Department of Computer Science
Langlois and Doug L. James, Inverse-Foley
Animation: Synchronizing rigid-body motions to sound,
ACM Transactions on Graphics (SIGGRAPH 2014),
33(4), August 2014.
ABSTRACT: In this paper, we introduce Inverse-Foley Animation, a technique for optimizing rigid-body animations so that contact events are synchronized with input sound events. A precomputed database of randomly sampled rigid-body contact events is used to build a contact-event graph, which can be searched to determine a plausible sequence of contact events synchronized with the input sound's events. To more easily find motions with matching contact times, we allow transitions between simulated contact events using a motion blending formulation based on modified contact impulses. We fine tune synchronization by slightly retiming ballistic motions. Given a sound, our system can synthesize synchronized motions using graphs built with hundreds of thousands of precomputed motions, and millions of contact events. Our system is easy to use, and has been used to plan motions for hundreds of sounds, and dozens of rigid-body models.
Langlois, Steven S.
An, Kelvin K. Jin, and Doug L. James, Eigenmode
Compression for Modal Sound Models, ACM
Transactions on Graphics (SIGGRAPH 2014), 33(4),
ABSTRACT: We propose and evaluate a method for significantly compressing modal sound models, thereby making them far more practical for audiovisual applications. The dense eigenmode matrix, needed to compute the sound model's response to contact forces, can consume tens to thousands of megabytes depending on mesh resolution and mode count. Our eigenmode compression pipeline is based on nonlinear optimization of Moving Least Squares (MLS) approximations. Enhanced compression is achieved by exploiting symmetry both within and between eigenmodes, and by adaptively assigning per-mode error levels based on human perception of the far-field pressure amplitudes. Our method provides smooth eigenmode approximations, and efficient random access. We demonstrate that, in many cases, hundredfold compression ratios can be achieved without audible degradation of the rendered sound.
Chadwick, Changxi Zheng
and Doug L. James, Faster
Acceleration Noise for Multibody Animations using
Precomputed Soundbanks, ACM/Eurographics Symposium on Computer Animation,
ABSTRACT: We introduce an efficient method for synthesizing rigid-body acceleration noise for complex multibody scenes. Existing acceleration noise synthesis methods for animation require object-specific precomputation, which is prohibitively expensive for scenes involving rigid-body fracture or other sources of small, procedurally generated debris. We avoid precomputation by introducing a proxy-based method for acceleration noise synthesis in which precomputed acceleration noise data is only generated for a small set of ellipsoidal proxies and stored in a proxy soundbank. Our proxy model is shown to be effective at approximating acceleration noise from scenes with lots of small debris (e.g., pieces produced by rigid-body fracture). This approach is not suitable for synthesizing acceleration noise from larger objects with complicated non-convex geometry; however, it has been shown in previous work that acceleration noise from objects such as these tends to be largely masked by modal vibration sound. We manage the cost of our proxy soundbank with a new wavelet-based compression scheme for acceleration noise and use our model to significantly improve sound synthesis results for several multibody animations.
and Doug L. James, Energy-based
Self-Collision Culling for Arbitrary Mesh Deformations,
ACM Transactions on
Graphics (SIGGRAPH 2012), August 2012.
ABSTRACT: In this paper, we accelerate self-collision detection (SCD) for a deforming triangle mesh by exploiting the idea that a mesh cannot self collide unless it deforms enough. Unlike prior work on subspace self-collision culling which is restricted to low-rank deformation subspaces, our energy-based approach supports arbitrary mesh deformations while still being fast. Given a bounding volume hierarchy (BVH) for a triangle mesh, we precompute Energy-based Self- Collision Culling (ESCC) certificates on bounding-volume-related sub-meshes which indicate the amount of deformation energy required for it to self collide. After updating energy values at runtime, many bounding-volume self-collision queries can be culled using the ESCC certificates. We propose an affine-frame Laplacian-based energy definition which sports a highly optimized certificate preprocess, and fast runtime energy evaluation. The latter is performed hierarchically to amortize Laplacian energy and affine-frame estimation computations. ESCC supports both discrete and continuous SCD with detailed and nonsmooth geometry. We observe significant culling on many examples, with SCD speed-ups up to 26x.
