SIGGRAPH 2011 Talks – Part 3

This is the third and last in a series of posts about the SIGGRAPH 2011 Talk program – see Part 1 and Part 2. If you found these useful you may also want to check out my previous series of posts about the SIGGRAPH 2011 Courses program (see Part 1, Part 2, Part 3, and Part 4). These posts are not intended as a general SIGGRAPH survey – they are focused on content related to real-time rendering and game development.

Show Me The Pixels

Three of the talks in this session have possibly relevant content:

  • Slow Art With a Trillion Frames Per Second Camera – I guess this one stretches the definition of “relevant” somewhat, but I just find it extremely cool and interesting. The talk describes some research done at MIT (in collaboration between the Media Lab and Department of Chemistry) in which a “trillion frames per second camera” captures how pulses of light travel within a scene, including bouncing off surfaces and scattering inside objects. Besides the general coolness factor, this may impart some insight into light behavior which could be useful when working on shading and lighting models.
  • Device-Independent Imaging System for High-Fidelity Colors – color management (including display calibration, color space management of data, etc.) is important for both game and film production. It turns out that getting good device-independent color reproduction is far from simple. This talk covers some advances in this field by SHARP Corporation and Shizuoka University.
  • Who Do You Think You Really Are? – augmented reality is becoming an important technology for handheld games (see examples on the Nintendo 3DS and iPhone); this talk discusses an interactive media installation at London’s Natural History Museum (in partnership with BBC Television) which includes augmented reality elements.

Hiding Complexity

This entire session is comprised of game industry talks:

  • Occlusion Culling in Alan Wake – occlusion culling is a key technology for many games, especially first-person shooters. This talk discusses the occlusion culling system (developed by Umbra Software) used in the game Alan Wake by Remedy Entertainment. Topics include visibility culling as well as shadow-caster culling for dynamic light sources.
  • Increasing Scene Complexity: Distributed Vectorized View Culling – another talk on visibility culling, this time focusing on the technical issues involved in parallelizing culling computations on current game platforms. The talk is given by Electronic Arts Blackbox.
  • Practical Occlusion Culling in Killzone 3 – the third occlusion culling talk of the session focuses on the implementation used by Guerrilla Games for the game Killzone 3. This implementation uses PlayStation 3 SPUs to rasterize a conservative depth buffer, against which occlusion queries are performed.
  • High-Quality Previewing of Shading and Lighting for Killzone 3 – another Killzone 3 talk but unrelated to occlusion culling, this talk by Guerrilla Games covers a content creation framework which supports high-fidelity previews of assets in Autodesk Maya.

Smokin’ Fluids

The talks in this session (three from the film industry and one from the academic research community) cover topics related to smoke and fluid simulation. Such simulations are currently too costly to be feasible for most games, though games such as the LittleBigPlanet and PixelJunk Shooter series (both featured at SIGGRAPH this year) include two-dimensional versions. In VFX and CG animation work smoke, fluid and fire simulations are common, forming one of the key elements differentiating film and game visuals. I firmly believe that as game platforms increase in computational power, we will start seeing full 3D simulations of this kind in games.

  • DB+Grid: A Novel Dynamic Blocked Grid For Sparse High-Resolution Volumes and Level Sets – The author, Ken Museth, has a history of developing novel data structures for level set and volumetric data and applying them for VFX, first at Digital Domain and now at DreamWorks Animation. His data structures have been constantly improving, from DT-Grid to DB-Grid and now DB+Grid, which is described in this talk.
  • Capturing Thin Features in Smoke Simulations – In production simulation work, there is a constant tension between the need to speed up simulation times for faster iteration (which implies reducing the resolution of the simulation grid) and the desire to simulate finer detail (which implies increasing the resolution). This talk covers a system developed by Sony Pictures Imageworks that allows thin smoke features to be captured even with low resolution simulation grids.
  • Implicit FEM and Fluid Coupling on GPU for Interactive Multiphysics Simulation – typically distinct simulation methods are used for fluids, rigid objects, deformable objects, etc. This can pose problems when different types of objects can affect each other, which requires coupling different simulation methods. This talk from INRIA and Université de Grenoble covers a GPU-based method for coupled simulation of deformable objects and fluids – interestingly “screen-space collision” is mentioned as one of the techniques employed.
  • Correcting Low-Frequency Impulses in Distributed Simulations – production rendering is typically distributed over a large number of machines. It is desirable to do the same for simulations, but often this is difficult since the simulation domain is not easily separable – each part of the simulation affects all other parts. This talk from Side Effects Software (developers of Houdini) describes a method for distributing level-set fluid simulations while keeping them coupled via a shared low-resolution pressure projection.

