
Christopher BattyAssistant ProfessorScientific Computation Group and Computer Graphics Lab David R. Cheriton School of Computer Science University of Waterloo Email: christopher.batty@uwaterloo.ca Office: 3605 Davis Centre (DC3605) I am always looking for talented students (and potentially postdocs) to join my lab. Recent news:

My research lies at the intersection of computer graphics and computational physics. My work has focused on various aspects of fluid animation, although
I am broadly interested in applying physical simulation as a fundamental tool for generating and predicting motion of all kinds. In my work, I strive to
design algorithms that are based on sound physical, mathematical, and geometric principles, while being amenable to efficient and robust implementation. Among other projects, I have developed methods for...
I created and continue to manage the PhysicsBased Animation blog, which catalogues papers, people, and software in this area. I have collected links to a few pieces of advice for students that you may find useful. 
Multimaterial MeshBased Surface Tracking F. Da, C. Batty, & E. Grinspun. To appear in ACM SIGGRAPH 2014 (Transactions on Graphics, 33(4), 2014). The first collisionsafe triangle meshbased surface tracking method for evolving multimaterial geometries, including strategies for multimaterial topological changes: merging, splitting, T1, and T2 processes. [PDF  High] [PDF  Low] [Project] [Video] [Code  Coming soon!] 

Discrete Viscous Sheets C. Batty, A. Uribe, B. Audoly, & E. Grinspun. ACM SIGGRAPH 2012 (Transactions on Graphics, 31(4), 2012). A method for animating thin sheets of highly viscous liquid, drawing on and extending techniques from the simulation of thin shells and cloth. [PDF] [Project] [Video] [Journal] 


A Simple Finite Volume Method for Adaptive Viscous Liquids C. Batty & B. Houston. ACM SIGGRAPH/Eurographics Symposium on Computer Animation 2011. An Eulerian approach to achieve higher detail animations of high viscosity liquid behaviour (buckling, coiling, etc.) on structured tetrahedral meshes. [PDF] [Video] 

A Simple Finite Difference Method for TimeDependent, Variable Coefficient Stokes Flow on Irregular Domains C. Batty & R. Bridson [arXiv preprint] 

Computational Physics in Film R. Bridson & C. Batty. Science 330(6012): 17561757. A perspective piece on the increasingly common use of physical simulation in visual effects for film, along with discussion of some major challenges that remain. [PDF] [Journal] 

Simulating Viscous Incompressible Fluids with Embedded Boundary Finite Difference Methods C. Batty. PhD Thesis, University of British Columbia. [PDF] [Thesis Repository] 

Matching Fluid Simulation Elements to Surface Geometry and Topology T. Brochu, C. Batty, & R. Bridson. ACM SIGGRAPH 2010 (Transactions on Graphics, 29(4), 2010). By adding simulation degrees of freedom exactly where they provide the most benefit, and using a triangle meshbased surface representation, we show how to achieve much greater detail in liquid animations. [PDF] [Project] [Journal] 

Tetrahedral Embedded Boundary Methods for
Accurate and Flexible Adaptive Fluids C. Batty, S. Xenos, & B. Houston. Eurographics 2010 (Computer Graphics Forum, 29(2), 2010). This paper demonstrates that combining embedded boundary methods with tetrahedrabased fluid simulation enables spatially adaptive liquid simulation with more accurate enforcement of air and solid boundary conditions. [PDF] [Project] [Journal] 

Accurate Viscous Free Surfaces for
Buckling, Coiling and Rotating Liquids C. Batty & R. Bridson. ACM SIGGRAPH/Eurographics Symposium on Computer Animation 2008. A simple method to enforce physically correct forces at the surface of viscous liquids, such as honey or syrup, which in turn lets us reproduce previously very difficult effects like buckling, coiling, and rotational motion. [PDF] [Project] [Journal] 

A Fast Variational Framework for Accurate
SolidFluid Coupling C. Batty, F. Bertails, & R. Bridson. ACM SIGGRAPH 2007 (Transactions on Graphics, 26(3), 2007). An optimizationbased framework for accurately incorporating irregularly shaped rigid objects into standard gridbased fluid simulations, eliminating spurious "stairstep" artifacts and leakage that plagued previous methods. [PDF] [Project] [Journal] 

Hierarchical RLE Level Set: A Compact and
Versatile Deformable Surface Representation B. Houston, M. Nielsen, C. Batty, O. Nilsson, & K. Museth. ACM Transactions on Graphics, 25(1), 2006. A compressed representation of level set implicit surfaces that avoids storing and processing irrelevant data far from the surface itself, allowing more efficient treatment of operations like morphing and liquid surface tracking. [PDF] [Project] [Journal] 

Regional Time Stepping for SPH P. Goswami & C. Batty. Eurographics Short Papers, 2014. A method to accelerate weakly compressible SPH simulations by exploiting spatially varying, asynchronous time integration. [PDF] 

