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Associate Professor

Graphics and Parallel Systems(GAPS) Lab
State Key Lab of CAD&CG
Zhejiang University
Email:  [first name][last name] [at] acm [dot] org 
      
Before returning to Zhejiang University to co-found the Graphics and Parallel Systems (GAPS) Lab with Prof. ZHOU Kun in Apr. 2010, I spent a happy five years in the Internet Graphics Group, Microsoft Research Asia, first as an intern then as an associate researcher. I received my Ph.D degree in computer science from Zhejiang University in March, 2007. I also hold a Master's degree in mechanical engineering and a Bachelor's degree in information engineering, both from Zhejiang University. My research interests include real-time rendering of soft shadows and participating media, spherical harmonics for real-time rendering, and real-time global illumination on GPUs.  My Ph.D thesis (in Chinese, with English abstract) is about precomputation-based methods in interactive global illumination. During the past several years, I've been really fortunate to work with my collaborators on the interesting graphics projects below. That's really a lot of fun.

In my spare time, I like Chinese calligraphy, music, and swimming.


Professional Activities
  • IPC member: Pacific Graphics 2010, 2013
  • reviewer: ACM SIGGRAPH 2012-2013, ACM SIGGRAPH Asia 2008/2010-2013, IEEE Vis 2010, PG 2009-2012, EG 2009,2014, HPG 2013, ESPGV 2011, Euro-Par 2013, TVCG, TOG, CGF, C&G, NSFC, JCAD.
Research Publications
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Cone Tracing for Furry Object Rendering
IEEE Transactions on Visualization & Computer Graphics © (to appear) IEEE
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cone tracing furry objects Overview
  • using cone tracing for hair/fur
  • approximate away in-cone variation of shading, opacity and occlusion of samples
  • form reflection/refraction cones using ray differential
Highlights
  • significant reduce rendering the time needed for generating noise free results due to reduced required supersampling rate
  • DOF, motion blur, reflection/refraction of fur/hair are natually supported
  • easy to integrate into existing ray tracing framework
Limitations
  • not suitable for rendering of thick fur strands
  • large cones bring down performance, as they may intersect large number of strands
  • motion blur support is preliminary

downloadable:

paper, video(58.5MB)
Analytic Double Product Integrals for All-Frequency Relighting
IEEE Transactions on Visualization & Computer Graphics © IEEE
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analytic double product integrals Overview
  • depict the boundaries of visible regions using piecewise linear functions
  • convert the shading computation into double product integrals
  • approximate the double product using Legendre polynomials locally in visible regions
Highlights
  • improve the shadow accuracy of existing real-time all-freq PRT method
  • triple product decomposed to a number of double products in the visible regions
  • on-the-fly extraction of visible regions from spherical signed distance functions (SSDFs)
Limitations
  • limited ability to handle complex visibility due to interpolations of SSDFs
  • currently no support for dynamic scenes

downloadable:

paper(1.4MB), supplements(334KB), multimedia, bibtex
Scalable Programmable Motion Effects on GPUs
Pacific Graphics 2012 (Computer Graphics Forum) © Eurographics and Blackwell
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scalable programmable motion blur Overview
  • process multiple frames of a pixel in parallel to maximize exploitable coherence
  • reduce required trace resampling rate using a parallel analytical visibility algorithm
  • precompute and store the intersections of view rays and the moving object to improve the runtime performance
Highlights
  • programmable motion blur made more practical
  • improved performance for rendering programmable motion blur for an order of magnitude
  • scalable to large scenes consist of hundreds of moving characters
Limitations
  • mesh connectivity requires to be constant
  • currently no support for shadows, reflections and refractions

downloadable:

divx(31.7MB), bibtex
Animating Bubble Interactions in a Liquid Foam
SIGGRAPH 2012 (ACM TOG) © ACM
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bubble teaser Overview
  • a more accurate and efficient particle-based algorithm to simulate bubble dynamics and interactions
  • an approximation of foam geometry, by treating bubble particles as the sites of a weighted Voronoi diagram
  • a set of bubble interaction forces to handle miscellaneous foam behaviors
Highlights
  • explicitly address the volume loss issue in foam simulation
  • accurately model various interaction effects among bubbles
Limitations
  • does not handle bubble surface deformation, therefore not suitable for large bubbles
  • nonlinear interaction forces in the real world cannot be modelled

downloadable:

