var ctrlman = m_Map.GetCtrlMan();
var ctrlstate = ctrlman.GetControlState();
var dpsize = ctrlstate.GetSizeDP();

var width_px = dpsize._CX/2 - 300;

alert(width_px);	

CXCtrlMan ctrlman = m_Map.GetCtrlMan();
CXUIMan uiman = ctrlman.GetUIMan();
CXControlState ctrlstate = ctrlman.GetControlState();
CXSize dpsize = ctrlstate.GetSizeDP(); 
CXUtility util = m_Map.GetUtility();		

long width_px = dpsize.get__CX()/2 - 250;

CString msg;
msg.Format(_T("width_px : [%lu]"), width_px);
AfxMessageBox(msg);