I3D

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If you’re a member of ACM, you have access to about 1200 books online through Safari and Books24x7. Safari’s catalog is here, Books24x7 is here. Just login using your ACM ID & password. I can’t say the book selection is that exciting, some are half a decade old or older (bad for books about APIs), though there are few that might be of interest. If nothing else, there are some guides to popular packages and languages that might help you out.

Worth a reminder: if you’re an ACM SIGGRAPH member, you also get access to essentially all computer graphics papers in the ACM’s Digital Library. I took a peek today to see if the I3D 2012 papers were up yet (the conference runs this weekend) – no joy there, though 2011′s are available. At least, I’m pretty sure 2012′s are not up. Personally, I find their searcher kind of poor if you want to search through proceedings, but is otherwise serviceable for individual articles. As usual, Ke Sen Huang’s page is the place to go to get most of the latest articles (with no membership needed).

Oh, just to reel off some other free books that might be of interest: Autodesk’s “Imagine Design Create” book, a free PDF. More for designers but full of pretty pictures and there’s stuff on game graphic design, along with films and much else. If you’d rather have the coffee-table version, get it on Amazon.

Me, I just finished the crowd-sourced sci-fi “Machine of Death” compilation, which has nothing to do with computer graphics but was an interesting bedtime read. Free as an ebook or audiobook, or again in physical form from Amazon.

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Any Southern California game industry graphics people who weren’t planning to attend I3D this year might want to reconsider; there is a great deal on registration prices for the last day (this Sunday). Sunday has been packed with the most highly relevant content for game developers (though there is some great stuff in the previous two days as well), and there is a special one-day registration price of $125. This sum gets you a panel on sharing technical ideas in the games industry (moderated by Marc Olano – the panelists are Mike Acton, Mark DeLoura, Stephen Hill, Peter-Pike Sloan, Natalya Tatarchuk, and myself), as well as three paper sessions. These sessions include the following papers:

Besides the technical sessions, I3D is a great opportunity to meet and talk to some of the top experts in real-time graphics; if you’re local and not already planning to attend, I warmly recommend it.

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The Symposium on Interactive 3D Graphics and Games (I3D) has long been one of my favorite conferences. Best described as a “real-time focused mini-SIGGRAPH”, I3D is a typical smaller conference in that it’s single-track (no worries about overlapping sessions), and the attendance is low enough (around 200 people) that you have a hope of meeting and talking to most of the people.

This year, the conference schedule has been structured to be especially friendly to game developers that are either flying into San Francisco the previous week to attend GDC or that are based close to the conference venue in Costa Mesa. If you belong to either of these two groups, you would do well to include I3D in your plans – the content is very strong this year.

The first day of I3D overlaps GDC, but the organizers were kind enough to occupy that day with content primarily targeted at other industries; game developers who fly down from GDC to catch the last two days of I3D over the weekend will get almost all of the relevant content. This scheduling is also useful to local game developers who aren’t going to GDC, since they won’t need to miss a day of work.

I3D’s papers have typically been of high quality (on average much more likely to be useful to game developers than SIGGRAPH papers), and this year is no exception. As usual, Ke-Sen Huang has a preprints links page up, and most of the papers are already available.

The most interesting paper sessions for game developers in my opinion are “GPU Rendering” (with the papers A Reconstruction Filter for Plausible Motion Blur, Decoupled Deferred Shading for Hardware Rasterization, and Rectilinear Texture Warping for Fast Adaptive Shadow Mapping), “Surfaces and Textures” (with the papers Surface Based Anti-Aliasing, Efficient Pixel-Accurate Rendering of Curved Surfaces, and Multiresolution Attributes for Tessellated Meshes), and “Global Illumination and Ray Tracing” (with the papers Real-Time Bidirectional Path Tracing via Rasterization, Delta Radiance Transfer, and Fast, Effective BVH Updates for Animated Scenes). Other paper sessions with material of interest to game developers include “Scattering and Reflection” and ”Motion Capture and Animation”. All of these paper sessions are on the last two days.

Besides papers, I3D 2012 will also feature a keynote by Prof. Dinesh Pai (a prominent sensorimotor researcher at the University of British Columbia), a CAD industry talk by Mauricio Vives (a graphics software engineer at Autodesk), a banquet dinner including a talk by a yet-to-be-determined speaker from NVIDIA, poster presentations, and a game industry session (the details of which have not yet been announced, but from what I’ve heard it promises to be very good). All of these sessions except for the keynote are on the last two days.

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Ke-Sen Huang, who in a perfect world would be given a stipend just to maintain his wonderful pages, has been on the job collecting I3D 2012 papers. See them here.

