User Interfaces - Fundamentals of Game Design - page 246

or backward movement, and a slider control or keys cause the helicopter to ascend
or descend. Left on the joystick causes the helicopter to turn counterclockwise
about its vertical axis but not to actually go in that direction unless it is also mov-
ing forward. Right causes the equivalent rotation to the right. Forward propels the
helicopter forward, and back the reverse. When the joystick returns to center, the
helicopter should gradually slow down through air friction until it remains hover-
ing above a fixed point in the landscape. A separate key set or slider controls
vertical movement.

NOTE Real helicop-
ters can also slide
sideways while facing
forward; to implement
this would require
extra controls, which
few games do.

SPACECRAFT
Most designers treat spacecraft as they would fixed-wing aircraft, although in one
variant left or right on the joystick causes the vehicle to yaw (the equivalent of pan-
ning a camera), turning about its vertical axis to face in a different direction, rather
than rolling.

Point-and-Click Navigation
Aerial or context-sensitive camera models in which the player can clearly see his
avatar, party, or units as well as a good deal of the surrounding environment can
use point-and-click navigation. In a game with a multipresent or party-based inter-
action model, the player first chooses which unit or units should move (unnecessary
in an avatar-based model), then in all cases the player selects a destination in the
environment, and the unit or avatar moves to that location automatically using a
pathfinding algorithm (an artificial intelligence technique to avoid obstacles).
Ty pically the player can select one of t wo speeds : W hen the player selects a loca-
tion, the avatar walks to it, but if he holds down a special key while selecting the
location, the avatar runs rather than walks.

This technique is most often used in real-time strategy and party-based role-play-
ing games in which many units may need to be given their own paths and the
player does not have time to control them all precisely. If a unit cannot get to the
location the player designated, that unit either goes as far as it can and then stops
or, upon receipt of the command, warns the player that it cannot proceed to an
inaccessible destination.

Using point-and-click navigation, the player can indicate precisely where he wants
the unit to end up without concerning himself about avoiding obstacles, a conve-
nience in cluttered environments where the player may not clearly see which
objects actually block the path. It is also helpful in context-sensitive camera models
because the player cannot always see clearly how the avatar should get from one
place to another and often has no freedom to move the camera.

At times, it can be a disadvantage that the player cannot control the path that the
unit takes, so allow the player to designate intermediate points, called waypoints ,
that the unit must pass through one by one on its way to the final destination.