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AMD warns of tesselation pitfalls

Soldato
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AMD is warning developers to think carefully about how they use the new tessellation features in DirectX 11, claiming that poor implementation can result in even the most powerful of GPUs becoming overwhelmed.

In a post on AMD's Game blog, vice president of the graphics division, Eric Demers, suggests that while DirectX 11's tessellation functionality allows for significantly higher detail in games, "careless use of the technology can quickly overwhelm the GPU and cause it to perform less efficiently with no visible benefit in image quality."

Without naming names, Demers goes on to highlight some of the major pitfalls that developers can run in to while adding tessellation to their DirectX 11-compatible games.

For those that don't know, tessellation is a function of DirectX 11 which allows developers to create small polygons out of larger models - increasing the complexity of the model, above and beyond what has previously been possible, while keeping memory and CPU utilisation at a minimum.

The first issue that Demers warns about is the over-use of the tessellation function to create ultra-tiny polygons of around a pixel in size. While that makes the model look incredibly detailed, it doesn't sit well with the 16-pixel rasterisation pipelines of most modern GPUs - resulting in the GPU's performance being absolutely crippled.

It's not just the rasterisation engine that gets a workout with over-tessellated models, either - the shader has to work eight times harder to add shadows to a model constructed of one-pixel triangles compared to a 25-pixel triangle - with very little benefit in terms of perceived image quality.

Finally, Demers warns that when a scene comprises large numbers of extremely small polygons, the efficiency of 'multi-sample anti-aliasing' - a technique for 'smoothing' the edges of a polygon - is drastically reduced.

Demers claims that AMD's 'developer relations engineers' are working with game producers to ensure that adaptive techniques are employed to keep image quality up without sacrificing performance: "This is done by using a variety of adaptive techniques that use high tessellation levels only for parts of a scene that are close to the viewer, on silhouette edges, or in areas requiring fine detail. Our goal is to keep polygon size at or above 16 pixels as much as possible. This allows for a fairly high polygon density, making scenes look great while also running well on all recent GPUs."

AMD hopes that its work on improved tessellation will give it an edge over its rival Nvidia, to the point where the company is developing a pre-tessellation engine that uses a GPU's vertex shaders to help reduce rendering bottlenecks - a technique that could give AMD the edge in many DirectX 11 games.

Demers denies that AMD will be keeping its performance-enhancing techniques to itself, however: "As gamers, we know that you just want a game that plays well. At AMD, we are committed to delivering the best possible gaming experience for all gamers, not just those using AMD hardware. To that end, we are continuing our work with developers of DirectX 11 games to help them use tessellation in the most efficient way possible."

It all boils down to one simple concept: 2011 is going to be a good year for gaming graphics.

http://www.thinq.co.uk/2010/12/1/amd-warns-tessellation-pitfalls/

I personally hope some of this is implemented as it should allow users of lower end cards to use some form of tesselation to good effect.
 
TL;DR version?

AMD suck at tesselation?

To be fair theres a lot of merit to what they are saying the problem is even with opptimisation and adaptive routines sometimes you have to go to pixel or sub-pixel levels at high quality settings to ensure high quality results on every part of a mesh. Tho its not such a problem for "normal" levels of tesselation... AMD want developers to not include true high quality options it seems.
 
Personally Id rather see better use of tesselation to remove the need for AA rather than the current method of using AA. This is one of the few remaining ways that games will get more and more realistic graphics and stopping at a specific point is abit daft to be fair.
 
I completely agree with where they are coming from, higher levels of tessellation are exponentially diminishing returns.

I don't know but I would guess that the original 5870 is probably good enough do do tessellation at such a level that it gives ~90% the image quality of a 580.

Trouble is it wont stop heavy tessellation benchmarks making it look like ATI is rubbish at tessellation or Nvidia bunging developers to add in an extreme tessellation option to their games that gives negligible increase in IQ but is just enough so the ATI cards get smoked.
 
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Come on lets face it most of the games you can't even tell if tesselation is on apart from the obvious frame rate hit look at AVP it's well used on this game you can really tell the models esp aliens have tessalation on but some games like dirt 2 you can't even tell it's just the water which you wizz past and you get a massive frame hit for it.
 
Yes, I would normally side with AMD anyway but I do harbor strong opinions about poor results as a fault of a developers lack of intelligence.

A good example would be Doom 3. Why did they have such a demanding game with so much eye candy when it was too dark to see most of it yet your system still had to render it?
If you loaded youtube and all the thumbnails of videos where replaced with 1080p videos which automatically play but muted, would you blame your system for not being able to handle it or the idiot who designed it to display like that?

It seems like some game company's have a "treat 'em mean to keep 'em keen" attitude, make it flashy and hard to play on good settings so it gets used as a benchmark and always in peoples minds when it comes to new hardware so there is so much talk people assume its something they need and they get more sales.
 
DX11 pretty much sucks every game that has it so far either

1. runs like crap
2. looks identical to DX9
 
DX11 pretty much sucks every game that has it so far either

1. runs like crap
2. looks identical to DX9

Problem is a lot of companies when they say the game is direct x 11 it simply means it uses the more efficient pathways over dx10, instead of any of the fancy new effects :(

The only two games I've noticed dx11 graphics on are metro 2033 and avp, but less so on avp if im honest.

On metro, some of the smoke and light interactions due to the way dx11 does volumetric fog looks absolutely real but due to the nature of the effect, its exceptionally hard to spot lol.
 
Problem is a lot of companies when they say the game is direct x 11 it simply means it uses the more efficient pathways over dx10, instead of any of the fancy new effects :(

I don't really have a problem with that. There was some good stuff introduced on DX10 that never seemed to be utilised properly.
 
Problem is a lot of companies when they say the game is direct x 11 it simply means it uses the more efficient pathways over dx10, instead of any of the fancy new effects :(

The only two games I've noticed dx11 graphics on are metro 2033 and avp, but less so on avp if im honest.

On metro, some of the smoke and light interactions due to the way dx11 does volumetric fog looks absolutely real but due to the nature of the effect, its exceptionally hard to spot lol.[/QUOTE]

Do you happen to have a youtube link showing that effect?

Not sure why the quote appeared like that... :p
 
AMD is warning developers to think carefully about how they use the new tessellation features in DirectX 11, claiming that poor implementation can result in AMD's most powerful of GPUs becoming overwhelmed.

Fixed.:D
 
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I do recall a thread where the person moved over to gtx480 sli and still could not max out metro as his fps was dipping into the 20's to much. Tesselation along with dof was having to big a hit. Had they used tesselation properly this probably would not have been the case. Theres not to many games out atm that use tesselation that amd fall drastically behind nvidia. It only seems to be extreme benchmarks.
 
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