A first beta of Cedilla, the manic text printer, is available from
http://www.pps.jussieu.fr/~jch/software/cedilla/
Regards,
Juliusz
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CEDILLA
¸
A best-effort text printer
Juliusz Chroboczek
Cedilla is a simple text printer that uses Unicode internally.
Using Unicode means that the set of characters that can appear in the input
is very large, and the user may very well have no font available that
contains glyphs for the characters that he wants to print. Cedilla attempts
to at least partially solve this problem using a number of techniques:
1. Cedilla can use an arbitrary number of downloadable fonts; for any given
print job, only the necessary fonts will be downloaded.
2. Cedilla will use its own built-in font.
3. Cedilla will retouch existing glyphs in order to e.g. remove dots or add
bars.
4. Cedilla will attempt to build composite glyphs (e.g. for accented
characters) on the fly.
5. Cedilla will use fallbacks for characters that are not supported by the
available fonts.
SOURCES OF GLYPHS
Cedilla will attempt to use glyphs from all of the following sources,
in decreasing order of preference:
1. Glyphs present in an available font.
This is the common case, and covers all simple characters but also,
depending on the used font, a number of composites.
Example: Être ou ne pas être ?
2. Built-in glyphs.
Cedilla has a built-in font which can be (partially) downloaded if
necessary.
Example: €.
3. Retouched glyphs
When no suitable glyph is available, Cedilla will sometimes attempt to
retouch an available glyph. The main application is to produce dotless
glyphs for further composition; another use is to provide barred glyphs.
Example: (Slovenian sentence containing đ.)
Example: Tiuj ĉi arĥaismoj neniam estos elĵetitaj.
3. Glyphs composed based on data accompanying the font.
The Adobe Font Metrics (AFM) format can include positioning information for
composites, and Cedilla will be glad to use such data. However, as few fonts
come with extra information in this form, this technique is seldom useful.
4. Glyphs composed out of components present in a single font.
If a glyph is missing from a font, but all the components needed to
construct it are present, Cedilla will build a composite glyph out of those.
While the positioning of the diacritical marks is approximate, the algorithm
used appears to be satisfactory with many standard fonts.
Example: Czy pamiętasz jak ze mną tańczyłaś Walca ?
When building such composites, Cedilla will, whenever necessary, replace
dotted letters with their dotless variants or retouch the base glyphs to
remove the dot (see Section 2 above).
Of course, Cedilla is not limited to using glyphs that are present in
Unicode in precomposed form. For example, the second letter of the third
word in the sentence below is a Latin small e followed with ‘Combining
Vertical Line Below.’
Example: Mo lè je̩ dígí, kò ní pa mí lára.
4. Glyphs composed out of components taken from different fonts.
As this sometimes leads to esthetically unpleasant results, Cedilla tries to
avoid this technique. It can be useful in some cases, however, and will in
particular enable printing almost legible Greek when no decent Greek font is
available:
Example:
Οὐχὶ ταὐτὰ παρίσταταί μοι γιγνώσκειν, ὦ
ἄνδρες ᾿Αθηναῖοι,
ὅταν τ᾿ εἰς τὰ πράγματα ἀποβλέψω καὶ ὅταν
πρὸς τοὺς
λόγους οὓς ἀκούω·
Note how the diacritical marks were taken from the primary font, while all
the other Greek glyphs came from the Symbol font.
(Actually, Polytonic Greek is difficult, and Cedilla needs some more work
before it can present it satisfactorily. Given suitable fonts — not
Symbol! —, Monotonic Greek appears okay, at least to my unexercised eyes.)
5. Fallbacks.
In cases when no glyph is directly available for a character, Cedilla will
fall back on ever less satisfactory alternatives. For example, a closing
double quotation mark will first be replaced with a sequence of two closing
single quotation marks which will, in turn, be replaced by a sequence of two
apostrophes.
The fallbacks mechanism is a rather complex beast (it currently consists of
four distinct phases), and interacts in wonderful and mysterious ways with
the glyph generation mechanisms, notably composite glyph generation. Its
exact mechanics are still in a state of flux, and will be described when
they have stabilised.