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I3D 2011 Report

This report about I3D 2011 is from Mauricio Vives, a coworker at Autodesk; he also has photos from the symposium. The papers listing can be found at Ke-Sen Huang’s page and at the ACM Digital Library’s page (tabbed version here). The ACM site has some interesting info, by the way, such as acceptance rates and “most downloaded, most cited” for all I3D articles. I should also remind people: if you’re a member of ACM SIGGRAPH, you automatically have access to all SIGGRAPH-sponsored ACM Digital Library materials (which is essentially almost all their graphics papers).


In case you missed them, Naty’s reports (so far) about I3D are also on this blog: Keynote, Industry Session, and Banquet Talk.

Papers



Session: Filtering and Reconstruction


A Local Image Reconstruction Algorithm for Stochastic Rendering

In a stochastic rasterizer, effects like defocus (depth of field) and transparency need a very large number of samples (64 – 256) to remove noise and look decent. This paper describes a technique to remove the noise using far fewer samples, through sorting to selectively blur samples. The results look quite good, though it does have the disadvantage of blurring transparency.


Subpixel Reconstruction Antialiasing for Deferred Shading

The post-process MLAA antialiasing technique works to find sharp edges in an image and smooth them. It provides pretty good results. This technique (SRAA) is similar, but operates with supersampled depth and normal data to produce even better results with predictable performance. For example, it looks comparable to 16x SSAA (super-sampled antialiasing) in just 2 ms on a GTX 480 at HD resolution. As with MLAA, only single-sample shading is used, and it is compatible with deferred lighting. [The use of depth and normals means it is focused on geometric edge finding, so the technique is not applicable to shadow edges and NPR post-process thickened edges, for example. - Eric]


High Quality Elliptical Texture Filtering on GPU

Elliptical filtering is necessary for removing artifacts from some high-frequency textures, but is too slow for real-time applications. This is a technique for approximating true elliptical filtering using hardware anisotropic filtering. They claim it is easy to integrate, and they provide drop-in GLSL code to replace existing texture lookups.


Session: Lighting in Participating Media


Transmittance Function Mapping

This is about rendering light and shadow in participating media (e.g. fog, smoke) with single scattering. Two techniques are described: a faster one called volumetric shadow mapping for homogeneous media, and a slower one called transmittance function mapping for heterogeneous media. This is suitable for both offline rendering and interactive applications, but it is not quite real-time (> 30 fps) yet.


Real-Time Volumetric Shadows using 1D Min-Max Mipmaps

This is again about volumetric shadows, but with real-time results for homogeneous media, using only pixel shaders. A combination of epipolar warping on the shadow map, and a 1D min-max mipmap for storage, makes this possible. This is a pretty clever combination of techniques. [This paper was the "NVIDIA Best Paper Presentation".]


Real-Time Volume Caustics with Adaptive Beam Tracing

This is an extension of previous beam-tracing work to allow for real-time caustics, with receiving surfaces and volumes handled separately. A coarse grid of beams of refined based on the geometry and viewer to put detail where it is needed most. This enhancement is something an effect like caustics certainly needs to look good.


Session: Collision & Sound


Sound Synthesis for Impact Sounds in Video Games

This paper was motivated by having very little memory on a game console to store physics-based sounds, e.g. for footsteps or colliding objects. This uses a combination of modal synthesis and spectral modeling synthesis to produce extremely small sound definitions that could be varied on demand to provide a variety of believable effects. I don’t know much about sound generation, but the audio results (from the only audio paper in the conference) were very good.


Collision-Streams: Fast GPU-based Collision Detection for Deformable Models

Fast Continuous Collision Detection using Parallel Filter in Subspace

Both of these papers address the same problem: how to quickly perform continuous collision detection, which works by interpolating motion between time steps. I am a novice when it comes to collision detection, so I didn’t take away much from these.


Session: Shadows

This is the session that was most interesting to me, as I work on shadow algorithms.


Shadow Caster Culling for Efficient Shadow Mapping

This paper has a simple idea: when rendering a shadow map, cull objects that don’t produce a visible shadow to improve performance. Here occlusion culling is used to determine which objects are visible from the light source, and then these are rendered to produce a receiver mask in the stencil buffer. The stencil occlusion query operation can then be used to skip irrelevant objects. There are a few methods to render the receiver mask, trading off complexity and accuracy. This was mostly tested with city scenes, where it offered the same images at about 5x speed.


Colored Stochastic Shadow Maps

This included a nice overview of the problem, terminology, and existing techniques: how to render colored shadows from translucent objects? This extends existing techniques for rendering stochastic transparency to also support colored transparent shadows. It has a filter that can be adjusted for performance and quality, being based on stochastic techniques. The paper has simple explanations of the algorithm, and it seems from the presentation that this is fairly easy to integrate in a system that already handles basic stochastic shadow maps.


