Tikz snake path has whitespace before/after node (MWE)

Question

I'm using tikz to draw a snake-coil edge/path between nodes, but some edges have whitespace before/after its start or end node. Here is a small example:

    \documentclass{standalone}
    \usepackage{tikz}
    \usetikzlibrary[positioning,decorations.pathmorphing]
    \begin{document}
    \begin{tikzpicture}

      \tikzstyle{enclosed} = [draw, circle, inner sep=0pt, minimum size=.15cm, fill=black]
      \tikzstyle{enclosedM} = [draw, circle, inner sep=0pt, minimum size=.15cm, fill=red]

      \node[enclosed, label={left: $x$}] (x) at (0,2) {};
      \node[enclosed, label={right: $y$}] (y) at (4,2) {};
      \node[enclosed] (w) at (2,0) {};
      \node[enclosed] (v) at (2,4) {};
      \node[enclosedM, label={above: $z$}] (z) at (2,1) {};
      \node[enclosedM, label={below: $t$}] (t) at (2,3) {};

      \draw[decorate,decoration={snake,amplitude=.2mm}]
        (x) -- (v)
        (v) -- (y)
        (x) -- (w)
        (w) -- (y)
        (x) -- (t)
        (v) -- (t)
        (y) -- (t)
        (x) -- (z)
        (w) -- (z)
        (z) -- (y);
    \end{tikzpicture}
    \end{document}

The result is:

Notice that there is some whitespace between the center bottom node and node z. Also, there is whitespace between the top node and node y.

This still occurs even when "amplitude" is set to 0mm, which I thought would be equivalent to if the edge was not decorated at all. Setting "post length" and "pre length" options with various combinations fixes some edges, but then it creates the same problem with other edges that were OK before.

If I remove the decorate, decorations={...} and use \draw as normal with no settings, it works fine but the edges are not wavy. How can I get rid of the whitespace so it behaves as a normal edge but semi-wavy?

Answer 1

You have to handle decoration with care. I do not exactly know why this happens, but obviously, it is because you put multiple segments into one single \draw command.

You should write one separate \draw for every line segment. Or, to make it similar to your original version, you could use the following code:

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning,decorations.pathmorphing}
\begin{document}

\begin{tikzpicture}

  \tikzset{
   enclosed/.style={draw, circle, inner sep=0pt, minimum size=.15cm, fill=black},
   enclosedM/.style={enclosed, fill=red}
  }

  \node[enclosed, label={left: $x$}] (x) at (0,2) {};
  \node[enclosed, label={right: $y$}] (y) at (4,2) {};
  \node[enclosed] (w) at (2,0) {};
  \node[enclosed] (v) at (2,4) {};
  \node[enclosedM, label={above: $z$}] (z) at (2,1) {};
  \node[enclosedM, label={below: $t$}] (t) at (2,3) {};

  \foreach\x in {
    (x) -- (v),
    (v) -- (y),
    (x) -- (w),
    (w) -- (y),
    (x) -- (t),
    (v) -- (t),
    (y) -- (t),
    (x) -- (z),
    (w) -- (z),
    (z) -- (y)
  }
   \draw[decorate,decoration={snake,amplitude=.2mm}] \x;

\end{tikzpicture}

\end{document}

Answer 2

Two comments (not a real answer): tikzstyle is deprecated and if you draw the lines one by one there is no issue. (I have not checked if the problem is due to tikzstyle.) UPDATE: compactified the code and a big thanks to @Zarko for catching the square brackets!

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning,decorations.pathmorphing}
\begin{document}
\begin{tikzpicture}
  \tikzset{Snake/.style={decorate,decoration={snake,amplitude=.2mm}},
    enclosed/.style={draw, circle, inner sep=0pt, minimum size=.15cm,
    fill=black},
    enclosedM/.style={draw, circle, inner sep=0pt, minimum size=.15cm,
    fill=red}}

  \node[enclosed, label={left:$x$}] (x) at (0,2) {};
  \node[enclosed, label={right:$y$}] (y) at (4,2) {};
  \node[enclosed] (w) at (2,0) {};
  \node[enclosed] (v) at (2,4) {};
  \node[enclosedM, label={above:$z$}] (z) at (2,1) {};
  \node[enclosedM, label={below:$t$}] (t) at (2,3) {};
  \foreach \X in {x,y,v} \draw[Snake] (t) -- (\X);
  \foreach \X in {x,y,w} \draw[Snake] (z) -- (\X);
  \foreach \X in {x,y}{\foreach \V in {v,w}  \draw[Snake] (\V) -- (\X);}    
\end{tikzpicture}
\end{document}