There has been some considerable confusion as of late about the various FSAA modes that NVIDIA has enabled in its 5.22 beta drivers. We are seeing various benchmarks and screenshots, but exactly what are those different modes and how do they work?
While information has been published about the 5.22 beta Detonator drivers and their support for various D3D FSAA modes, we personally have found the explanations found of the various settings to be confusing. Judging by the comments on various forums, we are not the only ones. This article explains (1) how NVIDIA performs FSAA and (2) what the various D3D FSAA settings or modes in the 5.22 beta drivers actually mean and what they do.
NVIDIA has implemented an Ordered Grid Super-sampling (OGSS) Technique. This is a technique that can be implemented on almost all 3D accelerators, given that they support rendering to an off-screen buffer. An off-screen buffer has room to store the frame's pixel colors, as well as the Z and Stencil values. However, it differs from a conventional front- or back-buffer in that it is never displayed directly on screen.
The OGSS method uses a regularly-patterned ordered grid of sub-samples for each pixel. Sub-samples arranged in a column and row-like way around the original pixel are used to create what is in essence a more detailed collection of adjacent texture samples for the original pixel. Below, I provide a step-by-step account of how NVIDIA appears to use hardware-based OGSS anti-aliasing. Although some people call this a software implementation, this is incorrect. This specific technique uses existing "hardware" features to create an anti-aliased result, as we'll explain.