latex/tikz macro conditional

Question

I'm writing a latex macro which includes a tikz drawing, now I'd like to draw one path only if the optional parameter is set.

How can you interact from within tikz with the parameters given from latex?

something like this:

\newcommand{\myTikzDrawing}[1][default]{
    \begin{tikzpicture}
        \draw (0,1) -- (1,1);
        \draw (0,0) -- (1,0); %this line should only be drawn, if #1 is set to the default value
    \end{tikzpicture}
}

Answer 1

You can use the is if key to introduce a conditional.

\documentclass{article}
\usepackage{tikz}
\newif\ifTikZdrawthis
\tikzset{draw this/.is if=TikZdrawthis,draw this/.default=true}
\newcommand{\myTikzDrawing}[1][draw this=true]{
    \begin{tikzpicture}[#1]
        \draw (0,1) -- (1,1);
        \ifTikZdrawthis
        \draw (0,0) -- (1,0); %this line should only be drawn, if #1 is set to the default value
        \fi
    \end{tikzpicture}
}
\begin{document}
\myTikzDrawing
\bigskip

\myTikzDrawing[blue]
\bigskip

\myTikzDrawing[red,draw this]
\end{document}