Big Bad Streets - Game Invaders: The Theory and Understanding of Computer Games - page 114

sometimes two for each attractor. In fact, it captures just about every important situ-
ation you are likely to encounter.
Let's now look at the larger perceptual structures we can identify from the Table
of Surprises. First of all, choice points; there are major choice points that arise at
junctions which are complex attractors offering us the possibility to continue our
current direction of travel or change it. There is far more to junctions than this as
entries A2 and A3 make clear. Changing direction is a matter of intention but the
complexities of moving traffi c complicate the matter, and we have a number of
choices as how to negotiate traffi c crossing or about crossing the junction in a
number of directions. Junctions therefore present choice points of two distinct types:
a choice between intentions and a choice as to how to achieve the chosen intention.
Choice points also arise when moving through traffi c between junctions. We are
constantly asked to choose between which side to pass traffi c on, which side of the
road to drive on, to drive on the road or sidewalk, and so on.
Another major choice point arises with A8 and A9 when we encounter a police
road block and we are not already being tailed. In this situation we have the choice
of fi nding a way through the road block—there is usually a way—or making a 180°
handbrake turn and fi nding another way to achieve the main intention of the level.
Notice that A10, where the road block is visible but we are also being tailed, invali-
dates the choice point as in the act of making the handbrake turn we will most likely
be rammed and thus embroiled in a whole mini-mission we could have avoided.
Routes in Driver are comprised of a series of major junctions and landmarks;
open spaces, for instance. We construct routes as we learn how to get to the destina-
tion that will mark the completion of the mission or a section of the mission. Routes
might not necessarily be the shortest route between the start and fi nish points but
might be chosen because they avoid diffi cult places to drive or known concentrations
of police.
Challenge points in Driver usually relate to sections of the city that are diffi cult
to negotiate because they are narrow and crowded. They are particularly challenging
when a turn, for instance, is required and police are present. The narrow causeway
road to the port in Miami is a good example. A15 also introduces a different form
of challenge point, as we have no alternative but to lose the police tail. A4 and A6
might also be considered in the same light.
There are a number of generic retainers (mini-missions) in Driver but mostly
these are dynamic in that they can occur anywhere in the city. The fi rst involves being
noticed as a felon by a patrolling police car which then gives chase; the challenge
point discussed in the previous paragraph which, in turn, gives rise to a retainer to
resolve it. This leads fi rst of all to a chase retainer in which we, the felon, attempt to
lose the police car by either swerving in and out of traffi c and other solid obstructions
in order to make it crash or by making a series of turns at junctions and losing it in
that way. This retainer also often occurs at the end of a level if we approach the alien
attractor with police already on our tail. A minor form of this also occurs when we
arrive at the end of mission sign too early and have to drive around to waste time.
If we do not lose the police car we will almost certainly end up being rammed
and forced into a crash retainer where we must try to fi nd a way out with as little