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 -