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I tested frame rates using FRAPS over the course of a 20-second sequence in which I blew stuff up with grenades. This test was about rigid bodies, and large numbers of 'em were onscreen during this sequence. No liquids were present onscreen during this test, and no cloth except for a few strips way in the background, and those were typically not affected by the action. As with GRAW, I tried to play through the scene the same way each time, and the results you see below are the average and median scores from five runs.

CellFactor appears to be capped at 45 FPS, by the way. The cap will no doubt keep average frame rates down.

The CPUs used to obtain the results below were all Athlon 64s with 1MB of L2 cache per core running at the speeds specified. (The 2.4GHz dual-core chip was an Athlon 64 X2 4800+, and the 2.8GHz one was an overclocked FX-62. The single-core 2.4GHz chip was an underclocked FX-57.) CellFactor was running with its default low-quality graphics settings.

The performance delta between the single-core CPU with and without PhysX is substantial, but that difference shrinks pretty dramatically when we add a second CPU core to the mix. Shockingly, the system with a 2.8GHz dual-core processor performs almost identically to the dual-core 2.4GHz system with a PhysX card.

Testing PhysX performance in this way may be mostly bogus, but these aren't the sort of results Ageia wants to see, no doubt. In fact, Ageia seems to have been tracking various forum discussions about CellFactor software mode performance, and they've taken several steps to address the question.

First, they released a new version of the CellFactor demo with some changes. In the new version, cloth is enabled in software mode, despite the fact that it causes major visual artifacts and brings frame rates to a near standstill. Ageia also claims rigid-body performance and explosions are faster with this new version of Cell Factor. For what it's worth, I tried the new R36 release of CellFactor with a PhysX card in our benchmarking sequence, and performance was essentially unchanged.

Second, Ageia's release notes for CellFactor R36 now have a section titled "Framerate Numbers" that says the following:

It should be noted that the use of software frame grabber applications like FRAPS, even just to display FPS numbers, can slow down the game by up to 10 FPS or more, depending on the system and its settings. Due to this significant performance impact, software like this is not an accurate representation of overall game performance.
Hmm. Denigrating a particular testing method when you don't like the results is a time-honored tradition in high-tech PR, but generally FRAPS has been one of the good guys in such debates, with 3DMark and timedemo functions getting the brunt of it. Now, the tables have turned. My, how times change!

I tried to test the impact of FRAPS on CellFactor frame rates in a very straightforward way. The CellFactor demo itself includes a metrics overlay, which you can see in my screenshots. I ran the demo with and without FRAPS and watched the demo's built-in frame rate counter to see if things ran slower. From what I could see, FRAPS has no noticeable impact on frame rates.

Ageia has also tackled the CellFactor software mode issue by publishing an interview with the demo's developer. The developer talks down rigid-body objects and collisions as "simple" and talks up cloth and fluids as the truly unique features in CellFactor. Here's one key question and answer:

AGEIA: So you mentioned a “software mode” – is it possible to run CellFactor without hardware? If so, how does it run?

JS: Only if you want to miss out on a lot of what makes the game fun! I read on a forum somewhere that a player had done a command line switch and disabled support for the PhysX card. Of course he benchmarked it and it came back with a decent result. The reason for that is pretty simple – we never really intended for players to actually play the game like that, so we stripped the more advanced features out of the software mode (such as fluid and cloth); let’s not forget that AGIEA makes a very powerful physics software engine as well, so doing rigid body collisions (where boxes get tossed around) isn’t too much for the highest-end CPU's to handle. With that said, in software mode, you’ll still notice a significant slow-down at moments of peak physics interaction on even the latest and greatest multi-core machines. That’s why we have the PhysX card listed as a requirement.

It's good to see that Ageia's PR folks are on the ball when it comes to this sensitive issue, but embedded in that answer—and in our CellFactor software benchmark results—is a noteworthy and inescapable truth: even the very large numbers of rigid-body collisions we see in CellFactor can be handled pretty well on a high-end, dual-core processor. The same would appear to be true for the particle effects we've seen in CellFactor and GRAW.