Complex objects in TikZ: pgfkeys scope and best practice

Question

I try to define a reusable object in TikZ and run into some troubles. The following minimal working example shows the problem.

\documentclass{article}

\usepackage{tikz}
%\usepackage{trace-pgfkeys}
\usetikzlibrary{calc}

\makeatletter

\pgfkeys{
  /object/.cd,
  angle/.initial=0,
}

\def\object[#1](#2,#3)#4;{
%  \pgfkeys{/object/.cd,#1,angle/.get=\@angle}
  \pgfkeys{/object/.cd,#1}
  \node (center) at (#2,#3) {#4};
  \coordinate (#4 center) at (center);
%  \draw [rotate around={\@angle:(center)}] ($(center)+(-1,-.5)$) coordinate (#4 a) rectangle ++(2,1);
  \draw [rotate around={\pgfkeysvalueof{/object/angle}:(center)}] ($(center)+(-1,-.5)$) coordinate (#4 a) rectangle ++(2,1);
%  \def\@angle{0}
}

\makeatother

\begin{document}
\begin{tikzpicture}
  \object[](0,0){A};
  \object[angle=30](3,0){B};
  \object[](6,0){C};

  \draw (A a) -- (B center);
\end{tikzpicture}
\end{document}

The mwe results in the following picture.

Object C is rotated as well, despite no angle is given. That tells me that I misunderstood how pgfkeys works and should be utilized. Desired is that the default value is used if the option angle is not given. How can it be done correct? And how can I get rid of the intermediate variable \@angle?

Bonus question: The manual states, that “.” shall not be used in coordinate names and it also does not work. But “object” coordinates defined by TikZ libraries make heavy use of “x.y” coordinate names. Is there a method to do it in the example above, since it would reflect how it is done by TikZ itself?

Related: this question.

Edit: I replaced some lines in the code so that the helper macro \@angle is no longer needed, see Answer of Qrrbrbirlbel.

Answer 1

Notes

• I have removed the calc library and used the keys xshift and yshift directly on the center node.

• The ; in your defintion of \object is actually not needed as you group the last argument anyway. With your definition, even \object[](,)text; is possible. Without the ; you must write \object[](,){text} (though an additional ; wouldn’t hurt than either).

  However, I have not changed your argument definition.

• I have provided an improved version of your macro:

  • I have replaced your \definition with a \newcommand that allows the first parameter to be optional.
  • The algorithm to create the rectangle is—with the help of another node—re-written.

---

The \pgfkeys in your macro sets the /object/angle key globally. Unless you make the change local (by including your macro in a set of braces { }) or backup its value it will not be changed.

The line

  \def\@angle{0}

will only change the \@angle macro, not the key!

There are other ways to “get” one value of PGF key. One would be the use of \pgfkeysgetvalue or \pgfkeysvalueof:

1. \pgfkeysgetvalue{<key>}{<macro>} saves the value of <key> in <macro>:

   \pgfkeys{/object/.cd,#1}
   \pgfkeysgetvalue{/object/angle}\@angle
   

2. \pgfkeysvalueof{<key>} expands to the current value of <key>:

   \pgfkeys{/object/.cd,#1} % and three lines later:
   \draw [rotate around={\pgfkeysvalueof{/object/angle}:(center)}] ([xshift=-1cm,yshift=-.5cm]center) coordinate (#4 a) rectangle ++(2,1);
   

You could also save the value directly to a macro:

1. Handler /.store in or /.estore in (expand its argument before saving):

   \pgfkeys{
     /object/.cd,
     angle/.store in=\@angle,
     angle=0,
   }
   

   Then \@angle can be used without the need to extra “get” the value inside the macro.

2. The handler .store in is just a short-cut, internally \def\@angle{#1} is used. In fact, we can use .code to even calculate the argument. In this case, that does not make much sense because we use the angle only with rotate or rotate around. These keys are already usable with a calculation (e.g. rotate=360-25+2*10).

   \pgfkeys{
     /object/.cd,
     angle/.code=\pgfmathsetmacro\@angle{#1},
     angle=0,
   }
   

Code

\documentclass[tikz]{standalone}
\makeatletter
\pgfkeys{
  /object/.cd,
  angle/.initial=0,
}

\def\object[#1](#2,#3)#4;{{
  \pgfkeys{/object/.cd,#1,angle/.get=\@angle}
  \node (center) at (#2,#3) {#4};
  \coordinate (#4 center) at (center);
  \draw [rotate around={\@angle:(center)}] ([xshift=-1cm,yshift=-.5cm]center) coordinate (#4 a) rectangle ++(2,1);
}}
\makeatother

\begin{document}
\begin{tikzpicture}
  \object[](0,0){A};
  \object[angle=30](3,0){B};
  \object[](6,0){C};

  \draw (A a) -- (B center);
\end{tikzpicture}
\end{document}

Output

Improvement (?)

Nodes do already understand the concept of rotation but not only is the shape rotated the content is too.

My solution provides two nodes that will be created:

• the un-rotated one with the text (in the example below in lightgray), name: x-<name>; and
• the rotated rectangle with text hidden, name: <name>.

Where <name> is either the name that is provided by the /object/name key or if that is empty the the node’s content (#4) is used.

The rotated node contains the text in \phantom so that it gets resized the same as the un-rotated node in case that the text is bigger than the minimum dimensions.

If you only want an \object to be rectangular, add shape=rectangle to the \node commands. Otherwise it could happen that a shape specification that is given to the command’s scope is used.

Code

\documentclass[tikz]{standalone}
\makeatletter
\pgfkeys{
  /object/.cd,
  angle/.initial=0,
  name/.initial={},
}

\newcommand*{\object}[1][]{\@object[#1]}
\def\@object[#1](#2,#3)#4;{{
  \pgfkeys{/object/.cd,#1}
  \pgfkeysgetvalue{/object/name}\@name% saves /object/name in \@name
  \ifx\@name\pgfutil@empty\edef\@name{#4}\fi% if no name is given use #4
  \node[
    draw=lightgray,% debug
             minimum width=2cm, minimum height=1cm, name/.expand once=x-\@name] at (#2,#3) {#4};
  \node[draw,minimum width=2cm, minimum height=1cm, name/.expand once=\@name, rotate=\pgfkeysvalueof{/object/angle}] at (#2,#3) {\phantom{#4}};
}}
\makeatother

\begin{document}
\begin{tikzpicture}
  \object(0,0){A};
  \object[angle=30](3,0){B};
  \object[name=C has another name](6,0){C};

  \draw (A.south west) -- (B.center);
  \draw[red] (B.north east) -- (x-B.north west) -- (C has another name.mid west);

  \draw[blue,bend right,->] (A) edge (B)
                            (B) edge (C has another name);
\end{tikzpicture}
\end{document}

Output

Answer 2

Here is a completely different approach using trapezium shape and shape border rotate key:

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{shapes.geometric}

\tikzset{
  rotated rectangle/.style={
    shape=trapezium,trapezium angle=90,
    shape border uses incircle,shape border rotate=#1,
    minimum width=2cm,minimum height=1cm,trapezium stretches=true,
  },
}

\begin{document}
\begin{tikzpicture}
  \node[draw,rotated rectangle=0] (A) at (0,0) {A};
  \node[draw,rotated rectangle=30] (B) at (3,0) {B};
  \node[draw,rotated rectangle=0] (C) at (6,0) {C};

  \draw (A.bottom left corner) -- (B.center);
  \draw[red] (B.top right corner) --  (C.mid west);
\end{tikzpicture}
\end{document}