Realtime Game Development

REALTIME GAME DEVELOPMENT

Rick D. Bess
MultiGen, Inc.
San Jose, California

INTRODUCTION

The next generation of video games is about to take over. The revolution at hand is RealTime 3-Dimensional (RT3D), enabled for new levels of interactivity and game play. In the RT3D game, the fantasy world will be more engaging and the action more exhilarating than ever before.

The RT3D game revolution is being fueled by the recent explosion of 3D graphics playback hardware. By the end of 1997, there will be an estimated 20 million game consoles and PCs with the power to run realtime 3D games. The present opportunity is not unlike the introduction of "talkies" to the Hollywood motion picture industry. The playback technology is developed, the "theaters" are built, and the audience is ready and eager.

Under these conditions, we are about to see a revolution in both game content and in the way new game titles are developed. Game artists will gain many more dimensions for their imagination and creativity, but also many more parameters to define and control. While development becomes more exciting and complex, deadline and budget pressures are not going to let up.

To harness the new power and freedom, a new class of authoring tools is needed. MultiGen's GameGen II Author addresses these needs.

ENTERTAINMENT MARKET GROWTH

With the improving performance of playback systems, the marketplace for RT3D entertainment title development is growing rapidly. According to the Hollywood Reporter, more than 1,700 new games titles were announced at the 1996 Electronic Entertainment Exposition. Worldwide there are an estimated 3,000 to 5,000 game development companies, located mostly in the title development centers of the Western USA, England, and Japan.

RT3D games are starting to arrive for the popular new game delivery platforms. Warhawk and Twisted Metal from Sony Interactive Studio America and SingleTrac, Super Mario 64 from Nintendo, and Blast Corps and Goldeneye 007 from Rare Limited are some examples.

PLAYBACK SYSTEM NIRVANA

Realtime 3D graphics used to be possible only for commercial and military flight simulation systems with million-dollar proprietary computers called image generators. Then came location based entertainment (LBE) and arcade machines. MultiGen tools have enabled developers to use high-end workstations from Silicon Graphics, Inc., to create RT3D scenes for LBE systems, such as Magic Edge's Vampire and Epcot's Aladdin ride.

Today, RT3D has become affordable at consumer levels. High-end Pentium PCs as well as dedicated game consoles, such as the Sony Playstation, Nintendo 64, and Sega Saturn, have reached the performance threshold for RT3D as shown in Figure 2. In 1996 and 1997, a new generation of 3D graphics chips and add-on boards for the PC will take playback systems a step closer to Nirvana with threshold texture rendering performance.

According to analyst projections, more than 20 million RT3D playback devices will be in the hands of users worldwide by the end of 1997. This means a huge draw for game content, especially since games can be developed for play across platforms. For a example, SingleTrac is taking the Warhawk game for the Sony Playstation and remastering it for the PC with a 3Dfx graphics board. And watch out, because Internet games and interactive worlds enabled for RT3D are on the horizon.

THE BASICS OF RT3D

Game legacy

Video games started with simple animated sprites on a painted two-dimensional background image. Character movement was limited in screen space, and the background scrolled to give an illusion of forward or backward motion. The player's vantage point was fixed, and there was no perspective view into the scene. Though game animation techniques have evolved, such as using 3D characters in front of 2-1/2 dimensional layered backgrounds, these approaches remain limited.

Game play benefits of RT3D

RT3D technology brings a new level of creativity to developers and heightened enjoyment to game players. It enables more complex characters and game worlds so that the game experience can be different every time. Figure 4 summarizes the benefits of RT3D technology.

How is RT3D different?

With the emergence of new game consoles, powerful PCs, and 3D graphics acceleration chips, Realtime 3-D breaks through the limitations of canned animation playback.

True RT3D is fundamentally different in three ways:

The game environment is fully defined in three dimensions. Developers are free from limitations on the size of the gamespace. Players can look at the gamespace and its elements from any vantage point, intensifying the experience of immersion in the game.
Motion in the scene, of the camera and game elements, is perceived as continuous. To achieve the sensation of continuous motion, each frame must be processed on the fly and, in animation terms, displayed at a rate of 15 to 30 frames per second.
Motion response to player input seems immediate, without perceptible delay. When a player moves a joystick, pulls the trigger, or runs his car into a wall, an event is triggered and rendered on the screen in less than 200 milliseconds. Immediate response is the key to interactivity, and canned animation playback cannot deliver it.

SingleTrac Entertainment Technologies, Inc., used MultiGen realtime 3D modeling tools in the development of its award-winning Twisted Metal and Warhawk titles for the Sony Playstation. Using MultiGen software, SingleTrac developers can view models and worlds from a true 3D perspective, import and export a variety of graphical formats, and develop games for multiple platforms. SingleTrac intends to expand its extensive use of the Windows NT environment. "We are excited about the additional capabilities GameGen II on Windows NT will bring.

RT3D media elements

With expanded freedom for the imagination comes more media elements to define and control. Consider elements of the 3D gamescape illustrated in Figure 6.