Chadwick, Changxi Zheng
and Doug L. James, Precomputed
Acceleration Noise for Improved Rigid-Body Sound, ACM Transactions on Graphics
(SIGGRAPH 2012), August 2012.
ABSTRACT: We introduce an efficient method for synthesizing acceleration noise--sound produced when an object experiences abrupt rigidbody acceleration due to collisions or other contact events. We approach this in two main steps. First, we estimate continuous contact force profiles from rigid-body impulses using a simple model based on Hertz contact theory. Next, we compute solutions to the acoustic wave equation due to short acceleration pulses in each rigid-body degree of freedom. We introduce an efficient representation for these solutions--Precomputed Acceleration Noise--which allows us to accurately estimate sound due to arbitrary rigid-body accelerations. We find that the addition of acceleration noise significantly complements the standard modal sound algorithm, especially for small objects.
|Steven S. An,
Doug L. James and Steve Marschner,
Synthesis of Cloth Sounds, ACM Transactions on Graphics
(SIGGRAPH 2012), August 2012.
ABSTRACT: We present a practical data-driven method for automatically synthesizing plausible soundtracks for physics-based cloth animations running at graphics rates. Given a cloth animation, we analyze the deformations and use motion events to drive crumpling and friction sound models estimated from cloth measurements. We synthesize a low-quality sound signal, which is then used as a target signal for a concatenative sound synthesis (CSS) process. CSS selects a sequence of microsound units, very short segments, from a database of recorded cloth sounds, which best match the synthesized target sound in a low-dimensional feature-space after applying a handtuned warping function. The selected microsound units are concatenated together to produce the final cloth sound with minimal filtering. Our approach avoids expensive physics-based synthesis of cloth sound, instead relying on cloth recordings and our motiondriven CSS approach for realism. We demonstrate its effectiveness on a variety of cloth animations involving various materials and character motions, including first-person virtual clothing with binaural sound.
|Cem Yuksel, Jonathan
M. Kaldor, Doug L. James, and Steve Marschner,
Stitch Meshes for Modeling
Knitted Clothing with Yarn-level Detail, ACM Transactions on Graphics
(SIGGRAPH 2012), August 2012.
ABSTRACT: Recent yarn-based simulation techniques permit realistic and efficient dynamic simulation of knitted clothing, but producing the required yarn-level models remains a challenge. The lack of practical modeling techniques significantly limits the diversity and complexity of knitted garments that can be simulated. We propose a new modeling technique that builds yarn-level models of complex knitted garments for virtual characters. We start with a polygonal model that represents the large-scale surface of the knitted cloth. Using this mesh as an input, our interactive modeling tool produces a finer mesh representing the layout of stitches in the garment, which we call the stitch mesh. By manipulating this mesh and assigning stitch types to its faces, the user can replicate a variety of complicated knitting patterns. The curve model representing the yarn is generated from the stitch mesh, then the final shape is computed by a yarn-level physical simulation that locally relaxes the yarn into realistic shape while preserving global shape of the garment and avoiding “yarn pull-through,” thereby producing valid yarn geometry suitable for dynamic simulation. Using our system, we can efficiently create yarn-level models of knitted clothing with a rich variety of patterns that would be completely impractical to model using traditional techniques. We show a variety of example knitting patterns and full-scale garments produced using our system.
| Moritz Beacher, Bernd Bickel,
Doug L. James and Hanspeter
Articulated Characters from Skinned Meshes, ACM Transactions on Graphics
(SIGGRAPH 2012), August 2012.
ABSTRACT: Articulated deformable characters are widespread in computer animation. Unfortunately, we lack methods for their automatic fabrication using modern additive manufacturing (AM) technologies. We propose a method that takes a skinned mesh as input, then estimates a fabricatable single-material model that approximates the 3D kinematics of the corresponding virtual articulated character in a piecewise linear manner. We first extract a set of potential joint locations. From this set, together with optional, user-specified range constraints, we then estimate mechanical friction joints that satisfy inter-joint non-penetration and other fabrication constraints. To avoid brittle joint designs, we place joint centers on an approximate medial axis representation of the input geometry, and maximize each joint’s minimal cross-sectional area. We provide several demonstrations, manufactured as single, assembled pieces using 3D printers.
