;Autor: Fluid Byte

EnableExplicit

Global lpPrevFunc

Procedure EditCtrlProc(hWnd,uMsg,wParam,lParam)
  Select uMsg
    Case #WM_CHAR
      If wParam = #VK_RETURN
        Select hwnd
          Case GadgetID(1)
            If SendMessage_(hwnd,#EM_GETLINECOUNT,0,0) = 4;Zeilen
              ProcedureReturn 0
            EndIf  
        EndSelect
      EndIf
  EndSelect
  
  ProcedureReturn CallWindowProc_(lpPrevFunc,hWnd,uMsg,wParam,lParam)
EndProcedure

If OpenWindow(0,0,0,500,250,"Window",#PB_Window_SystemMenu|#PB_Window_ScreenCentered)
  StringGadget(1,10,10,480,230,"",#ES_MULTILINE)
  
  lpPrevFunc = SetWindowLongPtr_(GadgetID(1),#GWL_WNDPROC,@EditCtrlProc())
Repeat : Until WaitWindowEvent() = #PB_Event_CloseWindow
EndIf