Draw a rectangle with partly invisible edges, only corners

Question

I want to create the following:

That is, a rectangle with partly invisible edges.

How can I do that?

What I have now:

\documentclass{article}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
\node[draw,rectangle,minimum width=8cm,minimum height=2cm] {lorem ipsum};
\end{tikzpicture}
\end{document}

Answer 1

Less elegant than Jasper Habicht's answer, but if you only need that box maybe it is simpler.

\documentclass{article}
\usepackage{tikz}

\newcommand{\mybox}[2][black]{%
  \begin{tikzpicture}
    \node[rectangle,minimum width=8cm,minimum height=2cm, font=\Large] (A) {#2};
    \draw[#1, line width = 3pt] 
      (A.north west) -- +(.3,0) -- (A.north west) -- +(0,-.4) 
      (A.north east) -- +(-.3,0) -- (A.north east) -- +(0,-.4) 
      (A.south west) -- +(.3,0) -- (A.south west) -- +(0,.4) 
      (A.south east) -- +(-.3,0) -- (A.south east) -- +(0,.4) 
      ;
   \end{tikzpicture}%
}

\begin{document}
\mybox{lorem ipsum}
\vspace{1cm}

\mybox[red]{lorem ipsum}
\end{document}

EDIT: parametric length

\documentclass{article}
\usepackage{tikz}

\newcommand{\mybox}[3][black]{%
  \begin{tikzpicture}
    \node[rectangle,minimum width=8cm,minimum height=2cm, font=\Large] (A) {#2};
    \draw[#1, line width = 3pt] 
      (A.north west) -- +(#3,0) -- (A.north west) -- +(0,-#3) 
      (A.north east) -- +(-#3,0) -- (A.north east) -- +(0,-#3) 
      (A.south west) -- +(#3,0) -- (A.south west) -- +(0,#3) 
      (A.south east) -- +(-#3,0) -- (A.south east) -- +(0,#3) 
      ;
   \end{tikzpicture}%
}

\begin{document}
\mybox{lorem ipsum}{.3}
\vspace{1cm}

\mybox[red]{lorem ipsum}{.3}
\vspace{1cm}

\mybox{lorem ipsum}{.4}
\vspace{1cm}

\mybox[green]{lorem ipsum}{.4}
\vspace{1cm}

\mybox{lorem ipsum}{.7}
\vspace{1cm}

\mybox[cyan]{lorem ipsum}{.7}
\end{document}

Answer 2

The best thing would probably be to create your own shape.

Here, it's also much easier to take the outer seps into account.

\documentclass{article}
\usepackage{tikz}
\pgfset{corners rectangle size/.initial=10pt}
\makeatletter
\pgfdeclareshape{corners rectangle}{%
    \inheritsavedanchors[from=rectangle]%
    \inheritanchorborder[from=rectangle]%
    \inheritanchor[from=rectangle]{north}%
    \inheritanchor[from=rectangle]{north west}%
    \inheritanchor[from=rectangle]{north east}%
    \inheritanchor[from=rectangle]{center}%
    \inheritanchor[from=rectangle]{west}%
    \inheritanchor[from=rectangle]{east}%
    \inheritanchor[from=rectangle]{mid}%
    \inheritanchor[from=rectangle]{mid west}%
    \inheritanchor[from=rectangle]{mid east}%
    \inheritanchor[from=rectangle]{base}%
    \inheritanchor[from=rectangle]{base west}%
    \inheritanchor[from=rectangle]{base east}%
    \inheritanchor[from=rectangle]{south}%
    \inheritanchor[from=rectangle]{south west}%
    \inheritanchor[from=rectangle]{south east}%
    \foregroundpath{
    % store lower right in xa/ya and upper right in xb/yb
      \southwest \pgf@xa=\pgf@x \pgf@ya=\pgf@y
      \northeast \pgf@xb=\pgf@x \pgf@yb=\pgf@y
      \pgfmathsetlength\pgf@xc{\pgfkeysvalueof{/pgf/outer xsep}}%
      \pgfmathsetlength\pgf@yc{\pgfkeysvalueof{/pgf/outer ysep}}%
      \advance\pgf@xa by \pgf@xc \advance\pgf@xb by -\pgf@xc
      \advance\pgf@ya by \pgf@yc \advance\pgf@yb by -\pgf@yc
      \pgfmathsetlength\pgfutil@tempdima{\pgfkeysvalueof{/pgf/corners rectangle size}}%
      \pgfpathmoveto{\pgfqpoint{\dimexpr\pgf@xa+\pgfutil@tempdima}{\pgf@ya}}%
      \pgfpathlineto{\pgfqpoint{\pgf@xa}{\pgf@ya}}%
      \pgfpathlineto{\pgfqpoint{\pgf@xa}{\dimexpr\pgf@ya+\pgfutil@tempdima}}%
      \pgfpathmoveto{\pgfqpoint{\dimexpr\pgf@xa+\pgfutil@tempdima}{\pgf@yb}}%
      \pgfpathlineto{\pgfqpoint{\pgf@xa}{\pgf@yb}}%
      \pgfpathlineto{\pgfqpoint{\pgf@xa}{\dimexpr\pgf@yb-\pgfutil@tempdima}}%
      \pgfpathmoveto{\pgfqpoint{\dimexpr\pgf@xb-\pgfutil@tempdima}{\pgf@ya}}%
      \pgfpathlineto{\pgfqpoint{\pgf@xb}{\pgf@ya}}%
      \pgfpathlineto{\pgfqpoint{\pgf@xb}{\dimexpr\pgf@ya+\pgfutil@tempdima}}%
      \pgfpathmoveto{\pgfqpoint{\dimexpr\pgf@xb-\pgfutil@tempdima}{\pgf@yb}}%
      \pgfpathlineto{\pgfqpoint{\pgf@xb}{\pgf@yb}}%
      \pgfpathlineto{\pgfqpoint{\pgf@xb}{\dimexpr\pgf@yb-\pgfutil@tempdima}}%
      \pgfsetarrowsstart{}%
      \pgfsetarrowsend{}%
    }%
}%
\makeatother
\begin{document}
\begin{tikzpicture}[minimum width=8cm, minimum height=2cm, nodes=corners rectangle]
\node[draw] {lorem ipsum};
\node[corners rectangle size=15pt, draw=red, thick] at (0, -3) (a) {lorem ipsum};
\foreach \ang in {5,...,20} \draw (a.\ang) --+(\ang:.5);
\end{tikzpicture}
\end{document}

