Antialiasing Quality - In practice
We start with output from Nonatainment's AA tester. It nicely shows off coverage sampling limitations at triangle intersections, while showing off its quality on free edges in conjunction with multisampling. We used
Override any application setting to set the AA levels in all cases. The order is 0x, 2x, 4x, 8x, 8xQ, 16x, 16xQ.
The interesting cases are 4x-vs-8x-vs-16x and 8xQ-vs-16xQ, because of the multisample counts for each of those modes. In the first case, where the black triangle meets the white one at their intersection, you can see AA quality is much the same (not completely identical though) despite more coverage samples being taken in each case. CSAA is therefore not always enabled per-pixel there and you get equivalent quality, whereas on the triangle edges where there's no intersection with other geometry, CSAA is allowed to work (and work well). It pays to remember that CSAA consumes stencil sample allocation, so depending on stencil tests, CSAA might be disabled per-pixel there too, even if the coverage data would have let it run.
The same happens in the second case with 8xQ and 16xQ, where multisample count is the same and CSAA doesn't help too much at the triangle intersection for those pixels and is broadly equivalent across the two modes. That's in contrast to edge quality where there's no intersection goes up, and which is higher for 16xQ due to CSAA.
Game Quality - Oblivion
We use a 200% zoomed crop from a 2560x1600 Oblivion screengrab to show (in a limited fashion, as much as one crop from one screen in one game is able to show you) AA effects in G80 in a shipping game title. Click for bigger versions. The order is 0x, 4x, 8x, 8xQ, 16x, 16xQ.
The effect of each mode is somewhat obvious, with diminishing but still obvious returns after 4x, and 16xQ looking subjectively fantastic. Combine a high level of AA in Oblivion via the driver control panel, with HDR and transparency AA, and the game can look very very pretty indeed. See? (2560x1600, 16xQAA, 16x High Quality AF, Transparency supersampling AA)
