FUNDAMENTALS OF GAME DESIGN, SECOND EDITION
The Dimensions of a Game World
Many different properties define a game's world. Some, such as the size of the world, are quantitative and can be given numerical values. Others, such as the world's mood, are qualitative and can only be described with words. Certain
properties are related to one another, and these groups of related properties are the dimensions of the game world. To fully define your world and its setting, you need to consider each of these dimensions and answer certain questions about them.
Video game worlds are almost always implemented as some sort of simulated physical space. The player moves his avatar in and around this space or manipulates other pieces or characters in it. The physical properties of this space determine a great deal about the gameplay.
Even text adventures include a physical dimension. The player moves from one abstract location, usually called a room even if it's described as outdoors, to another. Back when more people played text adventures, the boxes the games came in 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 the game offered.
The physical dimension of a game is itself characterized by several different properties: spatial dimensionality, scale, and boundaries.
One of the first questions to ask yourself is how many spatial dimensions your physical space will have. It is essential to understand that the dimensionality of the game's physical space is not the same as how the game displays that space (the camera model) or how it implements the space in the software. How to implement the space and how to display it are separate but related questions. The former has to do with technical design, and the latter has to do with user interface design. Ultimately, all spaces must be displayed on the two-dimensional surface of the monitor screen.
These are the typical dimensionalities found in video games:
■ 2D. A few years ago, the vast majority of games had only two dimensions. This was especially noticeable in 2D side-scrolling games such as Super Mario Bros. (see Figure 4.1). 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). Two-dimensional worlds have one huge advantage when you're thinking about how to display them: The two dimensions of the world directly correspond to the two dimensions of the monitor screen, so you don't have to worry about conveying a sense of depth to the player. On the other hand, a number of games with 2D game worlds still use 3D hardware accelerators for display so that objects appear three-dimensional even though the gameplay does not use the third dimension. Two-dimensional worlds may seem rather old-fashioned nowadays, but there are still many uses for them in casual browser-based games and smaller devices such as low-end mobile phones.
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■ 2.5D, typically pronounced "two-and-a-half D." This refers to game worlds that appear to be a three-dimensional space but in reality consist of a series of 2D layers, one above the other. StarCraft, a war game, shows plateaus and lowlands, as well as aircraft that pass over obstacles and ground units. The player can place objects and move them horizontally within a layer with a fine degree of precision, but vertically an object must be in one plane or another; there is no in-between. Flying objects can't move up and down in the air; they're simply in the air layer as Figure 4.2 depicts.
■ 3D. Three true dimensions. Thanks to 3D hardware accelerators and modeling tools, 3D spaces are now easy to implement on hardware that supports them. They give the player a much greater sense of being inside a space (building, cave, spacecraft, or whatever) than 2D spaces ever can. With a 2D world, the player feels as if he is looking at it; with a 3D world, he feels as if he is in it. 3D worlds are great for avatar-based games with exploration challenges, such as the Prince of Persia series (see Figure 4.3). Most large games for personal computers and consoles now use three dimensions, but many small casual games still need only two.
■ 4D. If you want to include a fourth dimension for some reason (not counting time), implement it as an alternate version of the 3D game world rather than an actual four-dimensional space. In other words, create two (or more) threedimensional spaces that look similar but offer different experiences as the avatar moves among them. For example, the Legacy of Kain series presents two versions of the same 3D world, the spectral realm and the material realm, with different gameplay modes for each. The landscape is the same in both, but the material realm is lit by white light while the spectral realm is lit by blue light, and the architecture is distorted in the spiritual realm (see Figure 4.4). The actions available to the player are different in each realm. The realms look similar but are 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.
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When you first think about the dimensionality of your game space, don't immediately assume that you want it to be three-dimensional because 3D seems more real or makes the best use of your machine's hardware. As with everything else you design, the dimensionality of your physical space must serve the entertainment value of the game. Make sure all the dimensions will contribute meaningfully. Many games that work extremely well in two dimensions don't work well in three. 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 added to it.
Scale refers to both the absolute size of the physical space represented, as measured in units meaningful in the game world (meters, miles, or light-years, for instance) 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 represents (if only partially) 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, especially in war games; the trick is to distort the scale without harming the player's suspension of disbelief too much.
In a sports game, a driving game, a flight simulator, or any other kind of game in which the player expects a high degree of verisimilitude, you have little choice but to scale things to their actual sizes. In old 2D sports games, it was not uncommon for the athletes to be depicted as 12 feet tall to make them more visible, but nowadays players don't tolerate a game taking such liberties with reality. Serious simulations need to represent the physical world accurately.
Similarly, you should scale most of the objects in first-person games accurately. Fortunately, almost all first-person games are set indoors or within limited areas, 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.
If you're designing a game with an aerial or isometric perspective, you might need to distort 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 display 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 the objects are clearly identifiable on the screen.
Games frequently distort 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. (See Figure 4.5 for an example.) 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 in the world. But if the camera is positioned too high, the people are hardly 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 products such as war games and role-playing games, it doesn't matter if heights are not accurate, as long as they're not so inaccurate as to interfere with suspension of disbelief.
Designers often make another scale distortion between indoor and outdoor locations. When a character walks through a town, simply going from one place to another, the player wants 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 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 (see the section "The Temporal Dimension" later in this chapter), 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
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pass over it in the blink of an eye. One solution is to do what the real military does and implement transport vehicles for ground troops. Another is simply to accept a certain amount of distortion and create jets that fly only four or five times as fast as people walk (StarCraft uses this trick). 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, as Chapter 9, "Gameplay," discusses in more detail.
Long Swordsman
Attack
Armor
Range
In board games, the edge of the board is the edge of the game world. Because computers don't have infinite memories, the physical dimension of a computer game world must have an "edge" as well. 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 help maintain the player's immersion.
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 players 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 flight simulators, setting the boundaries of the world creates even more problems. 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; when the player arrives there he can clearly see 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.
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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 is used to excellent effect in Bullfrog Productions' game Magic Carpet. Maxis's Spore actually displays the world as a sphere on the screen, not just a wrapping rectangle (see Figure 4.6).
Finally, you can solve the problem of boundaries by requiring the player to move among defined locations. For example, you might let a player fly from planet to planet in the solar system by clicking on the planet she wants to go to. The player cannot go beyond the boundary of the solar system because there are no planets in interstellar space. The user interface for movement creates a natural limit that requires no further explanation.
