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diff --git a/Master/texmf-dist/doc/luatex/base/luatex-fonts.tex b/Master/texmf-dist/doc/luatex/base/luatex-fonts.tex new file mode 100644 index 00000000000..9a1a7030e5c --- /dev/null +++ b/Master/texmf-dist/doc/luatex/base/luatex-fonts.tex @@ -0,0 +1,713 @@ +% language=uk + +\environment luatex-style +\environment luatex-logos + +\startcomponent luatex-fonts + +\startchapter[reference=fonts,title={Font structure}] + +All \TEX\ fonts are represented to \LUA\ code as tables, and internally as +\CCODE~structures. All keys in the table below are saved in the internal font +structure if they are present in the table returned by the \type {define_font} +callback, or if they result from the normal \TFM|/|\VF\ reading routines if there +is no \type {define_font} callback defined. + +The column \quote {\VF} means that this key will be created by the \type +{font.read_vf()} routine, \quote {\TFM} means that the key will be created by the +\type {font.read_tfm()} routine, and \quote{used} means whether or not the +\LUATEX\ engine itself will do something with the key. + +The top|-|level keys in the table are as follows: + +\starttabulate[|Tl|c|c|c|l|p|] +\NC \rmbf key \NC \bf vf \NC \bf tfm \NC \bf used \NC \bf value type \NC \bf description \NC \NR +\NC name \NC yes \NC yes \NC yes \NC string \NC metric (file) name \NC \NR +\NC area \NC no \NC yes \NC yes \NC string \NC (directory) location, typically empty \NC \NR +\NC used \NC no \NC yes \NC yes \NC boolean\NC indicates usage (initial: false) \NC \NR +\NC characters \NC yes \NC yes \NC yes \NC table \NC the defined glyphs of this font \NC \NR +\NC checksum \NC yes \NC yes \NC no \NC number \NC default: 0 \NC \NR +\NC designsize \NC no \NC yes \NC yes \NC number \NC expected size (default: 655360 == 10pt) \NC \NR +\NC direction \NC no \NC yes \NC yes \NC number \NC default: 0 \NC \NR +\NC encodingbytes \NC no \NC no \NC yes \NC number \NC default: depends on \type {format} \NC \NR +\NC encodingname \NC no \NC no \NC yes \NC string \NC encoding name \NC \NR +\NC fonts \NC yes \NC no \NC yes \NC table \NC locally used fonts \NC \NR +\NC psname \NC no \NC no \NC yes \NC string \NC This is the \POSTSCRIPT\ fontname in the incoming font + source, and it's used as fontname identifier in the \PDF\ + output. \NC \NR +\NC fullname \NC no \NC no \NC yes \NC string \NC output font name, used as a fallback in the \PDF\ output + if the \type {psname} is not set \NC \NR +\NC header \NC yes \NC no \NC no \NC string \NC header comments, if any \NC \NR +\NC hyphenchar \NC no \NC no \NC yes \NC number \NC default: \TEX's \type {\hyphenchar} \NC \NR +\NC parameters \NC no \NC yes \NC yes \NC hash \NC default: 7 parameters, all zero \NC \NR +\NC size \NC no \NC yes \NC yes \NC number \NC loaded (at) size. (default: same as designsize) \NC \NR +\NC skewchar \NC no \NC no \NC yes \NC number \NC default: \TEX's \type {\skewchar} \NC \NR +\NC type \NC yes \NC no \NC yes \NC string \NC basic type of this font \NC \NR +\NC format \NC no \NC no \NC yes \NC string \NC disk format type \NC \NR +\NC embedding \NC no \NC no \NC yes \NC string \NC \PDF\ inclusion \NC \NR +\NC filename \NC no \NC no \NC yes \NC string \NC the name of the font on disk \NC \NR +\NC tounicode \NC no \NC yes \NC yes \NC number \NC When this is set to~1 \LUATEX\ assumes per|-|glyph + tounicode entries are present in the font. \NC \NR +\NC stretch \NC no \NC no \NC yes \NC number \NC the \quote {stretch} value from \type + {\expandglyphsinfont} \NC \NR +\NC shrink \NC no \NC no \NC yes \NC number \NC the \quote {shrink} value from \type + {\expandglyphsinfont} \NC \NR +\NC step \NC no \NC no \NC yes \NC number \NC the \quote {step} value from \type + {\expandglyphsinfont} \NC \NR +\NC auto_expand \NC no \NC no \NC yes \NC boolean\NC the \quote {autoexpand} keyword from \crlf + \type {\expandglyphsinfont} \NC \NR +\NC expansion_factor \NC no \NC no \NC no \NC number \NC the actual expansion factor of an expanded font \NC \NR +\NC attributes \NC no \NC no \NC yes \NC string \NC the \type {\pdffontattr} \NC \NR +\NC cache \NC no \NC no \NC yes \NC string \NC This key controls caching of the \LUA\ table on the + \TEX\ end where \type {yes} means: use a reference to + the table that is passed to \LUATEX\ (this is the + default), and no \type {no} means: don't store the + table reference, don't cache any \LUA\ data for this + font while \type {renew} means: don't store the table + reference, but save a reference to the table that is + created at the first access to one of its fields in font. + Note: the saved reference is thread|-|local, so be + careful when you are using coroutines: an error will be + thrown if the table has been cached in one thread, but + you reference it from another thread. \NC \NR +\NC nomath \NC no \NC no \NC yes \NC boolean\NC This key allows a minor speedup for text fonts. If it + is present and true, then \LUATEX\ will not check the + character entries for math|-|specific keys. \NC \NR +\NC slant \NC no \NC no \NC yes \NC number \NC This has the same semantics as the \type {SlantFont} + operator in font map files. \NC \NR +\NC extent \NC no \NC no \NC yes \NC number \NC This has the same semantics as the \type {ExtendFont} + operator in font map files. \NC \NR +\stoptabulate + +The key \type {name} is always required. The keys \type {stretch}, \type +{shrink}, \type {step} and optionally \type {auto_expand} only have meaning when +used together: they can be used to replace a post|-|loading \type +{\expandglyphsinfont} command. The \type {expansion_factor} is value that can be +present inside a font in \type {font.fonts}. It is the actual expansion factor (a +value between \type {-shrink} and \type {stretch}, with step \type {step}) of a +font that was automatically generated by the font expansion algorithm. The key +\type {attributes} can be used to set font attributes in the \PDF\ file. The key +\type {used} is set by the engine when a font is actively in use, this makes sure +that the font's definition is written to the output file (\DVI\ or \PDF). The +\TFM\ reader sets it to false. The \type {direction} is a number signalling the +\quote {normal} direction for this font. There are sixteen possibilities: + +\starttabulate[|Tc|Tc|Tc|Tc|] +\NC \rmbf number \NC \rmbf meaning \NC \rmbf number \NC \rmbf meaning \NC\NR +\NC 0 \NC LT \NC 8 \NC TT \NC\NR +\NC 1 \NC LL \NC 9 \NC TL \NC\NR +\NC 2 \NC LB \NC 10 \NC TB \NC\NR +\NC 3 \NC LR \NC 11 \NC TR \NC\NR +\NC 4 \NC RT \NC 12 \NC BT \NC\NR +\NC 5 \NC RL \NC 13 \NC BL \NC\NR +\NC 6 \NC RB \NC 14 \NC BB \NC\NR +\NC 7 \NC RR \NC 15 \NC BR \NC\NR +\stoptabulate + +These are \OMEGA|-|style direction abbreviations: the first character indicates +the \quote {first} edge of the character glyphs (the edge that is seen first in +the writing direction), the second the \quote {top} side. Keep in mind that +\LUATEX\ has a bit different directional model so these values are not used for +anything. + +The \type {parameters} is a hash with mixed key types. There are seven possible +string keys, as well as a number of integer indices (these start from 8 up). The +seven strings are actually used instead of the bottom seven indices, because that +gives a nicer user interface. + +The names and their internal remapping are: + +\starttabulate[|lT|c|] +\NC \rmbf name \NC \rmbf remapping \NC\NR +\NC slant \NC 1 \NC\NR +\NC space \NC 2 \NC\NR +\NC space_stretch \NC 3 \NC\NR +\NC space_shrink \NC 4 \NC\NR +\NC x_height \NC 5 \NC\NR +\NC quad \NC 6 \NC\NR +\NC extra_space \NC 7 \NC\LR +\stoptabulate + +The keys \type {type}, \type {format}, \type {embedding}, \type {fullname} and +\type {filename} are used to embed \OPENTYPE\ fonts in the result \PDF. + +The \type {characters} table is a list of character hashes indexed by an integer +number. The number