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{{note|[[LuaTeX]] and [[MkIV]] allow advanced usage and manipulation of [[Open Type]] <i>open-type features</i>. Some features, such as <i>onum</i> (oldstyle) and <i>smcp</i> (smallcaps) are known to most users of Open Type fonts, and virtually every open type font has default features for kerning (<i>kern</i>) and ligatures (<i>liga</i>). More advanced OT fonts can have lots more, including the Stylistic Set feature <i>ss<nn></i> (where <i>nn</i> stands for any numeral between 01 and 99). = Features in general = In MkIV there are two kinds of font feature directly visible to the user: ''featureset'' and ''open-type feature''.  == Open-type features == The open-type features are specified in the font and are composed of individual "lookups" which specify each substitution and positioning action to be performed in the processing. These open-type features are plugged in and out of the "stack" of lookups to be processed in the MkIV open type handler. These features are represented by a 4-character name (<i>onum</i>, <i>smcp</i>, etc.) and in MkIV are associated with a keyval that turns it on ("yes") or off ("no"). For example, '[onum=yes]' turns on the lookup substitutions in the font which replace a line numeral with an oldstyle one. Here the key 'yes' means "include open-type feature ''onum'' into the processed stack"; the key 'no' means "do not include open-type feature ''onum'' in the processed stack". === Adding features on the fly === Sometimes you want to provisionally add OpenType features to a font. There are at least three ways to do this.# Use a low-level `font.handlers.otf.addfeature` callback function to define new OTF features. See Section 8.14 of [https://www.pragma-ade.com/general/manuals/fonts-mkiv.pdf fonts-mkiv manual] for details of the syntax, or refer to the examples [http://minimals.metatex.org/current/context/test/doc/context/tests/mkiv/fonts/extensions-001.tex here].# Define the new features in an `lfg` "goodies" file and load it with the `goodies` key. See [http://minimals.metatex.org/current/context/test/doc/context/tests/mkiv/fonts/greek-001.tex this example] with the corresponding [http://minimals.metatex.org/current/context/test/doc/context/tests/mkiv/fonts/oxoniensis.lfg lfg] file.# Use a feature file (in the `fea` format) and load it with the `featurefile` key. See [[Fontfeaturefiles]]. === Debugging features === For an OpenType to work properly, all the relevant glyphs must come from the same font (either the original font or one of the fallbacks). For example, the font [https://github.com/aminabedi68/Mikhak/tree/master/Font/ttf Mikhak] now misses glyphs for en dash and em dash, hence the `tlig` feature does not work to automatically change double or triple dashes to en and em dashes. This page is NOT finished yet}}would not work even if we added fallbacks for those two characters. However, if we also create a fallback for the dash character, then this will work. <texcode>\starttext