INSTALLING CEDILLA
Please see the file ‘INSTALL’ for information on installing Cedilla.
INVOKING CEDILLA
Please see the ‘cedilla(1)’ manual page for information on invoking
cedilla.
CONFIGURING CEDILLA
Cedilla is configured by inserting fontset definitions in a file named
‘cedilla-config.lisp’ which, by default, lives in ‘/etc/’. A fontset
definition is an invocation of the macro DEFINE-FONTSET with two
parameters: the name of the fontset and an ordered list of font
definitions.
(define-fontset "times"
‘((:afm "ptmr.afm" :omit ("mu"))
(:afm "psyr.afm")
(:afm "pzdr.afm" :encoding ,#’zapf-dingbats-encoding)
(:built-in :width 667 :height 662 :x-height 448)))
(define-fontset "utopia"
‘((:afm "UTRG____.afm" :resources ("UTRG____.pfa"))))
Every font definition is a list the first element of which is the
font's type.
If the TYPE is :AFM, then the entry specifies a font described by its
AFM file. The font definition is of the form
(:AFM filename . options)
where filename is the location of the AFM file describing the font, and
options is an alternating list of keyword/value (a ‘plist’ in Lisp
parlance).
Options supported for the :AFM font type include:
• :RESOURCES : specifies a list of resources that must be downloaded if the
font is to be used; currently, the only type of downloadable resource
supported are fonts in PFA format;
• :ENCODING : specifies that the font does not follow the Adobe glyph naming
guidelines; the argument is a function that maps normal CCS to glyph names.
• :FIXED-ENCODING : specifies that the font is hopelessly broken, and should
never, ever be reencoded; the argument is a function that maps normal ccs
to font indices.
• :OMIT : specifies a list of names of glyphs that should be ignored;
for most Latin fonts, this should be the list ("mu"), so that all
Greek glyphs are taken from the same font.
If the type is :BUILT-IN, then the entry specifies Cedilla's built-in font.
The entry is of the form
(:BUILT-IN . options)
where options include:
• :WIDTH : specifies the width of the glyphs in the font in units of one
thousandth of the font size. The width of the capital Latin letter C in
the principal font of the fontset is usually a good choice for this value.
• :CAP-HEIGHT : specifies the capital height of the glyphs in the font. The
height of the capital Latin letter H in the principal font is usually a
good choice for this value.
• :X-HEIGHT : specifies the height of small letters in the font. The height
of the small Latin letter x in the principal font is usually a good choice
for this value.
If the type is :SPACE, then the entry specifies a fake font that provides a
space glyph; this is meant for use with fonts that do not contain a useable
space glyph, such as some fonts designed for TeX. The entry is then of the
form
(:SPACE . options)
The only defined option is :WIDTH, the argument to which is an integer
specifying the width of the space that the font will provide.
EXTENDING CEDILLA
Cedilla uses data from the UnicodeData file and from the Adobe Glyph List.
As these data are not sufficient for our needs, they are complemented with a
table of (good) character alternatives, a table of (bad) character
fallbacks, and a table of alternate glyph names. See the comments at the
beginning of ‘unicode.lisp’ for information about the data structures
used, and the file ‘data-add.lisp’ for the addtional data provided.
The built-in font is defined in the file ‘built-in.lisp’. You should not be
afraid to add glyphs to this font, as Cedilla will be careful to only
download those glyphs that are needed for the current print job.
TODO
• Think some more about the fallback selection mechanism. Right now,
Cedilla is somewhat too keen on moving to a secondary font.
• Add more fallbacks.
• Work out how to typeset kra, Eng and eng. This would make Cedilla cover
all of Basic Latin, Latin-1 and Latin Extended A using standard fonts
only.
• Fine-tune the existing types of magic (only :DOTLESS and :BAR are
okay right now).
• Add magic for sub- and superscripts (requires a new subclass of
FONT-INSTANCE).
• PFB. CIDFont?
• fix Emacs.
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