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diff --git a/doc/context/sources/general/manuals/fonts/fonts-lookups.tex b/doc/context/sources/general/manuals/fonts/fonts-lookups.tex new file mode 100644 index 000000000..e9448b884 --- /dev/null +++ b/doc/context/sources/general/manuals/fonts/fonts-lookups.tex @@ -0,0 +1,410 @@ +% language=uk + +\startcomponent fonts-lookups + +\environment fonts-environment + +\startchapter[title=Lookups][color=darkblue] + +\startsection[title=Introduction] + +In traditional \TEX\ a font is defined by referring to its filename. A +definition looks like this: + +\starttyping +\font \MyFontA = lmr10 +\font \MyFontB = lmr10 at 20pt +\font \MyFontC = lmr10 scaled 1500 +\stoptyping + +The first definition defines the command \type {MyFontA} as a reference to the +font stored in the file \type {lmx10}. No scaling takes place so the natural size +is taken. This so called designsize is in no way standardized. Just look at these +three specimen: + +\startlines +{\definedfont[file:dejavuserif*default]Design Size (Dejavu)} +{\definedfont[file:cambria*default]Design Size (Cambria)} +{\definedfont[file:lmroman10-regular*default]Design Size (Latin Modern)} +\stoplines + +The designsize is normally 10 point, but as there is no real reference for this a +designer decides how to translate this into a visual representation. As a +consequence the \type {20pt} in the second line of the example definitions only +means that the font is scaled to (normally) twice the designsize. The third line +scaled by a factor \type {1.5} and the reason for using a value thousand times +larger is that \TEX's numbers are integers. + +The next three lines are typical for Latin Modern (derived from Computer Modern) +because this family comes in different design sizes. + +\starttyping +\font \MyFontD = lmr12 +\font \MyFontE = lmr12 at 20pt +\font \MyFontF = lmr12 scaled 1500 +\stoptyping + +Because the designsize is part of the font metrics the second line (\type +{\MyFontE}) is of similar size as \type {\MyFontB} although the 12~point variant +is visually better suited for scaling up. + +These definitions refer to files, but what file? What gets loaded is the file +with name \type {name.tfm}. Eventually for embedding in the (let's assume \PDF) +file the outlines are taken from \type {name.pfb}. At that stage, when present, a +\type {name.vf} is consulted in order to resolve characters that are combinations +of others (potentially from other \type {pfb} files). The mapping from \type +{name.tfm} to \type {name.pfb} filename happens in the so called map file. This +means that one can also refer to another file, for instance \type {name.ttf}. + +All this logic is hard coded in the engine and because the virtual font mechanism +was introduced later without extending the \type {tfm} format, it can be hard at +times to figure out issues when a (maybe obsolete) virtual file is present (this +can be the case if you have generated the \type {tfm} file from an \type {afm} +file that comes with the \type {pfb} file when you buy one. + +But, in \LUATEX\ we no longer use traditional fonts and as a consequence we have +more options open. Before we move on to them, we mention yet another definition: + +\starttyping +\font \MyFontG = lmr12 sa 1.2 +\stoptyping + +This method is not part of \TEX\ but is provided by \CONTEXT, \MKII\ as well as +\MKIV. It means as much as \quotation {scale this font to 1.2 times the +bodyfontsize}. As this involves parsing the specification, it does not work +as advertised here, but the next definition works okay: + +\starttyping +\definefont[MyFontG][lmr12 sa 1.2] +\stoptyping + +This indicates that we already had a parser for font specifications on board +which in turn made it relatively easy to do even more parsing, for instance for +font features as introduced in \XETEX\ and \LUATEX. + +\stopsection + +\startsection[title=Specifications] + +In \LUATEX\ we intercept the font loader. We do so for several reasons. + +\startitemize[packed] + +\startitem We want to make decisions on what file to load, this is needed when +for instance there are files with the same name but different properties. \stopitem + +\startitem We want to be able to lookup by file, by name, and by more abstract specification. +In doing so, we want to be as tolerant as possible. \stopitem + +\startitem We want to support several scaling methods, as discussed in the previous section. \stopitem + +\startitem We want to implement several strategies for passing features and defining non +standard approaches. \stopitem + +\stopitemize + +The formal specification of a font is as follows: + +\starttyping +\definefont[PublicReference][filename] +\definefont[PublicReference][filename at dimension] +\definefont[PublicReference][filename scaled number] +\stoptyping + +We already had that extended to: + +\starttyping +\definefont[PublicReference][filename] +\definefont[PublicReference][filename at dimension] +\definefont[PublicReference][filename scaled number] +\definefont[PublicReference][filename sa number] +\stoptyping + +So let's generalize that to: + +\starttyping +\definefont[PublicReference][filename