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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  • silverblue - Saturday, September 26, 2009 - link

    I think you may have been much happier with a 512-bit interface which would result in nearly 2.5x the bandwidth of the 4890, however it remains to be seen whether it'd be a waste or not. Having said that, it could mean for slower GDDR5 thus reducing costs, but wouldn't it be far more problematic to incorporate the wider bus anyway?

    If ATI throw out such a card with a single GPU on it, a direct comparison with the 5870 (and nVidia's top cards at the time) will be inevitable. The extra bandwidth may be rather under-utilised for anything less than Eyefinity gaming or Crysis at max details ;)

    Now all we need is AMD to come back at Intel with a domestic release of its Thuban die (or hurry up with Bulldozer, sheesh) and it'll be a very, very exciting time for people to upgrade.
    Reply
  • SiliconDoc - Sunday, September 27, 2009 - link

    I want to know how the pinout compares on the 5870 gpu to the 4870/90.
    Have they doubled the data pins, or is the data jamming in and jamming out, even at 4800mhz ?
    Maybe that's why 512bit would help.
    Perhaps faster data rate ram, needs also a wider data path, more pins, more paths in and out of the gpu.
    I will check the overclock sites that have already posted on this matter.
    Reply
  • JarredWalton - Sunday, September 27, 2009 - link

    I would assume that the pin count on 5870 isn't radically different from 4870. Granted, we know what assuming can get you, but with the same interface width there's not much reason for it to get substantially more pins. A few changes for power leads to deal with having more transistors, and other minor tweaks are likely, but my bet would be it's within 10% of the pin count of 4870. Reply
  • PorscheRacer - Monday, September 28, 2009 - link

    For all those people clamoring on about why ATI didn't go with a 512-bit memory controller I'm going to chime in here with some ATI 512-bit experience. If you're a sharp one reading this, you have already guessed that means I'm going to talk about the R600. Now you can hate the card all you want, but I quite enjoyed this card. First of all, in the R600 it was the last ring-bus. It was a true 512-bit, and large memory controller. I'm not certain on the amount, but I believe it owned about a quarter of the realstate on the die. That's a lot. It also was some of the cause for the chip running hot and why UVD was scrapped from that chip to save room.

    Now, to keep that 512-bit ring-bus fed, you needed to push large amounts of data to it. The more you increased system bandwidth, the faster the card would be in any task. I've run hundreds of benchmarks over the years and I'm pretty sure Jared and Anand can attest to this. Same goes for overclocking the card. Raising the core didn't do much, but cranking up the VRAM to feed that hungry ring-bus sure did. Prices anyone? I believe $450 and up depending on where you were located. It was on heck of a pricey chip for ATI to make. Enter the die shrunk 3000 series with the 256-bit memory controller and voila. A cheaper chip to make. It never came close to the theoretical performance of the 2900XT, but the 3870 was about 90% of the performance for a lot cheaper. Yeas I know the cores were tweaked and so on in the 3000 series, but they are very similar.

    If ATI ever went to a 512-bit bus, which means more PCB layers, higher cost in manufacturing and a larger die, I'd think they'd do it on something like Juniper or wait till 32nm. It's not feasible right now. They technically could go the MCM route with Juniper and get a mashed up version of a 512-bit bus, but I don't think the chips have been designed with that in mind.

    Anyways, most computers out there are starved to feed something like the 5870 and higher cards with a 512-bit bus. I just replaced my R600 with an RV740 (hah, went from 80nm to 40nm) and now I don't need to OC the heck out of my bus to keep the card fed. I'm running an old FX-60 setup due to a glowing review on here back in early 2006. Am I the norm? NO, I'm waiting to upgrade. Is the Core i7 9xx the norm? No. You have to build a card to a certain set of people. I'm building my pal a new computer and he's happy with the 5850. The 5870 is overkill for him. It's 80% of the 5870 but a hundred bucks cheaper. Now, I'm sure ATI looked at the 512-bit bus in much the same way. "Wow, that 512-bit bus sure flies, look at those numbers! Oh, it's going to cost us this much die space and more manufacturing costs.... Well, those 256-bit bus numbers are still pretty imperssive and within 80% of the gaming benchmark scores, so we'll go that way"

