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I’ve heard Havok FX referred to as SLI Physics as a kind of shorthand, but as far as I’m aware there is nothing in Havok FX to prevent it running on any Shader Model 3.0 graphics system, provided it has enough grunt to run the physics. If that’s the case then Havok FX will run equally well on an ATI CrossFire system, unless the game performs a sneaky driver check to make sure you’re running green graphics cards, rather than the red devils. To be absolutely clear, nVidia’s briefing document on Havok FX says ‘There are no announcements or demonstrations at GDC of Havok technology on ATI GPUs.’

There are conflicting views about these two approaches; the Havok FX method adds physical effects after the Artificial Intelligence has placed the characters and objects and at about the same time that the graphics card(s) add textures and lighting effects and then outputs the final result to the display. This means that it is nigh-on impossible to perform collision detection on the objects that are controlled by the physics part of the system, which means that while it adds to the eye candy it doesn’t greatly affect game play.

The Ageia approach is ‘proper’ physics, so one object can affect another. For instance as you pass through a corridor that is filled with smoke or fog, the game won’t simply treat it as a semi-opaque surface but instead the fog will swirl as you pass through the corridor, just like the real thing. The PhysX card acts like a co-processor so its work is added into the mix of the calculations that are performed by the CPU and the graphics card, and the result is that all of the objects can interact with each other.

In theory this will increase the total workload significantly as the PhysX card will create many more objects and will handle their behaviour and motion, however the appearance of the new objects will be passed off to the graphics card. This will make life easier for your CPU but potentially far harder for your GPU, which is fine if you have graphics power to spare. If, instead, you make a point of running your games at settings that deliver a frame rate that is just above the threshold of acceptability then you may find that a PhysX card means that you gain in one area but have to make adjustments in another, perhaps by lowering resolution or reducing anti aliasing.

Neither approach will be any good unless whichever technology you employ is fully supported by the engine in the game you are playing and at present physics aren’t part of DirectX, although that may change in the future.

nVidia hasn’t made any announcements about games that are being developed with Havok FX but the Havok engine is used in Age of Empires III, F.E.A.R., Half-Life 2 and Painkiller - among others – so there’s a strong chance that it will convert a good few developers to its cause.

Ageia, by contrast, has been pushing its PhysX engine and has only one notable name signed up - but it is a huge name: Unreal Tournament 2007. We’ll also see the PhysX technology used in Rise of Nations:Rise of Legends and Tom Clancy’s Ghost Recon Advanced Warfighter. In addition PhysX technology is lurking inside Xbox360 and PlayStation 3 so it has a significant toehold, but we’ll have to see whether it can leverage its position.

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