Apple Motion 4 - Manual (Page 1222)

Root-Level Behavior
At the root level of the project, 2D groups behave differently than when they are nested
inside 3D groups. (For more information about root-level groups, see
Relative Coordinates .)
2D groups at the root level are locked to the camera, even if the camera is animated. 2D
groups at the top of the Layers tab are always rendered in the foreground, and 2D groups
at the bottom of the Layers tab are always rendered in the background. Adjacent root-level
3D groups can intersect based on depth order.
Layers tab Result in Canvas
In the example above, the two gray balls in the 2D Foreground layer are always composited
on top of the rest of the scene. The 2D Background layer is always composited beneath
the rest of the scene. Group A and Group B intersect because they are 3D groups, but
neither of them can intersect with either of the 2D root-level groups.
2D and 3D Group Interaction
While 2D and 3D groups share a lot of common properties, there are distinct differences
in how they and their children behave and interact with other objects in a project. 2D
and 3D groups can be parents or children of each other; there are no restrictions on
mixing group types.
Important: Some operations, as well as the application of certain filters or a mask, cause
a group to be rasterized. When a group is rasterized, it is converted into a bitmap image.
Rasterization affects 2D and 3D groups in different ways. For more information, see
Groups
and Rasterization .
Group Tab in the Inspector
In the Inspector, the Group tab appears when a group is the selected object. The Group
tab contains the Type parameter, a pop-up menu that allows you to switch a group
between 2D and 3D mode. A 2D group has different available parameters than a 3D
group.
1222 Chapter 18 3D Compositing