Adobe AFTER EFFECTS CS3 PROFESSIONAL User Manual page 550

AFTER EFFECTS CS3 544
User Guide
A
B C D E
Expression interface in the Timeline panel in layer bar mode
A. Enable Expression switch B. Show Post-Expression Graph button C. Pick whip D. Expression Language menu E. Expression field
While you are editing an expression, previews of all sorts are suspended; a red bar appears at the bottom of panels
that are waiting for you to exit text-editing mode.
The values for a property that contains an expression appear in red or pink type.
Animation presets can include expressions, or even consist entirely of an expression. Animation presets that use
expressions instead of keyframes are sometimes called behaviors.
After you add an expression to a property, you can continue to add or edit keyframes for the property. An expression
can take the value of a property as determined by its keyframes and use that as input to generate new, modified
values. For example, the following expression on a layer's Position property preserves the layer's keyframed motion
and causes it to wiggle a little:
transform.position.wiggle(10, 10)
Note: Using the
expression is often much faster and easier than using the Wiggler.
wiggle
If an expression cannot be processed, After Effects displays a message explaining the error and automatically disables
the expression. A yellow warning icon appears next to the expression; click the warning icon to view the error
message again.
Some expressions rely on the names of layers or properties in your project; if you change the name of a layer or
property that is involved in an expression, After Effects will attempt to update the expression to use the new name.
However, in some complex cases, After Effects will be unable to automatically update the expression, in which case
the expression may produce an error message, and you must update the expression yourself.
Important: If you are running After Effects in a language other than the one for which an expression was written, or if
you have changed the names of items (such as layers, effects, or other property groups), then the expression may not work
until you modify the expression to use the new names or the strings that match the language in which you are running
After Effects. Because the examples in this document were created for the default state of After Effects running in English,
some examples in this document will not work without such modification.
Precomposing multiple layers will also cause expressions that refer to one of the layers' properties to produce an
error, requiring you to update these expressions to refer to the layer within the new composition. (See "About nesting
and precomposing" on page 117.)
Note: The arguments for some After Effects effects have changed from those in previous versions. If you have existing
expressions that use argument index references rather than argument names, you may need to update the expressions to
use argument names.