Sample Distribution Shadow Maps

This was the paper I was most interested in seeing, since it is an extension to cascaded shadow maps (CSM), a popular shadowing technique. The idea here is quite simple: reduce perspective aliasing with shadow maps by analyzing the distribution of samples visible to the viewer. This can be used to determine tight near/far planes for CSM partitions, and for tightly fitting the light frustum to just the visible shadow receivers.

The analysis requires a reduction operation, which can be done with rasterization (D3D9/10) or compute shaders (D3D11). Using this algorithm can result in sub-pixel sampling in many cases using a 2K shadow map; see the example below.


Session: Refraction & Global Illumination


Voxel-based Global Illumination

It wouldn’t be an interactive graphics conference without a paper about interactive global illumination, and here is one. The idea behind this technique is to create an atlas-based voxelization of the scene (every frame), and then perform fast ray casting into that grid. Direct lighting can be stored in the grid, or reflective shadow maps can be used; the latter seems to be preferred.

The technique is of course able to capture lighting and details that screen-space methods can’t. However, it can have artifacts that require a denser grid and a tuned offset to avoid self-intersections. Also, as noted earlier, it requires a texture atlas for generating the voxel grid. The results are interactive, if not quite real-time.


Real-Time Rough Refraction

Here the authors a solving the interesting, though somewhat specific, problem of rendering transparent materials (no scattering) with rough surfaces, which is different from translucent surfaces. Glossy reflection has been handled before; this is about glossy refraction. In this case, rays would be refracted twice, entering and exiting the surface, and this provides a fast way to perform what would otherwise be a double integration.

I wasn’t able to follow all of the math in this one, but the results are indeed real-time (> 30 fps), and comparable to what you would get out of a ray-tracer in dozens of seconds or minutes. There is also a cheap approximation for total internal reflection. This paper was selected as one of the best papers of the conference. An example with increasing roughness is shown below.


Screen-Space Bias Compensation for Interactive High-Quality Global Illumination with Virtual Point Lights

One of the problems with using virtual point lights (VPL) for global illumination is that you must apply a clamping above a certain amount of reflection to avoid pin-point light artifacts. This paper presents a fast way to compute the amount of light that was clamped away, which can then be added back to the VPL result. It is done in screen space, which can lead to some issues (as you might expect), but it is fully interactive and easy to integrate into other renderers that already have VPL.


Session: Human Animation

This is certainly not my area of expertise, so I only have a few comments about these papers.


Motion Rings for Interactive Gait Synthesis

This is human walking motion interpolation made more efficient, responding within a quarter-gait, which is necessary for interactive applications. It relies on a parameterized motion loop (called a “ring” here), and uneven terrain is handled with IK adjustments.


Realtime Human Motion Control with A Small Number of Inertial Sensors

This paper describes how to combine high-quality prerecorded motion capture data with live motion from just a few simple (noisy) sensors to enhance what would otherwise be very poor input. This is validated by comparing against the high-quality original data for motions like walking, boxing, golf swings, and jumping.


A Modular Framework for Adaptive Agent-Based Steering

Crowd simulations need hundreds of characters, but often lack local (per-person) intelligence. This paper presents a framework for dynamically choosing between one of several local steering strategies. This is able to handle fairly tight and deadlocked situations, such as two people walking toward each other down a narrow hall, though some of the resulting motion is awkward.


Session: Geometric and Procedural Modeling


Editable Polycube Map for GPU-based Subdivision Surfaces

This is an extension of previous “polycube map” work to allow transferring geometric detail from a high-resolution triangle mesh to subdivision surfaces. A simple modeling system was presented where the user creates a very coarse polycube and sketches a handful of correspondences between it and the high-resolution mesh. The results are really quite remarkable, and you can see the process below.


GPU Curvature Estimation on Deformable Meshes

It is not unusual to perform vertex skinning or iso-surface extraction on the GPU now. However, for some effects like ambient occlusion or NPR edge extraction, it is useful to have the mathematical curvature of the new surface, but this is slow or impossible to read back from the GPU. This paper presents a method for estimating curvature on the GPU in real-time, even for very detailed models, much faster than could be done on the CPU. [This paper was a "Best Paper - Honorable Mention".]


Urban Ecosystem Design

I have seen several papers at SIGGRAPH and elsewhere about procedurally generating urban environments: basically streets and buildings. This paper procedurally adds plants (mostly trees) to such urban layouts. City blocks are assigned a level of human “manageability” which determines how organized or wild the plants in that block will be. From there, growth and competition rules are applied. Only the city geometry is taken into account, so this can be used with systems where other information (like land use) is not available. It was implemented with CUDA, and as an example, it can simulate 70 years of growth for 250,000 plants in about two minutes.