    Or something along those lines....I'm sure that's why nVIDIA's GTX300 is delayed. It's a massive chip, 512-bit bus and so on. Great, they'll take the performance crown again. Will they take my money? If they have something in the $200-$300 range, they have a fighting chance, just like ATI does, or soon to be Intel. Best price for performance will win me over there. I don't care what the bus size is, or how the card could have been better, just as long as I'm happy with the performance for my money. In which case, I'll be here looking forward to a GPU roundoup in the best bang for buck in that price range. Of course it will have DX11, or else there's no point in me upgrading again.
    Reply
  • SiliconDoc - Wednesday, September 30, 2009 - link

    The GT200 is a 512 bit bus.
    All the whining and complaining about difficulty means NOTHING.
    ati goes the cheapskate sloppy lame route, cooks their cores, has 90C heat, few extra features, and a red raging fanbase filled with repeated tantric lies.
    I even posted their own forum here with their 4850 90C+ whines, after some rooster told me his worst fan in the world on his 4850 kept it in the cool 60's like the several Nvidia cards, of course.
    The 512bit HD2900 XTX was and is a great card, and even the 256 version still holds it's own. It was well over 500 bucks, was limited production, sold out quickly, and there was HD2900 512bit lesser version that could be flashed to full XTX with a bios upgrade, and it disappeared after it went well over $500.
    That HD2900XTX has 115GB bandwidth.
    It was REAL competition for the 8800GTX.
    --
    Of course ati cheaped out on producing any decent quantity, has been losing money, overcharged for it (and got it - but apparently like RUIZ, the "leadership" qualifies for "MORONS!"
    ---
    Now, we'll hear endless crying about expense, about 512bit, and endless crying about core size (nvidia's giant monster), then we'll hear how ati just kicks butt because more dies to a wafer, and they can make a profit, and they can then wipe out nvidia and make them lose money....
    BUT JUST THE OPPOSITE HAS BEEN GOING ON FOR SOME NUMBER OF YEARS IN A ROW.
    If ati is so pathetic it can't handle making 512bit and selling 512bit, well then , they're PATHETIC.
    And, yes, it seems they are PATHETIC.
    Someone ought to let ati know there's "competition" and the "competition" pumps out 512bit buses all the time.
    I guess when ati "finally catches up to the modern world" they can put out a 512bit again.
    In the mean time, they can stick with their cheap pcb with less layers, their cooking hot crammed full electromigration core, and have a bunch of looners that for the very first time in their lives, actually believe that the ghetto is better than Beverly Hills, because they goin fps shootin', man.
    Oh, it's so very nice so many gamers have as advice and worry ati's imbalanced sheet and how they can maintain it at a higher level. Such a concern on their minds, a great excuse for why ati cheaps out. I've never seen so many gaming enthusiasts with so much whoring for a company's bottom line. At the same time, nvidia is seen as an evil profit center that throws money around influencing the game production industry. LOL
    Yes, it's evil for big green to make money, employ reps, toss millions into game channels, be extremely flexible and pump out 20 differing flavors of cards, so it's not so boring, work so games run well on their product - yes what evil , evil ****rds.
    ...
    Perhaps the little red brokers could cheer some more when they feel ati "has improved it bottom line" by producing a cheap, knocked down, thinner, smaller, hotter, less featured, more negative driver issues, red card, because gamers are so concerned with economics, that they love the billions dollar losers plotted and carried out plans, and hate the company rolling in dollars and helping pump out games and a huge variety of gaming cards...
    LOL
    Yeah, the last red card that really was worth something, the HD2900512XTX.
    That's the other thing that is so funny from these little broker economy whizzes. After they start yakkin about ati's dirt cheap product scheme, it really burns em up that the real cadillac of videocards commands a higher price.
    Well, there's a reason a better made, more expensive process, more featured, wider supported in games videocard, is higher priced.
    "the great economists" then suddenly turn into raging little angry reds, screeching scalping and unfair and greedy... LOL
    Oh it's a hoot.
    Reply
  • Zak - Monday, October 5, 2009 - link

    I like Nvidia cards too, but if I was a moderator here you'd be banned by now. Relax. Take a pill. No one takes you seriously any more.

