Rendering compositions containing both 2D and 3D layers

If a composition contains both 2D and 3D layers, After Effects renders the 3D layers in independent, noninteractive groups that are separated by the 2D layers. For example, if the Timeline window contains (from top to bottom) two 3D layers, two 2D layers, and two 3D layers, After Effects renders the composition in the following order:

First

The bottom two 3D layers as a set, according to their spatial order in the Composition window.

Second

The 2D layers according to their Timeline window order, from bottom to top.

Third

The top two 3D layers as a set. These are rendered in a geometric space independent of the 3D layers at the bottom of the Timeline window.

Essentially, the 2D layers split the 3D space into separate universes. The result is that shadows cast by either set of 3D layers do not fall on the other set, and the two sets of 3D layers do not interact geometrically. The two sets of 3D layers do share cameras and lights because these two elements are global to the composition.