I am trying to call some audio rendering code in K...

# webassembly

[Phil Burk]

I am trying to call some audio rendering code in Kotlin from a WebAudio AudioWorkletProcessor in JavaScript.
I tried this: https://kotlinlang.org/docs/wasm-js-interop.html#functions-with-the-jsexport-annotation

//import exports from "./module.mjs"
import exports from "./composeApp.js"
console.log("Kotlin random code is " + exports.renderKotlinAudio());

But I always get:
SyntaxError: Unexpected identifier 'exports'

I am using Kotlin/Compose multi-platform code. My Kotlin WASM code has:

@OptIn(ExperimentalJsExport::class)
@JsExport
fun renderKotlinAudio(): Float {
    return Random.nextFloat()
}

I spent a lot of time with Gemini giving me increasingly complex solutions that did not work.
Has anyone actually done this successfully?

[turansky]

AFAIK for AudioWorkletProcessor you should have separate JS file

[Phil Burk]

Yes, when I use AudioWorkletProcessor it is in a separate JS file.

But first I am just trying to do a minimal call from JavaScript into Kotlin.
Is it possible? Any examples?

[Phil Burk]

With Gemini's help, I got this to work. The composeApp had not loaded yet so all I got was a Promise.
I had to wait for the Promise to load.

const kotlinModulePromise = window.composeApp;
kotlinModulePromise.then(kotlinModule => {
        console.log("renderKotlinAudio returns " + kotlinModule.renderKotlinAudio);
        console.log("renderKotlinAudio returns " + kotlinModule.renderKotlinAudio);
    }).catch(e => {
        // It's good practice to catch potential loading errors
        console.error("Error loading Kotlin module:", e);
        document.getElementById('output').textContent = "Error loading the application module.";
    });

[turansky]

AudioWorkletProcessor on Kotlin/JS example you can find here.

[turansky]

1. Kotlin/JS do per-file compilation - provides you separate JS file
2. Kotlin/JS supports extending from external

[Phil Burk]

import web.audio.AudioWorkletModule !!!
What is this? Is there existing support for AudioWorkletProcessor in Kotlin?!
Is this something you wrote? I found this:

https://github.com/JetBrains/kotlin-wrappers/tree/master/kotlin-browser

I was able to call Kotlin from JavaScript. But I cannot get that to work yet from an AudioWorkletProcessor.

I have been working on this but there may be an easier way...
https://github.com/philburk/kc-audio-bridge/

[Phil Burk]

I cloned Seskar and loaded it in Android Studio. The README says it is a "Gradle plugin".
It contains a test that uses a Kotlin wrapper for the AudioWorkletProcessor.
The relationship is not clear. Is Seskar needed to use the Kotlin wrappers for audio?
This might be what I am looking for. But the docs are not clear.

[turansky]

Is Seskar needed to use the Kotlin wrappers for audio?

Yes, Seskar supports Kotlin Wrappers declarations only

[turansky]

Is there AudioWorkletProcessor in other declarations?

[Phil Burk]

OK. I now think that the restrictions on sharing data between the AudioWorkletProcessor and the Main thread are too severe. They would require significant changes to my Audio API to support generic message passing on all platforms. The advantage would be that I could support callbacks for WebAudio. But I can only do fake callbacks for Android AudioTrack and JavaSound. So I will stick with my blocking-write API. Thanks for your help.

[turansky]

Can it be suspend calls?

[Phil Burk]

Can it be suspend calls?

The blocking write() does not use the suspend keyword.

https://github.com/philburk/kc-audio-bridge/blob/main/composeApp/src/commonMain/kotlin/com/mobileer/audiobridge/AudioBridge.kt

[turansky]

Will it be AudioBuffer sync calls?