Similar to the bending calculation, we create a smoothed representation of the hair using the function described in Section 2.1. We precompute the representation of the original core of the curl from the rest points, , where is the smoothing amount for core springs (see Figure 10 left). The resulting piecewise linear curve represents the direction of the center of the curl, giving a more natural representation to control its longitudinal stretch, as illustrated by Figure 6.