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diff --git a/Master/texmf-dist/doc/generic/FAQ-en/faq-bits+pieces.tex b/Master/texmf-dist/doc/generic/FAQ-en/faq-bits+pieces.tex new file mode 100644 index 00000000000..fed5b685db2 --- /dev/null +++ b/Master/texmf-dist/doc/generic/FAQ-en/faq-bits+pieces.tex @@ -0,0 +1,762 @@ +% $Id: faq-bits+pieces.tex,v 1.2 2009/08/25 20:58:46 rf10 Exp rf10 $ + +\section{Bits and pieces of \AllTeX{}} + +\Question[Q-dvi]{What is a \acro{DVI} file?} + +A \acro{DVI} file (that is, a file with the type or extension +\extension{dvi}) is \TeX{}'s main output file, using \TeX{} in its +broadest sense to include \LaTeX{}, etc. `\acro{DVI}' is supposed to +be an acronym for \acro{D}e\acro{V}ice-\acro{I}ndependent, meaning +that the file can be printed on most +kinds of typographic output device. The \acro{DVI} file is designed to be +read by a driver (\Qref{DVI drivers}{Q-driver}) to produce +further output designed specifically for a particular printer (e.g., a +LaserJet) or to be used as input to a previewer for display on a +computer screen. \acro{DVI} files use \TeX{}'s internal coding; a \TeX{} +input file should produce the same \acro{DVI} file regardless of which +implementation of \TeX{} is used to produce it. + +A \acro{DVI} file contains all the information that is needed for printing +or previewing except for the actual bitmaps or outlines of fonts, and +possibly material to be introduced by means of +\Qref*{\csx{special} commands}{Q-specials}. + +The canonical reference for the structure of a \acro{DVI} file is the +source of Knuth's program \ProgName{dvitype} (whose original purpose, +as its name implies, was to view the content of a \acro{DVI} file). +\begin{ctanrefs} +\item[dvitype]\CTANref{dvitype} +\end{ctanrefs} + +\Question[Q-driver]{What is a \acro{DVI} driver?} + +A \acro{DVI} driver is a program that takes as input a \acro{DVI} file +(\Qref{\acro{DVI} files}{Q-dvi}) and +(usually) produces a file that can be sent to a typographic +output device (which we will call a printer, for short), or to another +format. + +A driver will usually be specific to a particular printer, +although any \PS{} printer ought to be able to print +the output from a \PS{} driver. +% (these are also called \PS{} conversion programs). + +As well as the \acro{DVI} file, the driver also needs font information. +Font information may be held as bitmaps or as outlines, or simply as a +set of pointers into the fonts that the printer itself `has'. +Each driver will expect the font information in +a particular form. For more information on the forms of fonts, +see \Qref[questions]{\acro{PK} files}{Q-pk}, +% ! line break +\Qref[]{\acro{TFM} files}{Q-tfm}, +\Qref[]{virtual fonts}{Q-virtualfonts} +and \Qref[]{Using \PS{} fonts with \TeX{}}{Q-usepsfont}. + +\Question[Q-pk]{What are \acro{PK} files?} + +\acro{PK} files (packed raster) contain font bitmaps. The output +from \Qref*{\MF{}}{Q-useMF} includes a generic font (\acro{GF}) file +and the utility \ProgName{gftopk} produces the \acro{PK} file from +that. There are a lot of \acro{PK} files, as one is needed for each +font, that is each magnification (size) of each design (point) size +for each weight for each family. Further, since the \acro{PK} files +for one printer do not necessarily work well for another, the whole +set needs to be duplicated for each printer type at a site. In a +modern \TeX{} distribution, files are arranged according to the \TeX{} +directory structure \Qref*{\acro{TDS}}{Q-tds}, which has provision for +all this variety. + +\Question[Q-tfm]{What are \acro{TFM} files?} + +\acro{TFM} stands for \TeX{} Font Metrics; \acro{TFM} files hold +information about the sizes of the characters of the font in question, +and about ligatures and kerns within that font. One \acro{TFM} file is +needed for each font used by \TeX{}, that is for each design (point) +size for each weight for each family; each \acro{TFM} file serves for all +magnifications of `its' font, so that there are (typically) fewer +\acro{TFM} files than there are \acro{PK} files. \TeX{} (\LaTeX{}, etc.