XNA 4.0 Game Development by Example Beginner's Guide（Visual Basic Edition）

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Time for action – fading pieces

Add a new class to the Flood Control project called FadingPiece.
Add the following line to indicate that FadingPiece also inherits from GamePiece:
```
Inherits GamePiece
```

Add the following declarations to the FadingPiece class:

Public AlphaLevel As Single = 1.0
Public Shared AlphaChangeRate As Single = 0.02

Add a constructor for the FadingPiece class as follows:

Public Sub New(type As String, suffix As String)
    MyBase.New(type, suffix)
End Sub

Add a method to update the piece:

Public Sub UpdatePiece()
    AlphaLevel = MathHelper.Max(0, AlphaLevel - AlphaChangeRate)
End Sub

What just happened?

The simplest of our animated pieces, the FadingPiece only requires an alpha value (which always starts at 1.0f, or fully opaque) and a rate of change. The FadingPiece constructor simply passes the parameters along to the base constructor.

When a FadingPiece is updated, alphaLevel is reduced by alphaChangeRate, making the piece more transparent.

Managing animated pieces

Now that we can create animated pieces, it will be the responsibility of the GameBoard class to keep track of them. In order to do that, we will define a Dictionary object for each type of piece.

A Dictionary is a collection object similar to a List, except that instead of being organized by an index number, a Dictionary consists of a set of key and value pairs. In an array or a List, you might access an entity by referencing its index as in dataValues(2) = 12. With a Dictionary, the index is replaced with your desired key type. Most commonly, this will be a string value. This way, you can do something like fruitColors("Apple")="red".