Visual Simulation of Wispy
Smoke C. Batty & B. Houston. ACM SIGGRAPH Sketches, 2005. A description of the smoke simulation techniques used on Wes Craven's werewolf movie Cursed. [PDF] [Project] [Journal] 

Gigantic Deformable
Surfaces B. Houston, M. Nielsen, C. Batty, O. Nilsson, & K. Museth. ACM SIGGRAPH Sketches, 2005. A preview of the HRLE level set described more fully in the TOG paper above. [PDF] [Project] [Journal] 

RLE Sparse Level Sets B. Houston, M. Wiebe, & C. Batty. ACM SIGGRAPH Sketches, 2004. A compressed level set representation that was the precursor to the eventual HRLE level set above. [PDF] [Project] [Journal] 
Nonmanifold Simplicial Complex Mesh Library This is my own implementation of a nonmanifold simplicial complexbased mesh library, including arbitrary data associated to vertices, edges, triangles and tetrahedra. It's essentially my spin on the data structure outlined in "Building Your Own DEC at Home" with an API similar to "Design, Implementation, and Evaluation of the Surface_mesh Data Structure". The main goal is to allow nonmanifold geometry and mixed dimensional components (tets, tris, segments), while being relatively simple to manipulate. [GitHub link]  
3D Liquid Simulator code A minimal gridbased 3D liquid simulator and OpenGL viewer, using semiLagrangian advection, volumetric particles for the liquid, ghost fluid free surface conditions, and support for irregular solid boundaries using the variational/finitevolume approach from our SIG'07 paper. The only dependencies should be the GLUT library, so it's hopefully easy to set up and experiment with. Here's a sample clip. Update: I also added another version with our variational viscosity technique implemented in 3D. [Inviscid code, on GitHub] [With viscosity, on GitHub] 

2D Variational Viscosity code Sample code illustrating how to use our variational viscosity discretization to support rotation and buckling and variable viscosity within the liquid solver below. (The link for the comparable 3D code is above.) [Github link] 

2D Variational Pressure Projection code Sample codes illustrating how to use our variational pressure projection to support static irregular geometry within a very simple 2D "stable fluids" style fluid solver. Air  Single phase fluid solver with static obstacles. Liquid  Free surface liquid solver with static obstacles. This code combines our irregular solid boundary discretization with the 2nd order free surface pressure boundary condition of Enright et al. 2003. 

SDFGen: Signed Distance Field Generator for triangle meshes A simple commandline utility to construct a signed distance field from a triangle mesh, which is often useful for physicsbased animation, such as in processing collisions for rigid objects. [Github link] 

Watertight Stanford bunny I ran into some problems due to the holes in the bunny, and since I couldn't find a watertight version online, I made one myself (for noncommercial use, of course). It's also in OBJ format, rather than the original PLY. Thanks to the Stanford 3D Scanning Repository for the original model. 

2D Polygon Moment of Inertia Tensor
Code I couldn't find any convenient code for computing 2D inertia tensors from the vertices and edges of a simple polygon, so I adapted/specialized Michael Kallay's excellent 3D code from the Journal of Graphics Tools article Computing the Moment of Inertia of a Solid Defined by a Triangle Mesh. The article mentions how to handle 2D bodies, but the accompanying code supports only 3D objects. My code provides the corresponding 2D implementation, while retaining the speed, brevity, and clarity of the original. 

Higher Order Data Extrapolation in the Normal Direction A sample Matlab implementation of quadratic extrapolation in the normal direction of a function from a region defined by a given signed distance function into a surrounding undefined region, essentially following Ng et al. 2009, Min & Gibou 2007, and Aslam 2003. This can be useful for extrapolating known velocities from a fluid region into a solid region, such as in the Ghost Fluid Method, for example. [Buyer beware: I haven't actually rigourously verified the order of convergence.] 
For two years following my PhD (20112013) I was a postdoc in the Computer Science Department at the Columbia University in New York City, supported by an NSERC Banting Fellowship. My advisor was Dr. Eitan Grinspun.  
My PhD is from the Computer Science Department at the University of British Columbia in Vancouver, BC. I worked under the supervision of Dr. Robert Bridson, beginning in 2005 and defending in 2010. During my degree I consulted for Ottawabased Exocortex Technologies, and interned at Weta Digital in New Zealand, and Intel's Applications Research Lab in Santa Clara, California.  
Prior to my academic career, I spent 20042005 working at Frantic Films VFX (since bought by Prime Focus VFX), a Winnipegbased visual effects studio, where I was a Software Engineer in the Research and Development. My job was to develop physics tools for artists based on recent academic research, including smoke, water, and rigid and deformable bodies. These tools were used on various films, including Superman Returns, ScoobyDoo 2: Monsters Unleashed, and Cursed. (Much of the software division is now at Thinkbox Software.)  
I'm a graduate of the Computer Science Honours Coop program at the University of Manitoba, having completed my Bachelor of Computer Science degree in the fall of 2003. I also interned at OTI (original developers of Eclipse, now a subset of IBM) and Protegra, Inc.  