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authorPhilipp Gesang <phg42.2a@gmail.com>2014-07-13 15:30:16 +0200
committerPhilipp Gesang <phg42.2a@gmail.com>2014-07-13 15:30:16 +0200
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treefa315c4a27b4b42e4ba1769a0a5dec6d5cd288f6 /doc/luaotfload-main.tex
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downloadluaotfload-13dd80306495936deedf9ba81e44e7eb258098a4.tar.gz
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+%% Copyright (C) 2009-2014
+%%
+%% by Elie Roux <elie.roux@telecom-bretagne.eu>
+%% and Khaled Hosny <khaledhosny@eglug.org>
+%% and Philipp Gesang <philipp.gesang@alumni.uni-heidelberg.de>
+%%
+%% This file is part of Luaotfload.
+%%
+%% Home: https://github.com/lualatex/luaotfload
+%% Support: <lualatex-dev@tug.org>.
+%%
+%% Luaotfload is under the GPL v2.0 (exactly) license.
+%%
+%% ----------------------------------------------------------------------------
+%%
+%% Luaotfload is free software; you can redistribute it and/or
+%% modify it under the terms of the GNU General Public License
+%% as published by the Free Software Foundation; version 2
+%% of the License.
+%%
+%% Luaotfload is distributed in the hope that it will be useful,
+%% but WITHOUT ANY WARRANTY; without even the implied warranty of
+%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+%% GNU General Public License for more details.
+%%
+%% You should have received a copy of the GNU General Public License
+%% along with Luaotfload; if not, see <http://www.gnu.org/licenses/>.
+%%
+%% ----------------------------------------------------------------------------
+%%
+
+\beginfrontmatter
+
+ \setdocumenttitle {The \identifier{luaotfload} package}
+ \setdocumentdate {2014/**/** v2.5}
+ \setdocumentauthor {Elie Roux · Khaled Hosny · Philipp Gesang\\
+ Home: \hyperlink {https://github.com/lualatex/luaotfload}\\
+ Support: \email {lualatex-dev@tug.org}}
+
+ \typesetdocumenttitle
+
+ \beginabstractcontent
+ This package is an adaptation of the \CONTEXT font loading system.
+ It allows for loading \OpenType fonts with an extended syntax and adds
+ support for a variety of font features.
+ \endabstractcontent
+
+\endfrontmatter
+
+\typesetcontent
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\beginsection {Introduction}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+Font management and installation has always been painful with \TEX. A
+lot of files are needed for one font (\abbrev{tfm}, \abbrev{pfb},
+\abbrev{map}, \abbrev{fd}, \abbrev{vf}), and due to the 8-Bit encoding
+each font is limited to 256 characters.
+
+But the font world has evolved since the original \TEX, and new
+typographic systems have appeared, most notably the so called
+\emphasis{smart font} technologies like \OpenType fonts (\abbrev{otf}).
+
+These fonts can contain many more characters than \TEX fonts, as well
+as additional functionality like ligatures, old-style numbers, small
+capitals, etc., and support more complex writing systems like Arabic
+and Indic\footnote{%
+ Unfortunately, \identifier{luaotfload} doesn‘t support many Indic
+ scripts right now.
+ Assistance in implementing the prerequisites is greatly
+ appreciated.
+}
+scripts.
+
+\OpenType fonts are widely deployed and available for all modern
+operating systems.
+
+As of 2013 they have become the de facto standard for advanced text
+layout.
+
+However, until recently the only way to use them directly in the \TEX
+world was with the \XETEX engine.
+
+Unlike \XETEX, \LUATEX has no built-in support for \OpenType or
+technologies other than the original \TEX fonts.
+
+Instead, it provides hooks for executing \LUA code during the \TEX run
+that allow implementing extensions for loading fonts and manipulating
+how input text is processed without modifying the underlying engine.
+
+This is where \identifier{luaotfload} comes into play:
+Based on code from \CONTEXT, it extends \LUATEX with functionality necessary
+for handling \OpenType fonts.
+
+Additionally, it provides means for accessing fonts known to the operating
+system conveniently by indexing the metadata.
+
+\endsection
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\beginsection {Thanks}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\identifier{Luaotfload} is part of \LUALATEX, the community-driven
+project to provide a foundation for using the \LATEX format with the
+full capabilites of the \LUATEX engine.
+%
+As such, the distinction between end users, contributors, and project
+maintainers is intentionally kept less strict, lest we unduly
+personalize the common effort.
+
+Nevertheless, the current maintainers would like to express their
+gratitude to Khaled Hosny, Akira Kakuto, Hironori Kitagawa and Dohyun
+Kim.
+%
+Their contributions -- be it patches, advice, or systematic
+testing -- made the switch from version 1.x to 2.2 possible.
+%
+Also, Hans Hagen, the author of the font loader, made porting the
+code to \LATEX a breeze due to the extra effort he invested into
+isolating it from the rest of \CONTEXT, not to mention his assistance
+in the task and willingness to respond to our suggestions.
+
+\endsection
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\beginsection {Loading Fonts}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\identifier{luaotfload} supports an extended font request syntax:
+
+\beginnarrower
+ \nonproportional{\string\font\string\foo\space= \string{}%
+ \meta{prefix}\nonproportional{:}%
+ \meta{font name}\nonproportional{:}%
+ \meta{font features}\nonproportional{\string}}%
+ \meta{\TEX font features}
+\endnarrower
+
+\noindent
+The curly brackets are optional and escape the spaces in the enclosed
+font name.
+%
+Alternatively, double quotes serve the same purpose.
+%
+A selection of individual parts of the syntax are discussed below;
+for a more formal description see figure \ref{font-syntax}.
+
+\beginsyntaxfloat
+ {font-syntax}
+ {Font request syntax.
+ Braces or double quotes around the
+ \emphasis{specification} rule will
+ preserve whitespace in file names.
+ In addition to the font style modifiers
+ (\emphasis{slash-notation}) given above, there
+ are others that are recognized but will be silently
+ ignored: \nonproportional{aat},
+ \nonproportional{icu}, and
+ \nonproportional{gr}.
+ The special terminals are:
+ \smallcaps {feature\textunderscore id} for a valid font
+ feature name and
+ \smallcaps {feature\textunderscore value} for the corresponding
+ value.
+ \smallcaps {tfmname} is the name of a \abbrev{tfm} file.
+ \smallcaps {digit} again refers to bytes 48--57, and
+ \smallcaps {all\textunderscore characters} to all byte values.
