Why does a color meant for the first typeset line *only* (with package magaz) affect the *entire* document?

Question

I am trying to make a nice layout that gives a different style to the first line in a section using the package magaz. All examples I have seen feature some variation of small caps {\scshape text} or upper case \MakeUppercase{text}.

I would like to change the font and the color.

This works well for the font but the color unfortunately affects the entire document rather than just the first line.

\documentclass[12pt,english,american]{article}
\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}

\makeatletter

\usepackage{mathpazo}
\usepackage{xcolor} 
\usepackage{magaz}

\newcommand{\FirstLineCommand}[1]{\noindent\fontfamily{iwona}\fontseries{bc}\selectfont{\textcolor{red}{#1}}}

\renewcommand\FirstLineFont{\FirstLineCommand}

\makeatother

\usepackage{babel}
\begin{document}
\selectlanguage{english}%

Hello just testing.

Normal \textcolor{red}{color switching} should work.

\FirstLine{Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.}

Some more text.
\end{document}

As you can see, I define a command \FirstLineCommand to pass on to the magaz package as a \FirstLineFont

If I use instead

\newcommand{\FirstLineCommand}[1]{\noindent\fontfamily{iwona}\fontseries{bc}\selectfont{\MakeUppercase{#1}}}

that works just fine.

I am clearly not a guru when it comes to latex syntax, so after some tinkering with adding extra braces here and there and moving the color statement around (and trying {\color text} instead of \textcolor{text}, I'm still stumped.

I'd be happy if you could help me color the first typeset line of the paragraph only.

Answer 1

The reason that it fails for colour is that unlike fonts colour is not a primitive property of the box, colour is implemented by having colour change nodes at the start and end of a colour range. If you split up and re-organise a box after it is typeset those colour nodes can (and usually will) get separated from their text. Donald's package does more than the average amount of box re-arranging:-)

\documentclass[12pt,english,american]{article}
\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}



\usepackage{mathpazo}
\usepackage{xcolor} 
\usepackage{magaz}
\newcommand{\FirstLineCommand}[1]{\noindent\fontfamily{iwona}\fontseries{bc}\selectfont{#1}}

\renewcommand\FirstLineFont{\FirstLineCommand}


\makeatletter

\let\xfl\FirstLine
\long\def\foo#1\ifvoid\mz@firstbox#2!!{%
\def\FirstLine##1{#1%
\setbox\mz@firstbox\hbox to \textwidth{\textcolor{red}{\unhbox\mz@firstbox\unskip\unskip\unpenalty}}%
 \ifvoid\mz@firstbox
#2}}
\expandafter\foo\FirstLine{#1}!!

\makeatother

\usepackage{babel}
\begin{document}
\selectlanguage{english}%

Hello just testing.

Normal \textcolor{red}{color switching} should work.

\FirstLine{Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.}

Some more text.
\end{document}

---

The code above is a one-line patch to \FirstLine to add the colour at a safe place. It seems in comments that the patch trickery is obscuring what the code is doing so here is an equivalent version.

Replace the code above between \makeatletter \makeatother by the following which is identical to the code in magaz apart from the line marked %<<<<<<

