Moving a TikZ node depending on its size

Question

The following MWE is a very abstracted version of some code in a library that I'm writing:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
\begin{tikzpicture}
    \node[draw] at (1,0) (A) {A};
    \coordinate (connection) at ($(A.north west)!0.66!(A.south west)$);
    \path[draw] (0,0) -- (connection);
\end{tikzpicture}
\end{document}

What I want to do is to move the 'A' node and the 'connection' coordinate upward a little bit, such that the line becomes perfectly horizontal.

Previously that was no problem, because I knew the node height in advance and I could just use the calc library to calculate the correct yshift, before drawing the node and the coordinate. However, now I'd like to do this in a way that depends on the height of the node, which might depend on its contents. So it seems like I have to draw the node first, before calculating its height and then moving it.

I know that I can get the height dynamically, as explained at How can I get the height of a TikZ node and store it in a length?, but I don't know if it's possible to move the node after it's been drawn.

Alternatively, is there a way to simply say "position the node's anchor at a point exactly 2/3 of the way from its north west to its south west?" If that can be done (for an arbitrary fraction) it would solve my problem.

Answer 1

Notice that any of the two @Qrrbrbirlbel's answers here and here is much better than this hack...

I leave this answer here as an exercise on how to compute a border anchor.

You can use the border anchors if the node is a square (or with fixed proportions). In this case, the point on the right side at 2/3 height is at an angle of 198.435° from the horizontal, so:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
\begin{tikzpicture}
    \node[draw] at (1,0) (A) {A};
    \coordinate (connection) at ($(A.north west)!0.66!(A.south west)$);
    \path[draw] (0,0) -- (connection);
    % if the node is a square, use the border anchor:
    % atan( (1/6)/(1/2) \approx 18.435
    \draw (2,0) -- ++(1,0) node[draw, anchor=198.435]{A};
\end{tikzpicture}
\end{document}

If the node shape is not fixed, that's a much more complex (I do not know if the node size is available for the border angle calculation).

It's trivial, but for completeness:

If the node text size is not known, I discovered that it's possible to access the node's box from within the anchors; the following (hack?) seems to work, although it seems that there is still a bit of inaccuracy in the positioning of the anchor:

\documentclass[border=10pt]{standalone}
\usepackage[T1]{fontenc}
\usepackage{tikz}
\usetikzlibrary{calc}
\newcommand\anchorat[1]{%
    % this will fail is "minimum width" or "minimum height" is in force
    \fpeval{180+atand(
                ((#1)-0.5)*(\ht\pgfnodeparttextbox+\dp\pgfnodeparttextbox+
                2*\pgfkeysvalueof{/pgf/inner ysep}+2*\pgfkeysvalueof{/pgf/outer ysep})/
                (0.5*(\wd\pgfnodeparttextbox+
                2*\pgfkeysvalueof{/pgf/inner xsep}+2*\pgfkeysvalueof{/pgf/outer xsep}))
            )}
}
\newcommand{\markpoint}[2][red]{%
    \draw [#1] #2 --++(-.1,-.1) -- ++(.2,.2) ++(-.2,0) -- ++(.2,-.2);
}
\begin{document}
\begin{tikzpicture}[every node/.append style={draw=gray, align=center,
                    line width=1mm, inner sep=1mm}]
        \draw (0,0) -- ++(1,0)
            node[anchor=\anchorat{1/3}] (A) {A};
        \draw (0,-2) -- ++(1,0)
            node[anchor=\anchorat{2/3}] (B) {Alfa Beta Delta\\ Gamma \\ Epsilon\vrule width 1pt height 3pt depth 8pt };
        \markpoint{($(A.north west)!{1/3}!(A.south west)$)}
        \markpoint{($(B.north west)!{2/3}!(B.south west)$)}
        \markpoint[blue]{($(B.north west)!{0}!(B.south west)$)}
        \markpoint[blue]{($(B.north west)!{1}!(B.south west)$)}
        \markpoint[green]{(B.text)}
        \markpoint[green]{(B.center)}
\end{tikzpicture}
\end{document}

It should be quite easy to change the \anchorat macro to specify any point in the border...

