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書名： XNA 4.0 Game Development by Example Beginner's Guide（Visual Basic Edition）
作者名： Kurt Jaegers
本章字?jǐn)?shù)： 355字
更新時間： 2021-08-20 15:50:38

Time for action – GamePiece class methods – part 4 – GetSourceRect

Add the GetSourceRect() method to the GamePiece class:

Public Function GetSourceRectangle() As Rectangle
  Dim x As Integer = textureOffsetX
  Dim y As Integer = textureOffsetY

  If _pieceSuffix.Contains("W") Then
    x += PieceWidth + texturePaddingX
  End If

  y += (Array.IndexOf(PieceTypes, _pieceType) *(PieceHeight + texturePaddingY))

  Return New Rectangle(x, y, PieceWidth, PieceHeight)
End Function

What just happened?

Initially, the x and y variables are set to the textureOffsets that are listed in the GamePiece class declaration. This means they will both start with a value of 1.

Because the sprite sheet is organized with a single type of pipe on each row, the x coordinate of the rectangle is the easiest to determine. If the _pieceSuffix variable does not contain a W (signifying that the piece is filled with water), the x coordinate will simply remain 1.

If _pieceSuffix does contain the letter W (indicating the pipe is filled), the width of a piece (40 pixels), along with the padding between the pieces (1 pixel), are added to the x coordinate of the source rectangle. This shifts the x coordinate from a 1 to a value of 1 + 40 + 1, or 42, which corresponds to the second column of images on the sprite sheet.

To determine the y coordinate for the source rectangle, Array.IndexOf(PieceTypes, _pieceType) is used to locate the _pieceType within the PieceTypes array. The index that is returned represents the position of the tile on the sprite sheet (because the array is organized in the same order as the pieces on the image). For example, Left,Right returns 0, while Top,Bottom returns 1, and Empty returns 6.

The value of this index is multiplied by the height of a game piece plus the padding between pieces. For our sprite sheet, an index of 2 (the Left,Top piece) would be multiplied by 41 (PieceHeight of 40 plus texturePaddingY of 1), resulting in a value of 82 being added to the y variable.

Finally, the new rectangle is returned, comprised of the calculated x and y coordinates and the pre-defined width and height of a piece:

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

Time for action – GamePiece class methods – part 4 – GetSourceRect

What just happened?