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ChrisRay
07-20-05, 07:53 AM
SLI Antialiasing Preview

Introduction SLI AA : There are some instances where SLI can find it self CPU Bound (http://www.nvnews.net/vbulletin/showthread.php?t=47710&highlight=SLI) under various circumstances (http://www.nvnews.net/vbulletin/showthread.php?t=47587&highlight=SLI). Or in even the worse case scenerios where SLI does not prove to provide any performance benefits at all. The general idea of SLI AA is that it will work in everything. Without the need for a profile while providing an immediate benefit to all your current games. It does this by using both graphic cards to sample the scene and joining the final image.


How to enable

Step 1: First thing you'll need to do is install coolbits. You can get coolbits from several places such as SLI Zone (http://www.slizone.com) or this direct download. (http://members.cox.net/omega1979/SLI/coolbits2.reg)

Step 2: You'll need to enter your advanced settings as if you were going to setup a SLI Profile. (http://www.nvnews.net/vbulletin/showthread.php?t=47710&highlight=6800GT+SLI) From here you'll see a new SLI rendering known as SLI AA. Once you select this mode you should be able to return to your AA configuration and find two new options. Namely SLI 8x and SLI 16x.

Note: SLI AA is not compatible with previous modes of SLI rendering. There will not be an improvement in rendering performance. This is a quality improvement mode.


http://www.nvnews.net/articles/chrisray_iq/7800gtx/slipanel1.jpg


http://www.nvnews.net/articles/chrisray_iq/7800gtx/slipanel2.jpg



8xS AA verses 8xSLI AA

8xS AA: This mode has been available to Nv4x users for sometime. It combines 1x2 Super Sampling to with 4x RGMS and creates a fairly ideal result. Unfortunately this mode consumes significant amounts of bandwith and pixel fillrate to operate. This mode is available to all Geforce 6 + cards.

http://www.nvnews.net/articles/chrisray_iq/comparison/8xSpattern.jpg

SLI 8xAA: SLI 8xAA operates a bit differently. It does so by taking a 4x RGMS on each card and combining them together. Notice the super sampling portion of 8x SLI is Rotated Grid. This could provide an excellent image quality enhancement to standard 8xS. This is an SLI specific mode.


http://members.cox.net/omega1979/SLI/8xEER.JPG


16xS verses 16x SLI AA

16xS AA: The first 16xS AA mode ever available in a direct3d enviroment. This mode combines 2x2 OGSS and 4x RGMS. This mode is very fillrate/bandwith/framebuffer intensive and can send even 7800GTX SLI cards to their knees. Another limitation is that it cannot go beyond 1280x1024 resolution due to framebuffer requirements. For this reason it was not included in todays benches. This mode hidden and requires a registry tweak (http://www.nvnews.net/vbulletin/showthread.php?t=30641&highlight=Anti+aliasing) to be enabled.

http://www.nvnews.net/articles/chrisray_iq/comparison/new16xpattern.jpg

SLI 16xAA: This mode is fairly interesting. It is done by two cards rendering a 1x2 super sampling with 4x RGMS similar to the original 8xS mode. However like the 8x SLI mode it the samples are combined individually on the two cards and then rendered to to the final image. Notice the super sampling portion contains a slight shift from an ordered pattern. This mode is only available to SLI users.

http://www.nvnews.net/images/screenshots/16xEER.png

Note: From a quality perspective the new SLI modes are comparable to the old xS counterparts with minor variances in quality due to the differences in sample patterns. You can find some older quality comparisons done here. (http://www.nvnews.net/vbulletin/showthread.php?t=30641&highlight=Anti+aliasing)

Guild Wars Quality Screenshots

4xAA/16xAF

http://www.nvnews.net/articles/chrisray_iq/7800gtx/gw4xnorm.png

SLI 8xAA/16xAF

http://www.nvnews.net/articles/chrisray_iq/7800gtx/gw8xsli.png

SLI 16xAA/16xAF

http://www.nvnews.net/articles/chrisray_iq/7800gtx/gw16xsli.png

SLI 16xAA/16xAF (Transparency SuperSampling)

http://www.nvnews.net/articles/chrisray_iq/7800gtx/gw16xtransparency.png


Far Cry Performance


http://www.nvnews.net/images/screenshots/sliaaperf2.png

http://www.nvnews.net/images/screenshots/SLIAAperf.png

Performance Notes: As I mentioned before. Unlike previous SLI rendering modes SLI AA modes are not meant to improve performance. They are meant to provide an image quality enhancement to people with dual graphic cards. In the case of SLI 8xAA you will see a performance bonus over 8xS in single GPU rendering. 16xS AA however is an incredible edition and can be used practically in many olders titles @ 1600x1200 with 7800GTX cards in SLI. It can also be used in many current titles @ 1280x1024 and below with a 7800GTX SLI setup.


