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

Linearly interpolate between two EdgeInsets.

If either is null, this function interpolates from FractionalOffset.topLeft.

Source 

// TODO(abarth): Consider interpolating from [FractionalOffset.center] instead
// to remove upper-left bias.
static FractionalOffset lerp(FractionalOffset a, FractionalOffset b, double t) {
  if (a == null && b == null)
    return null;
  if (a == null)
    return new FractionalOffset(b.dx * t, b.dy * t);
  if (b == null)
    return new FractionalOffset(b.dx * (1.0 - t), b.dy * (1.0 - t));
  return new FractionalOffset(ui.lerpDouble(a.dx, b.dx, t), ui.lerpDouble(a.dy, b.dy, t));
}