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A look at PhysX in Mirror's Edge

Kicking ass and smashing glass

A year has passed since Nvidia announced plans to port the PhysX programming interface to its CUDA architecture, and it's been about six months since we last spent quality time looking at the fruits of its labor. Industry support for Nvidia's PhysX has been slow to grow, but after a highly visible recommitment to the endeavor at last month's Consumer Electronics Show, Nvidia has made it clear that PhysX will remain a key selling point for its graphics cards. And thanks to EA DICE's million-seller Mirror's Edge, Nvidia arguably has its highest-profile title yet with support for GPU-accelerated PhysX. I'd say we're about due for another look at the technology.

We've spent a lot of time talking about Mirror's Edge. If you've missed our other coverage, Cyril got the hype train rolling when the game was first announced, after which Geoff got his hands on the Xbox 360 version and shared his thoughts on the experience. Most recently, Cyril played through the PC release and had a blast—so much fun, in fact, that he was compelled to discuss the game again in our latest podcast. And after all of that, we're still not done talking about it.

I won't discuss the premise or merits of the gameplay in too much depth—you can check out some of our earlier coverage for that. Suffice to say, Mirror's Edge is a first-person 3D platformer with a small dose of combat to mix things up a bit. As in any good platformer, this game's environments present as much danger as the bad guys that inhabit them. The majority of your time is spent exploring your surroundings and figuring out how best to navigate them. Combined with the first-person parkour aspect, it becomes apparent very quickly that the set pieces are what drive gameplay.

Mirror's Edge was initially going to be a simultaneous cross-platform release for the 2008 holiday season, but the PC version was delayed, perhaps partly to incorporate PhysX effects. Xbox 360 and PlayStation 3 owners got their hands on the game first, but like most Windows releases, Mirror's Edge PC also brings sharper visuals and more flexible controls.

The pledge
So, what does PhysX bring to the table in Mirror's Edge? The designers at EA DICE took full advantage of the PhysX API throughout the single-player campaign, utilizing the extra horsepower of GPU-accelerated physics to drive a number of visual effects in the game world. Here's what you can look forward to:

  • Glass — There's a lot of it in Mirror's Edge, and more often than not, it's being shattered. With PhysX enabled, window panes send chunks of glass flying realistically through the environment when they break. Shards will react to the player as well as enemies, and if you dive through a window, you can expect to see pieces of glass follow you. Without PhysX, breaking a window triggers the same old type of animation you've seen in shooters for over a decade.
  • Cloth — Though not as prominently featured as their glassy counterparts, you'll find tarps, banners, and window shades just waiting to be shot throughout the game. As they're perforated by bullets, they eventually become little more than tatters that drift to the ground. And of course, any large vehicles like helicopters or trains will impart their presence upon soft objects thanks to the simulated wind. In most cases, disabling PhysX will simply remove these soft bodies from the environment.
  • Smoke — PhysX brings fully simulated smoke to Mirror's Edge. Unlike the static smoke animations you're used to seeing, here you'll find fluid dynamics in action. Both the player and enemy characters will leave trails through smoke, and like the soft bodies, smoke will react to wind sources. Once again, persistent smoke doesn't exist in the game world when PhysX effects are disabled.
  • Debris — Typically, when a bullet ricochets off of the environment, you get a stock animation that might consist of dust or sparks, depending on what it hits. With PhysX, debris will go flying through the environment, realistically bouncing off of walls and characters.

Of course, all of these promises raise a couple of questions: are the visual improvements noticeable and are they worth the performance trade-off? That's what we aim to find out.