This article provides a quick look at how the pros are creating games and other multimedia apps on Linux and in the cross-platform space. Any Linux programmer interested in writing games, multimedia applications, or other tools that make heavy use of Linux as a desktop would do well to read on.

Most people have heard of Microsoft's DirectX, even nonprogrammers. Many gamers have also heard of OpenGL, which is typically used as an interchangeable term, but in fact is only the 3D graphics alternative to this platform. Other technologies used in Linux and cross-platform game programming include OpenAL, PhysicsFS, SDL, and the loki_setup tool (this one's for the Linux and Unix space in particular).

OpenGL - Cross-Platform 3D Graphics Libraries

John Carmack at id Software (www.idsoftware.com) is often credited for the survival of OpenGL (www.opengl.org), as from the beginning he has insisted on the games coming out of his company being written for this graphics standard. According to Timothee Besset, also of id Software, "I can't speak for him, but I think the main [reasons that Carmack prefers OpenGL over DirectX] are that the API has less function calls overhead and is portable, and the overall design is more 'pragmatic,' if that makes any sense."

An advantage of developing using OpenGL these days is that it is the standard adopted by Apple for OS X as well, allowing game developers to get more bang for their buck by choosing this cross-platform option. OpenGL of course also works well on Windows, when a game developer chooses to use OpenGL instead of DirectX. (See "Gaming Roundtable Highlights" on page 48 for more on the issues involved here.)

OpenAL - Cross-Platform 3D Audio Libraries

OpenAL (www.openal.org) was introduced first by Loki, the sadly missed but now-defunct company that used to port many games to Linux. Its co-creator and current maintainer is Joe Valenzuela, and this particular technology gains high praise from Ryan "Icculus" Gordon, who says that the API for OpenAL is "significantly less frustrating to use than the platform-specific APIs," allowing for greater flexibility and performance without getting in his way. This technology works in conjunction with other sound standards, such as the Advanced Linux Sound Architecture (ALSA, www.alsa-project.org), which is now supported in the Linux kernel.

Gavriel State of TransGaming points out just how much steam OpenAL is gaining: "Our users have asked us to begin adopting the ALSA API in place of the older OSS [Open Sound System, www.opensound.com] APIs, and we've begun to look at how best to do that. One option that we're considering is switching to OpenAL, which now has a direct ALSA back end. Doing that right is going to require us to get some extensions added to OpenAL, which we're discussing with OpenAL developers such as Ryan Gordon; driver quality is still an issue. In some recent distributions, bugs in ALSA sound drivers caused some games running in WineX to slow to a crawl. Simply upgrading to a newer version of ALSA solved those issues, but we're always concerned about the qualities of the drivers."

PhysicsFS - Cross-Platform Filesystem Libraries

PhysicsFS (http://icculus.org/physfs) allows game programmers to focus on their specialties while leaving the actual work on what must be done in order to access the filesystem to a lower, "you don't need to know the details of how every operating system does this" level. Included in PhysicsFS are important features such as the ability to lock all game filesystem activities into a sand-box so that havoc cannot be wreaked on the rest of the machine's files.

SDL - Cross-Platform Device Driver Libraries

Simple DirectMedia Layer (SDL, www.libsdl.org) uses OpenGL for the 3D video drivers and handles the rest of a machine's devices itself. According to Ryan Gordon, "it also tends to be significantly less frustrating to use than the platform-specific APIs, like DirectX, or Quartz, or Xlib, without surrendering much in the way of needed flexibility or performance. Programmer time and sanity are important." Part of this quote should look familiar. OpenAL is considered to be of this same ease-of-use caliber.

loki_setup - Cross-Unix-Flavor Installer

Ryan Gordon points out that back when Loki was in business, "there was no user-friendly installer for Linux at all, so one was needed." The loki_setup program (http://icculus.org/loki_setup) was built for the purpose of not only installing a game regardless of what Linux or Unix flavor the user was running, but also for patching, repairing game installations, and more. Today, tools such as rpm, apt, and the components that run out to the Internet to grab needed dependencies (yum and apt-get, for example) take care of some of these needs better than what was available back then, but there are still games today that use loki_setup, and it does tend to give a game installation a more polished appearance.

Never one to be biased, Joe Valenzuela (another ex-Loki employee) adds, "Let's say that games that use loki_setup are universally awesome."

Happy Programming!

So there's your quick look at what the pros are actually using to create games and other multimedia applications on Linux, and in the cross-platform space in general. Now hie thee out there and write us some games!

• Mainstream Games on the Linux Desktop