preprint, mp4(97.5MB), bibtex
TransCut: Interactive Rendering of Translucent Cutouts
IEEE Transactions on Visualization & Computer Graphics ©IEEE
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transcut teaser Overview
  • discretize diffusion equation based on discrete divergences and derive analytic formulas can be derived for DE matrix elements
  • multi-resolution GPU DE solver that adapts to the frequent changes in topological structure of dynamic objects
  • enables interactive rendering of translucent cutouts
Highlights
  • allows interactive topology changes of translucent object
  • similar accuracy as the FEM solver based on Guassian quadrature integration
Limitations
  • per-vertex shading, representable details limited by mesh resolution
  • controlling of tetra aspect ration is required durring the cut

downloadable:

        preprint (2.1MB), paper (mov)(24.4MB), kinect interaction (mov)(6.3MB), bibtex
Interactive Rendering of Non-Constant, Refractive Media Using the Ray Equations of Gradient-Index Optics
EGSR 2010 (Computer Graphics Forum) © Eurographics and Blackwell
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gio teaser Overview
  • introduce the analytic form of non-linear rays in refractive media with constant refractive index gradient, based on which a ray tracing algorithm is developed;
  • extend the algorithm to general non-constant refractive media through tetrahedra-based representation or voxel-based representation;
  • derive the analytic form of non-linear rays in mirages.
Highlights
  • analytic forms of rays and fold points;
  • larger tracing steps, leading to superior performance.
Limitations
  • no simple analytic form for ray-scene intersections, need to resort to numeric methods;
  • piece-wise linear approxiation of refractive index function, may require impractical large number of tetra for very complex functions.

downloadable:

       preprint(3.7MB), avi(58.1MB), slides(40.9MB), bibtex
Interactive Hair Rendering Under Environment Lighting
SIGGRAPH 2010 (ACM TOG) ©ACM
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hair teaser Overview
  • decouple light integration complexity from light transport complexity;
  • model environment light with a set of SRBFs;
  • address light integration complexity by precomputation;
  • handle self shadowing by convolution optical depth map;
  • handle mutiple scattering by dual scattering and sparse sampling and interpolation.
Highlights
  • the first interactive hair rendering algorithm under environment lighting;
  • support light animation;
  • support dynamic hair volume.
Limitations
  • precomputation per scattering function;
  • ignore eccentricity in the scattering function.

downloadable:

        preprint, avi(35.2MB), slides(30.1MB), bibtex
Radiance Transfer Biclustering for Real-time All-frequency Bi-scale Rendering
IEEE Transactions on Visualization & Computer Graphics ©IEEE
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biclustering teaser Overview
  • tabulate per-vertex transfer from global incident directions to local incident directions;
  • use biclutering to directly compress the transfer matrix.
Highlights
  • all-frequency biscale transfer, support highly-detailed surface under env-lighting;
  • high compression ratio with no quality lost;
  • operates directly on pixel basis, fully dynamic env-lighting can be directly supported.
Limitations
  • static scene geometry;
  • rather costly pre-computation(~1 hour).

downloadable:

        abstract, preprint(8.3MB), mov(42.8MB), bibtex
RenderAnts: Interactive Reyes Rendering on GPUs
SIGGRAPH ASIA 2009 (ACM TOG) ©ACM
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renderants teaser Overview
  • move all stages of basic Reyes pipeline to GPU;
  • introduce a dynamic stage scheduling algorithm to maximize the available parallelism at each individual stage of the pipeline while keeping data in GPU memory;
  • minimize inter-GPU communication by a multi-GPU scheduling algorithm based on work stealing, which can be easily combined with the stage scheduling algorithm above;
  • implemented with BSGP.
Highlights
  • could be the fastest Reyes renderer on PCs;
  • support multi-GPU and out-of-core texture;
  • quality is comparable with PRMan.
Limitations
  •  system will fail if the grids and their bounding boxes do not fit into the vram;
  • currently only support basic Reyes features. no ray tracing, no photon mapping...(coming soon)

downloadable:

        tech report(6.2MB), preprint, wmv(50.8MB),  slides(26.8MB) bibtex
       source code,   test scenes
Gradient-based Interpolation and Sampling for Real-time Rendering of Inhomogeneous, Single-scattering Media
Pacific Graphics 2008 (Computer Graphics Forum) © Eurographics and Blackwell
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gradient teaser Overview
  • accurately evaluate source radiance and its gradient at a relative small number of  sample points in the volume, and use gradient-based interpolation to approximate the source radiance elsewhere;
  • sample the interpolation error in the valid sphere of each sample, and dynamically splitting those with higher estimated error on a hierarchical grid structure.
  • use source radiance splatting to construct the source radiance volume, followed by a ray march to  yield the radiance to the view.
Highlights
  • all-frequency lighting effects such as light shaft, volumetric shadows and inhomogeneous glowing;
  • editable media property;
  • good scalability with regard to volume resolution and number of lights;
  • precomputation can be avoided for analytical medium representations.
Limitations
  • single-scattering only (though it's possible to be combined with the technique below to incorporate multiple-scattering);
  • constant phase function.

