%D \module [
%D         file=t-letterspace,
%D      version=2011-03-15T12:59:48+0100 or later,
%D        title=\CONTEXT\ User Module,
%D     subtitle=Letterspacing commands,
%D       author=Philipp Gesang,
%D         date=\currentdate,
%D    copyright=Philipp Gesang,
%D      license=2-clause BSD,
%D ]

%C Read the license conditions in the file \type{COPYING}.



\writestatus{loading}{ConTeXt User Module / Letterspace}

\startmodule [letterspace]

\startinterface all
  \setinterfacevariable {letterspace} {letterspace}
  \setinterfacevariable {factor}      {factor}
  \setinterfacevariable {spaceskip}   {spaceskip}
  \setinterfacevariable {suppresskern}{suppresskern}
\stopinterface

\unprotect

\definenamespace [\v!letterspace] [
  command=yes,
  comment=Letterspace module,
  name=\v!letterspace,
  \s!parent=\v!letterspace,
  setup=list,
  style=no,
  type=module,
  version=hg-rev:3+,
]

%D \macros
%D    {letterspace}
%D
%D \useURL [wschuster] [https://bitbucket.org/wolfs/] [] [Wolfgang Schuster]
%D \from[wschuster]’s {\em fancybreak} and {\em annotation}
%D modules served as the primary source for the following code.
%D You’ll have to thank him if it works and blame me if it doesn’t.

\appendtoks
  \setuevalue{\currentletterspace        }{\doletterspace[\currentletterspace]}%
  \setuevalue{\e!start\currentletterspace}{\dostartletterspace[\currentletterspace]}%
  \setuevalue{\e!stop \currentletterspace}{\dostopletterspace}%
\to \everydefineletterspace

\definecharacterkerning [letterspace:current]

\unexpanded\def\doletterspace[#1]{%
  \edef\currentletterspace{#1}%
  \dosingleempty\dodoletterspace%
}

\def\dodoletterspace[#1]{%
  \iffirstargument
    \doifassignment{#1}{%
      \setupletterspace[\currentletterspace][#1]%
    }%
  \fi
  \dododoletterspace%
}

\definefontfeature [letterspace:kerning] [kern=yes]
\def\letterspace_truevalues{true,yep,yes}

\def\dododoletterspace#1{%
  \def\currentobject{#1}%
  \dontleavehmode
  \setupcharacterkerning[letterspace:current][factor=\letterspaceparameter{factor}]%
  \def\letterspace_setstuff{%
    \setcharacterkerning[letterspace:current]%
    \advance \spaceskip  \letterspaceparameter{spaceskip}%
    \advance \xspaceskip \letterspaceparameter{spaceskip}%
    \doifinset{\letterspaceparameter{suppresskern}}{\letterspace_truevalues}{%
      \subtractfontfeaturefromfont{letterspace:kerning}%
    }%
  }%
  \ifhmode\ifnum\lastnodetype=\@@gluenode
      \unskip{\letterspace_setstuff\ }%
    \fi
  \fi%
  {\letterspace_setstuff\currentobject}%
  % Hans’ macro \doifnextcharelse works a lot better than my
  % previously defined kludge …
  \doifnextcharelse{\ }{%
    {\letterspace_setstuff\ }%
    \gobblespacetokens%
  }{}%
}

%D \macros
%D    {startletterspace,stopletterspace}
%D
%D These rely even more shamelessly on \from[wschuster]’s code
%D from the {\em fancybreak} module.
%D
%D The \type{\[start|stop]letterspace} environment is provided
%D for sake of completeness.

\unexpanded\def\dostartletterspace[#1]{%
  \edef\currentletterspace{#1}%
  \dosingleempty\dodostartletterspace%
}

\def\dodostartletterspace[#1]{%
  \iffirstargument
    \setupletterspace[\currentletterspace][#1]%
  \fi
  \dododoletterspace\bgroup%
}

\let\dostopletterspace\egroup

%D \macros
%D    {setupletterspace}
%D
%D Initial setup.
%D The factor by which the {\em letter space} (i.e. space between
%D glyphs) will be increased is specified via the
%D \type{factor} key.
%D Additionally, it is wise with respect to legibility to enlarge
%D the {\em interword space} as well. That is what the
%D \type{spaceskip} key is for. The {\em spaceskip} should be an
%D ordinary dimension.

\setupletterspace [
  \v!factor=.125,
  \v!spaceskip=.5em,
  \v!suppresskern=false,
]

\defineletterspace[\v!letterspace]

\protect \stopmodule \endinput

% vim:ft=context:sw=2:ts=2