RT3D elements fall into three categories:

Static elements do not move in the world. These include the terrain skin, buildings, and props such as trees.
Dynamic elements move in the world. Vehicles, characters, animated effects such as explosions, and triggered events such as trap doors are all examples of dynamic elements.
Rendering elements include camera parameters, illumination sources, and visibility effects, such as fog.

Atari Interactive has used MultiGen tools to create its new driving game, in which players race at 200 mph through tight turns, patches of fog, and other dangers. This game is among the first to feature gouraud shading, force feedback, and 16-bit perspective-correct textures. "Without MultiGen, many of the games features such as lighting, fog, and distance cue wouldn't be feasible, especially in the time frame we've set forth."

A single element, such as a car, is a complex construction of 3D geometry and surface attributes, including color, material, and texture, all of which need to be defined and controlled in the course of the game. See Figure 7. This complexity requires more powerful tools.

DEVELOPING FOR THE RT3D ENVIRONMENT

These new games aren't being developed by the creative community in the same way as previous-generation video games. The new technology demands a new development process and an expanded team that includes the RT3D interactive artist.

The 3D storyboard&emdash;a new way to stimulate and refine ideas

The RT3D development process incorporates strategies from 2D sprite game development, frame-based animation, and flight simulation. Developing an RT3D title involves a cyclical three-phase process as shown in Figure 8.

Asset creation. Artwork can be built, bought, or imported.
Authoring. Content elements are assembled and prototyped.
Mastering. Content is transferred to the game device.

Each phase is revisited again and again to refine the game, until the optimal balance of art quality and game performance is achieved for the target platform.

"MultiGen and our hardware enable game developers to get content to market much quicker."- Ross Smith, 3Dfx

The revolutionary difference in RT3D development is 3D storyboarding. Unlike the traditional 2D storyboard, the 3D storyboard is dynamic. It lets the development team assemble 3D artwork in the context of the game itself, where they can preview it interactively from the point of view of the player. 3D elements are roughed out and dropped into the 3D storyboard where they are tested in action under the performance conditions of the target platform. The process is repeated over and over as the 3D elements and events are refined to perfection. The 3D storyboard serves the entire team throughout the development process to communicate ideas and stimulate creativity.

"The quicker you get your concept to reality, the easier it is to find out whether or not it works." - Peter Giokaris, Zipper Interactive

Understanding the graphics pipeline

A basic understanding of the graphics pipeline is essential for creating RT3D environments. In simple terms, the graphics pipeline is the specialty part of the game playback device that computes the graphic images on the fly and displays them on the screen. The performance specifications of this pipeline for the delivery device must be understood by the game artist so that optimum 3D gamescapes can created, resulting in the very best player experience.

As shown in Figure 9, the camera parameters of field of view and range define a pyramid that can be thought of as a graphics funnel. All polygons that define the gamescape within the camera's view enter the graphics pipeline through the neck of this funnel. If there is too much content pouring into the funnel or if the content requires more processing than the pipeline can keep up with, the pipeline gets backed up and the frame rate slows down.

"MultiGen is one of the few companies that understands how to harness realtime power." - Ross Smith, 3Dfx

Sizing the game application

For the game to operate in realtime, all the elements must be capable of being processed in 1/30 of a second from any vantage point in the game. For example, if the graphics pipeline processes 90,000 polygons/second, the pipeline can process up to 3,000 polygons per frame at 30 Hz. This is the best-case performance.

Performance can be adversely affected by sophisticated graphics techniques, such as texture mapping, smooth shading, local illumination sources, or fog. For this reason, sizing the game starts in the earliest stages of defining and composing elements. To achieve the optimum balance of art quality and performance and eliminate the time-consuming need for rework, sizing guidelines for the use polygons and rendering techniques must be communicated to the RT3D artists from the outset.

Making optimized RT3D models

Achieving peak realtime performance starts with sizing the set design and setting polygon and texture budgets. But it doesn't end there. Game designers need powerful tools that enable them to design, prototype, and fine tune RT3D models&emdash;interactively.

WYSIWYG modeling. Game developers need the instant feedback of seeing what they are modeling as they are modeling it within the context of the game. Modeling in a "what you see is what you get" - WYSIWYG environment provides an interactive preview during development to make sure models look good from all points of view. It allows developers to verify early in development that 3D artwork is viable for realtime play. And it enables them to see and quickly fix problems of art quality, such as cracks, texture misalignments, and non-coplanar faces.

"MultiGen gives me the ability to create worlds out of my own head, to be in those worlds and interact with them. You're inside the game when your modeling it." - Spencer Lindsay, Atari Interactive

Preparing and tuning of realtime graphics. Peak realtime performance requires special content and data hierarchy organization. For example, organizing the data hierarchy for level of detail (LOD) control reduces processing load as objects get smaller on the screen. To achieve lower processing load, LOD models have reduced polygon density, lower texture resolutions, and simpler rendering attributes on polygons. See Figure 10.

