Basic Game Objects - Learning C# by Programming Games - page 100

set the default color of the cannon to blue. The following two instructions achieve
that:
this .currentColor = colorBlue;
color = Color.Blue;
We also need to define the position and the origins of the barrel and the color indi-
cator disc, we do this as follows:
barrelOrigin = new Vector2(cannonBarrel.Height, cannonBarrel.Height) / 2;
colorOrigin = new Vector2(currentColor.Width, currentColor.Height) / 2;
position = new Vector2(72, 405);
Now all the member variables of the Cannon instance have a value, and the object
creation is complete. Note that we have not assigned a value to the angle member
variable explicitly. Because angle is of type float , which is a primitive type, it gets
assigned a default value of 0 by the compiler.
7.4.2 Adding Methods to the Cannon Class
Just like in the Painter class, it is possible to add our own methods to the Cannon
class. A very useful method is one that resets a game object to its initial state. Such
methods are especially useful in games. When the player restarts a game or a level
in a game, we simply reset all the game objects to their initial states by calling the
reset method. In order to provide for this, let us add a method called Reset to the
Cannon class.
The Reset method does not have any parameters. It simply sets the member vari-
ables in our class to some initial value. We do not have to reset all the member
variable values, only the ones that will be changed while playing the game. For ex-
ample, we do not have to give the cannon_barrel variable an initial value, since it will
not change while playing the game. The angle variable, however will change, so we
have to reset it. Also, we have to reset the color, since that may also change while
playing the game. As a result, we add the following Reset method to the Cannon
class:
public void Reset()
{
currentColor = colorBlue;
color = Color.Blue;
angle = 0.0f;
}
The Reset method is an example of a method that changes the object that it works
on. This is the general goal of methods: define behavior that modifies the member