nVidia GF100 Architecture: Alea iacta est

Tessellation: Efficiency is king, trouble for 5870 and 5970?

Demonstration what can be created with a simple LOD scaling

As we explained in the Architectural Overview, in order to implement Tessellation, nVidia went for the "clean sheet" approach. Henry claims that the Polymorph Engine is the right way to address the Tessellation, instead of having a centralized approach hitting multiple Cores.


Unigine Tessellation sequence - Dragon and Cobblestone Road Sequence

In order to show GF100 efficiency, nVidia used Unigine's DirectX 11 benchmark. In a 60-second snapshot showing Dragon and Cobblestone road sequence, the upcoming GF100 was 50-80% faster than the Radeon HD 5870. Given the results of dual-GPU HD5970 in the same test, one might argue that in a very limited sequence, GF100 is faster than a dual-GPU AMD card. However, when we take the whole test into equation the situation should naturally change.


Tessellation performance in selected tests - AMD HD5870 vs. nVidia GF100

All of the nVidia speakers claimed they have much higher efficiency in terms of Tessellation vs. non-Tessellation but we were unable to confirm that. We also asked nVidia that given the slides compared AMD vs. nVidia hardware using nVidia's own demos, does this mean nVidia will not deploy a GPU VendorID lock? The answer was surprisingly positive and we got confirmations from several nVidia staffers that you should have no issues running nVidia's DirectX 11 demos on AMD hardware. Performance is whole another issue, though.

In terms of the so-called Geometric Realism, one of things that nVidia pulled out of a magician's hat was a comparison in Shader and Geometry performance. GeForce GTX 280 had 150 times more shading performance than FX5800. However, it also had only three times more geometry performance. With GF100, nVidia increased geometry performance by a factor of eight times, meaning now GF100 will have 15 times more geometry performance than NV30, i.e. FX5800. We might call this a good start. Compared to the Radeon HD 5870, nVidia claims that GF100 is 4-6x faster when using Microsoft DirectX SDK Geometry Shader example [the infamous car demo].

Image Quality - Anti-Aliasing: Meet the "miraculous" 32x CSAA

One of key Architects on GF100 explains the way how 32xCSAA works

 32x CSAA is consisted out of eight color and 24 coverage samples and all samples are using Alpha to Coverage. 32xCSAA is able to detect 33 levels of transparency, a 33x improvement over previous generation. As you might have guessed, the GT200 series did not support coverage samples while AMD's Radeon HD 4000 and 5000 series did.
We will put this mode under a detailed test but for now, it looks promising. More importantly for the AA setting in general, GF100 comes with vastly improved Transparency Multi-Sampling AA. We took a look at Left 4 Dead and saw a great improvement - lack of any artifacts. Then again, using Age of Conan for demonstrating 32xCSAA isn't something we would do. In any case, if new Anti-Aliasing modes really work, that will mean nVidia caught up with AMD in this key aspect of image quality.


8xAA vs. 32xCSAA mode comparison in Age of Conan



nVidia was also criticized for its Anti-Aliasing implementation in the past, with GF100 hopefully being a chip that will change all of that.

This 8+24x mode allegedly comes at only a 8-15% penalty when compared to regular 8x AA mode while offering much better quality.

Naturally, we won't be able to check this until we receive the boards themselves, but the picture on the right shows performance penalty while using a single GPU. If you decide to venture into the world of multi-GPUs, the performance penalty should virtually disappear. Truth to be told, we saw many games where going from 4x to 8x cut down performance by 30% and more while the companies claimed 5-15%. Unlike the past, we now believe that with Radeon HD 5870 and GF100 will finally put those unfortunate titles to rest. Today's GPUs should have more than enough computational power to perform this level of comparison. Do bear in mind that the difference between 8x and this new 32x CSAA mode is nothing else but the computational power of the GPU at hand.