Volumes and Rendering

All four talks in this session (three from the film industry and one from the academic research community) contain potentially relevant content:

  • Gaussian Quadrature for Photon Beams in “Tangled” – rendering lighting effects in participating media (often called “light beams” or “god rays”) is a common problem in games and film, typically solved with various hacks. A recent Transactions on Graphics (ToG) paper presented a comprehensive analysis of the problem as well as a new rendering approach called “photon beams” which is both physically correct and efficient – it appears potentially feasible for real-time implementation. This talk (with authors from the University of Central Florida, Disney Research Zürich, and Walt Disney Animation Studios – including the first author of the aforementioned ToG paper) presents an efficient implementation of the photon beams technique in Renderman, extending it to artist-specified non-physical light attenuation curves. A broader overview of the artist-driven volumetric lighting in Tangled (of which this work is a part) is given in a Technical Paper.
  • Importance Sampling of Area Lights in Participating Media – in principle, ray tracers like the Arnold rendering engine (developed by Solid Angle SL and used by Sony Pictures Imageworks, among others) solve the participating media lighting problem in a straightforward manner by sampling the underlying integrals. In practice, achieving noise-free images in reasonable time requires a lot of engineering effort, mostly relying on various forms of importance sampling. This talk (with authors from both Solid Angle and Imageworks) presents an importance sampling method for single scattering of light from arbitrary area lights in homogeneous participating media.
  • Decoupled Ray Marching of Heterogeneous Participating Media – after two talks on the relatively easy problem of lighting homogeneous participating media, this talk (also from Sony Pictures Imageworks) covers heterogeneous media such as smoke. It covers a method for speeding up ray marching by decoupling lighting calculations from the sampling of volume properties. Ray marching is amenable to real-time implementation since it is easy to scale down (albeit with reduced visual quality) by reducing the number of samples – several companies have demonstrated real-time implementations (though I’m not sure if any shipping games yet use it). The technique presented in this talk can make raymarching for volumetric lighting even faster, so is definitely of interest.
  • Demand-Driven Volume Rendering of Terascale EM Data -unlike the other talks in this session which focus on volumetric lighting, this talk (from King Abdullah University of Science and Technology and Harvard University) focuses on a different issue – rendering volumetric datasets which are too large to fit in memory. Given a good solution to this problem, games should be able to precompute volumetric effects in certain situations and stream them from disk, so this looks interesting.

Heads or Tails

Rigging game or movie characters for animation is a very tricky problem – the rig needs to be powerful enough to handle all needed motions and deformations, while also being easy to control either via hand-keying or motion capture. This session includes two CG feature animation talks and one research talk, all covering the rigging problem from different angles (note that the game industry talk Modular Rigging in Battlefield 3 has been cancelled). Character rigging is one of the areas where film and game production are quite similar – there are differences in scale and complexity, but even these are not so large as differences in say, triangle count or shader instructions.