downloadable:

        preprint(5.8MB), video(34.6MB), slides(42.1MB), bibtex
Real-time Rendering of Smoke using Compensated Ray Marching
SIGGRAPH 2008 (ACM TOG) ©ACM
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smoke teaser Overview
  • as a preprocess, decompose density field into an analytical low-freq RBF representation and a residual field which can be compressed by perfect spatial hashing;
  • evaluate source radiance at RBF centers, taking into account only the RBF representation;
  • use SHEXP to accelerate single scattering computation, and BSGP to accelerate multiple scattering;
  • compensate for the residuals in the final ray marching pass.
Highlights
  • fast smoke rendering with single/multiple scattering effects and fine details;
  • editable smoke property;
  • moderate preprocessing time, less than an hour for a 600-frame animation.
Limitations
  • low-frequency lighting, can't handle strongly directional phase functions;
  • can't handle real dynamic medium due to the need for precomputation.

downloadable:

preprint, video(42.2MB), slides(31.9MB), bibtex

original smoke data:  rising bunny(1.5GB), dragon head(443MB)
scholarly use of the data is automatically granted without permission. the freely evolving smoke data used in the paper and video is from the authors of [Shi and Yu 2005], so it is not shared here. the format of the binary data: volume resolution(4 bytes) + number of frames(4 bytes) + sequence of density volumes. note that for some reason the data is split into files of 2GB or smaller and there's no headers for the files other than the first one.
Real-time Soft Shadows in Dynamic Scenes using Spherical Harmonic Exponentiation
SIGGRAPH 2006 (ACM TOG) ©ACM
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shexp teaser Overview
  • approximate block geometry with sphere blockers;
  • accumulate tabulated sphere SH visibilities, in log space;
  • approximate SH exponentiation by an optimal linear model + DC isolation & scaling/squaring techniques;
  • use sphere hierarchy + receiver clustering to accelerate run-time computation.
Highlights
  • fast rendering of soft shadows of skin-animated characters;
  • very small precomputation cost: the tabulation of the log visibility of a unit sphere is reused for all sphere blockers, and the sphere approximation for a rest pose of a character is skin-animated with the geometry.
Limitations
  • low-frequency lighting, very soft shadows;
  • can't support generic local lighting.
  • per-vertex shading, shadow quality and performance depend on model triangulation. (an extension to per-pixel shading by Peter-Pike Sloan et al. is available)

downloadable:

preprint, video(49.7MB), slides(31.9MB), supplements(3.1MB), test data#1(tumbling man)(8.9MB), test data#2(walking man)(5.2MB), test data#3(slipped walking man)(1.5MB), test data format, bibtex

note that the physical meaning of the term "log visibility" has been made clear in our smoke paper, and that is the negative optical depth. for opaque surfaces, the optical depth is infinite if the visibility is 0, and 0 if the visibility is 1.
Intersection Fields for Interactive Global Illumination
Pacific Graphics 2005 (The Visual Computer) ©Springer-Verlag
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ifield teaser Overview
  • tabulate the intersection of scene geometries in a 4D line space to form i-fields;
  • use visibility query & splatting in parameter space to accelerate run-time computation;
  • use photon splatting in parameter space to compute indirect bounces.
Highlights
  • visibility query made fast;
  • fast scan-line conversion for i-field generation;
  • reuse i-field for object instancing and object transformation.
Limitations
  • no compression, scalability is low;
  • limited shadowing feature reprensentability due to line space resolution.

downloadable:

preprint(0.6MB), video(11.9MB), slides(0.3MB), bibtex

A Survey on Real-time Rendering Algorithms for Dynamic Scenes under Complex Environment Lighting
Journal of Computer Aided Design ©jcad
(in Chinese, with English abstract. click to toggle details)
Complex environment lighting has been increasingly used in interactive graphics applications, such as games, to provide higher realism compared to conventional artificial light sources. This paper surveys the real-time rendering algorithms for dynamic scenes under complex environment lighting, and tries to characterize these algorithms by reviewing their base techniques, assumptions, limitations and range of utilization. Especially, we try to point out the main course of future research in this domain by analyzing the underlying relationships between the different algorithms.

downloadable:

paper(7.6MB)

REN Zhong, 2013.12.31.