Yes, that¶ just what I want.
You can do this several ways, but the easiest is to redefine the symbol definition in layout. Just type into your layout: code metapost def l_floorstep (expr P) = T:=identity; cas := 0; dlzka := arclength P; mojkrok:=adjust_step(dlzka, 0.25u); pickup PenD; forever: t := arctime cas of P; mark_ (P,t,0.2u); cas := cas + mojkrok; exitif cas > dlzka + (mojkrok / 3); % for rounding errors endfor; pickup PenC; thdraw P; enddef; endcode where 0.2u (in line: mark_ (P,t,0.2u);) is the size of the tick. You may change this number e.g. to 0.1u or 0.5u. This magic code comes from metapost symbol definitions source file (thLine.mp). This way, all symbols can be changed. There are probably some other hints in therion book. S.