High-Resolution Interaction with Corotational Coarsening Models

Rosell Torres, Alejandro Rodríguez, José Miguel Espadero, Miguel A. Otaduy

This paper presents a numerical coarsening method for corotational elasticity, which enables interactive large deformation of high-resolution heterogeneous objects. Our method derives a coarse elastic model from a high-resolution discretization of corotational elasticity with high-resolution boundary conditions. This is in contrast to previous coarsening methods, which derive a coarse elastic model from an unconstrained high-resolution discretization of regular linear elasticity, and then apply corotational computations directly on the coarse setting. We show that previous approaches fail to handle high-resolution boundary conditions correctly, suffering accuracy and robustness problems. Our method, on the other hand, supports efficiently accurate high-resolution boundary conditions, which are fundamental for rich interaction with high-resolution heterogeneous models. We demonstrate the potential of our method for interactive deformation of complex medical imaging data sets.

High-Resolution Interaction with Corotational Coarsening Models

Dispersion Kernels for Water Wave Simulation

José A. Canabal, David Miraut, Nils Thürey, Theodore Kim, Javier Portilla, Miguel A. Otaduy

We propose a method to simulate the rich, scale-dependent dynamics of water waves. Our method preserves the dispersion properties of real waves, yet it supports interactions with obstacles and is computationally efficient. Fundamentally, it computes wave accelerations by way of applying a dispersion kernel as a spatially variant filter, which we are able to compute efficiently using two core technical contributions. First, we design novel, accurate, and compact pyramid kernels which compensate for low-frequency truncation errors. Second, we design a shadowed convolution operation that efficiently accounts for obstacle interactions by modulating the application of the dispersion kernel. We demonstrate a wide range of behaviors, which include capillary waves, gravity waves, and interactions with static and dynamic obstacles, all from within a single simulation.

Dispersion Kernels for Water Wave Simulation

Enriching Triangle Mesh Animations with Physically Based Simulation

Yijing Li, Hongyi Xu, Jernej Barbič

We present a system to combine arbitrary triangle mesh animations with physically based Finite Element Method (FEM) simulation, enabling control over the combination both in space and time. The input is a triangle mesh animation obtained using any method, such as keyframed animation, character rigging, 3D scanning, or geometric shape modeling. The input may be non-physical, crude or even incomplete. The user provides weights, specified using a minimal user interface, for how much physically based simulation should be allowed to modify the animation in any region of the model, and in time. Our system then computes a physically-based animation that is constrained to the input animation to the amount prescribed by these weights. This permits smoothly turning physics on and off over space and time, making it possible for the output to strictly follow the input, to evolve purely based on physically based simulation, and anything in between. Achieving such results requires a careful combination of several system components. We propose and analyze these components, including proper automatic creation of simulation meshes (even for non-manifold and self-colliding undeformed triangle meshes), converting triangle mesh animations into animations of the simulation mesh, and resolving collisions and self-collisions while following the input.

Enriching Triangle Mesh Animations with Physically Based Simulation

An Efficient Hybrid Incompressible SPH Solver with Interface Handling for Boundary Conditions

Tetsuya Takahashi, Yoshinori Dobashi, Tomoyuki Nishita, Ming Lin

We propose a hybrid Smoothed Particle Hydrodynamics solver for efficiently simulating incompressible fluids using an interface handling method for boundary conditions in the pressure Poisson equation. We blend particle density computed with one smooth and one spiky kernel to improve the robustness against both fluid-fluid and fluid-solid collisions. To further improve the robustness and efficiency, we present a new interface handling method consisting of two components: free surface handling for Dirichlet boundary conditions and solid boundary handling for Neumann boundary conditions. Our free surface handling appropriately determines particles for Dirichlet boundary conditions using Jacobi-based pressure prediction while our solid boundary handling introduces a new term to ensure the solvability of the linear system. We demonstrate that our method outperforms the state-of-the-art particle-based fluid solvers.

An Efficient Hybrid Incompressible SPH Solver with Interface Handling for Boundary Conditions

A Multilevel SPH Solver with Unified Solid Boundary Handling

Tetsuya Takahashi, Ming Lin

We propose a geometric multilevel solver for efficiently solving linear systems arising from particle-based methods. To apply this method to particle systems, we construct the hierarchy, establish the correspondence between solutions at the particle and grid levels, and coarsen simulation elements taking boundary conditions into account. In addition, we propose a new solid boundary handling method to solve a pressure Poisson equation in a unified manner. We demonstrate that our method can handle general fluid simulation scenarios including two-way fluid-solid coupling, and the computational cost of this new solver scales nearly linearly with respect to the number of unknowns, unlike previous solvers for particle-based methods.

