Maximum degree of anisotropy on Parhelia?

[ram]

In order to do true 64 tap anisotropic filtering (8:1 with trilinear, like NV2x), they would have to be able to loop the pixel back through the pipeline 4 times or they would have to be able to combine all 4 pixel pipelines. Aside from the massive fillrate loss, is this possible at all with parhelia? If not, the maximum that part could do would be 2:1 anisotropy with trilinear, a feature we have since the Geforce256. Their "64 Sample" statement is not clear enough on this one, this could just be the sum of texels the whole chip can fetch per clock, but does not imply it can be applied to one pixel.

Edit: tab->tap

 

[Gunhead]

Good point! I'd like to see that one answered, too.

[As a very minor correction, it's "tap" not "tab". And since trilinear is just another specific filtering method, you couldn't really have "anisotropic with trilinear", but "anisotropic with MIPmapping". Who cares, tho, the terminology's never been too clear-cut.]

 

[ram]

You're right. To nail it on the head, I mean anisotropic filtering with MIP map interpolation, but not mipmap dithering. Kinda circuitous way to express the same thing.

 

[Basic]

The terms "anisotropic with bilinear" and "anisotropic with trilinear" makes sense, since the typical way of implementing anisotropic is to sample the texture in a few points in row, using the allready existant bilinear/trilinear filters. So if you want anisotropic filtering with linear interpolation between mipmaps and an anisotropy of 8, then you'd make 8 trilinear samples in a row and take the average.

This is of course not the only or most correct way to do it, just the most convenient and likely.

 

[Gunhead]

Okay. Thanks, Basic. Makes sense, actually.

Yeah, ram... You just go on and say "trilinear aniso" and I'll restrain my nitpicking

 

[Vince]

Isn't MIP map dithering just a preformance 'hack' or trick thats used (Especially in the past - V5 did it) to give the perception of Interpolation when Trilinear Filtering isn't capable of being preformed at acceptable speeds. Or am I thinking of something else?

 

[Reverend]

"Mipmap dithering" means no color blending. It is useful for approximating mipmap transitions.

Most (if not all) of the current 3D cards really won't need mipmap dithering for performance alone - they're fast enough with the number of texture units available (i.e. trilinear really is "free") as well as pure clock speed.