Public Const WM_PAINT As Long = &HF
 
Public Declare Function SendMessage Lib "user32" Alias _
  "SendMessageA" ( ByVal hWnd As Long, ByVal wMsg As Long, _
  ByVal wParam As Long, lParam As Any) As Long

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Call SendMessage(Form1.hWnd, WM_PAINT, Form1.hDC, 0&)