lerp method

BoxShadow lerp (BoxShadow a, BoxShadow b, double t)
override

Linearly interpolate between two box shadows.

If either box shadow is null, this function linearly interpolates from a a box shadow that matches the other box shadow in color but has a zero offset and a zero blurRadius.

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 BoxShadow lerp(BoxShadow a, BoxShadow b, double t) {
  assert(t != null);
  if (a == null && b == null)
    return null;
  if (a == null)
    return b.scale(t);
  if (b == null)
    return a.scale(1.0 - t);
  return BoxShadow(
    color: Color.lerp(a.color, b.color, t),
    offset: Offset.lerp(a.offset, b.offset, t),
    blurRadius: ui.lerpDouble(a.blurRadius, b.blurRadius, t),
    spreadRadius: ui.lerpDouble(a.spreadRadius, b.spreadRadius, t),
  );
}