Use varwidth with algorithm2e

Question

I’m trying to draw a box around an algortihm2e construct, like this:

I tried to use the varwidth package to get a box with the natural width of the content:

\documentclass{article}

\usepackage{algorithm2e}
\usepackage{varwidth}

\begin{document}
    \fbox{\begin{varwidth}{10cm}
        \If{condition}{
            loop content
        }
    \end{varwidth}}
\end{document}

Unfortunatly, the result looks like this: It looks like varwidth takes the maximum width when an \If or \For construct is used inside. How can I get a box with the natural width?

The concept of natural width does not apply. Like \vbox, it will fill the available space (\hsize}. — John Kormylo
– John Kormylo, Commented Aug 23, 2019 at 15:57

Roman Langrehr · Accepted Answer · 2019-08-28 08:53:20Z

Meanwhile, I came up with a hack myself: Overwriting the internal macro of algorithm2e that draws the blocks and use the varwidth environment there.

Here is a solution for the vlined option:

\documentclass{article}

\usepackage[vlined]{algorithm2e}
\usepackage{varwidth}

\makeatletter
\renewcommand{\algocf@Vline}[1]{%     no vskip in between boxes but a strut to separate them, 
    \strut\par\nointerlineskip% then interblock space stay the same whatever is inside it
    \algocf@push{\skiprule}%        move to the right before the vertical rule
    \vbox{\hbox{\vrule%
        \begin{varwidth}{\hsize}%
            \vbox{\algocf@push{\skiptext}%move the right after the rule
                \hbox{%
                    \algocf@addskiptotal%
                    \begin{varwidth}{\hsize}%
                        #1% inside the block
                    \end{varwidth}%
                }%
                \Hlne}%
        \end{varwidth}%
    }\vskip\skiphlne}%
    \algocf@pop{\skiprule}%\algocf@subskiptotal% restore indentation
    \nointerlineskip}% no vskip after

\renewcommand{\algocf@Vsline}[1]{%    no vskip in between boxes but a strut to separate them, 
    \strut\par\nointerlineskip% then interblock space stay the same whatever is inside it
    \algocf@bblockcode%
    \algocf@push{\skiprule}%        move to the right before the vertical rule
    \hbox{\vrule%               the vertical rule
        \begin{varwidth}{\hsize}%
            \vbox{\algocf@push{\skiptext}%move the right after the rule
                \hbox{\algocf@addskiptotal%
                    \begin{varwidth}{\hsize}%
                        #1% inside the block
                    \end{varwidth}%
                }}%
        \end{varwidth}%
    }%
    \algocf@pop{\skiprule}% restore indentation
    \algocf@eblockcode%
}
\makeatother

\begin{document}
    \fbox{\begin{varwidth}{\hsize}
            \If{condition}{
                loop content

                a line longer than the loop header
            }
    \end{varwidth}}
\end{document}

With other options for the block style \algocf@Noline might have to be adapted similarly (not tested).

John Kormylo · Accepted Answer · 2019-08-23 17:04:16Z

0

Here is a kludge using \tikzmarks to locate the top, bottom and right side (more or less).

Note that without the minipage, algorithm2e will use space outside the margins.

\documentclass{article}

\usepackage{algorithm2e}
\usepackage{tikz}
\usetikzlibrary{tikzmark}

\begin{document}
    \begin{minipage}{\textwidth}
      \tikzmark{A}\If{condition\tikzmark{B}}{
            loop content
        }\tikzmark{C}
    \end{minipage}%
    \begin{tikzpicture}[overlay, remember picture]
      %\draw[red] (pic cs:A) -- (pic cs:B) -- (pic cs:C);
      \path (pic cs:B) node[right, inner sep=0pt] (BB) {\phantom{ \textbf{then}}};
      \path (pic cs:C) ++(0,\baselineskip) coordinate (CC);
      \draw (pic cs:A) ++(0, \ht\strutbox)  rectangle (BB.east |- CC);
    \end{tikzpicture}
\end{document}

edited Aug 23, 2019 at 17:04

answered Aug 23, 2019 at 16:57

John Kormylo

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Your solution requires \tikzmark{B} to be placed at the end of the longest line, when the loop body is wider than the loop header. I’m interested in a more general solution that works independent of what is inside the loop body.

Roman Langrehr
– Roman Langrehr

2019-08-24 08:45:57 +00:00
Commented Aug 24, 2019 at 8:45

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