From e0c6872cf40896c7be36b11dcc744620f10adf1d Mon Sep 17 00:00:00 2001
From: Norbert Preining <norbert@preining.info>
Date: Mon, 2 Sep 2019 13:46:59 +0900
Subject: Initial commit

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+
+\documentclass[12pt,a4paper]{article}
+
+\catcode`\"=\active
+\def"{\begingroup\let"=\endgroup\tt
+  \catcode`\{=12 \catcode `\} = 12 \catcode`\^=12
+  \catcode`\|=0 \catcode`\\=12 } % Swap control characters inside "..."
+
+\title{A few words on fonts}
+
+\author{Timothy Murphy\\
+(\texttt{tim@maths.tcd.ie})}
+
+\date{20 June 1994}
+
+\begin{document}
+
+\maketitle
+
+\begin{abstract}
+The New Font Selection Scheme (NFSS)
+is now an official part of \LaTeX.
+The concept is beautifully executed
+but --- in this author's eyes ---
+poorly documented.
+This brief note is intended as a simple introduction
+to NFSS.\footnotemark
+\end{abstract}
+
+\footnotetext{Any comments, corrections or criticisms gratefully received.}
+
+\section{The 5 parameters}
+
+A font $F$ in \LaTeX\ is specified by 5 parameters:
+encoding, family, shape, series and size.
+In mathematical terminology, the font $F$ 
+is a function of 5 arguments,
+\[
+F(e, f, s, s', s''),
+\]
+where $e$ is the encoding, $f$ the family,
+$s$ the shape, $s'$ the series and $s''$ the size.
+
+The aim of the font selection mechanism
+is to associate to each such specification
+a real or virtual font at a particular magnification.
+For example, if the "12pt" option is given
+at the start of the document, eg
+\begin{verbatim}
+  \documentclass[12pt,a4paper]{article}
+\end{verbatim}
+then the default font is
+\[
+F("OT1", "cmr", m, n, 12) \mapsto "cmr12".
+\]
+(Where no magnification is specified, as here,
+it is understood that the font is unmagnified.)
+
+In other words, the font selection scheme
+sets up a mapping
+\[
+F: "encoding" \times "family" \times "shape" \times "series" \times "size"
+\to "font" \times "magnification".
+\]
+This mapping is usually defined
+in Font Definition (or ".fd") files,
+as we shall see shortly.
+
+Each of the 5 parameters can be changed 
+independently of the others by the commands:
+"\fontencoding", "\fontfamily", "\fontshape", "\fontseries" and "\fontsize",
+followed by an argument and "\selectfont".
+(A change only comes into effect
+when the command "\selectfont" is given;
+this allows more than 1 of the parameters to be changed at the same time.)
+For example, the command
+\begin{verbatim}
+  \fontshape{cmss}\fontseries{bx}\fontsize{12}\selectfont
+\end{verbatim}
+will change the font to
+\[
+F("OT1", "cmss", bx, n, 12) \mapsto "cmssbx10".
+\]
+
+\section{Short cuts}
+
+In practice these commands "\fontencoding", etc,
+rarely if ever appear in \LaTeX\ documents,
+because \LaTeX\ offers a number of simplifications.
+
+For example, one would normally write "\textss{...}"
+rather than \linebreak
+"\fontfamily{cmss}\selectfont".
+
+Similarly the only shape change encountered in most documents 
+is effected by "\emph{...}",
+which changes the shape from `roman' (upright) to italic,
+or italic to roman, according to the context.
+(Actually, most of these commands do a little more 
+than just change the font ---
+for example "\emph" also checks
+that there is appropriate spacing
+when coming in or out of the font change.)
+
+Again, the only series change commonly met is
+"\textbf{...}",
+which is (almost) equivalent to "\fontseries{bx}\selectfont".
+
+Font sizes are rarely expressed in absolute terms;
+rather, the commands "\small", "\large", "\Large",
+"\LARGE", "\huge", "\Huge" are used.
+The actual font sizes defined by these commands
+depend on the default font size.
+For example, if the "12pt" option was specified
+at the start of the document
+then "\large" is 14.4 points.