\definefontsynonym[mytestfont][LuaTeXfile:Mikhak-Medium.ttf][fallbacks=myfallback] and \definedfont[mytestfont*arabic] foo--ofo---oof [MkIV\char"002D][\char"2013] allow advanced usage and manipulation of [[Open Type]\char"2014]  \stoptext<i/texcode>font   OpenType featurescan be complicated to understand or debug. One useful command to see how they are working is {{cmd|showotfcomposition}}. <texcode>\starttext% -1 for the second argument means RTL. Leave it out for LTR text.\showotfcomposition{mikhak-medium*arabic}{-1}{سلام علیکم}\stoptext</itexcode>  == Featuresets == A featureset is a composed of a set of open-type features. Featuresets are specified using {{cmd|definefontfeature}}. Some features, such as For each given body font in the typeface we specify the ''global'' default set of <i>oldstyleopen-type</i> and features to be used for that font. This is usually done in the preamble to our document, an environment file, or a typescript file, or the like.  For example, using TeX-Gyre Schola we can specify the following default, global set open-type features in the preamble: <itexcode>smallcaps\definefontfeature [schola-preset] [mode=node,script=latn,language=dflt,kern=yes,liga=yes,lnum=yes] </itexcode>  {{cmd|definefontfeature}} All other open-type features in the font are known not included in the processing. Now when we want to most users change the default, we use {{cmd|definefontfeature}} to specify local featuresets. The command {{cmd|feature}} and its siblings is then used to control the action of Open Type fontsthose featuresets. More advanced OT fonts can have lots Here are the commands: <texcode>\addfeature [f:mine] \feature [more, including the Stylistic Set ][f:mine] \feature[+][f:mine]\subtractfeature [f:mine] \feature [less][f:mine] \feature[-][f:mine]\replacefeature [f:mine] \feature [new][f:mine] \feature[=][f:mine]\resetandaddfeature[f:mine] \feature[local][f:mine] \feature[!][f:mine]\revivefeature [f:mine] \feature [old][f:mine] \feature <i[>ss]\resetfeature \feature[reset] \feature[<nn>]</itexcode> (where  There are actually only six commands: Each row includes a set of three synonyms for one command. = Sample file with examples = Let us now go through a complete sample file with examples. Let us first define our global default featureset and activate it with a typescript: <itexcode>nn\definefontfeature [schola-preset] [mode=node,script=latn,language=dflt,kern=yes,liga=yes,lnum=yes]   \starttypescript [serif] [schola-preset] [name]\definefontsynonym [Serif] [name:texgyreschola-regular.otf][features=schola-preset]\stoptypescript  \starttypescript [serif] [schola-preset] [size] \definebodyfont [35.8pt,29.8pt,24.8pt,20.7pt,17.3pt,14.4pt,12pt,11pt,10pt,9pt,8pt] [rm] [tf=Serif sa 1] \stoptypescript  \starttypescript [schola-default] \definebodyfontenvironment [schola-default] [default] [interlinespace=2.7ex]\definetypeface [schola-default] [rm] [serif] [schola-preset] [schola-preset] % [default] \stoptypescript \usetypescript[schola-default] \setupbodyfont[schola-default,12pt]</itexcode> stands for any numeral between 01  In the above note that we start with just a global, default feature set of kerns, ligatures, and 99) line numerals.

