Trilinear Filtering Optimisations
One of the most scrutinised parts of NV40's image quality will be the difference between full trilinear and trilinear with optimisations, the selection of which is finally present in the driver.
Optimisations are off on the left, on on the right, and the difference is clear. There's a much smoother transistion between texture stages when optimisations are off, with the optimisation looking very much like NVIDIA's much criticised brilinear filtering method. The texture filter with optimisations enabled isn't really acceptable for best image quality, despite sometimes being hard to spot in motion, in some games. It most obviously manifests itself as texture aliasing, where you can clearly see the transitions between mipmaps and they can appear to creep during certain types of motion.
With the full trilinear filter obviously having an effect on performance, otherwise NVIDIA would have discarded the optimisations completely with NV40, let's examine its performance.
With optimisations off, performance is around 8% less.
At 1280x1024 performance drops nearly 14% without the optimisation.
There's clear performance difference between the two, something to bear in mind during the performance benchmarks you'll see later (that apply texture filtering), which were all done with the optimisations disabled and the full trilinear filter therefore enabled.