+
+\section{Font definition files}
+
+For convenience, the definition of the font selection mapping $F$
+is normally `hived off' into separate \emph{Font Definition} (".fd") files.
+
+When \LaTeX\ encounters a change of family
+it looks to see if there exists an appropriate ".fd" file,
+and if there is, it reads it in.
+The name of the ".fd" file is formed 
+by concatenating the encoding and the family name, 
+and adding the extension ".fd".
+For example
+if the family is "cmss", say, and the encoding is "OT1"
+(Knuth's original 128-character encoding)
+then the file is called "OT1cmss.fd".
+If the family is "cmr" and the encoding is "T1"
+(the new 256-character Cork encoding)
+\LaTeX\ will look for the file "T1cmr.fd",
+which specifies DC fonts, eg 
+\[
+F("T1", "cmr", m, n, 12) \mapsto "dcr12".
+\]
+
+Thus the effect of specifying "T1" encoding
+is to replace the usual CM fonts by their DC counterparts.
+The easiest way to do this is to use the "t1enc" package:
+\begin{verbatim}
+  \documentclass[12pt]{article}
+  \usepackage{t1enc}
+\end{verbatim}
+No further change is needed.
+
+(\LaTeX\ remembers which ".fd" files it has read in,
+and will not read them in a second time.
+In particular a number of standard ".fd" files
+such as "OT1cmr.fd"
+have already been read into the format file "latex.fmt"
+and so are always available.)
+
+\section{Introducing a new family}
+
+Now suppose we want to introduce a new font.
+In principal one can introduce a single font at a single size
+by a command like
+\begin{verbatim}
+  \font\quengwar = tengwar scaled \magstep2
+\end{verbatim}
+and then write eg "{\quengwar \^e l\^u\.r\'i \^l\^DR}".
+But it is almost as easy,
+and much more versatile,
+to introduce a new family, "Tengwar" say,
+with the command
+\begin{verbatim}
+  \newcommand{\quengwar}{\fontfamily{Tengwar}\selectfont}
+\end{verbatim}
+Now when \LaTeX\ reads "{\quengwar \^e l\^u\.r\'i \^l\^DR}",
+if this is its first encounter with Tengwar,
+it will read in the file "OT1Tengwar.fd".
+
+We are assuming here that "tengwar" is in the old (but still standard)
+Knuth "OT1" encoding,
+as will be the case unless the contrary is specified.
+If we had wanted to assign it the `unknown' encoding "U"
+we would have said
+\begin{verbatim}
+\newcommand{\quengwar}{\fontencoding{U}\fontfamily{Tengwar}\selectfont}
+\end{verbatim}
+and \LaTeX\ would have looked for the file "UTengwar.fd".
+
+But to tell the truth,
+the encoding does not make any practical difference;
+the only difference lies 
+in the contents of the corresponding ".fd" files.
+
+\section{Inside a font definition file}
+
+Let's suppose first that we have created the file "tengwar.tfm"
+from the \textsf{Metafont} file "tengwar.mf", eg by the command
+{\catcode`\"=12
+\begin{verbatim}
+  mf "\mode=nullmode; input tengwar"
+\end{verbatim}}
+Then the only "Tengwar" fonts at our disposal are "tengwar"
+at various magnifications.
+
+The following file "OT1Tengwar.fd" will serve our purpose
+\begin{verbatim}
+  \DeclareFontFamily{OT1}{Tengwar}{}
+  \DeclareFontShape{OT1}{Tengwar}{m}{n}{ <-> tengwar }{}
+  \endinput
+\end{verbatim}
+The first line here introduces the family name "Tengwar";
+while the second specifies that if Tengwar is encountered
+anywhere in normal text
+then the font "tengwar" is to be used at the appropriate magnification.
+For example, if the document is being printed in 12pt
+then the font "tengwar scaled 1200" will be used.
+
+(If we are using "dvips" ---
+and the same of true of some other drivers ---
+we do not need to create any "pk" files;
+they will be created automagically as and when required.)
+
+But suppose some Tengwar appears in the title of the document.
+The title is printed in bold type.
