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An Introduction to PhysX

written by: M.S. Smith•edited by: J. F. Amprimoz•updated: 5/26/2011

Hardware acceleration of physics has always been a holy grail of PC gaming, heralded by many but never truly obtainable. However, Nvidia has recently attempted to resolve the problem of physics acceleration by enabling PhysX on its video cards. So what is PhysX, and can you use it?

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    PhysX - Odd Name, Old Concept

    For years, physics in games has been a hot topic. The implementation of realistic physics is a difficulty that gaming has yet to overcome, and finding ways to enhance physics without hindering overall game performance is a priority for both game developers and or companies that make gaming hardware. The ability to render more realistic physics in a game means the ability to create a game world which is more believable and interesting than those of competing titles. If a game was hypothetically given a physics engine that perfectly mimicked reality, it would be seen as light-years beyond any other title. It is easy to think of physics as simply being what determines if the gun your character lets go of drops to the ground or floats in the air. But game physics is intertwined with many things. For example, a more advanced physics engine could depict shattering glass better, creating a graphical advantage over other games.

    The main roadblock limiting the pursuit of more advanced physics is one of computing horsepower. While throwing a basketball against a wall is simple in real life, recreating the way the basketball moves in a video game requires many advanced calculations which, combined, seriously tax the resources of your average gaming hardware. There have been numerous attempts at tackling this problem, and PhysX represents just one of those ways. But seeing as it supported by Nvidia, the most popular GPU manufacturer in a world, it is fair to say you'll be running into Physx more often than any other implementation.

    However, PhysX can be confusing. Only certain games will work, and only certain Nvidia hardware will support hardware acceleration of PhysX. This brief guide will give you the low-down on what PhysX is, and let you know how (and if) you can take advantage of it.

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    The Origins Of PhysX

    PhysX was originally the invention of a company called Ageia. Founded in 2002, Ageia was a company formed specifically to tackle the problem of physics acceleration. Unfortunately for Ageia, physics acceleration proved to be a more difficult problem than imagined, not only because physics acceleration is demanding, but also because getting various hardware manufacturers and game developers to settle on a standard is difficult. Ageia had hoped that by creating a standard method for accelerating physics, it would reap great profits. For a time, Ageia experimented with the idea of selling a dedicated physics acceleration card, which you would buy to accelerate physics just as you would buy a video card to accelerate graphics. But Ageia was never able to convince the market that there was a need for a separate physics acceleration card, and so Ageia continued to flounder until it was purchased by Nvidia in 2008.

    That is where things get more interesting. The purpose of Nvidia's purchase was clear from the start. Nvidia wanted to be able to offer its customers a way of accelerating physics with their GPUs, an ability that might make Nvidia seem like a better deal in the eyes of certain consumers. Nvidia does have a substantial amount of weight behind its brand, as well as a large marketing budget. However, while Nvidia has now taken on PhysX, hardware acceleration of physics is not a feature that you'll be able to use at all times.

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    What You Need For Hardware PhysX

    In order to use hardware acceleration of graphics, you'll need two things - a game which supports hardware acceleration of PhysX and a Nvidia video card which is both capable of hardware acceleration of PhysX and fast enough to use the feature once it is enabled.

    Nvidia lists the games which support PhysX on its website. The list is not very large to begin with, and not all of the games which are listed are games where having hardware accelerated PhysX is going to make a large difference. Take Age Of Empires III, for example - while it technically is listed as having hardware physics acceleration, I doubt anyone well notice much of a difference between playing that game with PhysX hardware acceleration on or playing with it off. Some of the games which do include notable beneifits include Mirror's Edge and Unreal Tournament III. Mirror's Edge enables a number of physics-based graphical effects when played with PhysX compatible hardware, and Unreal Tournament III has some special maps that make significant use of physics in gameplay.

    On the hardware side, you'll need to make sure that the Nvidia graphics card you own or are thinking of buying supports PhysX. Nvidia considers PhysX to be something of an off-shoot of its CUDA initiative, and so any CUDA-enabled graphics card will be able to use PhysX hardware acceleration. Nvidia has a full list of the GPUs that support CUDA posted on its website, but what it boils down to is this - you need to have a graphics card that is from the 8000 series or higher. The graphics card in question must also have a minimum of 256MB of memory, which I believe is not standard on all 8000 series graphics cards. You'll also need to have the hardware running with drivers that are up-to-date, as the original drivers released with most of Nvidia's older products are not going to support CUDA and, by extension, PhysX.

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    What To Expect

    If you have a game that makes use of PhysX and you have PhysX compatible hardware, than using it is a cinch. Most games will either detect and enable the hardware acceleration immediately, and those that don't should simply offer a setting in the games options.

    But don't expect PhysX to change the way you game just yet. Given that it still has only limited support, the results obtained from PhysX are more of a gimmick than anything else. That is not to say that playing Mirror's Edge with PhysX enabled is not awesome, because the little graphical extras add to an already atmospheric game. However, serious implementations of PhysX do ask a lot from your GPU, as can be seen while playing the special Unreal Tournament 3 maps which are aimed towards those with hardware PhysX acceleration. A FPS hit of about 30% is fairly common on 8000 series products, and it is very doubtful that someone with a 8600GT would be able to use any of the PhysX features at all, at least not without slowing the game they're playing to a crawl. And even in the most elaborate examples, PhysX does not effect gameplay in any significant way, as no developer wishes to commit significant time adding content which only a fraction of players will be able to enjoy.

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    Looking Ahead

    Recently, ATI announced that it also is going to be implementing a physics acceleration feature into its GPUs. However, their version is based off the competing Havok technology. What this boils down to, then, is more of a marketing war than anything else. As long as both ATI and Nvidia are developing their own independent solutions to physics acceleration, it is doubtful that any physics acceleration technology will become popular. In fact, physics acceleration probably won't become common until DirectX 11 becomes common, which is still many years off. That said, if you do currently have a PhysX capable card, there is no reason not to enjoy the advantages that provides you, even if only a limited of selection of games support the technology.