Havok FX

The Havok SDK is a major competitor to the PhysX SDK. Used in more than 150 games, including major titles like Half-Life 2, Halo 3 and Dead Rising.

To compete with the PhysX PPU, an edition known as Havok FX was to take advantage of multi-GPU technology from ATI (CrossFire) and NVIDIA (SLI) using existing cards to accelerate certain physics calculations.

Havok's solution divides the physics simulation into effect and gameplay physics, with effect physics being offloaded (if possible) to the GPU as Shader Model 3.0 instructions and gameplay physics being processed on the CPU as normal. The important distinction between the two is that effect physics do not affect gameplay (dust or small debris from an explosion, for example); the vast majority of physics operations are still performed in software. This approach differs significantly from the PhysX SDK, which moves all calculations to the PhysX card if it is present.

Since Havok's acquisition by Intel, Havok FX appears to have been shelved or cancelled.