is the \quote {internal code} \TEX\ knows this character by. + +Two very special string indexes can be used also: \type {left_boundary} is a +virtual character whose ligatures and kerns are used to handle word boundary +processing. \type {right_boundary} is similar but not actually used for anything +(yet). + +Other index keys are ignored. + +Each character hash itself is a hash. For example, here is the character \quote +{f} (decimal 102) in the font \type {cmr10 at 10pt}: + +\starttyping +[102] = { + ['width'] = 200250, + ['height'] = 455111, + ['depth'] = 0, + ['italic'] = 50973, + ['kerns'] = { + [63] = 50973, + [93] = 50973, + [39] = 50973, + [33] = 50973, + [41] = 50973 + }, + ['ligatures'] = { + [102] = { + ['char'] = 11, + ['type'] = 0 + }, + [108] = { + ['char'] = 13, + ['type'] = 0 + }, + [105] = { + ['char'] = 12, + ['type'] = 0 + } + } +} +\stoptyping + +The following top|-|level keys can be present inside a character hash: + +\starttabulate[|lT|c|c|c|l|p|] +\NC \rmbf key \NC \bf vf \NC \bf tfm \NC \bf used \NC \bf type \NC \bf description \NC\NR +\NC width \NC yes \NC yes \NC yes \NC number \NC character's width, in sp (default 0) \NC\NR +\NC height \NC no \NC yes \NC yes \NC number \NC character's height, in sp (default 0) \NC\NR +\NC depth \NC no \NC yes \NC yes \NC number \NC character's depth, in sp (default 0) \NC\NR +\NC italic \NC no \NC yes \NC yes \NC number \NC character's italic correction, in sp (default zero) \NC\NR +\NC top_accent \NC no \NC no \NC maybe \NC number \NC character's top accent alignment place, in sp (default zero) \NC\NR +\NC bot_accent \NC no \NC no \NC maybe \NC number \NC character's bottom accent alignment place, in sp (default zero) \NC\NR +\NC left_protruding \NC no \NC no \NC maybe \NC number \NC character's \type {\lpcode} \NC\NR +\NC right_protruding \NC no \NC no \NC maybe \NC number \NC character's \type {\rpcode} \NC\NR +\NC expansion_factor \NC no \NC no \NC maybe \NC number \NC character's \type {\efcode} \NC\NR +\NC tounicode \NC no \NC no \NC maybe \NC string \NC character's \UNICODE\ equivalent(s), in \UTF|-|16BE hexadecimal format \NC\NR +\NC next \NC no \NC yes \NC yes \NC number \NC the \quote {next larger} character index \NC\NR +\NC extensible \NC no \NC yes \NC yes \NC table \NC the constituent parts of an extensible recipe \NC\NR +\NC vert_variants \NC no \NC no \NC yes \NC table \NC constituent parts of a vertical variant set \NC \NR +\NC horiz_variants \NC no \NC no \NC yes \NC table \NC constituent parts of a horizontal variant set \NC \NR +\NC kerns \NC no \NC yes \NC yes \NC table \NC kerning information \NC\NR +\NC ligatures \NC no \NC yes \NC yes \NC table \NC ligaturing information \NC\NR +\NC commands \NC yes \NC no \NC yes \NC array \NC virtual font commands \NC\NR +\NC name \NC no \NC no \NC no \NC string \NC the character (\POSTSCRIPT) name \NC\NR +\NC index \NC no \NC no \NC yes \NC number \NC the (\OPENTYPE\ or \TRUETYPE) font glyph index \NC\NR +\NC used \NC no \NC yes \NC yes \NC boolean \NC typeset already (default: false)? \NC\NR +\NC mathkern \NC no \NC no \NC yes \NC table \NC math cut-in specifications \NC\NR +\stoptabulate + +The values of \type {top_accent}, \type {bot_accent} and \type {mathkern} are +used only for math accent and superscript placement, see the \at {math chapter} +[math] in this manual for details. + +The values of \type {left_protruding} and \type {right_protruding} are used only +when \type {\protrudechars} is non-zero. + +Whether or not \type {expansion_factor} is used depends on the font's global +expansion settings, as well as on the value of \type {\adjustspacing}. + +The usage of \type {tounicode} is this: if this font specifies a \type +{tounicode=1} at the top level, then \LUATEX\ will construct a \type {/ToUnicode} +entry for the \PDF\ font (or font subset) based on the character|-|level \type +{tounicode} strings, where they are available. If a character