SCA 19: Eurographics/SIGGRAPH Symposium on Computer Animation

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https://diglib.eg.org/handle/10.2312/2632835

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Browsing SCA 19: Eurographics/SIGGRAPH Symposium on Computer Animation by Subject "Computing methodologies"

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    Fast Simulation of Deformable Characters with Articulated Skeletons in Projective Dynamics
    (ACM, 2019) Li, Jing; Liu, Tiantian; Kavan, Ladislav; Batty, Christopher and Huang, Jin
    We propose a fast and robust solver to simulate continuum-based deformable models with constraints, in particular, rigid-body and joint constraints useful for soft articulated characters. Our method embeds degrees of freedom of both articulated rigid bodies and deformable bodies in one unified optimization problem, thus coupling the deformable and rigid bodies. Our method can efficiently simulate character models, with rigid-body parts (bones) being correctly coupled with deformable parts (flesh). Our method is stable because backward Euler time integration is applied to rigid as well as deformable degrees of freedom. Our method is rigorously derived from constrained Newtonian mechanics. In an example simulation with rigid bodies only, we demonstrate that our method converges to the same motion as classical explicitly integrated rigid body simulator.
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    Small Steps in Physics Simulation
    (ACM, 2019) Macklin, Miles; Storey, Kier; Lu, Michelle; Terdiman, Pierre; Chentanez, Nuttapong; Jeschke, Stefan; Müller, Matthias; Batty, Christopher and Huang, Jin
    In this paper we re-examine the idea that implicit integrators with large time steps offer the best stability/performance trade-off for stiff systems. We make the surprising observation that performing a single large time step with n constraint solver iterations is less effective than computing n smaller time steps, each with a single constraint solver iteration. Based on this observation, our approach is to split every visual time step into n substeps of length Δt/n and to perform a single iteration of extended position-based dynamics (XPBD) in each such substep. When compared to a traditional implicit integrator with large time stepswe find constraint error and damping are significantly reduced. When compared to an explicit integrator we find that our method is more stable and robust for a wider range of stiffness parameters. This result holds even when compared against more sophisticated implicit solvers based on Krylov methods. Our method is straightforward to implement, and is not sensitive to matrix conditioning nor is it to overconstrained problems.