Point<num> interpolate(Point<num> p1, Point<num> p2, num f)

Source 

static Point<num> interpolate(math.Point<num> p1, math.Point<num> p2, num f) =>
  new Point<num>(p2.x + (p1.x - p2.x) * f, p2.y + (p1.y - p2.y) * f);