    Z.
    Reply
  • SiliconDoc - Saturday, September 26, 2009 - link

    The core clock is not doubled, still 850.
    The memory data rate is not doubled 3600 to 4800.
    The bus width is not doubled still 256.
    The frame buffer is not doubled, still 1GB

    --- From Article Page 1 below ---
    " So what’s Cypress in a nutshell? It’s a RV790 (Radeon HD 4890) with virtually everything doubled,.."
    ---
    Ok, so pay attention to the word "virtually".
    Reply
  • JarredWalton - Saturday, September 26, 2009 - link

    There's no need to double the bus... either double the RAM data rate or double the bus width and you accomplish the same thing. But in a nutshell, everything is doubled relative to HD 4890 except for bandwidth, which only improves by 23%. Similarly, everything is more than double the 4870X2, you don't even need to deal with CrossFire stuff, but the 4870X2 has 50% more total bandwidth.

    ATI almost certainly isn't completely bandwidth limited with 4890/4870X2, but I think 5870 might just be fast enough that it's running into bandwidth limitations. On the other hand, bandwidth limitations are largely dependent on the game and algorithm. For instance, the Quake/Quake World/Doom games have been extremely bandwidth intensive in the past, and some of the titles Anand tested fall into that category. However, I know of other games that appear to be far less dependent on bandwidth, and the more programmable stuff going on, the more important shader performance becomes.

    In the past, Oblivion was a great example of this. NVIDIA's 7800/7900 cards had a lot of bandwidth relative to shader performance, while ATI went the other route. Oblivion was really a strong ATI title (X1800/X1900 series) up until NVIDIA released 8800, which greatly improved NVIDIA's shader performance. Most modern titles tend to be a combination of things.
    Reply
  • SiliconDoc - Sunday, September 27, 2009 - link

    Note: Edited for ease of response.

    Well noone makes double the ram data rate, there is NO SUCH DDR5. (No one ever said there was.)
    None of it runs at 7200 for videocards.
    NVIDIA is using the 512bit bus and 448bit+ on it's top cards, so what is ATI's problem, when that's the only thing available ? (They don't need it enough to increase the cost of the cards to get it.)
    Furthermore, the core is still 850, so have the data pins in and out of the core doubled ? I RATHER DOUBT IT. (Obviously it didn't - the specs say it's 256-bit. Did you not read the post?)
    So, concievably, we have twice the data to move, on the same core speed, with less than double the DATA PINS in and out. (No, we don't have twice the data to move, unless the 4890 totally maxed out what the RAM could provide. ATI doesn't think this happened, so they only marginally increased bandwidth.)
    If the bandwidth is NOT the problem, as you so claim, why then since everything ELSE you say has doubled, the conclusion we have is the ATI core is not up to the task. (If it truly had doubled in every area, and performance didn't double, we'd have a problem. The conclusion sane people will draw is that ATI looked at cost and benefit and decided a 256-bit bus was sufficient for the present. Otherwise they'd need a more complex circuit board, which would increase complexity and cost.)
    That's it, it's core tech is so much the same....
    LOL
    Just love those ATI arguments. (There was no argument, but I'm a troll so I created one!)
    When the CORE is overclocked, we will see a framerate increase.
    SOOOOO.....
    Tell me how the core handles TWICE THE DATA in and out - unless it's pinout count has doubled ? Is ther that much wasted time on the 4890 pins - on the current 5870 pins ? (No one said the core handles twice as much data; theoretically it can, but then deeper buffers would help.)
    It may handle double data or nearly internally, but that has to communicate with the ram- etc onboard.
    SORRY, once again, not agreeing. (Agreeing with what, that the bandwidth only increased by 23%? Wow, that's amazing. You'd disagree if someone said the sun rises in the east, wouldn't you? Try reading next time before responding instead of arguing for the sake of argument.)
    Reply
  • Zool - Sunday, September 27, 2009 - link

    The meaning of cache on the gpu is so it doesnt need to read and write to dram memmory too often. The speed of texture cache on 5870 is 1 TB/sec and its sram. And thats just the texture chache. It just shows how much speed is needed to utilize that raw comuting power on the chip. They surely tested the chip with higher speed memory and ended with this bandwith compromis.
    Also u cant compare the bare peak bandwith. The type of memmory controler and the speed of the GPU(and also cache) should change the real world bandwith like we see with wideferent CPU models and speeds.
    When u read xxx GB/s bandwith it doesnt mean it always this fast (they name it peak bandwith always).
    Reply

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