Ultimate Game Design : Building game worlds

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SCRIPTING
in games gives developers a pathway right
into the control of many critical aspects of
gameplay functionality, some of which are small and barely perceptible, while others
are rather large and looming. At this point in the book, you’re becoming familiar with
the process of building up a polygonal game environment (for example, by using geometric
primitives like planes, spheres, cones, and cylinders, and by “adding and sub
tracting” or merging these primitives together to form entirely new shapes) by introducing
characters, props, and items. Now we’re going to turn our attention to learning something
about how to control each of these scripts for the purposes of building up gameplay.
Many kinds of behaviors can be controlled by a script system. Script systems in total
are largely proprietary and currently vary greatly in approach among game developers.
Many game engines provide scripting languages that let you program complex behaviors
into your game. For instance, a monster might travel from the barn to the
farmhouse to the silo and back over and over again, but walk toward the player if it
sees him, run toward the player if the player is bleeding, and run away from the
player and toward the silo if the player has a weapon. As today’s games go, this is a
moderately complex behavior, and it would be tedious to encode this behavior directly
in C++. Scripting languages make it possible to “script” these actions so that you can
focus on the behavior rather than the programming.
Here’s a quick example of this behavior scenario:
behavior monster;
if (monster->idle) {
monster->walk(barn);
monster->walk(farmhouse);
monster->walk(silo);
}elsif (monster->sees(player)) {
if (player->bleeding) {
monster->run(player);
} elsif (player->has_weapon) {
monster->run(silo);
} else { monster->walk(player) }
}