TY - JOUR AB - Triangle mesh-based simulations are able to produce satisfying animations of knitted and woven cloth; however, they lack the rich geometric detail of yarn-level simulations. Naive texturing approaches do not consider yarn-level physics, while full yarn-level simulations may become prohibitively expensive for large garments. We propose a method to animate yarn-level cloth geometry on top of an underlying deforming mesh in a mechanics-aware fashion. Using triangle strains to interpolate precomputed yarn geometry, we are able to reproduce effects such as knit loops tightening under stretching. In combination with precomputed mesh animation or real-time mesh simulation, our method is able to animate yarn-level cloth in real-time at large scales. AU - Sperl, Georg AU - Narain, Rahul AU - Wojtan, Christopher J ID - 9818 IS - 4 JF - ACM Transactions on Graphics SN - 07300301 TI - Mechanics-aware deformation of yarn pattern geometry VL - 40 ER - TY - COMP AB - This archive contains the missing sweater mesh animations and displacement models for the code of "Mechanics-Aware Deformation of Yarn Pattern Geometry" Code Repository: https://git.ist.ac.at/gsperl/MADYPG AU - Sperl, Georg AU - Narain, Rahul AU - Wojtan, Christopher J ID - 9327 TI - Mechanics-Aware Deformation of Yarn Pattern Geometry (Additional Animation/Model Data) ER - TY - JOUR AB - We propose a method to enhance the visual detail of a water surface simulation. Our method works as a post-processing step which takes a simulation as input and increases its apparent resolution by simulating many detailed Lagrangian water waves on top of it. We extend linear water wave theory to work in non-planar domains which deform over time, and we discretize the theory using Lagrangian wave packets attached to spline curves. The method is numerically stable and trivially parallelizable, and it produces high frequency ripples with dispersive wave-like behaviors customized to the underlying fluid simulation. AU - Skrivan, Tomas AU - Soderstrom, Andreas AU - Johansson, John AU - Sprenger, Christoph AU - Museth, Ken AU - Wojtan, Christopher J ID - 8535 IS - 4 JF - ACM Transactions on Graphics SN - 07300301 TI - Wave curves: Simulating Lagrangian water waves on dynamically deforming surfaces VL - 39 ER - TY - JOUR AB - This paper introduces a simple method for simulating highly anisotropic elastoplastic material behaviors like the dissolution of fibrous phenomena (splintering wood, shredding bales of hay) and materials composed of large numbers of irregularly‐shaped bodies (piles of twigs, pencils, or cards). We introduce a simple transformation of the anisotropic problem into an equivalent isotropic one, and we solve this new “fictitious” isotropic problem using an existing simulator based on the material point method. Our approach results in minimal changes to existing simulators, and it allows us to re‐use popular isotropic plasticity models like the Drucker‐Prager yield criterion instead of inventing new anisotropic plasticity models for every phenomenon we wish to simulate. AU - Schreck, Camille AU - Wojtan, Christopher J ID - 8765 IS - 2 JF - Computer Graphics Forum KW - Computer Networks and Communications SN - 0167-7055 TI - A practical method for animating anisotropic elastoplastic materials VL - 39 ER - TY - JOUR AB - We introduce dynamically warping grids for adaptive liquid simulation. Our primary contributions are a strategy for dynamically deforming regular grids over the course of a simulation and a method for efficiently utilizing these deforming grids for liquid simulation. Prior work has shown that unstructured grids are very effective for adaptive fluid simulations. However, unstructured grids often lead to complicated implementations and a poor cache hit rate due to inconsistent memory access. Regular grids, on the other hand, provide a fast, fixed memory access pattern and straightforward implementation. Our method combines the advantages of both: we leverage the simplicity of regular grids while still achieving practical and controllable spatial adaptivity. We demonstrate that our method enables adaptive simulations that are fast, flexible, and robust to null-space issues. At the same time, our method is simple to implement and takes advantage of existing highly-tuned algorithms. AU - Hikaru, Ibayashi AU - Wojtan, Christopher J AU - Thuerey, Nils AU - Igarashi, Takeo AU - Ando, Ryoichi ID - 5681 IS - 6 JF - IEEE Transactions on Visualization and Computer Graphics SN - 10772626 TI - Simulating liquids on dynamically warping grids VL - 26 ER - TY - JOUR AB - Previous research on animations of soap bubbles, films, and foams largely focuses on the motion and geometric shape of the bubble surface. These works neglect the evolution of the bubble’s thickness, which is normally responsible for visual phenomena like surface vortices, Newton’s interference patterns, capillary waves, and deformation-dependent rupturing of films in a foam. In this paper, we model these natural phenomena by introducing the film thickness as a reduced degree of freedom in the Navier-Stokes