How to make existing \strut-based code work with accented letters?

Question

\strut-based solutions assume that heights cannot exceed 8.5 pt and depth - 3.5 pt. But with accented letters this assumption is not true. In the second example the last line is lower than in the first example. How to make the baselines the same in both examples without changing the main macro?

Example 1:

\input template
\font\tenrm=rm-lmr10 \tenrm
\marginalstar
X
\char'101
\bye

Example 2:

\input template
\font\tenrm=rm-lmr10 \tenrm
\marginalstar
X
\char'200
\bye

template.tex:

\def\marginalstar{\strut\vadjust{\kern-\dp\strutbox\smash{\llap{* }}\kern\dp\strutbox}}
\nopagenumbers
\hsize1em
\emergencystretch=1em
\noindent

If there does not exist a workaround so that existing code would work with accented letters, what guidelines should be followed in writing new code? Are \strut-based solutions bad and how to avoid them? How to make so that in all cases where \strut would be used, it was possible to do without it? (for example - to draw rules in tables; page 82 of TeXbook gives another example)

EDIT Two more examples to illustrate the point. In the second example the right border is torn.

Example 3:

\font\tenrm=rm-lmr10 \tenrm
\hsize=5em
\hrule
\settabs 2 \columns
\+ \strut\vrule\hfill W\hfill\vrule& \hfill X \hfill\strut\vrule&\cr
\hrule
\+ \strut\vrule\hfill \char'101\hfill\vrule& \hfill Z \hfill\strut\vrule&\cr
\hrule
\bye

Example 4:

\font\tenrm=rm-lmr10 \tenrm
\hsize=5em
\hrule
\settabs 2 \columns
\+ \strut\vrule\hfill W\hfill\vrule& \hfill X \hfill\strut\vrule&\cr
\hrule
\+ \strut\vrule\hfill \char'200\hfill\vrule& \hfill Z \hfill\strut\vrule&\cr
\hrule
\bye

So according to @David Carlisle it should be:

\setbox\strutbox=\hbox{\vrule height9.5pt depth2.5pt width0pt}

Because:

$ tftopl rm-lmr10|grep CHARHT|sort|tail -n1
   (CHARHT R 0.9205)
$ tftopl rm-lmr10|grep CHARDP|sort|tail -n1
   (CHARDP R 0.25)

Right?

Answer 1

\strut is not a built in command it is simply

  \setbox\strutbox=\hbox{\vrule height8.5pt depth3.5pt width\z@}
  \def\strut{\relax\ifmmode\copy\strutbox\else\unhcopy\strutbox\fi}

which is designed to fit 10pt computer modern English text set on a 12pt baseline.

If you have any other type of text you need to adjust \strutbox to have suitable height and depth,

In this case you get \lineskip of 1pt between the lines as the accented A is 9.20499pt high an the \strut is 3.5pt deep so they can not fit on a 12pt baselineskip.

You probably need to change the baselineskip to say 12.5pt and adjust the strut to be 9.3 high and 3.2 deep or some such, or you could try to squeeze it in to 12pt with a strut 9.2 high and 2.8 deep

---

to address the questions in comments in latex you could do

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\begin{document}


\showoutput
\expandafter\show\the\font
\sbox0{Ă \v{A}\c{c}g(Q)$\sum_0^n(x)_7^n$}
\typeout{\the\ht0+\the\dp0=\the\dimexpr\ht0+\dp0\relax}
\usebox{0}


\end{document}

which shows that latex/plain tex isn't really the issue it is the font choice. Using ec fonts as above, it looks like you can just get away with a strut of 9pt high and 3pt deep which isn't quite what you get from latex which resets it after every size change to

    \setbox\strutbox\hbox{%
      \vrule\@height.7\baselineskip
            \@depth.3\baselineskip
            \@width\z@}%

so for a 12pt baseline that's 8.4pt+3.6pt but you could redefine \set@fontsize to use .75 and .25 as the multipliers if you have a lot of accented capitals and no large descenders in the font.