Chadwick and Doug L. James, Animating Fire with Sound, ACM Transactions on Graphics
(SIGGRAPH 2011), 30(4), August 2011.
ABSTRACT: We propose a practical method for synthesizing plausible fire sounds that are synchronized with physically based fire animations. To enable synthesis of combustion sounds without incurring the cost of time-stepping fluid simulations at audio rates, we decompose our synthesis procedure into two components. First, a low-frequency flame sound is synthesized using a physically based combustion sound model driven with data from a visual flame simulation run at a relatively low temporal sampling rate. Second, we propose two bandwidth extension methods for synthesizing additional high-frequency flame sound content: (1) spectral bandwidth extension which synthesizes higher-frequency noise matching combustion sound spectra from theory and experiment; and (2) data-driven texture synthesis to synthesize high-frequency content based on input flame sound recordings. Various examples and comparisons are presented demonstrating plausible flame sounds, from small candle flames to large flame jets.
and Doug L. James, Toward
High-Quality Modal Contact Sound, ACM Transactions on Graphics
(SIGGRAPH 2011), 30(4), August 2011.
ABSTRACT: Contact sound models based on linear modal analysis are commonly used with rigid body dynamics. Unfortunately, treating vibrating objects as "rigid" during collision and contact processing fundamentally limits the range of sounds that can be computed, and contact solvers for rigid body animation can be ill-suited for modal contact sound synthesis, producing various sound artifacts. In this paper, we resolve modal vibrations in both collision and frictional contact processing stages, thereby enabling non-rigid sound phenomena such as micro-collisions, vibrational energy exchange, and chattering. We propose a frictional multibody contact formulation and modified Staggered Projections solver which is well-suited to sound rendering and avoids noise artifacts associated with spatial and temporal contact-force fluctuations which plague prior methods. To enable practical animation and sound synthesis of numerous bodies with many coupled modes, we propose a novel asynchronous integrator with mode-level adaptivity built into the frictional contact solver. Vibrational contact damping is modeled to approximate contact-dependent sound dissipation. Results are provided that demonstrate high-quality contact resolution with sound.
Theodore Kim and Doug L. James, Physics-based Character Skinning using Multi-Domain Subspace Deformations, In ACM SIGGRAPH / Eurographics Symposium on Computer Animation, August 2011. (Best paper award)
and Doug L. James, Rigid-Body Fracture Sound with
Precomputed Soundbanks, ACM Transactions on Graphics
(SIGGRAPH 2010), 29(3), July 2010, pp. 69:1-69:13.
ABSTRACT: We propose a physically based algorithm for synthesizing sounds synchronized with brittle fracture animations. Motivated by laboratory experiments, we approximate brittle fracture sounds using time-varying rigid-body sound models. We extend methods for fracturing rigid materials by proposing a fast quasistatic stress solver to resolve near-audio-rate fracture events, energy-based fracture pattern modeling and estimation of “crack”-related fracture impulses. Multipole radiation models provide scalable sound radiation for complex debris and level of detail control. To reduce soundmodel generation costs for complex fracture debris, we propose Precomputed Rigid-Body Soundbanks comprised of precomputed ellipsoidal sound proxies. Examples and experiments are presented that demonstrate plausible and affordable brittle fracture sounds.
and Doug L. James, Subspace Self-Collision Culling,
ACM Transactions on Graphics (SIGGRAPH 2010),
29(3), July 2010, pp. 81:1-81:9.
ABSTRACT: We show how to greatly accelerate self-collision detection (SCD) for reduced deformable models. Given a triangle mesh and a set of deformation modes, our method precomputes Subspace Self-Collision Culling (SSCC) certificates which, if satisfied, prove the absence of self-collisions for large parts of the model. At runtime, bounding volume hierarchies augmented with our certificates can aggressively cull overlap tests and reduce hierarchy updates. Our method supports both discrete and continuous SCD, can handle complex geometry, and makes no assumptions about geometric smoothness or normal bounds. It is particularly effective for simulations with modest subspace deformations, where it can often verify the absence of self-collisions in constant time. Our certificates enable low amortized costs, in time and across many objects in multi-body dynamics simulations. Finally, SSCC is effective enough to support self-collision tests at audio rates, which we demonstrate by producing the first sound simulations of clattering objects.