+ \smallcaps {csname} and \smallcaps {dimension} are the \TEX concepts.}
+%
+ <definition> ::= `\\font', {\sc csname}, `=', <font request>, [ <size> ] ;
+
+ <size> ::= `at', {\sc dimension} ;
+
+ <font request> ::= `"', <unquoted font request> `"'
+ \alt `{', <unquoted font request> `}'
+ \alt <unquoted font request> ;
+
+ <unquoted font request> ::= <specification>, [`:', <feature list> ]
+ \alt `[', <path lookup> `]', [ [`:'], <feature list> ] ;
+
+ <specification> ::= <prefixed spec>, [ <subfont no> ], \{ <modifier> \}
+ \alt <anon lookup>, \{ <modifier> \} ;
+
+ <prefixed spec> ::= `file:', <file lookup>
+ \alt `name:', <name lookup> ;
+
+ <file lookup> ::= \{ <name character> \} ;
+
+ <name lookup> ::= \{ <name character> \} ;
+
+ <anon lookup> ::= {\sc tfmname} | <name lookup> ;
+
+ <path lookup> ::= \{ {\sc all_characters} - `]' \} ;
+
+ <modifier> ::= `/', (`I' | `B' | `BI' | `IB' | `S=', \{ {\sc digit} \} ) ;
+
+ <subfont no> ::= `(', \{ {\sc digit} \}, `)' ;
+
+ <feature list> ::= <feature expr>, \{ `;', <feature expr> \} ;
+
+ <feature expr> ::= {\sc feature_id}, `=', {\sc feature_value}
+ \alt <feature switch>, {\sc feature_id} ;
+
+ <feature switch> ::= `+' | `-' ;
+
+ <name character> ::= {\sc all_characters} - ( `(' | `/' | `:' ) ;
+\endsyntaxfloat
+
+\beginsubsection{Prefix -- the \identifier{luaotfload}{ }Way}
+
+In \identifier{luaotfload}, the canonical syntax for font requests
+requires a \emphasis{prefix}:
+%
+\beginnarrower
+ \nonproportional{\string\font\string\fontname\space= }%
+ \meta{prefix}%
+ \nonproportional{:}%
+ \meta{fontname}%
+ \dots
+\endnarrower
+%
+where \meta{prefix} is either \inlinecode{file:} or \inlinecode {name:}.\footnote{%
+ The development version also knows two further prefixes,
+ \inlinecode {kpse:} and \inlinecode {my:}.
+ %
+ A \inlinecode {kpse} lookup is restricted to files that can be found by
+ \identifier{kpathsea} and
+ will not attempt to locate system fonts.
+ %
+ This behavior can be of value when an extra degree of encapsulation is
+ needed, for instance when supplying a customized tex distribution.
+
+ The \inlinecode {my} lookup takes this a step further: it lets you define
+ a custom resolver function and hook it into the \luafunction{resolve_font}
+ callback.
+ %
+ This ensures full control over how a file is located.
+ %
+ For a working example see the
+ \hyperlink [test repo]{https://bitbucket.org/phg/lua-la-tex-tests/src/5f6a535d/pln-lookup-callback-1.tex}.
+}
+%
+It determines whether the font loader should interpret the request as
+a \emphasis{file name} or
+ \emphasis{font name}, respectively,
+which again influences how it will attempt to locate the font.
+%
+Examples for font names are
+ “Latin Modern Italic”,
+ “GFS Bodoni Rg”, and
+ “PT Serif Caption”
+-- they are the human readable identifiers
+usually listed in drop-down menus and the like.\footnote{%
+ Font names may appear like a great choice at first because they
+ offer seemingly more intuitive identifiers in comparison to arguably
+ cryptic file names:
+ %
+ “PT Sans Bold” is a lot more descriptive than \fileent{PTS75F.ttf}.
+ On the other hand, font names are quite arbitrary and there is no
+ universal method to determine their meaning.
+ %
+ While \identifier{luaotfload} provides fairly sophisticated heuristic
+ to figure out a matching font style, weight, and optical size, it
+ cannot be relied upon to work satisfactorily for all font files.
+ %
+ For an in-depth analysis of the situation and how broken font names
+ are, please refer to
+ \hyperlink [this post]{http://www.ntg.nl/pipermail/ntg-context/2013/073889.html}
+ by Hans Hagen, the author of the font loader.
+ %
+ If in doubt, use filenames.
+ %
+ \fileent{luaotfload-tool} can perform the matching for you with the
+ option \inlinecode {--find=<name>}, and you can use the file name it returns
+ in your font definition.
+}
+%
+In order for fonts installed both in system locations and in your
+\fileent{texmf} to be accessible by font name, \identifier{luaotfload} must
+first collect the metadata included in the files.
+%
+Please refer to section~\ref{sec:fontdb} below for instructions on how to
+create the database.
+
+File names are whatever your file system allows them to be, except
+that that they may not contain the characters
+ \inlinecode {(},
+ \inlinecode {:}, and
+ \inlinecode {/}.
+%
+As is obvious from the last exception, the \inlinecode {file:} lookup will
+not process paths to the font location -- only those
+files found when generating the database are addressable this way.
+%
+Continue below in the \XETEX section if you need to load your fonts
+by path.
+%
+The file names corresponding to the example font names above are
+ \fileent{lmroman12-italic.otf},
+ \fileent{GFSBodoni.otf}, and
+ \fileent{PTZ56F.ttf}.
+
+\endsubsection
+
+\beginsubsection {Compatibility Layer}
+
+In addition to the regular prefixed requests, \identifier{luaotfload}
+accepts loading fonts the \XETEX way.
+%
+There are again two modes: bracketed and unbracketed.
+A bracketed request looks as follows.
+
+\beginnarrower
+ \nonproportional{\string\font\string\fontname\space = [}%
+ \meta{/path/to/file}%
+ \nonproportional{]}
+\endnarrower
+
+\noindent
+Inside the square brackets, every character except for a closing
+bracket is permitted, allowing for specifying paths to a font file.
+%
+Naturally, path-less file names are equally valid and processed the
+same way as an ordinary \inlinecode {file:} lookup.
+
+\beginnarrower
+ \nonproportional{\string\font\string\fontname\space= }%
+ \meta{font name}
+ \dots
+\endnarrower
+
+Unbracketed (or, for lack of a better word: \emphasis{anonymous})
+font requests resemble the conventional \TEX syntax.
+%
+However, they have a broader spectrum of possible interpretations:
+before anything else, \identifier{luaotfload} attempts to load a
+traditional \TEX Font Metric (\abbrev{tfm} or \abbrev{ofm}).
+%
+If this fails, it performs a \inlinecode {name:} lookup, which itself will
+fall back to a \inlinecode {file:} lookup if no database entry matches
+\meta{font name}.
+
+Furthermore, \identifier{luaotfload} supports the slashed (shorthand)
+font style notation from \XETEX.
+
+\beginnarrower
+ \nonproportional{\string\font\string\fontname\space= }%
+ \meta{font name}%
+ \nonproportional{/}%
+ \meta{modifier}
+ \dots
+\endnarrower
+
+\noindent
+Currently, four style modifiers are supported:
+ \inlinecode {I} for italic shape,
+ \inlinecode {B} for bold weight,
+ \inlinecode {BI} or \inlinecode {IB} for the combination of both.
+%
+Other “slashed” modifiers are too specific to the \XETEX engine and
+have no meaning in \LUATEX.
+
+\endsubsection
+
+\beginsubsection{Examples}
+
+\beginsubsubsection{Loading by File Name}
+
+For example, conventional \abbrev{type1} font can be loaded with a
+\inlinecode {file:} request like so:
+
+\beginlisting
+ \font \lmromanten = {file:ec-lmr10} at 10pt
+\endlisting
+
+The \OpenType version of Janusz Nowacki’s font \emphasis{Antykwa
+Półtawskiego}\footnote{%
+ \hyperlink {http://jmn.pl/antykwa-poltawskiego/}, also available in
+ in \TEX Live.