does not have a +sensible \UNICODE\ equivalent, do not provide a string either (no empty strings). + +If the font level \type {tounicode} is not set, then \LUATEX\ will build up \type +{/ToUnicode} based on the \TEX\ code points you used, and any character-level +\type {tounicodes} will be ignored. The string format is exactly the format that +is expected by Adobe \CMAP\ files (\UTF-16BE in hexadecimal encoding), minus the +enclosing angle brackets. For instance the \type {tounicode} for a \type {fi} +ligature would be \type {00660069}. When you pass a number the conversion will be +done for you. + +The presence of \type {extensible} will overrule \type {next}, if that is also +present. It in in turn can be overruled by \type {vert_variants}. + +The \type {extensible} table is very simple: + +\starttabulate[|lT|l|p|] +\NC \rmbf key \NC \bf type \NC \bf description \NC\NR +\NC top \NC number \NC top character index \NC\NR +\NC mid \NC number \NC middle character index \NC\NR +\NC bot \NC number \NC bottom character index \NC\NR +\NC rep \NC number \NC repeatable character index \NC\NR +\stoptabulate + +The \type {horiz_variants} and \type {vert_variants} are arrays of components. +Each of those components is itself a hash of up to five keys: + +\starttabulate[|lT|l|p|] +\NC \rmbf key \NC \bf type \NC \bf explanation \NC\NR +\NC glyph \NC number \NC The character index. Note that this is an encoding number, not a name. \NC \NR +\NC extender \NC number \NC One (1) if this part is repeatable, zero (0) otherwise. \NC \NR +\NC start \NC number \NC The maximum overlap at the starting side (in scaled points). \NC \NR +\NC end \NC number \NC The maximum overlap at the ending side (in scaled points). \NC \NR +\NC advance \NC number \NC The total advance width of this item. It can be zero or missing, + then the natural size of the glyph for character \type {component} + is used. \NC \NR +\stoptabulate + +The \type {kerns} table is a hash indexed by character index (and \quote +{character index} is defined as either a non|-|negative integer or the string +value \type {right_boundary}), with the values the kerning to be applied, in +scaled points. + +The \type {ligatures} table is a hash indexed by character index (and \quote +{character index} is defined as either a non|-|negative integer or the string +value \type {right_boundary}), with the values being yet another small hash, with +two fields: + +\starttabulate[|lT|l|p|] +\NC \rmbf key \NC \bf type \NC \bf description \NC \NR +\NC type \NC number \NC the type of this ligature command, default 0 \NC \NR +\NC char \NC number \NC the character index of the resultant ligature \NC \NR +\stoptabulate + +The \type {char} field in a ligature is required. + +The \type {type} field inside a ligature is the numerical or string value of one +of the eight possible ligature types supported by \TEX. When \TEX\ inserts a new +ligature, it puts the new glyph in the middle of the left and right glyphs. The +original left and right glyphs can optionally be retained, and when at least one +of them is kept, it is also possible to move the new \quote {insertion point} +forward one or two places. The glyph that ends up to the right of the insertion +point will become the next \quote {left}. + +\starttabulate[|l|c|l|l|] +\NC \bf textual (Knuth) \NC \bf number \NC \bf string \NC result \NC\NR +\NC \type{l + r =: n} \NC 0 \NC \type{=:} \NC \type{|n} \NC\NR +\NC \type{l + r =:| n} \NC 1 \NC \type{=:|} \NC \type{|nr} \NC\NR +\NC \type{l + r |=: n} \NC 2 \NC \type{|=:} \NC \type{|ln} \NC\NR +\NC \type{l + r |=:| n} \NC 3 \NC \type{|=:|} \NC \type{|lnr} \NC\NR +\NC \type{l + r =:|> n} \NC 5 \NC \type{=:|>} \NC \type{n|r} \NC\NR +\NC \type{l + r |=:> n} \NC 6 \NC \type{|=:>} \NC \type{l|n} \NC\NR +\NC \type{l + r |=:|> n} \NC 7 \NC \type{|=:|>} \NC \type{l|nr} \NC\NR +\NC \type{l + r |=:|>> n} \NC 11 \NC \type{|=:|>>} \NC \type{ln|r} \NC\NR +\stoptabulate + +The default value is~0, and can be left out. That signifies a \quote {normal} +ligature where the ligature replaces both original glyphs. In this table the~\type {|} +indicates the final insertion point. + +The \type {commands} array is explained below. + +\section {Real fonts} + +Whether or not a \TEX\ font is a \quote {real} font that should be written to the +\PDF\ document is decided by the \type {type} value in the top|-|level font +structure. If the value is \type {real}, then this is a proper font, and the +inclusion mechanism will attempt to add the needed font object definitions to the +\PDF. Values for \type {type} are: + +\starttabulate[|Tl|p|] +\NC \rmbf value \NC \rmbf description \NC\NR +\NC real \NC this is a base font \NC\NR +\NC virtual \NC this is a virtual font \NC\NR +\stoptabulate + +The actions to be taken depend on a number of different variables: + +\startitemize[packed] +\startitem + Whether the used font fits in an 8-bit encoding scheme or not. +\stopitem +\startitem + The type of the disk font file. +\stopitem +\startitem + The level of embedding requested. +\stopitem +\stopitemize + +A font that uses anything other than an 8-bit encoding vector has to be written +to the \PDF\ in a different way. + +The rule is: if the font table has \type {encodingbytes} set to~2, then this is a +wide font, in all other cases it isn't. The value~2 is the default for \OPENTYPE\ +and \TRUETYPE\ fonts loaded via \LUA. For \TYPEONE\ fonts, you have to set \type +{encodingbytes} to~2 explicitly. For \PK\ bitmap fonts, wide font encoding is not +supported at all. + +If no special care is needed, \LUATEX\ currently falls back to the +mapfile|-|based solution used by \PDFTEX\ and \DVIPS. This behaviour might +silently be removed in the future, in which case the related primitives and \LUA\ +functions will become no|-|ops. + +If a \quote {wide} font is used, the new subsystem kicks in, and some +extra fields have to be present in the font structure. In this case, \LUATEX\ +does not use a map file at all. + +The extra fields are: \type {format}, \type {embedding}, \type {fullname}, \type +{cidinfo} (as explained above), \type {filename}, and the \type {index} key in +the separate characters. + +Values for \type {format} are: + +\starttabulate[|Tl|p|] +\NC \rmbf value \NC \rmbf description \NC \NR +\NC type1 \NC this is a \POSTSCRIPT\ \TYPEONE\ font \NC \NR +\NC type3 \NC this is a bitmapped (\PK) font \NC \NR +\NC truetype \NC this is a \TRUETYPE\ or \TRUETYPE|-|based \OPENTYPE\ font \NC \NR +\NC opentype \NC this is a \POSTSCRIPT|-|based \OPENTYPE\ font \NC \NR +\stoptabulate + +\type {type3} fonts are provided for backward compatibility only, and do not +support the new wide encoding options. + +Values for \type {embedding} are: + +\starttabulate[|Tl|p|] +\NC \rmbf value \NC \rmbf description \NC \NR +\NC no \NC don't embed the font at all \NC \NR +\NC subset \NC include and atttempt to subset the font \NC \NR +\NC full \NC include this font in its entirety \NC \NR +\stoptabulate + +The other fields are used as follows: The \type {fullname} will be the +\POSTSCRIPT|/|\PDF\ font name. The \type {cidinfo} will be used as the character +set (the CID \type {/Ordering} and \type {/Registry} keys). The \type {filename} +points to the actual font file. If you include the full path in the \type +{filename} or if the file is in the local directory, \LUATEX\ will run a little +bit more efficient because it will not have to re|-|run the \type {find_xxx_file} +callback in that case. + +Be careful: when mixing old and new fonts in one document, it is possible to +create \POSTSCRIPT\ name clashes that can result in printing errors. When this +happens, you have to change the \type {fullname} of the font. + +Typeset strings are written out in a wide format using 2~bytes per glyph, using +the \type {index} key in the character information as value. The overall effect +is like