This month's column is another excerpt from Andrew Rollings' and my long-awaited book on game design, Andrew Rollings and Ernest Adams on Game Design (due out from New Riders Publishing this May).
Game settings are almost always implemented as some sort of physical space. The player moves his avatar in and around this space, or moves other pieces, characters, or units in it. The physical characteristics of this space determine a great deal about the gameplay.
Even text adventures include a physical dimension. The player moves from one abstract "room" or other discrete location to another. Back when more people played text adventures, the boxes used to carry proud boasts about the number of rooms in the game. Gamers could take this as a very rough measure of the size of the world they could explore in the game and, therefore, the amount of gameplay that thegame offered.
The physical dimension of a game is itself characterized by several different elements: dimensionality, scale, and boundaries.
One of the first questions you have to ask yourself is how many dimensions your physical space is going to have. A few years ago, the vast majority of games had only two dimensions. This was especially noticeable in side-scrolling games such as Super Mario Brothers. Mario could run left and right and jump up and down, but he could not move toward the player ("out" of the screen) or away from him ("into" the screen).
It is essential to understand that the dimensionality of the game's physical space is not the same as how the game will display that space or how it will implement the space in software. Ultimately, all spaces must be displayed on the two-dimensional surface of the monitor screen, but that's a problem for a programmer, not a designer. How to implement and display the space are separate but related questions. The former has to do with technical design, and the latter has to do with user interface design.
Nowadays, a great many computer game settings have a three-dimensional space, even though the game might implement it in various ways. Starcraft, a war game, shows you plateaus and lowlands, as well as aircraft that pass over obstacles and ground units. Starcraft's setting is clearly three-dimensional, but the space is actually implemented in a series of two-dimensional planes or layers, one above another. Objects can be placed and moved within a plane with a fine degree of precision, but vertically, an object must be in one plane; there is no "in between." Flying objects can't move up and down in the air; they're always at the same altitude -- in the "air layer."
Lemmings (top) was a hit, but Lemmings 3D (bottom) didn't translate into the same fun experience.
When first thinking about the dimensionality of your game space, it's tempting to immediately assume that you want it to be three-dimensional because that offers the greatest flexibility or seems more real. But as with everything else, the dimensionality of your physical space must serve the entertainment value of the game. Make sure all the dimensions will contribute meaningfully. Lemmings was a hit 2D game, but Lemmings 3D was nowhere near as successful because it was much more difficult to play. The addition of a third dimension detracted from the player's enjoyment rather than adding to it.
It's possible to have more than three spatial dimensions, but, in general, we don't recommend it. A computer can display a distorted approximation of four-dimensional space in the two dimensions of the monitor screen, just as it can display an approximation of three-dimensional space in two dimensions. However, because humans are not used to dealing with 4D spaces, most of us have a hard time navigating through them. If you want to include a fourth dimension for some reason, you might consider doing it as an "alternate plane of reality" rather than an actual four-dimensional space. In other words, you have two three-dimensional spaces that look similar, but there is something different about them. For example, the game Legacy of Kain: Soul Reaver contained two three-dimensional spaces, the spectral realm and the material realm. The landscape was the same in each, but the spectral realm was lit by a blue light while the material realm was lit by white light; the actions available to the player were different in the spectral real from the material realm. Although they were both implemented in software by the same 3D models, they were functionally different places governed by different laws. In the movie version of The Lord of the Rings, the world that Frodo inhabits while he is wearing the Ring can be thought of as an alternate plane of reality as well, overlapping the real world but appearing and behaving differently.
By scale, we mean both the total size of the physical space represented and the relative sizes of objects in the game. If a game is purely abstract and doesn't correspond to anything in the real world, the sizes of objects in its game world don't really matter. You can adjust them to suit the game's needs any way you like. But if you are designing a game that is at least somewhat representational of the real world, you'll have to address the question of how big everything should be to both look real and play well. Some distortion is often necessary for the sake of gameplay; the trick is to do it without harming the player's suspension of disbelief too much.
With a sports game, a driving game, a flight simulator, or any other kind of game in which the player will expect a high degree of verisimilitude, you have little choice but to scale things to their actual sizes. In old sports games, it was not uncommon for the athletes to be depicted as twelve feet tall to make them more visible, but nowadays players wouldn't tolerate a game taking such liberties with reality. Serious simulations need an accurate representation of the physical world.
Similarly, you should scale most of the objects in first-person games accurately. Fortunately, almost all first-person games are set indoors or within very limited areas that are seldom larger than a few hundred feet in any dimension, so this doesn't create implementation problems. Because the player's perspective is that of a person walking through the space, objects need to look right for their surrounding area. You might want to slightly exaggerate the size of critical objects such as keys, weapons, or ammunition to make them more visible, but most things, such as doors and furniture, should be scaled normally. As screen resolutions continue to improve, we'll no longer need to exaggerate objects for visual clarity, unless we want to do so for a comic or cartoonlike effect.
