A Completed Game: Belt Commander - Beginning iOS6 Games Development - page 276

 CGPoint center : The property center defines the location of the center of the
Actor in game coordinates.
 float rotation : The rotation property indicates the rotation of the Actor in
radians.
 float radius : The radius of the Actor describes how big it is. Together, center
and radius describe the area of the game occupied by the Actor .
 NSMutableArray* behaviors : The behaviors property is a collection of Behavior
objects. A Behavior object describes some sort of aspect of an Actor. It might
describe how it moves or when it is removed from the game. Each Behavior in
the behaviors array will be applied to the Actor on each step of the game.
 BOOL needsViewUpdated : Throughout a step of the game, an Actor may undergo
changes that require its UIView to be updated. These might include advancing
the image that should represent it or a change in state. This flag informs
the GameController that work is required to synchronize the Actor with its
representation.
 NSObject < Representation > representation : Each Actor in the game requires
an object conforming to Representation to describe how to create a UIView to
represent it in the game. Representations are discussed in the next section.
 int variant : It is common to have Actors in a game that differ only slightly.
Perhaps they are a different color or have a slightly different behavior. Since
this is a common requirement, the property variant provides a simple way of
distinguishing Actors of the same class.
 int state : The property state is used to describe the state of an Actor .
This state can be anything, and is up to the subclass to define exactly
what this indicates. The property state and variant work with the class
ImageRepresentation to figure out which image should be used for an Actor .
 float alpha : The property alpha describes how opaque an Actor is. An Actor
with an alpha of 0.0 is fully transparent, while an alpha value of 1.0 is fully
opaque. Transparent regions in an Actor's representation are unaffected.
 BOOL animationPaused : The property animationPaused is used to pause any
animation that is being applied to the Actor. It is up to the implementation of the
animation to honor this value. ImageRepresentation will not update the image, in
a sequence of images, used to represent an Actor if this property is true.
In addition to the properties that define an Actor, there are a handful of tasks that come with the
class Actor. These are the following:
 -(id)initAt:(CGPoint)aPoint WithRadius:(float)aRadius AndRepresentation:
(NSObject<Representation>*)aRepresentation : This task is the designated
constructor for the class Actor . It requires that each Ac t or has a center, a radius,
and a representation. All subclasses of Actor should be sure that this task gets
called when the Actor is created.