I followed the code that defines the size of the rectangle shape, and I am almost sure that the formulas here are correct (at least, they work for 0.0, 0.5, 1.0). Still, there is a clear error (although small) here. Still investigation.

Answer 2

Generic anchors provide an easy interface to add new anchors to (all) shapes. Though, in this case, they don't make much sense for circular nodes but just adding them to the rectangle shape (or declaring a new shape based on the rectangle) would restrict these new anchors only to this shape while they are practical for all rectangular shapes.

In this case, all nodes will always have all generated generic anchors (for a specific scope).

This does not add the horizontal line, for this to be part of a shape, we will indeed have to declare a new shape. (We could also cheat again and adjust the shape's path on-the-fly but at that point a proper shape declaration is much cleaner.) You might want to learn about \deferredanchor which allows more flexibility in anchors.

However, the various circuit shapes of TikZ und circuitkz are creating one shape with multiple instances with different numbers of, say, input anchors differently. These also draw some extra bit (a circle) if the input is negated.

You will need to adapt them to include the straight lines as part of the dynamically generated shape variations.

Code

\documentclass[tikz]{standalone}
\makeatletter
\pgfset{
  @generate anchor/.code args={#1:#2:#3:#4}{%
    \pgfdeclaregenericanchor{#1}{%
      \pgfpointlineattime{#2}
        {\pgf@sh@reanchor{##1}{#3}}{\pgf@sh@reanchor{##1}{#4}}}},
  generate anchors/.style n args={3}{
    /utils/tempa/.style={/pgf/@generate anchor={##1:#2:#3}},
    /utils/tempa/.list={#1}}}
\makeatother
\pgfset{generate anchors={in 1/2:.3333, in 2/2:.6667}{north west}{south west}}
\begin{document}
\begin{tikzpicture}
\node[draw, anchor=in 2/2] at (1, 0) (A) {A};
\draw (0,0) -- (A.in 2/2);
\end{tikzpicture}
\begin{tikzpicture}[
  shape example/.style={
    color=black!30, draw, fill=yellow!30,
    line width=+.5cm, inner xsep=+2.5cm, inner ysep=0.5cm},
  generate anchors=
    {in 1/3:.25, in 2/3:.5, in 3/3:.75}{north west}{south west},
  generate anchors=
    {out 1/4:.2, out 2/4:.4, out 3/4:.6, out 4/4:.8}{north east}{south east}]
\node[shape example] (s) {In Out Rectangle\vrule width 1pt height 2cm};
\foreach \anchor/\placement in
  {north west/above left, north/above, north east/above right,
%   west/left, center/above, east/right,
%   mid west/right, mid/above, mid east/left,
%   base west/left, base/below, base east/right,
   south west/below left, south/below, south east/below right,
%   text/left, 10/right, 130/above,
   {in 1/3}/left, {in 2/3}/left, {in 3/3}/left,
   {out 1/4}/right, {out 2/4}/right, {out 3/4}/right, {out 4/4}/right}
   \draw[shift=(s.\anchor)] plot[mark=x] coordinates{(0,0)}
     node[\placement] {\scriptsize\texttt{(s.\anchor)}};
\end{tikzpicture}
\begin{tikzpicture}[
    my anchors/.style = {
            generate anchors={in 1/2:.3333, in 2/2:.6667}{north west}{south west},
            generate anchors={mid 1/2:.3333, mid 2/2:.6667}{north}{south},
            generate anchors={out 1/2:.3333, out 2/2:.6667}{north east}{south east},
        }
    ]
    \node[draw, my anchors, anchor = mid 1/2] (a) at (0,0) {A};
    \node[draw, my anchors, anchor = mid 2/2] (b) at (1,0) {B};
    \draw[my anchors] (a.out 1/2) -- (b.in 2/2);
\end{tikzpicture}
\end{document}

Output

I'll say it again: The following rectangle also has the in 1/2 and in 2/2 anchors available that are defined in the preamble.

Answer 3

Here's a shape inout rectangle that supports multiple input and output anchors and the straight lines that come with it.

For now, only a maximum of 10 of those connections are supported. (The circuit shapes of TikZ allow for up to 1024 and also add the needed anchor definitions on-the-fly which I did not implement.) You will need to adjust the 10 yourself if you need more.

