This topic is included for completeness. For more detail see the source code located in the VC\atlmfc\src\mfc folder of your Visual Studio installation.
virtual void OnDrawButtonSeparator(
   CDC* pDC,
   CMFCToolBarButton* pButton,
   CRect rect,
   CMFCVisualManager::AFX_BUTTON_STATE state,
   BOOL bHorz
);
Parameters
[in] pDC
[in] pButton
[in] rect
[in] state
[in] bHorz
Requirements
Header: afxvisualmanager.h