Apple Motion 4 - Manual (Page 1184)

2 In the Layers tab, drag the shape object onto an emitter or replicator and pause, holding
down the mouse button.
A drop menu appears.
3 Choose Add Mask To Emitter or Add Mask to Replicator.
The shape is converted into a mask on the particle emitter or replicator.
Note: The 3D checkbox must be deselected in the Emitter or Replicator tab of the Inspector
for the drop menu to appear.
To convert a shape to a mask on text
1 In the Layers tab, select the text layer you want to mask.
2 In the Layout pane of the Text Inspector, ensure the Flatten checkbox is selected.
3 Use any of the shape tools to create a shape (or draw a paint stroke).
4 In the Layers tab, drag the shape object onto a text layer.
To convert a mask to a shape
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In the Layers tab, select a mask and do one of the following:
• Choose Object > Convert To Shape.
• Drag the mask between two objects in the Layers tab.
• Drag the mask onto the group layer and pause, holding down the mouse button. When
the drop menu appears, choose Move Shape To Group.
Manipulating Alpha Channels Using Filters
In addition to using shape and image masks to create transparency within layers, there
are also filters you can use to manipulate or even replace a layer’s alpha channel.
For example, all of the keying filters create transparency by generating an alpha channel
based on colors or luminance values in that layer. Keying filters are usually used on layers
that have no alpha channel information, and they add a new alpha channel to the layers
to which they’re applied. For more information on the use of the keying filters, see
Keying
Filters .
The process of improving a keying effect or of customizing an alpha channel created
using one or more shape or image masks may require the use of special filters. Although
you can apply any filter directly to a shape or image mask to modify that particular mask’s
effect, the filters described in this section modify a layer’s entire alpha channel directly,
including the sum total of all masks and other filters that have been applied to that layer.
1184 Chapter 17 Using Shapes, Masks, and Paint Strokes