[Tex/LaTex] tikz: How to mirror the path decoration “text along path”

tikz-pgf

I'd like to create labeled nested ellipses in tikz. The labels should follow the
shape of the ellipses. I used a path decoration with pre to move the label to
the right place, but I couldn't figure out: a): how to turn it [the mirror
option mirrors it in the wrong way] and b): as soon as I include pre and pre length, other options (such as raise or mirror) do not seem to be respected
anymore. Has anyone an idea how to solve this?

\documentclass{article}

\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage[american]{babel}
\usepackage{tikz}
\usepackage{xcolor}
\usetikzlibrary{shapes,arrows}
\usetikzlibrary{decorations.pathmorphing, decorations.text}

\begin{document}

\begin{tikzpicture}[decoration=zigzag]
  % ellipses
  \filldraw[fill=gray!10, draw=gray!80] (0,0) ellipse (6.4cm and 3.2cm);
  \filldraw[fill=gray!20, draw=gray!80] (0,0) ellipse (4.8cm and 2.4cm);
  \filldraw[fill=gray!30, draw=gray!80,
            postaction={decorate,
                        decoration={pre=moveto, pre length=3cm, raise=4mm, text along path, text={|\tt|Function 2}}}]
           (0,0) ellipse (3.2cm and 1.6cm);
  \filldraw[fill=gray!40, draw=gray!80] (0,0) ellipse (1.6cm and 0.8cm) node
  {\texttt{Function 1}};
\end{tikzpicture}
\end{document}

Best Answer

Instead of decorate the ellipse, you can decorate an arc of this ellipse. And you can choose the direction of this arc.

enter image description here

\documentclass{standalone}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{tikz}
\usepackage{xcolor}
\usetikzlibrary{shapes,arrows}
\usetikzlibrary{decorations.pathmorphing, decorations.text}
\begin{document}
\begin{tikzpicture}[decoration=zigzag]
  % ellipses
  \filldraw[fill=gray!10, draw=gray!80] (0,0) ellipse (6.4cm and 3.2cm);
  \path[postaction={decorate,
    decoration={
      raise=-1em,
      text along path,
      text={|\tt|Function 4},
      text align=center,
    },
  }] (0,0) ++(110:6.4cm and 3.2cm) arc(110:70:6.4cm and 3.2cm);
  \filldraw[fill=gray!20, draw=gray!80] (0,0) ellipse (4.8cm and 2.4cm);
  \path[postaction={decorate,
    decoration={
      raise=-1em,
      text along path,
      text={|\tt|Function 3},
      text align=center,
    },
  }] (0,0) ++(110:4.8cm and 2.4cm) arc(110:70:4.8cm and 2.4cm);
  \filldraw[fill=gray!30, draw=gray!80] (0,0) ellipse (3.2cm and 1.6cm);
  \path[postaction={decorate,
    decoration={
      raise=-1em,
      text along path,
      text={|\tt|Function 2},
      text align=center,
    },
  }] (0,0) ++(110:3.2cm and 1.6cm) arc(110:70:3.2cm and 1.6cm);
  \filldraw[fill=gray!40, draw=gray!80] (0,0) ellipse (1.6cm and 0.8cm) node
  {\texttt{Function 1}};
\end{tikzpicture}
\end{document}

Related Solutions

[Tex/LaTex] Rotate a node but not its content: the case of the ellipse decoration

The source of the difficulty is that ellipses are constructed in a particular way in TikZ. They are paths that start from the x-axis and proceed counter-clockwise around their centre. The vast majority of the time, the exact parametrisation doesn't matter. You appear to have found the one situation where it does!

In the actual question, you only want to be able to mirror the ellipse, and so draw it starting from the negative x-axis (the title of the question suggests a more flexible approach). That's actually not too hard since we can exploit the symmetry of the ellipse. The key is to provide it with a negative x-radius, since then it will start from the negative x-axis (and proceed clockwise, but we could correct for that by negating the y-radius as well). To do this, we interrupt the call from the node shape to the drawing command and flip the sign of the x-radius. The simplest way to do this is to redefine the \pgfpathellipse macro to do the negation and then call the original macro. The following code does this.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{decorations,shapes,decorations.markings}
\makeatletter
\let\origpgfpathellipse=\pgfpathellipse
\def\revpgfpathellipse#1#2#3{%
  #2%
  \pgf@xa=-\pgf@x
  \origpgfpathellipse{#1}{\pgfqpoint{\pgf@xa}{0pt}}{#3}}
\makeatother

\tikzset{
  reversed ellipse/.style={
    ellipse,
    reverse the ellipse%
  },
  reverse the ellipse/.code={
    \let\pgfpathellipse=\revpgfpathellipse
  }
}
\begin{document}
\begin{tikzpicture}
\node[ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,0) {hello world};

\node[reversed ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,-2) {hello world};
\end{tikzpicture}

\end{document}

Here's the result:

rotated ellipse

(the arrow got clipped, but you can see where it lies)

[Tex/LaTex] TikZ: Text along path

To avoid touching the path's ends, you could add pre length and post length options do the decoration, such as:

\draw[postaction={decoration={text along path,
  text = {merging a contiguous run}, text align=fit to path,
  pre length=2em, post length=2em},decorate}]
    (block7) -- ($(cblock7.north)!.5!(cblock7.south)$);

Best Answer

Related Solutions

[Tex/LaTex] Rotate a node but not its content: the case of the ellipse decoration

[Tex/LaTex] TikZ: Text along path

Related Question