Thoughts and Conclusions: When I was first told about SLI AA. My first thought was. "Whats the Point?". But after giving it some thought and seeing it in action. Theres alot of useful ways to benefit from it. Especially in older titles which dont scale with SLI due to CPU limitations. In the end you are just provided with more options. And who can argue with options? They produce excellent image quality and will allow SLI users to get more value from their setups. Kudos to Nvidia.

Final Note: I did not take any screenshots due to the unfortunate bug of it not being capturable with fraps. I have been informed that this bug is being worked on. A couple of comparison images are below. Please take note that these were not taken by me.

http://www.nvnews.net/articles/chrisray_iq/7800gtx/bf2_fence.gif

http://www.nvnews.net/images/screenshots/flightsim_exterior_2.gif

http://www.nvnews.net/articles/chrisray_iq/7800gtx/flightsim_tower_2.gif

MUYA : Fixed them screens :p

ChrisRay
07-20-05, 08:39 AM
Sorry this preview isnt as big. It was done on very short notice and there were also alot of technical restraints which prevented me from doing everything I would have liked.

Hopefully you can still find it informative and valuable.

Sazar
07-20-05, 08:41 AM
Which game did you test?

Nice info btw, hopefully you can grab a few screens later with a workaround.

ChrisRay
07-20-05, 08:42 AM
Yikes! I didnt list the Far Cry Title title! Wow.. all nighter.. what a screwup.

Edge
07-20-05, 08:43 AM
Interesting stuff, I thought multi-GPU AA was an interesting feature when I read it was going to be part of ATI's Crossfire, nice to see that Nvidia has added it to SLI as well. Hope to see some screenshots soon (once the bug is fixed...doesn't print-screen work either?), I'd like to see what kind of actual effect this has on image quality. Also, this makes me wonder how SLIed 6600gt cards would compare to a single 6800gt with both running the equivalent AA modes (8xS/8xSLI and 16xS/16xSLI).

Sazar
07-20-05, 08:46 AM
Yikes! I didnt list the Far Cry Title title! Wow.. all nighter.. what a screwup.

Lol, I read it about 5 times just to be sure. I'm in the same boat, not slept all night, everything all insane in da membrane.

ChrisRay
07-20-05, 08:46 AM
For those interested in screenshots. Please check out these animated Gifs. They are "Not" mine. But they were provided to to help illustrate the benefits of 16xAA.

http://www.nvnews.net/images/screenshots/bf2_fence.gif

http://www.nvnews.net/images/screenshots/flightsim_exterior_2.gif

http://www.nvnews.net/articles/chrisray_iq/7800gtx/flightsim_tower_2.gif

wEEt
07-20-05, 08:49 AM
Performance hit seems to be pretty big but I guess it's the best IQ we've ever seen :) That's what SLI is there for... ;)

Holy ****, 16xSLIAA looks amazing :eek:

BrianG
07-20-05, 08:54 AM
Going to try SLI 8X on the 6600GTs with Q3A and UT 2K3 when I get home. Hmm, 7800GTs in HL2 with SLI AA...

Hey Chris is there a transparency setting for 7800GTX still? Does the frame buffer combine apply AA to the Alphas?

ChrisRay
07-20-05, 08:56 AM
Going to try SLI 8X on the 6600GTs with Q3A and UT 2K3 when I get home. Hmm, 7800GTs in HL2 with SLI AA...

Hey Chris is there a transparency setting for 7800GTX still? Does the frame buffer combine apply AA to the Alphas?


Yes transparency options still work with SLI AA.

Sazar
07-20-05, 08:56 AM
Looks really nice :drooling:

How playable was Far Cry when you were running around? Its not a run and gun type game per se but was it chugging in spots?

ChrisRay
07-20-05, 08:58 AM
Looks really nice :drooling:

How playable was Far Cry when you were running around? Its not a run and gun type game per se but was it chugging in spots?


At 1280x1024 @ 16xAA far cry was entirely playable. It was a grey area at 1600x1200 though. All things considering though I think thats still pretty darn good.

mikechai
07-20-05, 10:45 AM
I hope their next high end card will make 1600x1200 SLI 16xAA playable.

