Filtering
The X850´s default filtering algorithm is unchanged with the X1800. Still, ATI introduced a new “high quality” filter in the drivers. If before the filtering level changed a lot depending on the viewing angle, this time with this option activated, filtering is almost optimal from any angle. Textures change to lower definition mipmap and are of better quality. We can see that with the following animated GIF where mipmap changes are coloured:
This is a very good thing even if we have to keep in mind that the cost to performance isn’t negligible. With the flight simulator, Pacific Fighters, which is particularly sensible to filtering speed, we reach 51.1 fps in 1920*1200, and fall to 39.2 fps with 8x anisotropic filtering and 30.7 fps with the same “quality mode”. The possibility to choose its activation is advantageous, because for certain cases the impact on performance can be significant.
With a newer game, which uses many shaders, the filtering cost has a reduced influence thanks to ATI’s architecture separating the texturing block from the pixel shading bloc. With Splinter Cell CT, we reached 76.4 fps in 1600x1200, 75.6 fps with 8x aniso activated and 75.4 with the “high quality” mode! In other words, the impact on performance is negligible and we thank ATI for improving filtering quality, something that had not happened for a very long time.
Anti aliasing
For anti aliasing, ATI recently made available a new hidden option called Adaptive antialiasing for the whole DirectX 9 line. Of course, this includes the X1800. Similar to the Transparency AA introduced by NVIDIA with the GeForce 7800 GTX, it consists of using a supersample anti-aliasing type instead of multi-sample for surfaces with alpha tests, which aren’t filtered when we simply use multi-sampling. Here are a few screenshots to see the quality differences:
ATI without AA, ATI AA4x, ATI AA4x + AAA, Nvidia without AA, Nvidia AA4x, Nvidia AA4x + TAAIt works for both manufacturers. Results aren’t identical for ATI and NVIDIA as solid parts of objects like grids seems to be thicker for NVIDIA. It is hard to know which is better from this example alone.
Looking at the table you can see that antialiasing cost is smaller with X1800 than it is with the X850, thus allowing ATI to increase its advantage over Nvidia with this mode.
The cost to performance due to this activation of what we will call “Transparency Supersampling” is variable according to the type of scene. Under Colin Mc Rae, compared to standard anti aliasing, we see that it is relatively significant, because of the presence of numerous types of foliage:
Costly for NVIDIA in AA 2x, the TS is however more so for ATI in 4x. Figures don’t show any specific optimisation for this function with the X1800 compared to the X850.
