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Engine Tuning
Arriving at sets of game rules that produce successfully emergent behavior involves a difficult and often time-consuming design process. It can only be completed through the kind of iterative design outlined in chapter 2. The rules for The Game of Life seem simple and elegant, but it took John Conway two years of testing and refinement to arrive at their final form. In the example from Populous:The Beginning, emergent behaviors were the result of what game designer Marc LeBlanc calls game tuning: iterative tweaking, testing, and refinement of game rules in order to create a rich play experience. Game tuning was also used in the design process for the PC game Gearheads. In that game, one or two players send wind-up toys across a playfield, trying to get as many toys as possible across to the other end of the screen. The longer a player waits to release a toy, the more energy it has and the further it will travel. Once a toy is released, a player has no control over it, so either player can use it to score. Some of the toys are slow, heavy, pushing toys like Big Al the wind-up bulldozer, or quick and light toys like Ziggy the mechanical cockroach. Some toys destroy other toys, like the Walking Time Bomb; still others can change their direction of movement, like Deadhead, a chattering skull that scares toys and reverses the direction they are facing. Each of the game's twelve toys has special abilities, and the interactions between the toys as they move across the playfield is a key aspect of the game's design. Very early in the design process, a playable prototype was created that allowed the designers to create new kinds of toys and tune their attributes. Inside the game application were pull-down menus with grids of statistics for each toy. As the attributes of each type of toy were altered, the changes immediately took effect in the game, so that even in the middle of a game the designers could easily make adjustments and see how the changes affected the overall game play. The iterative playtesting that took place throughout the 18-month development process helped create a balanced game.
During development, the designers discovered emergent combinations of toys. They found that although toys could be used as individual game units, the real richness of Gearheads arose from using toys in concert with each other. Often the toy combinations they discovered were highly surprising. Designers Frank Lantz and Eric Zimmerman coined the term engine to describe these toy combinations: like a mechanical engine, toy combinations were a set of interlocking parts that worked together to achieve a larger effect. We list a few examples of the many engines discovered in the system below: Punching Roaches. Although Ziggy the wind-up cockroach is the fastest toy in the game, his movement is erratic; when he bumps into another toy, he flips onto his back (a second encounter with a toy will flip him onto his feet again). Another toy, Kanga, is a punching kangaroo character that punches forward any toy it encounters. One simple engine is to release many Ziggys quickly onto the board, most of which end up on their backs. One or two Kanga toys released afterwards punch the light Ziggys, shooting them across the opposite side of the screen to score points. Bomb Shield. Two of the more destructive toys in the game are Disasteroid and the Walking Time Bomb. Disasteroid, a very slow-moving giant robot, shoots its forward-facing lasers at any toy it encounters, eliminating it. The Walking Time Bomb is a strong and medium-fast toy, but when it runs out of energy it explodes, eliminating all nearby toys—except for Disasteroid, which is the only one that the bomb can't destroy. One engine that uses these toys in combination is to release a Disasteroid, followed immediately behind by a Walking Time Bomb. Pushing from behind, the bomb speeds up the normally slow Disasteroid, which laser-blasts any toys that stand in its way, clearing a path for both toys to score. Even if the Walking Time Bomb explodes before the pair can reach the far side of the screen, Disasteroid still survives the blast and can possibly score on its own. Perpetual Motion. A more complex engine makes use of the toys Handy and Crush Kringle. Crush Kringle is a professional wrestling Santa Claus toy that moves steadily across the playfield, periodically pausing to stomp the ground. When he stomps, all nearby toys switch directions from left to right. Handy is a walking white glove, and its special ability is that when it encounters a toy on the play-field, it winds it back up, replenishing its energy. Although Crush Kringle is a powerful toy, it is very slow, which means that the player has to spend a long time winding it. However, a game engine provides a shortcut around this limitation. First, players release a very lightly wound Crush Kringle, followed by a Handy, followed by another lightly wound Crush Kringle, all on the same row of the playfield. The faster Handy bumps into the first Crush Kringle, replenishing its energy. The Crush Kringle then stomps, reversing the direction of the Handy, which runs backwards into the second Crush Kringle, which it then winds up as well. The second Crush Kringle toy eventually stomps, sending the Handy back to the first toy. In this way, the trio of toys make their way across the playfield, the Handy toy running back and forth between the two Crush Kringles. The toy-combination engines were not something designed directly into the rules of Gearheads. They were emergent patterns of play that arose out of the more simple set of attributes that defined each individual toy. In some cases, the toy attributes were refined in order to make a particular engine possible—but most of the time, engines were discovered as the game was played and developed.
As with the example from Populous: The Beginning, emergence in Gearheads manifests on many levels at once. The unexpected local interactions between toys creates larger patterns on the playfield. The player's own decision-making process is also a pattern that emerges as a result of the toy combinations, as players adjust their behavior to take advantage of emergent combinations. Players are encouraged to think in terms of emergence by selecting a limited number of toys before a match starts: experienced players include an engine or two in the four or five toy types they pick for a game. Another way that these engines entered into game development was the AI programming. In designing the computer opponent, engine-based heuristics were included, so that the program was aware of advantageous toy combinations and often used engines against the player. Some Gearheads players learn about certain engines simply by observing the behavior of the AI.
