8x OGAA - what's the point?

Discussion in 'General 3D Technology' started by BoddoZerg, Nov 19, 2002.

  1. BoddoZerg

    Regular

    Joined:
    Jul 8, 2002
    Messages:
    481
    Likes Received:
    0
    From Beyond3d's Geoff Ballew interview:
    I can't help but wonder - what's the point of an ordered grid 8x mode? If the sample pattern is 4x2, then for horizontal lines you'll only get 2 gradients. In terms of visual quality, nVidia's 8x may not be any better than ATi's 6x jittered grid!

    Seems to me that brute-force increasing the number of samples you take is a dumb way to improve FSAA quality.
     
  2. Tagrineth

    Tagrineth SNAKES... ON A PLANE
    Veteran

    Joined:
    Feb 14, 2002
    Messages:
    2,512
    Likes Received:
    9
    Location:
    Sunny (boring) Florida
    It isn't jittered-grid, it's rotated... ATi doesn't jitter subsamples. So at equal levels, 3dfx's FSAA is still a microstep above ATi's. By the way, yes, I have now seen a Radeon 9700 Pro in action, and the 4x FSAA looks fantastic, but still just a tiny bit less than 3dfx's... the jittered sampling really works wonders, even with the same sample 'pattern'.
     
  3. Thowllly

    Regular

    Joined:
    Feb 6, 2002
    Messages:
    551
    Likes Received:
    4
    Location:
    Norway
    Actually, you will only get 1 gradient (plus maybe some extra single pixel gradient colors). Several months ago I decided that my next gfx card should support at least 4xRGMS and 4x anisotropic filtering. So my next card will not be a GFFX. Simple as that.
     
  4. Joe DeFuria

    Legend

    Joined:
    Feb 6, 2002
    Messages:
    5,994
    Likes Received:
    70
    Actually, ATI doesn't just "rotate" the samples. ATI won't fully disclose what they do exactly, but it's not just a rotated grid. Jury is still out if ATI uses a consistent sample pattern for all pixels, or if they actively choose a sample pattern on a pixel by pixel (or per group of pixels) basis based on some criteria.

    http://www.beyond3d.com/reviews/ati/radeon9700pro/index.php?page=page15.inc
     
  5. Joe DeFuria

    Legend

    Joined:
    Feb 6, 2002
    Messages:
    5,994
    Likes Received:
    70
    The 8X mode might actually prove to be quite interesting, though we'd need more specifics. Looking at these two statements:

    Given that, with the 6XS and 8X modes (which are both combinations of super and multisampling according to the same interview), I'm inclined to think that nVidia may limit the multisampling aspect to a maximum 4X.

    So I'll postulate:

    1) So 6XS might be 4X ordered grid supersampling combined with 2X rotated grid multisampling, (Since GeForce4 can do 2X rotated grid multisampling, I assume GeForceFX can as well).

    2) 8X might be 4X ordered grid supersampling combined with 4X ordered grid multisampling. Hmmm....that doesn't make much sense though. ;)

    In any case, the supersampling aspect will help with those bloody alpha textures. On the down side, it should come with a significant performance hit: The color compression won't be as effective with the supersampling aspect of these AA modes.
     
  6. Reverend

    Banned

    Joined:
    Jan 31, 2002
    Messages:
    3,266
    Likes Received:
    24
    The "point" may well be a couple of things :

    1) "No one else has our 8x AA... that's the max on the market"
    2) It may simply be "cheaper" transistor-wise than 6X actually

    Of course, since everyone likes to do shootouts in a review, there cannot be any other modes by any other IHV to be compared to the GeForce FX's 8X.
     
  7. Joe DeFuria

    Legend

    Joined:
    Feb 6, 2002
    Messages:
    5,994
    Likes Received:
    70
    Well that's where you are quite wrong. Quite a few sites have benchmarked "maximum quality" settings in the past and directly compared performance.

    Would only be prudent to benchmark 8X on NV30 against 6X on R300 for an "apples to apples" comparison, no? ;)

    And for consistency sake, I hope those same sites use Nv-30's "conservative" setting for aniso, because that is it's maximum quality setting, against R-300s aniso...
     
  8. Gollum

    Veteran

    Joined:
    May 14, 2002
    Messages:
    1,217
    Likes Received:
    8
    Location:
    germany
    Great idea, try suggesting that to Anand please, I'm sure he'd be thrilled... ;)
     
  9. BoddoZerg

    Regular

    Joined:
    Jul 8, 2002
    Messages:
    481
    Likes Received:
    0
    Tell me again where these 125 million transistors are going to if everything in NV30 is cheaper.
     
  10. Althornin

    Althornin Senior Lurker
    Veteran

    Joined:
    Feb 6, 2002
    Messages:
    1,326
    Likes Received:
    5
    The shader pipelines?
    They are more advanced....
     
