#MSGF_MENU = 2

Procedure WindowCallback(hWnd.l,uMsg.l,wParam.l,lParam.l)
  Select uMsg
    Case #WM_ENTERIDLE
      If wParam = #MSGF_MENU
        GetClientRect_(lParam,mrc.RECT) 
        SetGadgetText(1,"Breite: "+Str(mrc\right))
        SetGadgetText(2,"Höhe: "+Str(mrc\bottom))
      EndIf
  EndSelect
  ProcedureReturn #PB_ProcessPureBasicEvents
EndProcedure

If OpenWindow(0,0,0,500,250,"Window",#PB_Window_SystemMenu|#PB_Window_ScreenCentered)
  TextGadget(1,10,10,100,20,"Breite: 0",0)
  TextGadget(2,10,30,100,20,"Höhe: 0",0)
  
  If CreatePopupMenu(1)
    For a=1 To 5
      MenuItem(a,"Item "+Str(a))
    Next
  EndIf
  
   SetWindowCallback(@WindowCallback())
Repeat
EventID=WaitWindowEvent()
Select EventID
  Case #WM_RBUTTONDOWN
    DisplayPopupMenu(1,WindowID(0))
EndSelect
If EventID=#PB_Event_CloseWindow
  Quit=1
EndIf
Until Quit=1
EndIf