Linearly interpolate between two offsets.
If either offset is null, this function interpolates from Offset.zero.
Source
static Offset lerp(Offset a, Offset b, double t) {
if (a == null && b == null)
return null;
if (a == null)
return b * t;
if (b == null)
return a * (1.0 - t);
return new Offset(lerpDouble(a.dx, b.dx, t), lerpDouble(a.dy, b.dy, t));
}