Kasm Ableton WASM C++ (Max4Live + source code)

Manipulating live notes on-the-fly with C++/WebAssembly (WASM)

This is a tutorial only (i.e. not an exciting new plugin) detailing a working example of how to manipulate MIDI data and potentially DSP audio signals using more efficient C++ code in Ableton Live 12.2 w/ Max4Live using WebAssembly in the newly added V8 Javascript engine

!! NOTE: this project needs Ableton Live 12.2 (or later) and Max4Live as it utilises the new V8 engine, i.e. you'll need Live 12.2 Suite or Standard + Max4Live add-in !!

Features includes:

Passing inlet parameters from JS into to C++

C++ code calling Max4Live outlet function (C++ code plays chords offset by semitones pssed in from Max4Live)

Max console debug post() messages from inside C++ code

How does it work, what does "Kasm" do for me?

There are three primary layers working together to enable C++ execution within Max4Live/V8:

C++ Code Layer: Your MIDI/Audio DSP logic compiled as WebAssembly

JavaScript Bridge Layer: Handles WASM bytecode loading, setups parameter marshalling for Max4Live integration

Max4Live Layer: V8 JavaScript engine with an basic example .amxd device showing two way communication with C++

Kasm then provides the base64-encoded WASM binary parts and compiles this as a blob for integration:

Base64 Decoding: Custom atob() implementation for Max4Live

WASM Compilation: Direct compilation from that decoded binary

Function Export: Cahing mapped C++ functions available to JavaScript

getStringFromWasm: Convert WASM memory strings into JavaScript strings, for Max Window console debugging

The example contains a heap of code comments, whilst you can figure it out from this it helps if you already know a bit about what WebAssembly is, Javascript and how to compile C++ code

Building and updating it is easy:

npm install

npm run build

This updates kasm_WASM_cpp.js which then compiles the WASM, you simply copy and paste that into any 'v8' Max4Live object

The example .amxd demonstrates the C++ functions being called and outlet and debugging messages from C++ code itself

kasm_midi_note_offset has two inlets and has one outlet simply offset the played note

kasm_midi_note_octave_hit shows how to generate chords and triggering MIDI events by calling the outlet() function from inside C++ and also debugging your code into Max4Live console using post()