silikone wrote:I was under the impression that the Geforce's Quadpipe allowed it to work with multiple adjacent pixels in parallel
Yes, quadpipe literally means 4 (pixel) pipelines.
silikone wrote:Also, why only two textures per pass on a Geforce when it is supposedly a four pipeline chip, like NVIDIA's trademark implies?
You have to separate pipelines and textures here.
A pipeline renders a single pixel. A single pixel may have 0 or more textures applied.
The amount of textures you can apply per pixel depends on a combination of the number of TMUs per pipeline, and how often these TMUs can be (re-)used, as mentioned above with the example of the Kyro II.
In the era of fixedfunction texturing, this was known as 'texture stages'. The GeForce supports two texture stages. So the pipeline can apply two textures (+ a texture blend function) to a pixel in a single pass.
The ATi Radeon in comparison supports three texture stages. And the aforementioned Kyro II supports 8 texture stages.
If you look here, you see that they mention the 'ratio' of "Pixel pipelines: texture mapping units: render output units"
https://en.wikipedia.org/wiki/List_of_Nvidia_ … orce_256_series
The GF256 is 4:4:4, so it has 4 pixel pipelines, 4 TMUs and 4 ROPs. So you have a straightforward pipeline of 4 pixels at a time, each with a single TMU (which can be re-used for dual texturing in a single pass).
The GF2 is 4:8:4, so they doubled the number of TMUs. This means it has twice the texture throughput, making dual texturing far more efficient. It also allows for more efficient trilinear filtering (where two mipmaps of the same texture are sampled). Although Wikipedia claims that the GF256 also has that second TMU, and can do the same efficient trilinear filtering. They claim that dual texturing was disabled because of a bug.