Justification of last line in caption

Question

I am using the caption package to style my captions.
Consider a small wrapfigure which has a wide caption that is broken into n lines.
I want the first n-1 lines of the caption to use justification=justified, whereas the last line (which does not fill the width available to the caption) shall be raggedleft.
Optimally I would love to be able to specify a different justification for the last line of a caption, independently of the the floating environment, e.g. by specifying
captionsetup{justification=justified, lastlinejustification=raggedleft} or some other value.
I know that the caption package provides centerlast, so something like raggedleftlast would also be great ;)

egreg · Accepted Answer

I know why it works.
A variation on John Kormylo's answer, without redefining internals of caption, but rather adding a justification mode.
documentclass{article}
usepackage{caption}
usepackage{wrapfig}
usepackage{lipsum}

DeclareCaptionOptionNoValue*{rjustified}{%
  caption@setformat{plain}%
  caption@setjustification{rjustified}%
}
DeclareCaptionJustification{rjustified}{rjustified}
makeatletter
newcommandrjustified{%
  let@fillcr
  leftskipz@@plus 1fil
  rightskipz@@plus -1fil
  parfillskipz@@plus 1filrelax
}
% don't bother with this if you don't plan to use  in a caption
protecteddef@fillcr{%
  let reserved@e relax
  let reserved@f relax
  @ifstar{let reserved@e vadjust let reserved@f nobreak
             @xnewlinefill}%
  @xnewlinefill}
def@xnewlinefill{@ifnextchar[% ] bracket matching
                  @newlinefill
                 {@gnewlinefillrelax}}
def@newlinefill[#1]{let reserved@e vadjust
                   @gnewlinefill {vskip #1}}
def@gnewlinefill #1{%
  ifvmode
    @nolnerr
  else
    unskip reserved@e {reserved@f#1}nobreak hfill break
  fi}
%%%% end of `no bother with this'
makeatother

begin{document}

begin{wrapfigure}{l}{4cm}
centering
captionsetup{justification=rjustified}
fbox{rule{3cm}{0pt}rule{0pt}{3cm}}
caption{lipsum[1][2-3]}
end{wrapfigure}

lipsum[1-2]

end{document}

If you don't plan to use  in captions when justification=rjustified is active, remove the let@fillcr instruction and the lines in the code above where @fillcr is defined mimicking @normalcr. Surely @centercr is not what you want here.
How does it work? Every line in a paragraph has glue at either side of amount leftskip and rightskip respectively. For a normal (justified) paragraph, they are both set to zero.
Here the former is set to zero but with positive infinite stretchability and the latter to zero with negative infinite stretchability. Therefore they normally cancel each other and nothing strange happens. However, TeX adds parfillskip glue to the last line of a paragraph; its value is normally 0pt plus 1fil (the same as is set here, just for safety). This glue will cancel the negative infinite stretchability of rightskip on the last line only, so in this line the positive stretchability of leftskip will act and move the last line to be flush right.
Of course you don't want to have more than one paragraph in the caption.
The @fillcr business is a variant of @normalcr where hfill is used instead of hfil, so the higher degree of infinity will prevail over the fil units of leftskip and rightskip.

John Kormylo · Answer

I don't know why it works, but it does.
documentclass{article}
usepackage{caption}
captionsetup{justification=centerlast}
usepackage{lipsum}% MWE only

makeatletter
renewcommandcenterlast{%
  let@centercr
  leftskipz@@plus 1fil%
  rightskipz@@plus -1fil%
  parfillskipz@@plus 1filrelax}
makeatother

begin{document}

begin{figure}
caption{LipsumPar{2}}
end{figure}

end{document}

Justification of last line in caption

2 Answers

Add your own answers!

Ask a Question