Evergreen/DX11 tessellators vs XBox 360′s

Similar but different

ONE OF THE FEATURES of the upcoming ATI Evergreen family, also known as the 5-series, is a tessellator. While this might be old news to graphics card enthusiasts, this time it really is different, mainly because Microsoft is finally backing the technology.

ATI has been putting tessellators in its hardware for generations. The 2000 series was one of the first, but there have been bits and pieces like 3D normal map compression long before. Depending on how you count, Evergreen is either the fourth or fifth generation of the technology.

ninjatessellationdemo 500 Evergreen/DX11 tessellators vs XBox 360s

Tesselators make lots of triangles. Here is a picture from AMD.

Most people count ATI’s 2xxx, 3xxx and 4xxx as its first three generations of graphics cards with tessellators, but they forget the most important one, the Xenos/R500 in the Xbox 360. Tessellation was roundly ignored on the PC side of game development because it wasn’t ubiquitous and lacked standards. Now with the Xbox 360 and DX11 both having the technology, it should mean an easy port from the Xbox 360 to the PC and back, right?

Yes and no. We are told that the tessellator in the R770/4870 cards is a strict subset of the ones in the Evergreen cards. Given that the technology – going back to the R600 family, and even the Xbox 360′s R500 – was done by the same company, it is likely that even those older version are also a fairly strict subset of the succeeding generations. So on the functionality side, the answer is a clear yes, you can port the code with little change.

On the no side there is the small problem of how you access the tessellators. With DX11, Microsoft pulled, well, a Microsoft, and changed how things are done. The DX11 way of calling the tessellators is different from the non-DX11 way of doing things. In Microsoft’s defense, the ‘old way’ was not a standard because it only existed in ATI cards and the 360, but you would think Microsoft would just use what was there.

So in the end, the functionality of Evergreen’s tessellators is a superset of that of the older series graphics cards, but how you get to them is different. The code underneath should be very similar if not the same, and more critically, optimizations should be very similar too. That means the differences are very likely able to be patched over with a smart compiler.

With progress in gaming being gated, or more aptly stymied, by console capabilities, this is a welcome bit of progress. As long as Microsoft can convince developers to use the tessellator on the Xbox 360, it looks like the ones in DX11 will be used as well. That might possibly lift PC gaming from the stone age of “next gen” consoles to the bronze age. Raise your stone axe and howl at the moon for progress.S|A

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 Evergreen/DX11 tessellators vs XBox 360s

Charlie Demerjian

Roving engine of chaos and snide remarks at SemiAccurate
Charlie Demerjian is the founder of Stone Arch Networking Services and SemiAccurate.com. SemiAccurate.com is a technology news site; addressing hardware design, software selection, customization, securing and maintenance, with over one million views per month. He is a technologist and analyst specializing in semiconductors, system and network architecture. As head writer of SemiAccurate.com, he regularly advises writers, analysts, and industry executives on technical matters and long lead industry trends. Charlie is also a council member with Gerson Lehman Group.