This paper discusses a system developed by Edwin Catmull to generate
movies of computer animated objects.  Catmull's purpose is to develop
a system that allows for concurrent actions of a
hierarchically-structured object, such as a hand.  It is necessary to
have a system that can handle concurrent movements/animation since
"typical programming languages are much too sequential for specifying
easily the kinds of simultaneous and overlapping action we expect to
see in a movie."  Catmull's solution is a new language called MOP,
which takes movement instruction input with the frame period in which
the action/movement is meant to be performed.  A separate routine then
interprets these instructions in the order of the frame period and
outputs a set of instructions that will yield the desired movement of
the object (e.g. a hand).  Solving the problem of generating a movie
requires a movie language with control over the context of frames, the
creation and manipulation of shapes and relations, how motion occurs,
avoiding undesirable actions, creating routines of motion, and a
naturalness in describing action.  Catmull uses the hidden surface
algorithm developed by Gary Watkins and the smooth shading method by
Henri Gouraud to properly display the objects.