Build Your Game: Vector Actors and Particles - Beginning iOS6 Games Development - page 159

gameCenter and the ImageRepresentation rep are passed to the super-initializer initAt:WithRadi
us:AndRepresenation: to create a Saucer object with a radius of 32. The object saucer is then set
as the delegate to the ImageRepresenation so we can specify the representational details with the
class Saucer . This works exactly like the actors in Chapter 6. Have a look at the source code to see
exactly how these tasks are implemented.
Once the saucer object is created, we want to initialize it with some details. We set which of the
three variants we want to use by calling setVariant: on saucer . We also set the max health and
current health properties to 100. Let's move on to the HealthBar class.
Instantiating the HealthBar Class
In order to render the health bar under the saucer, we create a HealthBar object and pass in the
saucer . We also set the healthBar property of saucer to the
healthBar so the saucer object can update the percentage displayed by healthBar
healthBar is added to the scene. Let's take a look at the constructor
HealthBar and understand how it is set up and behaves the way it does. See Listing 7-4.
VectorRepresentation* rep = [VectorRepresentation vectorRepresentation];
HealthBar* healthBar = [[HealthBar alloc] initAt:anActor.center WithRadius:anActor.radius
[rep setDelegate:healthBar];
[healthBar setColor:[UIColor blueColor]];
[healthBar setBackgroundColor:[UIColor colorWithRed:0 green:0 blue:0 alpha:.5]];
FollowActor* follow = [FollowActor followActor:anActor];
[follow setYOffset:[anActor radius]];
[healthBar addBehavior:follow];
return healthBar;
}
In Listing 7-4, we see the constructor task healthBar: and that it takes an Actor as an argument.
The Actor anActor is the actor that this HealthBar will stay under if anActor moves. In this example, the
Saucer associated with it does not move, but we are going to use this class in future examples, where
its actor does move. Before we look at the behavior FollowActor , notice that HealthBar is initialized by
passing an instance of VectorRepresentation instead of an ImageRepresentation object. This indicates
that we want to draw this object programmatically. We will look at how this works in the next section.
For now, let's continue to explore this example. The next class we want to inspect is FollowActor .
The Behavior FollowActor Class
The class responsible for keeping the HealthBar near the Saucer is the class FollowActor . This class
is a Behavior and provides the same sort of abstraction we found with the other Behavior classes.
Let's see how all of this fits together by looking at the class FollowActor . See Listing 7-5.