lerp method

BorderRadiusGeometry lerp (BorderRadiusGeometry a, BorderRadiusGeometry b, double t)

Linearly interpolate between two BorderRadiusGeometry objects.

If either is null, this function interpolates from BorderRadius.zero, and the result is an object of the same type as the non-null argument. (If both are null, this returns null.)

If lerp is applied to two objects of the same type (BorderRadius or BorderRadiusDirectional), an object of that type will be returned (though this is not reflected in the type system). Otherwise, an object representing a combination of both is returned. That object can be turned into a concrete BorderRadius using resolve.

The t argument represents position on the timeline, with 0.0 meaning that the interpolation has not started, returning a (or something equivalent to a), 1.0 meaning that the interpolation has finished, returning b (or something equivalent to b), and values in between meaning that the interpolation is at the relevant point on the timeline between a and b. The interpolation can be extrapolated beyond 0.0 and 1.0, so negative values and values greater than 1.0 are valid (and can easily be generated by curves such as Curves.elasticInOut).

Values for t are usually obtained from an Animation<double>, such as an AnimationController.

Implementation 

static BorderRadiusGeometry lerp(BorderRadiusGeometry a, BorderRadiusGeometry b, double t) {
  assert(t != null);
  if (a == null && b == null)
    return null;
  a ??= BorderRadius.zero;
  b ??= BorderRadius.zero;
  return a.add((b.subtract(a)) * t);
}