EnableExplicit

Global lpPrevFunc

Procedure ButtonProc(hWnd,uMsg,wParam,lParam)

  Select uMsg
    Case #WM_LBUTTONDOWN
      Debug "Linke Maustaste wird gedrückt"
    Case #WM_LBUTTONUP
      Debug "Linke Maustaste wurde losgelassen"
     
  EndSelect

  ProcedureReturn CallWindowProc_(lpPrevFunc,hWnd,uMsg,wParam,lParam)
EndProcedure

If OpenWindow(0,0,0,500,250,"Window",#PB_Window_SystemMenu|#PB_Window_ScreenCentered)
  ButtonGadget(1,10,10,100,20,"Button",0)

  lpPrevFunc = SetWindowLongPtr_(GadgetID(1),#GWL_WNDPROC,@ButtonProc())

  Repeat : Until WaitWindowEvent() = #PB_Event_CloseWindow
EndIf