DEV Community


#30daysofelm Day 27: Using WebSockets+ports to control TouchDesigner

kristianpedersen profile image Kristian Pedersen ・5 min read

This is day 27 of my 30 day Elm challenge

Today we're sending data back and forth between JavaScript and TouchDesigner, using web sockets and ports! We'll compile Main.elm to main.js, and add a few additional lines of JavaScript in index.html.

TouchDesigner might be the coolest programming environment out there. It's like having a mix of After Effects, basic 3D software, Python, and have all changes being reflected instantly.

Here's what today's project looks like:

Screenshot of browser and TouchDesigner

  • The top row is a 1x1 grayscale noise texture (0-1). We then get its red channel r and convert it to a number. Any value changes trigger the code inside chopexec1.
  • The other important part here are the two webserver nodes. The bottom one has Python code in it.
  • constant1 receives our Elm app's slider value! lag1 applies smoothing to it, which is very useful for inputs like mouse movements, or sensor data from an Arduino.

The slider value is one step behind in TD, but it's good enough for me!

If you want to learn TouchDesigner, I highly recommend going through Bileam Tschepe's fantastic beginner videos on YouTube.

A lot of the TouchDesigner setup today is taken from this tutorial:

I'm still a TouchDesigner beginner, so if you have any improvement suggestions, I would be very happy to hear those!

1. Main.elm

Today's Elm program is a simpler version of the Ports example in the guide.

There's some stuff in the code I wouldn't have remembered by heart, so I might have to revisit it later on. I find it fairly easy to read though, so I'm not worried:

port module Main exposing (..)

import Browser
import Html exposing (..)
import Html.Attributes exposing (..)
import Html.Events exposing (..)


main : Program () Model Msg
main =
        { init = init
        , view = view
        , update = update
        , subscriptions = subscriptions


port sendMessage : String -> Cmd msg

port messageReceiver : (String -> msg) -> Sub msg


type alias Model =
    { sliderValue : String
    , noiseValueFromTD : String

init : () -> ( Model, Cmd Msg )
init flags =
    ( { sliderValue = "50", noiseValueFromTD = "" }
    , Cmd.none


type Msg
    = ReceivedNoise String
    | NewSliderValue String

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of
        ReceivedNoise noiseValue ->
            ( { model | noiseValueFromTD = noiseValue }, Cmd.none )

        NewSliderValue v ->
            ( { model | sliderValue = v }, sendMessage model.sliderValue )

subscriptions : Model -> Sub Msg
subscriptions _ =
    messageReceiver ReceivedNoise


view : Model -> Html Msg
view model =
    div []
        [ p [] [ text <| "From TouchDesigner: " ++ model.noiseValueFromTD ]
        , input [ type_ "range", onInput NewSliderValue, Html.Attributes.min "0", Html.Attributes.max "100" ] []
        , p [] [ text <| "Slider value is " ++ model.sliderValue ]
Enter fullscreen mode Exit fullscreen mode

2. index.html / Compiling Main.elm with live reload

Basically, Main.elm will be compiled to main.js, which is referenced inside index.html.

Some of the HTML is copied from the Ports guide, and some of it is taken from the NODE Institute tutorial.

In the project root, I set up two terminals:

  1. nodemon --exec elm make --output=main.js, which re-compiles the Elm file when I hit CMD+S.
  2. live-server - reload browser on file change

If you don't have nodemon or live-server, get Node.js and run npm install -g nodemon live-server.

At first I tried running elm-live src/Main.elm, which is usually great for other Elm projects, but it overwrote my index.html file.

One important thing I've changed here is the WebSocket URL, which in our case is now ws://localhost:9980:


    <meta charset="UTF-8">
    <title>Elm + Websockets</title>
    <script type="text/javascript" src="main.js"></script>

    <div id="myapp"></div>

<script type="text/javascript">
    const app = Elm.Main.init({
        node: document.getElementById('myapp')

    const socket = new WebSocket('ws://localhost:9980');

    app.ports.sendMessage.subscribe(function sendToTD (message) {

    socket.addEventListener("message", function receiveFromTD (event) {

Enter fullscreen mode Exit fullscreen mode

The app constant is just standard boilerplate. app.ports.sendMessage.subscribe is quite a mouthful, which is why I named the function sendToTD.

Currently, we're just sending one value. I guess if we wanted to be specific, we would have to set up Elm to send something like this: { op = "constant1", value = sliderValue }.

Now we have everything we need in the browser - let's head over to TouchDesigner!

3. Brief explanation of TouchDesigner data types (CHOP/DAT/TOP)

TouchDesigner is a node-based programming tool for Windows and MacOS, which feels like a realtime version of After Effects + Python, with some 3D capabilities.

Only boxes of the same data type can be connected, although they can be converted.

There are a couple of other data types in TD, but these are the ones I'll mention today:

  • CHOP (Channel Operators): Numbers
  • DAT (Data operators): Strings/tables/code/text
  • TOP (Texture operators): Image data (computed on the GPU)

These all have separate menus, which are accessed by double-clicking anywhere, and hitting Tab to cycle between the different menus.

4. TouchDesigner server

Add a Web Server DAT, and set its active status to on. Hit p if its parameters are hidden.

This will set up a web socket server on localhost:9980.

Expand Web Server by pressing the pink arrow on its bottom right, and edit the code by hitting CTRL+E. A lot of this code is not needed, so I replaced it with a simplified version of the Node Academy tutorial code:

# This code goes in webserver1_callbacks

def onHTTPRequest(webServerDAT, request, response):
    target_operator = op(request['uri'])

    if target_operator.isDAT:
        response['data'] = target_operator.text
    if 'data' in response:
        response['statusCode'] = 200  # OK
        response['statusReason'] = 'OK'

    return response

# Slider value from Elm comes in here (gets converted from String to Int automatically - yikes! :D)
def onWebSocketReceiveText(webServerDAT, client, data):
    op('constant1').par.value0 = data

def onWebSocketOpen(webServerDAT, client, uri):
    op('table1').appendRow(client) # Adds connected address to our list

def onWebSocketClose(webServerDAT, client):
Enter fullscreen mode Exit fullscreen mode

For this code to work, we need a Constant CHOP with name "constant1", and a Table DAT with name "table1". Both of these names are automatic when you create a node.

We can now receive web socket messages from the browser, but how about sending messages?

5. Sending data from TouchDesign on value change

To send continuous data, we can use a CHOP Execute DAT.

Make sure Value Change is set to On, enter the name of the CHOP you want to toggle data sending (topto1 in my case), and add this code:

def onValueChange(channel, sampleIndex, val, prev):
    data = op("topto1")[0]
    client = op('table1')[1, 0].val
    op('webserver1').webSocketSendText(client, data)
Enter fullscreen mode Exit fullscreen mode

That's pretty much it, as far as I can see. You can actually also get images from TouchDesigner into the browser, but given the data amount, I guess still images are the best choice for this.

Very cool! :D

Discussion (0)

Editor guide