A Completed Game: Belt Commander - Beginning iOS6 Games Development - page 284

Listing 12-13. BeltCommanderController.m (doAddNewTrouble)
-(void)doAddNewTrouble{
if ([gameParameters includeAsteroids] && arc4random() % (5*60) == 0){
if ([[self actorsOfType:[Asteroid class]] count] < 20){
[self addActor:[Asteroid asteroid:self]];
}
}
if ([gameParameters includeSaucers] && arc4random() % (10*60) == 0){
if ([[self actorsOfType:[Saucer class]] count] < 3){
[self addActor:[Saucer saucer:self]];
}
}
if ([gameParameters includePowerups] && arc4random() % (20*60) == 0){
[self addActor:[Powerup powerup:self]];
}
doAddNewTrouble that is responsible for adding new Actors to
Actors we might add, we first check to see if gameParameters
gameParameters indicates that we should add an Actor of a
Asteroids
Actor we create it and call addActor: . The Actor's
Actor is created. We will now move on and
Collision Detection
Now we know how each Actor is added to the scene. Let's move on and look at how they interact.
If we consider the five main Actors in this game, there are several interactions that must be
considered, as follows:
 Bullets and Asteroids
 Asteroids and the Viper
 Bullets and the Viper
 Bullets and Saucers
 Powerups and the Viper
These interactions are handled in the task doCollisionDetection , the first part of which is shown in
Listing 12-14.
Listing 12-14. BeltCommanderController.m (doCollisionDetection, part 1)
-(void)doCollisionDetection{
NSSet* bullets = [self actorsOfType:[Bullet class]];
NSSet* asteroids = [self actorsOfType:[Asteroid class]];
NSSet* saucers = [self actorsOfType:[Saucer class]];
NSSet* powerups = [self actorsOfType:[Powerup class]];