July 2009

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When discussing things to do and see at SIGGRAPH, it is important to note the co-located conferences.  This year, SIGGRAPH is co-located with the Eurographics Symposium on Sketch-Based Interfaces and Modeling (SBIM), the Symposium on Computer Animation (SCA), Non-Photorealistic Animation and Rendering (NPAR), and High-Performance Graphics (HPG).  SCA has had good animation papers over the years, and is of interest to many game graphics programmers. NPAR is also a good conference for anyone interested in stylized rendering.  In this post I will focus on HPG, which is a new conference formed out of the merger of the venerable Graphics Hardware conference, and the newcomer Symposium on Interactive Ray Tracing.

HPG is a three-day conference; the first two days are just before SIGGRAPH, and the third overlaps the first day of SIGGRAPH (unfortunately conflicting with the excellent SIGGRAPH course, Advances in Real-Time Rendering in 3D Graphics and Games).

HPG has managed to line up two pretty amazing keynotes.  The first one is by Larry Gritz on film production rendering.  Larry is a legend in the field; he was with Pixar from the Toy Story days, and co-wrote one of the most well-regarded books on Renderman.  He since worked on several important renderers (BMRT, Gelato), and is now at Sony Pictures Imageworks.  The second keynote is by Tim Sweeney, on the future of GPUs.  As the outspoken chief architect of Epic’s Unreal Engine, Tim should need no introduction.

At the end of the conference, the two keynote speakers are joined by Steve Parker (NVIDIA) and Aaron Lefohn (Intel) for a panel on high-performance graphics in 7 year’s time.

HPG also has posters and “Hot 3D” systems presentations (hardware manufacturers talking about their latest designs).  Inexplicably, although the acceptance deadline for both has long since passed, the content of neither of these is listed on the conference website yet.

I briefly discussed HPG papers in a previous post, but then only paper titles were available, making it hard to judge relevance; now many of the papers have preprints linked from Ke-Sen Huang‘s HPG 2009 papers page.

Some of the papers look relevant to current or near-future work.  There are two interesting antialiasing papers: Morphological Antialiasing was covered by Eric in a recent post.  The other antialiasing paper (A Directionally Adaptive Edge Anti-Aliasing Filter) does not have a preprint, but the title is promising.  It is notable that one of the authors on this paper (Jason Yang) is listed as a speaker at the SIGGRAPH Advances in Real-Time Rendering in 3D Graphics and Games course; perhaps he will discuss the paper there.  Although the NVIDIA paper Image Space Gathering has no preprint (yet), some information on this technique was disclosed at GDC: it involves rendering reflections and shadows into 2D buffers and then performing cross bilateral filters to mimic glossy reflections and soft shadows.  I have seen similar techniques used in games, so it will be interesting to hear NVIDIA’s take on this concept.  Another promising paper title: Scaling of 3D Game Engine Workloads on Modern Multi-GPU Systems.

The paper Parallel View-Dependent Tessellation of Catmull-Clark Subdivision Surfaces deals with tessellation using GPGPU methods rather than the DX11 tessellation pipeline; I’m not an expert in this area so it’s hard for me to judge, but it might be of interest for people working in this field.

I’m a bit skeptical of depth peeling techniques in general, but recent work in this area has shown some promise.  The paper Bucket Depth Peeling lacks a preprint at this moment, but I look forward to learning more about it at the conference.

I found the title Data-Parallel Rasterization of Micropolygons With Defocus and Motion Blur promising because I am interested in the REYES micropolygon algorithm, and particularly in the way it handles defocus and motion blur effects.  The technique presented in this paper appears to be less efficient than the REYES method, except for cases with very high velocity and/or defocus.  The paper presents a GPU-efficient version of the REYES algorithm as well as an alternative algorithm which is faster in some cases.  One of the authors has a blog post that gives some interesting context for the paper.

