LOSTCIRCUITS

Higher Order Surfaces

There are some new buzz words beyond n-patches that we see with the R300. Among the new features of TRUFORM 2.0 are continuous tessellation, adaptive tessellation and displacement mapping (introduced with the Matrox Parhelia) that will add a new level of realism at faster speed to landscape mapping. These features may not be that critical for gamers, however, in virtual reality simulations as required by e.g. the military, these features will certainly come in very handy.

One of the strongest points of the RADEON 8500 was the elegance of its antialiasing method, using jittered 6 x random sample supersampling. The beauty of the approach was the fact that the randomness of each sample changed with every refresh of the image that is, within the limitation of the frame rates no edge would display the same stepping in two consecutive frames. This method was called "quasi-random" sampling at the introduction of the R200. The net result were temporal superimpositions of jagged edges, however, at "jag-rates" beyond the capability of the human visual system to detect them. In other words, what often looked like horribly jagged diagonals in still images or screen shots would temporally blend into the next screen and the randomness of the sampling algorithm would prevent any pattern detection by the viewer.

The RADEON 9700 uses multi-sampling, that is, within each pixel, 2, 4 or 6 samples are taken according to a programmable random sampling pattern where the "randomness" defines the position of the samples within the pixel. Any pixel that only partially falls into a triangle will show a weighted blend of the background and the triangle color. Multi sampling does not require rendering multiple samples of the same image and is therefore faster than super-sampling.

Flow diagram of how different samples are taken within the subpixel space of 4 adjacent pixels partially occupied by a triangle. All values are averaged to determine the resulting color of the pixels in, at the edge or outside the triangle and the pixels are rendered in the appropriate color.

There are pro's and con's to multi-sampling, the positive aspect being that multi -sampling is faster and does not blur textures since it is basically an edge antialiasing only, the negative aspecs being that sometimes the antialiasing quality is not as good as with super-sampling. SMOOTHVISION 2.0 uses up to 6 multi-sample antialiasing with programmable sampling locations to achieve maximum quality. The additional wealth of data is compressed using the HYPER Z III compression algorithms up to a 24:1 lossless compression.

Anisotropic Filtering

Textures applied to objects at sharp angles have a tendency to blur. This can be prevented by anisotropic filtering which means that multiple texture samples are taken fro each pixel. SMOOTHVISION 2.0 uses up to 16 texture samples per pixel. Modes of operation are bilinear and trilinear. SMOOTHSHADER 2.0 further uses an adaptive algorithm to determine which parts of an image actually benefits from anisotropic filtering to find the optimal compromise between performance and quality.

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