Session: Interactivity and Interaction


Data Management for SSDs for Large-Scale Interactive Graphics Applications

Here “SSD” refers to solid-state disks, so this is about organizing a graphics database to allow for efficient out-of-core rendering using SSDs instead of traditional hard disks with spinning platters. Since SSDs don’t need data ordering, locally (as opposed to globally) optimized layouts work well with them. The presentation seem to be lacking in detail, but the demo was fairly impressive: a very large scene on disk being displayed and edited very smoothly with very little RAM. For any developers working with large graphics databases I would certainly recommend reading this paper for getting some ideas.


Coherent Image-Based Rendering of Real-World Objects

This paper attempts to generate a depth map from images captured from a few cameras. The goal is to build a virtual dressing room with a “mirror”: the mirror is a display that shows you with different virtual clothes on. The entire system runs with CUDA on a single machine with a single GPU, at interactive rates even with full body movement. It exploits frame coherence, i.e., reusing parts of previous frames, to reduce latency. This was surprisingly the only paper on image-based rendering, despite the first keynote (below) being entirely about IBR.


Slice WIM: A Multi-Surface, Multi-Touch Interface for Overview+Detail Exploration of Volume Datasets in Virtual Reality

Here WIM is “world in miniature,” a technique that presents a small version of a virtual environment to help the user navigate the environment. This paper extends the technique to aid in the visualization of complex volume data generated from slices, especially for medical imaging. The resulting system consists of a large main display, a smaller horizontal touch display through which the user can manipulate the view and slices, and a head-tracked VR display for the WIM. Better to just show you! [This paper was a "Best Paper - Honorable Mention".]


TVCG Papers

A few papers from IEEE Transactions on Visualization and Computer Graphics were also presented as “guests” of the conference. There didn’t seem as relevant, but I list them here:

  • Interactive Visualization of Rotational Symmetry Fields on Surfaces
  • Real-Time Ray-Tracing of Implicit Surfaces on the GPU
  • Simulating Multiple Character Interactions with Collaborative and Adversarial Goals
  • Directing Crowd Simulations Using Navigation Fields


Posters

I didn’t spend much time looking at the posters this year, but I did make note of a few that I would like to investigate further; see below. The full poster list is here [ACM Digital Library subscribers and SIGGRAPH members can download from here].

  • gHull: A Three-dimensional Convex Hull Algorithm for Graphics Hardware
  • Interactive Indirect Illumination Using Voxel Cone Tracing  [This was "Best Poster - Winner".]
  • Level-of-Detail and Streaming Optimized Irradiance Normal Mapping
  • Poisson Disk Ray-Marched Ambient Occlusion


Talks


Image-Based Rendering: A 15-Year Retrospective

This talk was given by Rick Szeliski from Microsoft Research. As the title implies, it was an overview of image-based rendering research, covering topics such as panoramas, image-based modeling, photo tourism, and (in particular) light fields. The fundamental problem of such research is determine how to make a scene from an existing one. At one point he mentioned that Autodesk “probably” has something for image-based modeling, and indeed we do; I sent that link to him after the conference. Naty Hoffman of Activision has a longer discussion of this talk in an earlier blog posting.


From Papers to Pixels: How research finds its way into Games

This talk by Dan Baker of Firaxis was a light “rant” about what researchers should do to get their research into games. For example, they need to consider quality and ease of integration, and realize that hardware advances will make certain techniques obsolete quickly. Most of it was reasonable, but it included a number of controversial points, in my opinion. For example, “nobody uses OpenGL” and there is too much research into GPGPU.

He also started out by stating that the vast majority of the research for I3D is for games, and that everything else is “boring”… calling out “3D CAD” in particular as boring! By the end, I was quite tempted to provide an on-the-spot rebuttal from the Autodesk perspective.


A Game Developer’s Wishlist for Researchers

Chris Hecker, formerly of Maxis, presented his opinion on almost the same topic, i.e. what game developers want from researchers – I liked it better. His priorities are robustness, simplicity, and performance, in that order, but researchers often make the mistake of putting performance first. The nature of interactivity means that robustness is absolutely critical. For example, you can’t afford errors even every few hundred frames when you are rendering 30 fps. He also states that papers frequently exclude negative results and worst-case scenarios, which would be helpful for assessing robustness.

I could say more, but Chris has the full talk available here. See for yourself why he says, “We are always about to fail.”


GPU Computing: Past, Present, and Future

This was the banquet talk, given by David Luebke of NVIDIA. It was a fairly light look at the state of GPU computing, where it has come and where it will go. A lot of it went against Dan Baker’s earlier comments about GPGPU, and David made sure to point that out (and I agree).

