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View Full Version : Why does the GeForce4 have slow AA and AF performance?


imtim83
10-23-02, 10:48 AM
?

netviper13
10-23-02, 11:06 AM
Its AA performance is really good, I don't know what your issue is there. The AF issue has been corrected for OpenGL, but still exists for Direct3d. Nobody is really sure as to why performance isn't the greatest with AF.

imtim83
10-23-02, 11:11 AM
netviper13 does AA = FSAA?

If it does, how is FSAA performence really good? Like lets say how many fps do you lose from going from no FSAA to 2x and no FSAA to 4x?

Head_slinger
10-23-02, 12:19 PM
there are always going to be performance loss using AA or AF, On any card

Uttar
10-23-02, 01:26 PM
I'm guessing you're comparing the GF4 Ti to the Radeon 9700 AA/AF performance.

Well, for AF perf, there's the bug.
And for AA ( FSAA, it's the same thing ) performance, well...

If you want a complete document describing pipeline concurrency & stuff, try http://developer.nvidia.com/docs/IO/2650/ATT/GDC2002_PipePerformance.pdf - but it requires quite a bit of D3D programming knowledge to understand correctly.


Basically, the GPU got multiple performance bottlenecks ( the VS, the PS, Triangle Setup, Memory Bandwidth, ... )

The Radeon 9700 got vastly improved performance in all of those areas, but even MORE in the memory area because of the 256 bit memory bit width.

And to quote this very same developer document:
"FSAA hits memory bandwidth exclusively, no fill-rate hit with multi-sample"

And both Radeon 9700 and GF4 Ti use multi-sampling AA, so the only hit is on memory bandwidth. Which is where the Radeon 9700 shines the most - so it isn't as much of a bottleneck as on the GF4 Ti.

Did that answer your question?


Uttar

imtim83
10-23-02, 01:37 PM
Uttar Yes thank you! Very well appreicated!

StealthHawk
10-23-02, 02:09 PM
Originally posted by imtim83
netviper13 does AA = FSAA?

If it does, how is FSAA performence really good? Like lets say how many fps do you lose from going from no FSAA to 2x and no FSAA to 4x?

i think the question is more "why do you think the GF4 has bad FSAA peformance?"

the GF3 had superior performance compared to other cards that used SSAA(super sampling), and the GF4 had even better peformance than that. in general situations it probably boils down to something like 25% hit for 2x, and 50% hit for 4x.

CWB
10-23-02, 03:53 PM
I cant give you specific fps numbers, but I can tell you that 2x AA seems to be practically "free" on my GF4.

It costs 500+ 3DMarks, but the performance hit in real-life gaming is practically nil.

The sweetspot on my GF4 (325/725) & 21" Trinitron seems to be 1280x1204 w/2xAA & 4x Aniso (2x in some games). I personally find that once I reach 1280x1024, 2xAA is all I need.

I have no complaints since Im used to playing at 1600x1200 on my GF3 TI500 with neither AA nor Aniso, and now I can do 1280x1024 w/both and still get higher framerates than on my GF3 with neither!