\@) +itself needs only to know about the sizes of characters and their +interactions with each other, but not what characters look like. By +contrast, \acro{TFM} files are not, in principle, needed by the +\acro{DVI} driver, which only needs to know about the glyphs that each +character selects, so as to print or display them. + +\Question[Q-virtualfonts]{Virtual fonts} + +Virtual fonts provide a means of collecting bits and pieces together +to make the glyphs of a font: the bits and pieces may be other glyphs, +rules and other ``basic'' typesetting commands, and the positioning +information that specifies how everything comes together. + +Things that match the concept of virtual fonts for \TeX{} were first +implemented by David Fuchs in the very early days. However, for practical +purposes for the rest of us, virtual fonts date from when Knuth +specified a format and wrote some support software, in 1989 (he +published an article in \textsl{TUGboat} at the time, and a plain text +copy is available on \acro{CTAN}). + +Virtual fonts provide a way of telling \TeX{} about something more +complicated than just a one-to-one character mapping. The entities you +define in a virtual font look like characters to \TeX{} (they appear +with their sizes in a \acro{TFM} file), but the \acro{DVI} processor may +expand them to something quite different. + +From the virtual font file, the \acro{DVI} processor learns +details of what is in the virtual font, so as to know ``what to draw, +where''. The virtual font may contain commands: +\begin{itemize} +\item just to remap the glyphs of a single font, +\item to make a composite font with glyphs drawn from several + different fonts, or +\item to build up an effect in arbitrarily complicated ways (since a + virtual font may contain anything which is legal in a \acro{DVI} + file). +\end{itemize} + +% !this has to be generated as a new paragraph by the translator, so +% leave the blank line in place +In practice, the most common use of virtual fonts is to remap +Adobe Type 1 fonts (see \Qref[question]{font metrics}{Q-metrics}), +though there has also been useful useful work building `fake' maths +fonts (by bundling glyphs from several fonts into a single virtual +font). Virtual Computer Modern fonts, making a % ! line break +\Qref*{Cork encoded}{Q-ECfonts} font from Knuth's originals by using +remapping and fragments of \acro{DVI} for single-glyph `accented +characters', were the first ``Type~1 format'' Cork-encoded Computer +Modern fonts available. + +Virtual fonts are normally created in a single \acro{ASCII} +\acro{VPL} (Virtual Property List) file, which includes both sets of +information. The \ProgName{vptovf} program is then used to the create +the binary \acro{TFM} and \acro{VF} files. + +A ``how-to'' document, explaining how to generate a \acro{VPL}, +describes the endless hours of fun that may be had, doing the job by +hand. Despite the pleasures to be had of the manual method, the +commonest way (nowadays) of generating \acro{VPL} files is to use the +\ProgName{fontinst} package, which is described in detail +\htmlonly{together with the discussion of} +\Qref[in answer]{\PS{} font metrics}{Q-metrics}. +\Package{Qdtexvpl} is another utility for creating ad-hoc virtual +fonts (it uses \TeX{} to parse a description of the virtual font, and +\ProgName{qdtexvpl} itself processes the resulting \acro{DVI} file). +\begin{ctanrefs} +\item[fontinst]\CTANref{fontinst} +\item[\nothtml{\rmfamily}Knuth on virtual fonts]\CTANref{vf-knuth} +\item[\nothtml{\rmfamily}Virtual fonts ``how to'']\CTANref{vf-howto} +\item[qdtexvpl]\CTANref{qdtexvpl} +\end{ctanrefs} + +\Question[Q-whatmacros]{What are (\TeX{}) macros} + +\TeX{} is a \emph{macro processor}: this is a computer-science-y term +meaning ``text expander'' (more or less); \TeX{} typesets text as it +goes along, but \emph{expands} each macro it finds. \TeX{}'s macros +may include instructions to \TeX{} itself, on top of the simple text +generation one might expect. + +Macros are a \emph{good thing}, since they allow the user to +manipulate documents according to context. For example, the macro +\csx{TeX} is usually defined to produce ``TEX'' with the `E' lowered, +but in these \acro{FAQ}s the default definition of the macro is +overridden, and it simply expands to the letters ``TeX''. (\emph{You} +may not think this a good thing, but the author of the macros has his +reasons~-- see \Qref[question]{\TeX{}-related logos}{Q-logos}.) + +Macro names are conventionally built from a \texttt{\textbackslash } +followed by a sequence of letters, which may be upper or lower case +(as in \csx{TeX}, mentioned above). They may also be % ! line break +\texttt{\textbackslash \meta{any single character}}, which allows all +sorts of oddities (many built in to most \TeX{} macro sets, all the +way up from the apparently simple `\csx{ }' meaning ``insert a space +here''). + +Macro programming can be a complicated business, but at their very +simplest they need little introduction~--- you'll hardly need to be +told that: +\begin{quote} +\begin{verbatim} +\def\foo{bar} +\end{verbatim} +\end{quote} +replaces each instance of \csx{foo} with the text ``bar''. The +command \csx{def} is \plaintex{} syntax for defining commands; +\LaTeX{} offers a macro \csx{newcommand} that goes some way towards +protecting users from themselves, but basically does the same thing: +\begin{quote} +\begin{verbatim} +\newcommand{\foo}{bar} +\end{verbatim} +\end{quote} +Macros