+}
+in its condensed variant can be loaded as follows:
+
+\beginlisting
+ \font \apcregular = file:antpoltltcond-regular.otf at 42pt
+\endlisting
+
+The next example shows how to load the \emphasis{Porson} font digitized by
+the Greek Font Society using \XETEX-style syntax and an absolute path from a
+non-standard directory:
+
+\beginlisting
+ \font \gfsporson = "[/tmp/GFSPorson.otf]" at 12pt
+\endlisting
+
+\endsubsubsection
+
+\beginsubsubsection{Loading by Font Name}
+
+The \inlinecode {name:} lookup does not depend on cryptic filenames:
+
+\beginlisting
+ \font \pagellaregular = {name:TeX Gyre Pagella} at 9pt
+\endlisting
+
+A bit more specific but essentially the same lookup would be:
+
+\beginlisting
+ \font \pagellaregular = {name:TeX Gyre Pagella Regular} at 9pt
+\endlisting
+
+\noindent
+Which fits nicely with the whole set:
+
+\beginlisting
+ \font\pagellaregular = {name:TeX Gyre Pagella Regular} at 9pt
+ \font\pagellaitalic = {name:TeX Gyre Pagella Italic} at 9pt
+ \font\pagellabold = {name:TeX Gyre Pagella Bold} at 9pt
+ \font\pagellabolditalic = {name:TeX Gyre Pagella Bolditalic} at 9pt
+
+ {\pagellaregular foo bar baz\endgraf}
+ {\pagellaitalic foo bar baz\endgraf}
+ {\pagellabold foo bar baz\endgraf}
+ {\pagellabolditalic foo bar baz\endgraf}
+
+ ...
+\endlisting
+
+\endsubsubsection
+
+\beginsubsubsection{Modifiers}
+
+If the entire \emphasis{Iwona} family\footnote{%
+ \hyperlink {http://jmn.pl/kurier-i-iwona/},
+ also in \TEX Live.
+}
+is installed in some location accessible by \identifier{luaotfload},
+the regular shape can be loaded as follows:
+
+\beginlisting
+ \font \iwona = Iwona at 20pt
+\endlisting
+
+\noindent
+To load the most common of the other styles, the slash notation can
+be employed as shorthand:
+
+\beginlisting
+ \font \iwonaitalic = Iwona/I at 20pt
+ \font \iwonabold = Iwona/B at 20pt
+ \font \iwonabolditalic = Iwona/BI at 20pt
+\endlisting
+
+\noindent
+which is equivalent to these full names:
+
+\beginlisting
+ \font \iwonaitalic = "Iwona Italic" at 20pt
+ \font \iwonabold = "Iwona Bold" at 20pt
+ \font \iwonabolditalic = "Iwona BoldItalic" at 20pt
+\endlisting
+
+\endsubsubsection
+\endsubsection
+\endsection
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\beginsection {Font features}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\emphasis{Font features} are the second to last component in the
+general scheme for font requests:
+
+\beginnarrower
+ \nonproportional{\string\font\string\foo\space= "}%
+ \meta{prefix}%
+ \nonproportional{:}%
+ \meta{font name}%
+ \nonproportional{:}%
+ \meta{font features}%
+ \meta{\TEX font features}%
+ \nonproportional{"}
+\endnarrower
+
+\noindent
+If style modifiers are present (\XETEX style), they must precede
+\meta{font features}.
+
+The element \meta{font features} is a semicolon-separated list of feature
+tags\footnote{%
+ Cf. \hyperlink {http://www.microsoft.com/typography/otspec/featurelist.htm}.
+}
+and font options.
+%
+Prepending a font feature with a \inlinecode{+} (plus sign) enables it,
+whereas a \inlinecode{-} (minus) disables it. For instance, the request
+
+\beginlisting
+ \font \test = LatinModernRoman:+clig;-kern
+\endlisting
+
+\noindent activates contextual ligatures (\inlinecode{clig}) and
+disables kerning (\inlinecode{kern}).
+%
+Alternatively the options \inlinecode{true} or \inlinecode{false} can
+be passed to the feature in a key/value expression.
+%
+The following request has the same meaning as the last one:
+
+\beginlisting
+ \font \test = LatinModernRoman:clig=true;kern=false
+\endlisting
+
+\noindent
+Furthermore, this second syntax is required should a font feature
+accept other options besides a true/false switch.
+%
+For example, \emphasis{stylistic alternates} (\inlinecode{salt}) are
+variants of given glyphs.
+%
+They can be selected either explicitly by supplying the variant
+index (starting from one), or randomly by setting the value to,
+obviously, \inlinecode{random}.
+
+%% TODO verify that this actually works with a font that supports
+%% the salt/random feature!\fi
+\beginlisting
+ \font \librmsaltfirst = LatinModernRoman:salt=1
+\endlisting
+
+\beginsubsection {Basic font features}
+
+\begindescriptions
+
+ \beginaltitem {mode}
+ \identifier{luaotfload} has two \OpenType processing
+ \emphasis{modes}:
+ \identifier{base} and \identifier{node}.
+
+ \identifier{base} mode works by mapping \OpenType
+ features to traditional \TEX ligature and kerning mechanisms.
+ %
+ Supporting only non-contextual substitutions and kerning
+ pairs, it is the slightly faster, albeit somewhat limited, variant.
+ %
+ \identifier{node} mode works by processing \TeX’s internal
+ node list directly at the \LUA end and supports
+ a wider range of \OpenType features.
+ %
+ The downside is that the intricate operations required for
+ \identifier{node} mode may slow down typesetting especially
+ with complex fonts and it does not work in math mode.
+
+ By default \identifier{luaotfload} is in \identifier{node}
+ mode, and \identifier{base} mode has to be requested where needed,
+ e.~g. for math fonts.
+ \endaltitem
+
+ \beginaltitem {script} \label{script-tag}
+ An \OpenType script tag;\footnote{%
+ See \hyperlink {http://www.microsoft.com/typography/otspec/scripttags.htm}
+ for a list of valid values.
+ %
+ For scripts derived from the Latin alphabet the value
+ \inlinecode{latn} is good choice.
+ }
+ the default value is \inlinecode{dlft}.
+ %
+ Some fonts, including very popular ones by foundries like Adobe,
+ do not assign features to the \inlinecode{dflt} script, in
+ which case the script needs to be set explicitly.
+ \endaltitem
+
+ \beginaltitem {language}
+ An \OpenType language system identifier,\footnote{%
+ Cf. \hyperlink {http://www.microsoft.com/typography/otspec/languagetags.htm}.
+ }
+ defaulting to \inlinecode{dflt}.
+ \endaltitem
+
+ \beginaltitem {featurefile}
+ A comma-separated list of feature files to be applied to the
+ font.
+ %
+ Feature files contain a textual representation of
+ \OpenType tables and extend the features of a font
+ on fly.
+ %
+ After they are applied to a font, features defined in a
+ feature file can be enabled or disabled just like any
+ other font feature.
+ %
+ The syntax is documented in \identifier{Adobe}’s
+ \OpenType Feature File Specification.\footnote{%
+ Cf. \hyperlink {http://www.adobe.com/devnet/opentype/afdko/topic_feature_file_syntax.html}.
+ Feature file support is part of the engine which at the
+ time of this writing (2014) implements the spec only
+ partially.
+ See the
+ \hyperlink [\LUATEX tracker]{http://tracker.luatex.org/view.php?id=231}
+ for details.
