[Tex/LaTex] TikZ path decorated with coil or snake

decorationsdiagramspathstikz-pgf

A recurrent question on the forum is… How to draw a decorated path without a straight segment at the end?

Usually the path described are straight lines (See post1, post2 or post3), but there are also solutions for semi circle paths (see post4).

I'm interested in drawing a general path, decorated with a coil and a snake (with an entire number of wave length). I found an interesting solution for snake decoration HERE, however, no clue for coil decoration is given.

Question

How could a general path be decorated with a coil? constrained to have an entire number of wave length.

Update

It has been pointed out by percusse different problems in the definition of my question. So, I'll be less aggressive…

Question v.2.0

Assume that we have a sufficiently smooth path (without vertices or abrupt changes). Additionally, we want the end-points of the path to be centred on the amplitude of the coil. If possible, instead of giving a "wave length" for the coil, we'd like to control the number of turns.

How would such a construction be defined?

Best Answer

Here is one idea that don't work very well (because of the precision problems).

Take the length of the path
set the coil segment length ot 1/n of this length and decorate ...

Here is one experimentation.

\documentclass[varwidth,border=7mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}
\usetikzlibrary{decorations.markings,decorations.pathmorphing}
\tikzset{
  get length/.style = {
    preaction={decorate,
      decoration={ markings,
        mark = at position 1 with
        {
          \pgfkeysgetvalue{/pgf/decoration/mark info/distance from start}{\len}
          \xdef\pathlen{\len}
        }
      }
    }
  }
}

\begin{document}
  \begin{tikzpicture}
  \draw [get length] (0,0) circle(3);
  \draw[decoration={coil,amplitude=3mm,segment length={\pathlen /200}},
        decorate] (0,0) circle(3);
  \end{tikzpicture}
\end{document}

enter image description here

Related Solutions

[Tex/LaTex] TikZ finishes a morphed path with a straight segment

This is a slightly adapted version of my answer to Nicer wavy line with TikZ. This version doesn't insist on drawing a full sine wave, but will be happy with half periods as well (i.e. it can start and end with an upward arch, while the previous version would always start with an upward and end with a downward arch):

\documentclass[a4paper,12pt]{article}
\usepackage{tikz}
\usetikzlibrary{decorations}
\begin{document}

\pgfdeclaredecoration{complete sines}{initial}
{
    \state{initial}[
        width=+0pt,
        next state=upsine,
        persistent precomputation={\pgfmathsetmacro\matchinglength{
            \pgfdecoratedinputsegmentlength / int(\pgfdecoratedinputsegmentlength/\pgfdecorationsegmentlength)}
            \setlength{\pgfdecorationsegmentlength}{\matchinglength pt}
        }] {}
    \state{upsine}[width=\pgfdecorationsegmentlength,next state=downsine]{
        \pgfpathsine{\pgfpoint{0.25\pgfdecorationsegmentlength}{0.5\pgfdecorationsegmentamplitude}}
        \pgfpathcosine{\pgfpoint{0.25\pgfdecorationsegmentlength}{-0.5\pgfdecorationsegmentamplitude}}
    }
    \state{downsine}[width=\pgfdecorationsegmentlength,next state=upsine]{
        \pgfpathsine{\pgfpoint{0.25\pgfdecorationsegmentlength}{-0.5\pgfdecorationsegmentamplitude}}
        \pgfpathcosine{\pgfpoint{0.25\pgfdecorationsegmentlength}{0.5\pgfdecorationsegmentamplitude}}
}
    \state{final}{}
}

\begin{tikzpicture}[
    every path/.style={
        decoration={
            complete sines,
            segment length=1cm,
            amplitude=1cm
        },
        decorate,
        thick
    }]
\draw (0,0) -- (2,0);
\draw [yshift=-1.2cm] (0,0) -- (2.5,0);
\draw [yshift=-2.4cm] (0,0) -- (3,0);
\draw [yshift=-3.6cm] (0,0) -- (3.5,0);
\end{tikzpicture}
\end{document}

[Tex/LaTex] Modify TikZ coil decoration

Here is a proof-of-concept solution for drawing the coil by parametrizing it and drawing the front and back parts separately using plot paths:

\documentclass{article}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
    % Define a formula for the coil.
    % This is what the numbers mean:
    % 0.3 ... how far the rings are apart
    % 0.4 ... how much from the side the rings are seen (try 0 and the same as the radius)
    % 1.5 ... radius of the rings
    \def\coil#1{
        {0.3 * (2*#1 + \t) + 0.4*sin(\t * pi r))},
        {1.5 * cos(\t * pi r)}
        }

    % Draw the part of the coil behind the rectangle
    \foreach \n in {0,1,...,10} {
        \draw[domain={0:1},smooth,variable=\t,samples=15]
            plot (\coil{\n}); 
        }

    % Draw the rectangle
    \filldraw[fill=white] (-0.5,-1) rectangle (7,1);

    % Draw the part of the coil in front of the rectangle
    \foreach \n in {0,1,...,10} {
        \draw[domain={1:2},smooth,variable=\t,samples=15,
              preaction={draw,white,line width=3pt}     % remove if undesired
             ]
            plot (\coil{\n});
        }
\end{tikzpicture}
\end{document}

result

Update

Best Answer

Related Solutions

[Tex/LaTex] TikZ finishes a morphed path with a straight segment

[Tex/LaTex] Modify TikZ coil decoration

Related Question