[Tex/LaTex] Override \centering to left justify an image

algorithmsgraphicshorizontal alignment

Background

Dozens of source code snippets inserted into a document as images inside of Algorithm floats. Other images are screen captures, inserted as Graphics floats, to make a distinction. All Graphic floats should be centred, thus the preamble contains:

% Resize figures that are too wide for the page.
\let\oldincludegraphics\includegraphics
\renewcommand\includegraphics[2][]{%
  \oldincludegraphics[width=\ScaleIfNeeded]{#2}
  \centering
}

This works, as ScaleIfNeeded is defined elsewhere, resulting in all images being centred, including the Algorithm images.

Problem

The Algorithm floats also contain images, and these images are centred, which is undesirable. The code for each Algorithm resembles:

\begin{algorithm}[H]
\includegraphics{source/sql/query-formatted.sql.png}
\caption{\label{alg:Query-with-Formatting}Query with Formatting}
\end{algorithm}

Ideas

Tried:

% Centre algorithms.
\let\oldalgorithm\algorithm
\let\endoldalgorithm\endalgorithm
\renewenvironment{algorithm}[1][ht]{%
  \begin{flushleft}
  \oldalgorithm[#1]
  \end{flushleft}
  }%
  {\endoldalgorithm}

This results in a number of errors ("Missing } inserted", amongst others).

Question

How can images embedded exclusively within Algorithm floats be left-justified?

Bonus Question

How can a thick, left-hand vertical rule (or any stylistic change) be made to the Algorithm floats? For example, the left-hand border on the "batch source text" from this indirectly-related question. (Or any source code snippets on SuperUser.com, for that matter.)

Thank you!

Best Answer

This is untested, but how about something like the following?

\expandafter\def\expandafter\algorithm\expandafter{%
        \expandafter\let\expandafter\centering\expandafter\relax
        \algorithm
}

This makes \centering do nothing in the algorithm environment. (There's actually a better way to do such things with the etoolbox package.) If you want, you could replace \relax with \raggedright (or better \RaggedRight from the ragged2e package) if you really want that behavior. The flushleft environment is not what you want since that's going to add extra space.

Edit:
Actually, I've got a better idea than redefining \centering locally which just feels wrong. How about this:

\let\oldincludegraphics\includegraphics[2][]{%
        \oldincludegraphics[width=\ScaleIfNeeded]{#2}%
        \graphicsalignment
}
\expandafter\def\expandafter\algorithm\expandafter{%
        \expandafter\let\expandafter\graphicsalignment\expandafter\relax
        \algorithm
}
\let\graphicsalignment\centering

Bonus Question:
Here's one idea for getting a rule.

\newdimen\coderulewidth \coderulewidth=1em
\newdimen\coderulesep \coderulesep=1em
\newdimen\coderuleseptemp
\newbox\codebox
\newenvironment{coderule}[1][\coderulesep]{%
        \par
        \coderuleseptemp=#1\relax
        \setbox\codebox=\vbox\bgroup
                \linewidth=\dimexpr\linewidth-\coderulewidth-\coderulesep\relax
                \hsize=\linewidth
}{%
        \egroup
        \noindent
        \strut
        \hbox{%
                \vrule width\coderulewidth
                \kern\coderuleseptemp
                \box\codebox
        }%
}

As an example of usage, here are a few grafs with the thick rule on the left (this example needs the lipsum package).

\begin{coderule}
\lipsum[1-2]
\end{coderule}

For an algorithmic, the algorithm is already indented, so you can use the optional argument (or just redefine \coderulesep).

\begin{algorithm}
\begin{coderule}[0pt]
\begin{algorithmic}
\STATE $x\gets0$
\STATE $y\gets1$
\STATE $z\gets x+y$
\end{algorithmic}
\end{coderule}
\end{algorithm}

Related Solutions

[Tex/LaTex] Centering left justified text

To allow for a variable-width minipage environment, you need the varwidth package. From the package documentation:

The package deﬁnes a varwidth environment (based on minipage) which is an analogue of minipage, but whose resulting width is the natural width of its contents.