Some of this talk had the feel of a marketing presentation for NVIDIA’s CUDA and GPU computing products like Tesla, but it is hard to deny that this area is important. He cited several cases where GPU computing is saving lives, e.g. assisting in heart surgery, malaria treatment, and cancer detection. Of course, he also mentioned graphics, scientific computing, data mining, speech processing, etc. At one point he (amusingly) pointed out that all of this innovation and technology has its roots in humble VGA controller hardware.


Mobile Computational Photography

As someone who recently started going beyond point-and-shoot photography with a DSLR camera, this talk was quite interesting. Kari Pulli of Nokia described an API for controlling digital cameras called FCam… and it’s pretty cool what skilled hands are able to do with this. Note that this isn’t really about high-end cameras: the idea is to allow even cell phone cameras to take great photos.

FCam basically makes a supporting camera programmable, allowing you to do things that the camera normally can’t do. Most of it revolves around taking multiple images and combining them to produce a better result. For example, from his talk and the site:

… take two photos with different settings back-to-back. The first frame has a high ISO and short exposure time, and the second has a low ISO and longer exposure time. The first frame tends to be noisy, while the second instead exhibits blur due to camera shake. This application combines the two frames to create an output that’s better than either.

This is absolutely something I wish I could do with my current camera. Another example he showed was combining a few images with narrow depths of field into a single image with a wide depth of field (i.e. fully sharp). Another automatically took photos until one was captured with minimal camera shake, keeping only the “good” one. All of this is done right on the camera, which is a great improvement over the typical post-processing workflow, and it can leverage metadata that only the camera has.

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GDC has put a bit of a hiatus in my I3D posts; I better get them done soon so I can move onto the GDC posts.

This post describes a talk that David Luebke (Director of Research at NVIDIA) gave during the I3D banquet titled GPU Computing: Past, Present, and Future. Although the slides for the I3D talk are not available, parts of this talk appear to be similar to one David gave a few months ago, which does have video and slides available.

I’ll summarize the talk here; anyone interested in more detail can view the materials linked above.

The first part of the talk (which isn’t in the earlier version) covered the “New Moore’s Law”: computers no longer get faster, just wider; must re-think algorithms to be parallel. David showed examples of several scientists which got profound speedups – from days to minutes. He covered several different techniques, I’ll summarize the most notable four:

  1. A “photonic fence” that zaps mosquitoes with lasers, to reduce the incidence of malaria in third world countries. This application needs fast computer vision combined with low power consumption, which was achieved by using GPUs.
  2. A military vehicle which detects Improvised Explosive Devices (IEDs) using computer vision techniques. The speedup afforded by using GPUs enables the vehicle to drive much faster (an obvious advantage when surrounded by hostile insurgents) while still reliably detecting IEDs.
  3. A method for processing CT scans that enables much reduced radiation exposure for the patient. When running on CPUs, the algorithm was impractically slow; GPUs enabled it to run fast enough to be used in practice.
  4. A motion compensation technique that enables surgery on a beating heart. The video of the heart is motion-compensated to appear static to the surgeon, who operates through a surgical robot that translates the surgeon’s motions into the moving frame of the heart.

David started the next part of the talk (which is very similar to the earlier version linked above)  by going over the heritage of GPU computing. He did so by going over three separate historical threads: graphics hardware, supercomputing, and finally GPU Computing.

The “history of graphics hardware” section started with a brief mention of a different kind of hardware: Dürer‘s perspective machine. The history of electronic graphics hardware started with Ivan Sutherland’s SketchPad and continues through the development of the graphics pipeline by SGI: Geometry Engine (1982), RealityEngine (1993), and InfiniteReality (1997). In the early days, the graphics pipeline was an actual description of the physical hardware structure: each stage was a separate chip or board, with the data flow fixed by the routing of wires between them. Currently, the graphics pipeline is an abstraction; the stages are different threads running on a shared pool of cores, as seen in modern GPU designs such as the GeForce 8, GT200, and Fermi.

The second historical thread was the development of supercomputers. David covered the early development of three ways to build a parallel machine: SIMD (Goddard MPP, Maspar MP-1, Thinking Machines CM-1 and CM-2), hardware multithreading (Tera MTA) and symmetric multiprocessing (SGI Challenge, Sun Enterprise) before returning to Fermi as an example of a design that combines all three.

“GPU computing 1.0″ was the use (or abuse) of graphics pipelines and APIs to do general-purpose computing, culminating with BrookGPU. CUDA ushered in “GPU computing 2.0″ with an API designed for that purpose. The hardware supported branching and looping, and hid thread divergence from the programmer. David claimed that now GPU computing is in a “3.0″ stage, supported by a full ecosystem (multiple APIs, languages, algorithms, tools, IDEs, production lines, etc.). David estimated that there are about 100,000 active GPU compute developers in the world. Currently CUDA includes features such as “GPU Direct” (direct GPU-to-GPU transfer via a unified address space), full C++ support, and a template library.

