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

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Time for action – filling in the gaps

Add the FillFromAbove() method to the GameBoard class.

Public Sub FillFromAbove(x As Integer, y As Integer)
  Dim rowLookup As Integer = y - 1

  Do While (rowLookup >= 0)
    If GetSquare(x, rowLookup) <> "Empty" Then
      SetSquare(x, y, GetSquare(x, rowLookup))
      SetSquare(x, rowLookup, "Empty")
      rowLookup = -1
    End If
    rowLookup -= 1
  Loop
End Sub

What just happened?

Given a square to fill, FillFromAbove() looks at the piece directly above to see if it is marked as Empty. If it is, the method will subtract one from rowLookup and start over until it reaches the top of the board. If no non-empty pieces are found when the top of the board is reached, the method does nothing and exits.

When a non-empty piece is found, it is copied to the destination square, and the copied piece is changed to an empty piece. The rowLookup variable is set to -1 to ensure that the loop does not continue to run.

Generating new pieces

We can create a single method that will fill any empty spaces on the game board, use it when the game begins, and when pieces are removed from the board after scoring.