X-bit labs

Highly Defined: ATI Radeon HD 2000 Architecture Review (page 10)

Category: Video

by Anton Shilov , Yaroslav Lyssenko, Alexey Stepin

[ 05/15/2007 | 07:34 AM ]

Back to the Future: Hardware Tesselator

High-order surfaces and hardware tessellation is not something new to consumer 3D graphics: back in 2001 both ATI Technologies and Nvidia Corp. introduced technologies aimed at improving computer games’ level of detail without adding complex geometry (which would result in additional load on CPUs, busses, etc).

There are different types of higher order surfaces:

• Bezier
• N-Patches
• B-Spline, NURBs, NUBs
• Subdivision surfaces: Loop and Catmull-Clark

However, neither of them has become popular, on the one hand due to not ideal hardware implementation, on the other hand due to the lack if support from software makers. But as end-users and game creators demand higher quality geometry, ATI believes that hardware tessellation will return, as allowing game developers to enhance geometry detail without creating too complex models may be a valuable technology.

According to ATI, next-generation DirectX application programming interface from Microsoft Corp. will actually support programmable hardware tessellation, however, the company does not explain whether the hardware tesselator available inside the Radeon HD 2000-series GPUs will be compatible with the DirectX one.

ATI claims that its hardware tesselator can be programmed using vertex shaders, which is a surprise, as DirectX 10 features geometry shaders capable of adding vertexes to models. On the other hand, ATI claims that its hardware tessleator is similar to that of Xbox 360 GPU, which, being a DirectX 9-like chip, does not feature geometry shader.