User Guide

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ADOBE AFTER EFFECTS 5.0
User Guide
Creating a trail of images
This expression instructs a layer to be at the same position as the next higher layer in the
Timeline window, but delayed by a specified amount of time (in this case, .5 seconds). You
can set similar expressions for the other geometric properties. This expression requires
two or more layers.
To create a trail of images:
1 Start with two solids that are scaled to about 30%.
2 Create a motion path for the first layer.
3 Select the Position property for the second layer and choose Animation > Add
Expression.
4 Select the default expression text and type:
this_comp.layer(this_layer, -1).position.value_at_time(time - .5)
5 Duplicate the last layer five times.
6 Click outside the expression to activate it. All layers follow the same path, and each is
delayed .5 seconds from the previous.
Creating a bulge between two layers
Use an expression to synchronize the Bulge Center parameter of the Bulge effect in one
layer with the position of another layer. For example, move a magnifying glass over a layer
and make the contents under the magnifying glass bulge as the glass (or the underlying
layer) moves. This expression uses the “from_world” element, which makes the expression
work correctly regardless of whether you move the magnifying glass layer or the under-
lying layer. You can rotate or scale the underlying layer and the expression stays intact.
You can also use other effects, such as Ripple, with this expression.
To create a bulge between two layers:
1 Start with two layers. Make one layer a magnifying glass or similar object with a hole in
the middle and name it Magnifier.
2 Create a motion path for the magnifying glass layer.
3 Apply the Bulge effect to the other, underlying layer.
UG.book Page 323 Wednesday, February 21, 2001 12:05 PM