A Multilevel SPH Solver with Unified Solid Boundary Handling

SIGGRAPH Asia 2016

Real-Time Oil Painting on Mobile Hardware

Tuur Stuyck, Fang Da, Sunil Hadap, Philip Dutré

This paper presents a realistic digital oil painting system, specifically targeted at the real-time performance on highly resource constrained portable hardware such as tablets and iPads. To effectively use the limited computing power, we develop an efficient adaptation of the Shallow Water Equations that models all the characteristic properties of oil paint. The pigments are stored in a multi-layered structure to model the peculiar nature of pigment mixing in oil paint. The user experience ranges from thick shape-retaining strokes to runny diluted paint that reacts naturally to the gravity set by tablet orientation. Finally, the paint is rendered in real-time using a combination of carefully chosen efficient rendering techniques. The virtual lighting adapts to the tablet orientation, or alternatively, the front-facing camera captures the lighting environment, which leads to a truly immersive user experience. Our proposed features are evaluated via a user study. In our experience, our system enables artists to quickly try out ideas and compositions anywhere when inspiration strikes, in a truly ubiquitous way. They don’t need to carry expensive and messy oil paint supplies.

Real-Time Oil Painting on Mobile Hardware

Space-time sculpting of liquid animation

Pierre-Luc Manteaux, Ulysse Vimont, Chris Wojtan, Damien Rohmer, Marie-Paule Cani

We propose an interactive sculpting system for seamlessly editing pre-computed animations of liquid, without the need for any re-simulation. The input is a sequence of meshes without correspondences representing the liquid surface over time. Our method enables the efficient selection of consistent space-time parts of this animation, such as moving waves or droplets, which we call space-time features. Once selected, a feature can be copied, edited, or duplicated and then pasted back anywhere in space and time in the same or in another liquid animation sequence. Our method circumvents tedious user interactions by automatically computing the spatial and temporal ranges of the selected feature. We also provide space-time shape editing tools for non-uniform scaling, rotation, trajectory changes, and temporal editing to locally speed up or slow down motion. Using our tools, the user can edit and progressively refine any input simulation result, possibly using a library of pre-computed space-time features extracted from other animations. In contrast to the trial-and-error loop usually required to edit animation results through the tuning of indirect simulation parameters, our method gives the user full control over the edited space-time behaviors.

Space-time sculpting of liquid animation

Projective Fluids

Marcel Weiler, Dan Koschier, Jan Bender

We present a new method for particle based fluid simulation, using a combination of Projective Dynamics and Smoothed Particle Hydrodynamics (SPH). The Projective Dynamics framework allows the fast simulation of a wide range of constraints. It offers great stability through its implicit time integration scheme and is parallelizable in large parts, so that it can make use of modern multi core CPUs. Yet existing work only uses Projective Dynamics to simulate various kinds of soft bodies and cloth. We are the first ones to incorporate fluid simulation into the Projective Dynamics framework. Our proposed fluid constraints are derived from SPH and seamlessly integrate into the existing method. Furthermore, we adapt the solver to handle the constantly changing constraints that appear in fluid simulation. We employ a highly parallel matrix-free conjugate gradient solver, and thus do not require expensive matrix factorizations.

Projective Fluids

Simulating Visual Geometry

Matthias Müller, Nuttapong Chentanez, Miles Macklin

In computer graphics, simulated objects typically have two or three different representations, a visual mesh, a simulation mesh and a collection of convex shapes for collision handling. Using multiple representations requires skilled authoring and complicates object handing at run time. It can also produce visual artifacts such as a mismatch of collision behavior and visual appearance. The reason for using multiple representation has been performance restrictions in real time environments. However, for virtual worlds, we believe that the ultimate goal must be WYSIWYS – what you see is what you simulate, what you can manipulate, what you can touch. In this paper we present a new method that uses the same representation for simulation and collision handling and an almost identical visualization mesh. This representation is very close and directly derived from a visual input mesh which does not have to be prepared for simulation but can be non-manifold, non-conforming and self-intersecting.

Simulating Visual Geometry