03 - Ray Tracing

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

RAY TRACING

The other area in which film has traditionally been miles ahead of games is lighting, but PCs could be on the brink of a revolution in this field. Ray tracing, whereby a ray of light is traced around a scene, with the computer calculating all the reflections, shadows and angles of incidence, makes 3D scenes look incredibly realistic. Due to its phenomenal hardware demands, it isn't often used in the games industry where frames have to be rendered quickly in real time. However, Intel has recently been talking about making real-time ray tracing a possibility in games.

This concept came as a surprise to Cinesite's Sue Rowe, though, who said 'I can understand using ray tracing to mimic a scene from a live action set, but how would it work in games?' It's all very well to say that ray tracing will give games super-realistic lighting, but a 100 per cent accurate lighting system isn't always what you want. Rowe explains that 'ray tracing gives you exactly what the computer thinks it can see, and sometimes that isn't very pretty'. Maddocks concurs, adding that with CG, your aim is to 'create what the director wants, and that isn't always realism'.

Maddocks provides the example of the glass elevator in 'Charlie and the Chocolate Factory', which was created at Cinesite. 'Willy Wonka and his guests fly out of the factory in a glass elevator,' he explains. 'The glass is reflecting everything in the environment, but when the visual effects supervisor saw it, he asked, "Wouldn't we see chimneys reflected in the glass?" What he really meant was "please can I see some chimneys reflected in the glass?"'

As a result of the mathematically precise nature of ray tracing, chimneys weren't reflected in the glass because they weren't in the right place in the scene to be reflected. 'That's no good for dramatic storytelling though,' says Maddocks. 'The director wants to show that they're going around the factory, so you have to bend everything out of shape, such as building fake chimneys at odd angles that don't show up in the main scene, but show up in the reflections, just to fulfil what they want.'

This is fine when you have the ability to exclude unwanted elements from a scene, as with a film shot, since the viewer only sees it from the director's point of view. However, it's a different story in a game, where the director is effectively the player and they can move anywhere they like in a scene.

According to EA's Sanjay Mistry, this isn't necessarily a huge problem though. He points out that both films and games end up on a 2D screen, but games can be adjusted in real time. 'In a film, once it's done, it's done, but there's no stopping for the computer,' says Mistry.

As such, he explains that 'there are a lot of engineering elements going on behind the scenes, such as switching objects on and off within the scene, or including certain switches in the scene that, when activated, say "now we need to have subsurface scattering on in this area" or "bloom effects needs to be on" and so on'.

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