Now when we want to change the default, we use {{cmd|definefontfeature}} to specify featuresets. The command {{cmd|feature}} and its siblings is then used to control the action of those featuresets. At this stage which open-type feature is being plugged into or unplugged from the stack is invisible to the user. We just speak in terms of featuresets. TeX-Gyre Schola has a decent set of open-type features. Using a few of them, let us set up a few featuresets: <texcode>\definefontfeature[f:smallcaps] [smcp=yes]\definefontfeature[f:thinimacron] [ss04=yes]\definefontfeature[f:upsidedown] [dlig=yes]</texcode> Above, all of our featuresets are mapped to open-type features that plug into the stack. <texcode>\definefontfeature[f:newstyle] [onum=no]\definefontfeature[f:nocaps] [smcp=no]\definefontfeature[f:wideimacron] [ss04=no]\definefontfeature[f:rightsideup] [dlig= Features no]</texcode> We can also be redundant to the default open-type feature set: <texcode>\definefontfeature[f:ligatures] [liga=yes]\definefontfeature[f:noligatures] [liga=no]</texcode> Of course, a featureset set can include more than one open-type feature. In advanced applications this will be the norm: <texcode>\definefontfeature[f:oldstyle] [onum=yes,lnum=no]</texcode> NOTE: In this case we have to specify 'lnum=no' because it is already defined in general our default feature set in the preamble etc. The order of lookups in the font itself could conceivably have an impact as well. <texcode>\definefontfeature[f:oldstyleupsidedown] [onum=yes,dlig=yes]\definefontfeature[f:newstylerightsideup] [onum=no,dlig=no]</texcode> Above, each featureset is mapped to an open-type feature set that plugs into or unplugs from the stack. But we can mix things up: <texcode>\definefontfeature[f:oldstylewmacron] [ss04=no,onum=yes]\definefontfeature[f:newstylesmallcaps] [smcp=yes,onum=no]</texcode> The above two illustrate the point that featuresets hide from the user which actual open-type features are being plugged into or unplugged from the stack.  Now let's put some of the above featuresets in action. Note the use of synonyms in both the activated code and in the comments: <texcode>\definefontfeature [schola-preset] [mode=node,script=latn,language=dflt,kern=yes,liga=yes,lnum=yes]  \starttypescript [serif] [schola-preset] [name] \definefontsynonym [Serif] [name:texgyreschola-regular.otf][features=schola-preset] \stoptypescript  \starttypescript [serif] [schola-preset] [size] \definebodyfont [35.8pt,29.8pt,24.8pt,20.7pt,17.3pt,14.4pt,12pt,11pt,10pt,9pt,8pt] [rm] [tf=Serif sa 1] \stoptypescript  \starttypescript [schola-default] \definebodyfontenvironment [schola-default] [default] [interlinespace=2.7ex]\definetypeface [schola-default] [rm] [serif] [schola-preset] [schola-preset] % [default] \stoptypescript  \usetypescript[schola-default] \setupbodyfont[schola-default,12pt] \definefontfeature[f:smallcaps] [smcp=yes]\definefontfeature[f:thinimacron] [ss04=yes]\definefontfeature[f:upsidedown] [dlig=yes]  \definefontfeature[f:newstyle] [onum=no]\definefontfeature[f:nocaps] [smcp=no]\definefontfeature[f:wideimacron] [ss04=no]\definefontfeature[f:rightsideup] [dlig=no]  \definefontfeature[f:ligatures] [liga=yes]\definefontfeature[f:noligatures] [liga=no] \definefontfeature[f:oldstyle] [onum=yes,lnum=no] \definefontfeature[f:oldstyleupsidedown] [onum=yes,dlig=yes]\definefontfeature[f:newstylerightsideup] [onum=no,dlig=no] \definefontfeature[f:oldstylewmacron] [ss04=no,onum=yes]\definefontfeature[f:newstylesmallcaps] [smcp=yes,onum=no] \defineparagraphs[X][n=2, rule=on, width=10cm] \startTEXpage[offset=10pt] \define\SAMPLE{123 Idrīs ?` !` VA fi} \startX A) \SAMPLE\blank \feature[+][f:oldstyle] B) \SAMPLE \blank\feature[more][f:thinimacron] C) \SAMPLE \blank\addfeature[f:upsidedown] D) \SAMPLE \blank \feature[+][f:smallcaps] E) \SAMPLE \blank\nextX\addfeature[f:wideimacron] F) \SAMPLE \blank \feature[-][f:upsidedown] G) \SAMPLE \blank \feature[=][f:oldstyleupsidedown] H) \SAMPLE \blank \feature[!][f:smallcaps] I) \SAMPLE \blank \feature[<] J) \SAMPLE \blank\stopX\stopTEXpage</texcode> Now let us review the results: [[Image:Adding-featuresets.png]] Finally, we can mix featuresets using comma-separated lists. Here is an example: <texcode>\setupbodyfont[pagella] \starttext

<cmd>definefontfeaturetest 123 {\feature[+][smallcaps,oldstyle] test 123} \stoptext</cmdtexcode>

\addfeature [f:mine] \addff{featureset} % Add absolute font-feature [more][f:mine] \feature[+][f:mine]set -- replaces default set\subtractfeature [f:mine] \subff{featureset} % Subtract absolute font-feature [less][f:mine] \feature[set --][f:mine]replaces default set\replacefeature [f:mine] \feature [new][f:mine] \addfs{featureset} % Add font-feature[=][f:mine]set on top of current stack\resetandaddfeature[f:mine] \feature[local][f:mine] \feature[!][f:mine]\revivefeature [f:mine] \feature [old][f:mine] \feature[>][f:mine]\resetfeature \feature[reset] \subfs{featureset} % Subtract font-feature[<]set from current stack

[[Category:InternationalTools]][[Category:LuaTeX]] {{note|This page is NOT finished yet}}