'A mettre sur l'initialize du formulaire
Private Declare Function CreateEllipticRgn Lib "gdi32" (ByVal X1 As Long, ByVal Y1 As Long, ByVal X2 As Long, ByVal Y2 As Long) As Long
Private Declare Function SetWindowRgn Lib "user32" (ByVal hWnd As Long, ByVal hRgn As Long, ByVal bRedraw As Boolean) As Long
Sub CreateEllipseRegion(ByVal hWnd As Long, X1 As Long, Y1 As Long, X2 As Long, Y2 As Long)
    Dim hRgn As Long
    hRgn = CreateEllipticRgn(X1, Y1, X2, Y2)
    SetWindowRgn hWnd, hRgn, True
    DeleteObject (hRgn)
End Sub