Engines that Interpolate Values
111
Interpolator nodes are designed for linear, keyframed animation, that is, an interpolator
node defines a piecewise linear function, f(k), on the interval [-∞, ∞]. The piecewise linear
function is defined by n keys and n corresponding key values, f(k). The keys must be
monotonic and non-decreasing. An interpolator node evaluates f(k) given any value of k.
Interpolator Engine Terminology
Interpolator engines take one or more input values, perform a function on them, and
output a result. The relationship between the input and output values can be represented
by a graph where the x axis represents the input values and the y axis represents the
output values. Graphing the points (x
n
, y
n
) shows the shape of the engine’s function.
Interpolator engine methods use the following terminology:
• keys—input values represented on the x axis.
• key values—output values represented on the y axis.
• setFraction()—a method in interpolator engines that specifies a point on the y axis.
Figure 10-2 illustrates these terms.
Figure 10-2 Engine Terminology
x
y
Key values
Keys
setFraction()