scaling] +\stoptyping + +And in \MKIV\ we now have: + +\starttyping +\definefont[PublicReference][filename*featurenames scaling] +\definefont[PublicReference][filename:featurespecication scaling] +\definefont[PublicReference][filename@virtualconstructor scaling] +\stoptyping + +The second variant is seldom used and is only provided because some users +have fonts defined in the \XETEX\ way. Users are advised not to use this +method. The last method is special in the sense that it's used to define +fonts that are constructed using the built in virtual font constructors. This +method is for instance used for defining virtual math fonts. + +The first method is what we use most. It is really important not to forget the +feature specification. A rather safe bet is \type {*default}. In a next chapter +we will discuss the difference between these two; here we focus on the name part. + +The \type {filename} is in fact a symbolic name. In \CONTEXT\ we have always used +an indirect reference to fonts. Look at this: + +\starttyping +\definefont[TitleFont][SerifBold*default sa 2] +\stoptyping + +A reference like \type {SerifBold} makes it possible to define styles independent +of the chosen font family. This reference eventually gets resolved to a real +name and there can be a chain of references. + +Font definitions can be grouped into a larger setup using typescripts. In that +case, we can set the features for a regular, italic, bold and bolditalic for the +whole set but when a fontname has a specific feature associated (as in the +previous examples) that one takes precedence. + +so far we talked about fonts being files, but in practice a lookup happens by +file as well as by name as known to the system. In the next section this will be +explained in more detail. + +\stopsection + +\startsection[title=File] + +You can force a file lookup with: + +\starttyping +\definefont[TitleFont][file:somefilename*default sa 2] +\stoptyping + +If you use more symbolic names you can use the \type {file:} prefix in the +mapping: + +\starttyping +\definefontsynonym[SerifBold][file:somefile] +\definefont[TitleFont][SerifBold*default sa 2] +\stoptyping + +In projects that are supposed to run for a long time I always use the file based +lookup, because filenames tend to be rather stable. Also, as the lookup happens +in the \TEX\ directory structure, file lookups will rely on the general file +search routines. This has the benefit that case is ignored. When no match is found +the lookup will also use the font name database. Spaces and special characters are +ignored. + +The name alone is not enough as there can be similar filenames with different +suffixes. Therefore the lookup will happen in the order \ctxcommand { +concatcommalist { list = fonts.readers.sequence, separator = ", ", last = " and +", command = "type" } }. You can force a lookup by being more explicit, like: + +\starttyping +\definefont[TitleFont][file:somefilename.ttf*default sa 1] +\stoptyping + +\stopsection + +\startsection[title=Name] + +Say that we want to use a Dejavu font and that instead of filenames we want to +use its given name. The best way to find out what is available is to call for a +list: + +\starttyping +mtxrun --script font --list --all dejavu +\stoptyping + +This produces the following list: + +\startnarrowtyping +dejavusans dejavusans dejavusans.ttf +dejavusansbold dejavusansbold dejavusans-bold.ttf +dejavusansboldoblique dejavusansboldoblique dejavusans-boldoblique.ttf +dejavusanscondensed dejavusanscondensed dejavusanscondensed.ttf +dejavusanscondensedbold dejavusanscondensedbold dejavusanscondensed-bold.ttf +dejavusanscondensedboldoblique dejavusanscondensedboldoblique dejavusanscondensed-boldoblique.ttf +dejavusanscondensednormal dejavusanscondensed dejavusanscondensed.ttf +dejavusanscondensedoblique dejavusanscondensedoblique dejavusanscondensed-oblique.ttf +dejavusansextralight dejavusansextralight dejavusans-extralight.ttf +dejavusanslight dejavusansextralight dejavusans-extralight.ttf +dejavusansmono dejavusansmono dejavusansmono.ttf +dejavusansmonobold dejavusansmonobold dejavusansmono-bold.ttf +dejavusansmonoboldoblique dejavusansmonoboldoblique dejavusansmono-boldoblique.ttf +dejavusansmononormal dejavusansmonooblique dejavusansmono-oblique.ttf +dejavusansmonooblique dejavusansmonooblique dejavusansmono-oblique.ttf +dejavusansnormal dejavusans dejavusans.ttf +dejavusansoblique dejavusansoblique dejavusans-oblique.ttf +dejavuserif dejavuserif dejavuserif.ttf +dejavuserifbold dejavuserifbold dejavuserif-bold.ttf +dejavuserifbolditalic dejavuserifbolditalic dejavuserif-bolditalic.ttf +dejavuserifcondensed dejavuserifcondensed dejavuserifcondensed.ttf +dejavuserifcondensedbold dejavuserifcondensedbold dejavuserifcondensed-bold.ttf +dejavuserifcondensedbolditalic dejavuserifcondensedbolditalic dejavuserifcondensed-bolditalic.ttf +dejavuserifcondenseditalic dejavuserifcondenseditalic dejavuserifcondensed-italic.ttf +dejavuserifcondensednormal dejavuserifcondensed dejavuserifcondensed.ttf +dejavuserifitalic dejavuserifitalic dejavuserif-italic.ttf +dejavuserifnormal dejavuserif dejavuserif.ttf +\stopnarrowtyping + +The first two columns