Transparency antialiasing is a desirable feature that antialiases objects that are derived from alpha textures. The following example from 3Impact demonstrates how an alpha texture is created. Objects in the game world typically originate from basic geometric shapes, or primitives, which are antialiased using traditional multisampling algorithms. However, multisampling does not antialias objects that exist inside the geometry, such as an alpha texture.
Alpha Texture Mapping
The following demonstration shows the effects of the various antialiasing settings in a scene from Far Cry's Regulator map. Click the links underneath the image to display the respective screenshot.
Notice that in this example, both the 2x and 4x multisampling modes are ineffective in removing the jagged edges that appear on the tree's leaves and the crane's boom and wires.
TRANSPARENCY ANTIALIASING PERFORMANCE
The following results show the impact of supersampling transparency antialiasing on the average and minimum frame rate at various resolutions in S.T.A.L.K.E.R.
At 1680x1050, the average frame rate dropped from 59fps to 54fps on the EVGA GeForce GTX 260 Core 216 Superclocked, which was a hit of 8%. The drop in performance at the resolution of 1920x1200 was 10% and at 2560x1600 was 9%.
Next up is the impact of multisampling and supersampling transparency antialiasing on the average and minimum frame rate in Oblivion. The impact of transparency antialiasing on performance was much greater in Oblivion that it was in S.T.A.L.K.E.R.
At the resolution of 1920x1200, the average frame rate dropped from 62fps to 53fps with multisampling and to 43fps with supersampling transparency AA on the EVGA GeForce GTX 260 Core 216 Superclocked. This represented a drop in the average frame rate of 15% and 32% respectively.
Transparency Antialiasing Performance - Oblivion
The impact on the minimum frame rate was similar to the average.