User Guide

CHAPTER 7
252
Working with Masks and Transparency
When you use the Pan Behind tool to pan a layer behind a mask, the mask’s position
remains constant in the Composition window, but changes in the Layer window. The
masked layer’s Position values change in relation to the composition. As you pan past the
edges of the layer’s frame, the layer’s Mask Shape values also change. Using the Pan Behind
tool saves steps; without it, you would have to change the masked layer’s Position and
Mask Shape properties manually. You can animate a layer panning behind another
layer by setting keyframes for the masked layer’s Position and Mask Shape properties
(see “Setting keyframes” on page 163).
When you use the Pan Behind tool in the Composition window, After Effects
automatically makes two adjustments for you. In the Layer window, the
mask is moved in relation to its layer (top), while in the Composition win-
dow, the layer is moved in relation to the composition (bottom).
To move a mask:
1 Select the mask or masks you want to move. See “Selecting masks and control points”
on page 244 for information on selecting masks.
2 In the Composition window, drag the mask or masks to a new location. To constrain
the movement of the mask or masks to horizontal or vertical, press Shift after you start
dragging.
To pan a layer behind its mask:
1 Select the Pan Behind tool in the toolbox ( ).
UG.book Page 252 Wednesday, February 21, 2001 12:05 PM