equations and deriving their equations of motion. We discretize the equations on a nonmanifold triangle mesh surface and couple it to an existing bubble solver. In doing so, we also introduce an incompressible fluid solver for 2.5D films and a novel advection algorithm for convecting fields across non-manifold surface junctions. Our simulations enhance state-of-the-art bubble solvers with additional effects caused by convection, rippling, draining, and evaporation of the thin film. AU - Ishida, Sadashige AU - Synak, Peter AU - Narita, Fumiya AU - Hachisuka, Toshiya AU - Wojtan, Christopher J ID - 8384 IS - 4 JF - ACM Transactions on Graphics SN - 07300301 TI - A model for soap film dynamics with evolving thickness VL - 39 ER - TY - JOUR AB - We present a method for animating yarn-level cloth effects using a thin-shell solver. We accomplish this through numerical homogenization: we first use a large number of yarn-level simulations to build a model of the potential energy density of the cloth, and then use this energy density function to compute forces in a thin shell simulator. We model several yarn-based materials, including both woven and knitted fabrics. Our model faithfully reproduces expected effects like the stiffness of woven fabrics, and the highly deformable nature and anisotropy of knitted fabrics. Our approach does not require any real-world experiments nor measurements; because the method is based entirely on simulations, it can generate entirely new material models quickly, without the need for testing apparatuses or human intervention. We provide data-driven models of several woven and knitted fabrics, which can be used for efficient simulation with an off-the-shelf cloth solver. AU - Sperl, Georg AU - Narain, Rahul AU - Wojtan, Christopher J ID - 8385 IS - 4 JF - ACM Transactions on Graphics SN - 07300301 TI - Homogenized yarn-level cloth VL - 39 ER - TY - JOUR AB - The “procedural” approach to animating ocean waves is the dominant algorithm for animating larger bodies of water in interactive applications as well as in off-line productions — it provides high visual quality with a low computational demand. In this paper, we widen the applicability of procedural water wave animation with an extension that guarantees the satisfaction of boundary conditions imposed by terrain while still approximating physical wave behavior. In combination with a particle system that models wave breaking, foam, and spray, this allows us to naturally model waves interacting with beaches and rocks. Our system is able to animate waves at large scales at interactive frame rates on a commodity PC. AU - Jeschke, Stefan AU - Hafner, Christian AU - Chentanez, Nuttapong AU - Macklin, Miles AU - Müller-Fischer, Matthias AU - Wojtan, Christopher J ID - 8766 IS - 8 JF - Computer Graphics forum TI - Making procedural water waves boundary-aware VL - 39 ER - TY - JOUR AB - This paper investigates the use of fundamental solutions for animating detailed linear water surface waves. We first propose an analytical solution for efficiently animating circular ripples in closed form. We then show how to adapt the method of fundamental solutions (MFS) to create ambient waves interacting with complex obstacles. Subsequently, we present a novel wavelet-based discretization which outperforms the state of the art MFS approach for simulating time-varying water surface waves with moving obstacles. Our results feature high-resolution spatial details, interactions with complex boundaries, and large open ocean domains. Our method compares favorably with previous work as well as known analytical solutions. We also present comparisons between our method and real world examples. AU - Schreck, Camille AU - Hafner, Christian AU - Wojtan, Christopher J ID - 6442 IS - 4 JF - ACM Transactions on Graphics TI - Fundamental solutions for water wave animation VL - 38 ER - TY - JOUR AB - Multiple Importance Sampling (MIS) is a key technique for achieving robustness of Monte Carlo estimators in computer graphics and other fields. We derive optimal weighting functions for MIS that provably minimize the variance of an MIS estimator, given a set of sampling techniques. We show that the resulting variance reduction over the balance heuristic can be higher than predicted by the variance bounds derived by Veach and Guibas, who assumed only non-negative weights in their proof. We theoretically analyze the variance of the optimal MIS weights and show the relation to the variance of the balance heuristic. Furthermore, we establish a connection between the new weighting functions and control variates as previously applied to mixture sampling. We apply the new optimal weights to integration problems in light transport and show that they allow for new design considerations when choosing the appropriate sampling techniques for a given integration problem. AU - Kondapaneni, Ivo AU - Vevoda, Petr AU - Grittmann, Pascal AU - Skrivan, Tomas AU - Slusallek, Philipp AU - Křivánek, Jaroslav ID - 7002 IS - 4 JF - ACM Transactions on Graphics SN - 0730-0301 TI - Optimal multiple importance sampling VL - 38 ER -