AF - why such a huge perf hit on GF4s?

[Insomniak]

I'm a sucker for anisotropic filtering, but it's just atrocious on the GeForce 4s. Is this an issue with certain drivers, or a byproduct of the architecture? Just wondering if there's a way to alleviate the troubles besides OCing the GPU memory, which I've tried. It helps to a large extent (extra bandwidth is good stuff), but it'd be nice to play UT2k3 with 2x AF enabled....right now it's just too much of a performance hit.

Thanks for your time.

 

[Genx87]

My understanding of the GF4 is it applies AF at its fullest to all angles. This really tears into the performance. Something like the 9800 or 5900 uses an adaptive algorithm.

To my knowledge the R3.xx applies full AF to angles 90 and 0, half at 45 and 22.5 and basically 2x to anything in between.
I think the 5900 will do full at the angles of 0,90,45, and 22.5, with half inbetween.

Iti s interesting to note in AM3 the R3.xx part is having a hard time rendering AF at certain angles and was noted in the review at THG. This shouldnt be a surprise and I dont think it can be changed via software as it is a hardware issue.

 

[techwanabe]

If this is the case, they should be able to rewrite the algorithm to shallower angles in the drivers? maybe... so... Nvidia?

 

[modedepe]

No, they cannot simply rewrite it in drivers to make it more functional. So basically you're stuck with poor af performance.

 

[jiffylube1024]

Originally posted by: Insomniak
I'm a sucker for anisotropic filtering, but it's just atrocious on the GeForce 4s. Is this an issue with certain drivers, or a byproduct of the architecture? Just wondering if there's a way to alleviate the troubles besides OCing the GPU memory, which I've tried. It helps to a large extent (extra bandwidth is good stuff), but it'd be nice to play UT2k3 with 2x AF enabled....right now it's just too much of a performance hit.

Thanks for your time.

I'm pretty sure it's a byproduct of the GeForce 4's architecture. I think ATI has been dedicating die space on their GPU's since the 8500 to perform better/faster AF, whereas the GF4's GPU essentially has to do all the work itself (no specialization). That's what I understood from it...

 

[BFG10K]

Pre-NV30 nVidia cards perform full strength AF on all visible angles, unlike all Radeons and post NV30 cards that vary the strength according to the angle.

The NV25 (GF4) has a special problem because it changes to a 4x1 part when performing anisotropic filtering, thus loosing half of its texel fillrate. In some cases you can find benchmarks where a Ti500 beats a Ti4600 in AF.

 

[merlocka]

Originally posted by: BFG10K
Pre-NV30 nVidia cards perform full strength AF on all visible angles, unlike all Radeons and post NV30 cards that vary the strength according to the angle.

The NV25 (GF4) has a special problem because it changes to a 4x1 part when performing anisotropic filtering, thus loosing half of its texel fillrate. In some cases you can find benchmarks where a Ti500 beats a Ti4600 in AF.

I thought nv20 lost multi-texture in AF as well. Funny that they lost that on nv25.

 

[BFG10K]

I thought nv20 lost multi-texture in AF as well

Not as far as I know. I have seen benchmarks of a Ti500 beating a Ti4600 in AF.

 

[BenSkywalker]

I'm pretty sure it's a byproduct of the GeForce 4's architecture.

Yes, it does real anisotropic instead of the hacks we have with the current boards

It helps to a large extent (extra bandwidth is good stuff), but it'd be nice to play UT2k3 with 2x AF enabled....right now it's just too much of a performance hit.

Which drivers are you running? Try enabling the texture sharpening option and see if that intorduces too much texture aliasing for you, it has the same impact on the LOD bias as an additional notch of AF without the big performance hit. The Unreal2 engined games are the worst case scenario for AF on the NV25 boards. You can try enabling the 'performance' mode in the drivers for AF if you are running the newer Dets, it doesn't hose the image quality on the NV2x boards and offers a decent speed up(removes AF from lightmaps where it doesn't do any good anyway).