may have ``arguments'', which are used to substitute for marked +bits of the macro expansion: +\begin{quote} +\begin{verbatim} +\def\foo#1{This is a #1 bar} +... +\foo{2/4} +\end{verbatim} +\end{quote} +or, in \LaTeX{} speak: +\begin{quote} +\begin{verbatim} +\newcommand{\foo}[1]{This is a #1 bar} +... +\foo{3/4} +\end{verbatim} +\end{quote} +Macro writing can get very complicated, very quickly. If you are a +beginner \AllTeX{} programmer, you are well advised to read something +along the lines of the \Qref*{\TeX{}book}{Q-books}; once you're under +way, \Qref*{\TeX{} by Topic}{Q-ol-books} is possibly a more satisfactory +choice. Rather a lot of the answers in these \acro{FAQ}s tell you +about various issues of how to write macros. + +\Question[Q-specials]{\csx{special} commands} + +\TeX{} provides the means to express things that device drivers can +do, but about which \TeX{} itself knows nothing. For example, \TeX{} +itself knows nothing about how to include \PS{} figures into +documents, or how to set the colour of printed text; but some device +drivers do. + +Instructions for such things are introduced to your document by means +of \csx{special} commands; all that \TeX{} does with these commands is +to expand their +arguments and then pass the command to the \acro{DVI} file. In most +cases, there are macro packages provided (often with the driver) that +provide a human-friendly interface to the \csx{special}; for example, +there's little point including a figure if you leave no gap for it in +your text, and changing colour proves to be a particularly fraught +operation that requires real wizardry. \LaTeXe{} +has standard graphics and colour packages that make figure inclusion, +rotation and scaling, and colour typesetting relatively +straightforward, despite the rather daunting \csx{special} commands +involved. (\CONTeXT{} provides similar support, though not by way of +packages.) + +The allowable arguments of \csx{special} depend on the device driver +you're using. Apart from the examples above, there are \csx{special} +commands in the em\TeX{} drivers (e.g., \ProgName{dvihplj}, \ProgName{dviscr}, +\emph{etc}.)~that will draw lines at arbitrary orientations, and +commands in \ProgName{dvitoln03} that permit the page to be set in +landscape orientation. + +Note that \csx{special} provides rather different facilities in \PDFTeX{} +operation: since there is no device driver around, in this context. +In \PDFTeX{}, \csx{special} is only needed to generated \acro{PDF} for +which there is no existing defined \PDFTeX{} operation. + +\Question[Q-hyphen]{How does hyphenation work in \TeX{}?} + +Everyone knows what hyphenation is: we see it in most books we read, +and (if we're alert) will spot occasional ridiculous mis-hyphenation +(at one time, British newspapers were a fertile source). + +Hyphenation styles are culturally-determined, and the same language +may be hyphenated differently in different countries~--- for example, +British and American styles of hyphenation of English are very +different. As a result, a typesetting system that is not restricted +to a single language at a single locale needs to be able to change its +hyphenation rules from time to time. + +\TeX{} uses a pretty good system for hyphenation (originally designed +by Frank Liang~--- you may view his % ! line break +\href{http://tug.org/docs/liang/}{Ph.D.\ thesis online}), and while +it's capable of missing ``sensible'' hyphenation points, it seldom +selects grossly wrong ones. The +algorithm matches candidates for hyphenation against a set of +``hyphenation patterns''. The candidates for hyphenation must be +sequences of letters (or other single characters that \TeX{} may be +persuaded to think of as letters)~--- things such as \TeX{}'s +\csx{accent} primitive interrupt hyphenation. + +Sets of hyphenation patterns are usually derived from analysis of +a list of valid hyphenations (the process of derivation, using a tool +called \Package{patgen}, is not ordinarily a participatory sport). + +The patterns for the languages a \TeX{} system is going to deal with +may only be loaded when the system is installed. To change the set of +languages, a \Qref*{partial reinstallation}{Q-newlang} is necessary. + +\TeX{} provides two ``user-level'' commands for control of +hyphenation: \csx{language} (which selects a hyphenation style), and +\csx{hyphenation} (which gives explicit instructions to the hyphenation +engine, overriding the effect of the patterns). + +The ordinary \LaTeX{} user need not worry about \csx{language}, since +it is very thoroughly managed by the \Package{babel} package; use of +\csx{hyphenation} is discussed in +\begin{wideversion} + the context of +\end{wideversion} +% beware line wrap +\Qref[question]{hyphenation failure}{Q-nohyph}. + +\Question[Q-clsvpkg]{What are \LaTeX{} classes and packages?