Moving closer to a 'Matrix'-style virtual world

Bryn Nelson Columnist

What if a computer could make you a picture-perfect glass of milk, let you feel the tension as it pulled an ant’s leg from another room, and chat you up with the charisma of Oprah Winfrey? No one machine can do all three — yet. But some sophisticated new projects are showing just how far we’ve come toward creating an “I can’t believe it’s not real” virtual world.

Last month, Brookhaven National Laboratory computer scientist Michael McGuigan told New Scientist magazine he believed a “Matrix”-style virtual world, in which one cannot always distinguish between what’s real and what’s not, could be up and running in just a few years. His optimism derived in part from the impressive ramp-up in processing speed he obtained with the lab’s BlueGene/L supercomputer while running a conventional ray-tracing software program that mimics the effect of natural light.

The result? An eye-fooling virtual beam.

Henrik Wann Jensen, an associate professor of computer science and engineering at the University of California at San Diego, is among those leading the charge toward more powerful algorithms that yield, say, a convincing fog-shrouded lighthouse or a frosty glass of 2 percent milk. Best of all, the convergence of speed and power means those virtual stand-ins don’t necessarily require a room-sized supercomputer to produce them.

“Now is a pretty exciting time in graphics,” Jensen says. “We’ve reached a level now where we can make very realistic images: five to 10 hours to make images more or less perfect, where people say, ‘Wow, that’s a photograph!’ ”

Maintaining the same illusion for real-time animation isn’t as far along, largely due to its enormous appetite for computing power. But that limitation is quickly falling by the wayside, Jensen says, with the aid of muscular new graphics processors like Intel’s Larrabee chip and Nvidia’s CUDA technology.

Pushing the envelope
Jensen is attacking the problem of limited power from the other end by cutting the computational costs of graphics-producing algorithms known as ray tracing and photon mapping. Ray tracing follows a beam of light through a virtual environment, mimicking how the beam would interact with its surroundings. Photon mapping is essentially the reverse, and together, the two algorithms fit into what Jensen calls global illumination, a framework for simulating how light bends a spoon in a glass of water, cuts through the swirl of smoke around a spotlight stage, or penetrates a thick fog in the form of a lighthouse beam.

“In many ways, we’re just taking the physics of nature and trying to simulate that,” he says, but in a streamlined way that uses far less power. Instead of counting all the photons associated with a light source, Jensen’s algorithms start with a question: If you place a set of eyes at a specific spot in a scene, what would they see? Previous methods sampled photons here and there across a light source, but Jensen’s technique maps the relevant photons along the light’s entire pathway, letting a graphics interface follow the light around a scene and determine how much will be absorbed, reflected or scattered by other objects.

For the first “Shrek” movie, filmmakers told Jensen a scene with the Gingerbread Man and a glass of milk was one of the most difficult to produce. “They didn’t think of milk as a medium like fog,” Jensen says, and consequently used the wrong technology to simulate how light interacted with it.

“Shrek 2” incorporated some of Jensen’s early work to improve upon its milk simulation. Last August, at the annual SIGGRAPH computer graphics conference in San Diego, Jensen and colleagues went even further by showing how to mix water, protein, fat globules and B2 vitamins in different concentrations to yield a realistic glass of skim milk, whole milk, or even cream. (He is often called “the milk guy” at these conferences).

The movie and gaming industries are both pushing the envelope, Jensen says, and a virtual world that can quickly change yet look very realistic at the same time is on the horizon. “We need just a little bit more time and slightly better computer power to get it to the level where you’d think, ‘Wow! This is absolutely amazing!’”

Even so, creating a realistic human face that can talk in real time remains a big obstacle, and Jensen is working on improving the look of virtual skin. “We are, as humans, just trained to look at faces,” he says. “In a virtual environment, where you use a computer-generated figure that doesn’t look quite right, it’s a distraction from the action of the movie.”

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