NVIDIA's GeForce 8800 (G80): GPUs Re-architected for DirectX 10
by Anand Lal Shimpi & Derek Wilson on November 8, 2006 6:01 PM EST- Posted in
- GPUs
Our DX9FSAAViewer won't show us the exact sample patterns for CSAA, but we can take a look at where ATI and NVIDIA are getting their color sample points:
| ATI |  |
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| G70 |  |
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| G80 |  |
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| G80* |  |
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*Gamma AA disabled
As we can see, NVIDIA's 8x color sample AA modes use a much better pseudo random sample pattern rather than a combination of two rotated grid 4xAA patterns as in G70's 8xSAA.
While it is interesting to talk about the internal differences between MSAA and CSAA, the real test is pitting NVIDIA's new highest quality mode against ATI's highest quality.
G70 4X G80 16XQ ATI 6X
Hold mouse over links to see Image Quality
G70 4X G80 16XQ ATI 6X
Hold mouse over links to see Image Quality
Stacking up the best shows the power of NVIDIA's CSAA with 16 sample points and 8 color/z values looking much smoother than ATI's 6xAA. Compared to G70, both ATI and G80 look much better. Now let's take a look at the performance impact of CSAA. This graph may require a little explanation to understand, but it is quite interesting and worth looking at.
As we move from lower to higher quality AA modes, performance generally goes down. The exception is with G80's 16x mode. Its performance is only slightly lower than 8x. This is due to the fact that both modes use 4 color samples alongside more coverage samples. We can see the performance impact of having more coverage samples than color samples by looking at the performance drop from 4x to 8x on G80. There is another slight drop in performance when increasing the number of coverage samples from 8x to 16x, but it is almost nil. With the higher number of multisamples in 8xQ, algorithms that require z/stencil data per sub-pixel may look better, but 16x definitely does great job with the common edge case with much less performance impact. Enabling 16xQ shows us the performance impact of enabling more coverage samples with 8x multisamples.
It is conceivable that a CSAA mode using 32 sample points and 8 color points could be enabled to further improve coverage data at nearly the same performance impact of 16xQ (similar to the performance difference we see with 8x and 16x). Whatever the reason this wasn't done in G80, the potential is there for future revisions of the hardware to offer a 32x mode with the performance impact of 8x. Whether the quality improvement is there or not is another issue entirely.
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haris - Thursday, November 9, 2006 - link
You must have missed the article they published the very next day http://www.theinquirer.net/default.aspx?article=35...">here. saying they goofed.Araemo - Thursday, November 9, 2006 - link
Yes I did - thanks.I wish they would have updated the original post to note the mistake, as it is still easily accessible via google. ;) (And the 'we goofed' post is only shown when you drill down for more results)
Araemo - Thursday, November 9, 2006 - link
In all the AA comparison photos of the power lines, with the dome in the background - why does the dome look washed out in the G80 images? Is that a driver glitch? I'm only on page 12, so if you explain it after that.. well, I'll get it eventually.. ;) But is that just a driver glitch, or is it an IQ problem with the G80 implementation of AA?bobsmith1492 - Thursday, November 9, 2006 - link
Gamma-correcting AA sucks.Araemo - Thursday, November 9, 2006 - link
That glitch still exists whether or not gamma-correcting AA is enabled or disabled, so that isn't it.iwodo - Thursday, November 9, 2006 - link
I want to know if these power hungry monster have any power saving features?I mean what happen if i am using Windows only most of the time? Afterall CPU have much better power management when they are idle or doing little work. Will i have to pay extra electricity bill simply becoz i am a cascual gamer with a power - hungry/ ful GPU ?
Another question pop up my mind was with CUDA would it now be possible for thrid party to program a H.264 Decoder running on GPU? Sounds good to me:D
DerekWilson - Thursday, November 9, 2006 - link
oh man ... I can't believe I didn't think about that ... video decoder would be very cool.Pirks - Friday, November 10, 2006 - link
decoder is not interesting, but the mpeg4 asp/avc ENCODER on the G80 GPU... man I can't imagine AVC or ASP encoding IN REAL TIME... wow, just wooowwwI'm holding my breath here
Igi - Thursday, November 9, 2006 - link
Great article. The only thing I would like to see in a follow up article is performance comparison in CAD/CAM applications (Solidworks, ProEngineer,...).BTW, how noisy are new cards in comparison to 7900GTX and others (in idle and under load)?
JarredWalton - Thursday, November 9, 2006 - link
I thought it was stated somewhere that they are as loud (or quiet if you prefer) as the 7900 GTX. So really not bad at all, considering the performance offered.