More VSA-100 Distinctions

Big changes

While VSA-100 doesn't support the biggest buzzword of the next-generation (T&L), it does add hardware guardband clipping, where triangles not visible in the display area are extracted and not drawn. In addition, partial triangles are rasterized in a more efficient manner. According to Scott, guardband clipping saves on a very CPU-intensive process.

The entire pixel/textures microarchitecture on VSA-100 has been significantly optimized. All things being equal, this should equate to a 20-25% speed increase in multitexture applications alone, considering same clock/memory speed.

One of the biggest changes in VSA-100 is support for a true 2-pixel-per-clock raster engine. Voodoo3 on the other hand supported 1 pixel per clock cycle, and 2 textures per cycle, equating to a 183 Mpixel/sec fillrate, and 366Mtexel/sec texture fillrate. This means that for single-texture applications and scenes, we should see up to 2x the performance of Voodoo3. Scott was quick to point out that the vast majority of games today are not multitexture, and even well-known multitexture games such as Q3A use a number of single-texture effects (the parallax sky are actually comprised of 3 single texture passes).

Independent of pixel fillrate, VSA-100 now supports the ability to render two subsamples per pixel. On single-chip solutions, this allows for a simplified 2-sample anti-aliasing, which will look a little dirty at lower resolutions, but should be noticeably better than a non-anti-aliased image at higher resolutions such as 1024x768 or higher. The subsample ability doesn't take away from the dual-pixel pipeline, but it does take up twice the fill-rate of a non-subsampled image. In dual-VSA systems, there will be a user-selectable option in the control panel to force this 2-sample anti-aliasing, or the slower but more visually pleasing standard T-Buffer 4-sample anti-aliasing, which sucks up 4x the fillrate of a non-anti-aliased sample.

2D images

In the case 3dfx wants to introduce TV/multimedia VSA-100 product, support for the CCR-656 video format should make for more seamless transmissions from a TV tuner or video source. Prior Voodoo3 parts required external logic to convert the video output to a format understood by the processor.

On the 2D side, the rendering on the video display has been upped again, for support up to 4K resolution. Currently, only a few monitors support resolutions above 2048x1600, but as high fill rates are designed to high higher-resolution play, it makes sense to be looking towards the future in terms of revolution. Along these lines, I asked Scott whether or not there was more word on integrating a 400MHz RAMDAC (rather than the standard 350MHz version announced at Comdex). He replied that there was still no word, but it was looking to be a likely proposition.