Creating and Editing Expression Controls using Scripts

[Brian Charles]

Assuming you want to control the y position using an expression.

Add 2 slider controls to the layer.

Name the first Frequency and the second Amplitude.

You can pick whip the values to the sliders or use the expression below.

Add this expression to the position property of the layer:

x = transform.position[0];
y = effect(“Amplitude”)(“Slider”)*Math.sine(effect(“Frequency”)(“Slider”)*time);
[x,y]

Now you can keyframe the sliders to control the amplitude and frequency.

[Rutger]

Thanks for the suggestion, but that is not what I meant. I want to use scripts to set this up automatically. In other words: I select a layer, run the script and After Effects generates the slider controls and ‘pick wips’ them automatically and enters the proper expressions. This way, I can use this effect over and over again, and set this up in seconds in any project regardsless of what I am working on.

Any other suggestions are welcome.

Rutger

[Dan Ebberts]

You have to build the text for the expression. Something like this:

var myEffect = myLayer.Effect.addProperty("ADBE Slider Control");
var myExpr = "amp = effect(1)("Slider");" + "\r" +
             "freq = effect(2)("Slider");" + "\r" +
             "x =    ... etc.           ;";

myLayer.property("position").expression = myExpr;

Sorry – I haven’t tested it but it should give you the idea.

Dan

[Rutger]

Thanks Dan,

It is working now, and I also was able to rename the sliders by using the

myLayer.effect(1).name = “Amplitude” command so that all the sliders are properly labeled and organized.

By the way, now that I have your attention, I read in the After Effects Scripting Guide that there is no method built in After Effects that can record a series of actions and convert them into script. Do you know of any 3rd party plugins that would do this? It would essentially be a ‘macro’ recorder, as you see for instance in Visual Basic for Excel. I think such tool could be very handy for more entry level users that want to take advantage of scripting. But it may simply not exist.

Thanks again,

Rutger

[Dan Ebberts]

I’m not aware of any such tool. Sorry.

Dan

[Nicholas Petersen]

I’m curious about editing expression controls, but more so how to change their name. Here’s where I’m stuck…

app.project.activeItem.layer(4).effect.addProperty(“Slider Control”);
app.project.activeItem.layer(4).effect.(“Slider Control”).name = “Raise/Lower Arm”;

I’ve been pawing through the scripting guide, but I have not been able to find anything about changing an expressions name. I tried this, thinking that it might work, and obviously it didn’t. I got the following error message:

“Function (predicate expression) cannot work with this class””

What do I need to do to change the name of an expression control?

Thanks!