The Return of Supersample AA

Over the years, the methods used to implement anti-aliasing on video cards have bounced back and forth. The earliest generation of cards such as the 3Dfx Voodoo 4/5 and ATI and NVIDIA’s DirectX 7 parts implemented supersampling, which involved rendering a scene at a higher resolution and scaling it down for display. Using supersampling did a great job of removing aliasing while also slightly improving the overall quality of the image due to the fact that it was sampled at a higher resolution.

But supersampling was expensive, particularly on those early cards. So the next generation implemented multisampling, which instead of rendering a scene at a higher resolution, rendered it at the desired resolution and then sampled polygon edges to find and remove aliasing. The overall quality wasn’t quite as good as supersampling, but it was much faster, with that gap increasing as MSAA implementations became more refined.

Lately we have seen a slow bounce back to the other direction, as MSAA’s imperfections became more noticeable and in need of correction. Here supersampling saw a limited reintroduction, with AMD and NVIDIA using it on certain parts of a frame as part of their Adaptive Anti-Aliasing(AAA) and Supersample Transparency Anti-Aliasing(SSTr) schemes respectively. Here SSAA would be used to smooth out semi-transparent textures, where the textures themselves were the aliasing artifact and MSAA could not work on them since they were not a polygon. This still didn’t completely resolve MSAA’s shortcomings compared to SSAA, but it solved the transparent texture problem. With these technologies the difference between MSAA and SSAA were reduced to MSAA being unable to anti-alias shader output, and MSAA not having the advantages of sampling textures at a higher resolution.

With the 5800 series, things have finally come full circle for AMD. Based upon their SSAA implementation for Adaptive Anti-Aliasing, they have re-implemented SSAA as a full screen anti-aliasing mode. Now gamers can once again access the higher quality anti-aliasing offered by a pure SSAA mode, instead of being limited to the best of what MSAA + AAA could do.

Ultimately the inclusion of this feature on the 5870 comes down to two matters: the card has lots and lots of processing power to throw around, and shader aliasing was the last obstacle that MSAA + AAA could not solve. With the reintroduction of SSAA, AMD is not dropping or downplaying their existing MSAA modes; rather it’s offered as another option, particularly one geared towards use on older games.

“Older games” is an important keyword here, as there is a catch to AMD’s SSAA implementation: It only works under OpenGL and DirectX9. As we found out in our testing and after much head-scratching, it does not work on DX10 or DX11 games. Attempting to utilize it there will result in the game switching to MSAA.

When we asked AMD about this, they cited the fact that DX10 and later give developers much greater control over anti-aliasing patterns, and that using SSAA with these controls may create incompatibility problems. Furthermore the games that can best run with SSAA enabled from a performance standpoint are older titles, making the use of SSAA a more reasonable choice with older games as opposed to newer games. We’re told that AMD will “continue to investigate” implementing a proper version of SSAA for DX10+, but it’s not something we’re expecting any time soon.

Unfortunately, in our testing of AMD’s SSAA mode, there are clearly a few kinks to work out. Our first AA image quality test was going to be the railroad bridge at the beginning of Half Life 2: Episode 2. That scene is full of aliased metal bars, cars, and trees. However as we’re going to lay out in this screenshot, while AMD’s SSAA mode eliminated the aliasing, it also gave the entire image a smooth makeover – too smooth. SSAA isn’t supposed to blur things, it’s only supposed to make things smoother by removing all aliasing in geometry, shaders, and textures alike.


8x MSAA   8x SSAA

As it turns out this is a freshly discovered bug in their SSAA implementation that affects newer Source-engine games. Presumably we’d see something similar in the rest of The Orange Box, and possibly other HL2 games. This is an unfortunate engine to have a bug in, since Source-engine games tend to be heavily CPU limited anyhow, making them perfect candidates for SSAA. AMD is hoping to have a fix out for this bug soon.

“But wait!” you say. “Doesn’t NVIDIA have SSAA modes too? How would those do?” And indeed you would be right. While NVIDIA dropped official support for SSAA a number of years ago, it has remained as an unofficial feature that can be enabled in Direct3D games, using tools such as nHancer to set the AA mode.

Unfortunately NVIDIA’s SSAA mode isn’t even in the running here, and we’ll show you why.


5870 SSAA


GTX 280 MSAA


GTX 280 SSAA

At the top we have the view from DX9 FSAA Viewer of ATI’s 4x SSAA mode. Notice that it’s a rotated grid with 4 geometry samples (red) and 4 texture samples. Below that we have NVIDIA’s 4x MSAA mode, a rotated grid with 4 geometry samples and a single texture sample. Finally we have NVIDIA’s 4x SSAA mode, an ordered grid with 4 geometry samples and 4 texture samples. For reasons that we won’t get delve into, rotated grids are a better grid layout from a quality standpoint than ordered grids. This is why early implementations of AA using ordered grids were dropped for rotated grids, and is why no one uses ordered grids these days for MSAA.