} + +Current \LaTeX{} makes a distinction between the macros that define the +overall layout of a document, and the macros that tweak that layout +(to one extent or another) to provide what the author \emph{really} +wants. + +The distinction was not very clear in \LaTeXo{}, and after some +discussion (in the later stages of development of current \LaTeX{}) +the names ``class'' and ``package'' were applied to the two concepts. + +The idea is that a document's \emph{class} tells \LaTeX{} what sort of +document it's dealing with, while the \emph{packages} the document +loads ``refine'' that overall specification. + +On the disc, the files only appear different by virtue of their name +``extension''~--- class files are called \texttt{*.cls} while package +files are called \texttt{*.sty}. Thus we find that the \LaTeX{} +standard \Class{article} class is represented on disc by a file called +\File{article.cls}, while the \Package{footmisc} package (which +refines \Class{article}'s definition of footnotes) is represented on +disc by a file called \File{footmisc.sty}. + +The user defines the class of his document with the +\csx{documentclass} command (typically the first command in a +document), and loads packages with the \csx{usepackage} command. A +document may have several \csx{usepackage} commands, but it may have +only one \csx{documentclass} command. (Note that there are +programming-interface versions of both commands, since a class may +choose to load another class to refine its capabilities, and both +classes and packages may choose to load other packages.) + +\Question[Q-dtx]{Documented \LaTeX{} sources (\extension{dtx} files)} + +\LaTeXe{}, and most contributed macro packages, are now written in a +\Qref*{literate programming style}{Q-lit}, with source and +documentation in the +same file. This format, known as `doc', in fact originated before the +days of the \LaTeX{} project as one of the ``Mainz'' series of +packages. A documented source file conventionally has the suffix +\extension{dtx}, and will normally be `stripped' before use with +\LaTeX{}; an installation file (\extension{ins}) is normally provided, +to automate this process of removing comments for speed of loading. +To read the comments, you can run \LaTeX{} on the +\extension{dtx} file to produce a nicely formatted version of the +documented code. Several +packages can be included in one \extension{dtx} file (they're sorted +out by the \extension{ins} file), with conditional +sections, and there are facilities for indexes of macros, etc. + +Anyone can write \extension{dtx} files; the format is explained in +\Qref*{The \LaTeX{} Companion}{Q-books}, and a tutorial is available +from \acro{CTAN} (which comes with skeleton \extension{dtx} and +\extension{ins} files). + +Composition of \extension{dtx} files is supported in \ProgName{emacs} by +\Qref*{\acro{AUC}-\TeX{}}{Q-editors}. + +Another useful way of generating \extension{dtx} files is to write the +documentation and the code separately, and then to combine them using +the \ProgName{makedtx} system. This technique has particular value in +that the documentation file can be used separately to generate +\acro{HTML} output; it is often quite difficult to make % ! line break +\Qref*{\LaTeX{} to \acro{HTML} conversion}{Q-LaTeX2HTML} tools deal +with \extension{dtx} files, since they use an unusual class file. + +The \extension{dtx} files are not used by \LaTeX{} after they have been +processed to produce \extension{sty} or \extension{cls} (or whatever) +files. They need not be kept with the working system; however, for +many packages the \extension{dtx} file is the primary source of +documentation, so you may want to keep \extension{dtx} files elsewhere. + +An interesting sideline to the story of \extension{dtx} files is the +\Package{docmfp} package, which extends the model of the \Package{doc} +package to +\begin{narrowversion} + \MF{} and \MP{} (\Qref[see questions]{}{Q-MF} and \Qref[\nothtml]{}{Q-MP}) +\end{narrowversion} +\begin{wideversion} + \Qref{\MF{}}{Q-MF} and \Qref{\MP{}}{Q-MP}, +\end{wideversion} +thus permitting documented distribution of bundles containing code for +\MF{} and \MP{} together with related \LaTeX{} code. +\begin{ctanrefs} +\item[clsguide.pdf]\CTANref{clsguide} +\item[docmfp.sty]\CTANref{docmfp} +\item[docstrip.tex]Part of the \LaTeX{} distribution +\item[DTX tutorial]\CTANref{dtxtut} +\item[makedtx]\CTANref{makedtx} +\end{ctanrefs} + +\Question[Q-whatenc]{What are encodings?