The “future” part of the talk discussed the workloads that will drive future GPUs. Besides current graphics and high performance computing workloads, David believes a new type of workload, which he calls computational graphics, will be important. In some cases this will be the use of GPU compute to improve (via better performance or flexibility) algorithms typically performed using the graphics pipeline (image histogram analysis for HDR tone mapping, depth of field, bloom, texture-space diffusion for subsurface scattering, tessellation), and in others it will be to perform algorithms for which the graphics pipeline is not well-suited: ray tracing, stochastic rasterization, or dynamic object-space ambient occlusion.

David believes that the next stage of GPU computing (“4.0″) poses challenges to APIs (such as CUDA), to researchers, and to the education community. CUDA needs to be able to elegantly express programming models beyond simple parallelism, it needs to better express locality, and the development environment needs to improve and mature. Researchers need to foster new high-level libraries, languages, and platforms, as well as rethinking their algorithms. Finally, computer science curricula need to start teaching parallel computing in the first year.

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An industry session kicked off the second day of I3D (there were papers on the first day that I’m skipping over since I’ll do a paper roundup post later).

This session was comprised of two talks by game industry speakers – Dan Baker (Firaxis), and Chris Hecker (currently working on the indie game SpyParty). I’ll summarize each talk as well as the discussion that followed.

Dan Baker’s talk: “From Papers to Pixels: how Research Finds (or Often Doesn’t) its Way into Games”

Dan started by stressing that although most interactive graphics research has games as the primary target application, researcher’s priorities and the needs of the game industry are often misaligned. Game developers prize papers that enable increasing visual quality and/or productivity, describe techniques that are art-directable, and that inspire further work.

Dan complained that researchers appear to prize novelty over practicality. Often papers intended to inspire future research instead create things nobody needs, like a cheese grater-mousetrap combination (an actual patent registration). Papers are judged by other researchers who often lack the background needed to determine their utility.

As Dan pointed out, the vast majority of graphics papers over the years have not been used. He illustrated this by contrasting two papers which had citation rates wildly out of step with their actual real-world impact.

The first example was the progressive meshes paper – one of the most widely cited papers in the field, but it had very little practical impact. Why wasn’t it used? Dan identified three primary reasons:

  1. It solved an already solved problem – artists were already trained to create low-polygon models and weren’t looking for automatic tools which they couldn’t control and which would require changes to the tool chain. Building the mesh was a relatively small part of the art asset pipeline in any case.
  2. The process was fragile and the quality of the final result varied.
  3. Hardware advances rapidly reduced the importance of vertex and triangle throughput as bottlenecks.

In contrast, a paper on vertex cache optimization (written by the same author – Hughes Hoppe) had very low citation rates. However, it had a profound impact in practice. Almost every game pipeline implements similar techniques – it is considered professional negligence at this point not to. Why is this paper so heavily used by game developers?

  1. It was easy to implement and integrate into the asset pipeline.
  2. It did not impact visual quality.
  3. It increased performance across the board.
  4. It remained valuable in the face of ongoing hardware changes.

The reason papers languish is not developers apathy; if a paper offers promise of solving an important problem, game developers will try to implement it. Dan mentioned talking to graphics programmers at a game development conference shortly after the variance shadow maps paper was published – all of them had tried to implement it (although they eventually abandoned it due to artifacts). Dan gave three rules to help researchers seeking to do relevant research for game development:

  1. Hardware advances can rapidly render techniques irrelevant, but this can typically be predicted based on current trends.
  2. Give developers something they need – an incremental improvement to something useful is better than a profound advance in an esoteric area.
  3. Radical changes in the way things are done are difficult to sell.

Dan gave several examples of graphics research used by Firaxis in Civilization V (participating media, subsurface scattering, Banks and Ashikhmin-Shirley anisotropic BRDFs, wavelet splines, and smoothed particle hydrodynamics), and suggested that researchers interact more with game developers (via sabbaticals and internships). He ended by listing some areas he wants to see more research in:

  • MIP generation for linear reconstruction
  • Temporally stable bloom
  • Texture compression
  • Shader anti-aliasing
  • Better normal generation from height data
  • Better cloth shading

Chris Hecker’s talk: “A Game Developer’s Wish List for Researchers”

Chris recorded the audio of his talk, and has a flash animation of the slides synchronized to the audio (as well as separate downloads) on his website.

One comment Chris made resonated with me, although it was unrelated to the main topic of his talk. He said he thought games are around where films were in 1905 in terms of development. I’ve been looking a lot into the history of films lately, and that sounds about right to me – games still have a long way to go. Anyway, back to the theme of stuff game developers want from researchers. Chris stated that although it is commonly thought that the top (indeed only) priority for game developers is performance, the top three game technology priorities in his opinion are robustness, simplicity, and performance, in that order. He went into some more detail on each of these.

