Apple Motion 4 - Manual (Page 1066)

Masks, on the other hand, are used to create regions of transparency in layers. While
shapes work as objects by themselves, masks must be assigned to an object 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.
Object Mask Masked object
Like any other layers, shapes, masks, and paint strokes can be animated using behaviors
and keyframes. Shapes also have their own special category of behaviors. What’s more,
you can also 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 that are
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.
Bezier splines are good for drawing shapes for illustration. The controls used to manipulate
Bezier splines are similar to those found in many other drawing and compositing
applications, so they may already be familiar to you. Bezier controls lend themselves to
the creation of precise, detailed shapes. Tangent handles adjust the curvature of the
shape on either side of the control point, and this defines the surface of the shape.
Bezier control point
Tangent handles
1066 Chapter 17 Using Shapes, Masks, and Paint Strokes