having an encoding based on numbers instead of traditional (\POSTSCRIPT) +name|-|based reencoding. The way to get the correct \type {index} numbers for +\TYPEONE\ fonts is by loading the font via \type {fontloader.open} and use the table +indices as \type {index} fields. + +In order to make sure that cut and paste of the final document works okay you can +best make sure that there is a \type {tounicode} vector enforced. + +\section[virtualfonts]{Virtual fonts} + +You have to take the following steps if you want \LUATEX\ to treat the returned +table from \type {define_font} as a virtual font: + +\startitemize[packed] +\startitem + Set the top|-|level key \type {type} to \type {virtual}. +\stopitem +\startitem + Make sure there is at least one valid entry in \type {fonts} (see below). +\stopitem +\startitem + Give a \type {commands} array to every character (see below). +\stopitem +\stopitemize + +The presence of the toplevel \type {type} key with the specific value \type +{virtual} will trigger handling of the rest of the special virtual font fields in +the table, but the mere existence of 'type' is enough to prevent \LUATEX\ from +looking for a virtual font on its own. + +Therefore, this also works \quote {in reverse}: if you are absolutely certain +that a font is not a virtual font, assigning the value \type {base} or \type +{real} to \type {type} will inhibit \LUATEX\ from looking for a virtual font +file, thereby saving you a disk search. + +The \type {fonts} is another \LUA\ array. The values are one- or two|-|key +hashes themselves, each entry indicating one of the base fonts in a virtual font. +In case your font is referring to itself, you can use the \type {font.nextid()} +function which returns the index of the next to be defined font which is probably +the currently defined one. + +An example makes this easy to understand + +\starttyping +fonts = { + { name = 'ptmr8a', size = 655360 }, + { name = 'psyr', size = 600000 }, + { id = 38 } +} +\stoptyping + +says that the first referenced font (index 1) in this virtual font is \type +{ptrmr8a} loaded at 10pt, and the second is \type {psyr} loaded at a little over +9pt. The third one is previously defined font that is known to \LUATEX\ as font id +\quote {38}. + +The array index numbers are used by the character command definitions that are +part of each character. + +The \type {commands} array is a hash where each item is another small array, +with the first entry representing a command and the extra items being the +parameters to that command. The allowed commands and their arguments are: + +\starttabulate[|Tl|l|l|p|] +\NC \rmbf command name \NC \bf arguments \NC \bf type \NC \bf description \NC\NR +\NC font \NC 1 \NC number \NC select a new font from the local \type {fonts} table\NC\NR +\NC char \NC 1 \NC number \NC typeset this character number from the current font, + and move right by the character's width\NC\NR +\NC node \NC 1 \NC node \NC output this node (list), and move right + by the width of this list\NC\NR +\NC slot \NC 2 \NC number \NC a shortcut for the combination of a font and char command\NC\NR +\NC push \NC 0 \NC \NC save current position\NC\NR +\NC nop \NC 0 \NC \NC do nothing \NC\NR +\NC pop \NC 0 \NC \NC pop position \NC\NR +\NC rule \NC 2 \NC 2 numbers \NC output a rule $ht*wd$, and move right.\NC\NR +\NC down \NC 1 \NC number \NC move down on the page\NC\NR +\NC right \NC 1 \NC number \NC move right on the page\NC\NR +\NC special \NC 1 \NC string \NC output a \type {\special} command\NC\NR +\NC lua \NC 1 \NC string \NC execute a \LUA\ script (at \type {\latelua} time)\NC\NR +\NC image \NC 1 \NC image \NC output an image (the argument can be either an \type + {<image>} variable or an \type {image_spec} table)\NC\NR +\NC comment \NC any \NC any \NC the arguments of this command are ignored\NC\NR +\stoptabulate + +When a font id is set to~0 then it will be replaced by the currently assigned +font id. This prevents the need for hackery with future id's (normally one could +use \type {font.nextid} but when more complex fonts are built in the meantime +other instances could have been loaded. + +Here is a rather elaborate glyph commands example: + +\starttyping +... +commands = { + { 'push' }, -- remember where we are + { 'right', 5000 }, -- move right about 0.08pt + { 'font', 3 }, -- select the fonts[3] entry + { 'char', 97 }, -- place character 97 (ASCII 'a') + { 'pop' }, -- go all the way back + { 'down', -200000 }, -- move upwards by about 3pt + { 'special', 'pdf: 1 0 0 rg' } -- switch to red color + { 'rule', 500000, 20000 } -- draw a bar + { 'special','pdf: 0 g' } -- back to black +} +... +\stoptyping + +The default value for \type {font} is always~1 at the start of the +\type {commands} array. Therefore, if the virtual font is essentially only a +re|-|encoding, then you do usually not have create an explicit \quote {font} +command in the array. + +Rules inside of \type {commands} arrays are built up using only two dimensions: +they do not have depth. For correct vertical placement, an extra \type {down} +command may be needed. + +Regardless of the amount of movement you create within the \type {commands}, the +output pointer will always move by exactly the width that was given in the \type +{width} key of the character hash. Any movements that take place inside the \type +{commands} array are ignored on the upper level. + +\subsection{Artificial fonts} + +Even in a \quote {real} font, there can be virtual characters. When \LUATEX\ +encounters a \type {commands} field inside a character when it becomes time to +typeset the character, it will interpret the commands, just like for a true +virtual character. In this case, if you have created no \quote {fonts} array, +then the default (and only) \quote {base} font is taken to be the current font +itself. In practice, this means that you can create virtual duplicates of +existing characters which is useful if you want to create composite characters. + +Note: this feature does {\it not\/} work the other way around. There can not be +\quote {real} characters in a virtual font! You cannot use this technique for +font re-encoding either; you need a truly virtual font for that (because +characters that are already present cannot be altered). + +\subsection{Example virtual font} + +Finally, here is a plain \TEX\ input file with a virtual font demonstration: + +\startbuffer +\directlua { + callback.register('define_font', + function (name,size) + if name == 'cmr10-red' then + f = font.read_tfm('cmr10',size) + f.name = 'cmr10-red' + f.type = 'virtual' + f.fonts = {{ name = 'cmr10', size = size }} + for i,v in pairs(f.characters) do + if (string.char(i)):find('[tacohanshartmut]') then + v.commands = { + {'special','pdf: 1 0 0 rg'}, + {'char',i}, + {'special','pdf: 0 g'}, + } + else + v.commands = {{'char',i}} + end + end + else + f = font.read_tfm(name,size) + end + return f + end + ) +} + +\font\myfont = cmr10-red at 10pt \myfont This is a line of text \par +\font\myfontx= cmr10 at 10pt \myfontx Here is another line of text \par +\stopbuffer + +\typebuffer + +\section{The \type {font} library} + +The font library provides the interface into the internals of the font system, +and also it contains helper functions to load traditional \TEX\ font metrics +formats. Other font loading functionality is provided by the \type {fontloader} +library that will be discussed in the next section. + +\subsection{Loading a \TFM\ file} + +The behavior documented in this subsection is considered stable in the sense that +there will not be backward-incompatible changes any more. + +\startfunctioncall +<table> fnt = + font.read_tfm(<string> name, <number> s) +\stopfunctioncall + +The number is a bit special: + +\startitemize +\startitem + If it is positive, it specifies an \quote {at size} in scaled points. +\stopitem +\startitem + If it