1. override
T evaluate(Animation<double> animation)

Returns the interpolated value for the current value of the given animation.

This method returns begin and end when the animation values are 0.0 or 1.0, respectively.

Source 

@override
T evaluate(Animation<double> animation) {
  final double t = animation.value;
  if (t == 0.0)
    return begin;
  if (t == 1.0)
    return end;
  return lerp(t);
}