# GDC 2013 – Tuesday is Physics Day ….kinda

Tuesday was Day Two of the Math and Physics for Game Programmers tutorial. Monday was all about the mathematics, and Tuesday was supposed to be all about the physics. There was one great talk from which I was able to extract a better understanding of configuration space objects, but the rest of it was …meh. As with yesterday, those talks which were edited and tweaked from last year showed improvement, those that weren’t still sucked.

The day started out with a demonstration of a simulation of a Go stone. …yeah. A stone. It seemed that the speaker, Glenn Fiedler from Sony Santa Monica, was simply pleased with himself that he’d recreated the wheel. He went through the process of creating his stone model, then he described the basic translation and rotational dynamics he deployed without discussing the specific details. It might have been a more fruitful talk if there were more details in how he was integrating the motion, why the integration works the way it does, and described the fundamental principles involved. Although his simulation worked pretty well, during talk, there were a few conceptual errors, especially about the properties of the moment of inertia tensor. He kinda had the right idea, but not really. Granted it’s a tough thing to pick up on your own, but if you’re giving a talk on the topic, you should have a genuine and thorough understanding of the topic.

The second talk of the day was “The Separating Axis Test” by Dirk Gregorius from Valve. Gino van den Bergen of Dtecta gave a talk last year on collision detection using Minkowski differences and configuration space objects, but I must admit that the process was still fuzzy to me. Dirk’s talk on the issue really helped. Don’t get me wrong, Gino is the man and does a great job, and when his talk came up later in the afternoon, I was able to grasp a bit more about how CSOs work. I doubt that they’ll make it into the PHYS191 course in a formal way, but I may put a bonus section on it in the textbook this summer if for no other purpose than to ensure that I understand it correctly myself. No better way to see if you really understand something that to try to teach it to someone else. The rest of the afternoon was rather blah, unfortunately. Dirk’s and Gino’s talks certainly made up for the mediocrity of the others.

Since the Expo Hall isn’t open until Wednesday, during my downtime between when I left the physics tutorial and supper, I worked on taking some photos. I took some of this earlier in the morning on my way to breakfast, but was disappointed with the results. Yes, I was at the Rally in the 100 Acre Wood, but I didn’t work on many panning shots there so I’m really out of practice. That showed as I tried to get some panning shots of cyclists and streetcars. I gotta get back into proper form before the Kansas City Region SCCA season starts and definitely before the first IndyCar event I’ll work, the Indianapolis 500 Mile Race. Definitely have to have good panning skills there.

Of course, one thing that is ever-present in San Francisco around the touristy areas are the street performers. Most are simply annoying, but there are some, like this duo, that really sounded good!

One of the coolest new things I’ve seen at GDC so far is the Video Game History Museum alcove. They have several coin-ops including one of my favourite games, Asteroids! (where’s my two-liter of Shasta and my Rush mix-tape?) The also had several classic consoles, some well-known, others not as well-remembered. Of course they had the Atari VCS (later known as the 2600), but they also had a Vectrex! That’s a tough find! There weren’t too many of these machines made, and even fewer of them have survived in playable form.

The day ended with a stroll through Chinatown, a requisite visit every year. There wasn’t anything new, really. The same peddlers were peddling the same cheap, cheesy crap. One change that greatly disappointed me was the defacement of one of Banksy’s pieces. I now feel very fortunate to have imaged this a few years ago. It was a really cool work, but now in spite of the plexiglass overlay placed in hopes of preserving the street art, it’s been covered with simple scribbles of white spray. It’s a damn shame.

Next post will be all about swag! The Expo Hall opens on Wednesday, and with a light session load today, I’ll be cruising through as much as I can, collecting as many goodies as I can.

# GDC 2013 – Monday Math Madness

It was a bit sketchy, but we finally made it to San Francisco for the Game Developers Conference (GDC). The insanely late snowfall in Kansas City resulted in our flight being delayed, but at least it wasn’t cancelled. This was the first time I have been through the deicing process. It was interesting, if time-consuming. Once we were in the air and above the clouds, everything seemed far less dreary and dreadful.

