FUNDAMENTALS OF GAME DESIGN, SECOND EDITION

The Gaussian Curve

When you add dice together like this, the probability of each possible result forms a bell-shaped, or Gaussian, curve, a phenomenon familiar to mathematicians. Figure 10.6 shows a graph of all the possible results when rolling three six-sided dice and adding the resulting numbers.

It's important that you realize what this means for your game. If you use this addi­tive dice mechanism and you specify that a player must roll an 18 to succeed at a task, he has only one chance in 216 of actually rolling it. That's less than one-half of 1 percent. In other words, it will almost never happen. This system is not the same as rolling one die with 16 faces numbered from 3 to 18. With one such die, the chance of rolling an 18 is identical to the chance of rolling any other face, one in 16, or 6.25 percent. That's far more than one chance in 216.

These curves describe many phenomena in the universe, from the pattern of water droplets falling from a central point to the intelligence levels of animals (and humans). To put it succinctly, most things lie somewhere in the middle of the curve; rare things lie in the extremes. When that's the sort of effect you want in your game design, use a Gaussian distribution.

Summary

Now you have a clear understanding of what core mechanics are and what they do in games. Mechanics consist of algorithms and data that govern the way the game is played, and you have learned how to document them in the form of resources, simple and compound entities, and mechanics composed of events, processes, and conditions. We also examined the idea of an internal economy—a system whereby resources flow from place to place or from owner to owner, all governed by mechanics.

Be sure that you read Chapter 11 before you start designing your core mechanics.

Design Practice exercises

1. Devise and document the core mechanics for a traditional analog alarm clock. The alarm clock possesses the following indicators: an hour hand, a minute hand, a hand indicating the time at which the alarm should go off, and a buzzer. It also has the following input devices: a knob to set the time, a knob to set the time at which the alarm will go off, and a two-state switch that arms the alarm when the switch is in one position and cancels it in the other. (Assume that it is an electric clock and does not need to be wound.) Explain what entities are needed inside the clock, what processes operate within it, and what conditions and mechanics govern the functioning of the alarm. (Explain the movement of the hands in terms of the pas­sage of time not the workings of the clock.)

2. Research the history and rules of Tetris, then perform the following exercises:

a. Devise an entity that contains enough attributes to describe the tetromino (a Tetris block) that is currently under the player's control. Name each attribute in the entity; state whether it is symbolic or numeric; and if symbolic, list its possi­ble values. Your entity should include one cosmetic attribute.

b. Document the effect of each of the player actions allowed in Tetris on the attributes of the currently falling tetromino. Bear in mind that some actions have different effects depending on which tetromino is currently falling. Where this is the case, be sure to document the effects of the action on each different type of tetromino.

c. Document one of the scoring systems for Tetris (there are several; you may choose one), indicating what condition of the play field causes the score numeric entity to change and by how much. Your mechanic for changing the score should include as a factor the current game level (another numeric entity). Also document what makes the current game-level entity change.

3. Using a real-time strategy game or construction and management simulation of your choice (or one that your instructor assigns), write a short paper describing its resources, sources, drains, converters, production mechanisms that are not sources (if any), and traders (if any). Note whether the game has any feedback loops or mutual dependencies; if so, indicate whether any mechanism exists to break a pos­sible deadlock.

4. Define a mechanic for a trap that harms a character when it detects the charac­ter's presence and then must wait for a period before it can detect another character. Document the condition that triggers the trap (the nature of the sensing mechanism), the character attribute(s) that change when the trap is triggered, and the length of the reset wait period. Incorporate one or more nonuniform random numbers to determine the amount of damage done and explain how they are com­puted. Indicate what states the trap may be in and what causes it to change from state to state. Include a vulnerability in the sensing mechanism that could either (a) set off the trap without harming a character or (b) allow a character to move within range of the trap's sensor mechanism without setting it off. (For example, a pressure-sensor in the floor would not go off if the character weighed less than a certain amount.) Propose a means by which a clever player could exploit this vul­nerability to avoid the trap.