God of War AA coming to PC/360 ?
Custom anti-aliasing techniques are becoming increasingly popular among leading games developers. Last week LucasArts talked to Digital Foundry about the new AA techniques used in the forthcoming Star Wars: The Force Unleashed II. But the yardstick remains the quality level set by Sony's morphological anti-aliasing (MLAA) tech as seen in the phenomenal God of War III. Last week, AMD has released its own GPU-based MLAA implementation for PC and other developers are working on GPU solutions for Xbox 360. MLAA is going cross-platform.
Available now for the new Radeon HD 68x0 series of graphics cards (though available to 58x0 owners too via an unofficial hack), AMD's tech has received plenty of plaudits from the PC tech blogs, garnering particular praise for its excellent edge-smoothing capabilities along with the relatively unnoticeable impact on frame-rates. In good conditions MLAA can match the quality of 8x multi-sampling anti-aliasing (MSAA) but requires far less in the way of system resources. On the PS3, Sony's MLAA is parallelised over five SPUs and takes around 4ms of processing time - freeing up precious RSX resources.
AMD's solution has much in common with Sony's, but is fundamentally different in many ways. The fact that the God of War III MLAA operates on SPU has some very specific advantages - the Cell's satellite processors are far more flexible in terms of how they can be programmed, leading some to believe that GPU implementations will struggle to match the quality level.
More obvious to the end user, AMD's approach is a post-process filter that works through the entire completed frame, including the HUD and any on-screen text. This results in exactly the same kind of artifacting on text as seen with The Saboteur on PS3. As the MLAA algorithm works on the whole screen, it simply doesn't know the difference between a genuine edge and text, resulting in a noticeable impact to quality, along with occasional dot-crawl on HUD elements.
As AMD's MLAA is a post-process shader effect, it edge-smoothes the entire screen, including text, which suffers as a result. Sony's system gets to work on the image before the HUD is added.
Artifacts can be minimised by running at higher resolutions, and the cards that the MLAA mode runs on should be able to cope with most - if not all - games at 1080p and higher anyway. However, the effects can never be eliminated with the current implementation. Sony's MLAA tech, in contrast, works on the frame before the HUD and text are added, producing a noticeably cleaner result.
So just how good is the image quality from AMD's version? Images like this don't exactly inspire confidence, but screenshots dotted around the internet show plenty of promise. Here are a couple of comparison shots. Apparently, AMD's MLAA can't be picked up by the usual range of PC grabbing tools, but it's no problem for us since we take our data losslessly direct from the DVI port of the GPU via our TrueHD capture card. What your monitor displays, our capture tech records.
AMD's MLAA is best deployed at higher resolutions, such as 1080p in order to minimise the artifacts inherent in this technique. That Sony were able to minimise these issues and make it 720p-friendly is an exceptional achievement.
Based on the quality of the shots, MLAA in this guise comes across phenomenally well, but having witnessed it in motion, there's a definite sense that the implementation is closer to the original Intel proof of concept as opposed to Sony's refined version. We know a lot about this, having worked with a compiled version of the sample code and processed a number of different games with it.
At the time we were hugely impressed with the quality of the still shots, the quality of the games in motion was far less impressive, and DICE's rendering architect, Johan Andersson, shared his thoughts on the drawbacks of MLAA.
"On still pictures it looks amazing but on moving pictures it is more difficult as it is still just a post-process. So you get things like pixel popping when an anti-aliased line moves one pixel to the side instead of smoothly moving on a sub-pixel basis," he said.
"Another artifact, which was one of the most annoying is that aliasing on small-scale objects like alpha-tested fences can't (of course) be solved by this algorithm and quite often turns out to look worse as instead of getting small pixel-sized aliasing you get the same, but blurry and larger, aliasing which is often even more visible."
Andersson's comments, based on his own experiments with MLAA, appear to mirror closely the issues we see in AMD's tech. To illustrate, here's a 720p comparison of the PC versions of Danger Close's Medal of Honor (somewhat notorious for its "jaggies" and the inadequacies of its built-in AA option) and Rocksteady's Batman: Arkham Asylum.
No anti-aliasing up against the AMD MLAA implementation. Use the full-screen button for HD resolution or click on the EGTV link for a larger window.View this video in HD
In the Batman scene we can see both the good and bad of MLAA. Prominent foreground edges are effectively smoothed off, but far off geometry exhibits exactly the kind of pixel-popping that Andersson warned against. The blur effect is constant regardless of depth, making sub-pixel edges actually much more prominent than they are when there is no anti-aliasing in effect.
With the Medal of Honor clips, we see another perfect example of what Andersson describes - alpha-tested fences do indeed suffer because of the filtering, plus we see the effects of HUD artifacting and more pixel-popping.
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What this demonstrates fairly clearly is that the AMD implementation isn't really good enough for use on console, where the available 720p resolution simply isn't high enough to produce visually pleasing effects. It could perhaps be deployed on certain games though - The Saboteur, for example, might not be using pure MLAA, but the visual drawbacks are very similar, and it still looks pretty decent.
