Knowing What the Player Is Doing - Learning C# by Programming Games - page 67

Fig. 5.1 The tooltip that is
shown when you hover over
the word SpriteBatch
together methods, classes themselves can also contain declarations. An example of
a class that contains declarations is the Balloon class we programmed. This class de-
clares among others a variable called spriteBatch and a variable called balloonPosition .
Another example of a class that also declares variables is the Texture2D class, which
is used to represent a sprite:
balloon = Content.Load<Texture2D>("spr_lives");
This instruction loads a texture from a file, and stores it in a variable of type
Texture2D . Texture2D is a class, just like SpriteBatch and Balloon . You can verify this
yourself by hovering over the word with your mouse pointer in the code editor. Next
to a couple of methods, values of this class also contain variables because the im-
age data have to be stored somewhere after they have been loaded. Probably these
variables are quite complicated since an image contains a lot of information. We are
not that interested in what these variables internal to this class look like. However,
we do like to know how to use the methods in this class so we can do something
with this variable of type Texture2D . The variable balloon has as a type Texture2D and
therefore it contains the internal variables of the class Texture2D , as well as the meth-
ods that belong to the class. Variables such as balloon whose type is a class, are also
called objects .
5.3.1 Methods and Properties Can Manipulate an Object
The Texture2D class has a couple of useful methods. For example, it has a method
called SaveAsJpeg which allows us to save the loaded sprite as a JPEG image. This
method probably contains a lot of instructions that open a file, compress the image
information in the loaded sprite according to the JPEG standard, and that save the
compressed information in the file. But which sprite should this method save to a
JPEG file if we call the method? In the Balloon1 and Balloon2 programs, we have
declared the following two variables (among others):
background = Content.Load<Texture2D>("spr_background");
balloon = Content.Load<Texture2D>("spr_lives");
Suppose that we would call the method SaveAsJpeg as follows:
Texture2D.SaveAsJpeg(...);
How can we indicate that we want to save the balloon image as a JPEG file, and not
the background? The SaveAsJpeg method does not have a parameter where we can