Effect: Advanced Interpolators - JavaFX Special Effects - page 98

Listing 5-7. PolynomialInterpolator.fx
public class PolynomialInterpolator extends SimpleInterpolator{
public var solveFor = 0 on replace{
solve();
}
public var coefficients:Number[] = [1.0, 1.0, 1.0] on replace{
solve();
}
init{
solve();
}
public function solve():Void{
//given a + b + c = 1, then c = 1 - b - c, or a = 1 - c - b
if (solveFor != -1){
var solvedValue = 1.0;
for (index in [0..(sizeof coefficients)-1]){
if (index != solveFor){
solvedValue -= coefficients[index];
}
}
coefficients[solveFor] = solvedValue;
}
}
public override function curve(fraction:Number):Number{
var power = fraction;
var total = 0.0;
for (coeff in coefficients){
total += coeff*power;
power *= fraction;
}
return total;
}
}
Instead of specifying a, b, c, and so on, the implementation above uses a Sequence called
coefficients to store an arbitrary number of terms. It should be pointed out that coefficients stores in
the sequence in the reverse order of the function in Listing 5-7. So, coefficients[0] is the least
significant term.
The variable solveFor is used to keep track of which coefficient must be solved for when one of the
others changes. This is an improvement over the previous versions, where the least significant
coefficient was always solved for.
The function solve is called every time the Sequence coefficients changes and once during init
time. The function solve calculates a value for one of the coefficients to make sure the function always
creates a curve that passes through the origin and the point 1,1.