13 Introduction to Gameplay Systems

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p until now, everything we’ve talked about in this book has focused on
technology. We’ve learned that a game engine is a complex, layered soft -
ware system built on top of the hardware, drivers, and operating system of the
target machine. We’ve seen how low-level engine systems provide services
that are required by the rest of the engine; how human interface devices such
as joypads, keyboards, mice, and other devices can allow a human player to
provide inputs to the engine; how the rendering engine produces 3D images
on-screen; how the collision system detects and resolves interpenetrations be-
tween shapes; how the physics simulation causes objects to move in physi-
cally realistic ways; how the animation system allows characters and objects
to move naturally. But despite the wide range of powerful features provided
by these components, if we were to put them all together, we still wouldn’t
have a game!
A game is defi ned not by its technology but by its gameplay. Gameplay can
be defi ned as the overall experience of playing a game. The term game mechan-
ics pins down this idea a bit more concretely—it is usually defi ned as the set
of rules that govern the interactions between the various entities in the game.
It also defi nes the objectives of the player(s), criteria for success and failure,
the player character’s abilities, the number and types of non-player entities that
exist within the game’s virtual world, and the overall fl ow of the gaming expe-
rience as a whole. In many games, these elements are intertwined with a com-

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