1. override
Rect lerp(double t)

Returns the value this variable has at the given animation clock value.

Source 

@override
Rect lerp(double t) {
  if (t == 0.0)
    return begin;
  if (t == 1.0)
    return end;
  return new Rect.fromPoints(_beginArc.lerp(t), _endArc.lerp(t));
}