} + +Let's start by defining two concepts, the \emph{character} and the +\emph{glyph}. +The character is the abstract idea of the `atom' of a +language or other dialogue: so it might be a letter in an alphabetic +language, a syllable in a syllabic language, or an ideogram in an +ideographic language. The glyph is the mark created on screen or +paper which represents a character. Of +course, if reading is to be possible, there must be some agreed +relationship between the glyph and the character, so while the precise +shape of the glyph can be affected by many other factors, such as the +capabilities of the writing medium and the designer's style, the +essence of the underlying character must be retained. + +Whenever a computer has to represent characters, someone has to define +the relationship between a set of numbers and the characters they +represent. This is the essence of an encoding: it is a mapping +between a set of numbers and a set of things to be represented. + +\TeX{} of course deals in encoded characters all the time: the +characters presented to it in its input are encoded, and it emits +encoded characters in its \acro{DVI} (or \acro{PDF}) output. These +encodings have rather different properties. + +The \TeX{} input stream was pretty unruly back in the days when Knuth +first implemented the language. Knuth himself prepared documents on +terminals that produced all sorts of odd characters, and as a result +\TeX{} contains some provision for translating the input encoding to +something regular. Nowadays, +the operating system translates keystrokes into a code appropriate for +the user's language: the encoding used is often a national or +international standard, though many operating systems use ``code +pages'' defined by Microsoft. These standards and code pages often +contain characters that can't appear in the \TeX{} system's input +stream. Somehow, these characters have to be dealt with~--- so +an input character like ``\'e'' needs to be interpreted by \TeX{} in +a way that that at least mimics the way it interprets ``\csx{'}\texttt{e}''. + +The \TeX{} output stream is in a somewhat different situation: +characters in it are to be used to select glyphs from the fonts to be +used. Thus the encoding of the output stream is notionally a font +encoding (though the font in question may be a +% beware line break (twice) +\nothtml{virtual one~--- see }% +\Qref[question]{virtual font}{Q-virtualfonts}). In principle, a +fair bit of what appears in the output stream could be direct +transcription of what arrived in the input, but the output stream +also contains the product of commands in the input, and translations +of the input such as ligatures like % +\texttt{fi}\nothtml{\ensuremath\Rightarrow``fi''}. + +Font encodings became a hot topic when the +\Qref*{Cork encoding}{Q-ECfonts} +appeared, because of the possibility of suppressing +\csx{accent} commands in the output stream (and hence improving the +quality of the hyphenation of text in inflected languages, which is +interrupted by the \csx{accent} commands~--- see +% beware line break +\Qref[question]{``how does hyphenation work''}{Q-hyphen}). +To take advantage of the diacriticised characters represented in the +fonts, it is necessary to arrange that whenever the +command sequence ``\csx{'}\texttt{e}'' has been input +(explicitly, or implicitly via the sort of mapping of input mentioned +above), the character that codes the position of the ``\'e'' glyph is +used. + +Thus we could have the odd arrangement that the diacriticised character in +the \TeX{} input stream is translated into \TeX{} commands that would +generate something looking like the input character; this sequence of +\TeX{} commands is then translated back again into a single +diacriticised glyph as the output is created. This is in fact +precisely what the \LaTeX{} packages \Package{inputenc} and +\Package{fontenc} do, if operated in tandem on (most) characters in +the \acro{ISO}~Latin-1 input encoding and the \acro{T}1 font encoding. +At first sight, it seems eccentric to have the first package do a thing, and +the second precisely undo it, but it doesn't always happen that way: +most font encodings can't match the corresponding input encoding +nearly so well, and the two packages provide the sort of symmetry the +\LaTeX{} system needs. + +\Question[Q-ECfonts]{What are the \acro{EC} fonts?