NVIDIA was the first IHV that introduced Multisampling anti-aliasing to the
PC graphics market since 2001 with the GeForce3 class of accelerators (NV20).
It supported 2x rotated grid (RGMS), Quincunx (2xRGMS + 5-tap blur filter)
and 4x ordered grid (OGMS) Multisampling. Changes in NV25 (GF4Ti) and NV3x
(GF FX) were minor, with the difference that hybrid Super-/Multisampling modes
had been added.
The company received a lot of criticism – especially during the NV3x
era – for not supporting also 4xRGMS, while the competition did since
fall 2002. It’s not that there isn’t a quality difference at all
between 2xRG and 4xOGMS, yet it is in analogy that small, that it hardly justifies
the added performance penalty for 4xOGMS (especially in high resolutions),
considering that both modes result to a 2*2 sampling grid. Granted edge equivalent
resolution (EER) isn’t the “be all–end all” with anti-aliasing,
yet with pure Multisampling it gains in importance.
With the NV40 (GF 6) class of accelerators the company finally introduced
a 4xRGMS mode and thus finally delivers an equivalent sampling grid as the
competition with 4x sample MSAA. Hybrid modes still exist and some can be exposed
through 3rd party tweaking applications.
Let’s have a closer look at what each mode really looks like, with Colouless’ DX9FSAA
2xRGMS (2*2 EER):
4xRGMS (4*4 EER):
8x (4xRGMS + 1*2OGSS) (4*8 EER):
(Unofficial modes exposed through Rivatuner)
4xS (1*2xOGSS + 2xRGMS) (2*4 EER):
8xS (4xOGSS + 2xRGMS) (4*4 EER):
Of course are there other anti-aliasing modes I’ve left out (2x vertical
SS, 2x horizontal SS, 2*2 SS, Quincunx, 4x – 9-tap and 6xS) which can
be enabled via Rivatuner or 3Dcenter’s Atuner, yet they deliver only
minor differences compared to the modes above.
Update: I was obviously wrong since I concentrated too much on the VS2.0 test results.
The 6800 has besides one quad, also one VS unit disabled and thus 5 operational VS units after all.