Furthermore, when actually using NVIDIA's SSAA mode, we ran into some definite quality issues with HL2: Ep2. We're not sure if these are related to the use of an ordered grid or not, but it's a possibility we can't ignore.


4x MSAA   4x SSAA

If you compare the two shots, with MSAA 4x the scene is almost perfectly anti-aliased, except for some trouble along the bottom/side edge of the railcar. If we switch to SSAA 4x that aliasing is solved, but we have a new problem: all of a sudden a number of fine tree branches have gone missing. While MSAA properly anti-aliased them, SSAA anti-aliased them right out of existence.

For this reason we will not be taking a look at NVIDIA’s SSAA modes. Besides the fact that they’re unofficial in the first place, the use of a rotated grid and the problems in HL2 cement the fact that they’re not suitable for general use.

Angle-Independent Anisotropic Filtering At Last AA Image Quality & Performance
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  • SiliconDoc - Friday, September 25, 2009 - link

    LOL - you won't find me arguing, but that performance per dollar here is absolutely FAMOUS for guess whom, ati !
    Congratulations, for the first time someone other than myself conplained about it, of course, only when ATI has been implicated as a disaster in it.
    --
    PS - I think what the chart is saying is, use some common sense, not go for 9500, but in your range you hope to purchase, the chart can be handy for picking between several.
    --
    Also, the chart tells us, the 5870 is not bang for the buck.
    -
    So, so sorry, it upset you so badly, the tips above for proper useage should be fine.
  • KaarlisK - Wednesday, September 23, 2009 - link

    Actually, far more developers care about the next version of DirectX (pc-industry-wide vendor-independent development platform) than about PhysX (single vendor, low uptake currently). Not that PhysX would be unimportant.
  • SiliconDoc - Wednesday, September 23, 2009 - link

    Not quite time yet, you can "pre-order" one of 3 versions at tiger..LOL
    This is not a "hard launch", this is a red RUSE !
    --
    http://www.tigerdirect.com/applications/SearchTool...">http://www.tigerdirect.com/applications/SearchTool...
  • SiliconDoc - Wednesday, September 23, 2009 - link

    Ok, hurry, the paper launch finally "cracked" a bit and there's one card of 4 5870's on newwegg that is suposedly "available for purchase".
    http://www.newegg.com/Product/ProductList.aspx?Sub...">http://www.newegg.com/Product/ProductLi...1&na...
    It's 1:33pm on the 23rd, so no guarantees there's more than 0 for actual sale....
    Good luck on getting something other than paper. :-)
  • jabroni619 - Wednesday, September 23, 2009 - link

    I'd better not get paper... I was able to place an order at newegg at midnight when they were available and 18 hours later it's showing a status of shipped. ;)
  • SiliconDoc - Wednesday, September 23, 2009 - link

    7:08PM CST Wed. Sept 23rd, 2009 -
    Out of the 9 "reviews" by "customers" on newegg for the 5870 card, only ONE of them has the revealing:
    " This user purchased this item from Newegg " in blue by their name on the customer reviews tab.
    LOL
    So it looks like 8 posers and you. Hope you enjoy the XFX 5870,
    "WoostaR"
  • WoostaR - Friday, October 2, 2009 - link

    Thanks man, I actually went with 2 5870's. I know it's bit of overkill, yet future proof is better =)

    anyways, I have gotten over 17000 of 3dMark06. That's with Cpu.

    I am running Core i7 @ 4 ghz
    6GB of Gskill ram
    Dual 5870 @ CF
    750W Corsair.
    EVGA 3x SLI
  • jabroni619 - Thursday, September 24, 2009 - link

    Oh, and I didn't get the XFX, I got HIS. XFX wasn't even showing up when I placed my order. Only Sapphire, ASUS and HIS were, both the Sapphire and ASUS were OOS.
  • jabroni619 - Thursday, September 24, 2009 - link

    I haven't written a review yet as I haven't gotten the card. (hate it when people do that) I was a little worried up until just a few minutes ago when my UPS tracking# actually had some data. Estimated Delivery of 9/24/09. Hopefully it's waiting at the front door when I get home from work. I just spend the last 2 hours moving all the guts of my PC into a larger case to accommodate the card.
  • SiliconDoc - Friday, September 25, 2009 - link

    Apparently your luck is immaculate.
    http://www.fudzilla.com/content/view/15673/1/">http://www.fudzilla.com/content/view/15673/1/
    " We talked to partners and some of them might have a few cards next week and October is the month when things should get better.

    The big guys such as Newegg and Tigerdirect don’t have them, and in EU, a hundred plus cards are listed here, but none of them are available.

    A launch partner in the UK got 20 cards ...
    We hope that Radeon 5870 is not what AMD management calls a hard launch "
    ROFL - At least one place doesn't have to censor itself

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