} + +A font consists of a number of \emph{glyphs}. In order that the +glyphs may be printed, they are \Qref*{\emph{encoded}}{Q-whatenc}, and +the encoding is used as an index into tables within the font. For +various reasons, Knuth chose deeply eccentric encodings for his +Computer Modern family of fonts; in particular, he chose different +encodings for different fonts, so that the application using the fonts +has to remember which font of the family it's using before selecting a +particular glyph. + +When \TeX{} version 3 arrived, most of the excuses for the +eccentricity of Knuth's encodings went away, and at \acro{TUG}'s Cork +meeting, an encoding for a set of 256 glyphs, for use in \TeX{} text, +was defined. The intention was that these glyphs should cover `most' +European languages that use Latin alphabets, in the sense of including +all accented letters needed. (Knuth's \acro{CMR} fonts missed things +necessary for Icelandic and Polish, for example, but the Cork +fonts have them. Even Cork's coverage isn't complete: it misses +letters from Romanian, Eastern and Northern Sami, and Welsh, at +least. The Cork encoding does contain ``\acro{NG}'' glyphs that +allows it to support Southern Sami.) \LaTeX{} refers to the +Cork encoding as \acro{T}1, and +provides the means to use fonts thus encoded to avoid problems with +the interaction of accents and hyphenation % ! line break +(see \Qref[question]{hyphenation of accented words}{Q-hyphenaccents}). + +The only \MF{}-fonts that conform to the Cork encoding are the +\acro{EC} fonts. They look \acro{CM}-like, though their metrics +differ from \acro{CM}-font metrics in several areas. The fonts are +now regarded as `stable' (in the same sense that the \acro{CM} fonts +are stable: their metrics are unlikely ever to change). Their serious +disadvantages for the casual user are their size (each \acro{EC} font +is roughly twice the size of the corresponding \acro{CM} font), and +there are far more of them than there are \acro{CM} fonts. The simple +number of fonts proved problematic in the production of Type~1 +versions of the fonts, but \acro{EC} or \acro{EC}-equivalent fonts in +Type~1 or TrueType form (the latter only from +\begin{wideversion} + \Qref{commercial suppliers}{Q-commercial}). +\end{wideversion} +\begin{narrowversion} + % ( <- paren matching + commercial suppliers~--- \Qref{question}{Q-commercial}). +\end{narrowversion} +Free \Qref*{auto-traced versions}{Q-textrace}~--- the \acro{CM}-super +and the \acro{LGC} fonts, and the Latin Modern series (rather +directly generated from \MF{} sources), are available. + +%% Unfortunately, until corresponding fonts for mathematics are produced, +%% the \acro{CM} fonts must be retained, since some mathematical symbols +%% are drawn from text fonts in the \acro{CM} encodings. +Note that the Cork encoding doesn't cover mathematics (and neither do +``\acro{T}1-encoded'' font families, of course). If you're using +Computer-Modern-alike fonts, this doesn't actually matter: your system +will have the original Computer Modern mathematical fonts (or the those +distributed with the Latin Modern set), which cover `basic' +\TeX{} mathematics; more advanced mathematics are likely to need +separate fonts anyway. Suitable mathematics fonts for use with other +font families are discussed in % ! line break +``\Qref*{choice of scalable fonts}{Q-psfchoice}''. + +The \acro{EC} fonts are distributed with a +set of `Text Companion' (\acro{TC}) fonts that provide glyphs for +symbols commonly used in text. The \acro{TC} fonts are encoded +according to the \LaTeX{} \acro{TS}1 encoding, and are not viewed as +`stable' in the same way as are the \acro{EC} fonts are. + +The Cork encoding is also implemented by virtual fonts provided in the +\Qref*{\acro{PSNFSS} system}{Q-usepsfont}, +for Adobe Type~1 fonts, and also by the \Package{txfonts} and +\Package{pxfonts} font packages +% beware line wrap +(see \Qref[question]{``choice of scalable fonts''}{Q-psfchoice}). +\begin{ctanrefs} +\item[CM-super fonts]\CTANref{cm-super} +\item[CM-LGC fonts]\CTANref{cm-lgc} +\item[EC and TC fonts]\CTANref{ec} +\item[Latin Modern fonts]\CTANref{lm} +\end{ctanrefs} + +\Question[Q-tds]{What is the \acro{TDS}?} + + \acro{TDS} stands for the \TeX{} Directory Structure, which is a standard +way of organising all the \TeX{}-related files on a computer system. + + Most modern distributions conform to the \acro{TDS}, which +provides for both a `standard' and a (set of) `local' hierarchies of +directories containing \TeX{}-related files. The +\acro{TDS} reserves the name \texttt{texmf} as the name of the root directory +(folder) of the hierarchies. Files supplied as part of the +distribution are put into the standard hierarchy. The location of the +standard hierarchy is system dependent, but on a Unix system it might +be at +\path{/usr/local/texmf}, or +\path{/usr/local/share/texmf}, or +\path{/opt/texmf}, or +a similar location, but in each case the \TeX{} files will be under the +\path{/texmf} subdirectory. + +There may be more than on `local' hierarchy in which additional files +can be stored. In the extreme an installation can have a local +hierarchy and each user can also have an individual local hierarchy. The +location of any local hierarchy is not only system dependent but also user +dependent. Again, though, all files should be put under a local \path{/texmf} +directory. + +The \acro{TDS} is published as the output of a \acro{TUG} % beware line wrap +\Qref*{Technical Working Group}{Q-TUG*}. +You may browse an \href{http://tug.org/tds/}{on-line version} of the +standard, and copies in several other formats (including source) are +available on \acro{CTAN}. +\begin{ctanrefs} +\item[\nothtml{\rmfamily}\acro{TDS} specification]\CTANref{tds} +\end{ctanrefs} + +\Question[Q-eps]{What is ``Encapsulated \PS{}'' (``\acro{EPS}'')?