+ }
+
+ For a demonstration of how to set a \inlinecode{tkrn} feature consult
+ the file \inlinecode{tkrn.fea} that is part of \identifier{luaotfload}.
+ It can be read and applied as follows:
+
+ \inlinecode{\\font \\test = Latin Modern Roman:featurefile=tkrn.fea;+tkrn}
+ \endaltitem
+
+ \beginaltitem {color}
+ A font color, defined as a triplet of two-digit hexadecimal
+ \abbrev{rgb} values, with an optional fourth value for
+ transparency
+ (where \inlinecode{00} is completely transparent and
+ \inlinecode{FF} is opaque).
+
+ For example, in order to set text in semitransparent red:
+
+ \beginlisting
+\font \test = "Latin Modern Roman:color=FF0000BB"
+ \endlisting
+ \endaltitem
+
+ \beginaltitem {kernfactor \& letterspace}
+ Define a font with letterspacing (tracking) enabled.
+ %
+ In \identifier{luaotfload}, letterspacing is implemented by
+ inserting additional kerning between glyphs.
+
+ This approach is derived from and still quite similar to the
+ \emphasis{character kerning} (\texmacro{setcharacterkerning} /
+ \texmacro{definecharacterkerning} \& al.) functionality of
+ Context, see the file \fileent{typo-krn.lua} there.
+ %
+ The main difference is that \identifier{luaotfload} does not
+ use \LUATEX attributes to assign letterspacing to regions,
+ but defines virtual letterspaced versions of a font.
+
+ The option \identifier{kernfactor} accepts a numeric value that
+ determines the letterspacing factor to be applied to the font
+ size.
+ %
+ E.~g. a kern factor of $0.42$ applied to a $10$ pt font
+ results in $4.2$ pt of additional kerning applied to each
+ pair of glyphs.
+ %
+ Ligatures are split into their component glyphs unless
+ explicitly ignored (see below).
+
+ For compatibility with \XETEX an alternative
+ \identifier{letterspace} option is supplied that interprets the
+ supplied value as a \emphasis{percentage} of the font size but
+ is otherwise identical to \identifier{kernfactor}.
+ %
+ Consequently, both definitions in below snippet yield the same
+ letterspacing width:
+
+ \beginlisting
+\font \iwonakernedA = "file:Iwona-Regular.otf:kernfactor=0.125"
+\font \iwonakernedB = "file:Iwona-Regular.otf:letterspace=12.5"
+ \endlisting
+
+ Specific pairs of letters and ligatures may be exempt from
+ letterspacing by defining the \LUA functions
+ \luafunction{keeptogether} and \luafunction{keepligature},
+ respectively, inside the namespace \inlinecode {luaotfload.letterspace}.
+ %
+ Both functions are called whenever the letterspacing callback
+ encounters an appropriate node or set of nodes.
+ %
+ If they return a true-ish value, no extra kern is inserted at
+ the current position.
+ %
+ \luafunction{keeptogether} receives a pair of consecutive
+ glyph nodes in order of their appearance in the node list.
+ %
+ \luafunction{keepligature} receives a single node which can be
+ analyzed into components.
+ %
+ (For details refer to the \emphasis{glyph nodes} section in the
+ \LUATEX reference manual.)
+ %
+ The implementation of both functions is left entirely to the
+ user.
+ \endaltitem
+
+\ifcontextmkiv
+ \startbuffer [printvectors]
+ \directlua{inspect(fonts.protrusions.setups.default)
+ inspect(fonts.expansions.setups.default)}
+ \stopbuffer
+\fi
+
+ \beginaltitem {protrusion \& expansion}
+ These keys control microtypographic features of the font,
+ namely \emphasis{character protrusion} and \emphasis{font
+ expansion}.
+ %
+ Their arguments are names of \LUA tables that contain
+ values for the respective features.\footnote{%
+ For examples of the table layout please refer to the
+ section of the file \fileent{luaotfload-fonts-ext.lua} where the
+ default values are defined.
+ %
+ Alternatively and with loss of information, you can dump
+ those tables into your terminal by issuing
+ \unless \ifcontextmkiv
+ \beginlisting
+ \directlua{inspect(fonts.protrusions.setups.default)
+ inspect(fonts.expansions.setups.default)}
+ \endlisting
+ \else
+ \typebuffer [printvectors]
+ \fi
+ at some point after loading \fileent{luaotfload.sty}.
+ }
+ %
+ For both, only the set \identifier{default} is predefined.
+
+ For example, to define a font with the default
+ protrusion vector applied\footnote{%
+ You also need to set
+ \inlinecode {pdfprotrudechars=2} and
+ \inlinecode {pdfadjustspacing=2}
+ to activate protrusion and expansion, respectively.
+ See the
+ \hyperlink [\PDFTEX manual]{http://mirrors.ctan.org/systems/pdftex/manual/pdftex-a.pdf}%
+ for details.
+ }:
+
+ \beginlisting
+\font \test = LatinModernRoman:protrusion=default
+ \endlisting
+ \endaltitem
+\enddescriptions
+
+\endsubsection
+
+\beginsubsection {Non-standard font features}
+\identifier{luaotfload} adds a number of features that are not defined
+in the original \OpenType specification, most of them
+aiming at emulating the behavior familiar from other \TEX engines.
+%
+Currently (2014) there are three of them:
+
+\begindescriptions
+
+ \beginaltitem {anum}
+ Substitutes the glyphs in the \abbrev{ascii} number range
+ with their counterparts from eastern Arabic or Persian,
+ depending on the value of \identifier{language}.
+ \endaltitem
+
+ \beginaltitem {tlig}
+ Applies legacy \TEX ligatures\footnote{%
+ These contain the feature set \inlinecode {trep} of earlier
+ versions of \identifier{luaotfload}.
+
+ Note to \XETEX users: this is the equivalent of the
+ assignment \inlinecode {mapping=text-tex} using \XETEX's input
+ remapping feature.
+ }:
+
+ \unless \ifcontextmkiv
+ %% Using braced arg syntax with inline code appears to be
+ %% impossible within Latex tables -- just ignore the weird
+ %% exclamation points below.
+ \begintabulate [rlrl]
+ \beginrow `` \newcell {\inlinecode !``! } \newcell '' \newcell {\inlinecode !''!} \endrow
+ \beginrow ` \newcell {\inlinecode !`! } \newcell ' \newcell {\inlinecode !'! } \endrow
+ \beginrow " \newcell {\inlinecode !"! } \newcell -- \newcell {\inlinecode !--!} \endrow
+ \beginrow --- \newcell {\inlinecode !---!} \newcell !` \newcell {\inlinecode ?!`?} \endrow
+ \beginrow ?` \newcell {\inlinecode !?`! } \newcell \newcell \endrow
+ \endtabulate
+ \else
+ %% XXX find a way to wrap these in the tabulate environment
+ \startframed [frame=off,width=broad,align=middle]
+ \startframed [frame=off,width=\dimexpr(\textwidth/2)]
+ \startxtable [align=middle]
+ \startxrow \startxcell `` \stopxcell \startxcell \inlinecode {``} \stopxcell \startxcell '' \stopxcell \startxcell \inlinecode {''} \stopxcell \stopxrow
+ \startxrow \startxcell ` \stopxcell \startxcell \inlinecode {`} \stopxcell \startxcell ' \stopxcell \startxcell \inlinecode {'} \stopxcell \stopxrow
+ \startxrow \startxcell " \stopxcell \startxcell \inlinecode {"} \stopxcell \startxcell -- \stopxcell \startxcell \inlinecode {--} \stopxcell \stopxrow
+ \startxrow \startxcell --- \stopxcell \startxcell \inlinecode {---} \stopxcell \startxcell !` \stopxcell \startxcell \inlinecode {!`} \stopxcell \stopxrow
+ \startxrow \startxcell ?` \stopxcell \startxcell \inlinecode {?`} \stopxcell \startxcell \stopxcell \startxcell \stopxcell \stopxrow
+ \stopxtable
+ \stopframed
+ \stopframed
+ \fi
+ \endaltitem
+
+ \beginaltitem {itlc}
+ Computes italic correction values (active by default).
