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Game Dev, Physics, Science

GDC 2013 – Tuesday is Physics Day ….kinda

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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.

1364390049722The 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.

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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.

Chinatown_IntricateGraffiti_smThe 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.

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GDC12 – Thursday

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SWAG!!!

There really wasn’t too much unique or interesting in the way of swag this year. There were the usual pens and stress balls in addition to some bottle openers and pins. I do have several t-shirts in M through XL and a few digital picture frame keychains which are cool. Those you’ll have to earn!

I didn’t do much in the way of sessions, today, just attended one on the flood effects in Uncharted 3. To be honest, I thought the method they used was clunky and looked 2nd rate. They simulated a torrent of water cascading down a hallway using a hybrid of Eulerian fluid modeling, done once to capture the mesh animation, and laid a few particle emitters along the surface to create the splashes. It looked very blocky and segmented. To be honest, I don’t understand why they didn’t use SPH to model the water in this case. It seems like the perfect situation in which to deploy it. Oh well, they’re getting paid the big bucks and I’m not.

Game Dev, Physics

GDC12 – Wednesday

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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.

Game Dev, Physics

GDC12 – Tuesday

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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.