Public Declare Function SetLayeredWindowAttributes Lib "user32" (ByVal hwnd As Long, ByVal crKey As Long, ByVal bAlpha As Byte, ByVal dwFlags As Long) As Long
hwnd -- 透明窗体的句柄
crKey -- 为颜色值
bAlpha -- 透明度,取值范围是[0,255]
dwFlags -- 透明方式,可以取两个值:当取值为LWA_ALPHA时,crKey参数无效,bAlpha参数有效;当取值为LWA_COLORKEY时,bAlpha参数有效而窗体中的所有颜色为crKey的地方将变为透明