level of detail

As of last month, I’ve been at Firaxis Games for a year. That time just flew right past. The transition to game development has been challenging and rewarding (and frustrating). Every aspect of creating “pretty pictures” becomes much more difficult when working on a game. I imagine more than a few of you reading this to be internally commenting “No Shit, Sherlock”, but it cracks me up when I think about some of the things that I always took for granted when making demos at ATI/AMD. Things like shadowing, translucency, etc. are easily handled when you are making one-off demo apps over the course of a few weeks/months. Usually those apps have controlled camera angles, small scenes, a very specific technical goal and the privilege  of supporting a limited range of hardware. It’s certainly changed my perspective on what is impressive as far as real-time graphics goes.

I’ve joined a few friends and former schoolmates at Firaxis. Actually, my graduate school adviser, Marc Olano, has been here for the last year on sabbatical. Some of his work on filtering specular highlights from normal maps for ocean rendering in Civilization V was published at I3D 2010 under the title LEAN Mapping. Speaking of, he’s been posting a number of graphics tricks over at the UMBC Games and Interactive Media blog. Trick 1 reformulates the computation of a normal from a heightfield and Trick 2 deals with calculating the size of a mip chain via closed form equations. He’ll be posting a few more in the future, so add the RSS feed and check back in a week or so.

Many of the blogs I used to read on the regular have either gone silent or their authors have primarily moved to Twitter. I read a few people’s tweets but mostly I just haven’t made (or plan to make) that transition. I find it hard enough to post anything here without over-analyzing whether or not its even worth reading, let alone posting 8 times a day. And frankly as a reader I find the signal:noise ratio difficult to manage. A few of the good old fashioned web blogs I’ve been reading lately are Miles Macklin’s blog, Game Angst by Adrian Stone,  and Smash’s direct to video. On the less graphics focused front, The Witness blog starring Jon Blow and Ignacio Castaño, the Wolfire Games blog and Charles Bloom’s cbloom rants (as always). As a total hypocrite, I would like to call-out and encourage Brian Karis, Tim Farrar and Christer Ericsson to update their damn blogs.

Anyway, I’ve been reading more papers lately so maybe I’ll have some impetus to update this dumb blog. And if you still have my RSS feed in your reader, thanks!

As a side note, Civilization V was announced several weeks ago and has been available for pre-order on Steam. Go team!

I’m out at GDC now. The first two days have been pretty low-key. I spent the day yesterday in the Advanced D3D tutorial and today in the Insomniac PS3 programming tutorial. AD3D had some interesting tidbits, I think ATI and NVIDIA will have slides up shortly. Unfortunately I can’t access the slides that GDC has online for attendees for some reason. The Insomniac session had a really good introduction to Cell programming, how they do gameplay updates on SPUs, a talk on debugging the SPUs that went a bit over my weary head, and a talk on some of their PS3 graphics work for Resistance and Ratchet & Clank. They’re using a sort of halfway lighting pre-pass technique where they render out the normals and specular power, then compute deferred lighting into a buffer, then do a forward pass where they just grab the direct lighting from the previous pass’ results. It wasn’t exactly clear to me how they were doing this with MSAA. All the deferred lighting is computed once per pixel but their forward pass is MSAA. So inevitably their MSAA samples are going to be grabbing incorrect lighting information from the lighting buffer, or so it seems to me.

Overall it looks like attendance is way down this year. This is a shame because I think this year has the best content out of the three years I’ve gone. The lineup for the next three days is solid: Killzone 2 rendering, Gears of War 2 rendering, Larrabee talks, terrain rendering in Halo Wars, a few talks on PS3 programming, etc.

I got my copy of ShaderX7 in the mail the other day. There are lots of neat little articles packed within the monstrous 800 page book. Unfortunately,  myself and my co-authors were excluded from the bios and authors list due to some error, but the article found its way in (under the title “Deferred Occlusion from Analytic Surfaces”).

Organizers finally scheduled my talk at GDC 2009. It will be happening Friday 27th from 10:30am — 10:50am in Room 130, North Hall. The description of the talk is here (mirrored link). I’ll be showing one or more short demos as time allows. Come out and say hi.

Today I was waiting for a session to begin at SIGGRAPH ASIA and began to think about how there are several cool papers that exploit min/max  images. A min/max image is an image pyramid that is sort of like a quadtree. The bottom level of the hierarchy is the original image while the elements in each subsequent level of the hierarchy contain the minimum and maximum of four elements in the previous level. So it’s sort of like a mip map, but instead of averaging values, you store the min and max of the previous level. This min/max hierarchy can be generated quickly in log n passes but can be used for making conservative estimations for large regions of your image. Refer to the following papers:

Maximum Mipmaps for Fast, Accurate, and Scalable Dynamic Height Field Rendering by A. Tevs, I. Ihrke, H.-P. Seidel

- Uses min/max maps to ray trace height fields. I feel like this idea has been around for ages but here it is all packaged up with a neat little bow.

