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

Linearly interpolates between two BorderRadius objects.

If either is null, this function interpolates from BorderRadius.zero.

Source 

static BorderRadius lerp(BorderRadius a, BorderRadius b, double t) {
  if (a == null && b == null)
    return null;
  return new BorderRadius.only(
    topLeft: Radius.lerp(a.topLeft, b.topLeft, t),
    topRight: Radius.lerp(a.topRight, b.topRight, t),
    bottomRight: Radius.lerp(a.bottomRight, b.bottomRight, t),
    bottomLeft: Radius.lerp(a.bottomLeft, b.bottomLeft, t)
  );
}