Using a pgfplots-style legend in a plain-old tikzpicture

Question

I am using a plain-old tikzpicture to produce a pie-chart-like plot. Now, all other plots in my paper are handled using pgfplots (which doesn't do pie charts) and have their legend typeset by pgfplots.

It would thus be great if it were possible to create, re-using as many keys like /pgfplots/area legend as possible, to create a pgfplots-style legend in TiKZ. Has anyone done anything like this before?

Answer 1

Pgfplots has a couple of helper methods which do the job - and these methods are mostly independent of any axis. The only required things are the text labels and the styles for the individual images.

Here is a short draft which might do what you want:

\documentclass{article}

\usepackage{pgfplots}

% argument #1: any options
\newenvironment{customlegend}[1][]{%
    \begingroup
    % inits/clears the lists (which might be populated from previous
    % axes):
    \csname pgfplots@init@cleared@structures\endcsname
    \pgfplotsset{#1}%
}{%
    % draws the legend:
    \csname pgfplots@createlegend\endcsname
    \endgroup
}%

% makes \addlegendimage available (typically only available within an
% axis environment):
\def\addlegendimage{\csname pgfplots@addlegendimage\endcsname}

\begin{document}

\thispagestyle{empty}

\begin{tikzpicture}
    \begin{customlegend}[legend entries={$a$,$e^x$,C,$d$}]
    \addlegendimage{red,fill=black!50!red,area legend}
    \addlegendimage{red,fill=black!50!red,sharp plot}
    \addlegendimage{red,fill=black!50!red,mark=*,sharp plot}
    \addlegendimage{red,fill=black!50!red,ybar,ybar legend}
    \end{customlegend}
\end{tikzpicture}

\end{document}

The different \addlegendimage styles are a little bit ... inconsistent, but I wanted to experiment if they work. I guess that mesh legend might produce problems, so stick to the simpler ones...

Answer 2

And here is how to put a non-pgfplots style legend into pgfplots.

\documentclass{article}
\usepackage{pgfplots}
\begin{document}

\begin{tikzpicture}
\begin{axis}[xmin=0,xmax=10,ymin=-5,ymax=5,name=border]
\end{axis}

\node[draw=black,thick,rounded corners=2pt,below left=2mm] at (border.north east) {%
\begin{tabular}{@{}r@{ }l@{}}
 \raisebox{2pt}{\tikz{\draw[black] (0,0) -- (5mm,0);}}&black\\
 \raisebox{2pt}{\tikz{\draw[red] (0,0) -- (5mm,0);}}&red\\
 \raisebox{2pt}{\tikz{\draw[green] (0,0) -- (5mm,0);}}&green\\
 \raisebox{2pt}{\tikz{\draw[blue] (0,0) -- (5mm,0);}}&blue
\end{tabular}};

\end{tikzpicture}
\end{document}