HANDS ON GUIDE

02 - Count Those Polygons

The difficulties in delivering CG quality graphics in real time

COUNT THOSE POLYGONS

It's clear just how far hardware has to advance before we can even think about rendering this level of 3D detail at 25fps. Let's face it - one frame per hour would look diabolical on a benchmark graph. As EA's Sanjay Mistry remarks, 'A dinosaur in a film could have the highest values with regards to the polygon count, and you won't be restricted by your hardware, since you don't need to render it in real time. With a game, you have to think about how you construct your geometry.'

According to Mistry, the polygon count is always at the back of your mind when you're producing a game, despite shaders reducing the need for overly complicated geometry. 'It doesn't matter what you do,' says Mistry, 'The core level geometry is still polygons, so you need to ensure that these polygons are constructed in the correct way.' However, the polygon count is an aspect you don't need to consider in film. In fact, Cinesite's Simon Maddocks doesn't even know how many polygons he's working with half the time. The polygon count is almost arbitrary, he says, especially with the industry's heavy use of subdivision surfaces.

Subdivision surfaces were first used in film in Pixar's 'Geri's Game', in which an old man plays himself at chess. They were needed to recreate the perfect curves in Geri's wrinkled skin. The idea is that an object starts with its usual set of polygons, but a 'subdivision' mesh is then placed around it at render time, which automatically evens out the edges and calculates how many extra polygons are needed to create the illusion of a smooth object. Maddocks explains, 'If I build a model of a hand from 300 polygons, and then run a subdivision mesh on it, the model will instantly round itself off and become a far more detailed object. It will probably contain 100 triangles that need to be rendered if it's in the distance [of the scene], but if it's up close [to the camera], then there might be 10,000 triangles that need to be rendered.'

This is one area in which films have a distinct advantage over games, and the main reason for game characters often having angular heads, despite having detailed faces. Games rely on shaders to fill in the detail but, at the end of the day, you still need lots of polygons for an object to look realistic. Various experiments have been performed with subdivision surfaces in real time in games, though, and it's hoped that developments such as the geometry shader in DirectX 10 will help to accelerate this further. However, games are a long way from being able to create perfectly smooth objects like those you see in films without running into frame rate problems.

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