Virtual reality technology-3D navigation plus novel interfaces-is being used to bring improved entertainment experiences to greater and greater numbers of people. This chapter examines how principles of good game design dating back to the best 2D sprite-based games can enhance the design of newer, 3D entertainment environments. In addition, some problems found exclusively in 3D are described and solved. Everything described here has been implemented and tested in products under development.

The current excitement over creating 3D virtual environments has, for the most part, overemphasized the technology and lacked focus on the quality of the actual experience. The original Super Mario Bros. and Zelda series of games developed over the last ten years and published by Nintendo provide a greater virtual experience than 95 percent of the 3D games being published today. Virtual environment designers must carefully consider what made those early games so appealing and apply the same principles today, albeit in a different presentation style. This chapter examines the following list of key game design principles:

Then, the chapter addresses three problems inherent in 3D environments that must be solved in any good entertainment application:

Third-Person Presentation

The classic games (except some driving games) all have an amazing attribute in common-that of third-person point of view (POV). Many driving games, even today, that strive for a straight-through-the-windshield view still allow a third-person POV. By contrast, the vast majority of 3D VR games or experiences adopt a first-person point-of-view wherein your own character is not visible.

There are two good reasons for adopting the first-person POV:

The first-person POV is easier to implement in a 3D world (and nearly impossible in a 2D world) because several issues, as detailed shortly, are instantly sidestepped. Most importantly, management of depth perception is extremely easy: Game players or viewers simply draw straight lines from their view to anything they see: If it's big, it's close; if it's small, it's far away.

The first-person POV is easier to sell (in other words, to get someone excited about funding) because it provides a more visceral experience, and that's what the majority of game and interactive development today is about. Each game tries to top the previous top game's "rush" of graphics, which is easiest to do with first-person POV. However, this places enormous limitations on the depth of the experience that is possible.

First-person POV is a good first step for the industry, but it must evolve to support third-person POV in order to grow and to attract an audience beyond those looking for a rush. Admittedly, a VR skiing attraction might not be as much fun in third person, where one can see the skier one is controlling, because most of the fun of skiing is in the rush. Skiing (downhill skiing at established resorts) is not about exploring, learning, and discovering.

By contrast, the best 2D games are about these very things. While nearly all popular games, it seems, have an action component, the enduring games also create an environment-even in two dimensions-that invites the player to explore, learn, and discover.

Imagine we want to develop a 3D VR Web site for some commercial purpose. Our first thought will be to provide some kind of visceral experience to attract people. A 3D environment where the world whirls about will attract a certain number of people-mostly males, ages 18 to 35. But now that we have people visiting our Web site, it's probably more important that we encourage them to explore, learn, and discover. We want them to explore so that they'll stay active in our site. We want them to learn our product; otherwise, there's probably no commercial reason to create the site. We want them to discover because it's the internal feeling of "Aha!" that gives intense pleasure and rewards our visitors for coming to our site. This critically important Aha! experience can only be created through careful design; it's not something that comes via a purely visceral experience.

In a Mario Bros. game, the first thing you have to do is jump on a Koopa (that's an enemy sprite for the Mario-impaired). But the second thing you have to do is to navigate a series of blocks; this forces you to explore how your character moves and how the environment reacts to your character.

In a first-person POV game, your character's movement is very limited. In fact, your character doesn't move at all; instead, the world swirls around it. But there is a linear relationship between you, your character, and the world (Figure 13.1).

In a third-person POV game, the experience is more complex (Figure 13.2). This triangular relationship between you, your character, and the world provides much greater opportunities for interaction.

Why? Because of your ability to see your character in the world, your mind can see more complex relationships. Instead of a more intense "in-body" experience as with first-person POV, you have a transcendent "out-of-body" experience. That is the real potential of VR-to give you experiences not available in normal life-and third-person POV provides an increased context in which to act and react.

Discovery and Exploration

The act of discovery is what creates the Aha! experience and can be something as simple as realizing that a certain shape in the landscape means you can get help there. Discovery is what cruising the Web is about. Discovering new information is fine, but, in the design of a 3D environment, it's also important that visitors learn to discover "how to" and not just "what." In a Mario game, with a little experience, you learn that you can double-jump and whack two Koopas in one motion. In a 3D VR Web site, for example, where you've created an online store, you would want visitors to learn "how to" by exploring and discovering.

You may need to manipulate your visitors into having this Aha! experience. For instance, you might program your store-clerk character to purposefully get in the way of a new visitor so that your visitor learns to ask the clerk questions.

