By Lars Weinand - Editor In Chief RIVA Station / Editor Tom´s Hardware Guide

Smart Shader 2.1

The most interesting change from SmartShader 2.0 and 2.1 is the addition of the so-called "F-Buffer", which stands for "Fragment-Stream FIFO buffer". With this new technique, it's theoretically possible to run shader code of infinite length without having to resort to performance-reducing multi-pass operations - note the word "theoretically." In practice, the VPU's performance will quickly limit the length of code that can realistically be run.

The advantage is obvious, though. If the length of a certain piece of shader code exceeds the maximum length specified in DirectX 9, the effect has to be broken down into several steps or passes - if possible. The trouble is that each pass will again require bandwidth-intensive memory accesses (vertex processing, backface culling, triangle setup, texture sampling, pixel shading, stencil testing, Z testing, anti-aliasing). The F-Buffer solves this problem. The concept of the F-Buffer is built on the ideas of William R. Mark and Kekoa Proudfoot of Stanford University.

In practice, the F-Buffer probably won't play much of a role in the foreseeable future, since it will likely be a while yet before pixel shader 2.0 code makes an appearance in games, let alone exceeds the maximum code length. Current chips simply don't offer sufficient performance. By the same token, the extended programmability of the GeForce FX is only a theoretical feature at this point.

Copyright: 09.03.2003 -   RIVA Station 2003 - Lars Weinand
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