函数SetLayeredWindowAttributes
使用这个函数，可以轻松的实现半透明窗体。按照微软的要求，透明窗体窗体在创建时应使用WS_EX_LAYERED参数（用CreateWindowEx），或者在创建后设置该参数（用SetWindowLong），我选用后者。全部函数、常量声明如下：
Private Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long) As Long
Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Private Declare Function SetLayeredWindowAttributes Lib "user32" (ByVal hwnd As Long, ByVal crKey As Long, ByVal bAlpha As Byte, ByVal dwFlags As Long) As Long
其中hwnd是透明窗体的句柄，crKey为颜色值，bAlpha是透明度，取值范围是[0,255]，dwFlags是透明方式，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－－这个功能很有用：我们不必再为建立不规则形状的窗体而调用一大堆区域分析、创建、合并函数了，只需指定透明处的颜色值即可，哈哈哈哈！请看具体代码。
Private Const WS_EX_LAYERED = &H80000
Private Const GWL_EXSTYLE = (-20)
Private Const LWA_ALPHA = &H2
Private Const LWA_COLORKEY = &H1
代码一：一个半透明窗体
Private Sub Form_Load()
Dim rtn As Long
rtn = GetWindowLong(hwnd, GWL_EXSTYLE)
rtn = rtn Or WS_EX_LAYERED
SetWindowLong hwnd, GWL_EXSTYLE, rtn
SetLayeredWindowAttributes hwnd, 0, 200, LWA_ALPHA
End Sub

代码二：形状不规则的窗体
Private Sub Form_Load()
Dim rtn As Long
BorderStyler=0
rtn = GetWindowLong(hwnd, GWL_EXSTYLE)
rtn = rtn Or WS_EX_LAYERED
SetWindowLong hwnd, GWL_EXSTYLE, rtn
SetLayeredWindowAttributes hwnd, &HFF0000, 0, LWA_COLORKEY '将扣去窗口中的蓝色
End Sub