Kaldor, Doug L. James and Steve Marschner,
Efficient Yarn-based Cloth with Adaptive Contact
Linearization, ACM Transactions on Graphics
(SIGGRAPH 2010), 29(3), July 2010, pp. 205:1-105:10.
ABSTRACT: Yarn-based cloth simulation can improve visual quality but at high computational costs due to the reliance on numerous persistent yarn-yarn contacts to generate material behavior. Finding so many contacts in densely interlinked geometry is a pathological case for traditional collision detection, and the sheer number of contact interactions makes contact processing the simulation bottleneck. In this paper, we propose a method for approximating penalty-based contact forces in yarn-yarn collisions by computing the exact contact response at one time step, then using a rotated linear force model to approximate forces in nearby deformed configurations. Because contacts internal to the cloth exhibit good temporal coherence, sufficient accuracy can be obtained with infrequent updates to the approximation, which are done adaptively in space and time. Furthermore, by tracking contact models we reduce the time to detect new contacts. The end result is a 7- to 9-fold speedup in contact processing and a 4- to 5-fold overall speedup, enabling simulation of character-scale garments.
Chadwick, Steven An,
and Doug L. James, Harmonic Shells: A Practical
Nonlinear Sound Model for Near-Rigid Thin Shells, ACM
Transactions on Graphics (SIGGRAPH ASIA Conference
Proceedings), 28(5), December 2009, pp.
Theodore Kim and Doug L. James, Skipping Steps in Deformable Simulation with Online Model Reduction, ACM Transactions on Graphics (SIGGRAPH ASIA Conference Proceedings), 28(5), December 2009, pp. 123:1-123:9.
Zheng and Doug L. James, Harmonic Fluids, ACM Transaction on Graphics (SIGGRAPH 2009),
28(3), August 2009, pp. 37:1-37:12.
Steven An, Theodore Kim and Doug L. James, Optimizing Cubature for Efficient Integration of Subspace Deformations, ACM Transactions on Graphics (SIGGRAPH ASIA Conference Proceedings), 27(5), December 2008, pp. 165:1-165:10.
Danny M. Kaufman, Shinjiro Sueda, Doug L. James and Dinesh K. Pai, Staggered Projections for Frictional Contact in Multibody Systems, ACM Transactions on Graphics (SIGGRAPH ASIA Conference Proceedings), 27(5), December 2008, pp. 164:1-164:11.
Twigg and Doug L. James, Backward Steps in
Rigid Body Simulation, ACM Transactions on
Graphics (SIGGRAPH Conference Proceedings), 27(3),
August 2008, pp. 25:1-25:10.
Nils Thuerey, Doug L.
James and Markus
Gross, Wavelet Turbulence for Fluid
Simulation, ACM Transactions on Graphics
(SIGGRAPH Conference Proceedings), 27(3), August
2008, pp. 50:1-50:6.
Nicolas Bonneel, George Drettakis, Nicolas Tsingos, Isabelle Viaud-Delmon and Doug L. James, Fast Modal Sounds with Scalable Frequency-Domain Synthesis, ACM Transactions on Graphics (SIGGRAPH Conference Proceedings), 27(3), August 2008, pp. 24:1-24:9.
Jernej Barbič and Doug L. James, Six-DoF haptic rendering of contact between geometrically complex reduced deformable models, IEEE Transactions on Haptics, 1(1):39–52, 2008.
Waterfall: Animating Water Bottle Recycling Rates
This outreach animation was made to raise awareness about the surprisingly poor recycling rates of plastic water bottles.
and Doug L. James, Time-critical
distributed contact for 6-DoF haptic rendering of
adaptively sampled reduced deformable models, In Proceedings of ACM SIGGRAPH
Symposium on Computer Animation (SCA 2007), San
Diego, CA, August 2007. (Best paper award)
ABSTRACT: Real-time evaluation of distributed contact forces for rigid or deformable 3D objects is important for providing multi-sensory feedback in emerging real-time applications, such as 6-DoF haptic force-feedback rendering. Unfortunately, at very high temporal rates (1 kHz for haptics), there is often insufficient time to resolve distributed contact between geometrically complex objects.
Twigg and Doug L. James, Many-Worlds Browsing for
Control of Multibody Dynamics, ACM Transactions on Graphics
(Proc. SIGGRAPH 2007), 26(3), July 2007, pp.
