Animating masks

Animating a mask is a simple but dramatic effect. Any object can be used as a mask to reveal any other object. (See Making group masks.)

Note that if you are exporting to Macromedia Flash (SWF) format, the masking object should be a geometric object or a path shape that will export as a vector. For example, applying a double-burst gradient to a mask causes it to export as a bitmap, so it does not apply correctly to the underlying object.

Use the Preview Export Compression command to verify whether the mask will be a vector when exported.

To animate a mask:

1. To create the masking group, select both the object that is used as a mask and the object it reveals, and then choose Object > Group.

The text is used as a mask for the underlying bus image.
2. With this newly created group selected, choose Object > Top Object Is Mask.
3. In the Timeline window, expand the new Timeline object, "Masked Group of 2 objects."
4. Expand the mask object, and animate the mask as desired.

Animating the position of the masking object

To adjust the mask object in the Composition window without expanding the group, select it with the subgroup-selection tool .