One final note on third-person presentation: Very few movies are made in the first-person mode, yet moviemakers obviously want you to identify with the main character to develop an empathetic link. If you watch a young child (6 to 12 years old) play Mario Bros., you'll see that the child identifies so completely with Mario that the child "projects" into the 2D environment. You can create this same sense of identification in 3D without resorting to a first-person through-the-helmet view.

Movement Versus Animation

In a substantial VR world where objects may be extremely distant, the movement of an object in the world is more important than any fancy animated details. Up close and personal, animated nuances can provide all sorts of visual clues about the character you are interacting with. But more attention must be paid to how these characters or objects move within the environment than is currently being spent because, in a truly rich 3D VR world, there will be a huge number of objects but only a few that the viewer is attending to actively at any one time.

These objects may exist in the environment to attract the viewer's attention and encourage him or her to explore in a particular direction. Extremely detailed, complex character animation is wasted at such a time, when the object may be only a few pixels on the screen. But an amazing thing about people is that we can tell whether that's a person or a robot off in the distance by the motion of the object in the environment. If it bobs up and down like a person walks, then it's probably a person. If it glides a little too smoothly, it's probably not a person, at least as we know them. The simple motion of a few pixels bobbing up and down is enough to clue the viewer that "Hey, there's another person over there!" Particularly if the motion is oversampled and the motion is displayed in a subpixel, anti-aliased environment, very few pixels can express a great deal.

Player Control

Ask any player what he or she likes about Mario Bros. games, and the answer is always the same: control. It's certainly not the graphics. My early experience with VR Web browsers is that they leave me feeling horribly out-of-control of my experience. I'm never quite sure where I'm going to end up or why. There are a lot of technical reasons for this, including latency problems and erratic frame rates, but the problem can be solved even under these conditions by switching to a third-person POV. If I can see myself in the scene, and how I move in relationship to other objects in the scene, then I feel much more in control. If something is bumping me from behind, I can see it. I'm not left in a semiparanoid state where I have no idea what's affecting my character and therefore me.

Even if your user interface is dedicated to first-person POV, you can still increase the sense of player control in complex environments by allowing your viewer to move an icon, perhaps shaped like a camera, through the scene, position it in a safe place, and then switch to that view. I know from personal experience setting up architectural walk-through animations that it's easier to create an animation by manipulating a camera icon in the scene than by trying to animate by looking through the camera. The final goal is the same-a first-person experience of walking through a building-but the control necessary to navigate the environment is first provided through the third-person interface.

The Use of Maps

One way to overcome limitations of first-person presentation is by providing a map mode. Maps, in general, are pretty handy things to have when you have a goal but you don't know how to get there. Maps are also handy to create when you're exploring and want to remember what you've seen so that you can get back to it (again, the map is necessary to achieve a goal).

An incorrect use of maps, in my opinion, is to compensate for the lack of a sense of context that first-person presentation omits. If your game player or 3D VR user is constantly switching to the map to figure out what's going on, then you've failed in the design of your environment. So, when you want to encourage exploration, you want to make sure that maps are unnecessary, and that's done through the use of "wieners."

"Weenies"

This somewhat bizarre term was coined by Walt Disney, who suggested that when designing massive 3D environments (theme parks), it was necessary to lead visitors through the environment the same way one trains a dog-by holding a wiener and leading the dog by the nose.

Obvious weenies at Disneyland are Sleeping Beauty's Castle, which encourages guests to travel from the main entrance to the central hub; the former Rocket Jets, which encourage guests to explore Tomorrowland; the Mark Twain Steamship and dock, which encourage guests to explore Frontierland; and the King Arthur Carousel, which encourages guests to walk over the castle moat and into Fantasyland.

One of the biggest failures in weenie design ever is The Space Place. The Space Place is, in my opinion, an extremely cool, high-tech environment filled with plants and huge cathedral ceilings. It's a restaurant, and it's only open on days that Disneyland is very full. The reason is that nobody knows it's there. It's hidden between Space Mountain and the site of the former Mission to Mars. Even if you walk right up to it, you're hesitant to go inside because the lighting does not invite you in. It's so poorly placed that it's not clear how to improve it, without putting big arrows out in front that say "Come in here!"

Your 3D VR environment needs to have standout landmarks so that it's easy to navigate without a map. The best games, which have typically been designed with very limited graphics, always save a few graphics to denote special and interesting things that should be investigated.

[Gamasutra Editor's Note: For more about weenies, check out "Environmental Storytelling:
Creating Immersive 3D Worlds Using Lessons Learned from the Theme Park Industry" and "Environmental Storytelling, Part II: Bringing Theme Park Environment Design Techniques to the Virtual World".]