Answer 2

Update adds a patch of LaTeX's \selectfont to modify its way of defining \strutbox as per OP's request in a comment. To be further adapted to one's needs. When \set@fontsize is called, the new font isn't yet loaded, thus, I ended up adding some extra code at the very end of \selectfont rather than patching \set@fontsize.

---

TeX has a mechanism for setting lines \baselineskip apart which most of the time works fine. As explained in @DavidCarlisle's answer, the \strutbox is defined with an ad hoc .7:.3:1 rule for height:depth:baselineskip. Unfortunately this means that adding a \strut to a situation where things were otherwise well aligned will sometimes cause misalignments. Here below is an example where the depth coming from the strut plus the height coming from an accented character on the next line will have a total exceeding the baselineskip, because the .7\baselineskip falls short of the height of the accented character.

\documentclass[12pt]{article}
\usepackage [utf8]{inputenc}
\usepackage [T1]{fontenc}
\usepackage {multicol}

\begin{document}\pagestyle{empty}\thispagestyle{empty}

Without struts:
\begin{multicols}{2}
Etat de droit Etat de droit Etat de droit Etat de droit Etat de droit
Etat de droit Etat de droit Etat de droit\par
\columnbreak
\'Etat de droit \'Etat de droit \'Etat de droit \'Etat de droit \'Etat
de droit \'Etat de droit \'Etat de droit\par
\end{multicols}

With two added struts (the one on the left does no harm), the 
alignment is off!:

\begin{multicols}{2}
\strut Etat de droit Etat de droit Etat de droit Etat de droit Etat de droit
Etat de droit Etat de droit Etat de droit\par
\columnbreak
\strut État de droit État de droit État de droit État de droit État
de droit État de droit État de droit\par
\end{multicols}   
\end{document}

produces

This was discussed in a thread on a French newsgroup, the situation is worse with lmodern:

\documentclass[12pt]{article}
\usepackage [utf8]{inputenc}
\usepackage [T1]{fontenc}
\usepackage {multicol}
\usepackage{lmodern}

\begin{document}\pagestyle{empty}\thispagestyle{empty}

Without struts:
\begin{multicols}{2}
Etat de droit Etat de droit Etat de droit Etat de droit Etat de droit
Etat de droit Etat de droit Etat de droit\par
\columnbreak
\'Etat de droit \'Etat de droit \'Etat de droit \'Etat de droit \'Etat
de droit \'Etat de droit \'Etat de droit\par
\end{multicols}

With two added struts (the one on the left does no harm), the 
alignment is off!:

\begin{multicols}{2}
\strut Etat de droit Etat de droit Etat de droit Etat de droit Etat de droit
Etat de droit Etat de droit Etat de droit\par
\columnbreak
\strut État de droit État de droit État de droit État de droit État
de droit État de droit État de droit\par
\end{multicols}    

With more struts at the right, alignment even more off:
\begin{multicols}{2}
\strut Etat de droit Etat de droit Etat de droit Etat de droit Etat de droit
Etat de droit Etat de droit Etat de droit\par
\columnbreak
\strut État de droit État de droit État de droit \strut État de droit État
de droit État de droit État de droit\par
\end{multicols}

\end{document}

---

Code for patching \selectfont.

\documentclass[12pt]{article}
\usepackage [utf8]{inputenc}
\usepackage [T1]{fontenc}
\usepackage {multicol}
\usepackage{lmodern}

% patch \selectfont
\makeatletter
\newbox\igor@tempbox
% or \@tempboxa but perhaps some code calls \selectfont
% not expecting \@tempboxa to be modified

