Article about games physics processing by David Geer

Page 1

Computer

Published by the IEEE Computer Society

T E C H N O L O G Y N E W S

he trend in computer gam-

ing is always to provide

higher performance and

more realistic effects. Real-

ism is important, said Rob

Enderle, principal analyst with the

Enderle Group, a market research

firm, “whether it’s allowing objects

like grass and water to behave prop-

erly or cause-and-effect sequences to

look real.”

Gamers want large and small de-

tails to be more realistic, whether

it’s characters’ clothes moving natu-

rally with the wind, or explosions

causing appropriate amounts of

damage or debris. This greatly en-

hances the gaming experience,

Enderle explained.

However, even the best of today’s

games don’t look all that realistic.

With this in mind, graphics-engine

vendors are looking for ways to im-

prove the processing of the calcula-

tions necessary to create more

realistic effects and interactions be-

tween players and game objects.

These calculations simulate real-

world physical events and utilize the

same type of mathematics used in

areas such as classical physics, fluid

mechanics, and ballistics physics.

Until recently, CPUs running graph-

ics-processing-engine software have

performed the limited physics pro-

cessing needed for computer games.

Graphics-processing units (GPUs)

handle the work necessary to actually

render the images themselves.

However, Enderle noted, today’s

complex game-physics processing

entails many real-time calculations

and thus is too resource intensive

for CPUs.

Vendors are, therefore, turning to

new approaches. Ageia has developed

a stand-alone physics processing unit

(PPU), while GPU market leaders ATI

and Nvidia are using new physics en-

gines that run on their chips.

These approaches use massively

parallel architectures, thereby im-

proving physics-processing perfor-

mance.

However, they also add cost to

gaming systems and face other bar-

riers to adoption.

LET’S GET PHYSICAL

“Nvidia released the first GPU in

April 2000,” said Jon Peddie, presi-

dent of Jon Peddie Research, a mar-

ket analysis firm.

Companies developed GPUs be-

cause graphics processing differs

from standard data handling, par-

ticularly because the volume of in-

formation that must be handled

quickly by today’s applications re-

quires a massively parallel approach

that CPUs can’t offer, explained Raja

Koduri, ATI’s director of engineer-

ing. For example, he said, ATI’s

X1900 GPU has 48 arithmetic

logic units dedicated to parallel pixel

processing.

Gaming has become so popular

that GPU sales have risen steadily in

recent years. Between 2004 and

2008, the number of shipments of

GPUs and integrated chipsets that

include GPUs will increase from

240.1 million to 334 million, as

Figure 1 shows, with the resulting

revenue growing from $5.2 billion

to $8.1 billion, predicted analyst

Dean McCarron with Mercury

Research, a market analysis firm.

The current approach in which

CPUs handle physics limits the real-

ism of effects in today’s complex

games, as well as the ability of play-

ers to interact with multiple objects

in a scene. Thus, vendors are turn-

ing to physics schemes that imple-

ment parallelism.

In addition to adding a physics en-

gine, the new approaches change the

nature of communications within

graphics systems. The traditional

GPU-based scheme requires a sim-

ple data exchange in which the CPU

tells the GPU what to render, said

Jason Gripp, physics-engine pro-

grammer for S2 Games.

Physics processing, on the other

hand, requires more complex com-

munications. In this case, a physics en-

gine calculates the necessary realistic

response to an event in a game, such as

an explosion, and sends the informa-

tion to the CPU. The CPU then com-

municates with the GPU, which

renders the scene appropriately.

Ageia’s PPU

Ageia—a vendor of physics-accel-

eration hardware—makes the

PhysX PPU. “It is a true dedicated

hardware accelerator for physics

problems. It offloads the work from

Vendors Upgrade

Their Physics

Processing to

Improve Gaming

David Geer

Page 2

August 2006

manager. With multiple GPUs, one

chip can handle physics processing,

while the rest perform graphics pro-

cessing, or all the chips can share

graphics and physics processing.

The system works with Nvidia’s

SLI technology, which runs on its

own add-in card or cards and en-

ables multiple GPUs to work in tan-

dem to perform a task, such as

rendering or physics processing.

Havok’s FX engine handles effects

physics, according to Jeff Yates, the

company’s vice president of product

management. Effects physics creates

a richer, more immersive environ-

ment but doesn’t currently affect

game-playing activities.

In the system, the CPU does only

the processing necessary to deter-

mine which game objects are going

to move or hit one another. It then

passes this information to the GPU,

which does the rendering.

The system has been optimized

to create complex, highly detailed

shapes efficiently and quickly, ac-

cording to Nvidia spokesperson

Brian Burke.

According to Peddie, adding

physics engines to existing GPUs,

the CPU, which enhances perfor-

mance,” noted Peddie.

According to Ageia chair and

CEO Manju Hegde, his company’s

multichip approach works as fol-

lows: “The CPU thinks and orches-

trates, the GPU renders and

displays, and the PPU moves and in-

teracts.” In other words, the PPU

performs the physics processing nec-

essary to determine how to move the

objects that will be subsequently

rendered by the GPU.

The PhysX uses parallel process-

ing across 48 pipes—about four

times as many as a GPU—and sev-

eral dozen cores within the chip.

