LOSTCIRCUITS

Clipping, Culling and Rasterization

Clipping and culling are rather self explanatory, no vertices that are outside of the 2D viewpoint space (screen) need to be processed further. The next step involves breaking up or rasterizing the visible area into small 8x8 pixel "tiles" or matrices that are then "fed" through the texture pipelines.

The 8x8 pixel matrix corresponds to / coincides with the 64 texture processors, in other words, it is like stamp that is generated for each 8x8 pixel square that is then "printed into visiblity".

Textures

Textures are what make any picture visible in that they add color to an otherwise invisible wireframe of polygons defined by the different vertices. Conventional graphics adapters have 4 or 8 pixel pipelines with 1 or two texturing units per pipeline. Currently, the highest number of texturing units in conventional graphics cards is 8 texture units. The P10 processor uses a radically different approach in that it contains four pixel pipelines, each of which features no less than sixteen floating point texture coordinate generators and subsequent sixteen 32 bit integer texture shading processors, that is, a total of 64 texture shading processors.

64 texturing units comprised of 128 bit floating point texture coordinate generators and subsequent 32bit integer texture processors above and the corresponding workflow below

Each pixel pipe can execute up to 128 instructions and generate up to eight textures per pass. Moreover, the overall number of permutations can be increased by looping and sub routines of the texture command execution. Keep in mind that any pass spans over multiple clock cycles and, thus the number of textures in real life will deviate from the theoretical peak fill rate listed as 1 GTexel /sec. This number is surprisingly low in view of the latest offerings from e.g. ATI and nVidia that are in the 3GTexel range and we'll have more about this in the benchmark section.

The original claims by 3DLabs described the P10 as DX9 graphics processor, however, this information was released before the finalization of the DX9 specs, which then called for floating point pixel processors. Consequently, the P10 processors are not DX9 compliant in the sense of the word, what is more important, though, is that they will not run DX9 software, one example is the Mother Nature part of 3DMark2003.

Blending Processor

The final stage in the digital part of picture processing encompasses dithering, alpha blending and anti-aliasing which can be described as the final touch up of the scene. According to 3DLabs, the final pixel computation compensates for the lack of floating point precision in the pixel pipelines.

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