If you play PC games, you've probably heard about something called DirectX — it's hard to miss, because when you install a new game on a PC a dialogue box usually pops up that asks whether you'd like to upgrade to the latest version.

But most people know little about DirectX, or the fact that it promises to play a key role in pushing avid video game fans to upgrade to Windows Vista.

While the dialogue box is a common sight for gamers, what it doesn't tell you is what DirectX is, why you need the software upgrade, and what perks (if any) the latest version might offer.

So what is this mysterious-sounding DirectX, exactly?

In simple terms, DirectX is the means by which many multimedia applications (including video games) interact with Microsoft Windows operating systems. It basically tells a game how to get the most out of things like the video card and sound card installed in your computer.

In more technical terms, DirectX is a set of what programmers refer to as "low-level application programming interfaces" — commonly called APIs — comprised of software tools that help standardize the way Windows operating systems receive and process multimedia information. Think of it as a bridge between game software, the operating system, and graphics crunching hardware.

The best-known of DirectX's APIs is Direct3D, which undertakes the formidable challenge of generating the complex three-dimensional graphics found in modern games.

According to Microsoft's Phil Taylor, program manager for Microsoft’s in-house Aces game development studio, prior to DirectX developers "wrote directly to the metal."

That's tech jargon that means developing versions of software for specific pieces of hardware. In other words, programmers had to tweak their video games in different ways to work properly with the different video accelerators, sound cards and other bits of computer hardware that players might be using — a very labour-intensive way to write a program, given the huge variety of potential hardware combinations out there.

"DirectX represented a major improvement because it presented a standardized interface for programmers," he said.

It also meant that gamers would be able to install new components — such as video cards and sound cards — on their Windows computers secure in the knowledge that their games would still work under the new hardware configuration when they rebooted and wanted to play.

Industry standard

DirectX has become one of the major hubs around which the game industry revolves. Updates to DirectX help shape how new games will be developed, and what new multimedia features they'll be able to wow players with.

Ken Brown, public relations manager for video card maker NVIDIA, calls each major DirectX release a milestone for the industry.

"It dictates what features will need to be supported in the graphics hardware, so that game developers can be assured that their newest features will be supported in the hardware," he explained. "The vast majority of games are built using DirectX and every graphics processing unit [video card] has to support it."

DirectX is not the only player when it comes to multimedia APIs, but it's by far the dominant one. OpenGL, an API created by Silicon Graphics in 1992, was available four years before the first version of DirectX. OpenGL's newest iterations still work on Windows PCs, but its popularity on Microsoft platforms has withered over time.

A screenshot from the game Crysis, running on DirectX 9.

A screenshot from the game Crysis, running on DirectX 10.

A screenshot from Microsoft’s Flight Simulator X, running on DirectX 9.

A screenshot from Microsoft’s Flight Simulator X, running on DirectX 10.

A screenshot from the game Age of Conan: Hyborean Adventures, set for May release, running on DirectX 9.

A screenshot from the game Age of Conan: Hyborean Adventures, set for May release, running on DirectX 10.

The most talked about DirectX 10-compatible game yet released is Crysis, a violent and lifelike shooter developed by the German studio Crytek. It employs a new game engine designed specifically for DirectX 10.

Set on a jungle island, Crysis is an indisputable marvel of graphical innovation when it's running at maximum visual fidelity on a DirectX 10-equipped machine. Crysis provides the closest thing to real-world imagery that the video game industry has yet produced, with gorgeous effects such as sunlight that filters through water in dynamic beams, and objects that are rendered in mind-boggling detail, including plants and trees with bark and leaves that almost look like photographs of the real thing.

A free update recently released for Microsoft’s own Flight Simulator X adds plenty of DirectX 10 eye candy, including beautiful light-blooming effects (imagine the sun cresting an object, its light overpowering and obscuring the edge of that object), and realistic, dynamic shadows inside aircraft cockpits, as seen here.

Age of Conan: Hyborean Adventures, set for May release, is one of the most anticipated DirectX 10 games of 2008. The new API has allowed Funcom, the Norwegian studio behind this online role-playing game, to fill the game’s massive virtual world with a wide variety of highly realistic details, including greatly enhanced shadows, innumerable bumps and depressions in the terrain, and advanced lighting effects, such as the sunbeams seen here penetrating a forest canopy.

It's found a more receptive home on Macintosh computers and in the PlayStation 3, leaving DirectX as the effective standard for the Windows PC gaming industry.

Special effects: No limits?

