User Guide

253
ADOBE AFTER EFFECTS 5.0
User Guide
2 Click inside the mask area in the Composition window and drag the layer to a new
position.
Specifying one mask as the target for animation
As soon as you draw the first point on your first mask for a layer, the Layer window displays
a Target pop-up menu, which you use to specify a mask as the target for all new mask shapes.
When you create a new mask shape while a mask is selected in the Target pop-up menu,
the targeted mask is replaced by the new shape. You can change this behavior by selecting
None from the pop-up menu so that any new mask shape you create in the Layer window
creates a new mask instead of replacing an existing mask. You can also lock a mask to
prevent changes to it. See “Locking a mask” on page 259.
To specify a mask as the target of all new shapes:
In the Layer window, select the mask name from the Target pop-up menu.
To specify no mask as a target for changes:
In the Layer window, select None from the Target pop-up menu.
Animating a mask
You can change all of a layer’s Mask property values—Mask Shape, Mask Feather, Mask
Opacity, or Mask Expansion—over time by using keyframes (see “Understanding
keyframes” on page 160).
To animate a mask shape, After Effects designates the topmost control point at the initial
keyframe as the first vertex and “numbers” each successive control point in ascending
order from the first vertex. After Effects then assigns the same numbers to the corre-
sponding control points at all successive keyframes. After Effects interpolates the
movement of each control point from its initial position at one keyframe to the position
of the correspondingly numbered control point at the next keyframe. At any time during
an animation, you can designate another control point as the first vertex; this causes After
Effects to renumber the control points of the shape you assigned a new first vertex, and the
mask animates differently as After Effects now maps the new vertex numbers to the corre-
sponding “old” vertex numbers still saved at successive keyframes.
UG.book Page 253 Wednesday, February 21, 2001 12:05 PM