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A game engine is the core software component of a computer or video game or other interactive application with real-time graphics. It provides the underlying technologies, simplifies development, and often enables the game to run on multiple platforms such as game consoles and desktop operating systems such as Linux, Mac OS X and Microsoft Windows. The core functionality typically provided by a game engine includes a rendering engine (“renderer”) for 2D or 3D graphics, a physics engine or collision detection, sound, scripting, animation, artificial intelligence, networking, and a scene graph.

Overview

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Visual3D.NET's runtime visual game development tools

Advanced game engines such as Unreal Engine 3, the Doom 3 engine, CryENGINE2, RenderWare, Gamebryo, and Visual3D.NET provide a suite of visual development tools in addition to reusable software components. These tools are generally provided in an integrated development environment to enable simplified, rapid development of games in a data-driven manner. These games engines are sometimes called "game middleware" because, as with the business sense of the term, they provide a flexible and reusable software platform which provides all the core functionality needed out-of-the-box to develop a game application while reducing costs, complexities, and time-to-market—all critical factors in the highly competitive computer and video game industry.

Like other middleware solutions, game engines often provide platform abstraction, allowing the same game to be run on various platforms (including game consoles such as PlayStation, PlayStation 2, Xbox, Xbox 360, and Nintendo Gamecube, and operating systems such as Microsoft Windows, Linux, and Mac OS) with few, if any, changes made to the game source code. Often, game middleware is designed with a component-based architecture that allows specific systems in the engine to be replaced or extended with more specialized (and often more expensive) middleware components such as Havok for physics, FMOD for sound, or SpeedTree for rendering. Some game engines such as RenderWare are even designed as a series of loosely connected middleware components that can be selectively combined to create a custom engine, instead of the more common approach of extending or customizing a flexible integrated solution. However extensibility is achieved, it remains a high priority in games engines due to the wide variety of uses for which they are applied. Despite the specificity of the name, game engines are often used for other kinds of interactive applications with real-time graphical requirements such as marketing demos, architectural visualizations, training simulations, and modeling environments.

Some game engines only provide real-time 3D rendering capabilities instead of the wide range of functionality required by games. These engines rely upon the game developer to implement the rest of this functionality or assemble it from other game middleware components. These types of engines are generally referred to as a "graphics engine," "rendering engine," or "3D engine" instead of the more encompasing term "game engine." However, this terminology is inconsistently used as many full-featured 3D game engines are referred to simply as "3D engines." A few examples of graphics engines are: Axiom, Ogre, Power Render, Crystal Space, and Genesis3D. Modern game or graphics engines generally provide a scene graph, which is an object-oriented representation of the 3D game world which often simplifies game design and can be used for more efficient rendering of vast virtual worlds.

Hardware abstraction

Most often, 3D engines or the rendering systems in game engines are built upon a graphics API such as Direct3D or OpenGL which provides a software abstraction of the GPU or video card. Low-level libraries such as DirectX, SDL, and OpenAL are also commonly used in games as they provide hardware-independent access to other computer hardware such as input devices (mouse, keyboard, and joystick), network cards, and sound cards. Before hardware-accelerated 3D graphics, software renderers had been used. Software rendering is still used in some modeling tools or for still-rendered images when visual accuracy is valued over real-time performance (frames-per-second) or when the computer hardware does not meet requirements such as shader support or, in the case of Windows Vista, support for Direct3D 10.

History

The term "game engine" arose in the mid-1990s, especially in connection with 3D games such as first-person shooters (FPS). (See also: first person shooter engine). Such was the popularity of id Software's Doom and Quake games that rather than work from scratch, other developers licensed the core portions of the software and designed their own graphics, characters, weapons and levels—the "game content" or "game assets."

Later games, such as Quake III Arena and Epic Games's 1998 Unreal were designed with this approach in mind, with the engine and content developed separately. The licensing of such technology has proved to be a useful auxiliary revenue stream for some game developers, as a single license for a high-end commercial game engine can range from US$10,000 to $3,750,000 (Warcraft III) and the number of licensees reaching several dozens of companies (for the Unreal Engine). At the very least, reusable engines make developing game sequels much easier and faster, a valuable advantage in the competitive computer game industry.

The continued refinement of game engines has allowed a strong separation between rendering, scripting, artwork, and level design. It is now common (as of 2003), for example, for a typical game development team to be composed of artists and programmers in a 4:1 ratio.

