symbols-a4

Table 324 showcases these accents. The TEXbook [Knu86a] or another book on TEX primitives is indispensible
for understanding how the preceding code works. The basic idea is that \downparenthfill, \upparenthfill,
\downbracketfill, and \upbracketfill do all of the work; they output a left symbol (e.g., \braceld [“”]
for \downparenthfill), a horizontal rule that stretches as wide as possible, and a right symbol (e.g., \bracerd
[“”] for \downparenthfill). \overbracket, \underbracket, \overparenthesis, and \underparenthesis
merely create a table whose width is determined by the given text, thereby constraining the width of the
horizontal rules.
Table 324: Manually Composed Extensible Accents
abc \overbracket{abc} abc \overparenthesis{abc}
abc \underbracket{abc} abc
\underparenthesis{abc}
Note that the simplewick package provides mechanisms for typesetting Wick contractions, which utilize
\overbracket- and \underbracket-like brackets of variable width and height (or depth). For example,
“\acontraction{}{A}{B}{C}\acontraction[2ex]{A}{B}{C}{D}\bcontraction{}{A}{BC}{D}ABCD”
produces
ABCD .
See the simplewick documentation for more information.
Developing new symbols from scratch
Sometimes is it simply not possible to define a new symbol in terms of existing symbols. Fortunately, most, if
not all, TEX distributions are shipped with a tool called METAFONT which is designed specifically for creating
fonts to be used with TEX. The METAFONTbook [Knu86b] is the authoritative text on METAFONT. If you
plan to design your own symbols with METAFONT, The METAFONTbook is essential reading. You may also
want to read the freely available METAFONT primer located at http://metafont.tutorial.free.fr/. The
following is an extremely brief tutorial on how to create a new L ATEX symbol using METAFONT. Its primary
purpose is to cover the L ATEX-specific operations not mentioned in The METAFONTbook and to demonstrate
that symbol-font creation is not necessarily a difficult task.
Suppose we need a symbol to represent a light bulb (“”). 11 The first step is to draw this in METAFONT.
It is common to separate the font into two files: a size-dependent file, which specifies the design size and
various font-specific parameters that are a function of the design size; and a size-independent file, which draws
characters in the given size. Figure 2 shows the METAFONT code for lightbulb10.mf. lightbulb10.mf
specifies various parameters that produce a 10 pt. light bulb then loads lightbulb.mf. Ideally, one should
produce lightbulb〈size〉.mf files for a variety of 〈size〉s. This is called “optical scaling”. It enables, for
example, the lines that make up the light bulb to retain the same thickness at different font sizes, which looks
much nicer than the alternative—and default—“mechanical scaling”. When a lightbulb〈size〉.mf file does
not exist for a given size 〈size〉, the computer mechanically produces a wider, taller, thicker symbol:
vs. vs. vs. vs.
vs.
vs.
10 pt. 20 pt. 30 pt. 40 pt. 50 pt. 60 pt. 70 pt.
lightbulb.mf, shown in Figure 3, draws a light bulb using the parameters defined in lightbulb10.mf.
Note that the the filenames “lightbulb10.mf” and “lightbulb.mf” do not follow the Berry font-naming
scheme [Ber01]; the Berry font-naming scheme is largely irrelevant for symbol fonts, which generally lack bold,
italic, small-caps, slanted, and other such variants.
The code in Figures Figure 2 and Figure 3 is heavily commented and should demonstrate some of the
basic concepts behind METAFONT usage: declaring variables, defining points, drawing lines and curves, and
preparing to debug or fine-tune the output. Again, The METAFONTbook [Knu86b] is the definitive reference
on METAFONT programming.
11 I’m not a very good artist; you’ll have to pretend that “” looks like a light bulb.
109