Build Your Game: Vector Actors and Particles - Beginning iOS6 Games Development - page 160

Listing 7-5. FollowActor.m
#import "FollowActor.h"
#import "GameController.h"
@implementation FollowActor
@synthesize actorToFollow;
@synthesize xOffset;
@synthesize yOffset;
+(id)followActor:(Actor*)anActorToFollow{
FollowActor* follow = [FollowActor new];
[follow setActorToFollow:anActorToFollow];
return follow;
}
-(void)applyToActor:(Actor*)anActor In:(GameController*)gameController{
if (![actorToFollow removed]){
CGPoint c = [actorToFollow center];
c.x += xOffset;
c.y += yOffset;
[anActor setCenter: c];
} else {
[gameController removeActor:anActor];
}
}
@end
In Listing 7-5, we see the entire implementation of the class FollowActor . It is constructed with the
task followActor: , which takes the actor to follow as an argument. The task applyToActor:In:
is called for every step of the game and is responsible for repositioning the actor this behavior is
associated with. To do this, we simply set the property center of anActor to the property center of
the Actor we are following, adjusting by xOffest and yOffset . Looking at Listing 7-4, we see that the
HealthBar is configured to follow the saucer at an xOffset equal to the radius of saucer . This keeps
the HealthBar centered below saucer . Now let's explore the Bullet class.
The Bullet Class
We have seen how the Saucer and the HealthBar classes work together. We now want to look at the
Bullet class and understand why it behaves the way it does. Listing 7-6 shows Bullet 's constructor.
Listing 7-6. Bullet.m (bulletAt:WithDirection:)
+(id)bulletAt:(CGPoint)aCenter WithDirection:(float)aDirection{
VectorRepresentation* rep = [VectorRepresentation vectorRepresentation];
Bullet* bullet = [[Bullet alloc] initAt:aCenter WithRadius:4 AndRepresentation:rep];
[rep setDelegate:bullet];