ABSTRACT: Animation techniques for controlling passive simulation are commonly based on an optimization paradigm: the user provides goals a priori, and sophisticated numerical methods minimize a cost function that represents these goals. Unfortunately, for multibody systems with discontinuous contact events these optimization problems can be highly nontrivial to solve, and many-hour offline optimizations, unintuitive parameters, and convergence failures can frustrate end-users and limit usage. On the other hand, users are quite adaptable, and systems which provide interactive feedback via an intuitive interface can leverage the user’s own abilities to quickly produce interesting animations. However, the online computation necessary for interactivity limits scene complexity in practice.
|Alec R. Rivers and
Doug L. James, FastLSM:
Fast Lattice Shape Matching for Robust Real-Time
Transactions on Graphics (Proc. SIGGRAPH 2007),
26(3), July 2007, pp. 82:1-82:6.
ABSTRACT: We introduce a simple technique that enables robust approximation of volumetric, large-deformation dynamics for real-time or large-scale offline simulations. We propose Lattice Shape Matching, an extension of deformable shape matching to regular lattices with embedded geometry; lattice vertices are smoothed by convolution of rigid shape matching operators on local lattice regions, with the effective mechanical stiffness specified by the amount of smoothing via region width. Since the naive method can be very slow for stiff models--per-vertex costs scale cubically with region width--we provide a fast summation algorithm, Fast Lattice Shape Matching (FastLSM), that exploits the inherent summation redundancy of shape matching and can provide large-region matching at constant per-vertex cost. With this approach, large lattices can be simulated in linear time. We present several examples and benchmarks of an efficient CPU implementation, including many dozens of soft bodies simulated at real-time rates on a typical desktop machine.
Twigg, Andrew Cove
Y. Wang, Mesh Ensemble Motion Graphs:
Data-driven Mesh Animation with Constraints, ACM Transactions on Graphics,
26(4), October 2007, pp. 17:1-17:16.
ABSTRACT: We describe a technique for using space-time cuts to smoothly transition between stochastic mesh animation clips involving numerous deformable mesh groups while subject to physical constraints. These transitions are used to construct Mesh Ensemble Motion Graphs for interactive data-driven animation of high-dimensional mesh animation datasets, such as those arising from expensive physical simulations of deformable objects blowing in the wind. We formulate the transition computation as an integer programming problem, and introduce a novel randomized algorithm to compute transitions subject to geometric noninterpenetration constraints.
and Dinesh K. Pai,
Transfer: Output-sensitive, accurate sound generation
for geometrically complex vibration sources, ACM
Transactions on Graphics, 25(3), pp. 987-995, July
2006, pp. 987-995.
ABSTRACT: Simulating sounds produced by realistic vibrating objects is challenging because sound radiation involves complex diffraction and interreflection effects that are very perceptible and important. These wave phenomena are well understood, but have been largely ignored in computer graphics due to the high cost and complexity of computing them at audio rates. We describe a new algorithm for real-time synthesis of realistic sound radiation from rigid objects. We start by precomputing the linear vibration modes of an object, and then relate each mode to its sound pressure field, or acoustic transfer function, using standard methods from numerical acoustics. Each transfer function is then approximated to a specified accuracy using low-order multipole sources placed near the object. We provide a low-memory, multilevel, randomized algorithm for optimized source placement that is suitable for complex geometries. At runtime, we can simulate new interaction sounds by quickly summing contributions from each modes equivalent multipole sources. We can efficiently simulate global effects such as interreflection and changes in sound due to listener location. The simulation costs can be dynamically traded-off for sound quality. We present several examples of sound generation from physically based animations.
Twigg, Skinning Mesh Animations, ACM
Transactions on Graphics (ACM SIGGRAPH 2005), 24(3),
pp. 399-407, August 2005, pp. 399-407.
