Trilinear Filtering - Colored Mipmaps
With standard trilinear filtering selected, ATi's X800 sticks very close to Refrast. The image produced by NVIDIA's GeForce 6800 Ultra clearly shows that the card uses a different LOD calculation at 45-degree angles. You can see it by looking at the indented ellipse. Imagine a perfectly round tunnel, and the ideal LOD pattern would be a perfectly round circle, so even Refrast is not correct here.
Trilinear Filtering - Black/White
Looking at the textures, the effects are much less noticeable than the colored mipmap comparison might suggest. Nonetheless we can see the differences in the GF 6800 Ultra's image. The interesting thing is that X800 and Refrast look better on the screenshots in a head to head comparison. This is because of the higher level Mipmaps at 45-degree angles. Although this looks better on screenshots, it can cause sparkle in motion.
Here's what Microsoft has to say about it:
Quote: "The DX9 reference rasterizer does not produce an ideal result for level-of-detail computation for isotropic filtering, the algorithm used in NV40 produces a higher quality result. Remember, our API is constantly evolving as is graphics hardware, we will continue to improve all aspects of our API including the reference rasterizer."
