I can't get ligatures to work with Century Schoolbook L or URW Bookman L. This might be missing ligatures in the font or maybe doesn't support Type 1 fonts that well.
The TeX Gyre Schola font is based on Century Schoolbook L and contains proper ligatures. If it is installed in the TeX directory structure, you have to use
\setmainfont[
Ligatures=TeX,
Extension=.otf,
UprightFont= *-regular,
BoldFont=*-bold,
ItalicFont=*-italic,
BoldItalicFont=*-bolditalic
]{texgyreschola}
to call it (or just copy the font to ~/.fonts).
However, this does not work with XeTeX/fontspec included in Ubuntu 10.10 (and so presumably also not with 10.04). If you want to use XeTeX and fontspec, I strongly recommend that you always use the newest versions. Installing TeX Live directly (i.e. not via the package manager) is not too hard (just download the installation script, run it and set the path) and will give you the newest versions of the TeX engines and packages.
The problem with this font -- as far as its ligatures are concerned -- is that the ligature names in the internal font table are, shall we say, utterly non-standard. For instance, instead of going with standard names such as f_f and f_f_i for the ligatures, a search with the FontForge app reveals that the font uses the names Omega and approxequal. No joke!! (A not-uncharitable assessment of the situation might be that the font's name correspondence table got garbled at some point prior to compilation.)
Given this situation, it's probably not a surprise that LuaLaTeX and XeLaTeX are not able to figure out the name mappings without special help.
Using LuaLaTeX, I can think of two solutions to this mess. The first solution creates a custom "feature file", which informs the system about the ligature names actually used by the font. The second, shown further below, uses LuaTeX functionality directly to get the ligatures working.
With the help of FontForge I was able to find the "names" for all ten ligatures. These names are used to set up a so-called "Feature File", named addligs_HFTI.fea, that can be loaded via an instruction such as \addfontfeatures{FeatureFile=addligs_HFTI.fea}.
Unfortunately, despite having found the font's ligature "names" for all ten ligatures, this approach succeeds in activating only four of them (ct, ff, ffi, and ffl, to be specific). Maybe something else got garbled as well when the font was compiled?
% !TEX TS-program = lualatex
\RequirePackage{filecontents}
\begin{filecontents*}{addligs_HFTI.fea}
languagesystem DFLT dflt;
languagesystem latn dflt;
# Ligatures
feature liga {
sub a s by summation;
sub i s by Delta;
sub u s by divide;
sub c t by plusminus;
sub f f by Omega;
sub f i by fi;
sub f l by fl;
sub f f i by approxequal;
sub f f l by radical;
} liga;
\end{filecontents*}
\documentclass{article}
\newcommand\liglist{as is ct ff fi fl ffi ffl}
\usepackage{fontspec}
\defaultfontfeatures{Ligatures=Common}
\setmainfont{Historical-FellTypeItalic}
\begin{document}
w/o ligatures: \liglist
\addfontfeatures{FeatureFile=addligs_HFTI.fea}
with ligatures: \liglist
\end{document}
Addendum. Given that the feature file approach doesn't succeed in activating all ten ligatures present in the font, the following solution, which is entirely coded in Lua, may be worth considering. It uses the process_input_buffer callback to run a function that performs a "brute force" substitution of the ten character pairs and triples with the corresponding glyphs that represent the ligated versions. (Full disclosure: The code used below gratefully uses code originally provided by @michal.h21 in his answer to my recent posting, entitled LuaLaTeX: How to use a \char directive inside a string.gsub function?) Observe that special care had to be taken to ensure that any LaTeX macros that may include strings such as "ff", "fi", etc aren't caught up in the brute-force substitution.
% !TEX TS-program = lualatex
\documentclass{article}
\usepackage{fontspec}
\setmainfont{Historical-FellTypeItalic}
\usepackage{luacode,luatexbase}
\begin{luacode}
local uchar = unicode.utf8.char
function ligsub ( s )
local x = s:gsub('(\\?)([%a%@]+)',
function(back,text)
if back~="" then
return back .. text
end
text = text:gsub ( 'ffi', uchar(8776))
text = text:gsub ( 'ffl', uchar(8730))
text = text:gsub ( 'ff', uchar(937))
text = text:gsub ( 'fi', uchar(64257))
text = text:gsub ( 'fl', uchar(64258))
text = text:gsub ( 'as', uchar(8721))
text = text:gsub ( 'is', uchar(916))
text = text:gsub ( 'us', uchar(247))
text = text:gsub ( 'ct', uchar(177))
text = text:gsub ( 'st', uchar(9674))
return text
end)
print("x", x)
return x
end
\end{luacode}
\AtBeginDocument{%
\directlua{luatexbase.add_to_callback (
"process_input_buffer", ligsub, "ligsub" )}}
\newcommand\off{off} % dummy macro (see below)
\begin{document}
off fit fly office baffle
as is us act step
\off --note: no ff-ligature
\end{document}
Remark: The only downside I can see to taking this approach is that it's definitely going to mess up the work of a screen-reader: eight of the ten ligatures -- those for ff, ffi and fl, as, is, us, ct, and st -- get rendered as Ω, ≈, √, Σ, Δ, ±, and ◊, respectively. Argghh. (In contrast, fi and fl do get rendered correctly; probably not coincidentally, those are the two ligatures that have a "normal" name in the feature file, which was shown earlier.) That's not really the fault of the LuaLaTeX-based approach, though; rather, the font's messed-up name tables are to blame. Ideally, the authors and/or maintainers of the font would re-release it, this time with the name table cleaned up drastically.
Best Answer
This is not possible at LaTeX level; ligatures are defined in the
.tfmfile for the font and there's no way to change them (pdftexhas only the possibility of clearing the list of ligatures for a particular font).The strategy of making the
tactive in order to check if anothertfollows can work for limited amounts of text only, as it would break all command names containing at.