Closed Environments

The best games take place within a limited constrained space. In Myst, you're stuck on a series of islands. In The Seventh Guest, you're trapped in a mansion. In Clue, you're limited to the locations of the house. In chess, checkers, go, and Monopoly - in fact, in every board game - you are limited to the board. In Dungeons and Dragons, where you sometimes create your own environments, the Dungeon Master sets the limits.

One of the biggest problems in most flight simulators is the sense that you can fly anywhere. The trouble is, in most of "anywhere," there's nothing to look at. If you are creating a virtual environment, you should be sure that anywhere you can go is interesting and that the places you shouldn't go are off limits.

It's also best to disguise the edges of your virtual world. Your viewer shouldn't simply run out of data while cruising your environment; he or she should come to the end of it and want to turn around and go back. At the least, put a fence around the legal area for cruising. Or a force field. Or anything. But don't let your poor viewer walk out into the void. It's not polite.

Constant Positive Feedback with Sporadic Negative Feedback

If you want to exercise editorial control over the way viewers explore your VR environment, you'll want to use weenies to attract them to specific places. Once they arrive, you'll always want to reward them with a treat of some kind. It can be something as simple as a sound bite ("Great!"), or a quick, fun animation, or increasing the score counter, or anything that's special and easily associated with success (perhaps a flashing blue light). For this to work properly, you must always reward progress toward the goal you desire your visitor to achieve.

Now, from time to time, you'll want to dissuade your visitor from heading in a specific direction. You might decide to always display a discouraging sign or play a sound like a game show buzzer when someone goes the wrong way. Unfortunately, it's far easier to identify the good things you want someone to focus on than to enumerate every bad or irrelevant thing to avoid. So, it's best to provide sporadic, almost random negative feedback. The idea behind this is that your visitors will become slightly paranoid about straying off the beaten path. Combined with positive feedback, your visitors will learn to always search for those positive vibes that encourage them to go where you want. They'll be a little paranoid if they don't get some positive feedback soon, and they'll start looking for it because it's the only reliable way to avoid negative feedback.

This technique is really helpful when you're creating your own world for someone to explore because, in spite of all the technology, it's simply impossible to delineate every possible path or option. Since your site, if it's on a network, will likely be constantly under construction, you'll never have time to make sure every possible location and approach from every possible angle is complete and bug-free. So, you want your visitors to explore the places that are known to be safe and avoid the places where you might not have completed the job. To get them really paranoid, if they stray way off the beaten track, just terminate their connection from time to time. That'll get them to behave.

If you provide constant negative feedback that is reliably produced, then you'll find a lot of people will spend a lot of time exploring the edges of your universe, looking for this negative feedback. So, keep it sporadic so that they never know if it's coming or not.

Complexity Management and Slow Bullets

In well-designed, seemingly fast arcade games, where player reaction time is very important, the action is carefully orchestrated and, in fact, not really happening as fast as it seems.

One huge and common error in game design is to create a game where the moment you see something appear on the screen you have to react and shoot it. This is OK once in a while but overall provides for boring game play.

At first glance, you might think that all games are made this way: You see it, you shoot it. But, in fact, going all the way back to Space Invaders, the objects actually tend to move quite slowly; the difficulty comes from the number of objects marching toward you. If you look at the bombs that get dropped by the aliens at the top of the screen, you'll see they travel quite slowly. If those bombs were the only thing you had to deal with, the game would be pretty simple. But, in the context of all the other action, even one more slow-moving bullet can be overwhelming.

The majority of VR Web sites for the next few years will be fairly static environments where you mostly just wander around. But, as the ability of computers to download and manipulate individual objects increases, the amount of activity within sites, including seeing other visitors, will increase. It's at this point in time where careful attention to the complexity of the scene will become important.

You might think that a site where there are a lot of slow-moving objects (people) milling about talking to one another can't get too complicated. Not so. Just imagine the last overcrowded party you went to. Notice that most chat rooms available on the online services carefully limit the number of visitors per chat room.

Many computer and video games limit the number of active objects on the screen for technical reasons, but as these technical limitations are removed by fast hardware, it will be smart to limit the number of objects on the screen for psychological reasons. If you put too many active objects on the screen at once, no matter how slow and innocent they seem, you can quickly overwhelm your viewer.

Lack of Depth Perception (Even with Stereographic Glasses)

Stereo glasses seem like the next great thing. Stereo glasses that connect to your PC are now available for less than $100, making them a mass consumer item. But here's the problem: People only use their binocular capability for close-in work (say, up to 15 feet or less). After that, they depend on other visual cues, like atmospheric haze, to compute the distance to something.