Artists must be able to tune LOD transition ranges so that level of detail automatically decreases as models fade into the distance and increases as they come closer to the player.

Another key to seamless realtime performance is the ability to organize models in logical drawing order. Identifying and grouping model parts with common attributes results in faster realtime rendering.

Assigning surface attributes. Models are more than naked polygon geometry. Surface material, color, and texture are essential for engaging 3D models. However, these surface attributes can dramatically affect performance, so the RT3D artist must assign them prudently. The capability to search for and group data of common attributes can minimize pipeline bottlenecks.

Texture mapping. Texture mapping is the single most effective visual technique for creating compelling 3D gamescapes. Organizing texture maps in a visual palette makes them easy to access and apply to polygon surfaces through simple point-and-click or drag-and-drop operations. See Figure 12.

"One of the best tools MultiGen has is the texture capability. It allows us to manage our textures. We know exactly how many we're using and where we're using them before going to the platform. Frankly I don't think we can use anything else to do the kind of databases we're doing." - Peter Giokaris, Zipper Interactive

Rare Limited&emdash;producer of landmark video games such as Donkey Kong Country, Sabrewulf, and Battletoads&emdash;is applying its talents to Nintendo 64 titles, including Blast Corps and Goldeneye 007. Rare artists use GameGen to develop 3D models and background elements, including modeling, texturing, shading, and lighting, on a variety of Silicon Graphics Inc. workstations. After static models are created, Rare converts the MultiGen database to its target console.

Preparing for realtime access and gameplay. In addition to defining the geometry and surface attributes of 3D models, the RT3D artist defines the triggers and logic for events such as collision detection, weapons effects, and animated special effects that impact the models. See Figure 13. The RT3D artist can optimize models for realtime performance by subdividing the model into bounding volumes that set limits for collision detection and other event triggers.

Culling is another way performance is optimized for realtime gameplay. Model and scene parts that are outside the camera's field of view are automatically culled before entering the graphics pipeline. Only parts inside the camera's field of view are processed, resulting in improved realtime performance.

Authoring optimized RT3D worlds

Preparing Interactive dynamics. Interactive model dynamics immerse the player in the game. There is much RT3D artists can to do define game dynamics without custom programming or taking content to the delivery platform. They can create and control model dynamics by defining the range of motion for articulated model parts. They can create and edit flipbook animations for triggered events, such as explosions. And they can embed switch nodes in the data hierarchy that instructs the software how to change the visual conditions of models and scenes.

Assembling gamescapes. Once 3D assets are created, the piece parts need to be assembled into gamescapes, comprising indoor floors and walls or outdoor terrain skins. Scene composition tools such as Plant and Put enable the RT3D artist to place objects anywhere within the gamescape. External file references for model placement reduce data memory and storage requirements and make editing instanced models quicker and easier. Instead of storing duplicate data for instanced models, the database contains a pointer to the file with a positioning matrix. One change to the external file will change all instances of the model in the database.

"I like the MultiGen hierarchy editor. It's very interactive, very intuitive. I like the drag and drop capabilities of it. - Barry Dempsey, Xatrix Entertainment Inc.

Organizing worlds. RT3D artists must have the control and flexibility to organize the game world. For example, the ability to group elements of similar attributes can speed data access and improve scene management. Artists must also be able to organize the world into game levels that appropriately challenge both novice and expert players. They also need the flexibility to scale content to the performance specifications of different playback devices such as PCs, graphics acceleration boards, and game consoles.

Defining the environment. The RT3D interactive artists can direct the scene by controlling lighting, according to time of day and sky color. Illumination sources can be controlled as global or local lights, or models can be prelit. RT3D artist also control visibility effects such fog and haze to increase immersion into the game, and to hide the effects of bringing new elements into the view. See Figure 15.

HOW GAMEGEN II ENABLES THE RT3D PROCESS

GameGen II permits you to build gamescapes that harness realtime power, with attributes aligned to the features of playback hardware and software. It provides unique power tools for making RT3D models and authoring RT3D worlds. GameGen II gives you deep access to data content and to the organization of the data hierarchy. No other software comes close to GameGen II for the optimization of models and worlds for seamless realtime playback.

"MultiGen has helped us tremendously with the development of realtime, 3D video games. The software works much like virtual reality technology and essentially lets us choose where the camera goes. For realtime design, there is no equal." Atari Interactive

The foundation of GameGen II is the OpenFlight Scene Description Database format, an open standard in public domain. OpenFlight contains the optimal data types, structure, and logic essential for realtime performance and interactivity. It gives you the control to spatially group, order, and prioritize your RT3D worlds for optimum realtime computing. Its memory saving techniques such as LOD control, model instancing and visual property palettes, help you achieve the highest possible art quality within your memory budgets.

GameGen II is available for both Windows NT and Silicon Graphics Inc. workstations, making powerful RT3D technology widely accessible and affordable.
MultiGen is a registered trademark and GameGen and SmartScene are trademarks of MultiGen, Inc. All other trademarks mentioned herein are property of their respective companies.

Copyright 1997 MultiGen Inc.