You can access the coordinate system, which is used to plot functions by axis cs as in
\draw (axis cs:0,0) -- (axis cs:1,1);
For more on accessing axis coordinates in graphical elements, see section 4.17.1 on page 290 of the pgfplots manual.
\documentclass[tikz]{standalone}
\usepackage{pgfplots}
\begin{document}
\begin{tikzpicture}
\begin{axis}
\addplot[blue,thick] coordinates {(0,0)(0.2,0)(0.8,1)(1,1)};
\draw[red] (axis cs:0,0) .. controls (axis cs:0.2,0) and (axis cs:0.8,1) .. (axis cs:1,1);
\end{axis}
\end{tikzpicture}
\end{document}
\draw (20,12) -- ++(2,0) -- ++(0,2) -- ++(-3,0) -- ++(45:3);
Use ++ before each new incremental coordinate to make it relative to the last one and put the pencil there.
Here's a complete example:
\documentclass{article}
\usepackage{tikz}
\begin{document}
\tikz\draw (20,12) -- ++(2,0) -- ++(0,2) -- ++(-3,0) -- ++(30:3) {[rounded corners=10pt]-- ++(5,0) -- ++(0,-6)} -- ++(-7,0) -- cycle;
\end{document}
Of course, combining this with the -| or |- path operators can simplify the code even further; the following two pieces of code produce the same result:
\tikz\draw (20,12) -- ++(2,0) -- ++(0,2) -- ++(3,0) -- ++(0,1) -- ++(1,0) -- ++(0,-3) -- ++(2,0);\par\bigskip
and
\tikz\draw (20,12) -| ++(2,2) -| ++(3,1) -- ++(1,0) |- ++(2,-3);
I don't think that defining commands in this case adds anything; in fact, I think it reduces the functionality of the existing syntax (which is already simple). The example demonstrates that you can use, for example, polar coordinates and modify (up to TikZ limitations) the path attributes midways; even if the current question doesn't require this, it's a good thing to have the possibility to do those kind of modification if they are required.
Best Answer
Add
align=centerdoes the trick:Code: