创建透明窗体

Option Explicit
'从指定窗口的结构中取得信息
Private Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" (ByVal HWnd As Long, ByVal nIndex As Long) As Long
'在窗口结构中为指定的窗口设置信息
Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal HWnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
'设置窗口透明度
Private Declare Function SetLayeredWindowAttributes Lib "user32" (ByVal HWnd As Long, ByVal crKey As Long, ByVal bAlpha As Byte, ByVal dwFlags As Long) As Long
Private Const WS_EX_LAYERED = &H80000
Private Const GWL_EXSTYLE = (-20)
Private Const LWA_ALPHA = &H2
Private Const LWA_COLORKEY = &H1
Private Sub Form_Load()
Dim rtn As Long
    rtn = GetWindowLong(HWnd, GWL_EXSTYLE)  '返回扩展窗口样式
    rtn = rtn Or WS_EX_LAYERED '&H80000
    SetWindowLong HWnd, GWL_EXSTYLE, rtn
    SetLayeredWindowAttributes HWnd, 150, 200, LWA_ALPHA
  
End Sub
'SetLayeredWindowAttributes
'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。
'??????? LWA_ALPHA = 0x2???????
'LWA_COLORKEY=0x1 要使使窗体拥有透明效果,
'首先要有WS_EX_LAYERED扩展属性 (旧的sdk没有定义这个属性,所以可以直接指定为0x80000).
'WS_EX_LAYERED = 0x80000