Anti-aliasing - Sample Pattern Analysis
The base sample patterns for R420 haven't changed since R3x0, and for the best. It's widely acknowledged that ATI's anti-aliasing quality is the best on consumer graphics hardware. NV40 doesn't overtake R360 in that respect, so an unchanged scheme in R420 is fine.No anti-aliasing
Just a quick base grid that does no anti-aliasing, so we can get our bearings. Red squares are where the hardware samples geometry for that pixel, green squares are texture sample points.
No anti-aliasing
2X anti-aliasing
2X offset rotated grid multi-sampling
ATI's 2X multi-sample mode uses an offset 45° rotated sample grid. Its offset nature gives slightly higher IQ than a non-offset grid at the same angle.
4X anti-aliasing
4X sparse grid multi-sampling
4X SGMS provides maximum pixel coverage for a four-sample grid, giving rise to the highest image quality possible for a 4X multi-sample mode. It's no wonder that NVIDIA arranged such a similar mode for their newest hardware.
6X anti-aliasing
6X sparse grid multi-sampling
6X SGMS is ATI's maximum AA mode on R420, following on from identical modes on R3x0 class hardware. An 8X SGMS mode is counter productive to implement in a scattered grid fashion; cramming 8 pixel sample points into a single pixel space in scattered fashion doesn't give rise to much higher AA quality than their existing 6X grid.
ATI do have something else up their sleeves AA wise however, to appease those pining for new AA modes.
