User Guide

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ADOBE AFTER EFFECTS 5.0
User Guide
Determining which values are used in an expression
Different properties in After Effects have different value dimensions (1D, 2D, 3D, or 4D)
depending on the number of value parameters they have. In the expression language,
property values are either single values (numbers) or arrays (see “Numbers and arrays” on
page 320). Arrays, such as position values, are always enclosed in square brackets and
separated by commas; a single value, such as an opacity value, does not use brackets.
Following are examples of different property-value dimensions:
• 1D values: Rotation ° and Opacity %
• 2D values: Scale [x=width, y=height], Position [x, y], and Anchor Point [x, y]
• 3D values: Scale [width, height, depth], Position [x, y, z], and Anchor Point [x, y, z]
• 4D values: Color [red, green, blue, alpha]
To learn how to select a specific value in a vector or array, such as Position’s y value, see
“Accessing specific values in a vector or array” on page 321.
An example of using the pick whip
The following example shows how to use the pick whip to simulate dimming a light bulb
while rotating a dial.
Note: To learn what the text in an expression means, see “Understanding the expression
language” on page 317.
Linking opacity to rotation:
1 Start with a composition containing two solids: make layer 1 a circle named Light and
layer 2 a rectangle named Dial.
2 Create keyframes to animate the rotation of Dial.
3 Select the Opacity property for Light and choose Animation > Add Expression. A
default expression appears under the property.
4 Click the pick whip ( ) next to the Opacity expression and drag it to the Rotation
property for Dial. After Effects automatically fills in the following expression:
this_comp.layer("Dial").rotation
5 Press Enter on the numeric keypad or click outside of the expression to activate it.
UG.book Page 313 Wednesday, February 21, 2001 12:05 PM