DirectX was originally developed for Windows 95. The release of the software giant's most recent operating system, Windows Vista, brought with it the tenth major update to DirectX, appropriately (if somewhat unimaginatively) dubbed DirectX 10.

With each new version of DirectX, programmers have been given more options and resources with which to create ever more visually impressive games. DirectX 10 has been hailed as the most notable leap forward yet in terms of the programming freedom offered to developers who use DirectX APIs.

For example, DirectX 10 features a tool called Pixel Shader 4.0, a program that modifies the individual pixels that make up the image on the computer's screen by applying effects such as shadows, textures, and lighting. Whereas previous versions of Pixel Shader restricted programmers to a set number of instructions to modify what people would see on the screen when playing a game, Pixel Shader 4.0 offers them the ability to code a virtually unlimited number of instructions.

The caveat is that programmers are still limited by the level of detail the average users' computer hardware is capable of generating, so game developers will have to wait for faster generations of computers and video cards to reach the market in order to really test the limits of DirectX 10.

Other new features in DirectX 10 include a geometry shader that works to create more realistic visual effects, such as motion blur. There's support for video cards with a unified graphics processor architecture, which let several types of shaders work together rather than separately, theoretically providing a noticeable boost in graphics performance.

The concepts at work become much more technical the deeper one digs into the technology. Suffice it to say that DirectX 10 can boost a computer's graphics performance and offers programmers new tools that will help make games look better.

Windows XP gamers shunned?

But while DirectX 10 is designed specifically to improve PC gaming, not all PC gamers are keen to adopt it.

The loudest complaint is that DirectX 10 is compatible only with Windows Vista, and won't work with XP or other older versions of Microsoft's operating systems. That forces PC game lovers to migrate to Microsoft's new Vista operating system if they want to play the latest games with the latest, most innovative graphics.

According to Microsoft, DirectX 10's dependency on Vista was unavoidable.

"DirectX 10 makes use of new features found only in Vista," explained Taylor, adding that it would have lost many of its new efficiencies and multimedia enhancements had it been designed to work on older operating systems. "Vista and DirectX 10 are effectively joined at the hip."

Of course, as many critics have noted, Microsoft has an obvious stake in getting people to move to its new operating system. However, DirectX 10's link to Vista cannot be credited to Microsoft alone.

According to NVIDIA's Brown, each new version of DirectX 10 is a collaborative effort between Microsoft and industry heavyweights such as the top graphics hardware companies and game makers.

"Microsoft leads a graphics advisory board that includes members of NVIDIA, other independent hardware vendors, game developers, artists, and programmers," Brown said. "The board meets at various intervals to discuss which new graphics features are important to include in upcoming iterations of the DirectX API. We come together and map out what we expect to be the key 3D advances for the next few years."

In other words, Microsoft designs its API to handle the existing and expected future technologies from its industry partners. That means the game industry at large has a say in each update of DirectX, including their thoughts on operating system compatibility. DirectX 10 isn't compatible with earlier Windows operating systems because the industry as a whole is moving toward graphics functionality that is supported by Windows Vista and not Windows XP.

Vista: The inevitable future for PC gamers

The inescapable reality is that PC gamers will, eventually, be forced to upgrade to Windows Vista and DirectX 10 if they want to keep playing new games. At the moment, every game on the market that supports DirectX 10 also supports DirectX 9, but that won't always be the case.

Microsoft’s Taylor projects that the first DirectX 10-only (and, hence, Windows Vista-only) games, "will be available either by the end of this year or sometime in 2009."

NVIDIA's Brown agrees that DirectX 10-compatible games are set to quickly multiply. He said more than 30 million DirectX 10-compatible graphics processing units (which includes both video cards and video processors that are built into motherboards) have already been sold, and that most new add-in cards on sale today are DirectX 10 compatible.

"By 2009, nearly all PC games will offer DirectX 10 features," Brown said. Still, he noted that many consumers are still running hardware that only supports DirectX 9, which gives developers and publishers incentive to continue supporting the older API at least for the near future if they want to reach the largest possible market.

The big question, of course, is whether gamers have reason to look forward to their move to Vista and DirectX 10. According to Rahul Sood, head of Hewlett-Packard's gaming division and a high-performance hardware guru, they do.

"It will take time for the mainstream to realize … that PC gaming is getting much better because Vista has enabled it," said Sood. "When Vista first came out the drivers weren't very good, there was no real benefit to DirectX 10, and some older games wouldn't work. But now there's better graphics and better sound effects, as well as other performance features [that enhance PC games]."

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