+ \endaltitem
+
+\enddescriptions
+
+\endsubsection
+\endsection
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\beginsection {Font names database}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\label{sec:fontdb}
+
+As mentioned above, \identifier{luaotfload} keeps track of which
+fonts are available to \LUATEX by means of a \emphasis{database}.
+%
+This allows referring to fonts not only by explicit filenames but
+also by the proper names contained in the metadata which is often
+more accessible to humans.\footnote{%
+ The tool \hyperlink[\fileent{otfinfo}]{http://www.lcdf.org/type/}
+ (comes with \TEX Live), when invoked on a font file with the
+ \inlinecode {-i} option, lists the variety of name fields defined for
+ it.
+}
+
+When \identifier{luaotfload} is asked to load a font by a font name,
+it will check if the database exists and load it, or else generate a
+fresh one.
+%
+Should it then fail to locate the font, an update to the database is
+performed in case the font has been added to the system only
+recently.
+%
+As soon as the database is updated, the resolver will try
+and look up the font again, all without user intervention.
+%
+The goal is for \identifier{luaotfload} to act in the background and
+behave as unobtrusively as possible, while providing a convenient
+interface to the fonts installed on the system.
+
+Generating the database for the first time may take a while since it
+inspects every font file on your computer.
+%
+This is particularly noticeable if it occurs during a typesetting run.
+In any case, subsequent updates to the database will be quite fast.
+
+\beginsubsection[luaotfload-tool]
+ {\fileent{luaotfload-tool}}
+
+It can still be desirable at times to do some of these steps
+manually, and without having to compile a document.
+%
+To this end, \identifier{luaotfload} comes with the utility
+\fileent{luaotfload-tool} that offers an interface to the database
+functionality.
+%
+Being a \LUA script, there are two ways to run it:
+either make it executable (\inlinecode {chmod +x} on unixoid systems) or
+pass it as an argument to \fileent{texlua}.\footnote{%
+ Tests by the maintainer show only marginal performance gain by
+ running with Luigi Scarso’s
+ \hyperlink [\identifier{Luajit\kern-.25ex\TEX}]{https://foundry.supelec.fr/projects/luajittex/},
+ which is probably due to the fact that most of the time is spent
+ on file system operations.
+
+ \emphasis{Note}:
+ On \abbrev{MS} \identifier{Windows} systems, the script can be run
+ either by calling the wrapper application
+ \fileent{luaotfload-tool.exe} or as
+ \inlinecode {texlua.exe luaotfload-tool.lua}.
+}
+%
+Invoked with the argument \inlinecode {--update} it will perform a database
+update, scanning for fonts not indexed.
+
+\beginlisting
+ luaotfload-tool --update
+\endlisting
+
+Adding the \inlinecode {--force} switch will initiate a complete
+rebuild of the database.
+
+\beginlisting
+ luaotfload-tool --update --force
+\endlisting
+
+\endsubsection
+
+\beginsubsection{Search Paths}
+
+\identifier{luaotfload} scans those directories where fonts are
+expected to be located on a given system.
+%
+On a Linux machine it follows the paths listed in the
+\identifier{Fontconfig} configuration files;
+consult \inlinecode {man 5 fonts.conf} for further information.
+%
+On \identifier{Windows} systems, the standard location is
+\inlinecode {Windows\\Fonts},
+%
+while \identifier{Mac OS~X} requires a multitude of paths to
+be examined.
+%
+The complete list is is given in table \ref{table-searchpaths}.
+Other paths can be specified by setting the environment variable
+\inlinecode {OSFONTDIR}.
+%
+If it is non-empty, then search will be extended to the included
+directories.
+
+\tablefloat {table-searchpaths}
+ {List of paths searched for each supported operating system.}
+ {%
+ \unless \ifcontextmkiv
+ \begincentered
+ \begintabulate [lp{.5\textwidth}]
+ \beginrow
+ Windows \newcell \inlinecode !\% WINDIR\%\\ Fonts!
+ \endrow
+ \beginrow
+ Linux \newcell \fileent{/usr/local/etc/fonts/fonts.conf} and\hfill\break
+ \fileent{/etc/fonts/fonts.conf}
+ \endrow
+ \beginrow
+ Mac \newcell \fileent{\textasciitilde/Library/Fonts},\break
+ \fileent{/Library/Fonts},\break
+ \fileent{/System/Library/Fonts}, and\hfill\break
+ \fileent{/Network/Library/Fonts}
+ \endrow
+ \endtabulate
+ \endcentered
+ \else
+ \setuplocalinterlinespace [14pt]
+ \starttabulate [|l|p(.5\textwidth)|]
+ \NC Windows \NC \inlinecode {\% WINDIR\%\\ Fonts} \NC \NR
+ \NC Linux \NC \fileent{/usr/local/etc/fonts/fonts.conf} and\crlf
+ \fileent{/etc/fonts/fonts.conf} \NC \NR
+ \NC
+ Mac \NC \fileent{\textasciitilde/Library/Fonts},\crlf
+ \fileent{/Library/Fonts},\break
+ \fileent{/System/Library/Fonts}, and\crlf
+ \fileent{/Network/Library/Fonts} \NC \NR
+ \stoptabulate
+ \fi%
+ }
+
+\endsubsection
+
+\beginsubsection{Querying from Outside}
+
+\fileent{luaotfload-tool} also provides rudimentary means of
+accessing the information collected in the font database.
+%
+If the option \inlinecode {--find=}\emphasis{name} is given, the script will
+try and search the fonts indexed by \identifier{luaotfload} for a
+matching name.
+%
+For instance, the invocation
+
+\beginlisting
+ luaotfload-tool --find="Iwona Regular"
+\endlisting
+
+\noindent
+will verify if “Iwona Regular” is found in the database and can be
+readily requested in a document.
+
+If you are unsure about the actual font name, then add the
+\inlinecode {-F} (or \inlinecode {--fuzzy}) switch to the command line to enable
+approximate matching.
+%
+Suppose you cannot precisely remember if the variant of
+\identifier{Iwona} you are looking for was “Bright” or “Light”.
+The query
+
+\beginlisting
+ luaotfload-tool -F --find="Iwona Bright"
+\endlisting
+
+\noindent
+will tell you that indeed the latter name is correct.
+
+Basic information about fonts in the database can be displayed
+using the \inlinecode {-i} option (\inlinecode {--info}).
+%
+\beginlisting
+ luaotfload-tool -i --find="Iwona Light Italic"
+\endlisting
+%
+\noindent
+The meaning of the printed values is described in section 4.4 of the
+\LUATEX reference manual.\footnote{%
+ In \TEX Live: \fileent{texmf-dist/doc/luatex/base/luatexref-t.pdf}.
