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Introducing the GeForce4: nVidia strikes back

Introducing the GeForce4: nVidia strikes back

Accuview

Accuview is dedicated to the removal of so-called anti-aliasing artifacts. These artifacts mainly arise at the edges of objects and polygons because, for example, an inclined edge can only be represented by a fine staircase with the help of pixels. If you now increase the number of pixels significantly, this podium effect is reduced under normal circumstances. The really annoying element of these artifacts is mainly caused by movement. It can happen that the order of these steps changes very often, almost constantly jumping around, a flicker effect is the result, which is still clearly visible due to the movement even at very high resolutions such as 1600x1200.

Illustration of the aliasing effect

There are now different ones Methods to combat these aliasing effects are summarized under the term anti-aliasing.

The simplest type of AA is to simply render each individual image in a higher resolution frame buffer than the currently set resolution and the result back down to the original resolution at the end. So with a resolution of 800x600 virtual bsw. a 1600x1200 pixel framebuffer was set up and then scaled back down to 800x600. The artifact formation would be far on parmove higher resolution. However, since with this method called supersampling, almost the entire rendering process is carried out in a higher resolution, including all texture access etc., there is an extreme loss of performance.

The pioneer in the field of FSAA (Full Screen Anti-Aliasing ), the 3dfx that nVidia bought more than a year ago, used a more sensible variant of the FSAA in its VSA-100 chips. Thanks to the patented T-Buffer, the image to be calculated could be calculated several times, each with a slight offset, and only later, outside of the performance-limited rendering pipeline in the RAMDAC, could be combined again into one image. From a purely visual point of view, the process is almost unrivaled to this day, unfortunately the Voodoo5 was too weak and available too late to be able to score points in the mass market. Thanks to its higher raw performance, the GeForce2 achieved almost the same performance with the supersampling process in contrast to the RGAA (Rotated Grid Anti-Aliasing).

Since this feature was de facto not usable, nVidia tried to introduce a new procedure in the consumer sector, with anti-aliasing still usable and widely implemented as a must-have feature if the performance was still sufficient. This was marketed under the name “Quincunx” anti-aliasing and was based on the multisampling process and a downstream filter. Multisampling means that the edges are smoothed at least as well as with supersampling, but the textures are not treated with this process, so that in direct comparison to supersampling 'textures' those of the multisampling image do not look quite as sharp and also the flicker effect removed textures are not cleaned up.

The GeForce3 already offered dedicated hardware for this purpose, so that the additional 'samples'allegedly could be calculated at full (GPU) performance. Apparently for this purpose, since the GeForce3, the filling rate of the chips is no longer given in gigatexels/s, but in anti-aliased samples per second. It is hardly surprising that there are worlds between nVidia's chips and those of the competition in this reading, since it does not offer multisampling hardware in this form. That is why the filling rates in gigatexels and gigapixels are still given in our table.

Accuview is also based on this technology, but includes additional options that promise increased image quality and higher performance at the same time.

Accuview-AA with offset multisampling mask

The quincunx pattern, named after the arrangement of the five eyes on a cube, is retained, however, together with the additionally calculated samples, it is offset diagonally by 'half' a pixel. This skew is beneficial for edge smoothing, since the additionally generated pixels would now be 50% closer to an imaginary skew in both the y and x directions and thus the real position of the pixel, and the anti-aliasing effect increases due to the more exact approximation. This is particularly noticeable in the slightly inclined, almost horizontal lines.

Furthermore, when the Accuview anti- Aliasing saves complete access to the framebuffer. This may have happened through the integration of 3dfx technology, which has already been hotly traded in the rumor mill. Unfortunately, more details could not be found in advance.

However, it is certain that there will be a new FSAA mode that ' 4xS 'is designated. The 'S' stands for staggered and is intended to provide increased fidelity in textures by reading out 50% more texture values ​​and adding them to thefinal calculation included.

Furthermore, this time one wants to emphasize the positive effect of anisotropic filtering, i.e. to market it. This is a filtering that, contrary to conventional bilinear and trilinear filters, does not have the same strength in all directions, but is much more analogous to the viewing angle, e.g. in 3D games, mostly into the depth of the monitor, depending on the degree of filtering set than only uses the neighboring 4 pixels for filtering.

On the next page: nView