  11. Xmas

    Xmas Porous
    Veteran Subscriber

    Joined:
    Feb 6, 2002
    Messages:
    3,298
    Likes Received:
    137
    Location:
    On the path to wisdom
    With the same sample pattern, you get the same coverage result. There's no difference in saying the samples are 'jittered' or 'rotated' if it comes down to the same pattern.
    But 3dfx used supersampling, and ATI's AA is gamma-corrected.
     
  12. Reverend

    Banned

    Joined:
    Jan 31, 2002
    Messages:
    3,266
    Likes Received:
    24
    I have my own standards for a review and I do/can not speak for others.

    [edit]I think it is time to discard shootouts masquerading as reviews, especially with the availability of the R300 and NV30. As much as everyone likes to compare (and as much as various websites knows shootouts gets them higher views), shootouts lead to much confusion to most folks. Take a product, review it for what it's worth and leave it to folks to decide. Folks should take the time to read various reviews, look at all the screenshots and decide for themselves the IQ differences and trade-offs. Much more to rant about this but I'm off to bed!
     
  13. Joe DeFuria

    Legend

    Joined:
    Feb 6, 2002
    Messages:
    5,994
    Likes Received:
    70
    I'll have to respectfully disagree. Poorly done shootouts lead to much confusion and spread of misinformation.

    If properly done, a shoot-out would provide a valuable compliment to a stand-alone review.
     
  14. Tagrineth

    Tagrineth SNAKES... ON A PLANE
    Veteran

    Joined:
    Feb 14, 2002
    Messages:
    2,512
    Likes Received:
    9
    Location:
    Sunny (boring) Florida
    One set of samples might be "AccuView"-shifted while the other one is straight-up ordered grid? Meh, still, it'll look like crap compared to ATi's properly set up 6x Rotated.
     
  15. MistaPi

    Regular

    Joined:
    Jun 12, 2002
    Messages:
    357
    Likes Received:
    4
    Location:
    Norway
    I really like the 6x (4xS) FSAA on the GF4Ti, the super-sampling helps a great deal on texture shimmering.
    Do you guys really think 4xS would take a huge performance hit over 4x? I mean, the GF FX has alot fillrate to take from.
     
  16. Bambers

    Regular

    Joined:
    Mar 25, 2002
    Messages:
    781
    Likes Received:
    0
    Location:
    Bristol, UK
    4xS is not 6x its a skewed 4x grid.

    For performance hit I'd have thought you'd only get a noticable hit in situations with lots of alpha tranparencies etc and in situtations where pixel fillrate is limited due to use of pixel shaders.

    How would nvidia actually get 6xS?

    It sounds like they only have 2x1, 1x2 and 2x2 SSAA and 2xRG and 4xOG MSAA to work with. I'm stuggling to get 6 samples out of that lot :-?.

    Only thin I can think of is that 6xS uses a quincux or 9tap filter.
     
  17. Fred

    Newcomer

    Joined:
    Feb 18, 2002
    Messages:
    210
    Likes Received:
    15
    The only problem is its mathematically possible to define image quality.

    Ideally you'd want to equalize that scalar quantity between cards, and then run benchmarks.

    Of course, in practise its extremely complicated, and you'll probably see different indexes for various components of the image (at fourier frequency X we see this card with a great advantage compared to the other).

    The flamewars over which index to use would be .. hilarious =) (kinda like error analysts when they can't figure out which 'quantity' more clearly shows their points).

    So in the end it will realistically have to be subjective. Ie pick out modes which both 'look' good and similar when run side by side (Say using blindtesting to doublecheck yourself), then run you're benchmarks.
     
  18. Laa-Yosh

    Laa-Yosh I can has custom title?
    Legend Subscriber

    Joined:
    Feb 12, 2002
    Messages:
    9,568
    Likes Received:
    1,452
    Location:
    Budapest, Hungary
    Well maybe they render 3 differently shifted versions of the scene with 2X rotated grid multisampling. Sounds like good quality, but with a considerable performance hit...
     
  19. ram

    ram
    Newcomer

    Joined:
    Feb 6, 2002
    Messages:
    218
    Likes Received:
    0
    Location:
    Switzerland
    Assuming NVIDIA didn't change anything on the 2x and 4x multisampling pattern, these could be the sample patterns for 6xS and 8x:

    6xS:

    [​IMG]

    8X:

    [​IMG]

    Any other ideas? (Beside the oposite way of supersampling of course...)
     
  20. ERP

    ERP Moderator
    Moderator Veteran

    Joined:
    Feb 11, 2002
    Messages:
    3,669
    Likes Received:
    49
    Location:
    Redmond, WA
    The obvious variations on the above would be using a 3x3 filter in 8x case.

    And of course scaling the buffers in both directions rather than the one you propose and sampling down, it might not be possible to get exactly 6 or 8 samples perpixel this way, but it would probably look better.
     
Loading...

Share This Page

  • About Us

    Beyond3D has been around for over a decade and prides itself on being the best place on the web for in-depth, technically-driven discussion and analysis of 3D graphics hardware. If you love pixels and transistors, you've come to the right place!

    Beyond3D is proudly published by GPU Tools Ltd.
Loading...