Holding the shape in hair simulation

ABSTRACT

Hair simulation models are based on physics, but require additional controls to achieve certain looks or art directions. A common simulation control is to use hard or soft constraints on the kinematic points provided by the articulation of the scalp or explicit rigging of the hair [Kaur et al. 2018; Soares et al. 2012]. While following the rigged points adds explicit control during shot work, we want to author information during the setup phase to better follow the groomed shape automatically during simulation (Figure 1). We have found that there is no single approach that satisfies every artistic requirement, and have instead developed several practical force-and constraint-based techniques over the course of the making of Brave, Inside Out, The Good Dinosaur, Coco, Incredibles 2, and Toy Story 4. We have also discovered that kinematic constraints can sometimes be adversely affected by mesh deformation and discuss how to mitigate this effect for both articulated and simulated hair.

References

1. Hayley Iben, Mark Meyer, Lena Petrovic, Olivier Soares, John Anderson, and Andrew Witkin. 2013. Artistic Simulation of Curly Hair. In Proc. of the 12th ACM SIGGRAPH/Eurographics Symposium on Computer Animation. 63--71.
2. Avneet Kaur, Maryann Simmons, and Brian Whited. 2018. Hierarchical Controls for Art-directed Hair at Disney. In ACM SIGGRAPH 2018 Talks. 13:1--13:2.
3. Matthias Müller, Bruno Heidelberger, Matthias Teschner, and Markus Gross. 2005. Meshless Deformations Based on Shape Matching. ACM Trans. Graph. 24, 3 (July 2005), 471--478.
4. Olivier Soares, Samantha Raja, Rich Hurrey, and Hayley Iben. 2012. Curls Gone Wild: Hair Simulation in Brave. In ACM SIGGRAPH 2012 Talks. 22:1--22:1.
5. Christopher D. Twigg and Zoran Kačić-Alesić. 2011. Optimization for Sag-free Simulations. In Proceedings of the 2011 ACM SIGGRAPH/Eurographics Symposium on Computer Animation. 225--236.

Index Terms

• Computing methodologies

  • Computer graphics

    • Animation

      • Physical simulation