However, with AMD only officially supporting its new high-end HD 6850 and 6870 graphics cards, it's highly unlikely that you'll be using a resolution as low as 720p. So, let's run the same series of clips at 1080p. So we can stream them we're clipping the image to fit within our 720p player but still running at 1:1 per pixel, and it's clear that while a good deal of blur is added to the image overall, the negative elements of the MLAA are not so apparent.
Here we see the comparison at 1080p, though we have cropped the image to work within our 720p player. Once again, the full-screen button and EGTV link allow for full HD resolution.View this video in HD
Sony's MLAA solution is designed for a 720p framebuffer and produces outstanding results that the AMD post-process can't really compete with. However, the fact that AMD's MLAA is so light in terms of GPU resources means that there is nothing to stop you adding the effect in addition to hardware MSAA, so in theory you could deploy 2x MSAA to deal with a lot of the sub-pixel issues, then use the MLAA post-process to effectively kill off the close-up and ugly jaggies that remain.
Going forward though, it wouldn't be surprising if AMD decides to add in game-specific MLAA profiles. As its tech is running at the driver-level, it's difficult for it to get access to the raw image without the HUD, but perhaps with developer assistance game-specific setups could be deployed that minimise the artifacts and make it a more viable alternative to the performance and RAM-sapping MSAA.
While the AMD solution isn't really happy working at console resolutions, other developers are looking into producing a viable solution for the Xbox 360 and PC. While AMD has hit the headlines with its implementation, this cross-platform PC/360 project actually pre-dates the AMD work by several months. Jorge Jimenez, Belen Masia, Jose Echevarria, Fernando Navarro and Diego Gutierrez have collaborated on an MLAA system that they say produces effects approximate to 8x MSAA.
They've also posted a movie, demonstrating their tech.
The GPU MLAA tech looks promising and works on both Xbox 360 and PC, but this demo (best viewed in full-screen mode) is the only example we have of the tech in play.View this video in HD
The developers also include timings on processing frames from a range of AAA titles, showing an average cost of 3.79ms on Xbox 360. This isn't insignificant bearing in mind that a 30FPS title will want to render a frame in less than 33ms, and while it sounds like a figure in the same ballpark as the PS3's MLAA, it is worth remembering that Sony's tech operates on SPU, and is designed to be run in parallel with the RSX graphics chip. Any Xbox 360 solution will be GPU only. We asked Jorge Jimenez if it can really be described as a like-for-like alternative to Sony's offering.
"The RSX works in parallel with the Cell SPUs, that's true. But that also means the Cell SPUs aren't available while the MLAA algorithm is running. They moved the algorithm from the GPU to the CPU, giving extra time for the RSX to render better graphics (6ms as explained here), including improved shaders or increased geometry complexity," Jimenez says.
"But it also reduces time for physics calculations, artificial intelligence, etc. It is a wise decision, however, given that the RSX can easily be the bottleneck, given its weakness when compared with the PS3's CPU. Our case is similar, but we are exchanging GPU time for GPU time, as the CPU is not involved at all. In contrast with the PS3, Xbox 360 has a strong GPU when compared with its CPU, so we believe that moving the calculations to the CPU, in that particular case, would not make much sense."
Jimenez is keen to point a couple of differences between the two implementations, however.
"Firstly, using a Cell-based MLAA requires a level of SPU and GPU management that not all games can afford. In contrast, our approach is totally straightforward. Secondly, our solution is universal, it can run in DX9, DX10, DX11, Xbox 360 and, in theory, even on the PS3. So, to make a long history short, if we consider the machine as a whole, yes, our technique is a like-for-like alternative."
But does the new GPU implementation address any of the image quality issues we observed in both the Intel proof of concept and AMD code?
"We haven't had the time to make a more in-depth study of our algorithm in motion, but looking at our demo video, we think it looks quite comparable to 8x MSAA at 720p. However, as we have said before, we are studying temporal coherence... In the material we tried, we didn't observe many distracting artifacts when handling graphics in motion," Jimenez says.
"But still, as using 8x MSAA has a cost of around 5.192 ms and our technique only requires 0.44 ms in a GeForce 9800 GTX+, that gives plenty of room to enhance the quality. We are currently working in quality improvements in the PC version (and considering a more in-depth study of our MLAA approach in motion), and performance improvements in the Xbox 360."
On PC, the low cost of the team's MLAA means that a hybrid approach can make a lot of sense - Jimenez believes that an optimum configuration would be a 4x MSAA pass followed by the MLAA. The first pass would reduce the kind of sub-pixel issues that MLAA typically has problems with, while the second pass would tidy up additional edges.
The 360 MLAA work looks promising, and we hope to be able to put the tech through it paces in a follow-up feature: Sony's MLAA work is interesting in that it takes the existing concept work and turns it into a fully-fledged solution that might not solve some of the underlying problems but does an excellent job of working around them. If the 360/PC solution from Jimenez and his co-authors can match the quality, that would be quite an achievement. In the meantime, other developers are producing interesting work using alternative anti-aliasing algorithms, with LucasArts' DLAA looking really impressive...
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@ Mods, vul section e post korsi..
Please keu Eta ke Tech News e move kore den..
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