Apple Motion 4 - Manual (Page 1171)

Shape Type: This pop-up menu lets you change the type of control points that are used
to define the mask. For example, if you originally created a Bezier mask, you can choose
B-Spline from this menu to change how the mask is drawn. Changing the shape type
might dramatically change the mask’s form even though its control points remain fixed
at their original coordinates. There are three options:
• Linear: All of a mask’s control points are joined by hard angles, and the resulting mask
is a polygon. The control points of a Linear mask lie directly on its edge.
• Bezier: Control points can be a mix of Bezier curves and hard angles, creating any sort
of mask. The control points of a Bezier mask lie directly on its edge.
• B-Spline: Control points are all B-Spline points, with different degrees of curvature.
B-Spline control points lie outside the surface of the mask, but are connected by the
B-Spline frame.
Note: You can hide the B-Spline frame by turning off Lines in the View pop-up menu
above the Canvas.
Mask Blend Mode: Determines how a mask interacts with the alpha channel of the layer
to which it’s applied. When a layer has multiple masks, each mask can have a different
Mask Blend Mode. When this happens, each mask adds to, or subtracts from, the layer’s
alpha channel according to the selected mode. The final alpha channel is the combined
result of all the masks that are applied. There are four choices in this pop-up menu:
• Add: This is the default selection for new masks. Each new mask adds to the existing
alpha channel. This is useful for adding back regions of an image that other masks are
cutting out. In the following example, both the rectangle and circle masks are creating
opaque regions.
1171 Chapter 17 Using Shapes, Masks, and Paint Strokes