Robustness: this is important because of interactivity. Players can get arbitrarily close to things, look at them from different angles, etc. and everything needs to hold up. Chris describes several dimensions of robustness: what are the edge cases (when does it break), what are the failure modes (how does it break), what are the downsides to using the technique, is the parameter space simply connected (i.e. can you tweak and interpolate the parameters and get reasonable results), and are the negative results described (things the researchers tried that didn’t work). Published papers in particular have a robustness problem – when game developers try to implement them they typically don’t work. Page limits mitigate against a proper analysis of drawbacks, implementation tips, etc. Now that most journals and conference proceedings are going paperless, Chris claimed that there is no reason to have these restrictive page limits.

Simplicity: Chris stated that games are always at the edge of systemic complexity failure. If the toolchain is not on the edge of collapse, that means the game developers missed out on an opportunity to add more stuff. It’s the classic “straw that breaks the camel’s back” problem – the added complexity needed to implement a given technique might not seem large by itself, but the existing complexity of the system needs to be taken into account. If the technique does not provide a 10X improvement in some important metric, adding any complexity is not worth it. Simplicity, even crudeness, is a virtue in game development. Like robustness, simplicity also has many dimensions: are the implications of the technique explainable to artists, does it have few parameters, is the output intuitive, are the results art-directable, is it easy to integrate into the tools pipeline, what dependencies (code, preprocessing, markup, order, compatibility) does the technique have, etc.

Performance: As Chris described it, this is different than classic computer science performance. The constant matters, typically more than the O() notation. Researchers need to specify the time it takes for their technique to operate in milliseconds, instead of giving a frames-per-second count that is useless since it includes overheads for rendering some arbitrary scene. It’s important to discuss worst case performance and optimize for that, rather than for the average case. Researchers should not just focus on embarrassingly parallel algorithms, and should do real comparisons of their technique’s performance. A “real comparison” means comparing against real techniques used in practice, against real (typically highly optimized) implementations used in the field, using real inputs, real scenes and real working set sizes. The issue of “real scenes” in particular is more nuanced than commonly thought – it’s not enough to have the same triangle count as a game scene. Any given game scene will have a particular distribution of triangle sizes, and particular “flavors” of overdraw, materials, shadows, lighting, etc. that all have significant performance implications.

Chris talked about the importance of providing source code. Researchers typically think about their paper as being rigorous, and their source code as being “dirty” or “hacky”. However, the source code is the most rigorous description of the algorithm. You can’t handwave details or gloss over edge cases in source code. Availability of source code greatly increases the chance of games developers using the technique. Given that only a small fraction of papers are relevant to game developers (and a small fraction of those work as advertised), the cost of implementing each paper just to figure out if it works is prohibitively high.

As for what to research, Chris stated that researchers should avoid “solutions looking for problems” – they should talk to game developers to find out what the actual urgent problems are. If the research is in the area of graphics, it needs to integrate well with everything else. AI research is especially tricky since AI is game design; the algorithm’s behavior will directly affect the gameplay experience. In the case of animation research, it is important to remember that interactivity is king; the nicest looking animation is a failure if it doesn’t respond fluidly to player commands. Perceptual models and metrics are an important area of research – what is important when it comes to visuals?

Chris ended his talk with a few miscellaneous recommendations to researchers:

  • Don’t patent! If you do, warn us in the abstract so we can skip reading the paper.
  • Put the paper online, not behind a paywall.
  • Publish negative results – knowing what didn’t work is as important as knowing what did.
  • Answer emails – often developers have questions about the technique (not covered in the paper due to page limits).
  • Play games! Without seeing examples of what games are doing now, it’s hard to know what they will need in the future.

Following discussions:

These two talks sparked lots of discussion in the Q&A sections and during subsequent breaks. The primary feeling among the researchers was that game developers have a very one-sided view of the relationship. While researchers do want their research to have a practical impact, they also have more direct needs, such as funding. Computer graphics research used to be largely funded by the military; this source dried up a while ago and many researchers are struggling for funding. If it’s true that games are the primary benefactor of research into computer graphics research, shouldn’t the game industry be the primary funding source as well?

Regarding the use of “real” data, most of the researchers are anxious to do so, but very few game companies will provide it! Valve is a notable exception, and indeed several of the papers at I3D used level data from Left 4 Dead 2. More game developers need to provide their data, if they hope for research which works well on their games.

