3dfx

3dfx's Voodoo5 5500 makes use of its T-Buffer to achieve its FSAA effects. The T-Buffer, in theory, is very similar to what is known as an Accumulation Buffer and it works by allowing the VSA-100 chips to render multiple frames at once and blend them together before outputting them to the screen.

3dfx's FSAA works by using the T-Buffer's ability to blend multiple frames together in a single frame, but shifted around slightly, thus helping to get rid of any jagged edges that are present in a given scene.

The Voodoo5 5500 offers two FSAA settings, a two sample and a four sample setting. By definition, 3dfx's two sample setting renders the current frame twice before blending and outputting the frame and their four sample setting renders the current frame four times, hence the four samples.

Because of the fact that enabling FSAA is making the VSA-100 render either 2 or 4 times as many pixels (2 or 4 sample FSAA), the Voodoo5 5500's fill rate is either cut in half or into one fourth of what it normally would be. Theoretically, this reduction of fill rate would put the Voodoo5 5500 at either 333 Mpixels/s or 166 Mpixels/s depending on the number of samples selected.

Fill Rate Comparison
 
FSAA Disabled
2 Sample FSAA
4 Sample FSAA
3dfx Voodoo5 5500
667 MPixels/s
667 MTexels/s
333 MPixels/s
333 MTexels/s
166 MPixels/s
166 MTexels/s
3dfx Voodoo3 3500
183 MPixels/s
366 MTexels/s
NVIDIA TNT2 Ultra
300 MPixels/s
300 MTexels/s

 

As you can see by the above chart, enabling 2 sample FSAA brings the Voodoo5 5500's theoretical fill rate down to the level of a Voodoo3 3500, though almost twice as fast in single textured situations. For a better performance comparison, a Voodoo5 5500 with 2 Sample FSAA enabled has an 11% higher fill rate than a TNT2 Ultra.

Enabling 4 sample FSAA brings the fill rate of the card down to the level of a Voodoo3 3000 in single textured games and down below the level of a Voodoo2 in multi-textured games, in theory of course.

Index 3dfx Image Quality

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