ABSTRACT: We extend approaches for skinning characters to the general setting of skinning deformable mesh animations. We provide an automatic algorithm for generating progressive skinning approximations, that is particularly efficient for pseudo-articulated motions. Our contributions include the use of nonparametric mean shift clustering of high-dimensional mesh rotation sequences to automatically identify statistically relevant bones, and robust least squares methods to determine bone transformations, bone-vertex influence sets, and vertex weight values. We use a low-rank data reduction model defined in the undeformed mesh configuration to provide progressive convergence with a fixed number of bones. We show that the resulting skinned animations enable efficient hardware rendering, rest pose editing, and deformable collision detection. Finally, we present numerous examples where skins were automatically generated using a single set of parameter values.
and Doug L. James, Real-Time Subspace Integration of
St.Venant-Kirchhoff Deformable Models, ACM
Transactions on Graphics (ACM
SIGGRAPH 2005), 24(3), pp. 982-990, August 2005, pp.
ABSTRACT: In this paper, we present an approach for fast subspace integration of reduced-coordinate nonlinear deformable models that is suitable for interactive applications in computer graphics and haptics. Our approach exploits dimensional model reduction to build reduced-coordinate deformable models for objects with complex geometry. We exploit the fact that model reduction on large deformation models with linear materials (as commonly used in graphics) result in internal force models that are simply cubic polynomials in reduced coordinates. Coefficients of these polynomials can be precomputed, for efficient runtime evaluation. This allows simulation of nonlinear dynamics using fast implicit Newmark subspace integrators, with subspace integration costs independent of geometric complexity. We present two useful approaches for generating low-dimensional subspace bases: modal derivatives and an interactive sketch. Mass-scaled principal component analysis (mass-PCA) is suggested for dimensionality reduction. Finally, several examples are given from computer animation to illustrate high performance, including force-feedback haptic rendering of a complicated object undergoing large deformations.
|Doug L. James and Dinesh K. Pai,
BD-Tree: Output-Sensitive Collision Detection for
Reduced Deformable Models, ACM Transactions on
Graphics (ACM SIGGRAPH 2004), 23(3),
pp. 393-398, August 2004, pp. 393-398.
ABSTRACT: We introduce the Bounded Deformation Tree, or BD-Tree, which can perform collision detection with reduced deformable models at costs comparable to collision detection with rigid objects. Reduced deformable models represent complex deformations as linear superpositions of arbitrary displacement fields, and are used in a variety of applications of interactive computer graphics. The BD-Tree is a bounding sphere hierarchy for output-sensitive collision detection with such models. Its bounding spheres can be updated after deformation in any order, and at a cost independent of the geometric complexity of the model; in fact the cost can be as low as one multiplication and addition per tested sphere, and at most linear in the number of reduced deformation coordinates. We show that the BD-Tree is also extremely simple to implement, and performs well in practice for a variety of real-time and complex off-line deformable simulation examples.
|Doug L. James, Jernej Barbic, and Christopher D. Twigg,Squashing Cubes: Automating Deformable Model Construction for Graphics, In Proceedings of the SIGGRAPH 2004 Conference on Sketches & Applications. ACM Press, August 2004.|
James and Kayvon
Fatahalian,Precomputing Interactive Dynamic
Deformable Scenes, ACM
Transactions on Graphics (ACM SIGGRAPH 2003), 22(3), pp. 879-887, 2003.
ABSTRACT: We present an approach for precomputing data-driven models of interactive physically based deformable scenes. The method permits real-time hardware synthesis of nonlinear deformation dynamics, including self-contact and global illumination effects, and supports real-time user interaction. We use data-driven tabulation of the system's deterministic state space dynamics, and model reduction to build efficient low-rank parameterizations of the deformed shapes. To support runtime interaction, we also tabulate impulse response functions for a palette of external excitations. Although our approach simulates particular systems under very particular interaction conditions, it has several advantages. First, parameterizing all possible scene deformations enables us to precompute novel reduced coparameterizations of global scene illumination for low-frequency lighting conditions. Second, because the deformation dynamics are precomputed and parameterized as a whole, collisions are resolved within the scene during precomputation so that runtime self-collision handling is implicit. Optionally, the data-driven models can be synthesized on programmable graphics hardware, leaving only the low-dimensional state space dynamics and appearance data models to be computed by the main CPU.
|Paul G. Kry,
Doug L. James
and Dinesh K. Pai,
EigenSkin: Real Time Large Deformation Character
Skinning in Hardware, ACM SIGGRAPH Symposium on
Computer Animation, pp. 153-160, 2002.