is negative, its absolute value represents a \quote {scaled} + setting relative to the designsize of the font. +\stopitem +\stopitemize + +The internal structure of the metrics font table that is returned is explained in +\in {chapter} [fonts]. + +\subsection{Loading a \VF\ file} + +The behavior documented in this subsection is considered stable in the sense that +there will not be backward-incompatible changes any more. + +\startfunctioncall +<table> vf_fnt = + font.read_vf(<string> name, <number> s) +\stopfunctioncall + +The meaning of the number \type {s} and the format of the returned table are +similar to the ones in the \type {read_tfm()} function. + +\subsection{The fonts array} + +The whole table of \TEX\ fonts is accessible from \LUA\ using a virtual array. + +\starttyping +font.fonts[n] = { ... } +<table> f = font.fonts[n] +\stoptyping + +See \in {chapter} [fonts] for the structure of the tables. Because this is a +virtual array, you cannot call \type {pairs} on it, but see below for the \type +{font.each} iterator. + +The two metatable functions implementing the virtual array are: + +\startfunctioncall +<table> f = font.getfont(<number> n) +font.setfont(<number> n, <table> f) +\stopfunctioncall + +Note that at the moment, each access to the \type {font.fonts} or call to \type +{font.getfont} creates a \LUA\ table for the whole font. This process can be quite +slow. In a later version of \LUATEX, this interface will change (it will start +using userdata objects instead of actual tables). + +Also note the following: assignments can only be made to fonts that have already +been defined in \TEX, but have not been accessed {\it at all\/} since that +definition. This limits the usability of the write access to \type {font.fonts} +quite a lot, a less stringent ruleset will likely be implemented later. + +\subsection{Checking a font's status} + +You can test for the status of a font by calling this function: + +\startfunctioncall +<boolean> f = + font.frozen(<number> n) +\stopfunctioncall + +The return value is one of \type {true} (unassignable), \type {false} (can be +changed) or \type {nil} (not a valid font at all). + +\subsection{Defining a font directly} + +You can define your own font into \type {font.fonts} by calling this function: + +\startfunctioncall +<number> i = + font.define(<table> f) +\stopfunctioncall + +The return value is the internal id number of the defined font (the index into +\type {font.fonts}). If the font creation fails, an error is raised. The table +is a font structure, as explained in \in {chapter} [fonts]. + +\subsection{Projected next font id} + +\startfunctioncall +<number> i = + font.nextid() +\stopfunctioncall + +This returns the font id number that would be returned by a \type {font.define} +call if it was executed at this spot in the code flow. This is useful for virtual +fonts that need to reference themselves. + +\subsection{Font id} + +\startfunctioncall +<number> i = + font.id(<string> csname) +\stopfunctioncall + +This returns the font id associated with \type {csname} string, or $-1$ if \type +{csname} is not defined. + +\subsection{Currently active font} + +\startfunctioncall +<number> i = font.current() +font.current(<number> i) +\stopfunctioncall + +This gets or sets the currently used font number. + +\subsection{Maximum font id} + +\startfunctioncall +<number> i = + font.max() +\stopfunctioncall + +This is the largest used index in \type {font.fonts}. + +\subsection{Iterating over all fonts} + +\startfunctioncall +for i,v in font.each() do + ... +end +\stopfunctioncall + +This is an iterator over each of the defined \TEX\ fonts. The first returned +value is the index in \type {font.fonts}, the second the font itself, as a \LUA\ +table. The indices are listed incrementally, but they do not always form an array +of consecutive numbers: in some cases there can be holes in the sequence. + +\stopchapter + +\stopcomponent |