Companies in other industries do a much better job of working with academic researchers, establishing mutually beneficial relationships. Industry R&D groups (Disney Research, HP Labs, Adobe’s Advanced Technology Labs, Microsoft Research, Intel Research, NVIDIA Research, etc.) are a key interface between industry and academia; if more game companies established such groups, that could help.

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Provided by Mauricio Vives: feast your squinties. Lots of headshots, which I’m sure the speakers (and their moms) will appreciate. I certainly do; it’s great putting a face to a name.

Also, save the date: as the last slide shows, March 9-11 2012 is the next I3D, in Costa Mesa, California. I’m suitably impressed that next year’s co-chairs (Sung-Eui Yoon and Gopi Meenakshisundaram) already have a place and date. This was possible since they’re colocating I3D to directly follow IEEE VR, which is March 4-8.

One photo, “Carlo’s Models“:

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Today was the first day of I3D 2011. I3D (full name: ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games) is a great little conference – it’s small enough so you can talk to most of the people attending, and the percentage of useful papers is relatively high.

I’ll split my I3D report into several smaller blog posts to ensure timely updates; this one will focus on the opening keynote.

The keynote was titled “Image-Based Rendering: A 15-Year Retrospective”, presented  by Richard Szeliski (Microsoft Research), who’s been involved with a lot of the important research in this area. He started with a retrospective of the research in this area, and then followed with a discussion of a specific application: panoramic image stitching. Early research in this area lead to QuickTime VR, and panoramic stitching is now supported in many cameras as a basic feature. Gigapixel panoramas are common – see a great example of one from Obama’s inaugural address by Gigapan (360 cities is another good panorama site). Street-level views such as Google Street View and Bing’s upcoming Street Slide feature use sequences of panoramas.

Richard then discussed the mathematical basis of image-based rendering: a 4D space of light rays (reliant on the fact that radiance is constant over a ray – in participating media this no longer holds and you have to go to a full 5D plenoptic field). Having some geometric scene information is important, it is hard to get good results with just a 4D collection of rays  (this was the main difference between the first two implementations – lumigraphs and light fields). Several variants of these were developed over the years (e.g. unstructured lumigraphs and surface light fields).

Several successful developments used lower-dimensional “2.5D” representations such as layered depth images (a “depth image” is an image with a depth value as well as a color associated with each pixel). Richard remarked that Microsoft’s Kinect has revolutionized this area by making depth cameras (which used to cost many thousands of dollars) into $150 commodities; a lot of academic research is now being done using Kinect cameras.

Image-based modeling started primarily with Paul Debevec’s “Facade” work in 1996. The idea was to augment a very simple geometric model (which back then was created manually) with “view dependent textures” that combine images from several directions to remove occluded pixels and provide additional parallax. Now this can be done automatically at a large scale – Richard showed an aerial model of the city of Graz which was automatically generated in 2009 from several airplane flyovers – it allowed for photorealistic renders with free camera motion in any direction.

Richard also discussed environment matting, as well as video-based techniques such as video rewrite, video matting, and video textures. This last paper in particular seems to me like it should be revisited for possible game applications – it’s a powerful extension of the common practice of looping a short sequence of images on a sprite or particle.

Richard next talked about cases where showing the results of image-based rendering in a less realistic or lower-fidelity way can actually be better – similar to the “uncanny valley” in human animation.

The keynote ended by summarizing the areas where image-based rendering is currently working well, and areas where more work is needed. Automatic 3D pose estimation of the camera from images is pretty robust, as well as automatic aerial and manually augmented ground-level modeling. However, some challenges remain: accurate boundaries and matting, reflections & transparency, integration with recognition algorithms, and user-generated content.

For anyone interested in more in-depth research into these topics, Richard has written a computer vision book, which is also available freely online.

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Ke-Sen’s I3D 2011 papers page now has the full list. At the moment there are only 8 author preprints available out of 24 papers, but I’m sure more will appear soon. Some of the paper titles look very intriguing – I’ll write a followup blog post about them soon.

In addition, the I3D conference registration page is now up. Early registration prices range from $200-550, depending on whether you are a student, ACM member, etc. Judging from previous years, the quality of the conference is likely to be well worth the cost of attending, especially if you live in the San Francisco Bay Area and don’t have to worry about airfare and hotels.

The conference registration page also has details on hotel registration – the conference is at the Marriott Fisherman’s Wharf in San Francisco and there is a discount rate ($129 per night, only guaranteed until Jan 21, 2011). There are two ways to book a room with the discount rate:

  1. By phone: call 1-800-525-0956 and ask for the ACM Group rate.
  2. Online: go to the hotel registration webpage, enter your arrival/departure dates, Marriott reward number (if applicable), and then one of the following three codes in the ‘Group code’ option: ASSASSA (for single/double occupancy), ASSASSB (for triple occupancy), or ASSASSC (for quadruple occupancy).

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