mention the names that we can use to access a font. These +are normalized names in the sense that we only kept letters and numbers. The next three +definitions are equivalent: + +\starttyping +\definefont[TitleFont][name:dejavuserif*default sa 1] +\definefont[TitleFont][name:dejavuserifnormal*default sa 1] +\definefont[TitleFont][name:dejavuserif.ttf*default sa 1] +\stoptyping + +In the list you see two names that all point to \type {dejavusans-extralight.ttf}: + +\starttyping +dejavusansextralight +dejavusanslight +\stoptyping + +There are some heuristics built into \CONTEXT\ and we do some cleanup as well. +For instance we interpret \type {ital} as \type {italic}. In a font there is +sometimes information about the weight and we look at those properties as well. +Unfortunately font names (even within a collection) are often rather inconsistent +so you still need to know what you're looking for. The more explicit you are, the +less change of problems. + +\stopsection + +\startsection[title=Spec] + +There is often some logic in naming fonts but it's not robust and really depends on +how consistent a font designer or typefoundry has been. In \CONTEXT\ we can +access names by using a normalized scheme. + +\starttyping +name-weight-style-width-variant +\stoptyping + +The following values are valid: + +\starttabulate[|Bl|Tp|] +\NC weight \NC \ctxcommand { concatcommalist { list = fonts.names.knownweights } } \NC \NR +\NC style \NC \ctxcommand { concatcommalist { list = fonts.names.knownstyles } } \NC \NR +\NC width \NC \ctxcommand { concatcommalist { list = fonts.names.knownwidths } } \NC \NR +\NC variant \NC \ctxcommand { concatcommalist { list = fonts.names.knownvariants } } \NC \NR +\stoptabulate + +The four specifiers are optional but the more you provide, the better the match. Let's +give an example: + +\starttyping +mtxrun --script fonts --list --spec dejavu +\stoptyping + +This reports: + +\startnarrowtyping +dejavuserifcondensed normal normal normal normal dejavuserifcondensed dejavuserifcondensed.ttf +dejavuserif normal normal normal normal dejavuserif dejavuserif.ttf +dejavusansmono normal normal normal normal dejavusansmono dejavusansmono.ttf +dejavusanscondensed normal normal normal normal dejavusanscondensed dejavusanscondensed.ttf +dejavusans normal normal normal normal dejavusans dejavusans.ttf +\stopnarrowtyping + +We can be more specific, for instance: + +\starttyping +mtxrun --script fonts --list --spec dejavu-bold +\stoptyping + +\startnarrowtyping +dejavuserif bold normal normal normal dejavuserifbold dejavuserif-bold.ttf +dejavusansmono bold normal normal normal dejavusansmonobold dejavusansmono-bold.ttf +dejavusans bold normal normal normal dejavusansbold dejavusans-bold.ttf +\stopnarrowtyping + +We add another specifier: + +\starttyping +mtxrun --script fonts --list --spec dejavu-bold-italic +\stoptyping + +\startnarrowtyping +dejavuserif bold italic normal normal dejavuserifbolditalic dejavuserif-bolditalic.ttf +dejavusansmono bold italic normal normal dejavusansmonoboldoblique dejavusansmono-boldoblique.ttf +dejavusans bold italic normal normal dejavusansboldoblique dejavusans-boldoblique.ttf +\stopnarrowtyping + +As the first hit is used we need to be more specific with respect to the +name, so lets do that in an example definition: + +\starttyping +\definefont[TitleFont][spec:dejavuserif-bold-italic*default sa 1] +\stoptyping + +Watch the prefix \type {spec}. Wolfgang Schusters \type {simplefonts} module +nowadays uses this method to define sets of fonts based on a name only +specification. Of course that works best if a fontset has well defined +properties. + +\stopsection + +\startsection[title=Selectfont] + +The selectfont interface by Wolfgang Schuster can be used to define fonts +by name. For a long term project workflow you probably want to use filenames +but for average use names do well: + +\starttyping +\definefontfamily [mainface] [serif] [DejaVu Serif] +\definefontfamily [mainface] [sans] [DejaVu Sans] +\definefontfamily [mainface] [mono] [DejaVu Sans Mono] [features=none] +\definefontfamily [mainface] [math] [Dejavu Math] +\stoptyping + +This setup is triggered in the usual way: + +\starttyping +\setupbodyfont[mainface] +\stoptyping + +When you combine different designs you may need to apply a relative scale: + +\starttyping +\definefontfamily [mainface] [math] [XITS Math] [rscale=1.1] +\stoptyping + +Some fonts come in designsizes, like Latin Modern: + +\starttyping +\definefontfamily + [mainface] + [serif] + [Latin Modern Roman] + [designsize=auto] +\stoptyping + +You can define fallbacks, for example: + +\starttyping +\definefallbackfamily + [mainface] + [serif] + [DejaVu Serif] + [range=cyrillic] + +\definefontfamily [mainface] [serif] [TeX Gyre Pagella] +\stoptyping + +Here Pagella is used with missing characters taken from Dejavu. The ranges +are defined with: + +\starttyping +\definefontfamilypreset + [range:cyrillic] + [range={cyrillic, + cyrillicextendeda, + cyrillicextendedb, + cyrillicsupplement}] +\stoptyping + +For more details you can consult the wiki and the source file \type {font-sel.mkvi}. + +\stopsection + +\stopchapter + +\stopcomponent |