Free and commercial game engines

Commercially successful games usually score high with their perfect blend of breathtaking graphics, well-animated characters, realistic lighting, spectacular sound, and convincing effects. These features all can be developed from the bottom up; nowadays, game engines come into play in this process. Game engines can cater to 2D or 3D graphics, and some come complete with the necessary development modules.

The graphics engine takes care of textures, lighting effects, object animation, and so on. The physics engine ensures that the game objects conform to physical behavioral rules (rigid-body physics)  – which also applies to liquids. The sound system ensures a full sound so the player feels a part of the action. Further modules can handle network coordination, provide a scripting interface, and control the opponent's level of intelligence. Although some engines provide all these things, others are more specialized.

If you search online at the MobyGames website [1], you'll find 139 different game engines, but very few support Linux. Linux was always a niche market, so porting and cross-platform programming was not a priority for most gaming companies. Moreover, development was primarily for Windows and DirectX graphics interfaces – Linux users gazed into the void. Although many games ran – and still do run – under Wine, support was poor, and performance compared with Windows was clearly limited.

In the 1990s and into the millennium, first-person shooter (FPS) games dominated the market with their appealing graphics. Their engines were mostly based on commercial application code that developers placed under an open source license – probably with the notion of developing a vibrant fan base for a game. Thus, id Software released the source code for its Quake engine, which a series of graphically well-designed Linux shooters adopted, including Wolfenstein: Enemy Territory, Nexuiz, Alien Arena, Warsow, and OpenArena, as well as UFO: Alien Invasion. Even the source code for the Doom 3 engine (officially id tech 4 ) is under a GPL license [2]. Independent of these offerings is the Sauerbraten game engine, which – despite its weird name – has spawned a few successful games, among them Cube 2 and Red Eclipse.

Next Generation

When considering these games, it's clear that they no longer meet the requirements of modern game engines. Not only should they integrate the aforementioned modules, but they should run on most platforms, which should minimize the effort of publishing games on PlayStation 3, the PC, or iPad. Games today run on mobile devices and in browsers, so modern engines need to be jacks-of-all-trades.

Whereas smaller companies license external engines for their games, larger studios often develop their own. The Rockstar Advanced Game Engine (RAGE) that drives Grand Theft Auto IV, for example, was apparently designed not to reveal information on the Rockstar games to the new owner of the RenderWare engine used up to now. RAGE is, unfortunately, another example of an engine lacking Linux support; other companies are more advanced.

Unity

Unity is not only the Ubuntu desktop, it is also a game engine with the same name [3]. Since version 4, the game has supported Linux, but officially only Ubuntu so far. Perhaps it's no coincidence that the namesakes now work together in the game space. A representative of the company was at the Ubuntu Developer Summit in Copenhagen October 2012.

Unity exactly matches the aforementioned profile of a modern engine. The graphics are terrific, and the games developed from it run on the big three PC platforms, the main consoles (Wii, XBox, PS3), mobile devices (iOS, Android), and – thanks to the Unity Web Player plugins – browsers.

Because the engine is relatively cost-efficient, it's particularly popular among game developers. The games developed with Unity aren't necessarily the big blockbusters – Linux users might be familiar with Rochard (Figure 1) – but they are numerous [4].

Figure 1: Rochard was developed using the Unity engine and can be ordered via Software Center.