+}
+
+For a much more detailed report about a given font try the
+\inlinecode {-I} option instead (\inlinecode {--inspect}).
+\beginlisting
+ luaotfload-tool -I --find="Iwona Light Italic"
+\endlisting
+
+\inlinecode {luaotfload-tool --help} will list the available command line
+switches, including some not discussed in detail here.
+%
+For a full documentation of \identifier{luaotfload-tool} and its
+capabilities refer to the manpage
+(\inlinecode {man 1 luaotfload-tool}).\footnote{%
+ Or see \inlinecode {luaotfload-tool.rst} in the source directory.
+}
+
+\endsubsection
+
+\beginsubsection {Blacklisting Fonts}
+\label{font-blacklist}
+
+Some fonts are problematic in general, or just in \LUATEX.
+%
+If you find that compiling your document takes far too long or eats
+away all your system’s memory, you can track down the culprit by
+running \inlinecode {luaotfload-tool -v} to increase verbosity.
+%
+Take a note of the \emphasis{filename} of the font that database
+creation fails with and append it to the file
+\fileent{luaotfload-blacklist.cnf}.
+
+A blacklist file is a list of font filenames, one per line.
+Specifying the full path to where the file is located is optional, the
+plain filename should suffice.
+%
+File extensions (\fileent{.otf}, \fileent{.ttf}, etc.) may be omitted.
+%
+Anything after a percent (\inlinecode {\%}) character until the end of the line
+is ignored, so use this to add comments.
+%
+Place this file to some location where the \identifier{kpse}
+library can find it, e.~g.
+\fileent{texmf-local/tex/luatex/luaotfload} if you are running
+\identifier{\TEX Live},\footnote{%
+ You may have to run \inlinecode {mktexlsr} if you created a new file in
+ your \fileent{texmf} tree.
+}
+or just leave it in the working directory of your document.
+%
+\identifier{luaotfload} reads all files named
+\fileent{luaotfload-blacklist.cnf} it finds, so the fonts in
+\fileent{./luaotfload-blacklist.cnf} extend the global blacklist.
+
+Furthermore, a filename prepended with a dash character (\inlinecode{-}) is
+removed from the blacklist, causing it to be temporarily whitelisted
+without modifying the global file.
+%
+An example with explicit paths:
+
+\beginlisting
+% example otf-blacklist.cnf
+/Library/Fonts/GillSans.ttc % Luaotfload ignores this font.
+-/Library/Fonts/Optima.ttc % This one is usable again, even if
+ % blacklisted somewhere else.
+\endlisting
+
+\endsubsection
+\endsection
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\beginsection {Files from \CONTEXT and \LUATEX-Fonts}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\identifier{luaotfload} relies on code originally written by Hans
+Hagen for the \hyperlink[\identifier{\CONTEXT}]{http://wiki.contextgarden.net}
+format.
+%
+It integrates the font loader as distributed in
+the \identifier{\LUATEX-Fonts} package.
+%
+The original \LUA source files have been combined using the
+\fileent{mtx-package} script into a single, self-contained blob.
+In this form the font loader has no further dependencies\footnote{%
+ It covers, however, to some extent the functionality of the
+ \identifier{lualibs} package.
+}
+and requires only minor adaptions to integrate into
+\identifier{luaotfload}.
+%
+The guiding principle is to let \CONTEXT/\LUATEX-Fonts take care of
+the implementation, and update the imported code from time to time.
+%
+As maintainers, we aim at importing files from upstream essentially
+\emphasis{unmodified}, except for renaming them to prevent name
+clashes.
+%
+This job has been greatly alleviated since the advent of
+\LUATEX-Fonts, prior to which the individual dependencies had to be
+manually spotted and extracted from the \CONTEXT source code in a
+complicated and error-prone fashion.
+
+Below is a commented list of the files distributed with
+\identifier{luaotfload} in one way or the other.
+%
+See figure \ref{file-graph} on page \pageref{file-graph} for a
+graphical representation of the dependencies.
+%
+From \LUATEX-Fonts, only the file \fileent{luatex-fonts-merged.lua}
+has been imported as \fileent{luaotfload-fontloader.lua}.
+%
+It is generated by \fileent{mtx-package}, a \LUA source code merging
+too developed by Hans Hagen.\footnote{%
+ \fileent{mtx-package} is
+ \hyperlink [part of \CONTEXT]{http://repo.or.cz/w/context.git/blob_plain/refs/heads/origin:/scripts/context/lua/mtx-package.lua}
+ and requires \fileent{mtxrun}.
+ Run
+ \inlinecode {mtxrun --script package --help}
+ to display further information.
+ For the actual merging code see the file
+ \fileent{util-mrg.lua} that is part of \CONTEXT.
+}
+It houses several \LUA files that can be classed in three
+categories.
+
+\begindefinitions
+ \beginnormalitem
+ \emphasis{\LUA utility libraries}, a subset
+ of what is provided by the \identifier{lualibs}
+ package.
+
+ \begindoublecolumns
+ \begindefinitions
+ \beginaltitem {l-lua.lua} \endaltitem
+ \beginaltitem {l-lpeg.lua} \endaltitem
+ \beginaltitem {l-function.lua} \endaltitem
+ \beginaltitem {l-string.lua} \endaltitem
+ \beginaltitem {l-table.lua} \endaltitem
+ \beginaltitem {l-io.lua} \endaltitem
+ \beginaltitem {l-file.lua} \endaltitem
+ \beginaltitem {l-boolean.lua} \endaltitem
+ \beginaltitem {l-math.lua} \endaltitem
+ \beginaltitem {util-str.lua} \endaltitem
+ \enddefinitions
+ \enddoublecolumns
+ \endnormalitem
+
+ \beginnormalitem
+ The \emphasis{font loader} itself.
+ These files have been written for
+ \LUATEX-Fonts and they are distributed along
+ with \identifier{luaotfload}.
+ \begindoublecolumns
+ \begindefinitions
+ \beginaltitem{luatex-basics-gen.lua} \endaltitem
+ \beginaltitem{luatex-basics-nod.lua} \endaltitem
+ \beginaltitem{luatex-fonts-enc.lua} \endaltitem
+ \beginaltitem{luatex-fonts-syn.lua} \endaltitem
+ \beginaltitem{luatex-fonts-tfm.lua} \endaltitem
+ \beginaltitem{luatex-fonts-chr.lua} \endaltitem
+ \beginaltitem{luatex-fonts-lua.lua} \endaltitem
+ \beginaltitem{luatex-fonts-inj.lua} \endaltitem
+ \beginaltitem{luatex-fonts-otn.lua} \endaltitem
+ \beginaltitem{luatex-fonts-def.lua} \endaltitem
+ \beginaltitem{luatex-fonts-ext.lua} \endaltitem
+ \beginaltitem{luatex-fonts-cbk.lua} \endaltitem
+ \enddefinitions
+ \enddoublecolumns
+ \endnormalitem
+
+ \beginnormalitem
+ Code related to \emphasis{font handling and
+ node processing}, taken directly from
+ \CONTEXT.