Fast GPU Ray Tracing of Dynamic Meshes using Geometry Images by Nathan Carr, Jared Hoberock, Keenan Crane, John C. Hart.

- Uses min/max hierarchies of Geometry Images to accelerate the ray tracing of meshes.

Real-time Soft Shadow Mapping by Backprojection by Gaël Guennebaud, Loïc Barthe, Mathias Paulin
High-Quality Adaptive Soft Shadow Mapping by Gaël Guennebaud, Loïc Barthe, Mathias Paulin

-  I’ve ranted about these papers before. These works generate min/max hierarchies of shadow camera depth images to perform efficient blocker searches for soft shadow rendering, and also to determine penumbra regions for further optimization.

March of the Froblins SIGGRAPH course notes by Jeremy Shopf, Joshua Barczak, Christopher Oat, Natalya Tatarchuk

- Used a min/max hierarchy of the depth buffer to occlusion cull agents in our crowd simulation. Technically this only used the max portion of the hierarchy, but I didn’t want to title this Let’s have a Min/Max Party (Min is Optional).

Anyway, I think it’s kind of neat. I’m going to make another post tomorrow night about an awesome paper that’s here at the conference but I don’t want to write about it until I have a chance to clear up some nebulous parts of the paper with the author.

In other news, I received official word that the GDC lecture I proposed was accepted so I guess I will be seeing some of you in San Francisco next year in March. I’m excited about this talk because it came directly out of a post on this blog. Turns out this isn’t a waste of time after all!

Fantasy Lab, the game development studio started by Mike Bunnell (formerly of NVIDIA), has updated their website with information about their new real-time global illumination SDK called Radium. You’ll remember Fantasy Lab as the company that released the Rhinork GI demo and announced the game Danger Planet (covered here). The description boasts infinite bounces of light. Assuming that they are using the same disc-based transfer approached used in Bunnell’s GPU Gems 2 article (also check out the recent Pixar paper Point-Based Approximate Color Bleeding), I think this means that any number of bounces can be calculated as each bounce is an iteration in that algorithm. I’d definitely like to hear more details but I suppose that is unlikely to happen as they are trying to make a living

The group I work in at AMD is involved in a few presentations at SIGGRAPH this year. First, Chris Oat and Natalya Tatarchuk will be presenting a talk in the Advances in Real-Time Rendering in 3D Graphics and Games course on Monday on our latest demo “Froblins”. This talk will cover using the GPU and DirectX 10.1 for scene management, occlusion culling, terrain tessellation, approximations to global illumination, character tessellation, and crowd simulation.

I will be presenting a shorter talk on Thursday from 4:15-4:45 in the Beyond Programmable Shading: In Action course, focusing on how we used the GPU to do some general computing in the Froblins demo to allow our Froblin characters to navigate around the world and avoid each other. My addition to this course was a bit on short notice so I am fairly nervous, but how could I pass up an opportunity to speak at SIGGRAPH? I must say I am very jealous of my co-workers who will be done with all presenting duties on the first day of the conference!

I am always eager to meet new people so please feel free to introduce yourself if you will be in attendance!

Update: Here’s the link to the chapter from the course notes on our Froblins demo: March of the Froblins: Simulation and Rendering Massive Crowds of Intelligent and Detailed Creatures on GPU

*Shameless home-team raving content below*

The NDA on the new ATI hardware (R770) was lifted today, so a boat-load of reviews are out. And they’re all glowing. I’ve been with the company for about a year and a half and NVIDIA has had us pinned down from the day I started until now. It’s nice to have a winning product out there. If you’re thinking about buying a mid-range graphics card ($199-$299), or you want help ensure that I have a job in the future,  now is the time.

Techreport
Anandtech
Hexus
Hardware.fr (french)
arstechnica
Extremetech
Hardwarecanucks
computerbase (german)
Hothardware
Rage3d
hardocp

I haven’t really put much up here recently, but this blog is not dead! I’m just busy at work and haven’t had a terrific amount of time to devote to pursuing solo interests. Please feel free to post good papers you’ve read recently in the comments.

On a side note, NPAR (Non-Photorealistic and Artistic Rendering) 2007 papers are posted.