+Since we have not specified any bold Tengwar font,
+the rules of \LaTeX\ prescribe that the default font family
+(normally Computer Modern)
+should be used, in bold at the appropriate size.
+
+This is almost certainly not what we wanted.
+We can specify that we still want to use our single "tengwar" font
+in this situation
+by adding the following `substitution rule' to the ".fd" file
+(before the "\endinput"!):
+\begin{verbatim}
+\DeclareFontShape{OT1}{Tengwar}{bx}{n}{ <-> ssub * Tengwar/m/n }{}
+\end{verbatim}
+This specifies that the non-bold Tengwar font should be substituted
+whenever bold Tengwar is requested.
+Other substitution rules should be added if necessary,
+eg if Tengwar is likely to encountered in italic (or emphasized) text.
+
+It is not possible, unfortunately, to say that \emph{whenever} Tengwar
+is encountered the "tengwar" font is to be used.
+The various substitutions have to be specified individually.
+
+\section{Another example}
+
+We only had 1 Tengwar font, in a single size.
+Often of course a font is provided in several sizes.
+Consider for example Knuth's "concrete" fonts.
+The distribution contains the following ".mf" files:
+"ccr5.mf", "ccr6.mf", "ccr7.mf", "ccr8.mf", "ccr9.mf", "ccr10.mf",
+"cccsc10.mf", "ccmi10.mf", "ccsl10.mf", "ccslc9.mf", "ccti10.mf".
+We might start "OT1concrete.fd" with the lines
+\begin{verbatim}
+  \DeclareFontFamily{OT1}{concrete}{}
+  \DeclareFontShape{OT1}{concrete}{m}{n}
+    { <5> <6> <7> <8> <9> sgen * ccr <10-> s * ccr10 }{}
+\end{verbatim}
+This specifies that if the font is requested say at size 7
+then the file "ccr7" is to be used,
+while for any size $\ge 10$ the file "ccr10" is to be used,
+suitably magnified.
+(The `s' in "sgen" and "s *" stands for \emph{silent} ---
+meaning that we do not want to be told about font changes.)
+
+There doesn't appear to be a bold font included,
+so we might want to substitute the above fonts in this case, by
+\begin{verbatim}
+  \DeclareFontShape{OT1}{concrete}{bx}{n} { ssub * concrete/m/n }{}
+\end{verbatim}
+
+We can use "ccti10" for text italic, in all sizes:
+\begin{verbatim}
+  \DeclareFontShape{OT1}{concrete}{m}{it} { <-> ccti10 }
+\end{verbatim}
+
+As for substitutions, the simplest plan is to look at the file
+"OT1cmr.fd" and consider what combinations of shape and series
+are likely to arise.
+
+It remains to see how we can use the fonts.
+If we want to mix "concrete" and CM we could introduce the command
+\begin{verbatim}
+  \newcommand{\concrete}{\fontfamily{concrete}\selectfont}
+\end{verbatim}
+and then we could say, for example,
+\begin{verbatim}
+  The {\concrete concrete} fonts ...
+\end{verbatim}
+On the other hand, if we want to replace "cmr" throughout by "ccr"
+we can say
+\begin{verbatim}
+  \renewcommand{\familydefault}{concrete}
+\end{verbatim}
+in the preamble to our document,
+and the whole document will be printed using the "concrete" fonts.
+
+\section*{Am I too loud?}
+
+One last small point.
+You might consider the Tengwar font (say)
+too large in comparison with normal text.
+NFSS offers a simple solution.
+If we change the line in the "OT1Tengwar.fd" file to read, for example,
+\begin{verbatim}
+  \DeclareFontShape{OT1}{Tengwar}{m}{n}{ <-> s * [0.95] tengwar }{}
+\end{verbatim}
+then the font will be reduced in size by 5\%.
+
+\section*{Mathematical fonts}
+
+In this document we have only considered \emph{text} fonts.
+The use of fonts in mathematics (whether displayed or not)
+is another story, for another day \dots.
+
+\end{document}
+
+-- 
+Timothy Murphy  
+e-mail: tim@maths.tcd.ie
+tel: +353-1-2842366
+s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland
-- 
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