+ \begindoublecolumns
+ \begindefinitions
+ \beginaltitem{data-con.lua} \endaltitem
+ \beginaltitem{font-ini.lua} \endaltitem
+ \beginaltitem{font-con.lua} \endaltitem
+ \beginaltitem{font-cid.lua} \endaltitem
+ \beginaltitem{font-map.lua} \endaltitem
+ \beginaltitem{font-oti.lua} \endaltitem
+ \beginaltitem{font-otf.lua} \endaltitem
+ \beginaltitem{font-otb.lua} \endaltitem
+ \beginaltitem{font-ota.lua} \endaltitem
+ \beginaltitem{font-def.lua} \endaltitem
+ \beginaltitem{font-otp.lua} \endaltitem
+ \enddefinitions
+ \enddoublecolumns
+ \endnormalitem
+\enddefinitions
+
+Note that if \identifier{luaotfload} cannot locate the
+merged file, it will load the individual \LUA libraries
+instead.
+%
+Their names remain the same as in \CONTEXT (without the
+\inlinecode {otfl}-prefix) since we imported the relevant section of
+\fileent{luatex-fonts.lua} unmodified into \fileent{luaotfload-main.lua}.
+Thus if you prefer running bleeding edge code from the
+\CONTEXT beta, all you have to do is remove
+\fileent{luaotfload-merged.lua} from the search path.
+
+Also, the merged file at some point loads the Adobe Glyph List from a
+\LUA table that is contained in \fileent{luaotfload-glyphlist.lua},
+which is automatically generated by the script
+\fileent{mkglyphlist}.\footnote{%
+ See \fileent{luaotfload-font-enc.lua}.
+ The hard-coded file name is why we have to replace the procedure
+ that loads the file in \fileent{luaotfload-override.lua}.
+}
+There is a make target \identifier{glyphs} that will create a fresh
+glyph list so we don’t need to import it from \CONTEXT any longer.
+
+In addition to these, \identifier{luaotfload} requires a number of
+files not contained in the merge. Some of these have no equivalent in
+\LUATEX-Fonts or \CONTEXT, some were taken unmodified from the latter.
+
+
+\beginfilelist
+ \beginaltitem {luaotfload-features.lua}
+ font feature handling; incorporates some of the code from
+ \fileent{font-otc} from \CONTEXT;
+ \endaltitem
+ \beginaltitem {luaotfload-override.lua}
+ overrides the \CONTEXT logging functionality.
+ \endaltitem
+ \beginaltitem {luaotfload-loaders.lua}
+ registers the \OpenType font reader as handler for Postscript
+ fonts (\abbrev{pfa}, \abbrev{pfb}).
+ \endaltitem
+ \beginaltitem {luaotfload-parsers.lua}
+ various \abbrev{lpeg}-based parsers.
+ \endaltitem
+ \beginaltitem {luaotfload-database.lua}
+ font names database.
+ \endaltitem
+ \beginaltitem {luaotfload-colors.lua}
+ color handling.
+ \endaltitem
+ \beginaltitem {luaotfload-auxiliary.lua}
+ access to internal functionality for package authors (proposals
+ for additions welcome).
+ \endaltitem
+ \beginaltitem {luaotfload-letterspace.lua}
+ font-based letterspacing.
+ \endaltitem
+\endfilelist
+
+\figurefloat
+ {file-graph}
+ {Schematic of the files in \identifier{Luaotfload}}
+ {filegraph.pdf}
+
+\endsection
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\beginsection {Auxiliary Functions}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+With release version 2.2, \identifier{luaotfload} received
+additional functions for package authors to call from outside
+(see the file \fileent{luaotfload-auxiliary.lua} for details).
+%
+The purpose of this addition twofold.
+%
+Firstly, \identifier{luaotfload} failed to provide a stable interface
+to internals in the past which resulted in an unmanageable situation
+of different packages abusing the raw access to font objects by means
+of the \luafunction{patch_font} callback.
+%
+When the structure of the font object changed due to an update, all
+of these imploded and several packages had to be fixed while
+simultaneously providing fallbacks for earlier versions.
+%
+Now the patching is done on the \identifier{luaotfload} side and can
+be adapted with future modifications to font objects without touching
+the packages that depend on it.
+%
+Second, some the capabilities of the font loader and the names
+database are not immediately relevant in \identifier{luaotfload}
+itself but might nevertheless be of great value to package authors or
+end users.
+
+Note that the current interface is not yet set in stone and the
+development team is open to suggestions for improvements or
+additions.
+
+\beginsubsection {Callback Functions}
+
+The \luafunction{patch_font} callback is inserted in the wrapper
+\identifier{luaotfload} provides for the font definition callback
+(see below, page \pageref{define-font}).
+%
+At this place it allows manipulating the font object immediately after
+the font loader is done creating it.
+%
+For a short demonstration of its usefulness, here is a snippet that
+writes an entire font object to the file \fileent{fontdump.lua}:
+
+\beginlisting
+ \input luaotfload.sty
+ \directlua{
+ local dumpfile = "fontdump.lua"
+ local dump_font = function (tfmdata)
+ local data = table.serialize(tfmdata)
+ io.savedata(dumpfile, data)
+ end
+
+ luatexbase.add_to_callback(
+ "luaotfload.patch_font",
+ dump_font,
+ "my_private_callbacks.dump_font"
+ )
+ }
+ \font \dumpme = name:Iwona
+ \bye
+\endlisting
+
+\emphasis{Beware}: this creates a Lua file of around 150,000 lines of
+code, taking up 3~\abbrev{mb} of disk space.
+%
+By inspecting the output you can get a first impression of how a font
+is structured in \LUATEX’s memory, what elements it is composed of,
+and in what ways it can be rearranged.
+
+\beginsubsubsection {Compatibility with Earlier Versions}
+
+As has been touched on in the preface to this section, the structure
+of the object as returned by the fontloader underwent rather drastic
+changes during different stages of its development, and not all
+packages that made use of font patching have kept up with every one
+of it.
+%
+To ensure compatibility with these as well as older versions of
+some packages, \identifier{luaotfload} sets up copies of or references
+to data in the font table where it used to be located.
+%
+For instance, important parameters like the requested point size, the
+units factor, and the font name have again been made accessible from
+the toplevel of the table even though they were migrated to different
+subtables in the meantime.
+
+\endsubsubsection
+
+\beginsubsubsection{Patches}
+
+These are mostly concerned with establishing compatibility with \XETEX.
+
+\beginfunctionlist
+
+ \beginaltitem {set_sscale_dimens}
+ Calculate \texmacro{fontdimen}s 10 and 11 to emulate \XETEX.
+ \endaltitem
+
+ \beginaltitem {set_capheight}
+ Calculates \texmacro{fontdimen} 8 like \XETEX.
+ \endaltitem
+
+ \beginaltitem {patch_cambria_domh}
+ Correct some values of the font \emphasis{Cambria Math}.
+ \endaltitem
+
+\endfunctionlist
+
+\endsubsection
+
+\beginsubsection {Package Author’s Interface}
+
+As \LUATEX release 1.0 is nearing, the demand for a reliable interface
+for package authors increases.
+
+\endsubsubsection
+
+\beginsubsubsection{Font Properties}
+
+Below functions mostly concern querying the different components of a
+font like for instance the glyphs it contains, or what font features
+are defined for which scripts.