\def\igor@fixstrutbox{\setbox\igor@tempbox\hbox{ÉÈÙÀĂÅ}% 
% first we reset the \strutbox to not inherit a situation which
% could go through unmodified but would depend upon the sequence
% of earlier font changes, if you didn't make the change now.
%
           \setbox\strutbox\hbox{\vrule
               \@height.7\baselineskip 
               \@depth.3\baselineskip
               \@width\z@}%
           \ifdim\ht\igor@tempbox>\ht\strutbox
% comment out these two lines in real use cases
    \typeout{IGOR: MODIFYING DEFAULT STRUTBOX\on@line.}%
    \typeout{IGOR: old=\the\ht\strutbox, new=\the\ht\igor@tempbox}%
           \setbox\strutbox\hbox{\vrule
               \@height\ht\igor@tempbox % add some extra? 
               \@depth\dimexpr\baselineskip-\ht\igor@tempbox\relax
               \@width\z@}\fi }%


\expandafter\def
  \csname selectfont \expandafter\expandafter\expandafter
  \endcsname
  \expandafter\expandafter\expandafter
  {\csname selectfont \endcsname\igor@fixstrutbox}%
\makeatother

\begin{document}\pagestyle{empty}\thispagestyle{empty}

Without struts (no problems):
\begin{multicols}{2}
Etat de droit Etat de droit Etat de droit Etat de droit Etat de droit
Etat de droit Etat de droit Etat de droit\par
\columnbreak
État de droit État de droit État de droit État de droit État
de droit État de droit État de droit\par
\end{multicols}

With struts: (careful to put a strut also on left first line.)

\begin{multicols}{2}
\strut Etat de droit Etat de droit Etat de droit Etat de droit Etat de droit
Etat de droit Etat de droit Etat de droit\par
\columnbreak
\strut État de droit État de droit État de droit État de droit État
de droit État de droit État de droit\par
\end{multicols}

\Large

Changed size. 
\begin{multicols}{2}
\strut Etat de droit Etat de droit Etat de droit Etat de droit Etat de droit
Etat de droit Etat de droit Etat\par\hrule
\columnbreak
\strut État de droit État de droit État de droit \strut État de droit État
de droit État de droit État de droit\par\hrule
\end{multicols}

\sffamily

Other font.
\begin{multicols}{2}
\strut Etat de droit Etat de droit Etat de droit Etat de droit Etat de droit
Etat de droit Etat de droit Etat de droit\par\hrule
\columnbreak
\strut État de droit État de droit État de droit \strut État de droit État
de droit État de droit État de droit\par\hrule
\end{multicols}

\end{document}

Log (with \igor@fixstrutbox containing only É, and that was with an earlier version of the code):

(/usr/local/texlive/2015/texmf-dist/tex/latex/lm/t1lmr.fd
File: t1lmr.fd 2009/10/30 v1.6 Font defs for Latin Modern
)
IGOR: MODIFYING DEFAULT STRUTBOX on input line 30.
IGOR: old=10.14995pt, new=11.004pt
IGOR: MODIFYING DEFAULT STRUTBOX on input line 51.
IGOR: old=15.39993pt, new=15.68199pt
LaTeX Font Info:    Try loading font information for T1+lmss on input line 62.
(/usr/local/texlive/2015/texmf-dist/tex/latex/lm/t1lmss.fd
File: t1lmss.fd 2009/10/30 v1.6 Font defs for Latin Modern
)
IGOR: MODIFYING DEFAULT STRUTBOX on input line 73.
IGOR: old=10.14995pt, new=11.004pt

Switch to sans serif caused no adjustment, but if \igor@fixstrutbox is set-up with \hbox{ĂÉÈÅ} rather, one gets (again with earlier code, not re-compiled).

IGOR: MODIFYING DEFAULT STRUTBOX on input line 30.
IGOR: old=10.14995pt, new=11.004pt
IGOR: MODIFYING DEFAULT STRUTBOX on input line 51.
IGOR: old=15.39993pt, new=15.68199pt
LaTeX Font Info:    Try loading font information for T1+lmss on input line 62.
(/usr/local/texlive/2015/texmf-dist/tex/latex/lm/t1lmss.fd
File: t1lmss.fd 2009/10/30 v1.6 Font defs for Latin Modern
)
IGOR: MODIFYING DEFAULT STRUTBOX on input line 62.
IGOR: old=15.68199pt, new=15.97498pt
IGOR: MODIFYING DEFAULT STRUTBOX on input line 73.
IGOR: old=10.14995pt, new=11.004pt

The same with only \hbox{Ă} showing that this character is taller in sans serif than É at least in \Large font size.