  • Building the Birds of “Rio” – this talk covers the process and technology used at Blue Sky Studios to build control systems for the bird characters in the movie Rio – using the main character “Blu” as a case study.
  • “Kung Fu Panda 2”: Rigging a Peacock Tail – this talk describes the approach DreamWorks Animation used to create the tail rig for the peacock character in the film Kung Fu Panda 2.
  • Optimized Local Blendshape Mapping for Facial-Motion Retargeting -this talk from the Graphics Lab at the USC Institute for Creative Technologies details an automatic facial-motion retargeting method for blendshapes.

Speed of Light

Three of the talks in this session contain potentially relevant content:

  • Run-Time Implementation of Modular Radiance Transfer – Precomputed Radiance Transfer is a powerful rendering technique which has spun off many variations. This talk from Disney Interactive Studios, Disney Research Zürich, the University of Utah and the University of North Carolina at Chapel Hill covers a modular variant which enables warping and combining precomputed transport from a small library of simple shapes. The technique was implemented for platforms from mobile devices to high-end GPUs – the talk discusses various implementation issues involved.
  • Next-Generation Image-Based Lighting Using HDR Video – image-based lighting is becoming a key rendering technique in both film and games. This talk from Linköping University and Spheron VR describes a system for high-dynamic-range video capture, reconstruction, and modeling of real-world scenes for use in image-based lighting of synthetic objects placed in the scene.
  • Triple Depth Culling – real-time rendering applications such as games rely heavily upon hardware features such as hierarchical Z-culling for performance. However, this has some drawbacks – it requires either depth sorting or a previous depth prepass, and it doesn’t work well with shaders that modify depth. This talk proposes a technique to avoid these drawbacks – the authors show a pixel shader implementation, though for best performance they suggest that the technique be implemented in hardware. The talk abstract and video are both available online.

Capture and Construction

This session has one film talk of relevance: Building and Animating Cobwebs for Antique Sets. It describes a workflow used at DreamWorks Animation to model and animate cobwebs, including a specialized modeling tool, a physics-based solver, and a procedural-modeling engine. These types of specialized asset workflows can be extremely effective for games or movies which require many examples of a given kind of asset.

Light My Fire

This session has one game talk, as well as three relevant film talks:

  • Simulating Massive Dust in “Megamind” – in film production, there is a constant push for fluid simulations to continually increase in size and complexity, but the need for fine control by artists implies fast turnaround times. For this reason a lot of research and development is spent on making these simulations faster – research that I hope will eventually benefit real-time applications as well. This talk from t DreamWorks Animation covers a fast fluid simulation framework used for the movie Megamind. The presentation covers the specific numerical methods used to ensure efficiency and quality, as well as the setup and control framework that allowed artists to work efficiently.
  • “Megamind”: Fire, Smoke, and Data – another Megamind talk, this time focusing on the specific case study of an especially large and involved explosion effect. I like attending such “war story” talks – the most interesting film and game work is done when trying to push boundaries, and the solutions are often a mixture of technical cleverness and artistic inspiration.
  • Volumetric Effects in a Snap – grid-based simulation and volumetric rendering frameworks have become a staple of VFX and CG feature animation work; every studio has its own system with different strengths. I suspect similar systems will start cropping up in game studios when the hardware becomes a bit faster and memory capacities increase a bit more. This talk describes the creation of the “Snap” system developed at Animal Logic and used in the films Legend of the Guardians: The Owls of Ga’Hoole and Sucker Punch.
  • Fluid Dynamics and Lighting Implementation in PixelJunk Shooter 2 – games rarely incorporate fluid simulations – including 2D games, though current platforms can run two-dimensional simulations quite quickly. LittleBigPlanet notably incorporated 2D fluid simulations in its fire and smoke effects, but these did not affect gameplay. The game PixelJunk Shooter incorporated some very nice fluid-simulation-driven gameplay, including several types of fluids and gases that affected each other in different ways. The recent sequel expanded this gameplay element, adding some novel light/darkness gameplay as well. This talk from independent developer Q-Games covers the technical aspects of these elements.

Now that I’ve finished the courses and talks, my next few blog posts will cover the remaining SIGGRAPH 2011 programs.

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