3D Image Quality: Texture Filtering

The default filtering quality of SiS Xabre has every reason to be called awful. The level of detail (LOD) is too low compared with that by ATI and NVIDIA chips, the image suffers from terrible "ripples" and "seeming double" or simply missing pixels. Moreover, enabling tri-linear filtering in applications doesn't seem to work: there is no tri-linear filtering at all.

I will not load the article with the screenshots of all these horrors, I will just give you a couple of most vivid examples from the Serious Same: The Second Encounter game. On the left you can see bi-linear filtering performed by Xabre and on the right - normal bi-linear filtering in the same scene and testing conditions:

Bi-linear filtering by SiS Xabre		Normal bi-linear filtering

You can clearly see that starting from a certain MIP-level, Xabre implements some poor quality approximation instead of bi-linear filtering on a half of each MIP-level.

But this is not the end. Those halves of MIP-levels, which seem to have better quality, also cannot boast "fair" texture filtering: Xabre draws two pixels in a row with the same colour this way trying to save time and trouble processing extra texture samples and applying bi-linear filtering to them. This "doubling" is very noticeable: on the left you can see a screenshot with bi-linear filtering performed by Xabre and on the right - the same scene with coloured MIP-levels:

Bi-linear filtering by SiS Xabre		Same scene with coloured MIP-levels

Do you like it? I don't, actually.

Luckily, Xabre still does support some better quality texture filtering modes. When studying the drivers I came across the following section in the registry: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Video\{4EF3E084-AFC7-4AE5-9AB3-EB7231C834D8}\0000, where all Xabre drivers and utilities save their working settings:

This sections has a DWORD key responsible for the "speed-to-quality" ratio during texture filtering: SiS.3D.TexTurboMode. This key is set to 3 as default, and the image "quality" in this case has been already demonstrated above.

I managed to find two more working modes for this key: SiS.3D.TexTurboMode=1 and SiS.3D.TexTurboMode=0. In case of SiS.3D.TexTurboMode=1, the level of detail increases, texture bi-linear filtering becomes normal and it appears possible to enable fully-fledged tri-linear filtering.

In case of SiS.3D.TexTurboMode=0, that is when no "turbotexturing" is enabled, the level of detail increases even greater and nearly reaches that of NVIDIA GeForce3 Ti200.

The screenshots below are taken from Serious Sam: The Second Encounter in all three modes: on the left you can see bi-linear filtering and on the right - tri-linear filtering enabled in the games settings:

Bi-linear filtering		Tri-linear filtering
SiS.3D.TexTurboMode=3
SiS.3D.TexTurboMode=1
SiS.3D.TexTurboMode=0

Well, the filtering quality in case of SiS.3D.TexTurboMode=1 and SiS.3D.TexTurboMode=0 is incomparably higher than that provided by default.

For a better comparison, have a look at the same scene processed by NVIDIA GeForce3 Ti200. Again, you can see the results of bi-linear filtering on the left and tri-linear filtering on the right:

SiS.3D.TexTurboMode=0		SiS.3D.TexTurboMode=3 Multi-texturing disabled

By the way, the remarkable thing is that with disabled multi-texturing even with SiS.3D.TexTurboMode=3 you can still enable tri-linear filtering. In "Turbo mode" without multi-texturing Xabre provides almost as good filtering quality as in case SiS.3D.TexTurboMode=0.

Two screenshots below are taken from Serious Sam: The Second Encounter. On the left the scene with SiS.3D.TexTurboMode=0 and on the right - SiS.3D.TexTurboMode=3 with disabled multi-texturing:

Bi-linear filtering by NVIDIA GeForce3 Ti200		Tri-linear filtering by NVIDIA GeForce3 Ti200

Well, the things with texture filtering quality provided by SiS Xabre have become more or less clear now. As for the performance in all these modes considered (it is not for nothing that the developers taught Xabre to do "turbo-texturing"), we will return to it later in a special section devoted to performance.

3D Image Quality: Full-Scene Anti-Aliasing

Xabre from SiS allows enabling Full-Scene Anti-Aliasing either via Xabre 3D Wizard or with SiS.3D.FSAA and SiS.3D.FSAAMode keys. If you set these keys equal to 1 and 0 respectively, Xabre will implement 2x supersampling mode, and to be more exact - 1x2. In case of these keys set to 1 and 1 correspondingly, Xabre works in FSAA 4x mode.

The screenshots below are taken from Serious Sam: The Second Encounter without FSAA, with FSAA 2x, and with FSAA 4x:

No Anti-Aliasing
2x Anti-Aliasing by SiS Xabre
4x Anti-Aliasing by SiS Xabre

SiS Xabre implements FSAA via supersampling, which you can clearly see from the screenshots on the right, where not only polygon borders appeared smoothed but also transparent textures.

As is known, enabling super-sampling results into clearer textures. Xabre is not an exception here: anti-aliasing improves textures quality in "turbo-mode" (you can see a screenshot without FSAA on the left and the one with FSAA 4x on the right):

Speed mode: No FSAA		Speed mode: FSAA 4x

… as well as in "quality" mode (again, no FSAA on the left, FSAA 4x on the right):

Quality mode: No FSAA		Quality mode: FSAA 4x

For a better comparison you can see the same scene processed by NVIDIA GeForce3 Ti200: enabling 4x multi-sampling doesn't tell on the textures quality:

No FSAA by NVIDIA GeForce3 Ti200		FSAA 4x by NVIDIA GeForce3 Ti200

Unfortunately, the implementation of Full-Scene Anti-Aliasing turns into dramatic performance drops. The results of the FSAA performance tests in Quake3 Arena are given below. No comments will follow this disaster:

However, hope is usually the last thing to die, so we still have some vague hope that with the new drivers the performance of Xabre based solutions with enabled FSSA will improve up to some acceptable level.