The minimal example as presented in the package documentation gives a view on what means:

An example of the varwidth environment from the package documentation

So, alter Stefan's answer in the following way:

\usepackage{varwidth}% http://ctan.org/pkg/varwidth
\newenvironment{texto}{%
  \begin{center} % so the minipage is centered
  \begin{varwidth}[t]{\textwidth}
  \raggedright % so the minipage's text is left justified
}{%
  \end{varwidth}
  \end{center}
}

varwidth vs minipage

[Tex/LaTex] Centering clrscode3e codebox horizontally

Since the codebox is ultimately typeset in a tabbing environment, its width may vary. Moreover, it is typeset in a box which is only processed at the end of the codebox environment. As such, you would need a slight work-around in order to center it horizontally.

The varwidth package is capable of shrinking its width to the natural width of its contents. As such, wrapping the codebox environment within a varwidth environment allows for centering capability:

enter image description here

\documentclass{article}
\usepackage[showframe]{geometry}% http://ctan.org/pkg/geometry
\usepackage{clrscode3e}% http://www.cs.dartmouth.edu/~thc/clrscode/
\usepackage{varwidth}% http://ctan.org/pkg/varwidth
\begin{document}
\begin{center}
  \begin{varwidth}{\linewidth}
    \begin{codebox}
      \Procname{$\proc{Insertion-Sort}(A)$}
      \li \For $j \gets 2$ \To $\attrib{A}{length}$
      \li \Do $\id{key} \gets A[j]$
      \li \Comment Insert $A[j]$ into the sorted sequence $A[1 \twodots j-1]$.
      \li $i \gets j-1$
      \li \While $i > 0$ and $A[i] > \id{key}$
      \li \Do
            $A[i+1] \gets A[i]$
      \li $i \gets i-1$
          \End
      \li $A[i+1] \gets \id{key}$
      \End
    \end{codebox}
  \end{varwidth}
\end{center}
\end{document}

The varwidth environment is set to the maximum (\linewidth), since it will shrink to the desired width if the codebox is not as wide.

The showframe option to geometry allows for a visual of the text block boundaries.

My original approach was to use the savepos module of the zref package to mark the left-most and right-most points in the code via the macro \zsavepos{<label>}. Then, using \zposx{<ref>}, one can extract the x-coordinate (in small point sp units) of the label. So, marking the left-most point using \zsavepos{codeL} and the right-most point using \zsavepos{codeR},

\dimexpr\zposx{codeR}sp-\zposx{codeL}sp\relax

gives the horizontal width (or dimension) of the codebox. Subsequently, putting the entire codebox environment in a minipage of this width allows us to constrain the horizontal span and center the object. The correct width also avoids overfull \hbox warnings (if a chosen minipage width is too small) or incorrect centering (if a chosen minipage width is too large).

\documentclass{article}
\usepackage[showframe]{geometry}% http://ctan.org/pkg/geometry
\usepackage{clrscode3e}% http://www.cs.dartmouth.edu/~thc/clrscode/
\usepackage[savepos]{zref}% http://ctan.org/pkg/zref
\begin{document}
\begin{center}
  \begin{minipage}{\dimexpr\zposx{codeR}sp-\zposx{codeL}sp\relax}
    \begin{codebox}
      \Procname{\zsavepos{codeL}$\proc{Insertion-Sort}(A)$}
      \li \For $j \gets 2$ \To $\attrib{A}{length}$
      \li \Do $\id{key} \gets A[j]$
      \li \Comment Insert $A[j]$ into the sorted sequence $A[1 \twodots j-1]$.\zsavepos{codeR}
      \li $i \gets j-1$
      \li \While $i > 0$ and $A[i] > \id{key}$
      \li \Do
            $A[i+1] \gets A[i]$
      \li $i \gets i-1$
          \End
      \li $A[i+1] \gets \id{key}$
      \End
    \end{codebox}
  \end{minipage}
\end{center}
\end{document}

The above code (or procedure) was taken directly from the clrscode3e package documentation. The right-most label depends on the code segment being typeset, while the left-most label is typeset to the left of the procedure name. However, it is not necessary for the final production and centering capabilities. Since this uses the zref package, at least two compiles are required to obtain the correct positioning of the labels/references.