Suppress 2-letter ligature when 3-letter ligature would apply

Question

Automatic handling of ligatures in TeX seems notoriously difficult but I was wondering whether in a font that has an ff and an fl ligature but no ffl one, it was possible to suppress the usage of any ligatures for instances of "ffl" in the text. Example follows:

\documentclass[a5paper,12pt]{article}
\renewcommand*{\sfdefault}{uop}
\renewcommand{\familydefault}{\sfdefault}
\begin{document}
\thispagestyle{empty}
Muffling affluent waffles baffles sniffling Mifflin.

Muf{}f{}ling af{}f{}luent waf{}f{}les baf{}f{}les snif{}f{}ling Mif{}f{}lin.
\end{document}

As it stands now, the "ffl" words seem unbalanced because of the inappropriate ligature they contain (the "fl" is closer together than the "ff"). Manually fixing every word is not a solution I'd look forward to.

Answer 1

If you're willing to switch from pdfLaTeX to LuaLaTeX, you could employ the selnolig package -- full disclosure: I'm the author of this package :-) -- to easily disable the ff and fl ligatures for words that include the ffl triple. (Words that contain just ff or fl will see the corresponding ligatures preserved.) Ligature suppression can be switched off and back on via the package's \selnoligoff and \selnoligon macros.

% !TEX TS-program = lualatex
\documentclass{article}
\usepackage{fontspec}
\setmainfont[Ligatures=TeX]{Latin Modern Roman} 
\usepackage{selnolig} % for this example, load the package *without* a language option
\nolig{ffl}{f|f|l} % suppress both ff and fl ligatures in words that contain ffl
\begin{document}
``ffl'' ligature disabled:

Muffling affluent waffles baffles sniffling Mifflin

\medskip
but ``ff'' and ``fl'' ligatures still work:

off fly

\selnoligoff % turn off selnolig's work, i.e., re-enable ffl ligature
\bigskip
``ffl'' ligature can be re-enabled:

Muffling affluent waffles baffles sniffling Mifflin
\end{document}

Aside: I've used the "standard" Latin Modern fonts in this example since I don't have the "Classico" fonts on my system. Assuming there exists a package named, say, "classico.sty", that loads the Classico font family, you should be able to execute the macros (after loading fontspec) \usepackage{classico} and \renewcommand{\familydefault}{\sfdefault} to use this Classico font under LuaLaTeX.

Answer 2

The font has only the fi and fl ligatures, which are actually unnecessary; the ff, ffi and ffl ligatures are obtained in the virtual font by putting together two f's or an f with fi or fl respectively; here is the relevant part for ffl:

tftopl uopr7t

First of all, let's look at f:

(CHARACTER C f
   (CHARWD R 0.276)
   (CHARHT R 0.745999)
   (CHARDP R 0.0055)
   (COMMENT
      (LIG C i O 14)
      (LIG C f O 13)
      (LIG C l O 15)
   [...]

So ff is octal 13:

(CHARACTER O 13
   (CHARWD R 0.573)
   (CHARHT R 0.745999)
   (CHARDP R 0.0055)
   (COMMENT
      (LIG C i O 16)
      (LIG C l O 17)
   [...]

Thus ffl is at position octal 17.

vptovf uopr7t

[...]
(DESIGNSIZE R 10.0)
[...]
(MAPFONT D 0
   (FONTNAME uopr8r)
   (FONTCHECKSUM O 35406442446)
   (FONTAT R 1.0)
   (FONTDSIZE R 10.0)
   )

This says what font the glyphs are taken from. Let's see octal 17:

(CHARACTER O 17
   (CHARWD R 0.834)
   (CHARHT R 0.745999)
   (CHARDP R 0.0055)
   (COMMENT
      (KRN C v R -0.019)
      (KRN C y R -0.021)
      )
   (MAP
      (SETCHAR C f)
      (MOVERIGHT R 0.021)
      (SETCHAR O 3)
      )
   )

This says that the character f is typeset, there is a kern of 0.21pt (the design size is 10pt) and then character octal 3 is used; in the raw font, the fl ligature is there.

The same kerning is applied when building the ff ligature. However, this results in the two f's being farther apart than they would be without the ligature, as your picture shows.

It seems to have been done not too carefully; my suggestion is to disable all f ligatures.

\documentclass[a5paper,12pt]{article}
\usepackage{microtype}

\DisableLigatures[f]{encoding=*,family=uop}

\renewcommand*{\sfdefault}{uop}

\begin{document}
\thispagestyle{empty}

\noindent % show that ligatures are not disabled altogether
Muffling affluent waffles\\
baffles sniffling Mifflin.

\sffamily
\noindent % but only for the classico font
Muffling affluent waffles\\
baffles sniffling Mifflin.

\end{document}