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Masks are used to create regions of transparency in layers. Although shapes work as layers
by themselves, masks must be assigned to a layer to have an effect. For example, if you
have a picture in which you want to isolate the foreground subject, you can create a mask
to cut out the background.
Original layer
Mask Masked layer
You can animate shapes, masks, and paint strokes using behaviors and keyframes. Shapes
also have their own special category of behaviors. What’s more, you can animate the
control points used to create each shape or mask in your project. This allows you to
animate the actual form of each shape, in addition to the shape’s basic position, rotation,
and scale parameters.
Shape and Mask Drawing Tools
Shapes and masks (and paint strokes) are made with splines, and they’re created and
edited using similar tools. This section covers the two spline-drawing methods available
in Motion: Bezier splines and B-Splines. You can use Bezier shapes and B-Spline shapes
interchangeably for any task. The default shape type is Bezier.
1114 Chapter 20 Using Shapes, Masks, and Paint Strokes