Perhaps the most important visual clue is differential scrolling of the environment, used most notably and effectively in animated backgrounds (formerly created with multiple-plane camera animation stands). For instance, where I live in Washington state, there are forests on top of rolling hills. If I stand still, I really can't tell how far away one tree or another is, but if I am walking and bobbing up and down slightly, then I quickly get a sense of the distance to different trees.

In the game Doom, the player character bobs up and down while walking, and this does magnificent things in terms of providing a sense of depth. It's too bad there isn't an option to turn it off so that you could compare the effect both with and without.

A company called Vision III in Virginia has developed a 3D effect that doesn't require any special glasses. In their technique, the lens rotates around the axis of view at about 4.5 to 5 cycles per second. The amount of motion is small enough that you don't notice it directly, but the increased information transmitted to your brain from the subtle differential scrolling that occurs gives everything you see much more depth. The effect is subtle, and some people are more attuned to it than others. But it's a more sophisticated version of the bobbing up and down in Doom.

Management of Player Viewpoint

When you develop your 3D environment, you will be faced with a problem that moviemakers never have to face, namely, that your visitor might be able to see the backside of your sets. In the movies, the camera location is strictly controlled, so it's easy to paint only the front side of your sets. At Disneyland, where you can roam at will, everything needs to be painted, including parts of the backstage area that you might come across accidentally from time to time. The same will be true of your VR environment.

If you adopt a third-person presentation, you might consider locking down the camera, but visitors will quickly want to move it. Still, by constructing your "sets" so that it only makes sense to place the camera in friendly places and adding a small restriction (say, the camera can only be placed on the ground), you can avoid a lot of extra work dressing up the back sides of your buildings and walls.

In one VR viewer currently available on the Net, there is a Walk mode and a Fly mode for moving about in the environment. Some environment builders may want to disable flying in order to constrain the range of movement in their environment to something reasonable. A typical techweenie approach is to respond, "But this is VR! You should be able to do anything!" Not true. It's also wrong from a show business standpoint. You don't want a visitor to your VR site to do "just anything" anymore than Disneyland wants you poking around backstage.

Navigation and Targeting Support

Navigating in a 3D environment is tricky, from either a first-person or a third-person POV. In Doom, it's pretty easy because there are actually several constraints on what you can do-the designers know that you're spending most of your time in buildings and that you're not going to turn things upside down. In many VR viewers, there are not any restrictions, and you can turn yourself upside down very quickly.

Even if you can't turn yourself upside down, how do you specify "I want to go there"? If you point at an object and say, "Go there," should it take you there and leave you facing the thing? Most of the time you'll be staring at a wall. Should you have to walk everywhere as in Doom? That could be quite tedious if you're not busy blowing people away.

One approach I've been using is a targeting system for navigating. You point at an object, and your player character points at it. Then, as long as you only move forward or backward, slide right or left, or fly up or down, your player character stays pointed at this object. If you turn left or right, then the targeting lock is lost. This has the benefit of eliminating some of the degrees of freedom available, making it easier to move through the environment, without permanently restricting your movement. You can still see the sights as you cruise, but you're not constantly worried about getting lost because your player character is locked on the goal. If you come across something interesting on your way to your goal, you can break the target lock and look around.

If this targeting approach is part of your navigation system, then you can provide "way-points" for visitors. Just put up signs at interesting places; if your visitors click on the sign, that becomes their destination and they can quickly navigate there.

Summary

The best research investment you can make for virtual environment interface design is to buy a game machine and to sit down and play it for several hours a week. In discussing look-and-feel, it's always easier to discuss look because we have terminology (developed over many centuries). But for now, while interactive design is emerging from the garage into the mainstream of culture, it is still best to "feel" the interface directly, and the best way to do that is to play games.

Stephen Clarke-Willson [email] received his Ph.D. in Information and Computer Science from the University of California, Irvine, in 1986. As a research scientist at the Northrop Corporation, he developed computer graphics algorithms for the biggest (certainly the most expensive) video game ever created, the B-2 Stealth bomber. He was chief architect of the Patran 3 MCAE system from PDA Engineering. From 1990 until 1994, he was vice president of worldwide product development for Virgin Interactive Entertainment, where he supervised the development of all computer and video games released by the company. Today he is the owner and creative director of Above the Garage Productions [visit site], where he is developing a series of 3D games.


This article was originally published in Digital Illusion: Entertaining the Future with High Technology. Copyright 1998 by the ACM Press, a division of the Association for Computing Machinery, Inc. (ACM).