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Date:         Sat, 7 May 1994 19:52:32 EDT
From: David Wald <wald@THEORY.LCS.MIT.EDU>
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Subject:      PROPOSAL: Font variations for NFSS
Status: R

Summary: I'm proposing a general mechanism for handling systems of
font families in which each family can be considered a variant of the
others, distinguished by one or more selected features.  A prototype
implementation is included.

----------------------------------------------------------------------
I'll admit, I shudder slightly ever time I hear of a new
generalization of NFSS; it's just a personal neurosis.  Despite this,
I'm about to propose another generalization.

I'm currently involved in a project using fonts which have several
variations, by which I mean things like the use (or not) of the
old-style long "s", the presence (or absence) of certain extra
ligatures, etc.  These variations are orthogonal to questions of what
NFSS calls "shape" or "series"; e.g., I want to be able to select
italic or upright without knowing what variation is currently in use.

Thus, I'm using a family for each variant.  Unfortunately, some
variations are independent of others, and, again, I'd like to be able
to select one variation without affecting another that is independent
of it.

My current scheme for dealing with this is as follows: define, for
each variation and each font family in which it has an effect, the
family which results from applying the variation.  Thus, if "foo" is
my unadorned family, with "fancy" and "oldstyle" two variations, I
might have:

  \DeclareFontVariant{oldstyle}{foo}{foo-oldstyle}
  \DeclareFontVariant{oldstyle}{foo-fancy}{foo-oldstyle-fancy}
  \DeclareFontVariant{fancy}{foo}{foo-fancy}
  \DeclareFontVariant{fancy}{foo-oldstyle}{foo-oldstyle-fancy}

where foo-oldstyle, foo-fancy, and foo-oldstyle-fancy are the families
with these combinations of features.  This states that, for example,
the "oldstyle" variant changes family "foo" to "foo-oldstyle".  (The
change can be applied with, perhaps,

  \fontvariant{oldstyle}\selectfont

or some such syntax.)

Obviously, listing all possible pairings for a set of families would
be somewhere between tedious and absurd.  To mitigate the problem,
families can be assigned to classes, and a default behavior can be
given for a variation in a class.  Thus, given the relation between
the basic Computer Modern families, we have

  \DeclareFontClass{cm}{cmr,cmss,cmtt}
  \DefaultFontVariant{rm}{cm}{cmr}
  \DefaultFontVariant{sf}{cm}{cmss}
  \DefaultFontVariant{tt}{cm}{cmtt}

i.e., cmr, cmss and cmtt are all in class "cm", and the default
meaning of variant "rm" for a family in this class is to change to
"cmr" (and similarly for "sf" and "tt").  This default can be
overridden in any particular case with \DeclareFontVariant.

Note that this system generalizes the use \rmdefault, etc. to other
and more complicated systems of variations.

Any thoughts?  I need some mechanism like this for my particular
project, but it seems to me that the system might be more generally
useful, if there were a standard way to use it.  I've appended a sort
of proof-of-concept package file implementing the above commands, if
anyone wants to play around with it.  (I'd like to get some reactions
before I go ahead and properly 2e-ify the package.)

-David
======================================================================
% fontvariant.sty
%    by David Wald, May 6, 1994
%
% A prototype implementation of a system for selecting variant font
% families.
%
% Commands are:
%
%  \DeclareFontClass{fontclass}{fontfamilies}
%     where fontclass is any name, and fontfamilies a
%     comma-separated list of font family names.
%
%  \ExtendFontClass{fontclass}{fontfamilies}
%     similar, but adds fontfamilies to a preexisting fontclass
%
%  \DefaultFontVariant{variant}{fontclass}{newfamily}
%     where newfamily is the family resulting from applying variant to
%     any family in fontclass, unless this default is overridden by a
%     \DeclareFontVariant statement.
%
%  \DeclareFontVariant{variant}{oldfamily}{newfamily}
%     where newfamily is the family resulting from applying variant to
%     oldfamily.
%
%  \fontvariant{variant}
%     chooses the font family which results from applying variant to
%     the current font family.  Takes effect after the next
%     \selectfont.

\def\fileversion{0.1}
\def\filedate{1994/5/6}

\ProvidesPackage{fontvariant}[\filedate\space\fileversion]

\def\DeclareFontClass#1#2{%
   \@ifundefined{@FC@@#1@}%
      {\@namedef{@FC@@#1@}{#2}%
       \def\@tempa{#1}\@for\@tempb:=#2\do\@addtofontclass}
      {\font@warning{Font class #1 already defined; ignored.}}}

\def\ExtendFontClass#1#2{%
   \@ifundefined{@FC@@#1@}%
      {\font@warning{Font class #1 not defined; ignored.}}
      {\@namedef{@FC@@#1@}{#2}%
       \def\@tempa{#1}\@for\@tempb:=#2\do\@addtofontclass}}

\def\@addtofontclass{
   \@ifundefined{@FC@\@tempb @}%
      {\expandafter\edef\csname @FC@\@tempb @\endcsname{\@tempa}}
      {\font@warning{Font family \@tempb{} already assigned to class
                      \@nameuse{@FC@\@tempb @}; ignored.}}}

\def\DefaultFontVariant#1#2#3{%
     \@ifundefined{@FC@@#2@}%
        {\font@warning{Font class #2 not defined; ignored.}}%
        {\@namedef{@FC@#1@#2@}{#3}}}

\def\DeclareFontVariant#1#2#3{\@namedef{@FV@#1@#2@}{#3}}

\def\fontvariant#1{%
     \@ifundefined{@FV@#1@\f@family @}%
          {\@ifundefined{@FC@\f@family @}%
                {\def\@tempa{undefined}}%
                {\edef\@tempa{\@nameuse{@FC@\f@family @}}}%
           \@ifundefined{@FC@#1@\@tempa @}%
                {\font@warning{There's no #1 variant for \f@family; ignored.}}%
                {\fontfamily{\@nameuse{@FC@#1@\@tempa @}}}}%
          {\fontfamily{\@nameuse{@FV@#1@\f@family @}}}}

\endinput