HANDS ON GUIDE

7 - Real-time ray tracing

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WHAT IS IT?

Ray tracing is the movie industry’s preferred method to render images. The visual quality is far higher than the graphics of any computer game on the market, because the computationally expensive method of ray tracing doesn’t have to deliver a constant 30 frames per second. Instead, each frame of a ray traced film may take hours or days to render, using powerful graphics workstations. In a computer game, the PC has to constantly render frames and continually update the screen using a technique called Rasterisation, where mathematical coordinates of 3D objects are converted into pixels.

This distinction between graphics for movies and graphics for home computers is now beginning to look decidedly murky though, as Intel, ATI and Nvidia are looking to produce graphics cards that are capable of ray-tracing.

HOW DOES IT WORK?

A ray traced scene is one in which beams of light are calculated from the viewer’s vantage point, falling on each object and producing a scene with amazing photorealistic detail. A staggering number of computations are needed to do this, requiring hardware that is unaffordable to most home users.

However, GPUs are becoming more advanced and flexible, prompting many to believe that ray tracing may become possible in games. The stream processors, the ‘cores’ of a GPU, can perform more different types of calculation than ever, and are able to run more complex software. Nvidia has demoed a racing game rendered entirely with ray tracing on the Geforce GTX 280.

Intel’s forthcoming discrete graphics card, Larrabee, is being hyped-up as capable of bringing real time ray tracing to the desktop, by using multiple X86 cores. AMD’s Fusion architecture aims to unify the CPU and GPU, producing a heterogeneous architecture that (ideally) allows cores to be assigned as either a GPU or CPU. This extra processing power might be excellent for rendering ray traced scenes.

WHAT COULD GET IN THE WAY?

Intel has invested a lot of time into hyping Larrabee, but the task of ray tracing in real time is far from simple. Hardware may still have some way to go before all our games are rendered this way. Tom Forsyth, a software engineer working on Larrabee, confirmed that ray tracing will not the primary rendering method of the graphics card.

“I've been trying to keep quiet, but I need to get one thing very clear. Larrabee is going to render DirectX and OpenGL games through rasterisation, not through ray tracing”

There’s also the problem that game developers have spent a long time creating tools and engines that are optimised for rasterising a scene rather than ray tracing it. This makes it easy to port a title from PC to console, something developers like as it adds a layer of bulge to their wallets. If the next next-generation consoles (Xbox 720? Playstation 4?) still use rasterisation as their primary rendering method, it will be profitable to avoid ray tracing and stick with rasterised graphics.

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