\makeatletter

\renewcommand\FirstLine[1]{%
 \relax\if@inlabel\noindent\fi % produce any pending list item label
 \begingroup
 % typeset text 3 times: 1) using all breaks to count segments; 2) with
 % a full first line and \FirstLineFont to get first line and remaining
 % segments; 3) Using current font, keeping only `remaining segments'
 % on a single line. 
 \setbox\z@\box\mz@firstbox \setbox\z@\box\mz@remains % void the global boxes
 \setbox\@tempboxa\vbox{% 1) use all breaks
   \hbadness\maxdimen \hfuzz\maxdimen
   \hsize\z@ \leftskip\z@skip \rightskip\z@skip \parfillskip\fill
   \parshape\z@ \pretolerance\m@ne \tolerance\@ne 
   \doublehyphendemerits\z@ \finalhyphendemerits\z@
   #1\global\mathchardef\mz@spf\spacefactor\@@par
   \global\mathchardef\mz@numl\prevgraf
   %{\message{^^J^^J^^JText has \number\mz@numl\space segments:}\showhyphens{#1\unskip\unskip}}%
 }% end vbox "1)"
 \setbox\@tempboxa\vbox{% 2) first line, plus other segments
   \parshape \tw@ \z@\linewidth \z@\maxdimen 
   \doublehyphendemerits\z@ \finalhyphendemerits\z@
   %\linepenalty\z@
   % note no \hbadness\maxdimen \hfuzz\maxdimen at this stage
   \pretolerance\m@ne \parfillskip\fill
   {\FirstLineFont{#1}\@@par}%
   \ifnum\prevgraf>\tw@ % Bad argument: not simple text or too much text
     \mz@handlebad{#1}%
   \else
     \unskip\unkern\unskip\unpenalty \unskip\unkern\unskip\unpenalty
     \ifnum\prevgraf<\tw@ % All text fits on first line
       \global\setbox\mz@firstbox\lastbox % Grab that line
       %{\message{Entire text fits: }\showhyphens{\unhcopy\mz@firstbox\unskip\unskip\unpenalty}}%
       \setbox\z@\hbox{\unhcopy\mz@firstbox}%
       \begingroup
       \advance\linewidth-0.4em\relax
       \expandafter\endgroup
       \ifdim\wd\z@>0.97\linewidth
         %\message{^^JHandle wide first line: \the\wd\z@\space vs \the\linewidth. }%
         \global\setbox\mz@firstbox\hbox to\wd\mz@firstbox{%
             \unhcopy\mz@firstbox\unskip\unskip\unpenalty}% remove \parfillskip
         \global\setbox\mz@remains\hbox{}% Trigger keeping of full wide line
       \fi        % else \mz@remains remains void
     \else % 2 lines: text fills first line with some left over
       \setbox\z@\lastbox % remainders to \z@
       \ifvoid\z@ % could not grab last line 
         \mz@handlebad{#1}%
       \else 
         \unskip\unkern\unskip\unpenalty \unskip\unkern\unskip\unpenalty
         \global\setbox\mz@firstbox\lastbox % grab first line
         % Note: counting segments in this first line will be wrong if the line
         % ended with a hyphenation.  It could be possible to detect and adjust
         % for the resulting extra segment if it is deemed desirable to count the
         % first line directly.
         %{\message{First line is: }\showhyphens{\unhcopy\mz@firstbox\unskip}}%
         %{\message{Remaining segments are: }\showhyphens{\unhcopy\z@\unskip\unskip}}%
         %
         % 2a) break up "remaining segments":
         \hsize\z@ \hbadness\maxdimen \hfuzz\maxdimen
         \leftskip\z@skip \rightskip\z@skip \parfillskip\fill
         \parshape\z@ \pretolerance\m@ne \tolerance\@ne 
         {\everypar{}\noindent}% mid-par so no \everypar or \parindent
         \nobreak % \nobreak because leftskip adds breakpoint
         \unhbox\z@\unskip\unskip\unpenalty\@@par % gives number of "extra segments"
         %\message{There are \number\mz@numl\space segments in total and \the\prevgraf\space "remaining segments". }%
         \@tempcnta\mz@numl \advance\@tempcnta-\prevgraf 
         %\message{Number of segs in 1st line: \the\@tempcnta. }%
         \advance\@tempcnta\@ne % number of segs in 1st line plus 1
         \edef\@tempa{\the\@tempcnta\space}% 3) Collect "other segments"
         \@whilenum \@tempcnta>\@ne\do{% build \parshape lines
           \edef\@tempa{\@tempa \z@\z@}%
           \advance\@tempcnta\m@ne
         }%
         %\message{Parshape: \@tempa \z@\maxdimen}%
         \parshape \@tempa \z@\maxdimen
         #1\@@par
         \unskip\unkern\unskip\unpenalty \unskip\unkern\unskip\unpenalty
         \global\setbox\mz@remains\lastbox 
       \fi
     \fi
   \fi
 }% end vbox "2)"
 \endgroup
\setbox\mz@firstbox\hbox to \textwidth{\textcolor{red}{\unhbox\mz@firstbox\unskip\unskip\unpenalty}}%<<<<<<<<<<<<<<<<<<<<<<<<<<
 \ifvoid\mz@firstbox
   #1% Error case: just output the text
 \else
   {\everypar{}\noindent}\nobreak % everypar was captured in firstbox
   \ifvoid\mz@remains % partial line only
     % Unbox the partial line. This allows equal stretching of spaces across
     % the line, but admits a slight chance that some \FirstLineFont may
     % carry over to the second line.
     \unhbox\mz@firstbox 
     \unskip\unskip\unpenalty % remove \rightskip \parfillskip \nobreak
     \allowbreak % allow a break rather than get dragged to next line (??)
   \else % full first line 
     % Output whole box to prevent unexpected linebreaks, especially for
     % an overfull line and at the bogus discretionary that TeX leaves before
     % a final (used) hyphen.
     \box\mz@firstbox\break 
     \unhbox\mz@remains
     \unskip\unskip\unpenalty % remove \rightskip \parfillskip \nobreak
     % (or remove forced \break for empty remains)
   \fi
   \spacefactor\mz@spf
 \fi
}

\makeatother