Adobe AFTER EFFECTS 5.5 Help Manual page 397

Adobe After Effects Help
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(5.5) Expressions
Using Expression Controls
In After Effects 5.5, six new effects reside in the effects category Expression Controls. They
do not actually affect the footage you apply them to; instead, they provide controls to
which you can refer in any expression. A single control affects several properties at once.
You apply these effects to a null layer, and name the layer and effect to clarify their
purpose. For example, you can name the null layer "Controls," apply a slider effect to it, and
name the effect "Springiness." You can then refer to the layer and effect in an expression
on another layer as, for example:
spring = this_comp.layer("Controls").param("Springiness");
Expression Controls consist of the following:
Slider Control Contains a slider with a default value range of 0–100. To change the slider
range, right-click (Windows) or Control-click (Mac OS) the underlined slider value and
choose Edit Value from the context menu. Type the new values in the Slider Range text
box.
Angle Control Contains an angle adjustment control.
Checkbox Control Contains a single checkbox.
Color Control Contains a color swatch control and an eyedropper.
Point Control Contains an effect point control.
Layer Control Contains a layer menu that lists all of the layers in the active composition.
Creating an expression for a single property
When you write an expression in After Effects 5.5, you do not need to specify the property
on which the expression is written. The default object for the expression is now the
property on which the expression is written, followed by the layer containing the
expression. This shortens the expression. For example, a wiggle expression written on a
layer's Position property in After Effects 5.5 may merely read as follows:
wiggle(5,10)
In After Effects 5.0, by contrast, the same expression reads as follows:
position.wiggle(5,10);
You must still specify the layer and property when retrieving them from outside the layer
and property that the expression is written on—for example:
this_comp.layer("OtherLayer").position.wiggle(5, 10);
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(5.5) Expressions
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