Upon arrival, we did the usual things: take the noisy BART ride to Powell station, leave our bags at the hotel, wander aimlessly until check-in time, check-in, get our GDC badges when registration opens, and celebrate with Naan & Curry. I’ve been to many different conferences, some big, some small, and the folks running the GDC have the process down to a science! Once registration opened, we were in and out with our badges within a couple of minutes. It was amazingly quick!

Monday morning also began in the traditional way with me waiting for the rest of the crew down by the cable car turn-around at Powell St taking photos. I know that I end up taking a lot of the same types of shots year after year, and I need to work on my variety, but I just dig that spot so much for imaging the cable cars. Once everyone has mustered, we head off to the best breakfast joint in the area, Mel’s Drive-In. Mel’s is one of the best places around to have breakfast, and with steak-n-eggs only costing \$7.99, it’s tough to beat the price, especially in San Francisco!

Every year, I go to the Math and Physics for Game Programmers. Monday is all about the mathematics and Tuesday is all about the physics. The topics and presentations are usually the same with minor tweaks from year to year, but today the presentations were outstanding. Squirrel Eiserloh from Southern Methodist University gave his usual talk on interpolations and splines, but with more focus and less superfluous material than last year. Here’s last year’s presentation: http://essentialmath.com/GDC2012/GDC12_Eiserloh_Squirrel_Interpolation-and-Splines.ppt. Be sure to also download his OpenGL-based demo tool. It’s a fun little app for exploring the properties of the various types of curves and splines he describes in his talk.

The second talk of the day was by Jim Van Verth, who is notorious for losing his voice at GDC. Normally, this takes about half a day, but this year, he was tight and scratchy from the get-go. His energy level this year, however, was much higher, and he was a much more engaging speaker than in the past. He also did a LOT of work on his presentation. I found his previous presentations on rotations and quaternions rather unenlightening. This year he knocked it out of the park! I think I actually get this quaternion stuff! It helped that he related them back to quantum physics and spin groups, with a nice sprinkling of hyperspatial geometry thrown in for good measure. You know it’s a good conference when you hear a serious discussion of hyperspheres and how to visualize them. His 2013 slides aren’t up just yet, but you can check out his site, http://www.essentialmath.com/ in a couple of weeks. He’ll have them up before too long. If the rest of the conference were cancelled right now, I think that my finally understanding the nature, behaviour, and deeper mathematical roots of quaternions makes the whole trip worth it. The rest of the week is gravy!

Tomorrow is all about the physics! Last year, there were some great talks regarding integration methods and collision detection. Hoping that this year, I can finally wrap my head around this configuration-space stuff.

# GDC12 – Wednesday

It’s Swag Day!! The Expo Hall opened today along with the starting of the main part of the conference. Although the Math and Physics for Game Programmers tutorial of Monday and Tuesday were over, the math and physics discussions were just getting started!

Normally, the first event of the day on Wednesday is a keynote address from someone who had a significant influence on the industry such as Shigiru Miyamoto or Hideo Kojima. This year, they decided to instead have 100 of the presenters over three days of the conference pitch their talks in 45 seconds or less. This “Flash Forward” concept was interesting, entertaining, and it influenced my session choices, but I still miss hearing a talk from a legend in game development. I’m hoping they go back to the traditional format for next year.

