Unreal Technology Features

Tim Sweeney
Epic MegaGames, Inc.

Last Updated: 07/21/99

A Complete Solution

The biggest strength of the Unreal technology, relative to third-party and homegrown tools, is that it provides a complete solution that has stood the tough test of real-world game development.  While there are certainly some quality  third-party game components on the market, such as QSound, Motivate!, and Caviar, they all provide only a small part of the overall 3D game-development equation.  The saying "God is in the details" is very applicable to game engine development: a cool rendering algorithm can only be exploited  if it integrates seamlessly into an engine's collision, visibility, networking, AI, and file management subsystems.  All of Unreal's components have been designed together; they provide a consistent programming interface; and they fully interoperate.

As a technology developed in conjunction with a leading-edge, high-detail game, the tradeoffs that Unreal makes on detail versus realism are fundamentally sound and taylored to real-world constraints.  For example, some people may criticise Unreal's cyllindrical actor collision system as being low-tech compared to an IK-based system.  However, this decision was made with an accute awareness of all the ramifications it had on the overall product: cyllindrical collision makes AI, player control programming, and network predication much simpler, and it keeps performance up.  A collision system designed in isolation could easily be more advanced than Unreal's, and it would probably cause countless headaches when making it work with the rest of the codebase and making it run at a decent frame rate on 1998-1999 PC's.

Editing Tools

Mesh animation

Rich, organic surface support

State of the art mesh support

Artificial Intelligence

Digital Sound System

Digital Music System



Technical programming

Game programming




Realtime algorithmic texture engine

Dynamic scene graph technology

Dynamic scene graph (DSG) technology is a natural extension of portal technology.   A dynamic scene graph consists of a root node, corresponding to the player's immediate surroundings, and a hierarchical tree of child nodes.  Each DSG node has a coordinate system transformation, clipping volume, and other rendering state associated with it.  Unreal's rendering engine constructs a dynamic scene graph on-the-fly as each frame is rendered.  New scene graph nodes are generated as the viewer's visibility propagates outward through portals.  Scene graph nodes are the basic building blocks of many realistic effects and special effects, such as:

The strength of DSG rendering is that all of the node effects are fully interoperable.   For example, once a mirror DSG node is defined, mirrors are automatically supported recursively (for hall-of-mirror type effects);  mirrors work with skies;   mirrors work with warp portals;  warp portals work with skies, etc.

Unreal's dynamic scene graph technology is a basic building block which will be extended in future versions of the technology to incorporate such next-generation effects as seeing between levels, seeing across multiple servers on the Internet, and refractive water.

Tremendous Extensibility

Most of Unreal's subsystems are designed to be highly extensible, by defining an abstract base class (such as URenderDevice for a general rendering device) to expose the general functionality to other modulars, while implementing one or more specializations of the subsystem (such as UGlideRenderDevice for the 3dfx rendering code, or UOpenGlRenderDevice for the OpenGL rendering code).   The following are some of the modules which are designed for extensibility:

User interface & localization

Deliverables provided to licensees

Licensing & business information

Contact Mark Rein: mrein@epicgames.com.