---

As an easy workaround, you can make use of append after command and the like.

With \pgfsettransform we make sure that the same transformation are used that were applied to the node, making this independently from the path those corners are drawn on.

There's no consideration for outer sep or the line width.

\documentclass{article}
\usepackage{tikz}
\tikzset{
  draw corners/.style={
    append after command={\bgroup
      \pgfextra{\pgfsettransform{\csname pgf@sh@nt@\tikzlastnode\endcsname}}
      [to path=|-(\tikztotarget)]
                   ([yshift=-\pgfkeysvalueof{/tikz/draw corners size}]\tikzlastnode.north west)
          edge[#1] ([xshift= \pgfkeysvalueof{/tikz/draw corners size}]\tikzlastnode.north west)
                   ([yshift=-\pgfkeysvalueof{/tikz/draw corners size}]\tikzlastnode.north east)
          edge[#1] ([xshift=-\pgfkeysvalueof{/tikz/draw corners size}]\tikzlastnode.north east)
                   ([yshift= \pgfkeysvalueof{/tikz/draw corners size}]\tikzlastnode.south east)
          edge[#1] ([xshift=-\pgfkeysvalueof{/tikz/draw corners size}]\tikzlastnode.south east)
                   ([yshift= \pgfkeysvalueof{/tikz/draw corners size}]\tikzlastnode.south west)
          edge[#1] ([xshift= \pgfkeysvalueof{/tikz/draw corners size}]\tikzlastnode.south west)
      \egroup}},
  draw corners size/.initial=10pt}
\begin{document}
\begin{tikzpicture}[rectangle, minimum width=8cm, minimum height=2cm]
\path[rotate=30]node[rotate=10, draw corners] at (0,0) {lorem ipsum};
\tikzset{draw corners size=15pt}
\node[scale=.5, draw corners={red, thick}] at (0,-3) {lorem ipsum};
\end{tikzpicture}
\end{document}

---

You could also use path picture to avoid nesting paths:

\documentclass{article}
\usepackage{tikz}

\tikzset{
    draw corners/.style={
        path picture={
            \draw[#1]
                (path picture bounding box.north west) 
                    +(\pgflinewidth,-\pgfkeysvalueof{/tikz/draw corners size}) |- 
                    +(\pgfkeysvalueof{/tikz/draw corners size},-\pgflinewidth)
                (path picture bounding box.south west) 
                    +(\pgflinewidth,\pgfkeysvalueof{/tikz/draw corners size}) |- 
                    +(\pgfkeysvalueof{/tikz/draw corners size},\pgflinewidth)
                (path picture bounding box.north east) 
                    +(-\pgflinewidth,-\pgfkeysvalueof{/tikz/draw corners size}) |- 
                    +(-\pgfkeysvalueof{/tikz/draw corners size},-\pgflinewidth)
                (path picture bounding box.south east) 
                    +(-\pgflinewidth,\pgfkeysvalueof{/tikz/draw corners size}) |- 
                    +(-\pgfkeysvalueof{/tikz/draw corners size},\pgflinewidth);
        }
    },
    draw corners size/.initial=10pt
}

\begin{document}
\begin{tikzpicture}

\node[draw corners, rectangle, minimum width=8cm, minimum height=2cm] 
    at (0,0) {lorem ipsum};

