[VB6] Making a form transparent

Getting started

Here is a brief explanation on how to use the transparency based upon:
The desired format, including controls, according to a ratio.
Having the bottom of the form be invisible and controls, according to a ratio.

Restriction

Does not work on color having negative sign.
A color palette must be included.

In a module

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 bDefaut As Byte, ByVal dwFlags As Long) As Long

Private Const GWL_EXSTYLE       As Long = (-20)
Private Const LWA_COLORKEY      As Long = &H1
Private Const LWA_Defaut         As Long = &H2
Private Const WS_EX_LAYERED     As Long = &H80000

'
Public Function Transparency(ByVal hWnd As Long, Optional ByVal Col As Long = vbBlack, _
    Optional ByVal PcTransp As Byte = 255, Optional ByVal TrMode As Boolean = True) As Boolean
' Return : True if there is no error.
' hWnd   : hWnd of the window to make transparent
' Col : Color to make transparent if TrMode=False
' PcTransp  : 0 à 255 >> 0 = transparent  -:- 255 = Opaque
Dim DisplayStyle As Long
    On Error GoTo Exit
    VoirStyle = GetWindowLong(hWnd, GWL_EXSTYLE)
    If DisplayStyle<> (DisplayStyle Or WS_EX_LAYERED) Then
        DisplayStyle = (DisplayStyle Or WS_EX_LAYERED)
        Call SetWindowLong(hWnd, GWL_EXSTYLE, DisplayStyle)
    End If
    Transparency = (SetLayeredWindowAttributes(hWnd, Col, PcTransp, IIf(TrMode, LWA_COLORKEY Or LWA_Defaut, LWA_COLORKEY)) <> 0)
    
Exit:
    If Not Err.Number = 0 Then Err.Clear
End Function

Public Sub ActiveTransparency(M As Form, d As Boolean, F As Boolean, _
     T_Transparency As Integer, Optional Color As Long)
Dim B As Boolean
        If d And F Then
        'Makes color (here the background color of the shape) transparent
        'upon value of T_Transparency
            B = Transparency(M.hWnd, Color, T_Transparency, False)
        ElseIf d Then
            'Makes form, including all components, transparent
            'upon value of T_Transparency
            B = Transparency(M.hWnd, 0, T_Transparency, True)
        Else
            'Restores the form opaque.
            B = Transparency(M.hWnd, , 255, True)
        End If
End Sub

As used in a form

Private Sub Form_Load()
Dim i As Integer
    'Ex: all transparent at ratio 140/255
    'ActiveTransparency Me, True, False, 140, Me.BackColor
    'Ex: Form transparent, visible component at ratio 140/255
    'ActiveTransparency Me, True, True, 140, Me.BackColor
    
    'Example display the form transparency degradation
    ActiveTransparency Me, True, False, 0
    Me.Show
    For i = 0 To 255 Step 3
        ActiveTransparency Me, True, False, i
        Me.Refresh
    Next i
End Sub