很簡單，使用GDI的AlphaBlend函式就可以。可以設定全域性Alpha混合係數（0到255），也可以混合帶有Alpha通道的32位BMP。

如果要做稍複雜的處理，可以使用GDI+，裡面的所有繪圖手段都支援Alpha通道。

附AlphaBlend函式在VB中的宣告：

Public Type t_BLENDFUNCTION

BlendOp As Byte

BlendFlags As Byte

SourceConstantAlpha As Byte

AlphaFormat As Byte

End Type

Public Declare Function AlphaBlend Lib "msimg32" (ByVal hDestDC As Long, _

ByVal xDest As Long, _

ByVal yDest As Long, _

ByVal nWidthDest As Long, _

ByVal nHeightDest As Long, _

ByVal hSrcDC As Long, _

ByVal xSrc As Long, _

ByVal ySrc As Long, _

ByVal nWidthSrc As Long, _

ByVal nHeightSRC As Long, _

ByVal BLENDFUNCTION As Long) As Long