SCA 16: Eurographics/SIGGRAPH Symposium on Computer Animation

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https://diglib.eg.org/handle/10.2312/2630803

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Browsing SCA 16: Eurographics/SIGGRAPH Symposium on Computer Animation by Subject "I.3.3 [Computer Graphics]"

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    Art-Directed Muscle Simulation for High-End Facial Animation
    (The Eurographics Association, 2016) Cong, Matthew; Bhat, Kiran S.; Fedkiw, Ronald P.; Ladislav Kavan and Chris Wojtan
    We propose a new framework for the simulation of facial muscle and flesh that so significantly improves the technique that it allows for immediate mainstream use of anatomically and biomechanically accurate muscle models as a bread and butter technique in a high-end production quality pipeline. The key idea is to create a blendshape system for the muscles that gives the precise directability and controllability required in a high-end production environment. The blendshape muscles are used to drive the underlying anatomically and biomechanically motivated simulation in a way that is unbound by the typical restrictions of a simulation system while still retaining the desirable degree of freedom richness that leads to high quality results. We show that we are able to target production quality facial shapes, whether from scans or an animation system, and illustrate that the resulting nonlinear simulation in-betweens are of higher quality than those obtained from traditional linear blendshapes. We also demonstrate the ability to selectively improve areas on a given blendshape using the results of a simulation, as well as the ability to edit muscle shapes and paths in order to produce directability for animator control. Then, we show how these techniques can be used to transition from one blendshape to another or even track and selectively modify an entire performance. The efficacy of our system is further demonstrated by using it to retarget animation onto new creature models given only a single static rest pose as input.
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    Asynchronous Implicit Backward Euler Integration
    (The Eurographics Association, 2016) Zhao, Danyong; Li, Yijing; Barbic, Jernej; Ladislav Kavan and Chris Wojtan
    In standard deformable object simulation in computer animation, all the mesh elements or vertices are timestepped synchronously, i.e., under the same timestep. Previous asynchronous methods have been largely limited to explicit integration. We demonstrate how to perform spatially-varying timesteps for the widely popular implicit backward Euler integrator. Spatiallyvarying timesteps are useful when the object exhibits spatially-varying material properties such as Young's modulus or mass density. In synchronous simulation, a region with a high stiffness (or low mass density) will force a small timestep for the entire mesh, at a great computational cost, or else, the motion in the stiff (or low mass density) region will be artificially damped and inaccurate. Our method can assign smaller timesteps to stiffer (or lighter) regions, which makes it possible to properly resolve (sample) the high-frequency deformable dynamics arising from the stiff (or light) materials, resulting in greater accuracy and less artificial damping. Because soft (or heavy) regions can continue using a large timestep, our method provides a significantly higher accuracy under a fixed computational budget.
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    Constrained Neighbor Lists for SPH-based Fluid Simulations
    (The Eurographics Association, 2016) Winchenbach, Rene; Hochstetter, Hendrik; Kolb, Andreas; Ladislav Kavan and Chris Wojtan
    In this paper we present a new approach to create neighbor lists with strict memory bounds for incompressible Smoothed Particle Hydrodynamics (SPH) simulations. Our proposed approach is based on a novel efficient predictive-corrective algorithm that locally adjusts particle support radii in order to yield neighborhoods of a user-defined maximum size. Due to the improved estimation of the initial support radius, our algorithm is able to efficiently calculate neighborhoods in a single iteration in almost any situation. We compare our neighbor list algorithm to previous approaches and show that our proposed approach can handle larger particle numbers on a single GPU due to its strict guarantees and is able to simulate more particles in real time due to its benefits in regard to performance. Additionally we demonstrate the versatility and stability of our approach in several different scenarios, for example multi-scale simulations and with different kernel functions.
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    Real-time Simulation of Large Elasto-Plastic Deformation with Shape Matching
    (The Eurographics Association, 2016) Chentanez, Nuttapong; Müller, Matthias; Macklin, Miles; Ladislav Kavan and Chris Wojtan
    Shape matching is a popular method for simulating deformable objects in real time as it is fast and stable at large time steps. Although shape matching can simulate large elastic deformation and ductile fracturing, until now, they are limited to scenarios with relatively small plastic deformation. In this work, we present a method for simulating deformable solids undergoing large plastic deformation and topological changes using shape matching within the position based dynamics (PBD) framework. This expands the versatility of PBD which was previously shown to be able to simulate rigid bodies, liquids, gases, cloth, and deformable solids with moderate plastic deformation. Our novel contributions include local particle re-sampling, cluster re-sampling and skinning of an explicitly tracked surface mesh.