As usual, nice work Chris.
When it comes to AA, I will think about Chris first. :)

SH64
07-20-05, 01:53 PM
Nice! gonna try Morrowind & see how it performs under 16x SLI :cool:

threedaysdwn
07-20-05, 04:44 PM
Damn, I'm gonna need another GPU :P

SH64
07-20-05, 07:51 PM
Yep!
i just tested Morrowind(1600x1200) & Boiling Point (1280x1024) & they both ran very good @16xSLI!!

in Morrowind thought its kinda hard to spot the difference between 8xAA & 16x at such res but i already feel that i'm getting the best IQ possible for this game on the whole world :D

macachia
07-21-05, 07:30 AM
does fsaa sli work with afr or sfr? or it is impossible to get faster games with better fsaa?

ChrisRay
07-21-05, 07:50 AM
No. The modes are not compatible with AFR or SFR. They are strictly quality improvement modes for games that a single card is CPU limited or the rare occurances where AFR and SFR are not working.

Graphicmaniac
07-21-05, 08:38 AM
So leave me understand a moment

use SLI AA is like use a single 7800gtx but with 2 gpu cooperating just in AA an innothing else?

is like say that at an ipothetical SLI AA 0x games will run as with 1 single 7800GTX ?

Edge
07-21-05, 08:55 AM
So leave me understand a moment

use SLI AA is like use a single 7800gtx but with 2 gpu cooperating just in AA an innothing else?

is like say that at an ipothetical SLI AA 0x games will run as with 1 single 7800GTX ?
Yes. Basically with SLI-AA, the second GPU renders the exact same image, but with a different antialiasing sample pattern. So basically, you get double the AA with the same performance of a single GPU.

Graphicmaniac
07-21-05, 10:23 AM
Ah ok thanks.

The incompatibility of SFR and AFR with SLI AA is hardware or is something will be implemented later in some next driver?

Mr. Nice
07-21-05, 12:03 PM
The incompatibility of SFR and AFR with SLI AA is hardware or is something will be implemented later in some next driver?You're still missing the point. It's a completely different way to use that 2nd GPU. It's not an issue of "compatability". With SFR, each frame is split horizontally between the two cards, and one renders the top half, and the over the bottom half (aprox, load balancing means it's not exactly half). With AFR, each GPU renders every other frame. With SLI AA, both cards render all frames in their entirity, but with different AA patterns, which are then integrated together. Hence it is meaningless to talk about using AFR or AFR at the same time as SLI AA, it's like saying why can't you use AFR and SFR at the same time? The SLI8x mode is technically very similar to the existing 8xS mode, and the same with SLI16x compared to the existing 16x mode. They are slightly better because the texture samples are also on a rotated grid, not just the geometry samples.
So using AFR or SFR at the same time as 8xS (or 16x) is fairly close to what you want anyway ;). If you are currently using 8xS at the same time as A/SFR, try SLI8x instead, the AA quality will be slightly better, yet there is every chance the performance will be better, give it a whirl ;).

Graphicmaniac
07-21-05, 12:39 PM
ah ok now i understood

but now that make me born a new question:

using afr and using normal aa 8x wouldn't that be fast as sli 8x and with more quality?

Mr. Nice
07-21-05, 01:10 PM
using afr and using normal aa 8x wouldn't that be fast as sli 8x and with more quality?In theory the speed would be about the same, but simple theory says that SLI should be twice as fast as a single card, but we know that isn't true ;). So which is really faster is down to experimentation, and may easily vary from game to game. As I said though, the SLI8x should be better quality then the standard 8xS, since the texture samples are on a rotated grid with SLI8x, while on an ordered grid with 8xS. I suspect however that this is largely academic, with the difference not being visible, so just go with the speed. Also, don't forget that the SLI AA modes entirely avoid the compatability issues some games have with SLI rendering.

Grestorn
07-21-05, 03:32 PM
The most important difference between 8xS and SLI8xS is that the latter should be more compatible since it is completely transparent to the application.

If the application doesn't work with either SLI mode (SFR or AFR) it will (should) still be able to use SLI8xS.

So this new mode effectively closes the gap for those games which can't use SLI right now. Until now your second card would be completely useless in those games, now you can at least use it to get a better quality without any performance loss.

BTW, nHancer should be able to utilize these new modes in a couple of days.