transform method
Returns interpolated angles for the current position (t) on timeline.
Implementation
@override
double transform(double t) {
assert(t >= 0 && t <= 1, 'value must between 0.0 and 1.0');
if (t == 0.0) return interpolator.begin;
if (t == 1.0) return interpolator.end;
return lerp(t);
}