\end{tikzpicture}
\end{document}

Answer 3

One option whithout tikz: just a table.

\documentclass[twocolumn]{article}
\usepackage{lipsum,parskip}
\usepackage{tabulary}
\def\notecorner#1{\medskip\par{\noindent\centering\begin{tabulary}{\linewidth}{cJc}
\cline{1-1}\cline{3-3}\multicolumn{1}{|c}{}&&\multicolumn{1}{c|}{}\\
&#1&\\\multicolumn{1}{|c}{} &  & \multicolumn{1}{c|}{}\\
\cline{1-1}\cline{3-3}\end{tabulary}\medskip\par}}
\begin{document}

\lipsum[1][1-5]

\notecorner{\lipsum[2][1]}

\lipsum[3][1-5]

\end{document}

Answer 4

Here you have two more solutions.

The first one uses path picture option to define a TiKZ style with all node's corners. This way the extra path proposed by CarlaTeX is not needed.

The second defines a tcolorbox instead of a TiKZ node.

\documentclass{article}
\usepackage{tikz}

\usepackage[most]{tcolorbox}

\usepackage{lipsum}

\newtcolorbox{corners}[1][]{%
    enhanced, colback=white, sharp corners,
    colframe=blue,
    frame code={%
        \draw[tcbcolframe] ([xshift=5mm]frame.north west)-|+(-5mm,-4mm);
        \draw[tcbcolframe] ([xshift=-5mm]frame.north east)-|+(5mm,-4mm);
        \draw[tcbcolframe] ([xshift=5mm]frame.south west)-|+(-5mm,4mm);
        \draw[tcbcolframe] ([xshift=-5mm]frame.south east)-|+(5mm,4mm);
    },
    #1
}

\tikzset{
    corners/.style={%
        path picture={%
            \draw[#1] ([xshift=5mm]path picture bounding box.north west)-|+(-5mm,-4mm);
            \draw[#1] ([xshift=-5mm]path picture bounding box.north east)-|+(5mm,-4mm);
            \draw[#1] ([xshift=5mm]path picture bounding box.south west)-|+(-5mm,4mm);
            \draw[#1] ([xshift=-5mm]path picture bounding box.south east)-|+(5mm,4mm);
        }
    },
    corners/.default={}
}
\newcommand{\mybox}[2][black]{%
\begin{tikzpicture}
\node[minimum width=8cm,minimum height=2cm, font=\Large, corners=#1] (A) {#2};
\end{tikzpicture}%
}

\begin{document}
\mybox{lorem ipsum}
\vspace{1cm}

\mybox[green, line width=1mm]{lorem ipsum}

\begin{corners}
\lipsum[1][1-3]
\end{corners}

\begin{corners}[colframe=red]
\lipsum[1][2-4]
\end{corners}
\end{document}

Answer 5

Based on @CarLaTeX's answer, this one

• Supports using x=<dimen>, y=<dimen> to change the corner size,
• Makes sure each line segment is drawn only once. (Previously horizontal segments were drawn twice.)

\documentclass{article}
\usepackage{tikz}

\newcommand{\mybox}[2][black]{%
  \begin{tikzpicture}
    \node[rectangle, minimum width=8cm, minimum height=2cm, font=\Large] (A) {#2};
    \draw[x=.3cm, y=.4cm, line width = 3pt, #1]
      (A.north west) +( 1,0) -- (A.north west) -- +(0,-1) 
      (A.north east) +(-1,0) -- (A.north east) -- +(0,-1) 
      (A.south west) +( 1,0) -- (A.south west) -- +(0, 1)
      (A.south east) +(-1,0) -- (A.south east) -- +(0, 1)
      ;
   \end{tikzpicture}%
}

\begin{document}
\mybox{lorem ipsum}
\bigskip

\mybox[red, x=1.5cm, y=.2cm]{lorem ipsum}
\bigskip

\mybox[cyan!50, dotted, x=.5cm, y=.5cm, rounded corners=.2cm]{lorem ipsum}
\end{document}