Texture Filtering
We'll use SS:SE's Citadel demo to test the various filtering modes available on the Xabre 400. SS:SE's OpenGL renderer was used again, with the ExtremeGFX addon.
Xabre 400 does not feature any Anisotropic filtering modes, so we'll just take a look at the normal Bilinear and Trilinear rendering options.
| 640x480 | 800x600 | 1024x768 | 1280x1024 | 1600x1200 | |
| Bilinear | 78.7 | 73.7 | 54.6 | 36.5 | 25.7 |
| Trilinear | 67.0 | 74.4 | 56.2 | 37.0 | 26.4 |
| % Difference | -15% | 1% | 3% | 1% | 3% |
Its fairly odd to see that, 640x480 aside, the performance of Trilinear filtering is greater than that of Bilinear filtering. This could suggest that each of the texture units per pipe are Trilinear capable -- however the 640x480 score may suggest something entirely different.
Lets have a look at the IQ of each of the modes.
Trilinear
As we can see from the output of both the images, Trilinear filtering does not appear to be enabled, despite it being selected in the application. We've see this on other occasions, where the 'Colour Mip-Map' option doesn't necessarily tell the whole story if an alternate method of Trilinear filtering is utilised by the hardware. In this case, though, it doesn't look as though anything like this is occurring with the Xabre as the mip-map lines are visible in the normal Trilinear screenshot.
640x480 Trilinear
As the screenshots above show, if the resolution is dropped down to 640x480 normal Trilinear filtering comes into operation. It would appear from this, and the scores of the OpenGL benchmarks, that the drivers are just disabling Trilinear at resolutions above 640x480 under OpenGL in order to increase performance in these higher resolutions.