The amount of actual graphics hardware papers at the Graphics Hardware conference has been declining for years, which is probably one of the factors that precipitated the conference merger with IRT.  This year there is only one paper which is clearly about hardware design: PFU: Programmable Filtering Unit for Mobile Multimedia Applications on Graphics Hardware.  It has a fairly self-explanatory title, which is fortunate since it has no preprint available.  Texture filtering is the last unassailable bastion of fixed-function hardware; for example, it is the only fixed-function unit in Larrabee.  Programmable filtering is an intriguing concept; I look forward to the paper presentation.  There is one more paper that may be about hardware (Embedded Function Composition); but the title is a bit opaque and it also has no preprint, so it is hard to be sure.

Despite my claim in the previous blog post, there do indeed appear to be quite a few papers about ray tracing this year: Efficient Ray Traced Soft Shadows using Multi-Frusta Traversal, Understanding the Efficiency of Ray Traversal on GPUs, Faster Incoherent Rays: Multi-BVH Ray Stream Tracing, Accelerating Monte Carlo Shadows Using Volumetric Occluders and Modified kd-Tree Traversal, Selective and Adaptive Supersampling for Real-Time Ray Tracing, Spatial Splits in Bounding Volume Hierarchies, Object Partitioning Considered Harmful: Space Subdivision for BVHs, and A Parallel Algorithm for Construction of Uniform Grids.  Another paper, Hardware-Accelerated Global Illumination by Image Space Photon Mapping, combines image-space, GPU-accelerated methods for the initial bounce and final gather with ray-tracing for a complete photon mapping solution.

There are only three “GPGPU” papers this year; two on GPU stream compaction (copying selected elements of an array into a smaller array): Efficient Stream Compaction on Wide SIMD Many-Core Architectures and Stream Compaction for Deferred Shading, and one on computing minimum spanning trees for graphs (Fast Minimum Spanning Tree for Large Graphs on the GPU).

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An Intel research group has put their papers and code up for download. I had asked Alexander Reshetov about his morphological antialiasing scheme (MLAA), as it sounded interesting – it was! He generously sent a preprint, answered my many questions, and even provided source code for a demo of the method. What I find most interesting about the algorithm is that it is entirely a post-process. Given an image full of jagged edges, it searches for such edges and blends these accordingly. There are limits to such reconstruction, of course, but the idea is fascinating and most of the time the resulting image looks much better. Anyway, read the paper.

As an example, I took a public domain image from the web, converted it to a bitonal image so it would be jaggy, then applied MLAA to see how the reconstruction looked. The method works on full color images (though has to deal with more challenges when detecting edges). I’m showing a black and white version so that the effect is obvious. So, here’s a zoom in of the jaggy version:

zoomed, no antialiasing (B&W)

And here are the two smoothed versions:

zoomed, original zoomed, MLAA

Which is which? It’s actually pretty easy to figure: the original, on the left, has some JPEG artifacts around the edges; the MLAA version, to the right, doesn’t, since it was derived from the “clean” bitonal image. All in all, they both look good.

Here’s the original image, unzoomed:

original

The MLAA version:

MLAA

For comparison, here’s a 3×3 Gaussian blur of the jaggy image; blurring helps smooth edges (at a loss of overall crispness), but does not get rid of jaggies. Note the horizontal vines in particular show poor quality:

3x3 Gaussian blur

Here’s the jaggy version derived from the original, before applying MLAA or the blur:

jaggy B&W version

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Not directly relevant to real-time rendering (although there might be some tangentially related applications in areas like augmented reality), this SIGGRAPH 2009 paper is just painfully clever.  It exploits the phenomenon of bokeh (the large circular blobs that small intense light sources generate in out-of-focus images) to create tiny barcodes that can be seen from a distance by cameras.  They put a lenslet over the barcode, so that when viewed in a defocused manner you see a large circular blob – with a sharp image of the barcode in the center!