If you're designing a game with an aerial or isometric perspective, you might need to fudge the scale of things somewhat. The real world is so much larger and more detailed than a game world that it's impossible to represent objects in their true scale in such a perspective. For example, in modern mechanized warfare, ground battles can easily take place over a 20-mile front, with weapons that can fire that far or farther. If you were to map an area this size onto a computer screen, an individual soldier or even a tank would be smaller than a single pixel, completely invisible. Although the player will normally be zoomed in on one small area of the whole map, the scale of objects will have to be somewhat exaggerated so that they're clearly identifiable on the screen.
One of the most common distortions games make is in the relative heights of people and the buildings or hills in their environment. The buildings are often only a little taller than the people who walk past them. To be able to see the roofs of all the buildings or the tops of all the hills, the camera must be positioned above the highest point on the ground; but if the camera is too high, the people would hardly be visible at all. To solve this problem, the game simply does not include tall buildings or hills and exaggerates the height of the people. Because the vertical dimension is seldom critical to the gameplay in things such as war games and role-playing games, it doesn't matter if it's not accurate, as long as it's not so inaccurate that it interferes with suspension of disbelief.
Designers often make another scale distortion between indoor and outdoor locations. When a character is walking through a town, simply going from one place to another, the player will want the character to get there reasonably quickly. The scale of the town should be small enough that the character takes only a few minutes to get from one end to another, unless the point of the game play is to explore a richly detailed urban environment When the character steps inside a building, however, and needs to negotiate doors and furniture, you should expand the scale to show these additional details. If you use the same animation for a character walking indoors and outdoors, this will give the impression that the character walks much faster outdoors than indoors. However, this seldom bothers players-they'd much rather have the game proceed quickly than have their avatar take hours to get anywhere, even if that would be more accurate.
This brings up one final distortion, which is also affected by the game's notion of time, and that is the relative speeds of moving objects. In the real world, a supersonic jet fighter can fly more than a hundred times faster than an infantry soldier can walk on the ground. If you're designing a game that includes both infantry soldiers and jet fighters, you're going to have a problem. If the scale of the battlefield is suitable for jets, it will take infantry weeks to walk across; if it's suitable for infantry, a jet could pass over it in the blink of an eye. One solution to this is to do what the real military does and implement transport vehicles for ground troops. Another is simply to fudge it and pretend that jets fly only four or five times as fast as people walk. As long as the jet is the fastest thing in the game, it doesn't really matter how much faster it is; the "strike and retreat" tactic that jets are good at will still work. Setting these values is all part of balancing the game.
In board games, the edge of the board constitutes the edge of the game world. Because computers have a finite size, the physical dimension of a computer game world must have a finite size also. However, computer games are usually more immersive than board games, and they often try to disguise or explain away the fact that the world is limited, to maintain the player's suspension of disbelief.
In some cases, the boundaries of a game world arise naturally, and we don't have to disguise or explain them. Sports games take place only in a stadium or an arena, and no one expects or wants them to include the larger world. In most driving games, the car is restricted to a track or a road, and this, too, is reasonable enough.
Setting a game underground or indoors helps to create natural boundaries for the game world. Everyone expects indoor regions to be of a limited size, with walls defining the edges. The problem occurs when games move outdoors, where people expect large, open spaces without sharply defined edges. A common solution in this case is to set the game on an island surrounded by water or by some other kind of impassable terrain: mountains, swamps, or deserts. These establish both a credible and a visually distinctive "edge of the world."
In Populous: The Beginning, the game world was a globe, solving the problem of player boundaries.
In flight simulators, the boundaries of the world are even more problematic. Most flight simulators restrict the player to a particular area of the real world. Because there are no walls in the air, there's nothing to stop the plane from flying up to the edge of the game world, and the player can clearly see when he has arrived there that there's nothing beyond. In some games, the plane just stops there, hovering in midair, and won't go any farther. In Battlefield 1942, the game tells the player that he has left the scene of the action and forcibly returns him to the runway.
A common solution to the edge-of-the-world problem is to allow the flat world to "wrap" at the top, bottom, and sides. Although the world is implemented as a rectangular space in the software, objects that cross one edge appear at the opposite edge-they wrap around the world. If the object remains centered on the screen and the world appears to move beneath it, you can create the impression that the world is spherical. This was used to excellent effect in Bullfrog Productions' game Magic Carpet. In another Bullfrog game, Populous: The Beginning, the world was actually displayed graphically as a sphere on the screen, not just a wrapping rectangle.
Questions to Ask Yourself About the Physical Dimension