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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JarredWalton - Wednesday, November 8, 2006 - link
They did the same thing with the original Halo, porting it (and slowing it down) to DX9. MS seems to think making Halo 2 Vista-only will get people to upgrade to the new OS. [:rolls eyes:]stmok - Wednesday, November 8, 2006 - link
How else are they gonna get gamers to upgrade to Vista? :)(by cornering them into adopting Vista, using DirectX 10.0)
Its sad and pathetic at the same time.
DirectX 10.0 should be a "transitional" solution...That is, it covers both XP and Vista. This allows people to gradually upgrade their hardware, and if they wish, to Vista. What MS is doing now, is throwing everyone (developers and consumers) into the deep end, and expecting them to pay for the changes. (I suspect some would be put off by this, while the majority will continue to accept it...Which is unfortunate).
Great article BTW. Interesting to see the high-end stuff...But I doubt I can afford it in this lifetime!
I have two questions!
(1) Any chance of looking at a triple video card setup?
(I saw a presentation slide which had 2 video cards in SLI, while a third showed something else on screen).
(2) Any idea when the GF8600-series comes?
(mainstream market solution).
yyrkoon - Thursday, November 9, 2006 - link
Great, links arent working ?http://www.gamedev.net/reference/programming/featu...">http://www.gamedev.net/reference/programming/featu...
yyrkoon - Thursday, November 9, 2006 - link
http://www.gamedev.net/reference/programming/featu...">This article was written by a friend of mine back in April after an interview with ATI. Perhaps this will clear some things up.
yyrkoon - Thursday, November 9, 2006 - link
When you break all hardware/software ties to something that has been around for 4-5 years? Its not that easy making it "transitional". From a software perspective, D3D10 is not compatable with XP in the least.I for one, think this is a step in the right direction.
JarredWalton - Thursday, November 9, 2006 - link
Supposedly all of the changes to the WDDM make porting DX10 back to Windows XP "impossible", although I'm more inclined to think the correct term would be "difficult" and you also have to add in "it doesn't fit with MS marketing protocol". WDDM is quite different in Vista however, so maybe there's some substance to the claims.cosmotic - Wednesday, November 8, 2006 - link
On page 9:--Briefly explain what a sub-pixel is in the sentence before--
JarredWalton - Wednesday, November 8, 2006 - link
Due to the size of this article and the amount of time it took to get ready, let me preempt any comments about the spelling and grammar. I am in the process of editing the final document as I read through it, and there are spelling/grammar errors. If they bother you too much, check back in an hour. If you read this an hour from now and you still find errors, then you can respond, though it would be useful to keep all responses in a single thread like this one.Thanks in advance,
Jarred Walton
Editor
AnandTech.com
xtknight - Thursday, November 16, 2006 - link
On p 12 (gamma corrected AA):"This causes problems for thing like thin lines."
acejj26 - Wednesday, November 8, 2006 - link
"If DirectX 10 sounds like a great boon to software developers, the fact that DX10 will only be supported in Windows XP is certain to curb enthusiasm. "I believe this should say "DX10 will only be supported in Windows Vista..."
Not to be rude, but shouldn't the article be edited BEFORE being published??