In which cases can we find the tikz key "execute at begin to" useful

Question

In the the tikz/pgf manual, we can read in the subsection "14.13 The to path operation" about the key /tikz/execute at begin to but without any examples on how to use it concretely. So I am asking for some examples that may demonstrate how this key may be useful in practical cases. So please give one example by answer.

There already exist examples on this site, e.g. here and here. What precisely do you want to know about this key? — , Oct 03 '18 at 19:26
To find such things, do a google search with site:tex.stackexchange.com "execute at begin to" (the " are important). This is another cool example IMHO. — , Oct 03 '18 at 19:32
I just want to know how to use it with some working examples — Hafid Boukhoulda, Oct 03 '18 at 19:41
I would have liked to have some simpler examples just to grab the idea. — Hafid Boukhoulda, Oct 03 '18 at 19:52

score 6 · Accepted Answer · 2018-10-03T23:20:54.780

OK, here is a rather simple but perhaps not completely pointless example which draws a line parallel to the line you want to draw.

\documentclass[tikz,border=3.14mm]{standalone}
\usetikzlibrary{calc}
\tikzset{
illustrate at begin to/.style=
    {to path={
      (\tikztostart) -- (\tikztotarget) \tikztonodes
    },
    execute at begin to={
    \draw[blue] ($(\tikztostart)!5pt!90:(\tikztotarget)$) --
    ($(\tikztotarget)!5pt!-90:(\tikztostart)$) node[midway,above,sloped]{I'm parallel};}}
}

\begin{document}
\begin{tikzpicture}
\draw[illustrate at begin to] (0,0) to (5,1);
\draw[illustrate at begin to] (0,-2) to (4,-3);
\end{tikzpicture}
\end{document}

Just for fun, another application, using Jake's complete sines and motivated by (my interpretation of) this question. (No, this trick does not work for curved paths, just in case you're wondering. ;-)

\documentclass[tikz,border=3.14mm]{standalone}
\usetikzlibrary{decorations,calc}
\pgfdeclaredecoration{complete sines}{initial}
{
    \state{initial}[
        width=+0pt,
        next state=sine,
        persistent precomputation={\pgfmathsetmacro\matchinglength{
            \pgfdecoratedinputsegmentlength / int(\pgfdecoratedinputsegmentlength/\pgfdecorationsegmentlength)}
            \setlength{\pgfdecorationsegmentlength}{\matchinglength pt}
        }] {}
    \state{sine}[width=\pgfdecorationsegmentlength]{
        \pgfpathsine{\pgfpoint{0.25\pgfdecorationsegmentlength}{0.5\pgfdecorationsegmentamplitude}}
        \pgfpathcosine{\pgfpoint{0.25\pgfdecorationsegmentlength}{-0.5\pgfdecorationsegmentamplitude}}
        \pgfpathsine{\pgfpoint{0.25\pgfdecorationsegmentlength}{-0.5\pgfdecorationsegmentamplitude}}
        \pgfpathcosine{\pgfpoint{0.25\pgfdecorationsegmentlength}{0.5\pgfdecorationsegmentamplitude}}
}
    \state{final}{}
}

\begin{document}
\tikzset{fancy sines/.style={#1,decoration={
            complete sines,
            segment length=3mm,
            amplitude=1mm
        },decorate,to path={
      (\tikztostart) -- 
      ($(\tikztotarget)!{-5*\pgflinewidth}!-135:(\tikztostart)$)
      (\tikztotarget) \tikztonodes
    },
    execute at begin to={\foreach \X in {1,...,5}
    {\draw[decorate,#1]
    ($(\tikztostart)!{\X*\pgflinewidth}!45:(\tikztotarget)$) 
    -- ($(\tikztotarget)!{(-5+\X)*\pgflinewidth}!-135:(\tikztostart)$);}}}
}
\begin{tikzpicture}    
\draw[fancy sines=blue] (0,0) to (0,-3);
\draw[fancy sines=red] (0,0) to (3,0);
\draw[fancy sines=green!60!black] (3,0) to (0,-3);
\end{tikzpicture}
\end{document}

In which cases can we find the tikz key "execute at begin to" useful

1 Answers1