Other things to note are;

16-bit = 16-bit colour depth, Alpha Blending & 3D Filter Quality set to Automatic.

22-bit = 16-bit colour depth, Alpha Blending set to Sharper & 3D Filter Quality set to High.

32-bit = 32-bit colour depth, Alpha Blending & 3D Filter Quality are ignored.

Quake3 - 16 bit	Quake3 - 22 bit
Quake3 - 32bit

The post filter isn’t used at 32-bit colour depth (obviously) & neither is it used when X4 FSAA is used (regardless of colour depth). The reason for the post filter disabling at X4 FSAA is as follows (Thanks to Dave Barron of Beyond3D for this);

When using 4x FSAA 3dfx no longer uses the post filter. Instead, when they combine the 4 sub-pixels they actually get an improved result, but a similar one. The basic concept of the post filter is to take a 4 pixel matrix & using an adaptive blur, sort of fill in the blanks (areas that were dithered out to bring it to 16-bit). However, with 4 complete pixels you are actually averaging the values so you get an improved result.

Personally I rarely play using 32-bit colour depth for the simple reason that in most cases I could run the game at a higher resolution with 22-bit colour instead, e.g. 800*600*32 or 1024*768*22.

Texture compression

FXT1 is 3dfx’s own open-source Texture compression scheme. This offers compression rates of 8:1 at highest compression levels. 4 different compression schemes are used with the best one selected to achieve the highest quality results. The compression algorithms used being – CC_MIXED, CC_HIGH, CC_CHROMA & CC_ALPHA. S3TC in comparison offers only 1 algorithm for use.

If you want to read more about FXT1 then check out the 3dfx whitepaper on it.

The VSA-100 supports FXT1, DXTC & Narrow Channel texture compression in hardware. In OpenGL FXT1 can essentially emulate S3TC. Although it’s not a perfect emulation (For example, Soldier of Fortune supports S3TC, but FXT1 currently can’t be used), although Quake 3 engine games support it just fine.

Using texture compression has 2 effects – 1 is that it can improve performance, particularly on levels/games with a high amount of textures, the 2^nd effect is that it will cause some loss in graphical data. To be fair, the loss isn’t readily apparent, certain textures in a game may appear a bit weird & this is a result of it. Still, in Quake 3 the sky doesn’t get pixelated, at least not to the extent many GeForce owners have complained about when they have texture compression enabled.

Here’s 2 Quake 3 shots showing both Texture Compression Enabled & Disabled.

FXT1 enabled

FXT1 disabled

As you can see the only real difference appears with the sky. With texture compression enabled banding is more apparent than with texture compression disabled. No other discernible “loss” in image quality is noticeable however.

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