TouchDesigner | New Features | Bindings with Matthew Ragan

Hi folks, Elburz here. This week we have the pleasure of having Matthew Ragan guest post a great article he wrote on TouchDesigner’s new Binding feature here. Matthew Ragan is of course not an unfamiliar name for anyone in the TouchDesigner scene, but I highly recommend checking out his website and blog if you have here. Enjoy!

Spring time is lots of things – flowers, holidays, vigorous allergies, and the TouchDesigner Spring Update. For the second year running this is the time of year that features graduate from just being in experimental to being full fledged stable release features. Wowza.

This spring we’re seeing the a feature that’s flat out amazing, and likely a bit of a sleeper. Bindings. Elburz has a great shout out to bindings on a recent blog, and I wanted to take some time to dig in and step through an example of both why they’re important, the paradigm they’re built on, and why they matter.

So what are parameter bindings anyway? The Derivative wiki has a great segment describing bindings:

Bound parameters keep their values in sync and will respond to changes from either parameter. For each parameter that is a bind master, it will have one or more bind reference parameters.

The bind master holds the current value. It can have exports and expressions and generally works like any other parameter, but its value can be also changed indirectly by the bind references.

A bind reference holds the location of the bind master. A bind reference is in a fourth “Bind”Parameter Mode, and will show up as purple text in parameter dialogs. It can only be changed via its its bind master, its UI, and its val property.

Derivative Wiki article on Binding

Model View Controller – MVC

Errm. Okay, so what does that mean exactly? Bindings are based on an interface architecture paradigm called Model – View – Controller, or MVC. Wikipedia has a nice starter debrief on the idea for us, but it’s easy to understand if you’ve spent much time working in Touch either for live set, or for a client application. Let’s consider a live set to help us get our footing here. Suppose you have parameter that can be updated by multiple touch points both in your own UI and in the TD UI. We all know this game, as soon as you export a CHOP to a parameter, you can no longer change that parameter except through the exported CHOP.


So maybe instead of exporting from a single CHOP you instead write a bunch of scripts to handle this operation – only now you’re in a real pickle. Why? Well, because your script changes the parameter, but doesn’t update all of the UI elements that reflect the state of that parameter. So you write another script to update the UI. But now you’ve managed to save your project in a state where the UI and the parameters are not aligned. As soon as you change the UI everything is in sync – so you save over a few things, commit your changes, and now everything should be great. Until you need to load a saved preset state from disk. Now you’ve gotta write another set of scripts to do all of that updating, or hunker down for a more generalized solution – which probably means a code refactor. Who wanted to make some more sweet visuals anyway? There goes your night off. There goes your margin. Sigh.

The real world example of this is light switches. If you’ve ever lived in an apartment where multiple light switches control the same light / outlet, you understand this issue intimately. How do you know if the light is on or off? Only by looking at the light, because once the states of the light switches are out of phase they perform the opposite action.

The Model – View – Controller paradigm is a design architecture that’s intended to help resolve this issue. The MVC approach decouples the control of a UI element from the data it is manipulating. You could do this in touch before, you were just on the hook for doing all the set-up. This probably meant you had a master table or storage dictionary somewhere that was updated whenever a parameter was changed, that in turn would update all the other touch points. That’s a huge hassle, but it was the only way to solve this problem. It’s also the kind of silly thing you could really have a strangely strong opinion about – and consequently be convinced that your collaborators were doing it all wrong.

Enter Bindings

Okay, so as a refresher, Bindings are a new parameter mode – that’s the little multi-colored set of dots next to any parameter. This new mode is purple – one of the many colors of awesome. At the end of all of this, we’ll take a peek at the new widgets – and the UI redesign they offer, but to get started let’s build a use case for bindings so we can get a sense of what they’re good for.


We’re going to start with a good old fashioned slider. Why a slider?! Well, this is the kind of parameter we end up using all the time, and the fundamental nature of this UI piece should be foundational enough that if we can get a handle on this one, the jump to more abstract ideas should be a little easier.

Let’s get started by first adding a slider from the Op Create dialogue. We’re just going to add a run of the mill slider for now.

From here we’re going to customize our slider – let’s add a page called “Settings” and then a float custom parameter that we call “Slider” for now.

So far so good. The next step is where it’s gonna get a little weird, and where it’ll get different than before. From here, let’s dive into our slider. We’re going to delete our Panel CHOP, and add our own Constant CHOP.

Okay. Now here’s the wild part. On our new Constant CHOP we’ll use the new bindings parameter mode to write parent().par.Slider – that’s the reference to our newly created custom parameter.

If you’re not into that whole writing expressions exercise, you can also do this with a little drag-and-drop action:

Okay… so why is this interesting. Well, let’s see what happens when we move our new custom parameter, or move our Constant CHOP:

Slick. Okay. That’s fly. So if we update the our parameter or our CHOP both changes are reflected in the other operator. Now let’s make a few final changes so that when we interact with the sliders panel we update both of these values. We can do this with a Panel Execute DAT. Let’s add our DAT and modify the contents with the following:

def onValueChange(panelValue):
    parent().par.Slider = panelValue

We should now see that if we move the slider that our Slider parameter updates, and our Constant CHOP updates.

We’re very close now. All we need to do is to update the knob component in our slider. We need to change the expression there to be:


There we have it. Now we can change our custom parameter, our Constant CHOP, or the slider and all three stay in sync. MAGIC.


Early on I mentioned that we find this same behavior in Widgets. What exactly are widgets you ask – currently Widgets are rolling out as a huge overhaul to the TUIK interface building kit that was relatively ubiquitous in TouchDesigner networks. Widgets are more modern take on UI building, and offer significant advances to UI building approaches for Touch. There’s too much to cover about widgets here, but it’s worth pointing out that the same binding approach you see above is a fundamental element of the widget system. It allows for bidirectional control of both user interaction elements and parameters – the core principle we just explored. You can dig in and learn a little more about widgets by reading through the article on the Derivative Wiki.

Why Bind…

You might be looking at this and feeling like it’s outside of your wheelhouse, or your workflow. A reasonable reflection. Regardless, I’d encourage you to think about the times when you’ve wanted to both control from more than one location – the parameter itself, as well as some other control interface. If nothing else, give them a try to see where they might fit – if they’re no good for you, don’t use them… though I suspect you’ll find they have all sorts of exciting uses.

Happy Programming!

Elburz here again. I wanted to thank Matthew again for his time putting this together for us. I always love working with Matthew and we’re always trying to find new things we can try to do (like guest blost posts). I hope you enjoyed and don’t forget to check out Matthew’s website for more great content like this.

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