Bokode teaser image

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  • Books, books, and more books: I received review copies of two books. Best of Game Programming Gems is as it sounds, certainly cheaper than buying the seven books in this series, no real review needed (look inside). Game Engine Architecture is about just that, how to make a professional-grade game rendering system, from soup to nuts (you can look inside). Eberly’s two books are the previous notable works in this area, but are quite different than this new volume. While they focus almost exclusively on algorithms, this book attempts to cover the whole task of developing an engine: what to use for source control, dealing with memory management and in-game profiling, input devices, SIMD, and many other practical topics. There is also algorithmic coverage of rendering, animation, collision detection and physics, among other areas. Naturally, the amount of information on each area is limited by page count (the book’s a solid 860 pages), but in my brief skim it looks like most of the critical areas and concepts are touched on. You won’t become an expert in any one area from this volume, but it looks like you’ll have some reasonably deep understanding of the elements that go into making a game engine. Quite an impressive work, and I know of nothing else in this area that is so detailed. I hope I get a chance to read it (who am I fooling? Though I do wish I had the time…) – well, at the least, it’s a place I’ll first go if I want to learn about a topic in game development that I know little about. If you’d rather wax nostalgic about great game engines you have known, as well as what the state of the are is, this article is for you (oh, yeah, the author of this new book works at the company that made #3).
  • Looking around for titles I’d like to look over at SIGGRAPH, I found these: Game Graphics ProgrammingProgramming the Cell Processor: For Games, Graphics, and ComputationIntroduction to 3D Game Programming with DirectX 10Ultimate Game Programming with DirectX, 2nd Ed., Advanced Game ProgrammingGame Coding Complete. Which all sort of sound the same (except for the Cell book), but I’d be happy to page through each and see if it looks promising.
  • There’s a worthwhile comparison of average vertex normal computation methods on the MeshLab blog. He gives the nod to Thürmer and Wüthrich’s method. You can try each of the three using MeshLab itself.
  • Sure, Spore didn’t light the world on fire as many of us hoped, but a lot of cool technology was explored. Chris Hecker has a worthwhile rundown of some of the great stuff they worked on.
  • There are some surprisingly affordable 3D stereolithography objects available on Shapeways. I bought Spiral Cage (tiny, but impressive, and so cheap), Clematis (looks delicate, but is quite springy), and Gyroid (pricier, but more sizeable and a fun form). It’s great to see so many people exploring such areas; here’s a detailed summary of resources. Even if you never plan on getting involved, the Flickr area dedicated to such techniques is worth a browse.
  • This one amused me: a cloud computing company had a contest that was meant to show off Ruby and cloud computing strengths. It was won by people brute-forcing the problem with GPUs: 16 used by the first-place winner (plus 117 CPU cores, which had less performance total than the 16 GPUs), 4 by the second. Steve Worley and others talk about the GPU approach on the CUDA forum (his program, shared with the community there, was used to win second place).
  • I admire the dedication.

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I completely agree with this blog post by Humus on the uselessness of the performance numbers in most rendering papers.  This is something that often comes up when reviewing papers.  Frames-per-second (fps) numbers are less than useless, since they include extraneous information (the time taken to render parts of the scene not using the technique in question) and make it very difficult to do meaningful comparisons.  The performance measurement game developers care about is the time to execute the technique in milliseconds.

Some papers do get it right, for example this one.  The authors use milliseconds for detailed performance comparisons, only using fps to show how overall performance varies with camera and light position (which is a rare legitimate use of fps).

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The complete list of accepted posters can be found here.  Posters are in a sense the “smallest” SIGGRAPH contribution – each one constitutes a single (large) page of description.  All the posters are in one large room, so it doesn’t take long to just walk past them and see what looks interesting.  There are also two sessions (each one hour long) where a presenter stands besides each poster and discusses it with anyone who is interested.