A few things to consider:

• Requesting an input or output anchor number that's above the specified number of anchors only raises a warning and not an error. It successfully returns a point but outside of the shape.

• PGF adds half the line width on the ends of the small straights (which is barely noticeable in the first example and hidden due to the annotations in the second).

• You can use the /tikz/inout rectangle/every in out style to change the output of all of those lines.
  In addition, for each of those line the following styles are selectively tried:

  • /tikz/inout rectangle/every in and
  • /tikz/inout rectangle/every out whih allow for different styles for input and output lines as well as
  • /tikz/inout rectangle/in 1, /tikz/inout rectangle/in 2, … and the same for out which enables the customization of each line separately.

• The \pgscope\begingroup … \tikz@finish\endpgfscope is basically a TikZ \path …;. It might be better to actually use such a \path but I didn't notice any drawbacks in this example.

• out 2/.style={Circle[open, length=+0pt +3, sep=+0pt +-.5]}- is obviously a bad user-interface to implement a negated output. If this is needed, we can implement something similar to what the circuit libraries of TikZ do.

• The undocumented \pgfmathloop … \repeatpgfmathloop is used which offers a nice compromise between speed (over \foreach) and convenience (over loops that don't come with their own counter).

Code

\documentclass[tikz]{standalone}
\usetikzlibrary{arrows.meta}
\makeatletter
\tikzset{% this is explicitly a TikZ shape
  inout rectangle/in  length/.initial=1cm,
  inout rectangle/out length/.initial=1cm,
  inout rectangle/every in out/.style=draw,
  inout rectangle/inputs/.initial=3,
  inout rectangle/outputs/.initial=3,
  inout rectangle/.code=\tikzset{shape=inout rectangle,inout rectangle/.cd,#1}}
\def\pgf@sh@inoutrectangle@test#1#2#3{\ifnum#1>#2\relax\pgfwarning{#3put #1\space not defined for this node.}\fi}
\pgfmathloop
  \expandafter\edef\csname pgf@anchor@inout rectangle@input \pgfmathcounter'\endcsname{%
    \noexpand\pgf@sh@inoutrectangle@test{\pgfmathcounter}{\noexpand\inputs}{In}%
    \noexpand\pgfpointlineattime{\pgfmathcounter/(\noexpand\inputs+1)}
      {\noexpand\pgf@sh@reanchor{inout rectangle}{north west}}
      {\noexpand\pgf@sh@reanchor{inout rectangle}{south west}}}%
  \expandafter\edef\csname pgf@anchor@inout rectangle@input \pgfmathcounter\endcsname{%
    \noexpand\pgf@sh@inoutrectangle@test{\pgfmathcounter}{\noexpand\inputs}{In}%
    \noexpand\pgfpointadd{\noexpand\pgf@sh@reanchor{inout rectangle}{input \pgfmathcounter'}}{%
      \noexpand\inout\pgf@x=-\pgf@y \pgf@y=0pt }}%
  \expandafter\edef\csname pgf@anchor@inout rectangle@output \pgfmathcounter'\endcsname{%
    \noexpand\pgf@sh@inoutrectangle@test{\pgfmathcounter}{\noexpand\outputs}{Out}%
    \noexpand\pgfpointlineattime{\pgfmathcounter/(\noexpand\outputs+1)}
      {\noexpand\pgf@sh@reanchor{inout rectangle}{north east}}
      {\noexpand\pgf@sh@reanchor{inout rectangle}{south east}}}%
  \expandafter\edef\csname pgf@anchor@inout rectangle@output \pgfmathcounter\endcsname{%
    \noexpand\pgf@sh@inoutrectangle@test{\pgfmathcounter}{\noexpand\outputs}{Out}%
    \noexpand\pgfpointadd{\noexpand\pgf@sh@reanchor{inout rectangle}{output \pgfmathcounter'}}{%
      \noexpand\inout\pgf@x=\pgf@x \pgf@y=0pt }}%
  \ifnum\pgfmathcounter<10\relax % max number of anchors: 10
