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The Tech Challenges to Photorealistic Games

Shortcuts and future solutions

Unreal Engine 4: voxels in place of ray tracing

"Ray tracing takes so much computer power that it's not feasible in a game in the next few years," Jensen told us. "It's getting there — the technology will help push games to the next level."

Even taking into account Moore's law — the observation that computer capability has roughly doubled every two years since the 1960s — commercial gaming devices won't be able to run fully ray-traced scenes in just 10 years, Jensen says.

Epic Games, instead, has developed a technology called "Sparse Voxel Octree Global Illumination" (SVOGI). This technique is a modified version of ray tracing that uses voxels — or three-dimensional, cube-shaped pixels — to simulate light rays. Epic's Unreal Engine 4 creates "trees" of voxels, which have a measurable thickness, kind of like building lines of see-through, luminescent Legos within a scene. True ray- tracing uses rays of light, which are one-dimensional mathematical lines and do not have a measurable thickness.

But even SVOGI, if it's true SVOGI, is too demanding for commercial gaming devices; the technique would require a machine of at least 1 teraFLOP capacity. For perspective, that's 40 times more powerful than the Xbox 360.

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Epic Games has created a version of Unreal Engine 4 that uses a modified version of SVOGI and will run on next-generation consoles, the PlayStation 4 and Xbox One, as well as the Oculus Rift virtual-reality headset.

"It's clear now that voxels play a big role in the future," Sweeney told gaming news site Gamasutra in a March interview.

Path tracing shortcut?

Caustic Professional, a division of Imagination Tech that specializes in developing ray-tracing graphics technology, defines ray tracing as "the ability of the shader [that is] running for one object to be aware of the geometry of other objects." When the appearance of a given object is rendered, the ray-tracing calculation incorporates the location, brightness and reflectivity of other objects in the scene. By making one object's appearance mathematically dependent on all the other objects, the computer is able to produce a rendered scene that appears realistic. Caustic calls this method "path tracing," and the company believes this alternate technology will enable photorealism well within Sweeney's 10-year timeline.

"Three years from now, big triple-A game titles will look like movies," Caustic co-founder Luke Peterson told us. "We're very optimistic about the timeline, because we know what our technology is capable of," he said.

Peterson declined to go into specifics, however, saying he didn't want to reveal too much about what Caustic's clients were doing with the technology.

Even ray tracing isn't enough

Intel researcher Daniel Pohl has redone several classic video games, including "Quake" and "Wolfenstein," using true ray-tracing.

Pohl has demonstrated his "Wolfenstein" remake on a laptop. But that's deceiving. The laptop is not running the game — it's streaming the video from four dedicated servers, all running a high-end Intel multiprocessor nicknamed Knights Ferry. This multiprocessor was made available to a limited number of developers in 2010. A commercial release, called Knights Corner, was scheduled for a 2012 release, but it has yet to reach shelves. 

The architecture in Pohl's demos looks photorealistic, as does the chandelier he added to "Wolfenstein"; the fixture consists of 1 million polygons, rendered using glass's actual refractive index, an assigned number that represents how light passes through a substance.

However, the demos' other scenes fail the photorealistic test. The soldiers in Pohl's "Wolfenstein" demo all walk with an identical, stilting gait, and flames — notoriously difficult to animate — appear flat and soft, still a far cry from realistic.

Pohl's "Wolfenstein" demo shows that photorealism means more than correct lighting. "Ray tracing by itself is not enough to achieve [photorealism]," Jensen said. "You need to have the complex 3d models, the animation — all the elements work together to create the experience."

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