The poster list has no abstracts, just titles.  Judging from those, the ones that I find potentially interesting are:

  • Polygonal Functional Hybrids for Computer Animation and Games
  • The UnMousePad – The Future of Touch Sensing
  • Data-Driven Diffuse-Specular Separation of Spherical Gradient Illumination
  • Lace Curtain: Modeling and Rendering of Woven Structures Using BRDF/BTDF
  • Beyond Triangles: Gigavoxels Effects in Video Games
  • Cosine Lobe-Based Relighting From Gradient Illumination Photographs
  • Curvature-Dependent Local Illumination Approximation for Translucent Materials
  • Direct Illumination From Dynamic Area Lights
  • Gaussian Projection: A Novel PBR Algorithm for Real-Time Rendering
  • Interactive Lighting Manipulation Application on GPU
  • Reflection Model of Metallic Paints for Reflectance Acquisition
  • Variance Minimization Light-Probe Sampling

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These events are proposed and organized by SIGGRAPH attendees, not the conference organizers (who simply approve them and provide rooms).  They range from large, elaborate presentations to small meetings.  The list of Birds of a Feather (BoF) events (with dates, times, and locations) is available here.

The OpenGL BoF is one of the largest and longest-running.  Each year, it is the premier event to hear about the latest developments in OpenGL.  This year it is joined (actually, preceded, by one day) by the OpenCL BoF, which discusses this new API for GPU-based general computations.

Although most render farms are used for film production, many game developers also have render farms which they use for lighting and visibility precomputations.  For this reason, some game developers may wish to attend the Renderfarming, Job Queueing, and Distributed Rendering Performance event.

The Computer Graphics for Simulation BoF and the Dynamic Simulation Birds of a Feather also seem relevant for game developers, although they are not specifically concerned with rendering.

The Interactive Ray Tracing BoF has already been mentioned by Eric, and is of interest to many readers of this blog.

One of the uses of real-time graphics with which I have very little familiarity is visualization of molecules, which has its own BoF event (the Molecular Graphics BoF).

Besides BoFs for people interested in specific graphics topics or products, there are also BoF events for particular groups within the graphics community, such as the Women in Animation BoF and SIGGIG: Gays in Graphics.  One of the most interesting of these is the Computer Graphics Pioneers Reception, which is intended for people who have been contributing to computer graphics for at least 20 years (if you fit this description and are interested in being a registered Computer Graphics Pioneer, the membership details are here).

Other BoFs are intended for people from particular regions or who went to certain schools, like the Taipei ACM SIGGRAPH Reunion, the ACCAD/OSU Alumni Gathering, the Tokyo ACM SIGGRAPH Chapter Party, the UNC SIGGRAPH Alumni Reception, Reuniao dos Brasileiros – Brazilian BoF, Purdue University Reunion, RIT Alumni Reception, and Reunion de los Mexicanos – Mexican BoF.

Finally, many regular SIGGRAPH attendees like to go to the Sake Barrel Opening Party BoF.  I haven’t attended one yet, but perhaps I will this year.

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These are sponsored talks, which are specific to a single companies’ products.  Even so, they often have good information.  The complete list of exhibitor tech talks is here; NVIDIA is giving so many talks that it rates a separate page.

AMD has a talk called Next-Generation Graphics: The Hardware and the APIs which from the abstract, seems to be about AMD’s DirectX11-level hardware and how to access its features using OpenGL extensions.  NVIDIA has two talks about using CUDA for non-traditional graphics: Alternative Rendering Pipelines on NVIDIA CUDA and Efficient Ray Tracing on NVIDIA GPUs.  Although both talks discuss ray tracing, the first also discusses a CUDA implementation of the REYES algorithm (which powers Pixar‘s RenderMan).  I think REYES is far more interesting for real-time use than ray tracing; similar algorithms have dominated film rendering for many years (although ray tracing is slowly gaining).

Another interesting NVIDIA talk (3D Vision Technology – Develop, Design, Play in 3D Stereo) discusses stereo rendering.  This is an area that has had many false starts over the last ten years, but now it seems like it might actually make it into the mainstream, driven by stereo film content and advances in home television displays.

