LOSTCIRCUITS

Unlimited Outputs? Outputting Tens of Billions of Colors

No monitor is currently capable of generating the richness of colors generated internally in the pixel engine of the R300 and they don't actually need to. Therefore, the pixel precision of the RADEON 9700 is reduced to integer values by rounding to 10-bit RGB and 2 bit alpha transparency at the level of the RAMDAC. One might argue that 2 bit or 4 levels of transparency are not enough for the alpha channel, however, keep in mind that pixel shaders are capable of compensating for the lack of dynamic in transparency.

The left half is rendered without normal bump mapping and shows a flat hood without air-intakes that are added on the right by turning on bump mapping only.

The wire frame shows no difference in the polygon count between the drab left and the stunning right. The entire surface curvature is done by bump mapping.

Sixteen-bit normal bump-mapping

By definition, 3D games require 3-dimensionality and 3-dimensionality can be achieved by different means. The conventional way relies on polygon-based construction of the surface curvature, the higher the polygon count, the smoother the surface. The drawback, as we all know, is that each triangle needs three vertices and, thus, there is a high amount of data that needs to be pumped through both the AGP bus as well as the memory interface. A more simplistic approach to goose-bumps is to generate a rather flat surface and superimpose a bump map based on surface normals, that is vectors that stand out vertically from any given surface with the direction of the vector defining the plane and the length of the vector defining the depth of the impression.

Eight-bit vs. Sixteen-bit Normal Maps

Close-up of the bonnet (isn't that what they call it in Canada?) rendered with 8-bit normal precision on the left and 16-bit precision on the right. Instead of smooth curves, we have facets on the left.

Like in the case of color and brightness, the efficacy and precision necessary to generate the bumps depends on the number of possible normal values. That is, any 8-bit normal map will only contain 256 possible planes and result in facets rather than smoothly occurring transitions. A 16 bit normal with its 65000 possible planes map will, on the contrary, approximate much more closely real life curves wherever we encounter them.

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