\repeatpgfmathloop
\pgfdeclareshape{inout rectangle}{%
  \savedanchor\inout{% it's not a real anchor, it just saves two lengths in one macro
    \pgfpoint{\pgfkeysvalueof{/tikz/inout rectangle/in length}}%
             {\pgfkeysvalueof{/tikz/inout rectangle/out length}}}%
  \savedmacro\inputs {\pgfmathtruncatemacro\inputs {\pgfkeysvalueof{/tikz/inout rectangle/inputs}}}%
  \savedmacro\outputs{\pgfmathtruncatemacro\outputs{\pgfkeysvalueof{/tikz/inout rectangle/outputs}}}%
  \inheritsavedanchors[from=rectangle]\inheritanchor[from=rectangle]{base}%
  \inheritanchor[from=rectangle]{center}\inheritanchor[from=rectangle]{mid}
  \inheritanchor[from=rectangle]{north}\inheritanchor[from=rectangle]{south}%
  \inheritanchor[from=rectangle]{west}\inheritanchor[from=rectangle]{east}%
  \inheritanchor[from=rectangle]{mid west}\inheritanchor[from=rectangle]{base west}%
  \inheritanchor[from=rectangle]{north west}\inheritanchor[from=rectangle]{south west}%
  \inheritanchor[from=rectangle]{mid east}\inheritanchor[from=rectangle]{base east}%
  \inheritanchor[from=rectangle]{north east}\inheritanchor[from=rectangle]{south east}%
  \inheritanchorborder[from=rectangle]\inheritbackgroundpath[from=rectangle]%
  \behindbackgroundpath{% the lines are drawn behind the normal rectangle
    \ifnum\inputs>0
      \pgfmathloop
        \pgfscope\begingroup
          \tikzset{
            inout rectangle/every in out, inout rectangle/every in/.try,
            inout rectangle/in \pgfmathcounter/.try}%
          \pgfpathmoveto{\pgf@sh@reanchor{inout rectangle}{input \pgfmathcounter'}}%
          \pgfpathlineto{\pgf@sh@reanchor{inout rectangle}{input \pgfmathcounter}}%
        \tikz@finish\endpgfscope
        \ifnum\pgfmathcounter<\inputs\relax
      \repeatpgfmathloop
    \fi
    \ifnum\outputs>0
      \pgfmathloop
       \pgfscope\begingroup
         \tikzset{
            inout rectangle/every in out,  inout rectangle/every out/.try,
            inout rectangle/out \pgfmathcounter/.try}%
          \pgfpathmoveto{\pgf@sh@reanchor{inout rectangle}{output \pgfmathcounter'}}%
          \pgfpathlineto{\pgf@sh@reanchor{inout rectangle}{output \pgfmathcounter}}%
        \tikz@finish\endpgfscope
        \ifnum\pgfmathcounter<\outputs\relax
      \repeatpgfmathloop
    \fi
  }%
}
\makeatother
\begin{document}
\begin{tikzpicture}
\node[
  draw, inout rectangle={inputs=2, in 1/.style=path only, outputs=0},
  anchor=input 2'] (A) {A};
\end{tikzpicture}
\begin{tikzpicture}[
  shape example/.style={
    color=black!30, draw, fill=yellow!30,
    line width=+.5cm, inner xsep=+2.5cm, inner ysep=0.5cm}]
\node[
  shape example,
  inout rectangle={
    inputs=3,
    outputs=4,
    every in out/.append style={line width/.expanded=\the\dimexpr.5\pgflinewidth},
    out 2/.style={Circle[open, length=+0pt +3, sep=+0pt +-.5]}-
  }] (s) {Inout Rectangle\vrule width 1pt height 2cm};
\foreach \anchor/\placement in
  {north west/above left, north/above, north east/above right,
   south west/below left, south/below, south east/below right,
   input 1/left, input 2/left, input 3/left,
   input 1'/right, input 2'/right, input 3'/right,
   output 1/right, output 2/right, output 3/right, output 4/right,
   output 1'/left, output 2'/left, output 3'/left, output 4'/left}
   \draw[shift=(s.\anchor)] plot[mark=x] coordinates{(0,0)}
     node[\placement] {\scriptsize\texttt{(s.\anchor)}};
\end{tikzpicture}
\end{document}

Output