My first session of the morning set a theme for the entire day looking at fluid modelling. Carlos Gonzalez-Ochoa gave a brilliant talk, Water Technology of Uncharted, discussing the various techniques used to generate realistic looking water elements in the Uncharted series of games. This was a surface-mesh modeling technique, not a fluid simulation, but a vector field representing the bulk flow of the water was used to modulate textures and the wave directions. Rather than building a spectrum of wave frequencies and modelling that multi-harmonic wave motion, they instead created a random collection of “wave particles”, pulses that could be tweaked to be as round-topped or as peaky as desired by the artist by adjusting a single parameter. Rather than generating a spectrum of these wavicles, a single set of them is generated and then scaled down and replicated to model the higher frequency components of the total wave motion. Although these wavicles have their own random local velocity, the ensemble is modulated by the bulk flow vector field to generate a more realistic-appearing surface. The final piece of the modelling is to include larger amplitude long-wavelength modes to simulate swells, rollers, and retromotive waves in rivers or channels. Combining all of these together creates some absolutely stunning looking water with very believable dynamics and behaviour.

My next session was actually a talk on a topic that got me first excited about the technical sessions at the GDC when I first attended back in 2007. In my first trip to the GDC, I was blown away by the intense mathematics involved in many aspects of intensity-mapping and lighting. The talk was on the advantages of using radial basis functions as an alternative to spherical harmonics. This year, it was the radial basis functions that were under attack. Spherical harmonics still suck, but the presenters, Robin Green and Manny Ko, argued for the advantages of spherical needlets as an alternative to either spherical harmonics or radial basis functions. The talk itself began with a crash course in Hilbert spaces, overcomplete basis sets, and how to create good basis functions. That was all well and good, and interesting, but I would have preferred that they spent more time on the exact specifics of needlets, their advantages and disadvantages, and a demonstration of their usage. Unfortunately, there was not enough time in their talk for this.

There were a few other talks I attended today, which meant minimal swag-gathering in the Expo Hall. Tomorrow’s schedule of interesting talks looks to be more sparse, so I’ll be in full swag accumulation mode and will have pics then.

# GDC12 – Tuesday

Day Two of the 2012 Game Developers Conference was all about the physics for me. Today, there was an all day Physics for Game Programmers tutorial, and like with the previous day’s math tutorial, some of the talks were hits and some were misses. The day began with a great discussion of collision detection and a conceptually complex method utilizing something called a configuration space object. Details about the process of creating a utility object by sweeping one of the game objects with another. The properties of the object generated by this sweep, the configuration space object, allows for quick collision detection by determining if the coordinate system origin in configuration space lies within the CSO. Not only does this procedure allow for the detection of the collision, but it also allows for the rapid determination of the collision point, and the collision normal, both of which are critical for resolving the velocities after the collision. You can learn more about this procedure and download the code at http://www.dtecta.com/.

The second talk of the day was a party of tensors and Newton’s 2nd Law. I loved it! Solving Rigid Body Contacts by Richard Tonge of nVidia focused on collision resolution. Once you know that a collision has occurred, you then need to figure out how to handle that collision. One thing that I found interesting is that was that game devs use the term impulse to refer to a $\Delta \vec{v}$ as opposed to the physical definition of $\Delta \vec{p}$. After listening for a while, it was completely understandable why. Collision resolution happens instantaneously, and the change in the objects motion is achieved by applying the simple statement, $\vec{v_{new}} = \vec{v_{old}} + \Delta \vec{v}$. Getting this $\Delta \vec{v}$ physically right, doesn’t always result in physical behaviour from the simulation. Tweaking of collision-induced impulse is needed to produce more realistic appearing motion and reactions.

The afternoon sessions were all about ragdoll physics, which would have been very interesting if there was any depth to the talks, but they were all very high-level and filled with pretty video sims and devoid of any serious discussion of the physics modeling. Unfortunate, that. The salvation of the afternoon was a talk by the tutorial’s facilitator and organizer, Jim Van Verth. Jim talked about the basics of fluid simulation including introductions to the Navier-Stokes equation and methods for modeling and solving it.

The most straightforward way to model fluids is by gridding your space and evaluating the continuity and momentum equations discretely at the center of each grid element. This is robust, but expensive. It also only operates in the space in which you’ve established your grid. You won’t want to use it world-wide because of the computational costs, but it is useful for very localized fluid effects such as puffs of smoke during destruction events and the like. This method also doesn’t model splashes well. The fluid remains intact, rather than separating into droplets as a real fluid will.

