Binaryworld - Read and modify a TextBox control's formatting rectangle ... [ VB -> Forms & Controls ]

By sending appropriate messages to a multi-line TextBox control you can read and modify its formatting rectangle - that is, the inner portion of the control where the user can type. Modifying the size and position of this area can be useful, for example, to leave a left margin where you can add line numbers or other text markers. Here's is the complete source code for the two routines that read and modify the formatting rectangle:

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Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal _
  hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, _
  lParam As Any) As Long
Private Type RECT
  Left As Long
  Top As Long
  Right As Long
  Bottom As Long
End Type

Const EM_GETRECT = &HB2
Const EM_SETRECT = &HB3

' Get the formatting rectangle.

Sub TextBoxGetRect(tb As TextBox, Left As Long, Top As Long, Right As Long, _
  Bottom As Long)
  Dim lpRect As RECT
  SendMessage tb.hwnd, EM_GETRECT, 0, lpRect
  Left = lpRect.Left
  Top = lpRect.Top
  Right = lpRect.Right
  Bottom = lpRect.Bottom
End Sub

' Set the formatting rectangle and refresh the control.

Sub TextBoxSetRect(tb As TextBox, ByVal Left As Long, ByVal Top As Long, _
  ByVal Right As Long, ByVal Bottom As Long)
  Dim lpRect As RECT
  lpRect.Left = Left
  lpRect.Top = Top
  lpRect.Right = Right
  lpRect.Bottom = Bottom
  SendMessage tb.hwnd, EM_SETRECT, 0, lpRect
End Sub