We present a unified dynamics framework for real-time visual effects. Using particles connected by constraints as our fundamental building block allows us to treat contact and collisions in a unified manner, and we show how this representation is flexible enough to model gases, liquids, deformable solids, rigid bodies and cloth with two-way interactions. We address some common problems with traditional particle-based methods and describe a parallel constraint solver based on position-based dynamics that is efficient enough for real-time applications.

Unified particle physics for real-time applications

Sketching is a natural form of human communication and has become an increasingly popular tool for interacting with user interfaces. In order to facilitate the integration of sketching into traditional user interfaces, we must first develop accurate ways of recognizing users' intentions while providing feedback to catch recognition problems early in the sketching process. One approach to sketch recognition has been to recognize low-level primitives and then hierarchically construct higher-level shapes based on geometric constraints defined by the user, however, current low-level recognizers only handle a few number of primitive shapes. We propose a new low-level recognition and beautification system that can recognize eight primitive shapes, as well as combinations of these primitives, with recognition rates at 98.56%. Our system also automatically generates beautified versions of these shapes to provide feedback early in the sketching process. In addition to looking at geometric perception, much of our recognition success can be attributed to two new features, along with a new ranking algorithm, which have proven to be significant in distinguishing polylines from curved segments.

PaleoSketch: accurate primitive sketch recognition and beautification

Visual quality, low computational cost, and numerical stability are foremost goals in computer animation. An important ingredient in achieving these goals is the conservation of fundamental motion invariants. For example, rigid and deformable body simulation benefits greatly from the conservation of linear and angular momenta. In the case of fluids, however, none of the current techniques focuses on conserving invariants, and consequently, often introduce a visually disturbing numerical diffusion of vorticity. Just as important visually is the resolution of complex simulation domains. Doing so with regular (even if adaptive) grid techniques can be computationally delicate. In this article, we propose a novel technique for the simulation of fluid flows. It is designed to respect the defining differential properties, that is, the conservation of circulation along arbitrary loops as they are transported by the flow. Consequently, our method offers several new and desirable properties: Arbitrary simplicial meshes (triangles in 2D, tetrahedra in 3D) can be used to define the fluid domain; the computations involved in the update procedure are efficient due to discrete operators with small support; and it preserves discrete circulation, avoiding numerical diffusion of vorticity.

Stable, circulation-preserving, simplicial fluids

We present a new model reduction approach to fluid simulation, enabling large, real-time, detailed flows with continuous user interaction. Our reduced model can also handle moving obstacles immersed in the flow. We create separate models for the velocity field and for each moving boundary, and show that the coupling forces may be reduced as well. Our results indicate that surprisingly few basis functions are needed to resolve small but visually important features such as spinning vortices.

/pdf/model-reduction-for-real-time-fluids-4wjadtyz9t.pdf

Model reduction for real-time fluids

Computational support for sketching is an exciting research area at the intersection of design research, human–computer interaction, and artificial intelligence. Despite the prevalence of software tools, most designers begin their work with physical sketches. Modern computational tools largely treat design as a linear process beginning with a specific problem and ending with a specific solution. Sketch-based design tools offer another approach that may fit design practice better. This review surveys literature related to such tools. First, we describe the practical basis of sketching — why people sketch, what significance it has in design and problem solving, and the cognitive activities it supports. Second, we survey computational support for sketching, including methods for performing sketch recognition and managing ambiguity, techniques for modeling recognizable elements, and human–computer interaction techniques for working with sketches. Last, we propose challenges and opportunities for future advances in this field.

/pdf/computational-support-for-sketching-in-design-3olij4ewe1.pdf

Computational Support for Sketching in Design

In this paper, we present a method for visual simulation of gaseous phenomena based on the vortex method. This method uses a localized vortex flow as a basic building block and combines those blocks to describe a whole flow field. As a result, we achieve computational efficiency by concentrating only on a localized vorticity region while generating dynamic swirling fluid flows. Based on the Lagrangian framework, we resolve various boundary conditions. By exploiting the panel method, we satisfy the no-through boundary condition in a Lagrangian way. A simple and effective way of handling the no-slip boundary condition is also presented. In treating the no-slip boundary condition, we allow a user to control the roughness of the boundary surface, which further improves visual realism.

/pdf/vortex-fluid-for-gaseous-phenomena-425ogn097k.pdf

Vortex fluid for gaseous phenomena

A proper segmentation of pen marking enhances shape recognition and enables a natural interface for sketch-based modeling from simple line drawing tools to 3D solid modeling applications; user input is otherwise restricted to draw only one segment per one stroke. In general, the pen marking segmentation is achieved by detecting the points of high curvature-called, segmenting points-and splitting the pen marking at those points. This paper presents a curvature estimation method, which considers only local shape information. The proposed method can therefore estimate curvature on-the-fly while user is drawing on a pen-input display, such as tablet PCs.

A curvature estimation for pen input segmentation in sketch-based modeling

We present an extension of Greiner-Hormann polygon clipping that has been regarded as both computationally efficient and simple to implement. This extended version of the Greiner-Hormann polygon clipping elegantly handles the degenerate cases in a deterministic way, which in the previous approach is done by perturbing vertices in an indeterministic way.

An extension of polygon clipping to resolve degenerate cases

Sketch interactions based on interpreting multiple pen markings into a 3D shape is easy to design but not to use. First of all, it is difficult for the user to memorize a complete set of pen markings for a certain 3D shape. Secondly, the system will be waiting for the user to complete the sequence of the pen markings, often causing a certain mode error. To address these problems, we present a novel, interaction framework, suitable for interpretations based on single-stroke marking on pen-input display; within this framework 3D shape modeling operations are designed to create appropriate communication protocols.

A new modeling interface for the pen-input displays

Smooth motion generation is an important issue in the computer animation and virtual reality (VR) area. In general, the motion of a rigid body consists of translation and orientation. The former is described by a space curve in 3-dimensional Euclidean space, while the latter is represented by a curve in the unit quaternion space. Although there are well-known techniques for smoothing the translation curve in the Euclidean space, few results have been reported for smoothing motion as a whole. This paper improves the previous study and provides a more robust algorithm, which seeks to minimize the weighted sum of the strain-energy and the sum of the squared errors.

/pdf/noise-smoothing-for-vr-equipment-in-quaternions-2yya94u624.pdf

Myoung-Jun Kim

Papers

Vortex fluid for gaseous phenomena

A curvature estimation for pen input segmentation in sketch-based modeling

An extension of polygon clipping to resolve degenerate cases

A new modeling interface for the pen-input displays

Noise smoothing for VR equipment in quaternions