MQL5 ReferenceStandard LibraryPanels and DialogsCScrollHOnChangePos CreateIncCreateDecCreateThumbOnResizeOnChangePosOnThumbDragStartOnThumbDragProcessOnThumbDragEndCalcPos OnChangePos The virtual handler of the control "ChangePos" (position change) internal event. virtual bool OnChangePos() Return Value true - event processed, otherwise - false. OnResize OnThumbDragStart