A method that is more globally applicable and that does a good job of modeling splashes is Smooth Particle Hydrodynamics (SPH). SPH uses kinetic modeling of small particles with an attractor force, simulating a surface tension, to loosely bind the particle together. The ensemble of particles is then skinned to produce a realistic looking fluid surface. Splashes are well modeled by this technique, and since its a kinetic system, not a cell-based system, its globally applicable. You don’t need to grid out your space, and the fluid is free to flow wherever physics takes it in the world.

The last method demonstrated was a method of simply modeling the surface of a fluid, such as an ocean surface. Ocean waves are not of a simple single frequency, but are complex structures comprised by a multitude of wave modes. To generate realistic looking waves, a Fourier sum is used to add multiple wave modes to the entire surface and the wave speed is properly calculated via a frequency-dependent dispersion relationship. Building these modes in frequency-space and then using a FFT to transform back to time-space results in extremely realistic fluid surfaces. This is the method used to generate the ocean surface in the movie Titanic. Cool!

Last event of the day was the IGDA party. Its something that we attend every year, at least for a half-hour or so. Typically there have been munchies and various innovated board games scattered around. This year, there were vendor tables, no munchies, minimal board games, and a TON of people! Its probably a good thing the fire inspector didn’t stop by. They’d have shut the place down. Oh, yeah, and there were ribbon dancers. :S Just what kind of party is this? It wasn’t your typical professional organization party.

Wednesday, the main part of the conference begins and the expo hall opens! Yay swag! I’ll have pics of swag after my first swing through the expo hall. If you see something you like, be sure to leave a comment for me.

# GDC 2012 – Monday

The 2012 Game Developers’ Conference officially got started this morning. For me, it seemed like a late start with the first sessions beginning at 10am. For someone who’s up at 5am on a regular basis, that’s a lot of morning time to kill before getting started! Fortunately, my camera is with me everywhere and I had lots of time to explore before hitting Mel’s Drive-In Diner for breakfast.

The “discovering new experiences” part of the day started VERY early as I experienced my first earthquake. A 4.0 magnitude quake struck the Bay Area at 5:30 this morning. While it wasn’t that strong of a quake, it was still disconcerting while occupying a room on the 8th floor of an old, sketchy hotel! At least now I can scratch “survive an earthquake” off of my bucket list.

Sessions for the day were part of the Math for Game Programmers tutorial. In the past, this has been a weak tutorial, but I was pleasantly surprised by its evolution. While the oratory skills of the organizer had still not improved one bit, nor had his specific talk, the quality of the other presenters and presentations improved quite a bit. First out of the gate was a talk on Bezier curves and splines. Might have to see about working curves and splines into the MATH/PHYS 191 course. It would be a natural succession to introduce them after we discuss parametric equations.

There was also a good talk on collision detection methods which reaffirmed that the work we’re doing in the MATH/PHYS 191 course is in line with what’s being done in the field. All very interesting, and I’ll have links to the slides in time. The last talk of the day was about data as paramount when thinking about how to construct code. The speaker’s motto was “understand the data, and you understand the problem”. As a computational physicist, my reaction was, “Duh!” Preaching to the choir, there.

One of the great things about coming to San Francisco is having the opportunity to meet up with some of my friends and fellow IndyCar fans from Twitter. Tonight, I was introduced to a new place, Pesce, which specialized in tapas-style seafood dishes. It was fabulous! I would include a pic of the lobster ravioli and the pan-seared scallops, but they didn’t stick around long enough. Delicious!

So the first day was successful. At least more than it had been in past years. Tuesday, the second day of the tutorial, is all about Physics for Game Programmers. It will be interesting to see what new things they bring to the sessions this year. Also, the IGDA party is Tuesday night! It’s never been a real blow-out type of party, but at least there’s free food.