HANDS ON GUIDE

03 - Ray Tracing

Achieving visual realism through calculating how light creates shadows and reflections and how it bounces off objects.

While there are clearly ways around these potential problems with ray tracing in games, one major barrier is the power of today's hardware.

'A frame rate of 60fps using ray tracing may take several years to accomplish,' admits Mistry. 'It isn't something we'd discard, but it may take a while to get there.'

Maddocks uses ray tracing as another instance of why you can't open a whole 3D scene on a workstation, particularly when there are lots of characters and objects in a scene. He provides the example of a battle scene, where there are hundreds of soldiers, and each of them has weapons that reflect both armies. 'For this kind of scene,' Maddocks explains, 'you make an environment map (where the environment's reflection is mapped as a texture, rather than a calculated reflection) that contains some soldiers, so you can reflect this instead of ray tracing the armies.'

'Everyone loves ray tracing but it's overly demanding,' says Maddocks. 'Every time you're reflecting an object with ray tracing you have to prepare the entire environment. Rays are like cameras - they have to be pointing at something meaningful, even if they're bouncing off a phone booth. This is why we cheat. No one knows what the other side of the reflection is like in the real world; they just care that it looks good in the film.'

In fact, the processing power needed for ray tracing is so great that even a specialist CG firm such as Cinesite won't ray trace everything in a scene. 'In a scene that's very complicated,' explains Maddocks, 'we ray trace some individual parts, but not everything, as there's no gain. Some of the shading models are so simple that they don't demand the kind of accuracy that ray tracing provides.'

This hasn't deterred Intel from trying its hand at real-time ray tracing in games, though. The company hired German ray tracing whiz kid Daniel Pohl last year, who had previously ray traced Quake III and 4 as a personal project. At IDF in November 2007, the year in which Intel first announced its Larrabee graphics chip, which will comprise multiple processing cores probably based on the X86 architecture, Daniel Pohl demonstrated some amazing graphics using real-time ray tracing. At the time, he needed several Xeon rigs linked by 1Gb/sec network cables to run it, but Jim Hurley, the senior principal engineer at Intel's microcomputer graphics laboratory, told us at IDF that we could expect to see games using ray tracing in two to five years.

Bearing in mind the sheer level of processing power needed to ray trace in films, it's fair to say that the first generation of ray traced games won't be of the same quality as current films. Ray tracing's role in game graphics is a matter of some debate.

Nvidia in particular had expressed strong words for Intel's aggressive push towards ray tracing. While the firm concedes that ray tracing will have a part to play in the future, its representatives prefer to describe it as 'one more tool in the toolbox', rather than a replacement for current techniques of rasterising 3D scenes.

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