Although it is not strictly about real-time rendering, AMD’s GPU-Accelerated Production Rendering is part of an interesting trend where GPUs are used not for real-time rendering, but to accelerate offline rendering.  Some of the techniques used here may inform future high-quality real-time rendering.

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While at SIGGRAPH I like to look at new books at the booths. One you may wish to check out is Graphics Shaders: Theory and Practice, from AK Peters (or just use “Look Inside” on Amazon). I received a review copy and skimmed through it. If you’re interested in programming in GLSL 1.2 (part of OpenGL 2.1), consider looking at this one. A minor problem is that it’s not quite as up-to-date as the Orange Book (now on OpenGL 3.1), but the difference in core concepts between language versions is not large. The Graphics Shaders book is full color and comes with a lot of GLSL code examples. It has a bias towards scientific visualization, though not so much that it neglects the basics. I particularly enjoyed the chapter on noise, as it gave one of the clearest explanations I’ve seen on the differences between various types of basic interactive noise functions. One or two elements in the book are a little weak – the flowcharts for pipelines are often too small and difficult to read, for example – but all in all this looks like a solid contribution to the field. Don’t expect more elaborate effects, e.g., shadows are not touched upon. It does cover the basics, plus some additional topics like image post-processing (not normally covered in texts I’ve seen). One of the authors wrote a nice learning tool for GLSL, glman, free for download. If you find you like this tool, definitely consider the book.

Another book I noticed recently is Fluid Simulation for Computer Graphics. This is a topic I know little about, I was just interested to see that there’s any book at all. It looks pretty equation-filled, so is definitely for the serious practitioner.

Speaking of fluid simulation, Intel has an article on this topic for games. One of the chief strengths of any publication is that its staff makes a decision based on merit as to what is published and what is culled. So, I have to admit to being leery of anything that says, “Sponsored Feature”, as that means editorial review and decision-making are gone. I tend to err on the side of ignoring such articles (there’s plenty to read already). That said, Intel’s had quite a number of these articles recently, including such topics as instancing, ocean fog, FFT’s for image processing, and quite a few on parallelism.

In the “clearing the queue” category of links, I don’t think I ever pointed out this handy page, which presents all AMD/ATI and NVIDIA presentations at GDC 2009.

There’s now a (not very active, but at least it exists) Microsoft DirectX blog.

On the OpenGL front, NVIDIA has introduced bindless graphics to help avoid L2 cache misses. I will be interested to see how APIs evolve, as the elements in the current APIs that are bottlenecks are not so much CPU or GPU limitations as due to the API constructs themselves.

Thing for the day: an advertisement with interesting stippling.

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Seven more:

  • Michael Abrash has an in-depth article on rasterization on Larrabee. Perhaps a little too in-depth at times; just skim past the assembly instructions. I also found myself asking, “why do that?” – the key is to just keep reading. He tries to make his examples simple and comprehensible, but at the cost of sometimes feeling like they’re oversolving the problem. They aren’t, it’s just that the solution is in fact used in different circumstances in order to be efficient.
  • SIGGRAPH has an interactive rendering event summary page. This page is more for the art production side of things, though; Naty’s coursetalks, and production sessions summaries are more comprehensive and more useful for programmer attendees.
  • NVIDIA has a number of events they’re involved in at SIGGRAPH 2009. Here’s the list.
  • I love this sort of madness: a business-card ray tracer that does depth of field.
  • Accumulated SSAO: the idea of reprojection, of using previous results by finding where they lie on this frame’s view, is one that seems a tad expensive for interactive rendering. It’s hard to know anything about performance and quality from this page, but I thought it was interesting to see.
  • I mentioned Processing in the last post. Another language-related resource for graphics and game programming is pygame, a set of Python modules for writing games. A friend said he found this system to be pretty great, that he could whip up a fairly involved game idea in a few hours.
  • Scribblenauts sounds like the coolest game that will ever come out, period. Even if it’s only 1/10th as good as the previews read, it looks to be pretty darn entertaining.

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