(Ageia declined to say exactly how

many cores the chip has.) Each core

is dedicated to a different type of

physics calculation, such as ballistics

physics for gunfire or fluid mechan-

ics for liquid movement.

The PhysX has several high-speed

buses that provide about 2 Tbits per

second of bandwidth. This lets the

cores exchange calculation results

quickly. The cores must share infor-

mation because in game physics,

Hegde noted, the input of one equa-

tion frequently requires the output

of another.

For example, if a player tries to

use a cannon to damage a dam so

that water will inundate an enemy

village, the system must use the cal-

culations of the cannon shot to fig-

ure out the shell’s trajectory, which

would affect the resulting damage to

the dam. This will determine how

the escaping water would flow.

In GPUs, Hegde noted, vendors

didn’t design the pipes to communi-

cate with one another, as basic graph-

ics processing doesn’t require this.

The PhysX is implemented as part

of a PCI card and will work with

any graphics-chip manufacturer’s

hardware, communicating with the

CPU via the PCI bus.

The company has released a

PhysX software development kit for

game designers.

PPUs are good for complex games

whose effects and interactivity entail

a lot of physics. However, their op-

erations are so complex, they may

take considerable time to process

games that don’t require extensive

physics calculations, noted Enderle.

The PhysX’s principal disadvan-

tages include the $300 cost, which

might be too much for non-enthusi-

asts, and the current lack of support-

ing content, according to Enderle.

Current titles supporting the

PhysX include CellFactor: Combat

Training from Artificial Studios,

Tom Clancy’s Ghost Recon Ad-

vanced Warfighter from Ubisoft

Entertainment, Rise of Nations: Rise

of Legends from Microsoft Game

Studios, and City of Villains from

NCsoft. However, 65 game publish-

ers are currently working on 105

games that will support the PhysX.

The PPU is now in some Dell desk-

top computers and will soon be in

gaming machines by Alienware and

Falcon Northwest.

Nvidia’s GPU-based approach

Nvidia uses Havok’s FX physics

engine to process physics on one or

more Nvidia GPUs that are all on the

same add-in board, said Chris Seitz,

the company’s developer account

Source: Mercury Research

100

200

300

400

2004

2005

2006

Year

2007

2008

Units shipped (millions )

Figure 1.Largely because of gaming’s growing popularity,sales of graphics process-

ing units have increased steadily during the last few years and are predicted to con-

tinue doing so.

Page 3

Computer

T E C H N O L O G Y N E W S

The GPUs have a dedicated

branch execution unit and use PCI

Express to provide high-bandwidth

connections to the CPU and other

graphics cards.

ATI’s technology enables up to

three add-in cards with GPUs to split

up physics and rendering duties.

The company offers an API that

programmers can use to write

physics code for their games.

Games that support ATI’s system

include Alone in the Dark and

Hellgate: London.

IN THE MARKETPLACE

Ageia’s PhysX uses a PCI slot,

rather than the PCI Express slot that

Nvidia’s and ATI’s approaches use,

according to Enderle. PCs generally

have more PCI slots available, so

this gives PhysX a competitive ad-

vantage, he said.

In addition, he noted, PhysX of-

fers higher performance than GPU-

which are not designed for physics

processing, is less expensive but of-

fers less performance than using a

dedicated PPU.

Thus, Nvidia’s approach is best

for users who will need less-

complex physics processing, said

Enderle.

Games that support Nvidia’s sys-

tem include Eden Games’ Alone in

the Dark and Flagship Studios’

Hellgate: London.

ATI’s GPU-based approach

ATI’s approach works with

Havok’s FX engine and an add-in

card with either one ATI GPU, a

card with multiple GPUs, or multi-

ple cards that each has more than

one GPU.

ATI uses the massively parallel

pixel-processing portion of its GPUs

to run the Havok FX engine, ac-

cording to Raja Koduri, the com-

pany’s director of engineering.

based approaches and works with

any graphics chip manufacturer’s

hardware.

According to Enderle, Ageia could

dominate the market if it can get

motherboard makers to build PhysX

into their products. PCI buses,

which the PhysX uses, tend to get

saturated and cause data-transmis-

sion delays. Therefore, placing the

PhysX on the motherboard would

enable other ways to link the chips

into the graphics system and thereby

reduce the latency, he explained.

However, Enderle added, ATI and

Nvidia may have an advantage over

Ageia because they have more

money to spend on development and

marketing, which can be critical to

commercial success.

Several other factors might affect

how the new physics approaches

fare with consumers.

For example, Havok’s Yates said,

many consumers might not want to

spend money on a physics-only ap-

proach such as Ageia’s when they

could use less-expensive schemes

that handle physics, rendering, and

other graphics functions.

he new physics-processing ap-

proaches add cost to gaming

systems, frequently necessitate

the upgrade of other hardware, and

tax the CPU and GPU because of the

additional data exchange and pro-

cessing they entail. This could delay

their widespread adoption.

And, said Enderle, “Until there

are games that use the new physics

approaches, demand will be limited.

This kind of thing could gain

ground as compelling games come

to market.” ■

David Geer is a freelance technology

journalist based in Ashtabula, Ohio. Con-

tact him at david@geercom.com.

Editor: Lee Garber, Computer,

l.garber@computer.org

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