Draw offset of polylines

Question

I'm afraid that I have a followup question to this one.

Consider the following MWE

\documentclass{standalone}

\usepackage{tikz}
\usetikzlibrary{calc}

\begin{document}
  \begin{tikzpicture}[scale=.25]
    \tikzset{
      ncbar/.style={
        to path=%
        ($(\tikztostart)!#1!90:(\tikztotarget)$)
        -- ($(\tikztotarget)!($(\tikztostart)!#1!90:(\tikztotarget)$)!90:(\tikztostart)$)
      },
      ncbar/.default=0.5cm,
    }

    \draw[red,ultra thin] (0,0) -- (1,2) -- (2,0);
    \draw[blue,ultra thin] (0,0) to[ncbar=0.25cm] (1,2) to[ncbar=0.25cm] (2,0);

  \end{tikzpicture}
\end{document}

which yields: enter image description here

Note that the source of the second part of the blue path is not "correct". In turn, the second blue part is not parallel to the red counterpart. How can I fix this? Somehow reset/set \tikztostart?

Bonus question: How can I bridge the gap between the two blue parts using the missing part of a circle arc (this circle centered at the apex of the red curve and of radius 0.25cm in this example)?

Are your sure that your example works. I am getting the error: ! Package tikz Error: Cannot parse this coordinate. — Marco Daniel, Jun 05 '13 at 11:35
@MarcoDaniel: I re-pasted the code and double-checked. Works for me. — Dror, Jun 05 '13 at 11:45

score 11 · Answer 1 · answered Jun 05 '13 at 11:49

You have to include the final (\tikztotarget) in the to path definition (without the preceding --):

\documentclass{standalone}

\usepackage{tikz}
\usetikzlibrary{calc}

\begin{document}
  \begin{tikzpicture}[scale=.25]
\tikzset{
    ncbar angle/.initial=90,
    ncbar/.style={
        to path=($(\tikztostart)!#1!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztotarget)$)
        -- ($(\tikztotarget)!($(\tikztostart)!#1!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztotarget)$)!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztostart)$)
        (\tikztotarget)
    },
    ncbar/.default=0.5cm,
}

    \draw[red,ultra thin] (0,0) -- (1,2) -- (2,0);
    \draw[blue,ultra thin] (0,0) to[ncbar=0.25cm] (1,2) to[ncbar=0.25cm] (2,0);

  \end{tikzpicture}
\end{document}

Worked like a charm. I'll wait to see if someone will add something regarding the bonus part :) — Dror, Jun 05 '13 at 11:59

Draw offset of polylines

1 Answers1