Game Development Reference
In-Depth Information
the
Painter
class was a special version of the
Game
class. This is in fact an example
of inheritance. The
Game
class contains a lot of methods and properties (such as
Content
), and because we
inherit
from this class, we can use them in the
Painter
class
as well, since
Painter
is basically the same as
Game
, except that it is a special ver-
sion of it. You could also say that
Painter
is a
subclass
of
Game
, or that
Game
is the
superclass
,orthe
base class
of
Painter
. The inheritance relationship between classes
is widely used and in a good class design, it can be interpreted as 'is a kind of'. For
example,
Painter
is a kind of
Game
. You can also say that
Painter
is a
subclass
,ora
derived class
of
Game
.
10.3.1 Game Objects and Inheritance
The 'is a kind of' relationship also holds for the game objects in the
Painter
game.
A ball is a kind of game object, and so are the paint cans and the cannon. We can
make this inheritance relationship explicit in our program by defining a generic class
called
ThreeColorGameObject
, and then have our actual game object classes inherit
from that generic class. We can then put everything that defines what a three color
game object is inside that class, and the ball, the cannon, and the paint can will be
special versions of that class.
10.3.2 The
ThreeColorGameObject
Class
So let us now have a look at this
ThreeColorGameObject
class in more detail. We are
going to put all the member variables that are used by all the different types of game
objects in our game, into this class. So, we can define a basic skeleton of our class
as follows:
class
ThreeColorGameObject
{
Texture2D colorRed, colorGreen, colorBlue;
Texture2D currentColor;
Vector2 position, velocity;
Color color;
...
}
As a first step, let us define the constructor method of this class. Each game ob-
ject that inherits from this class will load different sprites for representing the three
different colors. Therefore, we add three parameters to the
ThreeColorGameObject
constructor: one for each of the sprites. Inside the constructor, we then assign these
parameter values to the member variables:
