Adobe After Effects CS3 Manual do Utilizador descarregar pdf (Página 564)

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101

AFTER EFFECTS CS3

User Guide

559

Generally, it is best to use the name of a layer, effect, or a mask instead of a number to avoid confusion and errors if

the layer, effect, or mask is moved, or if the arguments are changed during product updates and upgrades. When you

use a name, always enclose it in straight quotes. For example, the first expression below is easier to understand than

the second expression, and the first expression will continue to work even if you change the order of effects:

effect("Colorama").param("Get Phase From")

effect(1).param(2)

Expression time

Time within an expression is always in composition time (not layer time) and is measured in seconds. The default

time for any expression is the current composition time at which the expression is being evaluated. The following

expressions both use the default composition time and return the same values:

thisComp.layer(1).position

thisComp.layer(1).position.valueAtTime(time)

To use a relative time, add an incremental time value to the time argument. For example, to get the Position value 5

seconds before the current time, use the following expression:

thisComp.layer(1).position.valueAtTime(time-5)

Default time references to properties in nested compositions use the original default composition time, not

remapped time. However, if you use the

source function to retrieve a property, the remapped time is used.

For example, if the source of a layer in the parent composition is a nested composition, and in the parent composition

youhaveremappedtime,whenyouaccessthepositionvaluesofalayerinthenestedcompositionwiththefollowing

expression, the position values use the composition’s default time:

comp("nested composition").layer(1).position

However, if you access layer 1 using the source function, the position values use the remapped time:

thisComp.layer("nested composition").source.layer(1).position

Note: If you use a specific time in an expression, After Effects ignores the remapped time.

After Effects expression elements reference

Using the expression elements reference

Use the After Effects expression elements along with standard JavaScript elements to write your expressions. You can

use the Expression Language menu at any time to insert methods and attributes into an expression, and you can use

the pick whip at any time to insert properties.

If an argument description contains an equal sign (

=) and a value (such as t=time or width=.2), then the argument

uses the included default value if you don’t specify a different value.

Some argument descriptions include a number in square brackets—this number indicates the dimension of the

expected property or Array.

Some return-value descriptions include a number in square brackets—this number specifies the dimension of the

returned property or Array. If a specific dimension is not included, the dimension of the returned Array depends on

the dimension of the input.

• “Global objects” on page 560

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