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 - 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 - TY - JOUR AB - Multiple importance sampling (MIS) has become an indispensable tool in Monte Carlo rendering, widely accepted as a near-optimal solution for combining different sampling techniques. But an MIS combination, using the common balance or power heuristics, often results in an overly defensive estimator, leading to high variance. We show that by generalizing the MIS framework, variance can be substantially reduced. Specifically, we optimize one of the combined sampling techniques so as to decrease the overall variance of the resulting MIS estimator. We apply the approach to the computation of direct illumination due to an HDR environment map and to the computation of global illumination using a path guiding algorithm. The implementation can be as simple as subtracting a constant value from the tabulated sampling density done entirely in a preprocessing step. This produces a consistent noise reduction in all our tests with no negative influence on run time, no artifacts or bias, and no failure cases. AU - Karlík, Ondřej AU - Šik, Martin AU - Vévoda, Petr AU - Skrivan, Tomas AU - Křivánek, Jaroslav ID - 7418 IS - 6 JF - ACM Transactions on Graphics SN - 0730-0301 TI - MIS compensation: Optimizing sampling techniques in multiple importance sampling VL - 38 ER - TY - CONF AB - We present a thermodynamically based approach to the design of models for viscoelastic fluids with stress diffusion effect. In particular, we show how to add a stress diffusion term to some standard viscoelastic rate-type models (Giesekus, FENE-P, Johnson–Segalman, Phan-Thien–Tanner and Bautista–Manero–Puig) so that the resulting models with the added stress diffusion term are thermodynamically consistent in the sense that they obey the first and the second law of thermodynamics. We point out the potential applications of the provided thermodynamical background in the study of flows of fluids described by the proposed models. AU - Dostalík, Mark AU - Pruša, Vít AU - Skrivan, Tomas ID - 6642 T2 - AIP Conference Proceedings TI - On diffusive variants of some classical viscoelastic rate-type models VL - 2107 ER - TY - JOUR AB - The current state of the art in real-time two-dimensional water wave simulation requires developers to choose between efficient Fourier-based methods, which lack interactions with moving obstacles, and finite-difference or finite element methods, which handle environmental interactions but are significantly more expensive. This paper attempts to bridge this long-standing gap between complexity and performance, by proposing a new wave simulation method that can faithfully simulate wave interactions with moving obstacles in real time while simultaneously preserving minute details and accommodating very large simulation domains. Previous methods for simulating 2D water waves directly compute the change in height of the water surface, a strategy which imposes limitations based on the CFL condition (fast moving waves require small time steps) and Nyquist's limit (small wave details require closely-spaced simulation variables). This paper proposes a novel wavelet transformation that discretizes the liquid motion in terms of amplitude-like functions that vary over space, frequency, and direction, effectively generalizing Fourier-based methods to handle local interactions. Because these new variables change much more slowly over space than the original water height function, our change of variables drastically reduces the limitations of the CFL condition and Nyquist limit, allowing us to simulate highly detailed water waves at very large visual resolutions. Our discretization is amenable to fast summation and easy to parallelize. We also present basic extensions like pre-computed wave paths and two-way solid fluid coupling. Finally, we argue that our discretization provides a convenient set of variables for artistic manipulation, which we illustrate with a novel wave-painting interface. AU - Jeschke, Stefan AU - Skrivan, Tomas AU - Mueller Fischer, Matthias AU - Chentanez, Nuttapong AU - Macklin, Miles AU - Wojtan, Christopher J ID - 134 IS - 4 JF - ACM Transactions on Graphics TI - Water surface wavelets VL - 37 ER -