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PostPosted: Sat Oct 09, 2004 11:41 am 
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PHYSICS MEETS THE HIDEOUS BOG BEAST

-Science




Programmers are turning to physics to add more reality to computer games, but so far the early market tests have been disappointing

When you slime a hideous bog beast with your laser blaster in real life, the beast doesn't consult a table to figure out which way it is supposed to fall. In the virtual world of most computer games, however, that's exactly what happens. A programmer has carefully scripted each potential event--like the fall of the blasted bog beast--long before you tear the shrink-wrap off your new game. If a particular combination of causes and effects isn't found in the programmer's predetermined table of allowed possibilities, it just doesn't happen.

While this approach worked well enough when Pong was the state of the art in video games, many game designers think the traditional scripted game is becoming too restrictive. Their attempts to exploit advances in computer technology and inject more natural behavior into gaming have given birth to a whole new form of interactive entertainment: physics-driven computer games.

So far only one physics-driven game, Trespasser, has made it to market--where it flopped. Nevertheless, several companies are now spending millions of dollars developing new games and the software engines to drive them. In one sense, the computer game industry is driven by novelty, and the potential payoff of the first truly physics-driven game is huge. "We are all looking for the next big thing," says David Wu of Pseudo Interactive Inc., a Toronto-based game design company, "and physics is the biggest frontier in gaming right now."

Computer games are all about movement: prowling through a dungeon in search of treasure, skidding around corners in a high-speed chase, or sending an opponent tumbling with a well-placed flying drop kick. In a scripted game, movement is like a movie with several different endings. For each choice a player makes, a graphic designer has pre-recorded a video clip of the resulting motion. Although game designers are expert at linking the clips to produce an almost seamless illusion of continuous motion, they can't always cover every possibility. Inevitably, bugs creep into the animation code and the seams start to show.

Although serious gamers don't expect the virtual world to be perfectly true to -life, the last few years have seen dramatic advances in computer graphics that are raising players' expectations. "As the graphics get more realistic, your eye starts to pick out movement problems," says Chris Hecker, founder of the Seattle-based game company Definition Six. The inconsistencies can cause players to "lose the suspension of disbelief that makes a game fun," says Hecker.

But how can a programmer possibly account for all the complexities of real motion? That's where the physics comes in. Instead of scripting each event, the new generation of programmers uses physical laws to create objects that obey a specific set of rules in all circumstances. Instead of saying that a car traveling around a curve at high speed will always skid into the wall and then creating a film clip showing the crash, the programmer writes in the appropriate coefficient of tire friction. Then the computer handles the gritty work of summing all the forces on the moving car to determine where it moves next. And if the car hits the wall, the computer can even predict the flight path of errant tires as they bounce over the wall into the grandstands.

To apply the laws of physics, the game developer breaks down each physical object in the game into a collection of simple geometric components--cubes, spheres, or cylinders--connected by joints. "Then you assign masses to the parts of the body and add the properties of real joints, like a ball-and-socket or a hinge," explains Anselm Hook, a game-physics developer at the London-based company MathEngine. The objects can be as simple as a boulder or as complicated as the human body.

When two bodies interact, the physics "engine," the portion of the computer code that handles the physics, first computes the forces on each object, including gravity, collisional impulses, and friction. It then solves the constrained differential equations of motion governing the components of each body and moves them forward in real time.

As you might imagine, the physics engine soaks up precious computational resources. At any given moment, a game player's view might include several other creatures and various objects, and the engine must continuously monitor the forces on every item in the scene. "You can't forget about a box on a table if you want to keep it there with forces," says Hecker. Top-of-the-line home computers and commercial video games have only recently acquired the horsepower to drive these complex engines.

While the inexorable increase in computer speed should soon take care of that problem, physics-based games face other hazards. "Physics engines can get blown up" when a differential equation solver becomes unstable, says MathEngine's Bryan Galdrikian. Instability--a central problem in numerical analysis--happens when tiny differences between the numerical solution and the "real" solution accumulate, causing the computer to lose track of the "real" solution.

Instabilities were one explanation for the commercial failure of the first physics-based computer game, Trespasser. Based on the movie Jurassic Park 2: The Lost World, Trespasser placed players on an island filled with malevolent dinosaurs that obeyed only the laws of physics. After several years in development and almost $7 million, Trespasser was released with all the fanfare--and hopes for profitability--that a Jurassic Park tie-in can provide. Unfortunately, few people bought it. "It looked more like a research project than a game," says Wu. And Trespasser was plagued with instabilities that caused weird things to happen. "An object could suddenly sink into a rock," says Galdrikian.

Bloodied but unbowed by Trespasser's flop, game designers are turning to academics to learn how to build more robust engines. Wu, for one, is looking to the world of robotics for better ways to control the creatures in his games. "I spend a great portion of my time reading research papers and journals," says Wu. "If you want to innovate in game development, you must look deeper--into more focused and less applied research." But that can be a hard assignment for game designers. Hecker, an entirely self-taught physicist, estimates he has spent "3 years and counting" studying game-related physics.

Alan Milosevic thinks he has a better idea. "Game developers are not experienced in physics," he points out, "and they are gasping for help." Instead of forcing developers to learn physics, he argues, why not provide them with a general-purpose physics engine that they can plug directly into their game? With a prepackaged engine controlling movement in the game, designers would be free to worry about making the game fun.

Betting that developers would rather buy an engine than learn physics, his company MathEngine--and competitors Ipion and Telekinesys--are working furiously to get the first fully functional engine to market. MathEngine has hired several physicists to help with the design, but Milosevic says that potential employees need more than an advanced research degree to succeed in gaming. "We can't just solve the fluid dynamics equations," says Milosevic, "so our employees have to be able to improvise and imagine."

After all, physics-based games need to be more than physically consistent: They need to be fun. Some video game aficionados worry that physics-based games will be dully realistic. If you can't jump 30 feet, they say, what's the point? But Galdrikian argues that "realistic doesn't mean the game has to be completely real, and gravity doesn't have to equal Earth gravity, or even be constant. It could change in a game." Says Hecker: "The real motivation behind incorporating physics engines isn't reality at all," but creating total consistency. If all the objects in a game obey a consistent set of rules, a gamer's absorption is less likely to be disrupted by actions that don't "feel right."

Although game designers are betting that the "rightness" of physics-based games will eventually strike a chord with consumers, few are yet willing to risk years and millions of dollars to produce the next Trespasser. So, instead of sinking the entire investment into a game completely driven by physics, game designers are focusing on creating entertaining games while slowly incorporating more physics. For the time being, physics will be used "as eye candy, until we get used to it," says Hecker.


~~~~~~~~

By Mark Sincell


Mark Sincell is a science writer in Houston, Texas.








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DIAGRAM: Balancing act. Simulation calculates forces exerted by two balls on a bridge to determine movements of individual planks. (See http://www.mathengine.com)

PHOTO (COLOR): Tanking along. Rolling, bouncing, and sliding of joined tank is simulated mathematically.


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Copyright of Science is the property of American Association for the Advancement of Science and its content may not be copied without the publisher's express written permission except for the print or download capabilities of the retrieval software used for access. This content is intended solely for the use of the individual user. Copyright of Science is the property of American Association for the Advancement of Science and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.

Authors: Sincell, Mark
Source: Science; 10/15/99, Vol. 286 Issue 5439, p398, 2p, 1 diagram, 1c


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