Using Expression Controls effects

Use an Expression Controls effect to add a control that you can use to manipulate the values of one or many properties by linking the property to the control using expressions. A single control can affect several properties at once.

The names for the Expression Control effects indicate what type of property control they provide: Angle Control, Checkbox Control, Color Control, Layer Control, Point Control, Slider Control.

You apply Expression Controls effects to a layer in the same ways that you apply other effects, such as dragging the effect onto the layer from the Effects & Presets panel.

You can apply Expression Controls effects to any layer; however, it is useful to apply them to a null layer, which you can simply use as a controlling layer. You then add expressions to properties on other layers to take input from that control. For example, you can add the Slider Control effect to a null layer (Null 1), and then apply this expression to the Position properties of multiple layers:

  position+[0,10*(index-1)*thisComp.layer("Null 1").effect("Slider Control")("Slider")]

In this example, as you drag the slider, each layer with this expression moves. The layers with greater index numbers (layers toward the bottom in the Timeline panel) are shifted more than the layers with lower index numbers, at 10-pixel intervals. You can set keyframes for the slider on the null layer, and all of the other layers animate accordingly.

It is often useful to rename each instance of an Expression Control effect to indicate its use. For example, renaming an instance of the Color Control effect to sky color makes it easier to tell what the effect is controlling. You can rename each instance of an Expression Control effect just as you rename any other effect: select it in the Timeline panel or Effect Controls panel and press Enter on the main keyboard (Windows) or Return (Mac OS).

To modify the range of a control, right-click (Windows) or Control-click (Mac OS) the underlined property value for the control and choose Edit Value from the context menu.

Aharon Rabinowitz’s three-part “After Effects Expression Controls” series of video tutorials on the Creative COW website introduces the Expression Controls effects and shows some basic examples of their uses: www.adobe.com/go/learn_ae_cowaftereffects.

Harry Frank shows how to use an Expression Controls effect (the Slider Control effect) as part of his video tutorial about converting from RGB to HSL using expressions: www.adobe.com/go/learn_ae_harryrgb2hsl.