Problem while dragging a transparent RichTextBox

[iPrank]

I've created a transparent RTB and dragging it using Rhino's WM_NCLBUTTONDOWN code. The form has a picture.

But the problem is, when I try to drag the transparent RTB (Ctrl+LeftClick on the RTB and drag), the background doesn't get updated.

I tried to subclass the RTB for WM_MOVING / WM_WINDOWPOSCHANGING and SendMessage-ed WM_NCPAINT,WM_ERASEBKGND, WM_PAINT. But that didn't work.

I tried RedrawWindow, but that didn't work either.

Only, if I hide the RTB and show it again - that works (Command1_Click).

Any idea how to update the background while moving ?

Thanks in advance !

PS. I don't want to use DrawFocusRect or similar method to show a blank rectangle while dragging. I would like to show full contents of the rtb while dragging.

' Add a CommandButton and a RichTextBox in your form
Option Explicit

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 ReleaseCapture Lib "user32" () As Long
Private Declare Function SendMessageLong Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
'
Private Const GWL_EXSTYLE = (-20)
Private Const WS_EX_TRANSPARENT = &H20&
'
Private Const WM_NCLBUTTONDOWN = &HA1
Private Const HTCAPTION = 2

Private Sub Command1_Click()

    ' Backgrund updates only if you click this button
    RichTextBox1.Visible = False
    RichTextBox1.Visible = True

End Sub

Private Sub Form_Load()

    With RichTextBox1
        .Text = ""
        .SelColor = vbWhite
        .SelBold = True
        .SelText = "press Ctrl+LeftClick to drag"
    End With

    ' Make RichTextBox transparent -->
    ' If you run this code after the RTB becomes visible, you'll need to call Command1_Click
    SetWindowLong RichTextBox1.hwnd, GWL_EXSTYLE, WS_EX_TRANSPARENT
    '
    Me.Picture = LoadPicture("C:\WINDOWS\Web\Wallpaper\Wind.jpg")

End Sub

Private Sub RichTextBox1_KeyDown(KeyCode As Integer, Shift As Integer)

    If Shift And vbCtrlMask Then
        RichTextBox1.MousePointer = rtfSizeAll
    End If

End Sub

Private Sub RichTextBox1_KeyUp(KeyCode As Integer, Shift As Integer)

    If Not (Shift And vbCtrlMask) Then
        RichTextBox1.MousePointer = rtfDefault
    End If

End Sub

Private Sub RichTextBox1_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)
    
    ' Press Ctrl and LeftClick to drag
    If (Button = vbLeftButton) And (Shift And vbCtrlMask) Then
        ReleaseCapture
        SendMessageLong RichTextBox1.hwnd, WM_NCLBUTTONDOWN, HTCAPTION, 0&
        RichTextBox1.MousePointer = rtfDefault
    End If

End Sub