Precomping and Composition Nesting

Precomping and Composition Nesting

Precomping is often regarded as the major downside of
compositing in After Effects, because it obscures vital information
from view. Artists will let a composition become
completely unwieldy, with dozens of layers, rather than bite
the bullet and precomp. Yet precomping is an effective way
to solve problems and optimize a project, provided you
plan things out a little.
Just to get our terms straight, precomping is the action of
selecting a set of layers in a composition and assigning
them to a new subcomp. Closely related to this is composition
nesting, the action of placing one already created composition
inside of another.
Typically, you precomp by selecting the layers of a composition
that can and should be grouped together and choosing
Precompose from the Layer menu (keyboard shortcut
Ctrl+Shift+C/Cmd+Shift+C).
Two options are presented, the second one unavailable
if multiple layers are selected: to leave attributes (effects,
transforms, masks, paint, blending modes) in place or
transfer them into the new composition.

Why Precomp?

Precomping prevents a composition from containing too
many layers to be seen and managed in one Timeline, but
it also allows you to do the following:
. Reuse a set of elements and manage them from one
place.
. Fix render order problems, for example apply an effect
fi rst, then a mask.
. Organize your project; grouping elements that are
interrelated is a good idea in a nodal application such
as Nuke or Shake too, because it infl uences how you
think about the composite.
. Consider an element or set of layers “done” (and even
prerender them as proxies, as discussed later in this
chapter).