} + +\PS{} has been for many years a \emph{lingua franca} of powerful +printers (though modern high-quality printers now tend to require some +constrained form of Adobe Acrobat, instead); since \PS{} is also a +powerful graphical programming language, it is commonly used as an +output medium for drawing (and other) packages. + +However, since \PS{} \emph{is} such a powerful language, some +rules need to be imposed, so that the output drawing may be included +in a document as a figure without ``leaking'' (and thereby destroying +the surrounding document, or failing to draw at all). + +Appendix \acro{H} of the \PS{} Language Reference Manual (second +and subsequent editions), specifies a set of rules for \PS{} to +be used as figures in this way. The important features are: +\begin{itemize} +\item certain ``structured comments'' are required; important ones are + the identification of the file type, and information about the + ``bounding box'' of the figure (i.e., the minimum rectangle + enclosing it); +\item some commands are forbidden~--- for example, a \texttt{showpage} + command will cause the image to disappear, in most \TeX{}-output + environments; and +\item ``preview information'' is permitted, for the benefit of things + such as word processors that don't have the ability to draw + \PS{} in their own right~--- this preview information may be in + any one of a number of system-specific formats, and any viewing + program may choose to ignore it. +\end{itemize} +A \PS{} figure that conforms to these rules is said to be in +``Encapsulated \PS{}'' (\acro{EPS}) format. Most \AllTeX{} packages for +including \PS{} are structured to use Encapsulated \PS{}; +which of course leads to much hilarity as exasperated \AllTeX{} users +struggle to cope with the output of drawing software whose authors +don't know the rules. + +\Question[Q-adobetypen]{Adobe font formats} +\keywords{type1 type3} + +Adobe has specified a number of formats for files to represent fonts +in \PS{} files; this question doesn't attempt to be encyclopaedic, so +we only discuss the two formats most commonly encountered in the +\AllTeX{} context, types~1 and 3. In particular, we don't discuss the +OpenType format, whose has many advantages are somewhat ahead of the +\TeX{} world's mainstream (at time of writing). + +Adobe Type~1 format specifies a means to represent outlines of the glyphs +in a font. The `language' used is closely restricted, to ensure that +the font is rendered as quickly as possible. (Or rather, as quickly +as possible with Adobe's technology at the time the specification was +written: the structure could well be different if it were specified +now.) The format has long been the basis of the digital type-foundry +business, though nowadays most new fonts are released in OpenType format. + +%% Type~1 fonts are directly supported by some operating system software, +%% and at least one \TeX{} system, the commercial % line break! +%% \Qref*{\YandY{} system}{Q-commercial}, bases its entire +%% operation on the use of Type~1 fonts. + +In the \AllTeX{} context, Type~1 fonts are extremely important. Apart +from their simple +availability (there are thousands of commercial Type~1 text fonts around), the +commonest reader for \acro{PDF} files has long (in effect) \emph{insisted} on +their use (see below). + +Type~3 fonts have a more forgiving specification. A wide range of +\PS{} operators is permissible, including bitmap specifiers. Type~3 +is therefore the natural format to be used for programs such as +\ProgName{dvips} when they auto-generate something to represent +\MF{}-generated fonts in a \PS{} file. It's Adobe Acrobat Viewer's +treatment of bitmap Type~3 fonts that has made direct \MF{} output +increasingly unattractive, in recent years. If you have a \acro{PDF} +document in which the text looks fuzzy and uneven in Acrobat Reader, +ask Reader for the \texttt{File}\arrowhyph{}% +\texttt{Document Properties}\arrowhyph{}% +\texttt{Fonts ...