AMD's Radeon HD 5870: Bringing About the Next Generation Of GPUs
by Ryan Smith on September 23, 2009 9:00 AM EST- Posted in
- GPUs
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.
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.
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.
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SiliconDoc - Thursday, September 24, 2009 - link
Oh really ? Now wait a minute, spin master. When the site here whined about "paper launch" it was Derek who brought up a two or three year old nvidia card, and cried and whined about it. Then speculated the GTX275 was paper, and then "a phantom card".Well, that didn't happen.... no apologies about it ever either.
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The PAPER launches of late are ATI ATI ATI ! ! !
We have the 4770, and now this one !
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Gee, when ATI BLOWS IT, we suddenly talk in vague terms about "the companies" having "papery launches" as " the general rule of thumb of how it's done.." - and that makes us "not a fan boy!??!"
R0FLMAO !!!!
Yes, of course, since the red ati is bleeding paper launches and the last one from nvidia one can actually cite is YEARS AND YEARS ago, yes, of course, you're correct, it's "unnamed companies in the multiple" that "do it"....
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I swear to god, I cannot even believe the massive brainwashing that is a gigantic pall all over the place.
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If I'm WRONG, please be kind, and tell me what nvidia paper launches I missed.... PLEASE LET ME KNOW.
Genx87 - Wednesday, September 23, 2009 - link
Is\was a good idea to shoot for as this is most certainly what Nvidia is going to attempt to achieve. But I am a bit disappointed this care rarely achieved it.I do like angle independent AF though. Should be interesting to see what Nvidia brings to the table. But kind of like the CPU situation(i5) I am kind of meh. But will say this has more potential compared to its predecessor than the i5 series does compared to Core 2 Duo.
SiliconDoc - Wednesday, September 23, 2009 - link
I thought that was just great, those pretty pictures, and then I get to reading. I see the 4890 and SQUARES. I see the GTX285, with CIRCLES and an outer rounded octagon.Then the 5870- and it's "perfectly round" angle independent algorithm, but I still see some distortions.
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So I get to reading and am told "the 4890 and 285 are virtually the same". I guess the wheel was first made square, and rolled as well as when it became round. No chance the reviewer could tell the truth and remark that NVidia has the best, until today.. NOPE can't do that!
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Then, of course, the celebration for the "perfection" of the 5870 and ATI's superb success in the "round" category...
EXCEPT:
We get to the actual implementations and NO PERCIEVED DIFFERENCE IS VISUALLY THERE. It cannot be seen. The article even states they searched in vain for some game to show the difference. LOL
All that extra effort to for pete sakes show that ATI superiority...all WASTED EFFORT, but for red roosters I'm certain it was a very exciting quest, titillating, gee a change to take down big green...
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So bottom line is IT'S A BIG FAT ZERO, even the older, worse ati implementation is apparently "non distinguishable".
It is remarked that NVidia doesn't "officially" support this method in game, and of course, after much red rooster effort, one finds out why.
THERE IS NO DIFFERENCE in visual quality. Another phantom red "win".
Another reason NVidia makes money (why waste it on worthless crap in developement that makes no difference), while ATI does not.
Yeah, that was so cool.
So happy the "mental ideation of perfection in the card for ati fans" was furthered. ROFL
Dante80 - Wednesday, September 23, 2009 - link
A quick question. Why is there no 5850 review available atm?1> Was there a separate NDA for the 2 cards?
2> Were there no sample cards given by AMD to reviewers?
3> Did AMD ask reviewers to postpone said reviews due to market supply problems/glitches?
4> Was this a strategy decision by AMD, for marketing or other reasons?
Ryan Smith - Wednesday, September 23, 2009 - link
AMD only provided us with 2 5870s, the 5850 was not sampled. 5800 series cards are in short supply, even for reviewers.Dante80 - Thursday, September 24, 2009 - link
Thank you for the prompt answer, that was what I was guessing too. Cheers...^^Spoelie - Wednesday, September 23, 2009 - link
To get enough 5870 cards in the channel for a hard launch, they used every possible die.There are probably not enough harvested dies to create the 5850 line just yet. And they're not gonna use fully functional ones that can go in a 5870 when supply for them is tight already.
Once the 5850 is launched, demand for them is up and yields matured, they'll have to use fully functional dies to keep supply up, but now they're building up inventory for a hard launch during the coming weeks.
SiliconDoc - Wednesday, September 23, 2009 - link
Uhh, just a minute there feller. The SOFT or PAPER LAUNCH has already hit, the big LAUNCH DATE is today....Newegg is a big ZERO available... (one Powercolor was there 30 mins ago, the other 3 listed are NOT avaailable, I watched them appear last night).
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So, when Ati has a "hard launch" they get "many weeks after the launch date" to "ramp up production" and "fill the need".
ROFLMAO
I was here when this site and the red roosters whined about Nvidia and appear launches, and I believe it was the GTX275 that was predicted to be PAPER (not very long ago in fact) here, and the article EVEN SPECULATED IT WAS A PHANTOM CARD.
All the red roosters piled on, but.... the card was available on launch, it wasn't a PHANTOM, and all that bs was quickly forgotten and shoved into the memory hole like it never happened...
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Oh, but when it's ATI and not Nvidia, the 4770 can remain almost pure paper near forever, and this one, golly it can be 95% paper and it's just " getting ready for a hard launch" WEEKS BEYONDS the launch date!
ROFLMAO
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No bias here?!? "Where's da' bias?!?!" said the red rooster (to the green goblin)...
Give me a break.
chrnochime - Friday, September 25, 2009 - link
Just because you can't find it in the states doesn't mean it's a fake launch. And fake launch? What are you a 12 year old or something? You're like the nvidia version of snakeoil. Just go play with your nvidia part m'kay ?SiliconDoc - Sunday, September 27, 2009 - link
Well, since you insulted, and mischaracterized, I came across the reminder about the 4870 paper launch.Yes, that's correct, this is how ATI rolls, a big fat lying launch date, a piddle of a few cards, then wait a couple weeks or a month.
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" The cards are fast, but as many pointed out HD 5870 is not faster than Geforce GTX 295, which is something that many have expected. Radeon 5850 will also start selling in October time, but remember, last summer when ATI launched 4870, the card was almost impossible to buy and weeks if not months after, the availability finally improved. "
http://www.fudzilla.com/content/view/15643/1/">http://www.fudzilla.com/content/view/15643/1/
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Like I've kept saying, the bias is so bad... I keep discovering more big fat ati blunderous moves, that are instead ascribed to imaginarily to Nvida.
Thanks for the incorrect whining, anger, and standard PC e-mindless chatroom repeated, non original, heard ten thousand times, brainless insult, it actually helped me.
I learned ATI blew their 4870 launch with paper lies as well.
You're a great help friend.