Message-Id: <9311241427.AA26466@sc.ZIB-Berlin.DE>
Reply-To: Mailing list for the LaTeX3 project <LATEX-L@vm.urz.Uni-Heidelberg.de>
Date:         Wed, 24 Nov 93 06:24:32 PST
From: Donald Arseneau <asnd@ERICH.TRIUMF.CA>
Sender: Mailing list for the LaTeX3 project <LATEX-L@vm.urz.Uni-Heidelberg.de>
To: Multiple Recipients of <LATEX-L@vm.urz.Uni-Heidelberg.de>
Subject:      Re: \em and italic correction
Status: R


I made automatic italic correction macros a while ago; but nothing
can work automatically all the time.

The following explanation should appear sometime in TTN `hey it works'.

Donald Arseneau                         asnd@reg.triumf.ca

\documentstyle{article}
\begin{document}
%\showboxdepth999 \showboxbreadth999 \tracingoutput1
\begingroup

\def\optional#1{} % ignore optional text
% \def\optional{}  % do include optional text

\makeatletter

% Copy definition of \frac out of the TeXbook; call it \Frac because
% LaTeX has \frac
\newcommand\Frac[2]{\leavevmode\nobreak\hskip.1em
  \raise.5ex\hbox{\the\scriptfont0 #1}\kern-.15em
  /\kern-.15em\lower.25ex\hbox{\the\scriptfont0 #2}}


\let\@tempb\relax % strange bug in *Old* LaTeX

%===============================================================
% When get \em starting italic text, launch an italic correction aimed at
% the end of the group. When \em ends the italic, do a smart italic correction.

\@ifundefined{normalshape}{%
  \def\pem{\ifdim \fontdimen\@ne\font>\z@ \rm
    \else \it \expandafter\aftergroup \fi \smartitcor}%
}{%
  \def\pem{\@nomath\em \ifdim \fontdimen\@ne\font >\z@ \normalshape
    \else \it \expandafter\aftergroup \fi \smartitcor}%
}

\def\smartitcor{\ifhmode \expandafter \itpunclook \fi}
\def\itpunclook{\begingroup \futurelet \@tempa \itcortest}

\def\itcortest{\def\@tempb{\@tempa}%
\ifcat\noexpand\@tempa,% if next character could be punctuation,
   \setbox\z@\hbox{\@tempb}% check its size...
   \ifdim\ht\z@<.3ex % and if it is short,...
      \let\itcordo\endgroup % suppress italic correction
\fi\fi
\itcordo}

\def\itcordo{% Put \/ before any preceding space.
  \skip@\lastskip
  \ifdim\skip@=\z@skip \/\else\unskip \/\hskip\skip@ \fi
  \endgroup}


\noindent Many people are not aware of, or simply ignore, the ``italic
correction'' command (\verb"\/") that should be inserted after slanted
text for proper spacing (see The \TeX\-book, p.~14).
\optional{Compare d{\em d\hskip0pt}d % suppress automatic \/
with d{\em d}d. }% gets automatic \/ inserted
It is a tedious
and thankless task inserting such corrections in collaborators' flawed
\LaTeX\ input. Instead, it would be nice to have \LaTeX\ insert the
corrections automatically.  A problem that arises is that the \verb"\/"
should be omitted when followed by low punctuation (period or comma).
Furthermore, when the surrounding text is italic, \verb"\em"\,phasis
produces {\em roman} text, and the italic correction should be placed
{\em before}~it.  This is a particular problem for macros like
\verb"\newcommand{\abi}{{\em ab~initio\/}}" that do not know their
context.  Here is a replacement for \LaTeX's \verb"\em" command that
correctly inserts its own italic correction in these cases so you can
avoid typing \verb"\/" altogether.

First, modify the \verb"\pem" command slightly so that it inserts a
`smart' italic correction; either immediately if the text switches to
roman, or launching it towards the end of the group if the text
switches to italics.
\begin{verbatim}
  \def\pem{\ifdim \fontdimen 1\font>0pt \rm
    \else \it \expandafter\aftergroup \fi \smartitcor}
\end{verbatim}
\optional{or, for {\small NFSS}
\begin{verbatim}
  \def\pem{\@nomath\em \ifdim\fontdimen\@ne\font>\z@ \normalshape
    \else \it \expandafter\aftergroup \fi \smartitcor}
\end{verbatim}}

The smart italic correction is only executed in horizontal (\,rl\,)
mode.  When it is executed, it first looks at the next character
(token) to see if it is a comma or period (or something else that
is short).
\begin{verbatim}
  \def\smartitcor{\ifhmode \expandafter \itpunclook \fi}
  \def\itpunclook{\begingroup \futurelet \ITCtempa \itcortest}

  \def\itcortest{%           test next character (\ITCtempa)
   \def\ITCtempb{\ITCtempa}%     hide next when skipping
   \ifcat\noexpand\ITCtempa ,%   if it could be punctuation,...
      \setbox0\hbox{\ITCtempb}%  check its size...
      \ifdim\ht0<.3ex %          and if it is short,...
         \let\itcordo\endgroup % suppress italic correction
   \fi\fi \itcordo}%             otherwise, do it
\end{verbatim}
The \verb"\noexpand\ITCtempa" is used in case the next token is a
macro, which should not be expanded out of context. The extra level
of definition, \verb"\ITCtempb", is used in case the next token is a
conditional command like \verb"\if" or \verb"\fi" which could not be
skipped over properly when the \verb"\ifcat" is false.

Finally, the italic correction must {\em precede}
any spaces or it is useless.
\begin{verbatim}
\def\itcordo{% Put \/ before any preceding space.
  \skip0=\lastskip
  \ifdim\skip0=0pt\/\else\unskip \/\hskip\skip0 \fi
  \endgroup}
\end{verbatim}
Here we check for preceding space (glue or skip) by
comparing the length of \verb"\lastskip" with \verb"0pt".
If the previous glue was \verb"\hfil" there will be no
italic correction, but it is probably unnecessary in
that case anyway.

\optional{%
These definitions can be streamlined by using internal commands
such as \verb"\z@".  If you look at the source for the electronic
version of this newsletter, you will see that the macros {\em
really are} written that way.
}

These macros are intended for \verb"\em"
delimited by grouping, such as
\begin{verbatim}
 My book is called {\em You named the baby {\em what?!}}\\
 \begin{em}
 Sam Spade had {\em never} seen that {\em modus operandi} before.
 \end{em}
\end{verbatim}
\begin{center}
My book is called {\em You named the baby {\em what?!}}

\begin{em}
Sam Spade had {\em never} seen that {\em modus operandi} before.
\end{em}

\end{center}
There might be problems if you use \verb"\em" improperly as an on/off
switch or if you rely on implicit grouping; {\em e.g.},
if you use it in a save-box (\verb"\setbox") or in a primitive
\verb"\halign" without extra braces (although a tabular environment
works fine).  Even when it fails, the italic correction usually just
disappears harmlessly.  And hey, it works for the 99\Frac{44}{100}\%
of the time that you emphasize \verb"{\em this way}".


\endgroup
\end{document}