Coordinated Unit Movement
By
Dave C. Pottinger
Gamasutra
January 22, 1998
Vol. 3: Issue 3
Originally
Published in Game Developer Magazine, January, 1999.
| Coordinated Unit Movement |
Introduction
Movement
Issues Facing Game Developers
Simple
Movement Algorithm
Collision
Determination
Discrete
vs. Continuous Simulation
Predicted
Positions
Unit
to Unit Cooperation
Basic
Planning
Basic Definitions
|
Movement. The execution of a path.
Simple movement algorithms move a unit along a path, while more complex
systems check collisions and coordinate unit movement to avoid collisions
and allow otherwise stuck units to move.
Pathfinding. The act of finding a path (a planned route for a unit
to get from point A to point B). The algorithm used can be anything from
a simple exhaustive search to an optimized A* implementation.
Waypoint. A point on a path that a unit must go through to execute
the path. Each path, by definition, has one waypoint at the start and
one waypoint at the end.
Unit. A game entity that has the ability to move around the game
map.
Group. A general collection of units that have been grouped together
by the user for convenience (usually to issue the same order to all of
the units in the group). Most games try to keep all of the units in a
group together during movement.
Formation. A more complex group. A formation has facing (a front,
a back, and two flanks). Each unit in the formation tries to maintain
a unique relative position inside the formation. More complex models provide
an individualized unit facing inside of the overall formation and support
for wheeling during movement.
Hard Movement Radius. A measure of the volume of a unit with which
we absolutely do not allow other units to collide.
Soft Movement Radius. A measure of the volume of a unit with which
we would prefer not to collide.
Movement Prediction. Using the movement algorithms to predict where
a unit will be at some point in the future. A good prediction system will
take acceleration and deceleration into account.
Turn Radius. The radius of the tightest circle a unit can turn
on at a given speed.