I have edited the \igor@fixstrutbox to always reset first the \strutbox to the default LaTeX definition, because if not the decision to keep the \strutbox or modify it would depend on the history of earlier font changes, as LaTeX calls only in certain circumstances \set@fontsize which gives non \relax meaning to \size@update (executed by \selectfont). I have not updated the image and logs above after that change.

Answer 3

I am providing another answer, which exploits a feature of XeTeX, its parameter \XeTeXuseglyphmetrics. The idea is the following:

\XeTeXuseglyphmetrics 0

and all character boxes will have identical heights and depths. Set the height of the strutbox to this common height, and its depth to the value needed so that the sum of the two add up to \baselineskip.

Then you can reset

\XeTeXuseglypmetrices 1

for the default boxes.

This is illustrated by the xetex code below. It containes a \fbox macro which frames its material adding no extra height or depth or width. The \TEST macro is supposed to display some such boxes, containing characters and struts, or only a strut, or also normal characters and a \vrule. We see most of the time lineskip glue added because always height + depth exceeds baselineskip if we find an accented letter and a strut (the strut has too big a depth).

Then at bottom we set up a better strut, and see that there no more extra vertical interline spaces. This final step done with "Times New Roman" which is a system font on my Mac.

forgot the code:

\newdimen\fboxrule
\fboxrule 0.4pt

\def\mycolor {rgb 0 0 1}
\def\fbox #1{\leavevmode
              {\special{color push \mycolor}%
              \hbox{\vtop{\vbox{%
              \hrule height \fboxrule
              \kern -\fboxrule
              \hbox{\vrule width \fboxrule\kern-\fboxrule
                    \special{color pop}%
                    #1%
                    \special{color push \mycolor}%
                    \kern-\fboxrule\vrule width \fboxrule}%
              }\kern-\fboxrule
              \hrule height\fboxrule}}%
              \special{color pop}%
              }%
}

\def\TEST {\noindent
     \fbox{\strut\kern1cm
    {\def\mycolor{rgb 1 0 0 }\fbox {A}\fbox{E}\fbox{C}\fbox{gg}%
                 \kern1cm\strut}}
     ABCD
     \fbox{\strut\kern.5cm\strut}
     \vrule height\ht\strutbox
            depth \dp\strutbox

     \noindent
    \fbox{\strut\kern1cm
    {\def\mycolor{rgb 1 0 0 }\fbox {A}\fbox{É}\fbox{Ç}\fbox{gg}%
                 \kern1cm\strut}}
     ABCD
     \fbox{\strut\kern.5cm\strut}
     \vrule height\ht\strutbox
            depth \dp\strutbox
     \par
      }

\font\lmfont=rm-lmr10

\lmfont

Latin Modern

\the\ht\strutbox, \the\dp\strutbox, \the\baselineskip

\XeTeXuseglyphmetrics=1

\TEST

\XeTeXuseglyphmetrics=0

\TEST

\font\times="Times New Roman"

\times

Times New Roman

\XeTeXuseglyphmetrics=1

\TEST

\XeTeXuseglyphmetrics=0

\TEST

\setbox0\hbox{A}\the\ht0, \the\dp0, common height plus depth of strut=
\the\dimexpr\ht0+\dp\strutbox\relax, bigger than
\the\baselineskip

With better strut:

\setbox\strutbox\hbox{\vrule height\ht0
                             depth\dimexpr\baselineskip-\ht0\relax}

\XeTeXuseglyphmetrics=0

\TEST

\XeTeXuseglyphmetrics=1

\TEST

\nopagenumbers
\bye