}, and it will likely show some font or other as +``Type~3'' (usually with encoding ``Custom''). The problem has +disappeared with version 6 of Acrobat Reader. See % line break +\Qref[question]{\acro{PDF} quality}{Q-dvips-pdf} for a discussion of +the issue, and for ways of addressing it. + +Type~3 fonts should not entirely be dismissed, however. Acrobat +Reader's failure with them is entirely derived from its failure to use +the anti-aliasing techniques common in \TeX{}-ware. Choose a +different set of \PS{} graphical operators, and you can make pleasing +Type~3 fonts that don't ``annoy'' Reader. For example, you may not +change colour within a Type~1 font glyph, but there's no such +restriction on a Type~3 font, which opens opportunities for some +startling effects. + +\Question[Q-resolns]{What are ``resolutions''?} + +``Resolution'' is a word that is used with little concern for its +multiple meanings, in computer equipment marketing. The word suggests +a measure of what an observer (perhaps the human eye) can resolve; yet +we regularly see advertisements for printers whose resolution is +1200dpi~--- far finer than the unaided human eye can distinguish. The +advertisements are talking about the precision with which the printer +can place spots on the printed image, which affects the fineness of +the representation of fonts, and the accuracy of the placement of +glyphs and other marks on the page. + +In fact, there are two sorts of ``resolution'' on the printed page +that we need to consider for \AllTeX{}'s purposes: +\begin{itemize} +\item the positioning accuracy, and +\item the quality of the fonts. +\end{itemize} +In the case where \AllTeX{} output is being sent direct to a printer, +in the printer's ``native'' language, it's plain that the \acro{DVI} +processor must know all such details, and must take detailed account +of both types of resolution. + +In the case where output is being sent to an intermediate distribution +format, that has potential for printing (or displaying) we know not +where, the final translator, that connects to directly to the printer +or display, has the knowledge of the device's properties: the +\acro{DVI} processor need not know, and should not presume to guess. + +Both \PS{} and \acro{PDF} output are in this category. While \PS{} is +used less frequently for document distribution nowadays, it is +regularly used as the source for distillation into \acro{PDF}; and +\acro{PDF} is the workhorse of an enormous explosion of document +distribution. + +Therefore, we need \acro{DVI} processors that will produce +``resolution independent'' \PS{} or \acro{PDF} output; of course, the +independence needs to extend to both forms of independence outlined +above. + +Resolution-independence of fonts was for a long time forced upon the +world by the feebleness of Adobe's \ProgName{Acrobat} +\ProgName{Reader} at dealing with bitmap files: a sequence of answers +starting with one aiming at the % ! line break +\Qref*{quality of \acro{PDF} from \PS{}}{Q-dvips-pdf} addresses +the problems that arise. + +Resolution-independence of positioning is more troublesome: +\ProgName{dvips} is somewhat notorious for insisting on positioning to +the accuracy of the declared resolution of the printer. +One commonly-used approach is to declare a resolution of 8000 (``better +than any device''), and this is reasonably successful though it does +have its \Qref*{problems}{Q-8000}. + +\Question[Q-fontname]{What is the ``Berry naming scheme''?} + +In the olden days, \AllTeX{} distributions were limited by the +feebleness of file systems' ability to represent long names. (The +\MSDOS{} file system was a particular bugbear: fortunately any current +Microsoft system allows rather more freedom to specify file names. +Sadly, the ISO~9660 standard for the structure of \CDROM{}s has a +similar failing, but that too has been modified by various extension +mechanisms.) + +One area in which this was a particular problem was that of file names +for Type~1 fonts. These fonts are distributed by their vendors with +pretty meaningless short names, and there's a natural ambition to +change the name to something that identifies the font somewhat +precisely. Unfortunately, names such as ``BaskervilleMT'' are +already far beyond the abilities of the typical feeble file system, +and add the specifier of a font shape or variant, and the difficulties +spiral out of control. + +Thus arose the Berry naming scheme. + +The basis of the scheme is to encode the meanings of the various parts +of the file's specification in an extremely terse way, so that enough +font names can be expressed even in impoverished file name-spaces. The +encoding allocates one letter to the font ``foundry'', two to the +typeface name, one to the weight, and so on. The whole scheme is +outlined in the \Package{fontname} distribution, which includes +extensive documentation and a set of tables of fonts whose names have +been systematised. +\begin{ctanrefs} +\item[fontname distribution]\CTANref{fontname} +\end{ctanrefs} + |