document.location.origin;
const $ = (elemId, callback) =>
document.getElementById(elemId).addEventListener("click", callback);
$("playButton", "click", () => {
engine = new Engine();
engine.init(origin);
engine.play();
})
Note that the engine will make its operations depend on the origin
URL for instance for loading audio samples, which should be pointed to using a relative path to the origin like so:
$("loadSamplesButton", "click", () => {
if(engine){
try{
engine.loadSample("909.wav", "/audio/909.wav");
engine.loadSample("909b.wav", "/audio/909b.wav");
engine.loadSample("909closed.wav", "/audio/909closed.wav");
engine.loadSample("909open.wav", "/audio/909closed.wav");
} catch (error) {
console.error("ERROR: Failed to compile and eval: ", error);
}
}
else throw new Error('ERROR: Engine not initialized. Press Start engine first.')
})
$("learnerButton", "click", async () => {
if(engine){
try{
learner = new Learner();
await engine.addLearner('l1', learner);
}catch(error){
console.error("ERROR: Error creating or initialising learner: ", r);
}
}
});
</script>
To compile the livecode, you need to do it against its grammar language specification, with the compile
function. Only then you can inject the resulting code in the engine and evaluate it.
For the JS code, we provide getBlock
, an utility function that pulls code from an editor block. Blocks in a Codemirror editor instance are delimited by ____
(3 or more underscores).
const evalLiveCode = () => {
if(engine){
try{
const { errors, dspCode } = compile( editorGrammar.getValue(), editorLivecode.getValue() );
if(dspCode){
console.info(editorLivecode.getValue());
engine.eval(dspCode);
}
} catch (err) {
console.error("ERROR: Failed to compile and eval: ", err);
}
}
else throw new Error('ERROR: Engine not initialized. Please press Start Engine first.')
}
const evalJs = async () => {
if(learner && editorJS){
const code = getBlock(editorJS);
learner.eval(code);
}
else throw new Error('ERROR: Learner not initialized. Please press Create Learner first.')
}
Prerequisites
The emscripten SDK is required, https://emscripten.org/docs/getting_started/downloads.html
Build
If you are cloning this library for the first time:
- Initialise the Maximilian submodule
git submodule update --init --recursive
- Install dependencies
npm i
- Build the Maximilian native JS and WebAssembly modules
make
- Build the sema-engine library into UMD and ES modules
npm run build
- Test the sema-engine library in a local example
npm run dev
To update submodule if there are any upgrades
git submodule update --remote --merge
Tests and Examples
The sema-engine library uses Mocha for unit and integration tests.
The development build outputs the example above, which you can use to learn and test out how to work with the engine.
Documentation
The sema-engine has small API surface that you can find more about on this project's wiki.
Contributing
Pull requests are welcome, please observe the Contributing guidelines.
Related Publications
Bernardo, F., Kiefer, C., Magnusson, T. (2020). A Signal Engine for a Live Code Language Ecosystem. Journal of Audio Engineering Society, Vol. 68, No. 1, October, DOI: https://doi.org/10.17743/jaes.2020.0016
Funding
This project has received funding from the UKRI/AHRC research grant MIMIC: Musically Intelligent Machines Interacting Creatively (Ref: AH/R002657/1)