Flash MX 2004 Games : Art to ActionScript

Chapter 18: Sports simulations
Updating the players
By the time the ‘update’ function is called for the players, all user input has been gathered and
the nearest player to the ball has been stored. There are two different update methods; either the
player is under keyboard control in which case the movement has taken place, or the player is
the computer-controlled player nearest the ball, in which case the function ‘opponentMove’ has
already been called to update their position. If neither of these possibilities applies to the current
player then the function ‘moveToTarget’ is used. Each player has a target position at which they
are aiming, which is a simple mechanism to get the players to work as a team, rather than every
player heading towards the ball. The function works by first creating a vector from the current
position of the player to the target position. If the target has been achieved then the square of
this vector will be less than the constant ‘TARGETMIN’. If this is the case then a new target
is calculated. Some players are set to be attacking players and the others are defenders. The new
target is calculated taking into consideration an arbitrary location on the pitch and the current
ball position; attacking players use more of the ball position in deciding on a new target, whereas
defenders tend to stay inside their own half. The function closes with a call to ‘setDirection’.
1 function moveToTarget(){
2 x = _x - targetx;
3 y = _y - targety;
4 if ((x*x + y*y)