+
+\beginfunctionlist
+
+ \beginaltitem {aux.font_has_glyph (id : int, index : int)}
+ Predicate that returns true if the font \luafunction{id}
+ has glyph \luafunction{index}.
+ \endaltitem
+
+ \beginaltitem {aux.slot_of_name(name : string)}
+ Translates an Adobe Glyph name to the corresponding glyph
+ slot.
+ \endaltitem
+
+ \beginaltitem {aux.name_of_slot(slot : int)}
+ The inverse of \luafunction{slot_of_name}; note that this
+ might be incomplete as multiple glyph names may map to the
+ same codepoint, only one of which is returned by
+ \luafunction{name_of_slot}.
+ \endaltitem
+
+ \beginaltitem {aux.provides_script(id : int, script : string)}
+ Test if a font supports \luafunction{script}.
+ \endaltitem
+
+ \beginaltitem {aux.provides_language(id : int, script : string, language : string)}
+ Test if a font defines \luafunction{language} for a given
+ \luafunction{script}.
+ \endaltitem
+
+ \beginaltitem {aux.provides_feature(id : int, script : string,
+ language : string, feature : string)}
+ Test if a font defines \luafunction{feature} for
+ \luafunction{language} for a given \luafunction{script}.
+ \endaltitem
+
+ \beginaltitem {aux.get_math_dimension(id : int, dimension : string)}
+ Get the dimension \luafunction{dimension} of font \luafunction{id}.
+ \endaltitem
+
+ \beginaltitem {aux.sprint_math_dimension(id : int, dimension : string)}
+ Same as \luafunction{get_math_dimension()}, but output the value
+ in scaled points at the \TEX end.
+ \endaltitem
+
+\endfunctionlist
+
+\endsubsubsection
+
+\beginsubsubsection{Database}
+
+%% not implemented, may come back later
+\beginfunctionlist
+% \beginaltitem {aux.scan_external_dir(dir : string)}
+% Include fonts in directory \luafunction{dir} in font lookups without
+% adding them to the database.
+%
+ \beginaltitem {aux.read_font_index (void)}
+ Read the index file from the appropriate location (usually
+ the bytecode file \fileent{luaotfload-names.luc} somewhere
+ in the \fileent{texmf-var} tree) and return the result as a
+ table. The file is processed with each call so it is up to
+ the user to store the result for later access.
+ \endaltitem
+
+ \beginaltitem {aux.font_index (void)}
+ Return a reference of the font names table used internally
+ by \identifier{luaotfload}. The index will be read if it
+ has not been loaded up to this point. Also a font scan that
+ overwrites the current index file might be triggered. Since
+ the return value points to the actual index, any
+ modifications to the table might influence runtime behavior
+ of \identifier{luaotfload}.
+ \endaltitem
+
+\endfunctionlist
+
+\endsubsubsection
+
+\endsubsection
+\endsection
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\beginsection {Troubleshooting}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\beginsubsection {Database Generation}
+
+If you encounter problems with some fonts, please first update to the
+latest version of this package before reporting a bug, as
+\identifier{luaotfload} is under active development and still a moving
+target.
+%
+The development takes place on \identifier{github} at
+\hyperlink {https://github.com/lualatex/luaotfload} where there is an issue
+tracker for submitting bug reports, feature requests and the likes.
+
+Bug reports are more likely to be addressed if they contain the output
+of
+
+\beginlisting
+ luaotfload-tool --diagnose=environment,files,permissions
+\endlisting
+
+\noindent Consult the man page for a description of these options.
+
+Errors during database generation can be traced by increasing the
+verbosity level and redirecting log output to \fileent{stdout}:
+
+\beginlisting
+ luaotfload-tool -fuvvv --log=stdout
+\endlisting
+
+\noindent or to a file in \fileent{/tmp}:
+
+\beginlisting
+ luaotfload-tool -fuvvv --log=file
+\endlisting
+
+\noindent In the latter case, invoke the \inlinecode {tail(1)} utility on the
+file for live monitoring of the progress.
+
+If database generation fails, the font last printed to the terminal or
+log file is likely to be the culprit.
+%
+Please specify it when reporting a bug, and blacklist it for the time
+being (see above, page \pageref{font-blacklist}).
+
+\endsubsection
+
+\beginsubsection {Font Features}
+
+A common problem is the lack of features for some
+\OpenType fonts even when specified.
+%
+This can be related to the fact that some fonts do not provide features
+for the \inlinecode {dflt} script (see above on page \pageref{script-tag}),
+which is the default one in this package.
+%
+If this happens, assigning a noth script when the font is defined should
+fix it.
+%
+For example with \inlinecode {latn}:
+
+\beginlisting
+ \font \test = file:MyFont.otf:script=latn;+liga;
+\endlisting
+
+You can get a list of features that a font defines for scripts and
+languages by querying it in \fileent{luaotfload-tool}:
+
+\beginlisting
+ luaotfload-tool --find="Iwona" --inspect
+\endlisting
+
+\endsubsection
+
+\beginsubsection {\LUATEX Programming}
+
+Another strategy that helps avoiding problems is to not access raw
+\LUATEX internals directly.
+%
+Some of them, even though they are dangerous to access, have not been
+overridden or disabled.
+%
+Thus, whenever possible prefer the functions in the \luafunction{aux}
+namespace over direct manipulation of font objects. For example, raw
+access to the \luafunction{font.fonts} table like:
+
+\beginlisting
+ local somefont = font.fonts[2]
+\endlisting
+
+\noindent can render already defined fonts unusable.
+%
+Instead, the function \luafunction{font.getfont()} should be used
+because it has been replaced by a safe variant.
+
+However, \luafunction{font.getfont()} only covers fonts handled by the
+font loader, e.~g. \identifier{OpenType} and \identifier{TrueType}
+fonts, but not \abbrev{tfm} or \abbrev{ofm}.
+%
+Should you absolutely require access to all fonts known to \LUATEX,
+including the virtual and autogenerated ones, then you need to query
+both \luafunction{font.getfont()} and \luafunction{font.fonts}.
+%
+In this case, best define you own accessor:
+
+\beginlisting
+ local unsafe_getfont = function (id)
+ local tfmdata = font.getfont (id)
+ if not tfmdata then
+ tfmdata = font.fonts[id]
+ end
+ return tfmdata
+ end
+
+ --- use like getfont()
+ local somefont = unsafe_getfont (2)
+\endlisting
+
+\endsubsection
+\endsection
+
+\beginsection {License}
+
+\identifier {luaotfload} is licensed under the terms of the
+\hyperlink [GNU General Public License version 2.0]%
+ {https://www.gnu.org/licenses/old-licenses/gpl-2.0.html}.
+Following the underlying fontloader code \identifier {luaotfload}
+recognizes only that exact version as its license.
+The „any later version” clause of the original license text as
+copyrighted by the \hyperlink [Free Software Foundation]{http://www.fsf.org/}
+\emphasis {does not apply} to either \identifier {luaotfload} or the
+code imported from \CONTEXT.
+
+The complete text of the license is given as a separate file \fileent
+{COPYING} in the toplevel directory of the
+\hyperlink [\fileent {Luaotfload} Git repository]{https://github.com/lualatex/luaotfload/blob/master/COPYING}.
+Distributions probably package it as \fileent
+{doc/luatex/luaotfload/COPYING} in the relevant \fileent {texmf} tree.
+
+\endsection
+
+\endinput
+