Interpolation-Based Animation - Computer Animation: Algorithms and Techniques - page 118

FIGURE 4.7
Sample Houdini dataflow network and the object it generates.
other nodes, and data are passed from node to node by arcs of the graphics that are interactively spec-
ified by the user. A node represents an operation to perform on the data being passed into the node, such
as an object description. A transformation node will operate on an object description passed into the
node and will produce a transformed object representation as output. Inputs to a node can also be used
to parameterize a transformation or a data generation technique and can be set interactively, set accord-
ing to an articulation variable, or set according to an arbitrary user-supplied procedure. This is a very
effective way to visually design and represent the dependencies among various computations, func-
tions, and values.
4.2.5 Actor-based animation languages
Actor-based languages are an object-oriented approach to animation in which an actor (encapsulated
model [ 24 ]) is a graphical object with its associated data and procedures, including geometric descrip-
tion, display attributes, and motion control. Reynolds [ 30 ] popularized the use of the term actor in ref-
erence to the encapsulated models he uses in his ASAS system.
The basic idea is that the data associated with a graphical object should not only specify its geom-
etry and display characteristics but also describe its motion. Thus the encapsulated model of a car
includes how the doors open, how the windows roll down, and, possibly, the internal workings of
the engine. Communication with the actor takes place by way of message passing; animating the object