 

[InlineFive]

I have a GeForce4 Ti 4200 also, I was playing a game at 60fps and when I enabled AF at same settings it went to 10fps. I think perhaps it's because nVidia's algorithms stink on this front but that's all I can tell you. ATI is better for AF and sometimes for AA also, that's why I bought one.

-Por

 

[merlocka]

Originally posted by: BFG10K

I thought nv20 lost multi-texture in AF as well

Not as far as I know. I have seen benchmarks of a Ti500 beating a Ti4600 in AF.

Good to know. Just one more reason for me to stick with my Geforce3 until I see how Q4 pans out for the video card market

 

[Insomniak]

Originally posted by: BenSkywalker

I'm pretty sure it's a byproduct of the GeForce 4's architecture.

Yes, it does real anisotropic instead of the hacks we have with the current boards

It helps to a large extent (extra bandwidth is good stuff), but it'd be nice to play UT2k3 with 2x AF enabled....right now it's just too much of a performance hit.

Which drivers are you running? Try enabling the texture sharpening option and see if that intorduces too much texture aliasing for you, it has the same impact on the LOD bias as an additional notch of AF without the big performance hit. The Unreal2 engined games are the worst case scenario for AF on the NV25 boards. You can try enabling the 'performance' mode in the drivers for AF if you are running the newer Dets, it doesn't hose the image quality on the NV2x boards and offers a decent speed up(removes AF from lightmaps where it doesn't do any good anyway).

Uh....enabling texture sharpening hoses performance just as much as AF for me. I'm running the 41.09 dets, always in performance mode (I can't see an IQ difference between modes honestly. If it is there, I'm blind to it.) usually with 2x AA.

Coolbits enabeled of course. So far I've managed to OC from 275/552 to 312/625 stably. Hell of a card.

 

[BenSkywalker]

Uh....enabling texture sharpening hoses performance just as much as AF for me. I'm running the 41.09 dets, always in performance mode (I can't see an IQ difference between modes honestly. If it is there, I'm blind to it.) usually with 2x AA.

Just checked, I'm currently running the 45.23 drivers and while I see a performance drop off, it's nothing like what you are talking about(with 2x the hit is very low, texture sharpening without AF the hit is miniscule, 1%-2% range I would estimate). With your current clockrate, UT2K3 should be running very nicely, even using 4x AF shouldn't be that large of a blow to your framerate. What resolution are you running at? Do you see the same huge performance hit without AA enabled?

I'd try updating your drivers, I don't recall which version was the first that implemented the faster AF for the GF4. If you do, post back and let us know how it goes.

 

[Insomniak]

The 45.23, IIRC, degrade image quality for speed, although in my benchmarking I found I got both better IQ and performance from the 41.09. Oh, UT2k3 runs fine - I run at 1024x768x32 @ 85 Hz and with all details maxed out. 2x AA.

But when I turn on AF, ow.... eats a good 15 frames or so @ 2x.

I'll try AA off and AF on and see if anything changes....enabling AA all the way up to 4x only degrades my FPS about 2 - 8 depending on whether its 2x, Quincunx, or 4x. 4xS gets a bit slow for me.

EDIT: Just tried AF with AA off. No different. FPS still gets pantsed.

 

[BenSkywalker]

The 45.23, IIRC, degrade image quality for speed

On the FX line of boards, I haven't seen any IQ drops(I'm running a GF4).

Judging from the fact that disabling AA doesn't change the performance equation it doesn't sound like bandwith is the issue for you. I'd say give the 45.23s a shot and if you notice any IQ degredation then revert back to the 41.09s. The IQ issues that people are bringing up with the nV boards and drivers are based on the FX line of parts, and most of those deal with shaders being 'dumbed down' for performance increase.

 

[Insomniak]

Alright, I'll give em a shot and see if anything gives. But I'm not too optimistic.

Just to clarify, the game is still playable with AF on, but only barely. I average around, say 35 FPS with me and 5 bots in DM-Antalus. Without the AF, I'm averaging 55-65, which is more like it.