TouchDesigner | Evaluate DAT Magic

Let’s say you’re an ambitions person, maybe too ambitious, and all of a sudden you have a control panel with 68 buttons that need to trigger various scenes, effects, and transitions. Let’s also say that your TouchDesigner network is  vast enough that you need (and I mean in a big way) a simple method for getting information about what’s active in your network. If you find yourself programming the media for a live theatrical event with these same kinds of concerns, the Evaluate DAT might just be the best friend that you didn’t know that you needed.

My example above might sound a little far fetched, so let’s instead look at a more concrete example. Let’s imagine that we have a digital puppet that we’d like to trigger to enter and exit with a button set to toggle. Just to make this more interesting, let’s say that you actually have three puppets and three visual effects that you’d like to all control with buttons from a single control panel. If all of your puppets and effects are all located in a similar place this might not be a huge hassle for you, if however, you’re building a complicated network it will soon become very important to be able to call the states of these buttons across your network.

Here’s my example set-up for us – a control panel that has all of our controls, a base component where we’re going to store the status of our buttons, and a scene where our puppet needs to make an entrance and an exit based on our button’s active state.

I’m going to assume that you’re already familiar with working with control panels in TouchDesigner, but if that’s not the case you can learn a little more here before you keep reading. Lets start by taking a look inside of our “trigger_ref” base component where we are going to store the status of our buttons to use other places in our network.

This should look pretty impressively boring at first glance. To really get a feel for what’s happening here, let’s take a closer took how how this is being driven by our control panel.

Alright, so here we can see that Puppet 1, 2, and 3 all act as Toggle switches, VFX 1 acts as a momentary trigger, and VFX2 and VFX3 both act as toggles. Before we start to look at why this is important, let’s first see how this is working.

To really make our Evaluate DAT sing we need to start by feeding a table with some instructions about what information we would like it to evaluate. In my case I’ve made a table with a name for the item that I’d like to call in one column, and the pathway to the operator and channel that’s being evaluated in the other column.

If we were to write these instructions in English they might read something like: “TouchDesigner, please watch operator ‘button0’ in ‘ctrl’ and tell me when it’s v1 changes, and give that the name ‘Puppet1’. It’s important note that the formatting and syntax of your request to the Evaluate DAT matters. In my case I needed to put the names in the first column in quotations. I also made sure to tell the evaluate DAT that I wanted an integer (you’ll notice that in front of the operator’s pathway I’ve int() to specify that I want an integer returned to me). Next in the Evaluate DAT I need to check a few settings in the operators parameters.

The most important parameter to take note of here is that I’ve told the Evaluate DAT that I’d like the output in Expressions. This ensures that my input table is being evaluated.

Okay, but why is this interesting / important / worth your attention? While it might be tempting to avoid an organization method like this, it means that when you’re working with a large control panel, or a large cue stack, that you can refer to a button by its name rather than by a complicated network pathway. Better yet, once you write the expression to call this value from our Evaluate DAT it becomes easy to copy and paste that expression and only need to change the name of the value that you’re calling. Let’s go back to our puppet example.

Here I have my video that I’d like to change with my puppet button. I’ve already set up my network with a few operators. First I have a constant CHOP, and a trigger CHOP. Next I have a Movie in TOP, a Level TOP, and a Null TOP. I’d like to use my trigger CHOP to change the opacity of my Movie.

To start let’s make sure that our constant CHOP is set up with a channel that we’ll name “Puppet1” .

Let’s also make sure that our trigger is set to have a sustain value of 1, and let’s make sure that we’re happy with how the trigger is going to fire and release. For now I’m only interested in making sure that my sustain is changed.

 Next we’re going to write a quick expression that will allow our level TOP to reference the trigger CHOP. In your level top we’re going to use the expression on the opacity Parameter on the Post page of Level TOP:

op( “trigger1” )[ “Puppet1” ]

Now we’re going to go back to our constant CHOP to see how this really makes our network programming fun. Here for the value of the Puppet1 channel we’re going to write the following expression:

op( “../trigger_ref/buttons” ) [ “Puppet1” , 1 ]

Now, let’s finally see what this means when we use this in conjunction with our control panel.

Great, so now we toggle the opacity of a video on and off with a button. What’s important here is that what if you suddenly decide that you want this action to happen with the Puppet 2 button instead? Now, rather than having to look up where your original button was, along with it’s reference you can instead just change the expression in the Constant CHOP to be:

op( “../trigger_ref/buttons” ) [ “Puppet2” , 1 ]

Right? We’ve changed all of those button values into a table that we can centrally reference by name. If you’re just getting started with TouchDesigner this might not seem like a huge revelation, but once you start to build more complicated networks the ability to call something by a name (maybe even a name that’s in your cue sheet) becomes hugely important.