First-person shooter games remain the predominant users of third-party game engines, but they are now also being used in other genres. For example, the RPG Morrowind and the MMORPG Dark Age of Camelot are based on the NetImmerse engine, the MMORPG Lineage II is based on the Unreal Engine. Game engines are used for games originally developed for home consoles as well; for example, the RenderWare engine is used in the Grand Theft Auto and Burnout franchises.

Modern game engines are some of the most complex applications written, frequently featuring dozens of finely tuned systems interacting to ensure a finely controlled user experience.

Although the term was first used in the 1990s, there are a few earlier systems in the 1980s that are also considered to be game engines. For example, Sierra's AGI and SCI systems, LucasArts' SCUMM system and Incentive Software's Freescape engine. However, unlike most modern game engines, these game engines were never used in any third-party products.

Middleware

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SpeedTree forest-rendering middleware

Some companies now specialize in developing software suites known as "middleware." Middleware developers attempt to "pre-invent the wheel" by developing robust software suites which include many elements a game developer may need to build a game. Most middleware programs provide facilities that ease development, such as graphics, sound, physics and AI functions. Gamebryo and RenderWare are two such widely used middleware programs.

Some middleware only do one thing, but do it more convincingly than general purpose engines. For example, SpeedTree is being used to render the realistic trees and vegetation in the new Xbox 360, Playstation 3 and Microsoft Windows RPG The Elder Scrolls IV: Oblivion.

Two widely-used packages that provide subsystems of functionality include Havok and several of RAD Game Tools' systems. Havok provides a robust physics simulation system and RAD Game Tools develops systems for video rendering, audio playback and 3D rendering.

Some middleware contains full source code, others just provide an API reference for a compiled binary library. Some middleware programs can be licensed either way, usually for a higher fee for full source code.

MMOG Middleware

Middleware for massively-multiplayer online games is far more complex than for single-player video games. However, the increasing popularity of MMOGs is spurring development of such middleware packages. Some prominent solutions include:

• Multiverse Network
• HeroEngine
• Gamebryo
• Kaneva Game Platform
• RealmCrafter
• Project Darkstar

Hobbyists

Game engine development is a popular project amongst computer science students, hobbyists, and game developers alike. It can require strong interdisciplinary understanding of geometry, color theory, and computing. Being largely visual, however, these developers consider it fun and rewarding. Crystal Space, for example, is a popular (free) open source multiplatform game engine.

A very popular and inexpensive game development environment was created beginning in 1999 by Mark Overmars. His Game Maker object oriented interpreter makes development of 2 dimensional games extremely easy. The system can support many game formats including role-playing games (RPGs).

The top ten commercial engines (most of which are low cost and used by hobbyists and indie developers), according to DevMaster.net, are:

• Torque Game Engine
• TV3D SDK 6
• 3DGameStudio
• C4 Engine
• Unity
• Cipher
• 3Impact
• Reality Engine
• Deep Creator
• Beyond Virtual

FPS game engines

Main article: First person shooter engine

A well-known subset of game engines are 3D first-person shooter (FPS) game engines. Groundbreaking development in terms of visual quality is done in FPS games on the human scale. While flight and driving simulators and real-time strategy (RTS) games increasingly provide realism on a large scale, first-person shooters are at the forefront of computer graphics at smaller, more human scales.

The development of the FPS graphic engines that appear in games can be characterized by a steady increase in technologies, with some breakthroughs. Attempts at defining distinct generations lead to arbitrary choices of what constitutes a highly modified version of an 'old engine' and what is a brand new engine.

The classification is complicated as game engines blend old and new technologies. Features considered advanced in a new game one year, become the expected standard the next year. Games with a mix of older generation and newer feature are the norm. For example Jurassic Park: Trespasser (1998) introduced physics to the FPS games, but it didn't become common until around 2002. Red Faction (2001) featured destructible walls and ground, something not common in engines even in 2004. Battlezone (1998) and Battlezone II: Combat Commander (1999) added vehicle based combat to the usual FPS mix, which did not hit the mainstream until later. Tribes 2, Battlefield 1942, Halo: Combat Evolved and Unreal Tournament 2004 fully realized the potential for vehicular-combat and first person shooter integration.

See also

• List of game engines
• Game programmer
• Level designer
• Video game developer
• Video game publisher
• First person shooter engine

External links

• GameMiddleware.org, a reference website concerning game middleware and game engines available for commercial use
• 3D Game and Graphics Engines Database, a comprehensive database of today's graphics and game engines
• Terrain in Games, an extensive overview of terrain rendering in 1997-2000 game engines