ABSTRACT: We present a technique which allows subtle nonlinear quasi-static deformations of articulated characters to be compactly approximated by data-dependent eigenbases which are optimized for real time rendering on commodity graphics hardware. The method extends the common Skeletal-Subspace Deformation (SSD) technique to provide efficient approximations of the complex deformation behaviours exhibited in simulated, measured, and artist-drawn characters. Instead of storing displacements for key poses (which may be numerous), we precompute principal components of the deformation influences for individual kinematic joints, and so construct error-optimal eigenbases describing each joint's deformation subspace. Pose-dependent deformations are then expressed in terms of these reduced eigenbases, allowing precomputed coefficients of the eigenbasis to be interpolated at run time. Vertex program hardware can then efficiently render nonlinear skin deformations using a small number of eigendisplacements stored in graphics hardware. We refer to the final resulting character skinning construct as the model's EigenSkin. Animation results are presented for a very large nonlinear finite element model of a human hand rendered in real time at minimal cost to the main CPU.
|Doug L. James
and Dinesh K. Pai,
DyRT: Dynamic Response Textures for Real Time
Deformation Simulation with Graphics Hardware, ACM Transactions on
SIGGRAPH 2002), 21(3), pp.
||Doug L. James and Dinesh K.
Pai, Real Time Simulation of Multizone
Elastokinematic Models, 2002 IEEE Intl.
Conference on Robotics and Automation, Washington
DC, May 2002.
ABSTRACT: We introduce precomputed multizone elastokinematic models for interactive simulation of multibody kinematic systems which include elastostatic deformations. This enables an efficient form of domain decomposition, suitable for interactive simulation of stiff flexible structures for real time applications such as interactive assembly. One advantage of multizone models is that each zone can have small strains, and hence be modeled with linear elasticity, while the entire multizone/multibody system admits large nonlinear relative strains. This permits fast capacitance matrix algorithms and precomputed Green's functions to be used for efficient real time simulation. Examples are given for a human finger modeled as a kinematic chain with a compliant elastic covering.
|Doug L. James and Dinesh K.
Pai, Multiresolution Green's Function Methods for
Interactive Simulation of Large-scale Elastostatic
Objects, ACM Transactions on
Graphics, 22(1), pp.
|Doug L. James, Multiresolution
Green's Function Methods for Interactive Simulation of
Large-scale Elastostatic Objects and other Physical
Systems in Equilibrium, Ph.D. Thesis, Institute of
Applied Mathematics, UBC, 2001.
|Dinesh K. Pai,
Kees van den
Doel, Doug L. James, Jochen Lang,John E. Lloyd,
L. Richmond, Som H. Yau, Scanning
Physical Interaction Behavior of 3D Objects, Proceedings
of ACM SIGGRAPH 2001, pp.
ABSTRACT: We describe a system for constructing computer models of several aspects of physical interaction behavior, by scanning the response of real objects. The behaviors we can successfully scan and model include deformation response, contact textures for interaction with force-feedback, and contact sounds. The system we describe uses a highly automated robotic facility that can scan behavior models of whole objects. We provide a comprehensive view of the modeling process, including selection of model structure, measurement, estimation, and rendering at interactive rates. The results are demonstrated with two examples: a soft stuffed toy which has significant deformation behavior, and a hard clay pot which has significant contact textures and sounds. The results described here make it possible to quickly construct physical interaction models of objects for applications in games, animation, and e-commerce.
|Doug L. James and Dinesh K. Pai,
A Unified Treatment of Elastostatic Contact
Simulation for Real Time Haptics, Haptics-e,
The Electronic Journal of Haptics Research (www.haptics-e.org),
Vol. 2, Number 1, September 27, 2001.
James and Dinesh K. Pai, ARTDEFO:
Accurate Real Time Deformable Objects, Proceedings
of ACM SIGGRAPH 99, pp.
ABSTRACT: We present an algorithm for fast, physically accurate simulation of deformable objects suitable for real time animation and virtual environment interaction. We describe the boundary integral equation formulation of static linear elasticity as well as the related Boundary Element Method (BEM) discretization technique. In addition, we show how to exploit the coherence of typical interactions to achieve low latency; the boundary formulation lends itself well to a fast update method when a few boundary conditions change. The algorithms are described in detail with examples from ArtDefo, our implementation.